Larval fish nurseries are facing a tiny, yet dangerous new enemy: Microplastics

*This post is by Alexa Torres, a student in Marc's 'Causes and Consequences of Diversity' class.

Recent research has shown that many larval fish species from various ocean habitats are ingesting large quantities of microplastics within their preferred nursery habitat.

Approximately 300 million tons of plastic gets manufactured per year, with around 5 to 13 million tons of it ending up in our oceans. Much of this is in “macro” form such as plastic packaging, fishing nets, and buoys that are quite easy to spot littering shorelines or swirling around the enormous circular currents of the world's oceans. Microplastics constitute pieces of plastic too small in size to be filtered out of sewage systems: synthetic fibers,  microbeads commonly used in cosmetics and industrial cleaners, as well as minuscule scraps that are broken off from any type of plastic. 

Polyethylene beads extracted from cosmetic products, as shown in an electron micrograph, regularly pass through sewage and treatment plant filters, later ending up in open waters.

Image courtesy of Adil Bakir and Richard Thompson (Plymouth University, UK)

A growing number of research as of late have been dedicated to investigating precisely where microplastics are found and their effects on marine life. While much  evidence has shown that adult fish are ingesting plastic, recent studies show that fish at their larval stage are also consuming plastics, as early as mere days after they have been spawned. Larval fish make up the next generation of adult fish of who will supply resources of protein and nutrients to populations around the world, yet little is understood as to the ocean processes that affect the survival of these quintessential organisms.

Surface slicks are naturally occurring, ribbon-like, smooth patches of water on the ocean surface. These water features typically contain high densities of larval fish as well as aggregate plankton, which are an important food source for them. In addition, surface slick nurseries concentrate lots of planktonic prey, providing an oasis of food that is critical for the development and survival for fish in their larval stages. However,  NOAA’s Pacific Islands Fisheries Science Center and an international team of scientists conducted a field study sampling coastal waters of Hawaii and discovered that the same ocean processes that were allowing for the aggregation of prey for larval fish also concentrated passively floating microplastics. “We were shocked to find that so many of our samples were dominated by plastics,” said study co-lead Dr. Jonathan Whitney, a marine ecologist for the Joint Institute for Marine and Atmospheric Research and NOAA. Plenty of times, plastics found in surface sinks, and therefore larval fish nurseries, can be on average eight times higher than plastic densities found in other ocean habitats.

Larval fish lay a foundation to ecosystem function, representing the future of adult fish populations. These organisms are highly sensitive to environmental and food changes. With nurseries and larval fish populations being surrounded by and ingesting toxin-laden plastics that provide no nutrition at their utmost vulnerable life-history stage, it indicates a call for attention and cause for alarm. Plastics ingested by adult fish induce malnutrition, stemming from gut blockages and accumulation of toxins. As a more unfamiliar subject, researchers are not fully aware of the exact harm plastics cause to larval fish, however, they can predict that microplastics may play a role in negative impacts to development and even reduce survivorship of those that ingest them.

Despite calls for classification of plastics to be categorized as hazardous, there has been a lack of legislation to restrict marine debris accumulation as it is still hindered by a lack of evidence to show the exact ecological harm caused. The productivity of fisheries, as well as overall marine biodiversity, are currently threatened by a large number of anthropogenic stressors including climate change, habitat destruction, and overfishing. Modern studies have suggested that pollution of microplastics to fish nurseries and ingestion of them at larval stages are now emerging as a novel issue and have since become the lists’ newest addition.

References

Galloway, T., & Lewis, C. (2016). Marine microplastics spell big problems for future generations. Proceedings of the National Academy of Sciences of the United States of America, 113(9), 2331-2333. Retrieved February 19, 2020, from www.jstor.org/stable/26468516

Katsnelson, A. (2015). News Feature: Microplastics present pollution puzzle: Tiny particles of plastic are awash in the oceans—but how are they affecting marine life? Proceedings of the National Academy of Sciences of the United States of America,112(18), 5547-5549.

