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The future of the world's coral reefs is uncertain, as the impact of global heating continues to escalate. However, according to a study published in Nature Climate Change, the response of the Great Barrier Reef to extreme temperatures in 2017 was markedly different to one year earlier, following two back-to-back bouts of coral bleaching. Remarkably, corals that bleached and survived 2016 were more resistant in 2017 to a recurrence of hot conditions.

Researchers found that the response of corals to heat stress during the second of two unprecedented back-to-back bleaching events on the Great Barrier Reef was markedly different from the first [Credit: Tane Sinclair-Taylor]

"Dead corals don't bleach for a second time. The north lost millions of heat-sensitive corals in 2016, and most of the survivors were the tougher species. As a result of bleaching, the mix of species is changing very rapidly," said lead author Prof Terry Hughes, Director of the Australian Research Council Centre of Excellence for Coral Reef Studies (Coral CoE), headquartered at James Cook University.

"We were astonished to find less bleaching in 2017, because the temperatures were even more extreme than the year before," he said.

The new research highlights the extent of damage, or "geographic footprint" of multiple coral bleaching events across the 2,300 km length of the world-heritage listed area.

The back-to-back heatwaves bring the total number of mass bleaching events on the Great Barrier Reef to four over the past two decades (in 1998, 2002, 2016 and 2017). The scientists found that only 7% of the Great Barrier Reef escaped bleaching entirely since 1998, and after the 2017 event, 61% of reefs have now been severely bleached at least once.

During an underwater survey, a researcher records the bleaching severity of a massive Porites coral colony on the Great Barrier Reef [Credit: Justin Marshall]

"We found, using the National Oceanic and Atmospheric Administration's (NOAA) satellite-based coral bleaching tools, that corals in the north of the Great Barrier Reef were exposed to the most heat stress in 2016. A year later, the central region saw the most prolonged heating," said co-author Dr Mark Eakin, from NOAA's Coral Reef Watch program, in Maryland, USA.

The southern third of the Great Barrier Reef was cooler in both years due to local weather conditions, and escaped with only minor bleaching.

"It's only a matter of time before we see another mass-bleaching event, triggered by the next marine heatwave, driven by global heating," said co-author Dr Andrew Hoey of Coral CoE at James Cook University. "One of the worst possible scenarios is we'll see these southern corals succumb to bleaching in the near future."

"The outcome in 2017 depended on the conditions experienced by the corals one year earlier. We called that 'ecological memory,' and show that these repeating events are now acting together in ways that we didn't expect," said Prof Hughes.

"We've never seen back-to-back mass coral bleaching before on the Great Barrier Reef, in two consecutive summers. The combined footprint has killed close to half of the corals on two-thirds of the world's largest reef system," said Dr Hoey.

"We need urgent global action on greenhouse emissions to save the world's coral reefs. Australia should be -- but regrettably isn't -- at the forefront of tackling global heating," said Prof Hughes.

Source: ARC Centre of Excellence in Coral Reef Studies [December 10, 2018]

With rapid efficiency, a mysterious parasite is seeking out and killing a giant species of clam found only in the Mediterranean Sea. Unless scientists can find a way of stopping it soon, they say the mollusk could go extinct.

A diver observes a pen shell on the seabed in the Aegean Sea [Credit: Yiannis Issaris/AP]

For thousands of years, the emblematic noble pen shell has been intrinsically connected to human civilization. The largest bivalve in the Mediterranean can grow to more than a meter (three feet) long and has provided food and one of the world’s rarest materials: sea silk spun from fibers it uses to secure itself to the seabed. The mollusk also contributes to clear water by filtering out organic particulates.

The pen shell, Pinna nobilis, has been on the European Union’s protected species list for decades because of overfishing, pollution and the destruction of its natural habitat, meaning any fishing is banned. But the ban is often poorly enforced, with the animal harvested for food or for its shell, which is used for decorative purposes.

