It’s sea otter awareness week, which seems like a great time to reveal something heroic about this charismatic animal. A recent study from UC Santa Cruz concluded that sea otters are helping to save the ocean—with their appetites.

When you think of sea otters, you may think “cute and cuddly,” but these playful marine mammals are top predators, like great white sharks and tigers, and their hunt for food is helping to maintain ecosystem health along portions of California’s coastline.

The sea otter’s role in ecosystem management begins with one of its preferred foods: crabs. Sea otters eat crabs. Crabs in turn eat sea slugs and small crustaceans. The slugs and crustaceans eat algae off sea plants, keeping them green and healthy. It’s a relatively typical food web but now it’s clear: The healthier the crab-eating otter population is, the healthier the plants tend to be.

Sea plants, like eelgrass, along the west coast are important habitat for fish such as Pacific herring, halibut and salmon. They also protect shorelines from storms and waves, and they soak up carbon dioxide from seawater and the atmosphere.  Thus, a healthy coastal ecosystem has the right mix of otters eating crabs and invertebrates eating algae.

Unfortunately, seagrass meadows have been declining worldwide, partly due to excessive nutrients from agricultural and urban runoff entering coastal waters.  When sewage and agricultural waste like fertilizers spill into the sea, ecosystems suffer. Excessive nitrogen and phosphorus in the water spawns excessive algae growth, which can block sunlight and limit plant growth. Coastal areas that would otherwise be swaying in seagrass and kelp turn brown, murky, and barren of important marine species. But, not when sea otters are around.

Brent Hughes from the University of California, Santa Cruz and his colleagues studied 50 years’ worth of data, comparing areas with or without otters. The team discovered that otters trigger the above ecological chain reaction that protects seagrass meadows and can stave off algal blooms.

“The seagrass is really green and thriving where there are lots of sea otters, even compared to seagrass in more pristine systems without excess nutrients,” Hughes says.

Sea otters were hunted to near extinction in the 19^th and 20^th centuries. Populations on the California coast are slowly recovering now, and one of those places otters have called home since the 1980s is Elkhorn Slough, an estuary in Monterey Bay. Hughes and his colleagues determined that the re-colonization of that estuary by sea otters has been an important factor in the seagrass comeback.

In Tomales Bay, a nearby inlet with far lower levels of incoming nutrients, but no otters, the beds don’t look nearly as good. Hughes told Ed Yong of National Geographic:

The seagrass looks relatively unhealthy: it’s brown, covered in algae, and slumped over. The crabs are four times more abundant and 30 percent bigger than they are in Elkhorn Slough.

The findings in Elkhorn Slough suggest that expansion of the sea otter population in California and re-colonization of other estuaries will likely be good for seagrass habitat—and coastal ecosystems—throughout the state.

“This provides us with another example of how the strong interactions exerted by sea otters on their invertebrate prey can have cascading effects, leading to unexpected but profound changes at the base of the food web,” Hughes says. “It’s also a great reminder that the apex predators that have largely disappeared from so many ecosystems may play vitally important functions.”

The study was published last month in the Proceedings of the National Academy of Sciences.

(Sea otters also play a heroic role in the next Academy planetarium show! Currently in production and set for a fall 2014 opening date, the latest production from our visualization studio will highlight complex relationships in ecosystems—and how humans fit into the picture.)

Jami Smith is a science geek-wannabe and volunteers for Science Today.

Image: Robert Scoles/NOAA

Welcome to Sea Otter Awareness Week! Started 11 years ago to increase the public’s awareness about sea otters, the event “is an annual recognition of the vital role that sea otters play in the nearshore ecosystem,” according to seaotterweek.org.

Tomorrow we will explore that vital role a little more; for today’s article, we checked in with Moe Flannery, from the Academy’s Ornithology and Mammalogy department, to better understand the health of local sea otters.