Rochman, C., Browne, M., Underwood, A., Van Franeker, J., Thompson, R., & Amaral-Zettler, L. (2016). The ecological impacts of marine debris: Unraveling the demonstrated evidence from what is perceived. Ecology, 97(2), 302-312. Retrieved February 19, 2020, from www.jstor.org/stable/24703091

University of Hawaii at Manoa. (2019, November 11). Prey-size plastics are invading larval fish nurseries. ScienceDaily. Retrieved February 17, 2020 from www.sciencedaily.com/releases/2019/11/191111150636.htm

The “man” in mangroves: How does the Anthropocene impact biodiversity in these ecosystems?

 *This post is by Nina Adamo, a student in Marc's 'Causes and COnsequences of Diversity' class.

Mangroves are among the most biologically important forest ecosystems on Earth, found in the intertidal zone between land and sea along tropical and subtropical coasts around the world.⁷ Mangrove ecosystems provide habitat for a wide range of terrestrial as well as aquatic organisms including plants, fish, mollusks, birds, reptiles, and crustaceans, among many others.¹

Mangroves also serve as nursery habitats for various fish and crab species found in coastal regions, as mangroves provide high abundances of food and shelter for developing wildlife living in coastal regions.⁷ Since many species use mangroves as nursery grounds, fish diversity and abundance in neighbouring coastal ecosystems has been positively linked to the proximity of mangrove areas, suggesting that mangrove habitat is critical in supporting biodiversity in surrounding coastal ecosystems.⁵

Figure 1: Many species such as fish and crustaceans use mangroves as a nursery site for their young, where shelter from predators and food is abundant.⁹

Along with supporting a wide range of biodiversity along coastal ecosystems, mangroves also provide many essential ecosystem services to humans. Some of these societal benefits include natural resources such as fish and timber, coastal protection from storms, and assisting in mitigating climate change by removing carbon dioxide from the atmosphere and storing it.¹¹

Despite the critical role mangroves play in supporting coastal biodiversity and providing ecosystem services to society, mangroves have been disappearing globally at an alarming rate of 1-2% per year due to anthropogenic activities and accelerated global climate change.⁴ The main threats to these ecosystems are rising sea levels causing coastal erosion, environmental condition changes due to climate change, land-use changes, deforestation, and overexploitation of natural resources.⁴ This has led to the loss of about 50% of mangrove coverage across the globe since 1950.¹⁰

In recent years, there have been a great number of studies that have explored the impacts of anthropogenic activities and climate change on the biodiversity of vegetation, benthic meiofauna, and benthic fauna found in mangrove ecosystems.

Figure 2: A stilt mangrove tree in a mangrove forest coastal ecosystem on an island in East Kalimantan, Indonesia.⁸

In the Sundarbans, which is the world’s largest remaining natural mangrove ecosystem located on the border of Bangladesh and India, there has been a homogenization of tree species composition over the span of 28 years from the 1980s to the 2010s.¹⁰ In other words, the largest remaining mangrove ecosystem has experienced a loss in community biodiversity of mangrove plant species over time due to anthropogenic activities and the environmental impact of climate change.

The loss of biodiversity in ecosystems is a crucial issue because higher biodiversity in most ecosystems typically leads to higher ecosystem functioning, so if biodiversity is lost through stressors such as habitat loss or extreme environmental conditions such as those produced through global climate change, it could have severe impacts on the diversity of an ecosystem and hence the functioning of the ecosystem as a whole.²

The biodiversity of benthic meiofauna, which are very small invertebrates that live in the bottom of aquatic mangrove ecosystems, are also negatively impacted by anthropogenic disturbances. In a comparison study of disturbed and undisturbed mangrove areas, disturbed areas displayed a 20% loss of benthic meiofauna biodiversity compared to undisturbed mangrove areas.² Since many juvenile fish species that use mangrove ecosystems as nursery grounds rely heavily on meiofauna for food, this loss of biodiversity through anthropogenic causes could cause a reduction in ecosystem functioning not only within mangrove communities but in surrounding coastal ecosystems as well.²

