How far do mosquitoes fly?

There is no single answer to one of the most commonly asked questions I’m asked. “How far does a mosquito fly?” Notwithstanding those blown long distances by cyclonic winds or transported in vehicles, the distances travelled by mosquitoes varies greatly from mosquito to mosquito. But how do scientists work it out?

My latest published research demonstrates that Australia’s saltmarsh mosquito (Aedes vigilax) flies many kilometres from urban estuarine wetlands. This has great implications for improving our understanding of their role in outbreaks of mosquito-borne disease as well as designing mosquito control programs.

There are a few different ways you can work out how far mosquitoes fly.

Firstly, given we know that mosquitoes are closely associated with certain habitats, it is sometimes possible to track back collections of mosquitoes to their preferred habitats. For example, knowing a coastal wetlands mosquito is found many kilometres away from the nearest estuarine wetland may indicate it disperses widely.

Secondly, scientists can conducted mark-release-recapture experiments. In these studies, mosquitoes are marked with some kind of substance, released, and then specimens collected in traps operated in a surrounding network can be checked to see how many of those marked mosquitoes have been recaptured and how far they’ve travelled.

In this recently published study, I marked over 200,000 Aedes vigilax with a fluorescent powder (usually used to create paint) and released them close to their larval habitats in estuarine wetlands along the Parramatta River. For the next week, I set dozens of traps around the local area hoping to recollect some of those marked mosquitoes. By scanning the mosquitoes under a UV light, the marked mosquitoes were (relatively) easily identified.

Recapture rates for these types of experiments are notoriously low. While I was only able to recapture less than 1% of those marked mosquitoes released, marked mosquitoes were recaptured many kilometres from their release point. The results demonstrated that these mosquitoes of pest and public health concern disperse so widely from saltmarsh and mangrove habitats that their impacts can be felt quite widely, highlighting the need for targeted mosquito control to minimise potentially widespread pest and public health impacts.

There is an important implication here for current “mosquito aware” urban planning strategies. The incorporation of “buffer zones” between residential developments and mosquito habitats is often proposed but this research clearly demonstrated that this strategy just isn’t practical when it comes to saltmarsh mosquitoes. They just fly too far!

While this study demonstrated marked mosquitoes were travelling up to 3km, other work I’ve done has highlighted how differently the dispersal ranges of mosquitoes can be.  In a study of yellow fever mosquitoes (Aedes aegypti) in far north QLD, we found marked mosquitoes were only traveling between 100-200m. Similarly, other work with Australian backyard mosquitoes (e.g. Aedes notoscriptus) has shown they don’t fly more than 200m. That’s still enough to fly over from your neighbour’s backyard full of mosquito breeding opportunities.

There is a practical application to this work for the management of dengue in far north QLD. Knowing that the mosquitoes involved in transmission are flying less than 200m, mosquito surveillance and control can be concentrated around the homes of those infected individuals. A great example of how understanding mosquito biology can better inform cost-effective response strategies.

There is still plenty to learn about the dispersal of mosquitoes in Australia. I’ve got some ideas so if you’re looking for a research projects, get in touch!

Check out the Journal of Medical Entomology for the full paper titled “Dispersal of the Mosquito Aedes vigilax (Diptera: Culicidae) From Urban Estuarine Wetlands in Sydney, Australia“.

The abstract is below:

Aedes vigilax (Skuse) is a pest and vector species associated with coastal wetlands and the abundance of this mosquito has been identified as contributing to increased risk of mosquito-borne disease outbreaks. As urban development continues to encroach on these coastal wetlands, pest and public health impacts are becoming of increasing concern and in the absence of broadscale mosquito control. Urban planners are looking to buffer zones and other land use planning options to minimize contact between mosquitoes and humans but gaps in the understanding of dispersal ranges of mosquitoes hamper the adoption of these strategies. A mark-release-recapture experiment was conducted to measure the dispersal of this mosquito from an urban estuarine wetland in Sydney, Australia. An estimated total of over 150,000 wild caught female mosquitoes were marked with fluorescent dust and then released. A network of 38 traps was then operated for 5 d within an area of 28 km². A total of 280 marked mosquitoes was recaptured, representing less than 1% of the estimate 250,000 marked mosquitoes released. Marked mosquitoes were recaptured up to 3 km from the release point, providing an insight into the dispersal range of these mosquitoes. The mean distance traveled by marked mosquitoes was 0.83 km, a result reflecting the greater proportion of marked mosquitoes recaptured near release point. The findings of this study indicate that effective buffer zones between estuarine wetlands and high-density urban developments would be an impractical approach to minimizing pest and public health impacts associated with this mosquito.

Join the conversation on Twitter or check out some of the other articles I’ve written on mosquitoes and other biting insects at The Conversation. You can also learn more about Australia’s wonderful mosquitoes in the award winning field guide available from CSIRO Publishing.

 

 

 

Ross River virus in Sydney, should we be worried?

Health authorities in NSW recently released warnings to avoid mosquito bites following the detection of Ross River virus in wetlands along two major river systems in metropolitan Sydney. Whats going on and should these findings be something to be worried about?

What is Ross River virus?

Ross River virus is the most commonly reported mosquito-borne disease in Australia. The virus is spread by the bite of a mosquito and about 40 different mosquito species have been implicated in its transmission.

The disease caused by Ross River virus is not fatal but it can be severely debilitating.

Thousands of Australian’s are infected each year. We have some idea of the quantity of infections as Ross River virus disease is classified as a notifiable disease. While the official statistics indicate there are around 5,000 cases of illness across the country (there are between 500 and 1,500 cases per year in NSW), there are likely to be many more people that experience a much milder illness and so never get blood tests to confirm infection. These people won’t appear in official statistics.

What makes Ross River virus a fascinating pathogen to study is also what makes it extremely difficult to predict outbreaks. Transmission cycles require more than just mosquitoes. Mosquitoes don’t emerge from local wetlands infected with the virus, they need to bite an animal first and become infected themselves before then being able to pass on the pathogen to people.

It is generally thought that kangaroos and wallabies are the most important animals driving outbreak risk. However, we’re starting to better understand how the diversity of local wildlife may enhance, or reduce, likely transmission risk.

How was the virus found in Sydney?

The recent warnings have been triggered by the results of mosquito trapping and testing around Sydney. NSW Health coordinates an arbovirus and mosquito monitoring program across the state and this includes surveillance locations within metropolitan Sydney.

Mosquitoes are collected using traps baited with carbon dioxide. They trick the mosquitoes into thinking the trap is an animal. By catching mosquitoes, we can better understand how the pest and public health risks vary across the city and the conditions that make mosquitoes increase (or decrease) in numbers.

It mostly occurs around the metropolitan region’s northern and southern river systems and generally associated with estuarine or brackish-water wetlands. In these areas, there are often abundant mosquitoes and wildlife. Along the Parramatta River, there are often abundant mosquito populations but given the heavily urbanised landscape, there aren’t many kangaroos and wallabies.

The nuisance impacts of mosquitoes, such as Aedes vigilax, dispersing from the estuarine wetlands of the Parramatta River can create challenges for local authorities. These challenges include targeted wetland conservation and rehabilitation strategies along with ecologically sustainable mosquito control programs.

Is the detection of the virus in Sydney unusual?