The US Geological Survey’s Western Ecological Research Center conducts annual population surveys of the southern sea otter (Enhydra lutris nereis), a federally listed threatened species found in California. Flannery says the southern sea otter’s range extends from Pigeon Point near Half Moon Bay down to Point Conception in Santa Barbara County.

This year’s USGS survey was released earlier this month and the news is cautiously optimistic: sea otter numbers are up, due largely to an increase in the number of pups.

In its 2013 report, the USGS estimates the population to be 2,941. For southern sea otters to be considered for removal from threatened species listing, the population estimate would have to exceed 3,090 for three consecutive years, according to the threshold established under the Southern Sea Otter Recovery Plan by the US Fish and Wildlife Service. The USGS has been conducting the population surveys since the 1980s.

“Population growth in central California has faltered recently, so the fact that we’re seeing a slightly positive trend is a basis for cautious optimism,” says Tim Tinker, a USGS biologist who supervises the annual survey. “Certainly, sea otters have made an impressive recovery in California since their rediscovery here in the 1930s.”

“We counted a record number of pups this year, which led to the uptick in the 3-year average,” says USGS biologist Brian Hatfield, coordinator of the annual survey. “A high pup count is always encouraging, although the number of adult otters counted along the mainland was almost identical to last year’s count, so we’ll have to wait and see if the positive trend continues.”

USGS scientists also annually update a database of sea otter strandings—the number of dead, sick or injured sea otters recovered along California’s coast each year. Flannery leads the Academy as one of the organizations that responds to these strandings as part of the national Marine Mammal Stranding Network.

This year’s stranding number was 368. Flannery says that a remarkable number of sea otters wash up with shark bites. “The shark populations have been increasing because elephant seal populations are increasing,” she says. “The sharks appear to take a bite of the sea otters, but don’t consume them. As bony, skinny and furry as sea otters are (with up to one million hairs per square inch!), they’re probably less desirable than fat, blubbery elephant seals.”

Sharks aren’t the only threat to sea otters. Mainland diseases, such as toxoplasmosis from cat fecal matter, also plague the animals.

Because of their threatened status, all sea otter necropsies (animal autopsies) are performed by the California Department of Fish and Wildlife. However, many of the specimens end up here, in the Academy’s collections. The result is that we have the largest collection of southern sea otter specimens in the world. The number was up to 1,300 specimens last year, but several hundred have yet to be cataloged and processed, according to Flannery.

Researchers come from all over the world to study the specimens—last year scientists from UC Davis came to study dental pathologies in 1200 sea otter skulls!  They found that 93% of our southern sea otter specimens had problems with their teeth.

Luckily, most of us don’t have to study 1200 sea otter skulls to learn more about these engaging animals. For events around Sea Otter Awareness Week, including this week’s Nightlife at the Academy, click here. Celebrate!

Image: Mike Baird/Wikipedia

When researchers found fire salamanders (Salamandra salamandra) in the Netherlands dying at a rapid rate from a skin fungus, they thought the infection looked familiar.

Globally, amphibian numbers are declining in large part due to a chytrid fungus known as Batrachochytrium dendrobatidis or Bd. Bd attacks the skin of its host causing “the outer layers of the epidermis to thicken,” says the Academy’s amphibian expert, Dave Blackburn. “Bd disrupts the function of amphibian’s skin by interfering with electrolyte transport.”

Bd is quick and deadly: its effects may have wiped out more than 200 species of amphibians worldwide.

Similarly, the fire salamanders are dying at a rapid rate. Since first seeing dead animals in the Netherlands in 2010, scientists have observed that the population has fallen to around 10 individuals, less than four per cent of the original numbers.

But the similarities end there. The infected fire salamanders display skin lesions or ulcers and when the animals were tested, they were negative for Bd.

So what gives? According to a paper published last week in the Proceedings of the National Academy of Sciences, a new chytrid fungus.

Batrachochytrium salamandrivorans or Bs is closely related to Bd, but an entirely new chytrid fungus species.