A similar observation is also found with the biodiversity of benthic fauna in mangrove ecosystems in the Philippines, where protected mangrove ecosystems have significantly higher diversity and abundance of crab species than reforested mangrove ecosystems that have been disturbed by humans.¹ This suggests that environmental factors influenced by climate change and human influences in mangrove ecosystems can have a negative impact on the biodiversity of benthic fauna, one of the most dominant groups in these systems, which could impair the overall functioning of the ecosystem.¹

With the increasing loss of mangrove habitat and the biodiversity within it across the globe due to anthropogenic activities and climate change, it is essential that humans intervene with utilizing other paradigms such as the flagship species paradigm to increase mangrove conservation and policies to protect mangrove habitat,¹¹ well-researched and well-managed mangrove planting restoration,⁶ and more research on innovative manmade artificial mangroves that may help to restore these ecosystems.³

Figure 3: Locations of the various megafauna found in mangroves (locations of mangrove areas shown in green) around the globe, with the orange representing terrestrial and the blue representing aquatic megafauna. Some examples of megafauna found in mangroves (from top-left to bottom-left in a clockwise direction) include the Key deer, Manatee, Sailfin lizard, Sawfish, Three-toed sloth, Spotted deer, Bengal tiger, Otter, Green turtle, Crocodile, and the Proboscis monkey.¹¹

The focus of much of the recent research on mangrove conservation has utilized an ecosystem services approach, where the benefits that mangroves provide to humans is stressed as an incentive for conservation.¹¹ For this reason, most of the research has been focused on smaller benthic invertebrates such as crabs and shrimp, rather than larger charismatic megafauna that are found in mangroves around the world such as sloths, Bengal tigers, green turtles, and proboscis monkeys.¹¹

Conservation awareness of mangrove ecosystems could be improved by using the flagship species paradigm which uses larger charismatic species found in mangrove ecosystems in marketing campaigns that would protect the entire ecosystem in which they are found. Since charismatic megafauna have been observed in mangrove habitats across the globe, using the flagship species paradigm in conjunction with the ecosystem services paradigm could increase public awareness of the threats facing these extremely diverse and productive ecosystems.¹¹

Conserving mangrove ecosystems around the world is important as these ecosystems provide ecosystem services to human society and play a critical role in supporting biodiversity within mangrove systems and in neighbouring coastal systems. With the increasing threat of anthropogenic activities and global climate change, the conservation and protection of mangroves is essential to reduce the decline in ecosystem functioning and biodiversity in these ecologically important ecosystems that many animals and humans alike rely on in order to live productive and successful lives.

References

1.     Bandibas, M. B., & Hilomen, V. V. (2016). Crab biodiversity under different management schemes of mangrove ecosystems. Global Journal of Environmental Science and Management, 2(1), 19–30. https://doi.org/10.7508/gjesm.2016.01.003

2.     Carugati, L., Gatto, B., Rastelli, E., Lo Martire, M., Coral, C., Greco, S., & Danovaro, R. (2018). Impact of mangrove forests degradation on biodiversity and ecosystem functioning. Scientific Reports, 8(1), 1–11. https://doi.org/10.1038/s41598-018-31683-0

3.     Florida Atlantic University. (2018). Humanmade mangroves could get to the “root” of the problem for threats to coastal areas. ScienceDaily. Retrieved February 20, 2020, from https://www.sciencedaily.com/releases/2018/08/180829115627.htm

