Preserve and protect? Exploring mosquito communities in urban mangroves

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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?

 

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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?

mangroves_webb_SOPA_November2015

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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

 

Can social media help track environmental change?

saltmarshrehabilitation_KGIA picture may well tell a thousand words but what if that picture is tweeted, shared and liked? Could social media help engage the community with local wetlands? Could it assist in crowd sourced tracking of environmental change?

After the fire comes the photos

Using photography to track post-bushfire environmental change is common in Australia where bush fires are a part of life. Scientific publications and technical reports produced across the country have used “before and after” photos to highlight the dramatic change, and equally dramatic recovery, seen in the Australian bush after fire.

How can we incorporate social media in tracking this post-fire recovery? Perhaps it could even play a role in boosting the spirits of the local community seriously impacted by bushfire? The recovery of communities is as important as recovery of the environment. A recent study has highlighted the importance of social networks in the community and perhaps opportunities to share interactions with the environment through social media would provide further opportunities for engagement.

Bushfires are a natural part of the Australian environment and photography plays a key role in reminding us that our vegetation can respond remarkably after even the most intense fires (Source: CSIRO)

Bushfires are a natural part of the Australian environment and photography plays a key role in reminding us that our vegetation can respond remarkably after even the most intense fires (Source: CSIRO)

An example of engaging social media in bushfire recovery comes out of California. I’m particularly taken by the use of social media as a critical component of the program tracking recovery from bush fires that swept through Mt. Diablo in 2011. The project is coordinated by the Nerds for Nature team, inspired by the initiative of Sam Droege and his Monitor Change project.

The idea is based around members of the community taking photos at set locations with set perspectives and compiling those photographs shared through social media, to create a crowd sourced time lapse animations of post-bush fire recovery (you can read a little more about it here). What makes this so neat is the simplicity. Clear signage and a simple bracket for lining up your camera/phone. The website interface is great too. The team behind the project have provided some detailed instructions that form a great basis for adapting this approach to a local environment (they also point out that this project may not be as simple to implement as you may think…).

Tracking bushfire recovery with crowd sourced photographs! (Originally tweeted by Sergei Krupenin in reference to Nerds for Nature program)

An Australian take on crowd sourced “environmental change” photography

Another example of using photography to track environmental change is the Australian Fluker Post project. Similar to the approach by the Nerds for Nature team, this project, coordinated by Dr Martin Fluker at Victoria University, is a “citizen science system designed to allow community members to contribute towards the ongoing care of various natural environments by taking photographs”.

“Fluker Posts” are installed at key locations and members of the community can use their own cameras to take photos and then email them to coordinators. As well as collecting material to assist local land managers, this project may have a more subtle influence on conservation by engaging the community with the local environment. By providing an opportunity for local residents (as well as regular visitors) to track the changes in their local environment, it would be hoped that a connection and care for the local environment would increase. As well as directly changing behaviour that may threaten local habitats or wildlife, the community (and by extension local decision makers) are more likely to be supportive of rehabilitation efforts.

An example of a newly installed Fluker Post ready to help track environmental change (Source: The Fluker Post Project)

An example of a newly installed Fluker Post ready to help track environmental change (Source: The Fluker Post Project)

You can see examples of photos from the various Fluker post locations here but you can also keep up to date with various projects at the Fluker Post Facebook page. A relatively new venture has just kicked off using this “technology” to engage with school students – a great idea!

Tracking tidal changes

Another great example of crowd-sourced tracking of the potential environmental change is the  Witness King Tides program. The program is coordinated by Green Cross Australia and calls of members of the community to submit photos taken during king tide events (the highest of the spring tides each month) to help generate an indication of what may happen in the future with sea level rise. There is a wonderful collection of photo albums here from across Australia.