The detection of Ross River virus is not that unusual. Detection of Ross River virus (as well as other mosquito-borne viruses such as Stratford virus) along the Georges River in southern Sydney is an almost annual occurrence. The local health authorities routinely issue warnings and in recent years have successfully used social media to spread their messages.

Ross River virus has also previously been detected along the Parramatta River.

While there have been confirmed local clusters of locally acquired Ross River virus in the suburbs along the Georges River, there have been no confirmed cases of Ross River virus disease in the suburbs along the Parramatta River.

There are a few reasons why more disease isn’t reported. Health authorities are active in promoting personal protection measures, sharing recommendations on insect repellent use and providing regular reminders of the health risks associated with local mosquitoes. It isn’t unreasonable to think these actions raise awareness and encourage behaviour change that reduces mosquito bites and subsequent disease.

Along the Georges River, there is clearly a higher risk of infection given the more significant wildlife populations, especially the wallabies common throughout Georges River National Park. By comparison, along the Parramatta River there are fewer bushland areas and virtually no wallabies (except for the occasional one hopping across the Sydney Harbour Bridge). Even in the wetland areas around Sydney Olympic Park, there is abundant bird life, meaning mosquitoes are probably more likely to be biting the animals than people. A study looking at the blood feeding preferences of mosquitoes in the local area found that animals were more likely to be bitten, mosquitoes actually only fed on humans about 10% of the time.

It is important that if you’re spending a lot of time outdoors in these areas, especially close to wetlands and bush land areas at dawn and dusk when mosquitoes are most active, take measure to reduce the risk of being bitten. Cover up with long sleeved shirts and long pants and apply an insect repellent. Choose a repellent that contains either DEET (diethlytoluamide), picaridin, or oil of lemon eucalyptus. Apply it to all exposed skin to ensure there is a thin even coat – a dab “here and there” doesn’t provide adequate protection. More tips here.

Also, keep in mind that just because cooler weather has arrived, the health risks associated with mosquitoes remain. That means keeping in mind that mosquitoes will be out and about just as football and netball seasons start so take along some mosquito repellent to training nights.

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Wetlands, climate change, and managing mosquitoes

I’ve spent over twenty years sloshing about in wetlands around Sydney and surrounds. They’re changing. They’re changing due to shifts in climate, sea level rise, and urbanisation. The 2019 World Wetlands Day is a time to stop and reflect on the state of wetlands around the world and how we can keep them health under the threat of climate change.

World Wetlands Day is held every year on 2 February,  this day marking the adoption of the Convention on Wetlands on 2 February 1971 in Ramsar, Iran. The theme of the 2019 World Wetlands Day is “Wetlands and Climate Change” and we shouldn’t just think about the impact of climate change on wetlands but also how wetlands can help us as we face the challenges of a changing climate.

Coastal wetlands around Sydney are impacted in many ways. Mangrove forests and saltmarshes are degraded through direct and indirect human activity. There is recent research indicating that sea level rise is impacting mangroves along the Parramatta River in Sydney. This requires active management to ensure substantial degradation and die back occurs, as has been seen elsewhere in Australia.

Some of our research even suggests that degraded mangroves are more productive when it comes to mosquitoes. Effective rehabilitation of these habitats may actually reduce the mosquitoes flying out of these environments and impacting the community nearby. Similarly, urban planning should consider the risk posed by mosquitoes in wetlands adjacent to new and expanding residential developments. This includes major wetland rehabilitation projects.

The challenges facing wetlands isn’t unique to Australia. Released in conjunction with World Wetlands Day preparations was The Global Wetland Outlook. A document that provides “a current overview of global wetlands: their extent, trends, drivers of change and the responses needed to reverse the historical decline in wetland area and quality”.

While we think of rainforests and coral reefs under greatest threat, it is a sobering thought to think that up to 87% of the global wetland resource has been lost since 1700. These are environments that were, until relatively recently, considered wastelands. With this lack of perceived value came greater susceptibility to abuse and degradation.

Along with the unsurprising loss of wetland area and decline in biodiversity associated with these environments come some interesting findings. The most interesting from a mosquito management point of view is that artificial wetlands are actually increasing in some areas. Notwithstanding an assessment of the ecosystem services they provide, they’re more likely to be closer to human habitation, so any mosquitoes associated with them may have relatively greater impact.

In recent years, the value of wetlands has increased. There is an understanding now that these environments provide critical ecosystem services. There is also a growing understanding of the wetland’s roles in mitigating the impacts of climate change. Coastal wetlands in particularly provide protection from increasingly severe storm events and trap valuable carbon stores that assist in mitigating the impacts of climate change.

This then raises the issues of mosquitoes. Mosquitoes are a natural part of wetland ecosystems. While often their pest impacts may indicate the poor health of the wetlands, at other time, abundant mosquito populations are a natural occurrence that fluctuate in their intensity from year to year. How do best manage mosquitoes associated with these wetlands?

I’ve written about how I think mosquito control should actually be considered an important component of coastal wetland rehabilitation. How climate change may be impacting mosquito threats and that even hot and dry summers under the influence of El Nino may not necessarily mean that mosquitoes are less problematic.

Based on the experience during the 2018-2019 summer, mosquitoes seem to persist in plague proportions despite the extreme temperatures being experienced in NSW.

It is important to remember that there are many mosquito species associated with wetlands, especially freshwater habitats, that pose no substantial threat to humans. There are hundreds of mosquitoes in Australia, less than a dozen really pose a substantial pest or public health threat. Many mosquitoes may play an important ecological role in wetland ecosystems. This may include representing a locally important food source for insectivorous wildlife or possibly pollinating plants.

A balance is required. If we’re going to continue squeezing an increasing human population into a narrow stretch of land up against the coast, there are many issues to consider here and they’re not just about how human activity is impacting those coastal wetlands. Pollution is a problem, our physical damage is another. Worst still, we’re taking away the opportunity of these normally resilient habitats to adapt to a rising sea levels and increasingly frequent storm events. Our cities and their infrastructure provide a hard and unforgiving edge against the wetlands.

Our wetlands even battle against themselves sometime. The threat of mangrove incursion into saltmarsh habitats is of increasing concern. Its counter-intuitive but perhaps we need to be pulling out mangroves to save some coastal wetlands.

Expanding, modifying, and creating new coastal wetlands will require local authorities to turn their mind to the issue of mosquitoes. Firstly, consideration needs to be given to what may constitute a tolerable level of mosquito exposure. How many mosquito bites are too many? How many cases of mosquito-borne disease are considered “normal” each year. Once these thresholds are drawn and exceeded, who is responsible for the decisions on active mosquito control? Who pays?

Another ecosystem disservice to consider is how the nuisance-biting of mosquitoes may discourage engagement with local wetlands. less engagement may mean less support for conservation and rehabilitation efforts. Less community interest, support, and activism may then result is less political drive to protect local wetlands by local authorities.

Importantly, decisions regarding the management of coastal wetlands, as well as those peppered throughout the city, need to be made with some consideration of mosquitoes and their potential impact. How do you convince the local community about the overall benefits of carbon sequestration, wildlife conservation, and protection of infrastructure is worthwhile if their quality of life is degraded through summer swarms and nuisance-biting mosquitoes?

More details on managing the risks associated with estuarine mosquitoes is provided in this book chapter included in the free Sydney Olympic Park Authority’s guide to managing urban wetlands.

For more about World Wetlands Day activities in Australia see here.

