Category Archives: Marine Invertebrate

It Took Almost 25 Years, But They Finally Identified (A) Waldo

waldoWhere’s Waldo? The more relevant question here is, what’s a Waldo? Waldo is a genus name, belonging to a group of bivalves that have been found in various spots around the world. Now two scientists working on the Pacific Coast of North America have found a new species — Waldo arthuri — though it took nearly 25 years to figure it all out. The scientists report their findings in Zookeys.

Back in 1989, two scientists found a peculiar tiny mollusk, a type of clam, in locations 1,000 miles apart, off the coasts of Santa Barbara, California and Vancouver Island in Canada. The researchers had met up at a scientific conference and talked clams over one of the breaks, quickly realizing they had each found the same thing. But they couldn’t figure out exactly what they had found.

The bivalves were tiny, only a few millimeters in length, with thin, translucent shells and long tentacles. One of the researchers, Diarmaid Ó Foighil of the University of Michigan’s Museum of Zoology, was able to collect some live specimens. “We were looking closely at sea urchins and noticed something crawling on the fine spines covering the urchin body,” Ó Foighil said in a statement. “We were amazed to see that there were minute clams crawling all over the sea urchin.” (In the image above, the clam can be seen among sea urchin spines.)

Why it took a couple decades to determine that the mollusk was a new species isn’t completely described in the paper, but it seems that W. arthuri looks a lot like other members of its genus. Eventually the researchers turned to DNA sequencing — using the help of another scientist who’s a specialist in clam DNA — to tease out the differences in the bivalves. W. arthuri is indeed a species separate from its closest relative, which lives all the way in the south Atlantic off the coast of Argentina.

The researchers write that finding sister taxa in separate ocean basins isn’t an uncommon phenomenon, but it’s a little odd in this case because all the other known Waldo species live far away in high-latitude southern oceans.

The true range of W. arthuri may be even larger than the stretch from California to Canada. The sea urchin Brisaster latifrons, on which the clam lives, can be found from the Galapagos Islands to the Bering Sea, off the coast of Alaska. It’s possible, the scientists say, that the new Waldo can be found all along that area as well.

Image by Diarmaid O’Foighil, via EurekAlert

July 18, 2013Permalink Leave a comment

More Than Just Seagulls Munch On The Seashore

journal.pone.0068221.g005Walk along pretty much any beach and at the high tide mark will be a line of debris. There may be seaweed or shells, bits of driftwood or plastic debris. You probably won’t see any fish, though. And that’s a little odd, because fish do die, and their bodies have to go somewhere. Surely some would wash ashore.

A group of researchers in Australia think that they’ve figured out where the fish go – the fish quickly get scavenged by the critters that live along the shore. But there’s more than just seagulls finding their meals here, the team reports in PLOS One.

The scientists set up a series of experimental plots along a sandy beach on North Stradbroke Island on the east coast of Australia. They picked a spot far from humans, where dogs and beachgoers would be scarce. Then they set out 20 plots, three meters by 10 meters each, and for eight days added about five kilograms of flathead mullet fish to half the plots about two hours before sunset.

The beach was nearly picked clean. Over the eight days, 720 fish were set out and 97 percent were completely eaten. Gulls (silver gulls in this case) ate some of the mullet, but there were several other birds species as well: Torresian crows, whistling kites (b in image above), brahminy kites (a), and white-bellied sea eagles (c and d)

These avian scavengers scoured the beach most often at sunrise and in the first few hours of morning. On three occasions at night, however, red foxes (f) visited the plots, snapping up the easy meal. And on one day, a lace monitor (e) – a large, carnivorous lizard – was spotted on the beach snacking away. That was a surprise because there have been few reports of terrestrial reptiles scavenging on a beach.

One invertebrate also got in on the action. The researchers measured the diameter of ghost crab burrows and, using burrow size as a proxy for crab size, discovered that when they added fish to the experimental plots, bigger ghost crabs moved in to take advantage of the free food.

But birds were the dominant consumers of the carrion fish. And they probably play an important role in this seashore ecosystem, the researchers say, helping to transfer nutrients from the sea onto land and providing a vital link between water and soil.

Image used under Creative Commons license, Schlacher TA, Strydom S, Connolly RM, Schoeman D (2013) Donor-Control of Scavenging Food Webs at the Land-Ocean Interface. PLoS ONE 8(6): e68221. doi:10.1371/journal.pone.0068221

July 17, 2013Permalink Leave a comment

How A Sea Star Handles The Heat

seastar

If you’re a human, the rocky intertidal zone can be a great place to explore. There are plenty of interesting critters to find. But if you’re one of those creatures, life can be rather rough — in addition to putting up with humans that may pull you out of your home, there’s dangers ranging from predatory birds to punishing waves to dramatic temperature fluctuations that come from being submerged in water and exposed to air over and over. And many of the animals that live in this zone either don’t move or don’t move fast.

