Leg 6: April 16, 2012

Day 9: Comparing clams

Today we finished our biological sampling of Site 7; it was previously visited during Leg 4 by Peter Brewer and Leg 5 by Charlie Paull. We aimed to see how diverse the clam populations were at this location. Discrete patches of seep-associated clams are typically composed of individuals of a similar size and one species. Since the scientists on Leg 5 already collected some clams here, our goal was to search for patches with clams of varying sizes.

We sampled several of these patches and when we examined them onboard the R/V Western Flyer, our expectation turned out to be correct. At least two species of clams inhabited these patches: the larger clams commonly found at Gulf of California seeps, and smaller oval-shaped clams that we had not seen here before. Perhaps the smaller clams are new to science, or they may be one of the species that was described following dredge-tows in the gulf in the late nineteenth century. We will compare the shells of our clams with museum specimens from these old collections and try to match existing species names with some potentially new faces.

Close-up of cold seep clams with their siphons extended, clustered together on the seafloor.

Close-up of cold seep clams with their siphons extended, clustered together on the seafloor.

We will also obtain DNA sequences from the new clams to develop a DNA bar-coding system to help future scientists tell these clams apart. Very often, shell sizes and shapes are deceptive because growing clams are affected by local environmental conditions. On the other hand, it is also common to find two or more species that have virtually identical shell shapes and sizes. These situations are precisely when DNA analysis is the only way to tell things apart.

Commercial DNA analyses are now relatively inexpensive and accessible to ecologists and biogeographers. It is often quicker to send a DNA sample to a commercial lab for typing than to send a whole specimen to a taxonomist in a museum for identification. Museum taxonomists are essential contributors to biodiversity studies, but they are often overwhelmed with backlogs of materials to examine, and have limited time and, unfortunately, limited funds. Only a few large university museums remain viable in the US and elsewhere. Some government and privately funded museums like the Smithsonian Institution and the California Academy of Science in San Francisco remain viable, but they too are struggling with limited funds.

The development of DNA markers for identifying and cataloging species has become a convenient tool for rapidly cataloging Earth’s biological diversity. How can we know what to preserve and protect if we don’t have adequate documentation for most of Earth’s diversity, especially from the oceans? MBARI has played a significant role in advancing the technology and efforts to catalog marine biodiversity in the eastern Pacific region.

—Bob Vrijenhoek

MBARI's mapping AUV, the


Gulf of California 2012 Expedition