Unintended consequences of wildlife conservation, could more frogs mean more mosquitoes?

We need to do all we can to protect our urban wildlife but what if the ways we do that increases mosquito risk? PhD candidate Jayne Hanford will be presenting the results of her research at the Ecological Society of Australia conference in Tasmania.

Mosquitoes can share their aquatic habitats with many other animals.

The 2019 Ecological Society of Australia conference will be held in Tasmania, 24-29 November. The conference theme, “Ecology: science for practical solutions”, is closely aligned with much of the work my collaborators and myself undertake each summer. We’re trying to ensure that recommendations on managing the pest and public health risks associated with mosquitoes is informed by the best available science.

Practical solutions to the challenges of balancing mosquito management while also ensuring positive outcomes from the environment too.

Jayne Hanford will be presenting her research in the “Field-based manipulative experiments for under-standing environmental change” symposium. She has been studying the aquatic biodiversity of urban wetlands as part of her PhD. This recent project aimed to determine what impacts management of urban wetlands to enhance conditions for local frog populations may have on local mosquito populations.

The research was undertaken at Sydney Olympic Park where an extensive network of freshwater ponds make up Narawang Wetlands. These wetlands are home to the endangered Green and Golden Bell Frog (Litoria aurea) but they’re also home to the plague minnow (Gambusia holbrooki). The plague minnow is essentially the cane toad of Australia’s waterways, introduced around 100 years ago to control mosquito populations, this aggressive predatory fish has impacted much of our local aquatic life, especially frogs. Populations of this fish need to be managed to enhance conditions for local frogs and, especially, their tadpoles.

Jayne has already found that mosquitoes avoid water bodies where the fish are found. The next step was to see how the seasonal draining of the local wetlands impacted the abundance and diversity of mosquito populations.

Immature mosquitoes and other aquatic macroinvertebrates were sampled from drained and undrained ponds within the wetland network. Once the drained ponds had been at least partially reflooded, mosquitoes were more likely to be found. This wasn’t too surprising given the results of previous experiments. Mosquitoes like to avoid habitats with fish but also, if they do lay eggs in those habitats, mosquito larvae aren’t likely to last long!

The results are useful for those authorities looking to manage waterbodies for wildlife conservation. Removal of the plague minnow may result in more suitable conditions being created for mosquitoes. It may be good for the frogs but we also know that their tadpoles aren’t eating the mosquito larvae. Strategies may be required to manage the pest and public health risks associated with local mosquitoes in these habitats.

You can catch Jayne’s work in the poster session but also as part of the symposium at 3pm on Monday 25 November in Chancellor 5!

The full abstract for Jayne’s presentation is below:

Unintended impacts of managing urban wetlands for conservation

Jayne K. Hanford^1,2*, Cameron E. Webb^2,3 , Dieter F. Hochuli¹

¹ School of Life and Environmental Sciences, The University of Sydney, Australia; ² Marie Bashir Institute for Infectious Diseases and Biosecurity, The University of Sydney, Australia; ³ Medical Entomology, NSW Health Pathology, Westmead Hospital, Westmead, Australia.

Urban wetlands are increasingly being recognised as valuable conservation resources that support significant biodiversity. Concerns around the pest and public health risks of mosquitoes will restrict how we manage these wetlands, as outbreaks of mosquito-borne diseases fuel public fear and foster dislike of mosquitoes. Understanding the ecological and public health consequences of wetland management practices is vital to maximise the conservation value of urban wetlands without negatively impacting public health. Our aim was to determine how wetland management to benefit a threatened species affects mosquitoes and aquatic biodiversity. A group of six urban wetlands in Sydney, Australia, were drained to reduce the abundance of an invasive fish, Gambusia holbrooki, and then refilled to provide breeding habitat for a threatened frog, Litoria aurea. We collected and compared aquatic macroinvertebrates, mosquito larvae, and mosquito adults from these refilled wetlands, and six adjacent undrained wetlands, on four occasions across summer and autumn. Wetland draining had a significant effect on aquatic macroinvertebrates and larval mosquitoes, although differences between drained and undrained wetlands decreased over time. Draining did not affect adult mosquito assemblages associated with the wetlands. The number of constructed and rehabilitated wetlands in urban areas continues to grow, and while conserving threatened habitats and species is imperative, our results highlight how wetland management can impact non-target species with potentially negative effects on humans. It is vital that future design and management of urban wetlands around the world also considers the impact on vectors of human disease.

 

If you’re at the conference, why not join the conversation on Twitter using the official conference hashtag #ESAus19 or reaching out to Jayne or myself!

 

 

 

 

 

 

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.