This is life for the purple sea star, Pisaster ochraceus, which is a common find on Pacific shores. The sea star (or starfish, if you must) is an ectotherm, meaning that it’s body temperature is determined by its environment, not the organism. But a study published last week in the Journal of Experimental Biology finds that this sea star does appear to have a little control about where that heat goes in its body. The key is hot arms.

A trio of researchers from the University of South Carolina in Columbia and the University of California, Davis started with 70 purple sea stars collected from the California coast. When they viewed the invertebrates with an infrared camera they discovered that the sea stars’ arms were warmer than the core. This was surprising — they had expected the arms to be cooler.

The scientists then subjected groups of sea stars to increasingly warm temperatures by placing them under heat lamps. The temperatures ranged from 26 degrees Celsius (comfortable) to 42 degrees (deadly). At lower temperatures, a sea star’s arms were a couple degrees warmer than its core. At middle temperatures, the arms were also warmer, but after a couple days in this heat, many sea stars would shed one or more arms. And at even higher temperatures, when sea stars’ core temperature got above 35 degrees, they died within 24 hours; their arms, though, were cooler than the core.

The arms are likely acting as heat sinks for the sea stars, the scientists say. That would imply that the invertebrates have the ability to transfer heat from the core to the arms. Though the animals don’t have a circulatory system like we do (that’s what allows humans to transfer heat through our bodies and do things such as conserving heat in our core when it’s cold), sea stars can move fluid within themselves.

“Under this scenario,” the scientists write, “directional movement of fluid within the body might facilitate the transfer of heat from right below the dorsal integument, where solar energy is collected, to the arms where heat can be released to the environment.”

That heat movement alone only works so much, though. If there’s too much heat for the arms to contain, the sea star sheds an arm in an attempt to keep its core below 35 degrees. That’s not a great choice — regrowing an arm is costly — but it’s better than death. But even that won’t work when it’s just too darn hot.

Image courtesy of flickr user Jerry McFarland

June 3, 2013Permalink Leave a comment

What The Oatmeal Might Have Gotten Wrong About Mantis Shrimp

OdontodactylusScyllarusMantis shrimp are amazing little creatures. I was delighted to write about their superfast punch in a story last year. And that punch was one of the highlights in a fabulous online comic published by The Oatmeal yesterday, titled “Why the mantis shrimp is my new favorite animal.” But before getting to the punch, the comic discusses the critter’s vision. Here’s a sampling of what it says (minus the illustrations):

Our eyes contain millions of light sensitive cells, called rods and cones. Rods enable us to see light and motion. Cones enable us to see color….

When it comes to color vision, butterflies are almost the top of the food chain. There is one animal that has better vision than the butterfly: the mantis shrimp.

…this marvelous creature has not two, not three, not five, but sixteen color-receptive cones. The rainbow we [humans] see stems from just three colors, so try to imagine a mantis’ rainbow created from sixteen colors. Where we see a rainbow, the mantis shrimp sees a thermonuclear bomb of light and beauty.

This makes for a very pretty comic, but it may not be quite true, as demonstrated by a color test that was given to one mantis shrimp species, Haptosquilla trispinosa. The test, which was described in Science News last year, was carried out by Hanne Thoen, of the University of Queensland in Brisbane, Australia, who presented her results at a scientific meeting in Maryland:

Thoen tested the color vision of mantis shrimp by training them to scoot out of their burrows toward a pair of optical fibers and punch at the one glowing a particular color. As she narrowed the color gap between the two fibers, she could tell when the animals no longer discerned a difference.

People can distinguish some colors that are only a nanometer or two different. But mantis shrimp “flunked” this color test when the colors were 15 nanometers apart. So on a test like this, human vision might actually be better than that of mantis shrimp.

Researchers are still working out the reasons why the mantis shrimp might not be as discerning as we are when it comes to color, but brainpower might explain it. From Science News:

People and other animals studied so far distinguish colors through brainpower by interpreting competing activity in different kinds of light-receptor cells. Instead of doing such fancy brainwork, mantis shrimp may just rely on what a particular specialized cell responds to strongly. Wavelengths that tickle the purple-sensitive cells may be just plain purple regardless of whether they’re more toward the blue or the ultraviolet.