To stay up to date with my adventures in local wetlands, you can follow me on Instagram here.

 

 

 

Talking wetlands, wildlife and mosquitoes at the 2017 Australian Entomological Society Meeting

I’ll be in Terrigal, on the NSW Central Coast, for the 2017 Australian Entomological Society conference and taking the opportunity to present a summary of a number of collaborative projects undertaken in recent years, from working out how surrounding landuse influences the mosquito populations in urban mangroves to how important mosquitoes are to the diet of local bats.

Together with a range of colleagues, I’ve been undertaking research into the factors driving mosquito and mosquito-borne disease risk in urban wetlands. It is a complex puzzle to solve with more than just mosquitoes determining local pest and public health risks. However, with outbreaks of mosquito-borne Ross River virus on the rise in recent years, including urban areas of Australia, there is a need to better understand the factors at play.

There is a range of factors that may increase the risk of Ross River virus, they include suitable wetlands, wildlife reservoirs of the pathogen and mosquitoes. Understanding the mosquitoes associated with urban estuarine and freshwater wetlands is critical.

Investigating the role of surrounding landuse in determining the mosquito communities of urban mangroves, we found that industrial and residential areas tended to increase abundance of mosquitoes, perhaps due to direct or indirect impacts on the health of those mangroves. We’ve found previously that mosquitoes problems are often associated with estuarine wetlands suffering poor health, perhaps this is determining the increased mosquito risk we identified? You can read more in our publication here.

Expanding the investigation to look at urban freshwater wetlands, it was found that there was a high degree of variability in local mosquito populations and that each wetland needed to be assessed with consideration to be given to site-specific characteristics. You can read more about our work investigating mosquito assemblages associated with urban water bodies in our publication here.

More research is underway in this field and my PhD student, Jayne Hanford, has already started collecting some fascinating data on wetland biodiversity and local mosquito populations.

While the focus of our studies is often prompted by concern about Ross River virus, interestingly, in recent years we’ve found considerable activity of Stratford virus. This is not currently considered a major human health concern but given how widespread it is, it raises concerns about the suitability of local wildlife, even in Western Sydney, to represent important reservoirs of mosquito-borne pathogens. You can read more about Stratford virus in our publication here.

The final piece of the puzzle is to understand the ecological role of mosquitoes. Where their potential health threats are deemed significant, how could management of mosquito populations have unintended consequences for other wildlife. What about the animals that eat mosquitoes? A number of years ago we did some research to determine the importance of mosquitoes in the diet of coastal bats. While there was no indication that mosquitoes are a critical component of their diet, they are still being snacked on and mosquito control programs need to consider any local ecological impacts.

Now, how am I going to squeeze all this into 15 minutes….

The presentation abstract is below:

What drives mosquito-borne disease risk in urban wetlands?

Webb, C. (1, 2), J. Hanford (3), S. Claflin (4), W. Crocker (5), K. Maute (5), K. French (5), L. Gonsalves (6) & D. Hochuli (3)

(1) Department of Medical Entomology, NSW Health Pathology, Westmead Hospital, NSW 2145; (2) Marie Bashir Institute of Infectious Diseases and Biosecurity, University of Sydney, Camperdown, NSW 2006; (3) School of Life and Environmental Sciences, Faculty of Science, The University of Sydney, Camperdown, NSW, 2006; (4) Menzies Institute for Medical Research, University of Tasmania, Hobart, TAS, 7000; (5) Centre for Sustainable Ecosystem Solutions, Biological Sciences, Faculty of Science, Medicine & Health, University of Wollongong NSW, 2522; (6) School of Arts and Sciences, Australian Catholic University, North Sydney, NSW, 2060.

Managing pest and public health risks associated with constructed and rehabilitated urban wetlands is of increasing concern for local authorities. While strategic conservation of wetlands and wildlife is required to mitigate the impacts of urbanisation and climate change, concomitant increases in mosquitoes and mosquito-borne disease outbreak risk must be addressed. However, with gaps in our understanding of the ecological role of mosquitoes, could control strategies have unintended adverse impacts on vertebrate and invertebrate communities? A series of studies were undertaken in urban wetlands of greater Sydney to investigate the role of land use, wetland type and wetland aquatic biodiversity in driving the abundance and diversity of mosquito populations. A diverse range of mosquitoes, including key pest an vector species, were found in urban environments and mosquito-borne pathogens were detected in local populations, implicating local wildlife (e.g. water birds and macropods) as potential public health risk factors. Estuarine wetlands are locally important with the percentage of residential land and bushland surrounding wetlands having a negative effect on mosquito abundance and species richness while the amount of industrial land had a significant positive effect on species richness. Mosquito control in these habitats is required but insectivorous bats were identified as mosquito predators and the indirect implications of mosquito control should be considered. The aquatic biodiversity of urban freshwater wetlands influenced the species richness of local mosquito populations indicating vegetation plays an important role in determining local pest species. However, the matrix of wetland types also influences the abundance of mosquitoes in the local area. These results demonstrate the need for site-specific investigations of mosquito communities to assist local authorities develop policies for urban development and wetland rehabilitation that balance the need for conservation with reduced public health risks.

To keep up to date on what’s happening at the conference, check out the program online or follow the conversation on Twitter.

 

What do dogs and bird drawings have to do with conservation?

Ask a dog owner why they let their pets chase shorebirds across the local mudflats and the response will usually be “Don’t worry, they never catch ‘em”. But dogs don’t have to catch the birds to have a serious impact on them, especially when they’re chasing them off wetlands full of mud dwelling invertebrates that the birds love munching on.

Perhaps if the community was more aware of how vulnerable the shorebirds are,  maybe they’d be more likely to keep their dogs on a leash, off the local mudflats and the birds could feed in peace. But how can we get the message across to local residents?

A global traveller and annual visitor to local wetlands

The Bar-tailed Godwit, Limosa lapponica, is a migratory bird that flies all the way from Alaska to feed in Australia’s coastal wetlands each summer. A medium sized brown and white bird with a distinctively long upturned bill, the Bar-tailed Godwits are commonly seen feeding on aquatic insects and molluscs along the muddy foreshore of Sydney’s Parramatta River. They’ve become an iconic bird of the region, even featuring as one of the “mascots” of the “Our Living River”, an initiative to improve the health of the  Parramatta River.

Each spring they make the trip from the Arctic to Australia (non-stop flight around 11,000km has been recorded!) but to make the long flight back to Alaska, the Bar-tailed Godwits rely on finding enough food among the wetlands during their time along the river. The birds are commonly seen from spring to early autumn, often in flocks of a dozen or more, foraging in local mudflats. But their habitats are under constant threat from pollution and the encroachment of mangroves.

One location where the birds are commonly seen is Hen and Chicken Bay in the City of Canada Bay Council local government area. The suburbs of Abbotsford, Wareemba and Five Dock are nearby and the foreshore pathways and parklands are popular locations for exercise and recreation by both residents and visitors (please check out my favourite cafe, The Cove Dining Co, when you’re next visiting).

Unfortunately, the ever increasing human population, together with the easy access to the foreshore, brings threats to the Bar-tailed Godwits and their habitats.

People, pets and wildlife conservation

The Bar-tailed Godwits are quite tolerant of people. They’re happy to keep feeding while people and pets walk past. It provides a wonderful opportunity for the community to see these unique global travellers up close.