4.     Hapsari, K. A., Jennerjahn, T. C., Lukas, M. C., Karius, V., & Behling, H. (2019). Intertwined effects of climate and land use change on environmental dynamics and carbon accumulation in a mangrove-fringed coastal lagoon in Java, Indonesia. Global Change Biology. https://doi.org/10.1111/gcb.14926

5.     Henderson, C. J., Gilby, B. L., Schlacher, T. A., Connolly, R. M., Sheaves, M., Flint, N., Borland, H. P., & Olds, A. D. (2019). Contrasting effects of mangroves and armoured shorelines on fish assemblages in tropical estuarine seascapes. Ices Journal of Marine Science, 76(4), 1052–1061. https://doi.org/10.1093/icesjms/fsz007

6.     Kodikara, K. A. S., Mukherjee, N., Jayatissa, L. P., Dahdouh‐Guebas, F., & Koedam, N. (2017). Have mangrove restoration projects worked? An in-depth study in Sri Lanka. Restoration Ecology, 25(5), 705–716. https://doi.org/10.1111/rec.12492

7.     Nagelkerken, I., Blaber, S. J. M., Bouillon, S., Green, P., Haywood, M., Kirton, L. G., Meynecke, J.-O., Pawlik, J., Penrose, H. M., Sasekumar, A., & Somerfield, P. J. (2008). The habitat function of mangroves for terrestrial and marine fauna: A review. Aquatic Botany, 89(2), 155–185. https://doi.org/10.1016/j.aquabot.2007.12.007

8.     Rante, A. (2019, December 12). A stilt mangrove tree in a protected area on Semama Island in East Kalimantan. Supertrees: Meet Indonesia’s mangrove, the tree that stores carbon. [Image].Vox. Retrieved February 20, 2020 from https://www.vox.com/2019/12/12/21009910/climate-change-indonesia-mangroves-palm-oil-shrimp-negative-emissions-blue-carbon

9.     Rante, A. (2019, December 12). In the water lapping at mangrove roots, young fish and plankton take refuge from predators. Supertrees: Meet Indonesia’s mangrove, the tree that stores carbon. [Image].Vox. Retrieved February 20, 2020 from https://www.vox.com/2019/12/12/21009910/climate-change-indonesia-mangroves-palm-oil-shrimp-negative-emissions-blue-carbon

10.  Sarker, S. K., Matthiopoulos, J., Mitchell, S. N., Ahmed, Z. U., Mamun, Md. B. A., & Reeve, R. (2019). 1980s–2010s: The world’s largest mangrove ecosystem is becoming homogeneous. Biological Conservation, 236, 79–91. https://doi.org/10.1016/j.biocon.2019.05.011

11.  Thompson, B. S., & Rog, S. M. (2019). Beyond ecosystem services: Using charismatic megafauna as flagship species for mangrove forest conservation. Environmental Science & Policy, 102, 9–17. https://doi.org/10.1016/j.envsci.2019.09.009

Intellectual death by a thousand cuts

My business is thinking. Let me be a little less succinct. My profession as a Professor of Biology is my passion, and I am fortunate enough to be paid to think about how the natural world works and to come up with possible solutions to global problems. I was trained to do this and my past training (all 11 years) and my current salary are paid by taxpayers to do this. This all seems rather straightforward, but yet why does it feel like the universe is conspiring to prevent this intellectual work from being done?

As pointed out brilliantly by Cal Newport in the Chronicle of Higher Education, in an article titled “Is E-mail Making Professors Stupid?”, Professors are being buried under a pile of administrative work at the expense of intellectual pursuits. The amount of time and effort spent on managing people and money, sitting on departmental/university committees, representing the university externally, and applying for research funds and awards have all increased significantly over time. Professors are increasingly being converted into middle managers, the victims of a culture of bureaucratization and downloading.

At the organizational level, this all makes sense. The necessary regulatory obligations and internal checks and balances are very robust, and appear, to outside scrutiny, as though tax-payer funds are being used correctly and efficiently. However, the reality is that university bureaucracies have grown substantially over the past couple of decades while student enrollment and faculty numbers at many institutions has been stagnant or even declining. And a byproduct of this increased bureaucracy has been an increase in internal programs and procedures that require communication and paperwork.