This was only one simple test of one species, and scientists are still figuring things out, so we can’t say for certain that mantis shrimp don’t have amazing vision. But humans also beat the shrimp in another area of sight, because the invertebrates aren’t great at seeing light in the red range. Those are the first wavelengths absorbed by water, so there’s not much need for cells to detect a color that doesn’t exist in their world. The wavelengths they can detect can vary, however. Scientists have found that mantis shrimp can tune their vision to the environment they grow up in, so those that live in shallow water will see different colors than those from the deep.

One place that the shrimp definitely have us bested in terms of vision, though, is ultraviolet — at those wavelengths, they can see things we never will. Whether that means the mantis shrimp can see a “thermonuclear bomb of light and beauty,” well, it’s hard to tell. But they certainly are beautiful, awesome creatures nonetheless.

Image of a mantis shrimp (Odontodactylus scyllarus) courtesy of Silke Baron, via wikimedia commons

April 10, 2013Permalink 9 Comments

If You Like To Eat King Or Snow Crab, Worry About Climate Change

red_king_crabIf you eat crab, there’s a decent chance you’ve had king crab or snow crab — the type they often sell in grocery stores and restaurants as just big red arms — which are brought up from chilly waters in places like the Bering Sea off Alaska. The future for these species is uncertain; as with many tasty critters, they’re overfished and on the decline. But more worryingly, finds a study in PLOS One, the crabs are vulnerable to climate change.

Researchers from the National Marine Fisheries Service Kodiak Laboratory in Alaska studied two species of crab: the red king crab (the most sought-after kind of king crab) and a snow crab known as the Tanner crab. They raised young crabs for a little over half a year in tanks with sea water at one of three pH levels — 8.0, 7.8, and 7.5 — and then tracked the crabs’ growth.

The scientists were interested in the effects of ocean acidification on the crabs. As we pump more and more carbon dioxide into the atmosphere, the ocean absorbs some of that gas, which causes the water to become more acidic over time. Some areas of the world will be affected more than others, and northern regions are expected to become more acidic than tropical ones. The three different pH levels range from the current state of the water (8.0) to what will exist at the end of the century (7.8) to what could exist in the not-too-distant future (7.5).

Ocean acidification is a particular worry for organisms that rely on calcium carbonate to construct their skeleton or shell, like coral and crabs. If the pH of the water is too acidic, it will be too difficult, too costly for these organisms to turn calcium and carbonate into calcium carbonate to build their bodies.

At the 8.0 pH level, the crabs grew just fine. Some crabs died, but that’s normal. At a pH of 7.8, more crabs died; less than 40 percent of the red king crabs and about half of the Tanner crabs survived to the end of the study period. And at the 7.5 pH level, less than 40 percent of the Tanner crabs lived to the end, and all of the red king crabs died within 95 days. Growth rates were also affected by the acidic waters, with the crabs not growing as well when pH was low.

Given these results, the researchers predict that ocean acidification will cause a serious decline in these species by the end of the century, with red king crabs affected first. Even before then, though, small increases in acidity could affect crab growth. Because smaller crabs are more vulnerable to predators, they’re more likely to get eaten and not survive too long. Their smaller size could affect the predators that eat them (they won’t be as satiated by their crab meals), and that’s just the beginning of a host of changes that could sweep through the food web, affecting species that may not be directly impacted by water pH.

Crabs and other species may be able to adapt to more acidic waters. There are some cousins to the red king and Tanner crabs that live in deep places with lower pH, which shows that such adaptation is possible. But greater acidity at the surface could also open up these waters to the deep-sea species, resulting in a crab competition. What this means for the species we love to eat, well, only time will tell.

Image of red king crab courtesy of The Children’s Museum of Indianapolis, via wikimedia commons

April 8, 2013Permalink Leave a comment

An Invasive Crab Is Helping Cape Cod’s Marshes To Recover

crabInvasive species are generally not good for an ecosystem. Zebra mussels, snakehead fish, feral hogs, nutria, domestic cats, purple loosestrife — I could probably fill inches of your screen with the names of species that have caused havoc when moved into a new landscape. But not all species prove troublesome when transported out of where they are traditionally found, and now there’s a case where an invasive crab is actually helping an ecosystem to get healthier.

The case comes from Cape Cod, where overfishing has removed most of the predators from the salt marshes. Without those predator species to keep it in check, the crab Sesarma reticulatum has grown in numbers. The species denudes the marshes of the cordgrass that holds the land together, and also burrows into the ground, making that soil more susceptible to erosion.