A pen shell stands on the seabed of the Aegean Sea [Credit: Yiannis Issaris/AP]

The pen shells, which have a life span of several decades and take years to reach reproductive age, were already dying faster than they could be replaced. So the spread of the microscopic parasite, which first appeared in the western Mediterranean in late 2016 and was identified just this year as a new species, has alarmed experts.

Exactly how the parasite kills isn’t completely clear, although scientists have found it attacks the pen shell’s digestive system. The infected animal is also unable to close its shell, incapacitating its defense against predators. Once infected, death is almost certain.

Yiannis Issaris, marine ecologist and research associate at the Hellenic Center for Marine Research, holds a dead noble pen shell, or Pinna nobilis, in Anavyssos, south of Athens [Credit: Thanassis Stavrakis/AP]

“In less than a year it wiped out (the pen shell population of) the Spanish coast,” said Maria del Mar Otero of the International Union for Conservation of Nature.

Soon parts of France, Malta, Tunisia and Italy were affected. In recent weeks, tests confirmed the same parasite, Haplosporidium pinnae, is responsible for pen shell die-offs in parts of Greece, and researchers have reported mass mortality as far east as Turkey and Cyprus.

Pen shells stand on the seabed in the Aegean Sea [Credit: Yiannis Issaris/AP]

Scientists are now racing to understand how the parasite spreads and its life cycle — essential information for a successful rescue program. One theory is that it could be spreading through phytoplankton, the bivalve’s food source, but nobody knows for certain.

“We cannot be sure of anything at this point,” said Pantelis Katharios, senior researcher at the Institute of Marine Biology, Biotechnology and Aquaculture of the Hellenic Center for Marine Research, or HCMR.

A dead pen shell stands open in a seagrass meadow in the Aegean Sea's Saronic Gulf [Credit: Elena Becatoros]

“What we know now is that the Pinnas are dying, that the cause is this parasite, and we know that it’s spreading very, very rapidly,” he said. “And that is going to be a huge problem (for) the ecology and the balance of the ecosystem in the Mediterranean.”

Yiannis Issaris, marine ecologist at the HCMR’s Institute of Oceanography, initially noticed widespread pen shell death off the coast of Anavyssos, southeast of Athens, in mid-summer. He suspected the culprit could be the same one causing mortality in Spain — and testing proved him right.

A pen shell stands anchored in the seabed of the Aegean Sea [Credit: Yiannis Issaris/AP]

Now the question is how to tackle the outbreak.

“This is very fresh for the scientific community,” Issaris said. “We’re still at the stage of recording where it has spread to.”

Yiannis Issaris, marine ecologist and research associate at the Hellenic Center for Marine Research, takes measurements of a dead noble pen shell, or Pinna nobilis, in Anavyssos, south of Athens [Credit: Thanassis Stavrakis/AP]

Some parts of Greece still have healthy populations of the mollusks, he noted, whereas in other areas they have been wiped out.

Protecting the pen shell in its natural habitat — sandy seabeds or seagrass meadows — appears “difficult to impossible,” Issaris said, particularly without knowing how the parasite spreads. In Spain, some healthy individuals were moved to aquariums.

Yiannis Issaris, marine ecologist and research associate at the Hellenic Center for Marine Research, takes measurements of a dead noble pen shell, or Pinna nobilis, in Anavyssos, south of Athens [Credit: Thanassis Stavrakis/AP]

Although tests are pending in some Mediterranean countries witnessing mass die-offs, experts have little doubt what the results will show.

“It’s very, very, very likely” to be the same parasite, Otero said. “There’s almost no question.”

Christina Pavloudi, foreground, post-doctoral researcher at the Hellenic Center for Marine Research laboratory on the Greek island of Crete, and Georgia Sarafidou, a student at the same facility, carry out tests on samples of noble pen shells stricken by a new parasite [Credit: Thanassis Stavrakis/AP]

One thing’s clear: the parasite is very particular in its choice of victim. A smaller, related species, the Pinna rudis, which also exists outside the Mediterranean, is unaffected.

