Sea Otters Again Prove Their Worth

seaotterIf you take a class in ecology, sea otters inevitably come up. They’re a classic example of a keystone species — that is, an animal or plant or other organism that has a critical role in the ecosystem such that, if you take it out of the system, everything collapses. Sea otters are a keystone species in the kelp forests off California. If the sea otters aren’t around to munch on sea urchins and keep the urchin population in check, urchins proliferate and graze the kelp to death. Without the kelp, other animals that depend on the vegetation — including crabs and geese — suffer. All that happens because there are no sea otters.

Now a group of scientists from California have found that sea otters play a similar keystone role in another coastal California ecosystem — the seagrass beds of Elkhorn Slough. The study was published this week in PNAS.

Elkhorn Slough is an estuary near rich fields of strawberries and artichokes. Those farm fields are a problem because when water drains off them into the estuary, it carries nutrients (from fertilizer) and pesticides. Nutrient loading is a particular problem in marine ecosystems as it changes the abundance of certain organisms and sets everything out of whack in the food web. Some critters thrive, but many suffer. And in Elkhorn Slough, seagrass beds have been on the decline.

Scientists suspected, however, that sea otters may play an important role in this area. When the researchers looked at a 50-year record of nutrient levels, seagrass and sea otters, they noticed a pattern. There were no sea otters in the area between 1965 and 1984. During that time, when nutrient levels started to increase, the seagrass beds declined. But when the sea otters were reintroduced to the area, the seagrass beds again thrived, even though the nutrient levels continued to increase.

The researchers suspected that the link between the sea otters and seagrass was not sea urchins, as in the kelp forests, but crabs: The sea otters eat the crabs. Without so many crabs around, grazing herbivore species thrive. Those grazers eat algae that lives on and harms the seagrass, and as a result, the seagrass thrives.

But when there are no otters around, this all falls apart. The crabs outcompete the algae grazers, letting the algae proliferate. And with the nutrients boosting the algae population, the seagrass beds suffer.

“This estuary is part of one of the most polluted systems in the entire world, but you can still get this healthy thriving habitat, and it’s all because of the sea otters,” study author Brent Hughes of the University of California, Santa Cruz, told BBC News. “So it’s almost like these sea otters are fighting the effects of poor water quality.”

This new pattern is a bit more complex than the classic sea otter–kelp story, but it’s yet another example of how important top predators are and the disaster that can follow their removal.

Image courtesy of flickr user Blake Matheson

Secrets Of A Cape Fur Seal Pup’s Coat

sealA Cape fur seal doesn’t become a marine mammal until it is several weeks old, spending that time only on land. Stuck on shore with little shade available, the pups have to endure the hot sun, usually unable to take a quick dunk to cool off as its parents would do because the waters are too dangerous. So how does a pup cool off? It doesn’t have to, say scientists reporting in PLOS ONE. When they’re young, these animals have a special coat that keeps them cool.

The researchers studied six Cape fur seal pups that were born between 2010 and 2012 at Zoo Rostock in Germany. They measured the pups’ surface temperatures with an infrared camera as well as skin temperature and rectal temperature with increasingly invasive techniques (there’s never going to be a good way to get that last one remotely).

As long as a pup’s fur was dry, it was able to maintain a stable internal body temperature. But when a pup got wet — when its mom took it for a quick dunk, or it rained — its hair became flattened and stringy, and the pup’s body temperature dropped. Sometimes they shivered. (Adorable note: The pups would shake themselves like dogs when they came out of the water.)

The researchers conclude that the pup’s fur is adapted to the terrestrial lifestyle that marks these animals’ early lives. The fur traps a layer of air near the skin that insulates against heat and cold. The tradeoff is that this fur doesn’t insulate well in water. This fur coat has to change as the seals age and adapt to the marine life.

The fluffy fur may protect a seal pup against the heat, but it’s made it vulnerable to human predators. The Namibian government lets people kill 80,000 Cape fur seal pups each year; a pelt can be sold for $7.

Image courtesy of flickr user DragonWoman

What’s A Manatee Doing In Virginia?

manateeVirginians are excited this week because a manatee has come to visit. It was spotted this weekend in the Appomattox River (see video below). Manatees are residents of Florida, so what’s this one doing so far up the East Coast? Well, it’s not actually all that far out of its territory if you consider that manatees have swum as far north as Cape Cod. It seems that sometimes Florida’s state marine mammal likes to wander. But why?