They have a tough time though when constantly chased by dogs or disturbed by people. Many times I’ve seen dogs running along the low tide shoreline, no doubt it is fun for both the pet and their owner. I have no doubt there is complete ignorance of the unintended consequences and that this may be a problem for the birds.

Awareness of shorebird conservation issues among those sharing habitats is a critical issue to address.

Reducing the impact of dogs on shorebirds is an issue faced by authorities around Australia as well as overseas. Beyond wetland habitats, studies have also shown dog walkers can have a negative impact on bushland birds too.

Putting a fence up around the wetlands isn’t a solution. The use of buffers is impractical and nobody wants to start setting traps or baits to stop the dogs. What else could be tried?

Illustration and wildlife conservation

Inspired by a project in Ku-Ring-Gai Council where school students drew signs encouraging dog owners to pick up after their pets, a similar approach was proposed for Hen and Chicken Bay. Could signs featuring the artwork of local students help get the message across?

Jointly funded by the Abbotsford Public School Parents and Citizens Association, and City of Canada Bay Council (Council’s Bushcare Department contributed funds in additional to a Canada Bay Community Grant), a series of educational signs were installed along the foreshore pathway of Hen and Chicken Bay as well as nearby Henry Lawson Park and Halliday Park.

When trying to decide on the design of the signs, it was important that there was some community ownership of the messages, they were aesthetically pleasing and lacked a serious authoritarian tone.

A competition was launched among students at Abbotsford Public School to draw Bar-tailed Godwits, one illustration was selected from each grade to be showcased on the signs. While the student’s drawing may not have been taxonomically accurate, they certainly reflected the great enthusiasm for the birds and this conservation process.

The school itself was wonderful and a component of the curriculum involved the students learning about the Bar-tailed Godwits and the importance of local wetlands. A local author, Jeannie Baker, had recently published the wonderful children’s book “Circle”, and a copy was purchased for almost every classroom and became a reference point for learning about the birds and their amazing global migratory journal to the local wetlands each year. Directly involving the students not only yielded some wonderful illustrations to personalise the signs but it also engaged the broader school community and assisted raising the profile of the project.

Along with an unique illustration on each sign, the key messages promoted were that the Bar-tailed Godwits visits the local mudflats from the Northern Hemisphere each year between August and April and to please don’t allow your dog onto the mudflats and please don’t allow off-leash dogs to chase birds. Dog owners were also directed towards to local off leash area in a nearby park.

An attitudinal study of dog owners in Victoria, Australia found that “Dog owners were more likely to feel obliged to leash their dog when they believed other people expected dogs to be leashed, and when they believed their dog was a threat to wildlife or people.” While this study was associated with beach-nesting birds, perhaps a similar attitude exists among those dog owners prone to allowing their dogs to run across bird-filled mudflat?

The signs were unveiled at an official launch in December 2016 by the Mayor of Canada Bay Council, Helen McCaffrey, and in attendance were representatives of Birdlife Australia, Our Living River and dozens of Abbotsford Public School students. Judy Harrington, Sydney Olympic Park Authority, kindly gave a talk to students on the day about the Bar-tailed Godwits and in the shadow of an approaching summer storm, a class alongside the local wetlands was a wonderful way to launch a novel and engaging project of environmental conservation.

Got any other ideas about how we can protect our local wetlands wildlife? Join the conversation on Twitter!

 

Preserve and protect? Exploring mosquito communities in urban mangroves

This is a special guest post from Dr Suzi Claflin. Suzi found herself in Sydney, Australia, (via Cornell University, USA) in 2015 to undertake a research project investigating the role of urban landscapes in determining mosquito communities associated with urban mangroves. She was kind enough to put this post together to celebrate the publication of our research in Wetlands Ecology and Management!

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Sometimes you’ve got to make hard choices for the greater good. These situations can arise anywhere, but here – as usual – we are concerned with mosquitoes. There’s a balancing act carried out by public health officials and wetland managers trying to both preserve endangered habitat and protect human health. In this guest post, I’ll explain the science behind research I recently published in collaboration with Dr Cameron Webb, and suggest one way forward for addressing human and environmental health concerns in urban wetlands.

During my PhD, I studied how the landscape surrounding small-scale farms affects the spread of a crop virus and the community of insect pests that carry it. When I came to Australia to work with Cameron, I was surprised to find myself applying the same type of landscape ecology to mosquitoes and mangroves in urban Sydney.

The misfortune of mangroves

Mangroves are real team players. They provide a range of services to the surrounding ecosystem and to the humans lucky enough to live near them. Mangroves are extremely effective at protecting the shoreline (but this can sometimes be a problem). They prevent erosion by gripping the soil in their complex root systems and buffer the beach by serving as a wave break. By filtering sediment out of the water that flows over them, mangroves also prevent their neighbouring ecosystems, such as coral reefs and seagrass forests, from being smothered.

Despite all their good work, mangroves have an almost fatal flaw; they prefer waterfront property. Unfortunately for them, so do humans. Urban and agricultural development has eaten away at mangroves, leaving them highly endangered.

The mosquito menace

Mozzies are a public health menace, because they spread human diseases like Ross River virus (RRV). Because of this, public health officials rightly spend time considering how to supress mosquito populations in order to reduce the risk of disease transmission.

Here’s where things get tricky: mangroves are great for mosquitoes.

That leaves public health officials and wetland managers in a difficult position. On the one hand, mangroves are delicate, at-risk ecosystems that need to be preserved. On the other, mangroves and surrounding habitats potentially harbor both the animal carriers of the RRV (e.g. wallabies) and a load of mosquitoes, which means that people nearby may need to be protected.

How can we do both?

 

Dr Suzi Claflin trapping mosquitoes in the mangroves along the Parramatta River, Sydney, Australia.

 

The potential power of prediction

This is a hard question to answer. One approach is prediction: using measurements of the environment, like rainfall and tide level, to estimate what the mosquito community will look like in a given region. The mosquito community determines what management actions, like spraying an insecticide, need to be taken, based on the threat it poses to public health.

We set out to explore how the way we use land (e.g. for residential areas or industrial areas) near urban mangroves affects the mosquito communities that live in those mangroves. The project involved dropping over retaining walls, slipping down banks, and tromping through muddy mangroves along the Parramatta River in Sydney. We set mosquito traps (billy cans of dry ice with a container on the bottom) and left them overnight to capture the mozzies when they are most active. We did this at two points in the summer, to see if there was any change over time.

We found that yes, the way we use land around a mangrove makes a difference. Mangroves with greater amounts of bushland and residential land in the surrounding area had fewer mosquitos, and fewer species of mosquitos. On the other hand, mangroves with greater amounts of industrial land surrounding them had a greater number of mosquito species, and those surrounded by greater amounts of mangrove had more mosquitos.

And, just to muddy the waters a bit more (pun intended), several of these relationships changed over time. These results show that although prediction based on the surrounding environment is a powerful technique for mangrove management, it is more complicated than we thought.

Another way forward: site-specific assessments

Our work suggests another way forward: site-specific assessments, measuring the mosquito community at a particular site in order to determine what management approaches need to be used. This is a daunting task; it requires a fair number of man-hours, and mangroves are not exactly an easy place to work. But it would be time well spent.

By assessing a site individually, managers can be confident that they are taking the best possible action for both the mangroves and the people nearby. It turns out that the best tool we have for striking a balance between environmental and public health concerns, the best tool we have for preserving and protecting, is information. In mangrove management—as in everything—knowledge is power.

