Background

There has been much concern among scientists about the future of shellfish in a warmer, more acidic ocean. Many are worried that greater dissolved carbon dioxide levels due to anthropogenic climate change as well as higher temperatures will result in physiological stress and other negative consequences for marine organisms. While it is not the case for all shellfish, a positive story can be found in the case of the geoduck. This species' fitness has not been deterred with rising ocean temperatures and acidifying waters, but rather its population has been quite successful in the midst of climate change. This success story bodes well for the state of Washington because its economy is heavily reliant on the geoduck population. While geoducks do appear to be adapting to warmer and acidifying oceans, this species needs to be continually monitored in order to ensure this trend continues. But first lets dive deep and learn some background information about geoducks...


Ever wonder how this organism got such a... unique name? "Geoduck" actually comes from the Nisqually Indian name gweduc, which means "dig deep".

http://seattletimes.nwsource.com/html/localnews/2018041537_geoduck22m.html 

As the diagram above demonstrates, geoducks use their foot to dig themselves about three feet deep into the intertidal or subtidal substrate, where they anchor themselves. These organisms are filter feeders, which means they extend their siphon to pull in water, which they filter for food. Geoducks subsist primarily on phytoplankton, mostly diatoms and flagellates. These siphons can stretch up to a meter in length- that's the length of a baseball bat!


Geoducks can live for nearly 150 years and weigh up to a surprising 15 pounds (Smithsonian, 2009). These amazing statistics make them the largest burrowing clam in the world and one of the oldest animals in the world. Another interesting fact is that geoducks deposit annual growth rings in their shell each winter, earning them the nickname of the trees of the sea. These rings can provide climatologists with high quality records of sea surface temperatures. Rates of shell growth demonstrate a strong positive linear correlation with temperature. In other words, in warmer sea surface temperature geoducks demonstrate greater rates of shell accretion (Strom et. al, 2004). This ability to serve as a potential climate proxy was initially discovered by Noakes and Cambell (1992).

The map to the left illustrates the range of geoducks (the line along the Pacific coast delineates this). Geoduck's habitat range extends from southeast Alaska to California but the highest density of geoducks are found in Puget Sound bays and estuaries. These clams prefer to live between 10 and 80 meters below the average low tide mark (WA Department of Ecology).


Taxonomy
Phylum: Mollusca
Class: Bivalvia
Subclass: Heterodonta
Order: Myoida
Superfamily: Hiatelloidea
Family: Hiatellidae
Genus: Panopea
Species: generosa

(Figure: Strom et. al., 2004)

Clamoring for more information? Turn to the next page to learn how ocean acidification is affecting geoduck populations...