“We don’t know how it has appeared in the Mediterranean... We only know that it causes mortality only in the Pinna nobilis,” Issaris said.

Yiannis Issaris, marine ecologist and research associate at the Hellenic Center for Marine Research, holds a dead noble pen shell, or Pinna nobilis, in Anavyssos, south of Athens [Credit: Thanassis Stavrakis/AP]

In the clear, shallow waters south of the Greek capital, dozens of dead pen shells lie scattered in a seagrass meadow, testament to the devastation.

Peering through a microscope at the tissue of an infected individual in his office in Crete, Katharios points out the culprit: small, oval-shaped parasites spread throughout the sample.

Scientists are puzzling over why an organism would be so lethal to the very species it depends on for its own survival.

Pantelis Katharios, senior researcher at the Institute of Marine Biology, Biotechnology and Aquaculture of the Hellenic Center for Marine Research on the Greek island of Crete, checks microscope imaging of a new parasite killing  the noble pen shell, or Pinna nobilis [Credit: Elena Becatoros]

“Normally parasites in nature do not have any benefit from harming the host, because they depend on the host,” Katharios explained. “But once in a while we may come across incidents like this, where we have massive mortalities.”

This could just be a natural phenomenon in which the parasite will eventually be wiped out along with its host, he said. Another possibility is that it originated in a different species and for some reason jumped to the pen shell. A third is that the pen shell’s immune system has been compromised by factors such as pollution, climate change or water temperature fluctuations.

“It’s extremely, extremely difficult to find the truth at this stage,” Katharios said.

Author: Elena Becatoros | Source: Associated Press [December 04, 2018]

Tests on more than 100 sea turtles—spanning three oceans and all seven species—have revealed microplastics in the guts of every single turtle.

Credit: Belle Co, Pexels.com

Researchers from the University of Exeter and Plymouth Marine Laboratory, working with the Greenpeace Research Laboratories, looked for synthetic particles (less than 5mm in length) including microplastics in 102 sea turtles in the Atlantic, Pacific and Mediterranean.

Synthetic particles were found in all of the turtles, the most common being fibres, which can potentially come from sources including clothing, tyres, cigarette filters and maritime equipment such as ropes and fishing nets.

"The effect of these particles on turtles is unknown," said lead author Dr. Emily Duncan, of the Centre for Ecology and Conservation on the University of Exeter's Penryn Campus in Cornwall.

"Their small size means they can pass through the gut without causing a blockage, as is frequently reported with larger plastic fragments. However, future work should focus on whether microplastics may be affecting aquatic organisms more subtly. For example, they may possibly carry contaminants, bacteria or viruses, or they may affect the turtle at a cellular or subcellular level. This requires further investigation."

In total, more than 800 synthetic particles were found in the 102 turtles studied. But researchers only tested part of each animal's gut—so the total number of particles is estimated to be about 20 times higher.

Researchers do not currently understand how synthetic particles are ingested by turtles, but the likely sources are polluted seawater and sediments, and eating via prey or plants.

Professor Brendan Godley, senior author of the study, added: "It really is a great shame that many or even all of the world's sea turtles have now ingested microplastics. At the moment, this is not the main threat to this species group but it is a clear sign that we need to act to better govern global waste."

Necropsies were carried out on the turtles after they died either by stranding or bycatch (accidental catching in fishing). The study sites were North Carolina, USA (Atlantic), Northern Cyprus (Mediterranean) and Queensland, Australia (Pacific).

The turtles with the most synthetic particles were in the Mediterranean—thought to have higher rates of contamination than the Atlantic or Pacific—but this study's sample sizes and methodology did not allow for detailed geographical comparisons.

Dr. Penelope Lindeque, of Plymouth Marine Laboratory, said: "While this study has been successful, it does not feel like a success to have found microplastic in the gut of every single turtle we have investigated.