Check out the abstract for our paper, Surrounding land use significantly influences adult mosquito abundance and species richness in urban mangroves, and follow the link to download from the journal, Wetlands Ecology and Management:

Mangroves harbor mosquitoes capable of transmitting human pathogens; consequently, urban mangrove management must strike a balance between conservation and minimizing public health risks. Land use may play a key role in shaping the mosquito community within urban mangroves through either species spillover or altering the abundance of mosquitoes associated with the mangrove. In this study, we explore the impact of land use within 500 m of urban mangroves on the abundance and diversity of adult mosquito populations. Carbon dioxide baited traps were used to sample host-seeking female mosquitoes around nine mangrove forest sites along the Parramatta River, Sydney, Australia. Specimens were identified to species and for each site, mosquito species abundance, species richness and diversity were calculated and were analyzed in linear mixed effects models. We found that the percentage of residential land and bushland in the surrounding area had a negative effect on mosquito abundance and species richness. Conversely, the amount of mangrove had a significant positive effect on mosquito abundance, and the amount of industrial land had a significant positive effect on species richness. These results demonstrate the need for site-specific investigations of mosquito communities associated with specific habitat types and the importance of considering surrounding land use in moderating local mosquito communities. A greater understanding of local land use and its influence on mosquito habitats could add substantially to the predictive power of disease risk models and assist local authorities develop policies for urban development and wetland rehabilitation.

Dr Suzi Claflin completed her PhD at Cornell University exploring environmental factors driving the spread of an aphid-borne potato virus on small-scale farms. She is now a postdoctoral research fellow at the Menzies Institute for Medical Research in Hobart, TAS. In her spare time she runs her own blog, Direct Transmission, focusing on disease and other public health issues (check it out here). To learn more about her doctoral research, follow this link!

Should we start pulling out mangroves to save our wetlands?

You have no idea how badly I wanted to jump down into the thick black mud.

I don’t remember much about primary school but I do have strong recollections of an assignment on the importance of mangroves to the ecology of the Parramatta River. Perhaps not the assignment itself, but I do remember Mum and Dad taking me down to the river and I drew some pictures of the twists and turns of branches and trunks and the finger-like pneumatophores punching up through the thick dark grey mud. It may only have been 10 minutes drive from home in Western Sydney but it was a glimpse into a world so strange and alluring, how could it not have made an impact on me?

I remember the great disappointment of my parent’s stern words keeping me from jumping down below the high water mark and into the mud. The same feelings of frustration and disappointment when stopped from doing other fun things like playing in stormwater drains, letting off firecrackers or swimming in rips!

Mangroves don’t just attract the attention of young environmental scientists. Exploiting a unique place between the land and sea, mangroves have intrigued and fascinated many before me with the first descriptions, by Greek mariners, thought to date back to 325BC. What were these plants that seemed to defy logic, growing half submerged in salty water?

Almost thirty years after my primary school assignment, with sandshoes replaced by gumboots, that childhood disappointment of adventure squashed is now matched by the realisation that mangroves aren’t perfect. In fact, they’re a threat to some of the other plants and animals found in our local local estuaries.

Now I spend most of my summer coated in that same dark grey mud, covered in mosquito bites and thinking about how important mangrove management will be for the future of our coastal wetlands.

More than mangroves

There is little doubt mangroves are an ecologically important habitat. They provide a home for a wide range of creatures, from bacteria to birds. Rich in nutrients and hiding places, mangroves are perfect nurseries for fish and crustaceans. Bird and bats and rodents and reptiles all find a home here too.

They’re threatened by climate change but they may also play a critical role in protecting our shoreline against sea level rise and storm surges. Sea level rise itself may knock out mangrove forests too but mangroves could also mitigate the impacts of climate change by storing carbon. In fact, the role estuarine wetlands may play in keeping carbon dioxide out of the atmosphere could be critical.

Make no mistake, mangroves are important. Thing is, it is also important to also remember that estuarine wetlands are more than just mangroves.

When we talk about estuarine wetlands, we’re grouping together a number of habitats that  include seagrass, saltmarsh, sedgelands and mudflats as well as mangroves. Each of these habitats play an important role in the functioning of the estuary as a whole but they each, individually, provide something specific to the wildlife that utilise the wetlands.

Saltmarshes are critically important and are in desperate need of conservation. In NSW they’re listed as Endangered Ecological Communities. As well as urbanisation and pollution, a changing climate and sea level rise risk severely degrading the quality of these habitats.

One of the key threats facing saltmarshes is a native plant. A native estuarine wetland plant. Mangroves.

The encroachment of mangroves into saltmashes is a serious problem. This is happening in many parts of the world. It is a strange situation in which one native plant is taking over another and with these ecological shifts, there are knock-on effects to other components of the wetland ecosystem. Most importantly, nesting and feeding shorebirds.

Are mangroves really a threat?

The mangroves are just doing what mangroves do. The reason they’re threatening saltmarshes is due to our modification of local environments.

Urban runoff reduces the salinity of these wetlands and this reduced salinity not only removes the ecological advantages of salt-tolerent saltmarsh plants, such as Sarcocornia quinqueflora and Sporobolus virginicus, but it helps mangrove seeds and seedlings survive the otherwise harsh environmental conditions of saltmarshes. Lower the salinity, increase the invasive potential of mangroves.

Frequent dryness and highly salty conditions are a saltmarsh’s best defense against invading mangroves.

Filling in wetlands and the construction of seawalls, roadways and other infrastructure give saltmarshes little refuge or respite from these threats. While mangroves encroach from the sea, there is nowhere for saltmarshes to migrate to when dealing with sea level rise.

They’re cornered and under attack but even where the plants are persisting, the quality of habitat they provide for local wildlife is slowly degraded by colonising mangrove seedlings.

There are many waterbirds that use our local estuaries that are under threat. Saltmarshes are great habitats for migratory shorebirds. There are plentiful resources in the form of insects and other invertebrates within the sediments. The birds can nest on the marsh and as they can see all around, predators are easy to spot. They feel safe.

There have been declines in the White-fronted Chat populations around Sydney. Many other populations of wading birds associated with Australia’s coastal wetlands are in decline too. Mangrove invasion isn’t the only thing to blame but it is an issue that needs to be addressed.

For many of these birds, the encroachment of mangroves into mudflats and saltmarshes is a problem. Its a problem for their foraging and nesting. Once mangrove seedlings start popping up on the middle of the saltmarsh, all those advantages of a wide open habitat in which predators are easy to spot are lost.

Imagine you’re a black-winged stilt. You’re trying to find a safe place to nest. A perfect place would be a raised area of saltmarsh surrounded by water. A dead flat saltmarsh with clear lines of sight for dozens of meters around. You’ll be able to see an approaching predator (like a fox or a feral cat) from far enough way to escape with plenty of time to spare. Now, stick a few mangrove seedlings here and there. They start to obscure your view. They’ll give sneaky predators a place to hide. Even if there are not predators about, you’ll probably get nervous. You’ll probably spend more time thinking about the threat of predators and less time foraging for food.

As mangroves move in, the birds will leave. Long before the saltmarsh is over run by mangroves, out-competed by the shade of establishing young mangroves, the quality of the habitat for many shorebirds will have already been lost. There may be some plants remaining but the ecological role of the habitat is gone.

