Costa Rica Rocks!

Abominable snowman crabs, people-sized worms, giant microbes, encountered on deep sea voyage

An interdisciplinary team of scientists that returned March 8 from a research cruise off Costa Rica say their 16-day expedition has yielded a wealth of tantalizing new scientific data, including a high probability that some of the species they encountered have never before been studied.

The CRROCKS! (Costa Rica Rocks) research cruise, led by scientists at Scripps Institution of Oceanography at UC San Diego, the California Institute of Technology (Caltech), and Indiana State University, was one of the first scientific expeditions concentrating on the biological aspects of rocks found at the continental margin area near Costa Rica.

During 13 dives using the deep submergence vehicle Alvin, the researchers conducted up-close investigations of seeps, areas where methane gas and sulfide rise from the earth's crust into ocean-bottom sediments and rocks. During the night they studied low-oxygen zones, extracted sediment cores for examination, and mapped seafloor topography. During the day, they studied carbonate rocks made by microbes from methane, and probed various habitats, including mussel and clam beds, massive mats of bacteria, as well as corals and dead wood habitats, at water levels spanning 400 to 1,800 meters (1,312 to 5,905 feet) deep.

"The Costa Rican margin has not been extensively studied from this perspective," said Lisa Levin, a Scripps professor of biological oceanography and leader of the National Science Foundation-funded expedition. "The focus on rocks and the interfacing of methane seeps with the oxygen-minimum zone has yielded animal assemblages not studied before, with a high probability of many new species that have novel food sources."

There were thickets of tubeworms, some extending up to two meters (6.5 feet) in length. The tubeworms burrow into and protrude out of rocks, and live in association with crabs, limpets, and snails. One of the most enticing findings was the so-called "yeti" crabs, animals with thick white coats of bacteria along their front claws. The researchers were mesmerized by images of the rare animals, part of a crab family only first described in 2005, as they waved their furry claws hypnotically in the seawater. As with many of the species encountered during the expedition, the yeti's claw bacteria live in a symbiotic relationship with the host crabs.

"The working hypothesis is that the yeti crabs wave their arms to get chemicals to their symbionts, which they then use as a source of food," said Scripps graduate student Andrew Thurber, one of the researchers on the cruise.

Prior to the expedition only three yeti crab specimens had ever been collected. The Costa Rican cruise yielded a yeti crab bonanza, with more than 50 specimens collected.

The scientists also collected starfish, limpets, sea anemones, brittle stars, and scallops, and they encountered deep-sea bacteria that measured more than one millimeter, a gigantic size for microbes.

Hundreds of invertebrate specimens were collected, with the majority destined to become part of the Scripps Benthic Invertebrate Collection, said Greg Rouse, curator of the collection and one of the CRROCKS expedition leaders. Other specimens were taken by Costa Rican collaborators on the voyage to become part of the Universidad de Costa Rica collections.

"We already know that more than a dozen new species were found (possibly worms, clams, mussels, and other invertebrates) and upcoming DNA sequencing may reveal even more," said Rouse.

To properly capture and study such a diversity of creatures, Thurber and Levin worked with Ken Duff and David Malmberg of the Scripps Marine Science Development Center to develop unique specimen housing containers. The specially designed aquarium collection bins (nicknamed CRROCKS boxes) allowed the researchers to insulate and isolate the specimens and rocks, partition animal extractions into separate compartments, and return them to the ship at naturally cold temperatures. Transparent compartment walls allowed them to be viewed intact inside the ship's cold room. The boxes offer a leap forward from previous designs that lumped specimens indistinguishably together and heated them as they traveled through the warm ocean surface waters, potentially damaging their tissues and DNA.

In addition to Levin and Rouse, other researchers leading the expedition included Victoria Orphan of Caltech and Tony Rathburn of Indiana State University. Other Scripps participants included postdoctoral researchers Paola Lopez and Hank Carson, staff research associate Jennifer Gonzalez, and graduate students Christina Tanner and Danwei Huang.

—Mario C. Aguilera

April 2009