This increase in internal communication and administration has been paired with increasing external demands for professors’ time. Increasing requests to perform grant and manuscript reviews, participate in panels, pressure to include outreach and knowledge mobilization in research projects, and the inundation of predatory journals and conference requests have been experienced by all researchers.

All these forces conspire to eat away at the ability for professors to do the thing they are actually paid to do –literally the death of the intellectual by a thousand cuts. If I were to properly answer all of the e-mails I receive, I would be spending 3+ hours a day doing this one task. Not to mention meetings. Professors spend much more of their time in meetings today than a generation ago. I just looked at the next week in my calendar (an uneventful week by my standards), and there are 14 hours of meetings scheduled. I also need to schedule these meetings myself an increasingly frustrating activity that requires multiple attempts. So e-mail and meetings alone would amount to about 25-32 hours a week.

 

What should I be doing with my time? Well, working on manuscripts (my students and my own), editing and reviewing for journals, writing grant proposals, teaching, participating in student committees, data analyses, research projects and training, and reading are all necessary. My estimation of the time needed to optimize these, or at least do a minimally acceptable job, would be about 30 hours a week. So, either I work a minimum of 60 hours a week, or something has to give. I am fortunate that I have the resources to hire a lab manager and do not need to deal with lab management and ordering supplies, etc., which would require an additional 4-8 hours a week.

At the moment I am faced with a dichotomous decision, work evenings and weekends or purposefully prioritize certain activities over others. And to the frustration of colleagues and administrators, e-mail tends to the bottom of the priority list. But this cost of bureaucratization should not be burdened by professors alone.

Cal Newport highlights several mechanisms to relieve this burden in his article. Minimally, professors should schedule e-mail time, like one hour a day. And, filed under “do as I say, not as I do”, professors should say 'no' to many of the unsolicited requests that pull them away from their core responsibilities. Yet institutions have a role to play. Newport suggests that Professors require executive assistants to manage e-mail correspondence, scheduling and paperwork and these should come with their positions (not one to one, perhaps shared amongst groups of faculty). Since professors routinely work extra hours to stay on top of all the demands, they should start to be compensated for this additional work. Further, there should be an agreed upon fixed amount of administrative service they are required to do (e.g., 10 hours a week), and going beyond this should require teaching buyouts or other forms of compensation (e.g., funds for assistant).

While the onslaught of demands seems so overwhelming, there are solutions. They just need to be pursued and pushed to university administrations.

Life isn't all Rainbows and Butterflies...

Guest post by Carolyn Thickett, MSc. Candidate at the University of Toronto-Scarborough

Life isn't all Rainbows and Butterflies...

… especially in an age of extreme habitat loss, chemical pollution, invasions by alien species and climate change. All of these pressures are contributing to the dramatic decline of insects currently being observed all around the world.

In Canada, the general public is responding by trying to contribute their time and knowledge in any way that they can. Citizen Science programs encourage people with little or no previous experience to participate by working with staff from one of the conservation areas in the Greater Toronto Area. These programs are aimed at engaging the general public in conservation efforts for the purpose of education, but with the added benefit of reducing the cost of expensive conservation work.

Many more events are happening out of the public eye, not advertised, even held in secret. I attended one such event this past June, held in an undisclosed location, in Eastern Ontario. This was an invitation-only event, attended by a consortium of people concerned about the status of the Mottled Duskywing Butterfly in Ontario, spearheaded by butterfly enthusiast Jessica Linton.