Do historic paintings provide conflicting evidence to the commonly held view that mangroves have always been present along the Parramatta River? (Parramatta River, c. 1837, Conrad Martens (1801-78) via Australian Art Auctions)

Painting the picture of change in the local wetlands

How can we predict what will happen in the future if we haven’t learned from the past?

Tracking change in these wetlands is important. The use of photography has played an important role in tracking environmental change for a long time. Aerial photography and satellite imagery have helped reveal dramatic changes in vegetation associated with Australia’s coastal wetlands. This analysis has demonstrated the encroachment of mangroves into saltmarshes and this encroachment is considered a key threatening process of this endangered ecological community.

How can we track the encroachment of mangroves? While technology has helped reveal current changes in mangrove encroachment, other uses of imagery can explore relatively recent “urban myths” about historic mangrove distribution.

Thinking back to that school assignment, I remember being told how important mangroves were to the local environment. We we taught that, here in Sydney, that mangroves were always part of the Parramatta River estuary, that they have alwasy been a critical component of the river’s ecology. Was this really the case?

There has been some brilliant detective work done to determine the historic distribution of mangroves along the Parramatta River in this paper titled “Estuarine wetlands distribution along the Parramatta River, Sydney, 1788–1940: implications for planning and conservation“. The authors have used old photos and, in particular, some of the earliest paintings from the Sydney region (together with notes from settlers at the time) and found that the estuary was dominated by mudflats and saltmarsh habitats and that extensive areas of mangroves did not occur until the 20th Century.

To quote the author, Lynette C. McLoughlin:

“These historical sources indicate that in the 19th century extensive mudflats and saltmarsh communities dominated the inter-tidal zone, with mangroves more limited to creek fringes and some patches in bays for much of the period. In the upper river from Subiaco Creek to Parramatta, there is no evidence for the presence of mangroves until the 1870s. Following settlement and increased sedimentation, inter-tidal mudflats expanded, mangroves colonised up river and out onto mudflats in bays in the latter part of the 19th century, followed by expansion into saltmarsh in the 20th century.”

It is only relatively recently that mangroves have really flourished along the river.

There is absolutely no doubt they were always present, tucked away in the tiny bays and inlets of what became known as Sydney Harbour but it was the mudflats and saltmarshes that dominated much of the estuary. These habitats, no doubt, provided a rich and productive habitat for shorebirds and other wildlife.

So, where to from here?

Globally, mangroves are a critical component of wetland ecosystems. There is little doubt of that, and little doubt that in many parts of the world, even here in Australia, they are under threat. But so is saltmarsh and, saltmarsh is far less likely to be given the chance to demonstrate the resilience that mangroves will to continued changed environmental conditions results from a rising sea level and surging urbanisation.

Not just saltmarsh but mudlfats too.

Coastal authorities are increasingly aware of the need to balance protection of mangrove forests and the benefits they provide but also the conservation of saltmarsh and mudflats that are so critical to shorebirds.

The reality is, there will need to be a program of mangrove culling to sustain conservation of saltmarsh habitat. You need a permit to remove mangrove seedlings but a seasonal program of removal would be greatly beneficial in stopped the spread of mangroves into saltmarsh habitats. Local authorities are incorporating mangrove removal programs in their local wetland rehabilitation programs.

Removing young seedlings is easy, you can pull them straight out of the wet mud. Wouldn’t take much to organise a team of volunteers to move through the local saltmarsh removing seedlings. Perhaps in Autumn when the migratory shorebirds have left and the mosquito populations aren’t so bad?

The idea that native vegetation should be actively removed from habitats sounds at odds with environmental conservation. However, we need to maintain our wetlands for our future generations and the next generations of birds, and fish and crustaceans that rely on them now where few other opportunities exist.

2 February is World Wetlands Day. Please get out into your local wetlands, or at least make a pledge to visit your nearby wetlands sometime soon.

Learn more about Australia’s amazing mangroves by dropping by MangroveWatch and picking up the excellent Australia’s Mangroves by Norm Duke. There is also an extremely useful text on Australian Saltmarshes that is essential.

Finally, check out one of the most extensive resources on urban wetland management, including estuarine wetlands, via the free eBook produced by the Sydney Olympic Park Authority titled “Workbook for Managing Urban Wetlands in Australia“. Read a brief article on our analysis of the use of this resource in the latest issue of Wetlands Australia, see “Insights from the use of an online wetland management resource” by Webb and Paul (pages 26-27).

What are you doing for World Wetlands Day? Join the conversation on Twitter!

Want to learn more about the amazing world of Australian mosquitoes? Check out “A Field Guide to Mosquitoes of Australia” out now through CSIRO Publishing. Over 200 pages containing a pictorial guide to almost 100 different mosquitoes along with tips on beating their bite and protecting your family from the health risks of mosquitoes. You can order online or through your favourite local bookstore or online retailer.

 

Putting a value on science communication

For many scientists, communicating the ideas that underpin their areas of expertise to the public and policy makers is critical. Sharing the findings of research could make a difference to people’s lives, even if it is just to increase their appreciate of science and the world around them. But how do we value the communication of science by scientists?

Scientists often bemoan the lack of acknowledgment of their scientific communications and community engagement efforts. There is little doubt that these “outreach” activities receive far less “academic credit” than publication in high impact journals.

Writing for “popular science” outlets is often perceived to be a career negative. While some argue there needs to be capacity for the community engagement efforts of scientists to be acknowledged in the assessment of academic accomplishment, others argue against it. Regardless of your motivations, if you’re going to engage in science communication, it is best to make the most of your activities but even when your research goes vial, how can you put a value on this?

How can you value your science communications in a way that may be recognised for employment, promotion, grant applications etc?

One of my recent articles for The Conversation, why mosquitoes seem to bite some people more, went a little bit viral. Almost 1.3 million people clicked on that article. Would I swap it for an article in Nature (or any other scholarly publication with a high impact factor) that only 20 people read? Probably as it would make a far more valuable contribution to my career…but would it have the same potential to change people’s awareness and behaviour in avoiding mosquito bites? Probably not.

I’ve written before about the importance of social media in getting the public health messages informed by my research out to the public. A blog post I wrote about the shortcomings of mosquito repellent wrist bands in protecting people against mosquito bites is the most read post on my blog. Since first published, the article “Do mosquito repellent wrist bands work?” has been read by around 47,000 people. The original paper, published in a journal without an impact factor, may have been read by only dozens of people if I hadn’t written about it on my blog.

I’m increasingly asked to provide evidence of “engagement” or “translation” activities associated with my research. This is particularly the case for my activities with Centre for infectious Disease and Microbiology Public Health where translating research for improved public health outcomes is a key objective. Those outcomes have generally been focused on providing informed guidance to local authorities on infectious disease surveillance, diagnosis and treatment.

What about community engagement?

I wanted to share how I’ve been trying to value my science communication activities in recent years. My general approach to this is to document as much detail as possible about individual activities, try to quantify the reach of activities (as much as possible) and to try to use my experience with these activities into what could be best described as my “core” activities.

In the same way you may incorporate a new laboratory technique or statistical analysis into your research, why not incorporate your science communication activities similarly?

Every summer I find myself standing in the mangroves talking to a camera (while being bitten by mosquitoes)

Media activities

In the summer past, I’ve been interviewed about 50 times on research findings, disease outbreaks and topical issues associated with mosquitoes and mosquito-borne disease. This level of activity clearly holds the potential to engage the wider community with important public health messages as well as (hopefully) improve their understanding of local scientists and their research.