"From our work over the years we have found microplastic in nearly all the species of marine animals we have looked at; from tiny zooplankton at the base of the marine food web to fish larvae, dolphins and now turtles. This study provides more evidence that we all need to help reduce the amount of plastic waste released to our seas and maintain clean, healthy and productive oceans for future generations."

Louise Edge, plastics campaigner at Greenpeace, said: "This important research demonstrates the breadth of our plastics pollution problem. Our society's addiction to throwaway plastic is fuelling a global environmental crisis that must be tackled at source."

The paper is published in the journal Global Change Biology.

Source: University of Exeter [December 04, 2018]

Sharks that use a whip-like tail to stun their prey, rays with saws on their faces, and river rays half the length of a bus are among the most unique species at risk of extinction according to the latest ranking from international conservation charity ZSL's (Zoological Society of London) pioneering EDGE of Existence programme.

The largetooth sawfish (Pristis pristis) is not only #1 on the EDGE sharks and rays list, but is also the highest ranking  EDGE species across all the different animal groups ranked, including corals, reptiles, amphibians, mammals and birds [Credit: (c) Simon Fraser University]

The new list revealed today (4 December) ranks the world's 50 most Evolutionarily Distinct and Globally Endangered (EDGE) sharks, rays and chimeras - known collectively as Chondrichthyes.

These mythical-sounding (but very real) creatures have no bones in their bodies, only cartilage and appeared more than 400 million years ago, roaming the seas when dinosaurs lived. Each species on this list has few or no remaining close relatives, effectively representing distinct branches of the tree of life and making each of them truly irreplaceable. If they go extinct, we will have nothing like them left on the planet.

Topping the new list, at number one is the largetooth sawfish (Pristis pristis), which also holds the distinction of being the highest-ranking EDGE species in the world. Using an elongated snout (rostrum) lined with teeth on each side to slash at its prey, the large-tooth sawfish is facing threats from unsustainable fishing activities as it's often caught as by-catch in nets.

Despite the fearsome reputation of the great white shark and the well-recognised appearance of the hammerhead, sharks are one of the least-studied groups of animals - some so elusive they've never been captured on camera. Many of these species are threatened by targeted fishing, driven by a desire for shark fins or other body parts, as well as being unintentionally caught (bycatch).

Habitat degradation, due to coastal development, mangrove deforestation, water pollution and trawling, is also to blame for the steep decline in many of these populations. However, the new EDGE List gives conservationists another tool to identify and prioritise species where there is a most pressing need for action.

EDGE Sharks co-ordinator and marine biologist, Fran Cabada said: "Sharks, rays and chimeras - making up the cartilaginous fish, have been around since the age of the dinosaurs, but due to human activities, their modern relatives are facing threats all over the world. They're found in almost every aquatic environment and as many are apex predators, i.e., at the top of the food chain - they're crucial to maintaining healthy ecosystems.

Representative phylogeny tree (taxon-complete) of Chondrichthyes. Red dotes highlight nodes defining orders [Credit: Stein et al. (2018)/EDGE]

"Unfortunately, sharks have a bad image. This means people often can't see beyond the negative, and usually exaggerated stories, and don't understand just how threatened and important they are.

"The new EDGE Sharks and Rays list gives us the opportunity to highlight the most unique sharks and rays on our planet which are also the most endangered, so that we can target conservation efforts where it's needed most. Many are overlooked and poorly known, so conservation actions targeted at these survivors of ancient lineages should be prioritised."

ZSL's Marine and Freshwater Conservation Programme Manager, Dr. Matthew Gollock added: "The EDGE Sharks and Rays list comprises some of the most interesting and unique fish we have on this planet. The modern extinction of a single species from this list would cause the loss of millions of years of evolutionary history.

"Since 2013, we have been working in collaboration with partner organisations in the Canary Islands for the conservation of the angel shark (Squatina squatina), #5 in the EDGE list, increasing our knowledge of this species and working with divers, fishers and policymakers to improve management and policy.