Mottled Duskywing Butterfly. Photo: Carolyn Thickett

Dr. Gard Otis, a bee and butterfly researcher from the University of Guelph, is unveiling new
information about these specialist butterflies and their unique habitat requirements. The Mottled Duskywing depends on New Jersey Tea (Ceanothus americanus), a plant that is common to alvars as well as sandy soils supporting oak savannas, a critically endangered habitat in Canada. Land management issues related to the preservation and restoration of grassland habitats, such as oak savannas, must then be included in the Mottled Duskywing recovery strategy.

One of those issues is fire suppression, originally put into practice due to the inherent risk to
property and human lives. The suppression of fire over time promotes plant succession, which is the process by which grasslands turn into shrublands, then into thickets and eventually into forests. Succession is detrimental to New Jersey Tea. It is a grassland plant that requires full sun and is unable to compete with the increasing canopy density of a forest. But what if fire wasn’t suppressed? Wouldn’t New Jersey Tea burn too?

As it turns out, New Jersey Tea is not only tolerant of fire, but it produces vigorous growth shortly after a fire disturbance (Throop & Fay, 1999). So, there is a threatened population of butterflies… living in a rare habitat… and scientists are setting it on fire?? Yup. It’s called prescribed burning.

But how do the butterflies survive such a disturbance? Sites are burned in sections, creating a patchwork of habitat with some portions left for conditions required by the butterflies. Some research by Swengel and Swengel (2007) suggests that some permanent unburned areas within the landscape may be important for specialist Lepidopterans, such as the Mottled Duskywing and the Karner Blue Butterfly (Lycaeides melissa samuelis), which is extirpated in Canada. Additionally, fire can provide many benefits which can even outweigh the risks. Recent work by Henderson et al. (2018) shows the short-term positive effect on another grassland butterfly to prescribed fire regimes. The diagrams below illustrate the results of their study and show the positive benefit derived from regular, and even frequent, burns.

Dr. Otis and myself walked transects through specific locations within the landscape, recording the location of each Mottled Duskywing that we encountered, the quantity of New Jersey Tea plants and keeping tally of the totals. Dr. Otis’ study will examine how Mottled Duskywings respond to the prescribed burns by utilizing different portions within the landscape. The next prescribed burn will occur early next spring by property staff, then the butterfly populations will again be assessed and compared with the baseline data.

In addition, staff at the Cambridge Butterfly Conservatory are currently working on determining the caterpillar rearing requirements of a related species, the Wild Indigo Duskywing. At this point they have had success getting females to lay eggs in captivity and rearing the larvae. The knowledge gained with the Wild Indigo Duskywings will be applied to the Mottled Duskywings, working towards reintroduction to one or more sites where they used to occur within the province, perhaps as early as 2020.

The Mottled Duskywing butterfly population we surveyed is the largest in Canada. At the end of the count, we received word that 4 teams of observers recorded 210 butterflies. This was great news for the researchers as the population appears to be stable, although the true population can only be determined through a detailed mark-recapture study which is tentatively being planned for summer 2019.

Mottled Duskywing conservation is gaining momentum… work has already started on habitat recovery and caterpillar rearing protocols. The information gathered and recovery actions taken could have implications for many other native prairie and grassland species. The same can be said for every other count, assessment, or restoration event. Whether you are a researcher or a concerned citizen, get involved. Know that your efforts could have massive implications for biodiversity, you could even SAVE a species from extinction!

To get involved in conservation, visit citizen science.

For more information on Mottled Duskywing butterflies, read the recovery strategy.

References

Fickenscher, J.L., Litvaitis, J.A., Lee, T.D. & Johnson, P.C. Insect responses to invasive shrubs:
Implications to managing thicket habitats in the northeastern United States. Forest Ecology
and Management 322 (complete), 127-135 (2014).

Henderson, Richard A., Meunier, Jed, & Holoubek, Nathan S. Disentangling effects of fire,
habitat, and climate on an endangered prairie-specialist butterfly. Biological Conservation 218
(complete), 41-48 (2018).