While keeping a track of the interviews and their details (date, topic, journalist, outlet etc) is handy, it is also possible to go beyond that to record audience reach and assign a relative value. This is where you’ll need the help of your institute’s media and communications unit. They should be able to obtain reports from media monitoring organisations that keep track of details (interview summary points and duration, audience size, estimated value) associated with media activities.

For example, on 16 January 2015 I did a live cross to Channel 7’s Sunrise program. The interview ran for just over 3 minutes, issues about mosquito-borne disease risk and personal protection measures were covered, it had an estimated audience of over 500,000 and was valued at around $200,000.

Over the course of a year (or perhaps a research project), it is possible to assign both a financial and engagement value? For me, the media activities over the 2014-2015 summer had an estimate audience of around 8 million and value of over $600,000. This extra level of detail adds so much extra weight to the value of science communications activities.

Mosquito Bites is the bulletin of the Mosquito Control Association of Australia. Distributed to members throughout Australia and many other countries, it provides information on the operational aspects of mosquito and mosquito-borne disease management.

Popular science writing

I regularly contribute articles to non-scholarly publications, these include newsletters, bulletins and magazines produced by local community groups, industry bodies and scientific associations. As well as recording the specific details about each article, it is also possible to record circulation as a measure of engagement.

If you need to add a financial value to these articles, why not consider what the current rates are for freelance journalists? They seem to be around $0.40-1.00 per word, that makes any (non-scholarly journal) writing associated with research projects as an “in kind” contribution valued at around $500-600? Planning on writing an article associated with an upcoming research project, why not include this extra value as an “in kind” contribution?

I regularly write for The Conversation. The website provides excellent data on the readership of individual articles (including with respect to other contributors from your institution) in addition to republication and social network sharing. Most of my articles receive around 6,000-8,000 reads but many have also reached around 20,000. Again, this is typically substantially greater exposure than received by my articles in scholarly journals. Recording this additional information would help make a handy argument that non-academic writing holds value, especially when arguing about research translation.

Output from @mozziebites Twitter Analytics for February 2015 showing data on impressions and engagement with my Tweets during the month.

Social media activity

Got a Twitter account or Facebook page? It is obviously great to keep track of your follower numbers, retweets, likes and shares of tweets and posts. It is a way to demonstrate engagement with the community. I started tracking my activity on Twitter early on. I was partly interested in whether people would engage with tweets about mozzies but I also wanted to demonstrate to my “bosses” that using social media for “work purposes” had some benefits in line with the public health objectives of my research activities. There was also a very nice paper published in 2012 that provided a framework for assessing the engagement of health authorities with social media and I wanted to gather similar data.

For Twitter users, you can access data on your own account via Twitter Analytics. It provides plenty of useful information, especially engagements (i.e. total number of times a user interacted with a Tweet, including retweets, replies, follows, favorites, links, cards, hashtags, embedded media, username, profile photo, or Tweet expansion), impressions (i.e. times a user is served a Tweet in timeline or search results) and link clicks (i.e. clicks on a URL in the Tweet). This kind of data can help demonstrate the extent to which the online community is interacting with your own social media activity.

It will also help if you engage with your institution on social media. Help promote their activities and those of your colleagues and collaborators. In turn they’ll help raise your profile too.

Speaking at public events provides opportunities to meet a wide cross section of the community….even celebrities such as Jimmy Giggle at the ABC community event at Parramatta Park, April 2014.

Community presentations

Every year i speak at a range of community events. In the past year or so I’ve spoken at such diverse events as Sydney Olympic Park Authority’s Life in the Park, Australian Skeptics in the Pub, Cumberland Birds Observer’s Cub meeting, Oatley Flora and Fauna Conservation Society meeting and Pint of Science. This provides an opportunity to speak to a wide cross section of the community but is also an opportunity to document experience in communicating to different audiences.

As well as keeping track of these speaking engagements (date, title, location, hosting organisation), I also try to record the number of attendees and most of the time I make a note of questions asked. This, again, is a way to document engagement/translation of research. It can also form a foundation for how you may shape research, it has particularly been the case for me reviewing the way we share public health information relating to the promotion of insect repellent use.

Communications and publications

Finally, think about ways you can parlay your experience with science communication into output that’s recognised by your organisation or institute. Why not write a perspectives piece, commentary or letter to the editor? I’m regularly seeing articles popping up in peer reviewed journals explaining the benefits of using social media, why not target a journal within your field that may not have covered the topic. You only need to see the metrics on this paper, ‘An Introduction to Social Media for Scientists‘, to realise that there is plenty of interest and having an extra journal article under your belt won’t hurt either.

Similarly, if you’re being asked to speak at conferences and workshops on your use of social media and/or science communication strategies, make sure you’re recording all those details too.

To conclude, there may not (yet) be a magic number to assign to your science communications activity in the same way impact factors and altmetrics help measure the success of traditional academic output. However, that doesn’t mean you cannot record a bunch of “metrics” associated with science communications, both online and off, that will hopefully better place you for that next job offer or promotion.

What do you think? How do you document your scientific communications activities? Join the conversation on Twitter.

Secret sounds beneath the water surface

What can you hear? Are you listening? 18 July is World Listening Day and the theme this year is “H2O”. Take a listen to some of the secret sounds beneath the water surface.

One of my hobbies is sound recording. While I’m having a lot of trouble finding time for this these days with a hectic work and family life, I like to try and make some time every year for World Listening Day. The event is the result of collaboration between World Listening Project, the Midwest Society for Acoustic Ecology and Biosphere Soundscapes. The date was chosen because it is the birthday of educator, philosopher, visual artist, and composer R. Murray Schafer whose seminal book, The Tuning of the World, inspired global interest in a new field of research and practice known as Acoustic Ecology. The theme for World Listening Day this year is “H2O”. Why? Well as the coordinators explain “The global water crisis means 750 million people around the world lack access to safe water. Water is rapidly becoming the commodity of the 21st century and the catastrophic effects of climate change often involve negative associations with water. Rising sea levels, devastating floods, melting ice in Antarctica and droughts spreading throughout the globe, all highlight our increasingly unpredictable and extreme relationship with water.” I’ve always had an interest in water. From years spent surfing up and down the east coast of Australia to my research in and around coastal wetlands, I seem to have spent much of my life in either in gumboots or wetsuits. Since investing in my first hydrophone a few years ago, the underwater sounds of wetlands have opened up a new world. I try to keep my recording gear handy during field trips and capture sounds from new locations. I think I’ve grown more interested in the sounds beneath the water than above. The sounds beneath the water are fascinating but they can also be disruptive. Many studies have highlighted the impacts of “noise pollution” on wildlife. All this noise is the “smog of the sea“. My contribution to World Listening Day 2015 is a piece assembled from (mostly) hydrophone recordings from along the Parramatta River, Sydney. The recordings were taken from a series of locations between the Gladesville Bridge and Charles Street Weir and include both “natural” and “unnatural” sounds. From footsteps on wharves to waves surging through mangroves and from the clattering of crustaceans to the clicking of frogs. Tune into the secret sounds beneath the Parramatta River. https://soundcloud.com/seaworthy/world-listening-day-2015-secrets-of-the-parramatta-river Join the conversation on Twitter and check out other World Listening Day activities.