"Our successes from this project have allowed us to expand our work to Wales, UK, where we have taken a similar stakeholder-lead approach to collect sightings and community memories of the angel shark in order to better understand and conserve this Critically Endangered species across its range."

First established in 2007, the EDGE of Existence programme has previously published lists for amphibians, birds, corals, mammals and reptiles. The EDGE lists provide conservationists worldwide with a scientifically rigorous method of focusing their conservation efforts on animals and plants that represent a significant amount of threatened evolutionary history.

ZSL's EDGE of Existence programme works with partners including the National Geographic Photo Ark and Fondation Segré to fund early-career conservationists striving to secure the future of EDGE species all around the world, through the EDGE Fellowship initiative. The first ever EDGE Fellowships on Sharks and Rays will begin in early 2019, implementing conservation actions for the largetooth sawfish and the pelagic thresher shark (Alopias pelagicus) in Asia.

For more information please see the original paper presenting ED values for these species.

Click here to explore the Top 50 EDGE Sharks and Rays List.

Click here for the latest EDGE Sharks and Rays List.

Source: Zoological Society of London [December 04, 2018]

The International Union for Conservation of Nature's (IUCN) Red List of Threatened Species is a powerful tool for researchers and policymakers working to stem the tide of species loss across the globe. But adding even a single species to the list is no small task, demanding countless hours of expensive, rigorous and highly specialized research.

This map shows the predicted levels of risk to more than 150,000 species of plants located worldwide. Using vast amounts of open-access data, the researchers trained a machine learning algorithm to assign a probability that a given species would qualify for at-risk designation on the International Union for the Conservation of Nature's Red List of Threatened Species. Warmer colours denote areas with larger numbers of potentially at-risk species, while cooler colours denote areas with low overall predicted risk [Credit: Anahí Espíndola and Tara Pelletier]

As a result of these limitations, a large number of known species have not yet been formally assessed by the IUCN and ranked in one of five categories, from least concern to critically endangered. This deficit is quite apparent in plants: Only about 5 percent of all currently known plant species appear on IUCN's Red List in any capacity.

A new method co-developed by Anahí Espíndola, an assistant professor of entomology at the University of Maryland, uses the power of machine learning and open-access data to predict species that could be eligible for at-risk status on the IUCN Red List. The research team created and trained a machine learning algorithm to assess more than 150,000 species of plants from all corners of the world, making their project among the largest assessments of conservation risk to date. According to the results, more than 10 percent of these species are highly likely to qualify for an at-risk IUCN classification.

The algorithm is a predictive model that can be applied to any grouping of species at any scale, from the entire globe to a single city park. Espíndola and her colleagues published their findings online in the Proceedings of the National Academy of Sciences on December 3, 2018.

"Our method isn't meant to replace formal assessments using IUCN protocols. It's a tool that can help prioritize the process, by calculating the probability that a given species is at risk," Espíndola said. "Ultimately, we hope it will help governments and resource managers decide where to devote their limited resources for conservation. This could be especially useful in regions that are understudied."

Espíndola and her collaborators built their predictive model using open-access data from the Global Biodiversity Information Facility (GBIF) and the TRY Plant Trait Database. Lead author Tara Pelletier, an assistant professor of biology at Radford University, worked together with Espíndola to perform the machine learning analysis.

Espíndola and Pelletier then trained the model using GBIF and TRY data from the relatively small group of plant species already on the IUCN Red List. This allowed the researchers to assess and fine-tune the model's accuracy by checking its predictions against the listed species' known IUCN risk status. The Red List sorts non-extinct species into one of five classification categories: least concern, near-threatened, vulnerable, endangered and critically endangered.

The researchers then applied the model to the many thousands of plant species that remain unlisted by IUCN. According to the results, more than 15,000 of the species--roughly 10 percent of the total assessed by the team--have a high probability of qualifying as near-threatened, at a minimum.