This study is incredibly important, Blackburn says. “It clearly shows three things: 1) Bs is a new species of chytrid, 2) it presents different pathology than Bd (these lesions), and 3) it may have different host specificity.”

Bs, like Bd, doesn’t kill every amphibian it meets. “Midwife toads, Alytes obstetricans, are among the most susceptible of European frogs to Bd,” Blackburn says. But the study researchers infected the toads with new fungus Bs, and they were not susceptible to that fungus.

But the evidence the study provides only brings more questions for Blackburn. “When we think some amphibians around the world were killed by Bd, could it have been something else? Bs? Yet another species of chytrid?”

He gives an example of the thermal range for Bs and Bd. “People trying to predict how Bd spreads and where it would thrive—the fungus may be absent from that location now, but where it might flourish given the right conditions—by modeling where the disease is now with information on climatic conditions. In the past, have we been looking at the thermal range for Bd only or might we have confused some records of Bd with what we now know as Bs? Each may have different thermal conditions and there could be errors to where we’ve predicted that the disease could thrive.”

Testing for the new chytrid fungus also presents a conundrum. Although tests have been developed to screen for Bd, it is not clear whether these might sometimes be detecting Bs instead. The authors of the new study have developed primers to test for Bs, and Blackburn and his lab will obtain these to test animals here at the Academy.

Blackburn and other scientists came back with live frogs from Cameroon earlier this summer. The team hopes to raise and breed the animals here, displaying them for the public. As we reported in a story a few weeks ago, the frogs are part of a new initiative at the Academy focused on amphibian conservation and biodiversity education.

The Cameroonian frogs were screened and tested positive for Bd. They are being treated with a proven microbial solution, but now Blackburn is worried about Bs. “How widespread is Bs?”

And Blackburn has more and more questions… “Does it only affect salamanders? We’ve seen salamander declines in Central America—it looks like Bd, but could it be Bs? We found skin lesions on amphibians in Cameroon with mortality events, Bd was not present when tested. Could we have found Bs, instead?

“How is it spread, is it totally different from Bd? Why are we seeing these now? How is climate change affecting the emergence, spread, and change of prevalence? How do you stop them?

“Bs really opens the door for further research,” Blackburn says.

Image: Didier Descouens/Wikipedia

Batrachochytrium dendrobatidis (Bd) is the deadly chytrid fungus killing amphibians worldwide. Researchers have tracked the fungus to African clawed frogs (Xenopus laevis) in South Africa back to 1934, but how did it leave Africa—and those frogs—to cause the recent decline and extinction of 200 frog species worldwide?

Vance Vredenburg of San Francisco State University wants to know. In 2008, he witnessed a population of frogs he studied in Sequoia and Kings Canyon National Park drop 99.9% due to Bd.

Working with a team of researchers at Stanford, Vredenburg began looking at the herpetology collection here at the Academy. Our own Jens Vindum offered the team several specimens of African clawed frogs to swab for DNA samples. The scientists focused on specimens collected from wild populations in California between 2001 and 2010.

African clawed frogs were imported to the US between the 1930s and 1950s for use in pregnancy tests. The frogs ovulate when injected with a pregnant woman’s urine.

“Today, these frog populations are often found in or near urban areas, probably because hospitals released them into the wild when new pregnancy testing methods were invented in the 1960s,” Vredenburg says. Since then, the frogs have established feral populations throughout North America, including Golden Gate Park.

Sure enough, the Academy’s California specimens of African clawed frogs carried Bd. “This is the first evidence of the disease among introduced feral populations in the US, and it suggests these frogs may be responsible for introducing a devastating, non-native disease to amphibians in the United States,” says Vredenburg.

And although the species is a known Bd carrier, these amphibians don’t succumb to the fungus. “It’s amazing that more than half a century after being brought to California, these frogs are still here, and they still carry this highly infectious disease,” remarks Vredenburg. “This implies that there must be a stable relationship between the pathogen and the frogs, whereas there are other frog species, for example in the Sierra Nevada, which have been wiped out by the pathogen.”

