Preventing home invasions means fighting side-by-side for coral-dwelling crabs and shrimp

Mar 30, 2012
A cushion seastar, bottom foreground, approaches a coral head of the genus Pocillopora looking for a meal. Credit: Photo courtesy Seabird McKeon

As any comic book lover knows, when superheroes band together the bad guys fall harder. The strength that comes in numbers is greater than the sum of its parts.

The same holds true, researchers have recently learned, when different species of (genus Trapezia) and snapping shrimp (Alepheus lottini) in the central Pacific band together to defend their homes from hungry seastars. In these frequent conflicts "one-plus-one doesn't always equal two, sometime it is more," explains Seabird McKeon, a at the National Museum of Natural History's Smithsonian Marine Station in Fort Pierce, Fla.

The crustaceans are much more effective when they fight together than when they fight alone, a process McKeon calls the Multiple Defender Effect.

"It is a clear example of synergy, and one that underscores the importance of biodiversity in the ocean."

This is Trapezia serenei, a tiny coral-dwelling crab. Credit: Photos courtesy Seabird McKeon

Even in a comic book one would be hard pressed to find an enemy more bizarre than the "cushion" seastar (Culcita novaeguineae), an animal used by McKeon in recent with living corals (genus Pocillopora) and their defenders. To consume a coral, the seastar pushes its stomach outside its body and lays it over the coral like a cushion. It then hugs the coral close and "eats," letting stomach acids and do their work.

The stationary coral is defenseless, yet the that live among its branches come to its aid, snipping and prodding an intruding seastar with their claws.

"The coral itself is like a cauliflower head, a main central stem and lots of little branches," McKeon explains. "Crabs gain protection from fish by living inside the coral structure."

Once a mating pair of crabs takes up residence on a coral head they do not tolerate the presence of other crabs of their same species. Crabs of other species, however, are ignored, as are snapping shrimp. As a result, some coral heads may have as many as five different species of defensive crustaceans living on them, all pairs of different species.

This is Alpheus lottini, a snapping shrimp. Credit: Photo courtesy of Seabird McKeon

In repeated experiments McKeon and colleagues measured the effectiveness of a single crab pair in preventing a seastar from eating their home coral. He found that one pair of crabs reduced the volume of coral eaten by about 19 percent, compared to a coral with no defenders. Two pairs of crustaceans working together, however, were able to reduce the volume of coral eaten by as much as 65 percent—the multiple defender effect.

The take-home lesson here, McKeon says, "is these crabs don't allow others of their same species on their coral, yet the synergy of different pairs fighting together is critical to the defense of the coral. The multiple defender effect is an important new angle on why we must conserve biodiversity in the ocean."

"Multiple defender effects: synergistic coral defense by mutualist crustaceans," by C. Seabird McKeon; Adrian C. Stier of the University of Florida; Shelby McIlroy of the University at Buffalo and Banjamin Bolker of McMaster University; appeared recently in the scientific journal Oecologia.

Explore further: Current residential development research is a poor foundation for sustainable development

Related Stories

Semporna may have richest marine biodiversity in the world

Feb 24, 2011

The preliminary results of the Semporna Marine Ecological Expedition (December 2010) indicate that Semporna may have the world's highest marine biodiversity. The expedition yielded a record number of 43 species of mushroom ...

Shape-shifting coral evade identification

Feb 24, 2009

The evolutionary tendency of corals to alter their skeletal structure makes it difficult to assign them to different species. Researchers writing in the open access journal BMC Evolutionary Biology have used genetic marker ...

Recommended for you

Study provides detailed projections of coral bleaching

10 hours ago

While research shows that nearly all coral reef locations in the Caribbean and Gulf of Mexico will experience bleaching by mid-century, a new study showing in detail when and where bleaching will occur shows ...

Germany restricts fracking but doesn't ban it

16 hours ago

The German cabinet drew up rules Wednesday on the hitherto unregulated technology of "fracking" in Germany, narrowly restricting its use, but stopping short of an outright ban.

Life in the poisonous breath of sleeping volcanos

16 hours ago

Researchers of the University Jena analyze the microbial community in volcanically active soils. In a mofette close to the Czech river Plesná in north-western Bohemia, the team around Prof. Dr. Kirsten Küsel ...

Eggs and chicken instead of beef reap major climate gains

17 hours ago

Beef on our plates is one of the biggest climate villains, but that does not mean we have to adopt a vegan diet to reach climate goals. Research results from Chalmers University of Technology show that adopting ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.