In recent years, though, some of those marshlands have started to recover, and the cordgrass began to return. That recovery can be tied to the arrival of another crab, the European green crab (Carcinus maenas), say researchers from Brown University in a study in Ecology.

“When we started seeing the marshes recover, we were baffled,” study coauthor Mark Bertness said in a statement. “To see very quickly the marshes start to come back, at least this veneer of cordgrass, it seemed pretty impressive. When we started seeing this recovery we started seeing loads of green crabs at the marshes that were recovering. We went out and quantified that.”

The researchers looked for crabs in healthy and recovering marshes. There weren’t many green crabs in the healthy marshes, and there also weren’t many Sesarma burrows in those areas. But in recovering marshes, there were lots of burrows and lots of green grabs using them.

They then tried an experiment, putting a Sesarma crab and a green crab in a cage near a burrow. The green crab not only took over the burrow, but it often killed the other crustacean. In another test, they caged the crabs in a plot of grass. When a Sesarma crab was on its own, it would eat a lot of grass, but when it had a companion of the other species, it was put off its feast, even when the green crab was restrained from attack.

What’s happening in these recovering marshes, the researchers say, is that the green crabs are finding refuge from predators and the sun in the burrows of Sesarma crabs, and then feeding on the Sesarma crabs. Those crabs are not only getting reduced in numbers through this competition and predation, but they’re also reducing their cordgrass destruction because they’re afraid of the green crabs.

“Non-consumptive effects can be much more powerful because whereas a consumptive effect is one crab eats another crab, a non-consumptive effect is one crab scares dozens of crabs,” Bertness said. “The ecological effect can be much greater much quicker.”

The result is that the cordgrass in those recovering areas is getting the chance to grow back. And when the grass recovers, other species may follow.

The researchers — and I — called the green crab an “invasive species” but that’s probably not right in this context. The definition of an invasive species is “an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.” The green crab may be an alien, but we probably need another term for one that causes an environmental benefit.

Image (a European green crab) credit: Catherine Matassa/Northeastern University

April 4, 2013Permalink Leave a comment

How The Clean Water Act Helped A Sea Slug’s Return

seaslugThis striking sea slug, Felimare californiensis (a.k.a. the California chromodorid), used to be a common find along the California coast, from Point Conception to San Diego, and along the Channel Islands. One early 20th-century guidebook, for example, described the invertebrate as “fairly abundant in the tide pools from Monterey to San Diego.”

But by 1983, this species had disappeared from California. Researchers and amateurs searched for the nudibranch, but it could no longer be found outside Mexican waters.

Until 2003, when it again turned up in small numbers around Santa Catalina Island. And in 2011, it reappeared off of Santa Cruz Island and near San Diego. Researchers now say that the sea slug is poised for a comeback.

So what happened? According to a study led by the University of California Santa Barbara and published in Marine Biology, the decline of the sea slug can be traced to water pollution. But the pollution didn’t affect F. californiensis directly; the researchers conclude that because similar sea slug species were unaffected. Instead, the pollution somehow affected the quality or abundance of the sea slug’s main prey, the sponge Dysidea amblia, possibly by having some sort of effect on symbiotic cyanobacteria that could serve as sources of defensive metabolites or provide chemical cues used in the sea slug’s reproductive cycle.

Pollution along the California coast reached its peak around the time that F. californiensis was on the decline. But water quality turned around in the years following the passage of the Clean Water Act in 1972. And when El Niño events brought the sea slugs up from Mexico, they were able to reestablish themselves in the cleaner water.

“Since the passage of the Clean Water Act in 1972, big strides have been made in reducing pollutants in the Southern California Bight, especially from large wastewater outfalls, and these improvements may have allowed Felimare californiensis to regain a foothold in the region,” study coauthor Jeff Goddard of UCSB said in a statement.

Whether this sea slug can make a full return to its previous range can’t be known. But no one should assume that its recovery is guaranteed. As the researchers point out in their paper, though the Clean Water Act did have a profound impact on water quality, there are still plenty of other pollutants to worry about. They write, “a vast array of chemicals unregulated, illegally used, or not previously considered as contaminants (e.g., pharmaceuticals, hormones, and antibiotics) flow increasingly into [the water] through multiple pathways, presenting daunting environmental challenges.”

Those are challenges faced by many species across the country. Whether we do anything about it, well, that remains to be seen.

Image credit: Kenneth Kopp, via EurekAlert

March 21, 2013Permalink Leave a comment