Well, no one has ever asked the manatees (or if they have, they never got a good answer), but news reports describing various incidences of manatees in the north have plenty of speculation: The AP report about Virginia’s current visitor, for example, says that manatees sometimes leave Florida when waters there get too warm; they go north to cool off. A 2006 story about a Cape Code manatee says that it’s common for manatees to travel up to the shallow areas off the Carolinas. USGS wildlife biologist Cathy Beck speculated that the manatee followed a warm current up the coast to Massachusetts.

Manatee sightings north of the Carolinas are not uncommon these days. Baltimore has even had a repeat visitor, nicknamed Chessie, that has shown up multiple times since 1994. But whether more manatees are swimming north in the summer or more people are noticing them isn’t known.

But for now wandering manatees are just an interesting oddity, and perhaps a distraction from the bigger problems that the species faces. See, the Florida manatee (a subspecies of Trichechus manatus) is in trouble. The IUCN lists them as endangered and says there are fewer than 2,500 individuals. More than 200 manatees died in a deadly algal bloom earlier this year. They’re victims of habitat loss and often in conflict with the fishing industry (manatees get entangled in fishing gear). Boat collisions are also a huge danger. In 2010, for instance, 83 animals were killed in encounters with boats. One newspaper estimated that this year manatees are dying from all these various causes at a rate of 100 per month.

Some groups in Florida have petitioned to have the manatee’s status upgraded from Endangered to Threatened, noting that aerial surveys of the animals show that the Florida population has increased in recent years. But Caryn Self-Sullivan, a conservation biologist at Nova Southeastern University in Florida, argued in a blog post earlier this year that there’s little reason to change the mammal’s classification. Aerial surveys don’t produce reliable counts; mild winter conditions and poor visibility can skew the results. And changing the manatee’s status to Threatened would still indicate that they were in danger of extinction and in need of protection. “To reduce protection would likely produce a significant and deleterious effect on the manatee population in Florida,” she writes.

Classifying the manatee as Threatened wouldn’t immediately change any of the laws that protect the animals. But this is all moot for now; the reclassification discussion is on hold. That would seem to be good news, except that the hold is in response to this year’s high death rate. Manatees just can’t get a break.

Image courtesy of flickr user NOAA’s National Ocean Service; video from cody_beeler on Instagram

Human Presence Takes A Toll On Galapagos Sea Lions

sea_lionWhen you think about the Galapagos Islands, there are a few things that come to mind. There’s Charles Darwin, of course, and the studies he made there that contributed to his development of the idea of evolution. And the amazing wildlife, including tortoises and iguanas and a whole host of birds. What you don’t think of are things like pollution and invasive species, but these are growing problems, especially in the areas inhabited by humans.

Some islands are still pristine, though, and that gave a group of biologists, led by the Zoological Society of London, a chance to see how one species, the Galapagos sea lion, is affected by the presence of humans. The researchers compared immune activity and body condition of two populations, one in Bahia Paraiso on the undeveloped island of Santa Fe and another that lives in the center of the rapidly growing town of Puerto Bazquierizo Moreno on San Cristobal. The study was published last week in PLOS One.

None of the animals appeared to have signs that they were sick, but those that lived in town had more active immune systems. And among the pups in that colony, those that had higher levels of antibodies had thinner skinfolds and were skinnier.

“A tell-tale sign of an unhealthy sea lion is a thinner than normal layer of blubber, which is what we saw in the sea lions on San Cristobal,” study coauthor Paddy Brock of the ZSL said in a statement. The more active immune systems could indicate “a threat of infectious disease, which could mean human activity is increasing the chance of potentially dangerous diseases emerging in the Galapagos sea lion,” Brock said.

Puerto Bazquierizo Moreno does not seem like it would be a great place to be a sea lion. The bay is home to more than 200 boats and filled with fecal contamination from the vessels and sewage from the town. And the land has a bunch of animal threats, including people’s pets, feral cats and rats. If these factors are impairing the immune systems of the sea lions that live in the area, the impaired immunity could reduce the marine mammals’ ability to hunt, the researchers say.

And the Galapagos sea lions don’t need anything else to hamper their survival. The species was listed as endangered by the IUCN after its already-small population declined by more than 50 percent in the last three decades. The sea lions, which are a bit smaller than the more familiar California species, are not afraid of humans and like to hang out on rocky shorelines and sandy beaches (above). That can put them in direct contact with the human population and make them vulnerable to threats like uncontrolled dogs that will kill sea lion pups.

These sea lions have figured out ways to deal with some threats — they’ve been known to mob Galapagos sharks that approach their rookeries — but they haven’t yet evolved to deal with the ones humans have brought to them. Their immune systems didn’t evolve to exist in a sewage-filled, pet-dominated environment. And it appears that’s put them at even more risk of disappearing from the planet.