Swengel, A. B. & Swengel, S. R. Benefit of permanent non-fire refugia for Lepidoptera
conservation in fire-managed sites. Journal of Insect Conservation 11, 263–279 (2007).

Throop, Heather L. & Fay, Philip A. Effects of fire, browsers and gallers on New Jersey tea
(Ceanothus herbaceous) growth and reproduction. The American Midland Naturalist 141 (1),
51 (1999).

Amphibian Chytrid Crisis: A Deep Dive into a Deadly Disease

Guest post by Tristan Williams, MEnvSc Candidate at the University of Toronto-Scarborough

We currently live in an era of mass extinction, where many species around the world are at high risk of being lost forever, and among these species, amphibians are at much higher risk of extinction than any other (Wake and Vrendenburg, 2008). This comes from a combination of many factors, including climate change, habitat destruction and human land use, the presence of invasive species, and as we’ll be looking at here: the fungal infection chytridiomycosis.

Chytridiomycosis is a skin disease caused by a chytrid fungus, either Batrachochytrium dendrobatidis (Bd), or Batrachochytrium salamandrivorans (Bsal). Though these fungi may be small, they are a big deal when it comes to the health and stability of amphibian populations. They have been implicated for the heavy decline or even outright extinction of a large number of amphibian species, making it potentially the most impactful wildlife disease known (Scheele et al., 2014). These fungi have a number of traits that make it easy for them to spread to amphibians. One such trait is the ability to reside within a host without causing infection, using it as a reservoir from which it can spread to more vulnerable species (Fisher, 2017). This can be seen in the example of the midwife toad and alpine newt, which are carriers for Bsal, and can lead to infection of fire salamander populations.

Figure 1: Potential pathways for the spread of Bsal in Europe, from Fisher 2017.

The zoospores of these fungi also have two forms which contribute to their spread among amphibian population. The first is the motile aquatic form, which allows them to establish infection during the tadpole stage (Fisher, 2017). The second is the non-motile form, called an encysted spore, which has a thick cell wall, and are highly resilient. These encysted spores are capable of persisting in the environment while retaining their infectiousness, without needing a host at all for a long period of time. And if that wasn’t enough, it could be the case that birds can act as carriers for these encysted spores, bringing the fungus to new locations and further contributing to the spread of disease over larger distances. As noted by Fisher et al. (2017), it really does seem like amphibians really are in peril from a perfect pathogen. But what exactly do these fungal infections do to amphibians that make it such a problem?

Amphibians are cutaneous respirators. They “breathe” through their skin, allowing them to maintain the correct osmotic balance of electrolytes and water within the body. This is what makes chytrid fungi such a unique threat to amphibians. To other organisms the development of a cutaneous chytrid infection is usually not a big deal, but to amphibians it can directly interfere with their ability to respire (Voyles et al., 2009). The ensuing loss of electrolytes impairs the ability of the heart to function, blood flow to the rest of the body is reduced, and cardiac arrest leads to death as a result of complete collapse of the circulatory system. However, even before that occurs, the now physically impaired and lethargic individual is likely to become a victim of predation or a combination of other stressors as well. As an example of the potential severity of this disease, fire salamanders in the Netherlands that were infected with Bsal experienced a mortality rate of over 96% (Fisher, 2017). A very morbid and unfortunate situation our amphibian friends find themselves in.