This idea of a crowd-sourced collection of photographs tracking tidal events has been tried in the past. Most notable was a collection of photos contributed to by over 250 people taken during a major tide event in 2009. A useful document was produced by NSW Office of Environment and Heritage. It highlights an important issue in relation to potential impacts of sea level rise. The first wave of impacts may not be catastrophic but they will be disruptive.

While images of major cities underwater often accompany media reports of rising sea levels and plans for adaptive responses, in many parts of Australia, increasing frequency of these “higher than usual” tides will cause disruption to cities and townships in other ways. Blocking stormwater systems, forcing the closure of roads and delays with ferry services. In addition to this, there is the increasing risk of coastal erosion and loss of amenities in coastal regions.

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“Before and after” shots of a cycleway through Sydney Olympic Park in January 2014. Higher than expected spring tides flooded many of the pathways, cycleways and boardwalks in the local area causing much disruption; perhaps a sign of things to come if rising sea levels make these event more frequent.

One of the problems with this method, however, is that these photographs end up being “one offs”. Without a comparison to “normal” conditions, it can sometimes be difficult to gauge the significance of tidal inundation without being familiar with the local area. Fortunately, there are many examples where contributors send both “before” and “after” tidal inundation shots and they do provide a stunning visual representation of the disruption sea level rise may cause. Perhaps the incorporation of “photography points” (following the examples from the Flucker Post or Nerds For Nature teams) at key locations would be a useful addition to the program?

This approach has been adopted bytThe City of Manduarh in Western Australia with their  Tidal Image Mandurah Project. The community has been asked to take photos at key locations with a view that images of tidal events such as storm surges, high tide and erosion will help track change. Nothing too fancy in these locations either, just a strategically placed spray painted blue camera!

An example of the spray-painted blue camera on a beachside post inviting members of teh community to take and share a photo of Florida Beach (Source City of Mandurah)

An example of the spray-painted blue camera on a beachside post inviting members of the community to take and share a photo of Florida Beach (Source: City of Mandurah)

Tracking constructed wetland change

Where would I like to see this implemented? I’ve had the opportunity to work in and around many newly constructed wetlands. These have ranged from small freshwater wetlands in urban areas to extensive rehabilitated estuarine wetlands. The common denominator across all these sites has been vegetation change. I cannot be out there every week taking photos but it would be great if there was a collection of photos being shared by the local communities that I could tap into.

There are some great examples of interpretive signage around our local wetlands. There is also a shift in thinking from traditional interpretive signage to take advantage of new technologies so why not include social media to engage visitors and local community further? Perhaps social media networking should be included in wetland management plans?

Signage at Gungahlin Wetlands, ACT

Signage at Gungahlin Wetlands, ACT. An example of structures associated with urban wetlands that can be modified to include opportunities for social media use through the use of recommended hashtags (for Twitter or Instagram) and/or brackets for placing cameras/smartphones

A simple addition of a bracket and details on sharing photographs could easily be incorporated into local signage as it is installed and/or updated. As well as tracking changes in vegetation growth in and around constructed and rehabilitated wetlands, the encroachment of mangroves into mudflats or sandy shores along urban estuaries could be a focus too. Of course, storm events and unusually high tides could be documented too. An added bonus would be if some rare or unusual wildlife popped up in photographs.

Educational signage of this nature are common place around wetlands in Sydney, could the inclusion of some guidelines for social sharing images help track mangrove incursion into shoreline habitats?

Educational signage of this nature is common place around wetlands in Sydney, could the inclusion of some guidelines for social sharing images help track mangrove incursion into shoreline habitats?

There are plenty of other ways social media can assist environmental conservation and rehabilitation. Pozible and Landcare have recently announced the launch (and called for the submission of proposals) of a new global crowdfunding partnership called The Landcare Environment Collection, an opportunity to showcase and support the crowdfunding campaigns of environmental groups in Australia and around the world.

Perhaps I need to prepare a proposal for the installation of some “social sharing” camera stands…

Why not join the conversation on Twitter and help share other examples of where social media could help track environmental change.