Image credit: ZSL_Paddy Brock, via EurekAlert


Seal Versus Sea Lion

A publication that will remain anonymous here (since I hope to write for them one day), mixed up seals and sea lions on Twitter today. It’s easy enough to see why — they start off the same when you’re typing, and if you’re not paying attention, you’ve written one when you mean the other.

It probably also doesn’t help that they’re both marine mammals — pinnipeds, in fact — that look quite similar (seal on the left, sea lion on the right):seal-sealion Sea lions and true seals (I’m going to ignore fur seals to make this a little less confusing) are separated by some 28.5 million years of evolution, according to TimeTree. The two animals are now in separate families, Otariidae (sea lions) and Phocidae (seals). There are many different species of both seals and sea lions, but all these animals have a basic, similar body shape: streamlined with flippers instead of feet.

But look closer and you’ll find subtle differences. The front flippers on seals are small, stubby, and hairy, with claws. Their back flippers don’t rotate but instead let seals be efficient swimmers. Sea lions have longer, skin-covered front flippers and back flippers that they can rotate underneath them, letting them walk, or at least shuffle about, on land. That makes sea lions the animals you’re most likely seeing basking on a rock at the zoo.

True seals sometimes have the name the “earless” seals because they don’t have anything covering the holes that lead into the hearing apparatus in their heads. Sea lions, though, have small flaps that cover their ear holes. There are also some differences in the whiskers, but I doubt many of us will ever get close enough to one of these animals to tell the difference.

Sea lions are also more vocal and more social than seals. Perhaps that means that sea lions are extroverts and seals are introverts.

Image credit: NOAA

Polar Bears Survive Disappearance Of Sea Ice By Moving To Land


Polar bears live an incredibly specialized existence in the Arctic. Though born on land, they prefer to live on sea ice, from which they can hunt the seals that make up the majority of their diet. But with sea ice disappearing, there’s been well-founded worry about what will happen to the polar bear (Ursus maritimus).

It might be easy to assume that the bears will give up their icy lives and move to land. And a study of the polar bears of the Western Hudson Bay, published by theĀ Journal of Animal Ecology, has found that the bears do just that — moving onto shore when the sea ice retreats and returning to the ice when it grows again later in the year. By tracking more than 100 female polar bears for over a decade, the researchers found that the bears’ migration could be timed to the movements of the sea ice.

But that time between the sea ice retreat and return has been getting longer and longer as the Arctic warms, with the result that the bears are spending more and more time on land.

“The data suggest that in recent years, polar bears are arriving on shore earlier in the summer and leaving later in the autumn. These are precisely the kind of changes one would expect to see as a result of a warming climate and may help explain some other studies that are showing declines in body condition and cub production,” the study’s lead author, Seth Cherry of the University of Alberta in Canada, said in a statement.

The problem is that on land the bears don’t hunt, or at least not enough to matter; they live off their stores of fat. Subadult bears, like the one above, are particularly vulnerable because, due to their smaller size, they have less fat to rely on. And their survival rate has been dropping. This might also explain the trend in decreasing litter size. Females don’t have enough fat to both survive the long summer and give birth to, and maintain, multiple cubs.

Which all makes me wonder: What happens when the summer gets too long for even the fattest bears to survive?

Image copyright Andrew Derocher, Univeristy of Alberta, via EurekAlert

Dolphins Help One Of Their Own

Despite Flipper’s reputation for adorableness, dolphins really are dangerous, aggressive animals. That said, there are times when we’re all reminded why they’re known for cuteness.

Kyum Park of the Cetacean Research Institute in Ulsan, South Korea, and colleagues in July 2008 spotted one pod of long-beaked dolphins carrying out a display of particularly bittersweet behavior. According to the story reported in Marine Mammal Science, a female of the group was in trouble. Her pectoral flippers were paralyzed, and she was having difficulty swimming or even staying afloat.

But others in her group soon helped out, trading off swimming with their injured companion, and creating a raft of dolphins to keep her from drowning.

Sadly, they weren’t able to save her. But as she sank, five of her friends stayed with her, touching her body, as if they were mourning her loss.

It’s difficult to assign motives to such actions — after all, we can’t ask a dolphin why it did something — but Karen McComb of the University of Sussex in Brighton, U.K., told New Scientist that rescuing an injured member of the group could help the pod to maintain its territory, preserve shared genes, or maintain the group’s bond. “It makes a lot of sense in a highly intelligent and social animal for there to be support of an injured animal,” McComb said.

Whether the actions constitute empathy is harder to say. But with such feelings sometimes lacking in the human world, it certainly is good to see something like it, even among deadly animals.