Espíndola and her colleagues mapped the data and noted several major geographical trends in the model's predictions. At-risk species tended to cluster in areas already known for their high native biodiversity, such as the Central American rainforests and southwestern Australia. The model also flagged regions such as California and the southeastern United States, which are home to a large number of endemic species, meaning that these species do not naturally occur anywhere else on Earth.

"When I first started thinking about this project, I suspected that many regions with high diversity would be well-studied and protected. But we found the opposite to be true," Espíndola said. "Many of the high-diversity areas corresponded to regions with the highest probability of risk. When we saw the maps, we were surprised it was that clear. Endemic species also tend to be more at risk because they are usually confined to smaller areas."

The model also flagged a few surprising areas not typically known for their biodiversity, such as the southern coast of the Arabian Peninsula, as having a high number of at-risk species. Some of the most imperiled regions have not received enough attention from researchers, according to Espíndola. She hopes that her method can help to fill in some of these knowledge gaps by identifying regions and species in need of further study.

"Let's say you wanted to assess every species of wild bee on one continent. So you do the assessment and find that only one species is at risk. Now you've used all those resources to identify an area with low risk, which is still helpful, but not ideal when resources are limited. We want to help prevent that from happening," Espíndola said. "Our analysis was global, but the model can be adapted for use at any geographic scale. Everything we've done is 100 percent open access, highlighting the power of publicly-available data. We hope people will use our model--and we hope they point out errors and help us fix them, to make it better."

The research paper was published online in the Proceedings of the National Academy of Sciences.

Source: University of Maryland [December 03, 2018]

Scientists are worried about the platypus, with a national risk assessment led by UNSW Professor Richard Kingsford suggesting declines of up to 30 percent.

A UNSW-led project has raised concerns about the decline of platypus populations [Credit: Taronga Zoo: G Anderson]

Mounting evidence that platypus populations are falling has concerned scientists who are nearing the end of a three-year national survey of the iconic species.

The UNSW-led Australian Research Council-funded project has compiled a comprehensive database of the distribution and abundance of the platypus over the last two centuries, combining this with data from systematic capture surveys to conduct a national risk assessment for the species.

"We have great concerns about the future survival of this unique species," says project leader Professor Richard Kingsford, director of the UNSW Centre for Ecosystem Science.

New research reveals the extinction of plant or animal species from extreme environmental change increases the risk of an 'extinction domino effect' that could annihilate all life on Earth.

Virtual earths modelling shows an 'extinction domino effect' risk ten times higher than forecast, indicating rising global temperatures due to climate change could wipeout entire species [Credit: Flinders University]

This would be the worst-case scenario of what scientists call 'co-extinctions', where an organism dies out because it depends on another doomed species, with the findings published in the journal Scientific Reports.

Think of a plant's flower pollinated by only one species of bee -- if the bee becomes extinct, so too will the plant eventually.

"Even the most resilient species will inevitably fall victim to the synergies among extinction drivers as extreme stresses drive ecosystems to collapse." says lead author Dr Giovanni Strona of the European Commission's Joint Research Centre based in Ispra in northern Italy.

Researchers from Italy and Australia simulated 2,000 'virtual earths' linking animal and plant species. Using sophisticated modelling, they subjected the virtual earths to catastrophic environmental changes that ultimately annihilated all life.

Examples of the kinds of catastrophes they simulated included runaway global warming, scenarios of 'nuclear winter' following the detonation of multiple atomic bombs, and a large asteroid impact.

"What we were trying to test is whether the variable tolerances to extreme global heating or cooling by different species are enough to explain overall extinction rates,"


"But because all species are connected in the web of life, our paper demonstrates that even the most tolerant species ultimately succumb to extinction when the less-tolerant species on which they depend disappear."

"Failing to take into account these co-extinctions therefore underestimates the rate and magnitude of the loss of entire species from events like climate change by up to 10 times," says co-author Professor Bradshaw of Flinders University in South Australia

Professor Bradshaw and Dr Strona say that their virtual scenarios warn humanity not to underestimate the impact of co-extinctions.