The team also tested archived Academy specimens collected in Africa between 1871 and 2010 and found evidence confirming that Bd was present among indigenous populations of this species before they were exported worldwide.

Although no longer used in pregnancy testing, African clawed frogs are still imported to the US for use in biomedical and basic science research. Because of their suspected role as a carrier of the Bd fungus and other potential pathogens, eleven states have already restricted the importation of these frogs, by requiring special permits and not allowing them to be sold as pets.

The study was published last week in PLoS One.

Stay tuned—this summer, Science Today will document Vredenburg’s and Academy researcher Dave Blackburn’s fight against Bd.

Image: Michael Linnenbach/Wikipedia

Not only are they the only mammals that can fly, but bats also show off with their immunity to viruses and other diseases. What gives?

Well, according to a recent study in Science, these two abilities—flight and immunity—might be related in the winged animals.

A group of international researchers sequenced the entire genomes of two species of bats—the fruit bat Pteropus alecto and the insectivore Myotis davidii. These two species are from the two distinct sub-orders of bats—P. alecto is a megabat and M. davidii, a microbat. By comparing and contrasting the two species’ genomes and those of other mammals (human, rhesus macaque, mouse, rat, dog, cat, cow, and horse), the scientists could refine bats’ place in the tree of life as well as determine the evolution of some of their bat-traits.

Study co-author Chris Cowled, of the Australian Animal Health Laboratory, describes how remarkable these traits are. “Bats are a natural reservoir for several lethal viruses, such as Ebola and SARS, but they often don’t succumb to disease from these viruses. They also live a long time compared to animals similar in size.”

It turns out the trick for this trait is flight. Flying is a very energy intensive activity that also produces toxic by-products, and bats have developed some novel genes to deal with the toxins. Some of these genes are implicated in the development of cancer or the detection and repair of damaged DNA.

“What we found intriguing was that some of these genes also have secondary roles in the immune system,” says Cowled. “We’re proposing that the evolution of flight led to a sort of spill over effect, influencing not only the immune system, but also things like aging and cancer.

“A deeper understanding of these evolutionary adaptations in bats may lead to better treatments for human diseases, and may eventually enable us to predict or perhaps even prevent outbreaks of emerging bat viruses,” says Cowled.

Sounds bat-tastic.

Image: James Niland/Wikipedia

A group of scientists who study biodiversity and infectious diseases, reviewed several dozen research papers published in the last five years and found a link between biodiversity loss and an increase in transmittable disease.  Specifically, they discovered that species losses in ecosystems from forests to fields results in increased pathogens in the system.

The pattern holds true for various types of pathogens—viruses, bacteria, fungi—and for many types of hosts, whether humans, other animals, or plants. The researchers found two familiar human diseases that fit this pattern—West Nile virus and Lyme disease.

Sadly, the animals, plants, and microbes most likely to disappear as biodiversity is lost are often those that buffer infectious disease transmission. Those that remain tend to be species that magnify the transmission of infectious diseases.

In one example, three different studies found strong links between low bird diversity and increased occurrence of West Nile encephalitis in the United States. Ecosystems with low bird diversity contained bird species more susceptible to the virus; thus increasing infection rates in mosquitoes and people. In comparison, ecosystems that contained a higher diversity of birds had many species that were unfit as hosts for the virus.

The authors are hoping these results will spur action. For humans and other species to remain healthy, it will take more than a village—we need an entire planet, the scientists say, one with its diversity thriving.

Global biodiversity has declined at an unprecedented pace since the 1950s. Current extinction rates are estimated at 100 to 1,000 times higher than in past epochs, and are projected to increase at least a thousand times more in the next 50 years.

“When a clinical trial of a drug shows that it works,” says lead author Felicia Keesing of Bard College, “the trial is halted so the drug can be made available. In a similar way, the protective effect of biodiversity is clear enough that we need to implement policies to preserve it now.”

Image of West Nile virus by PhD Dre/Wikipedia