Does wetland rehabilitation need mosquito control?

Mosquitoes can be more than a nuisance. They pose health risks but could also erode the good will of the community for wetland rehabilitation projects. Wetland rehabilitation needs mosquito control.

It’s a warm February evening. A small and anxious group of residents have gathered in a local community hall to discuss the implications of a local wetland rehabilitation project. Some are angry. One of the first questions comes from an elderly gentleman. Close to tears, he explains how his grandchildren no longer visit due to the plagues of mosquitoes that engulf his property day and night. “What are you guys going to do about it?” he pleads.

I learnt a valuable lesson that night. Trying to explain the best mosquito repellent to use doesn’t go down too well when an audience is facing some significant nuisance-biting impacts around their homes. It doesn’t matter how much DEET is in the repellent, it may well work but is it something you need to wear all day just to get the day to day jobs done around the house? Something more substantial is required and, with hindsight, should have been in place before the first waves of mosquitoes left the local wetlands.

Coastal wetlands are under threat

Sea level rise and climate change  is putting pressure on saltmarshes and urbanisation is eating away land that would otherwise accommodate a landward shift in estuarine habitats. There is nowhere for saltmarshes to spread to so they’re destined to be swallowed up by mangroves. While the mangroves are valuable themselves, they don’t provide the same critical habitats required by many of the internationally protected migratory shorebirds that rely on saltmarshes. Saltmarsh habitats could well disappear from much of the east coast in coming decades if sea levels rise as expected and mangroves continue their march landward.

Estuarine wetlands and mosquitoes

Saltmarshes are home to one of our most important pest and vector mosquito species. While it is important to remember that Aedes vigilax is an Australian native animal and just as much a part of our wetland ecosystems as fish and birds, there is little doubt that it can have substantial impacts with regard to nuisance-biting and the transmission of Ross River virus.

Historically, many of the saltmarshes along the east coast were drained or filled to enable increased cattle grazing (although much of it was under the guise of protection from flooding). Tidal flows were cut off with the construction of levee banks and installation of flood gates. Notwithstanding the impacts of grazing, without tidal exchange, the habitats became brackish water to freshwater dominated systems with a dramatic change in vegetation. Saltmarsh and sedgeland vegetation was steadily replaced by reeds and rushes. Invasive plants such as Phragmites quickly took over many of these wetlands.

Bringing back the tides

To combat the degradation of wetlands and impending loss due to climate change, there has been some ambitious wetland rehabilitation projects planned. One of the largest in the southern hemisphere is the Hexham Swamp Rehabilitation Project. Much can be learned from the experience in this wetland just west of Newcastle, NSW, and applied to rehabilitation projects, not only in Australia but overseas as well.

Rehabilitation of Hexham Swamp involved the staged opening of existing floodgates to reinstall tidal flows to an otherwise freshwater system. Many aspects of this project were considered and it is unsurprising that one major issue was the possible impact of mosquitoes. Mosquito populations were something of legend in this area, enough so that there is a “big mosquito” outside the local bowling club affectionately known as “Ossie the Mossie” (coincidently, “Ossie” celebrated her 20^th birthday in March 2014).

One of the important considerations when assessing mosquito risk was that there had been a dramatic transformation of the areas surrounding the wetlands in the last 20 years. What was once agricultural land was now residential. This is the same situation right along the east coast of Australia, the rapid urbanisation and swelling residential populations along the coast have put people in the firing line of Aedes vigilax.

The prospect of mosquito control was raised in the early stages of the rehabilitation planning but there was great reluctance from the local authorities to head down that path. The problem is that broad scale mosquito control and ecological rehabilitation are often seen at opposite ends of the wetland management spectrum. I’ve experienced this many times first hand, from scepticism regarding the non-target impacts of biological larvicides to “Apocalypse Now” jokes as helicopters go about routine spraying of local wetlands.

Is there such a thing as “environmentally friendly” mosquito control?

The hangover from the actual and perceived impacts of pesticide use more than 50 years ago is still present in the minds of many responsible for managing local wetlands. I say perceived as the development of environmentally sustainable mosquito control programs over the past two decades may not be appreciated amongst those charged with managing wetlands and wildlife.

I feel we need to continue building the case for the range of mosquito control strategies available for our coastal wetlands. Not only do we need to convince local authorities that mosquito populations can be minimised without adversely impacting the local environment but that mosquito control should be a critical consideration in wetland rehabilitation projects. It also has the potential to reduce mosquito-borne disease.

We know that the direct non-target impacts of Bacillus thuringiensis israelensis and s-methoprene are minimal and there is growing evidence that the indirect impacts on local wildlife due to reduced mosquito populations isn’t a major concern. Well-designed projects can also minimise the frequency of treatments while reducing peaks in mosquito activity.

It seems our coastal bats populations are mostly eating moths, not mosquitoes so there is unlikely to be any significant impact on these bats resulting from reduced food. There is no reason why the judicious use of larvicides can’t knock the top off abundant mosquito populations, reduce the pest impacts on local community and not pose a risk to local wildlife. Perhaps it should be considered a critical component of wetland rehabilitation?

Mosquito control and wetland rehabilitation

In speaking with wetland managers, I try to instil with them the importance of mosquito control. There is a risk that swarms of nuisance biting mosquitoes may erode the good will in the community for wetland rehabilitation. These systems, particularly in the early phases of rehabilitation don’t represent pristine environments and while there may not be a desire to establish ongoing mosquito control programs, some control may prove useful while the wetland comes back into balance with the changed environmental conditions.

Rehabilitation takes time and while there is substantial breakdown of freshwater vegetation it is not going to be ideal for fish and other mosquito predators. It is likely to provide ideal conditions for mosquitoes. Over time, however, fish are likely to increase in both their abundance and penetration into the wetlands and greater tidal flushing will make many of the wetland habitats generally unsuitable for mosquitoes.

Perhaps there is benefit in undertaking control as a show of good will to the local community? After all, engagement with the local community will be critical in the success of wetland rehabilitation projects.

The restoration of tidal flows to Hexham Swamp resulted in an initial increase in the abundance of Aedes vigilax. These increases resulted in substantial nuisance-biting impacts. However, in subsequent seasons, the populations of Aedes vigilax levelled out to comparable levels to those of the surrounding estuarine wetlands. The net result has generally been that the long-term moderate increases in Aedes vigilax populations have been balanced by reductions in Culex annulirostris and Coquilettidia linealis populations as the wetlands shifted from freshwater to saline. The health of the wetlands, as well as the local estuary, is improving.

Mosquito control is only a short-term fix and if the rehabilitation of estuarine wetlands is not carefully planned, there may well be ongoing mosquito impacts. However, reducing any initial impacts will go a long way to ensuring continued engagement of the community with the local wetlands. Cost and the operational considerations may be a barrier for organisations unfamiliar with broadscale mosquito control but these issues can be overcome with the expertise that exists in many parts of the country.

In summary, it is important that mosquito management be considered in the planning process of major wetland rehabilitation projects. There is little doubt that such projects will be required into the future as saltmarsh habitats and other estuarine wetlands are threatened but protection wetlands shouldn’t mean increasing mosquito populations. A balance is required between conservation of environmental health and protection of human health.

A longer version of this article originally appeared in “Mosquito Bites” (the Bulletin of the Mosquito Control Association of Australia).