"Not taking into account this domino effect gives an unrealistic and exceedingly optimistic perspective about the impact of future climate change", warns Professor Bradshaw.

It can be hard to imagine how the demise of a small animal or plant matters so much, but the authors argue that tracking species up to total annihilation demonstrates how the loss of one can amplify the effects of environmental change on the remainder.

"Another really important discovery was that in the case of global warming in particular, the combination of intolerance to heat combined with co-extinctions mean that 5-6 degrees of average warming globally is enough to wipe out most life on the planet", says Dr Strona.

Professor Bradshaw further warns that their work shows how climate warming creates extinction cascades in the worst possible way, when compared to random extinctions or even from the stresses arising from nuclear winter.

Source: Flinders University [November 29, 2018]

Indigenous communities have used muskrat fur to make clothing for generations and the animal's meat is considered a seasonal delicacy. But it turns out decades of trapping are not primarily responsible for the animal's decline across North America.

Stanford research shows the drying trend in Canada’s Peace-Athabasca Delta is linked to  the long-term decline in populations of the semi-aquatic muskrat [Credit: iStock]

Instead, 46 years of satellite imagery show the Peace-Athabasca Delta has been drying since the 1970s, significantly reducing muskrat habitat. Stanford University researchers published their findings in the journal Environmental Research Letters.

"The ecological impacts are not limited to muskrat - they extend far beyond that," said lead author Ellen Ward, a doctoral candidate in Stanford's School of Earth, Energy & Environmental Sciences (Stanford Earth). "These results suggest that maybe the widespread continental-scale decline in this animal is actually being driven by a large-scale loss in wetland and aquatic habitat."

More than just muskrat

Located in northeast Alberta, the Peace-Athabasca Delta is a Ramsar Wetland of International Importance and North America's largest inland freshwater delta. The area comprises habitat for about 200 bird species as well as the threatened wood bison, which is among the largest land animals on the continent. The semi-aquatic muskrat is native to North America and an important ecological indicator since the species is highly sensitive to changing hydrologic conditions.

The researchers constructed maps of the 46-year record of surface water with Landsat satellite imagery from 1972 to 2017. Those images revealed that suitable muskrat habitat dwindled by 32 percent over a time when muskrat numbers also plummeted.

Muskrat serve as a convenient indicator for habitat loss because they construct easily counted "houses" for shelter. They rely on vegetation for food and to build their dwellings in lakes, small ponds, streams, rivers and wetlands - and within the delta, they reside in the areas that are most susceptible to drying out.

"We basically constructed a map showing where every muskrat house count was measured, and they're located in these smaller water bodies," Ward said.

Long-term consequences

Although the idea that the delta has been drying is not new, nobody had directly mapped the loss and it had never before been clearly linked to the long-term decline in muskrat. Now resource managers can see where exactly the drying has occurred over time.

"Our result is timely because this UNESCO World Heritage Site is currently being considered for designation as a wetland with "in danger" status," said co-author Steven Gorelick, the Cyrus F. Tolman Professor in the Department of Earth System Science.

"If you look across the 46 years, you can see how much of the time each minute area was under water in those 46 years," Ward said.

Previous research has suggested that the drying delta is primarily a result of climate change. If it continues, the decline of muskrat in the region will have impacts throughout the food chain, as muskrat are prey to many animals, including lynx, fox and mink. Their existence is critical to Indigenous people in the area, since muskrat are a part of treaty rights to hunt, fish and trap.

By addressing the importance of hydrology on the decline of an animal species, the researchers hope to encourage other scientists to move beyond the prevailing focus on plant-water relationships in ecohydrology.

"I hope that this paper shows hydrologists that looking at viable habitat through a water lens can actually tell you a lot about environmental change as it affects animals - traditionally, hydrologists have stayed away from that area," Ward said. "I hope that we have contributed to ecohydrology by broadening the discussion."

Author: Danielle Torrent Tucker | Source: Stanford University [November 26, 2018]