Normally, the mucus layer present on the skin of amphibians contains a number of antimicrobial peptides and lysozymes, as well as symbiotic bacteria which all contribute to innate defenses against invading pathogens (Rollins-Smith et al., 2011). Amphibians have also shown to be capable of developing an acquired immune response to chytrid fungi after exposure, with some even developing Bd specific antibodies. So then why is chytridiomycosis such a problem for amphibians? The answer appears to be because chytrid fungi are capable of suppressing immune responses in many species before these defenses are capable of protecting against infection (Ellison et al., 2014). Other environmental stressors can also interfere with the ability of amphibians to mount an appropriate immune defense. Lack of food resources, temperature stress, or exposure to chemicals like pesticides can all increase the likelihood of fungal infection (Rollins-Smith et al., 2011). Furthermore, the amphibian life cycle itself can impair the ability of an individual to resist infection. When a tadpole undergoes metamorphosis into an adult, the immune system also goes through a drastic transition to maturity. This period of time provides an opening for infection to develop while the defenses of the amphibian aren’t at full capacity. Ultimately, this means that the ability for a species of amphibian to defend against chytrid fungi varies heavily based on the level of innate and acquired defenses mounted, the health of the habitat, the climate, and what part of the life cycle the species in question is in.

 It is abundantly clear that amphibian populations are in great danger as a result of this disease outbreak, so the obvious follow-up question is what can we do about this ongoing threat? While there is no silver bullet for stopping chytridiomycosis outright, there are a number of potentially promising forms of intervention that could help to bring mortality rates down to less extreme levels. In short-term or small scales, the direct treatment of individuals with antifungals is shown to be an effective method of temporarily controlling an outbreak, but more long-term measures are needed to ensure success in restoring populations (Garner et al., 2016). Scheele et al. (2014) provide a framework of three potential classes of action to protect amphibians from fungal infection. The first class is Environmental Manipulation. As mentioned previously, there are a number of environmental factors that influence the chance of successful infection. Reducing the presence chemical pollutants can reduce stress on amphibian populations are lower infection rates. The creation of warm regions in the habitat, such as warm pools of water, areas of high sun exposure to bask in, or the introduction of artificial heat sources can also allow species to initiate behavioural fever, raising their body temperature to levels that are no longer ideal for chytrid fungi to survive. Finally, methods such as bio-augmentation, which involves introducing microbes with the ability to inhibit chytrid fungi to the environment, can potentially provide an ecosystem-wide treatment, so long as proper testing is done to ensure that this will not negatively impact the environment in any way. 

Artificial ponds for the captive breeding of the endangered Pseudophryne corroboree.

(Figure 2 from Scheele et al., 2014)

When manipulation is not a reasonable solution, the Amphibian Introduction class is next in line. This involves the translocation of amphibian populations to refugia: environments that are ideal for the species, but poor for chytrid fungus. This method does require that it is ensured that this translocation will not cause any impacts in the new environment. Alternatively, captive bred amphibians can be added to wild populations in order to increase the buffering capacity of the ecosystem, allowing higher likelihood of survival for a population even after an chytrid epidemic. Finally, failing the previous two classes, the last class is Ex-Situ Conservation, which involves keeping colonies in captivity. Infected individuals are treated with chemicals or heat to kill the fungus, and individuals are bred in order to improve resistance among the population while maintaining genetic diversity (Scheele et al. 2014).

While these treatments are still in development and have not been used in proper field tests yet, they definitely have the potential to rescue amphibian populations. However, the fact remains that many amphibians around the world are critically imperilled, so there is clear need for feasibility research as soon as possible if we want to prevent any more extinctions. The loss of mass amounts of amphibians could lead to huge impacts on many ecosystems around the world, and it is all but guaranteed to happen unless we take action.

Literature Cited:

Ellison AR et al. 2014. Fighting a Losing Battle: Vigorous Immune Response Countered by Pathogen Suppression of Host Defenses in the Chytridiomycosis-Susceptible Frog Atelopus zeteki. G3-Genes Genom Genet 4(7): 1275-1289.

Fisher MC. 2017. Ecology: In peril from a perfect pathogen. Nature 544(7650): 300-301.

Garner TWJ et al. 2016. Mitigating amphibian chytridiomycoses in nature. Philos T Roy Soc B 371(1709).

Rollins-Smith LA et al. 2011. Amphibian Immune Defenses against Chytridiomycosis: Impacts of Changing Environments. Integr Comp Biol 51(4): 552-562.

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