NOAA 03-125
Contact: Ben Sherman
NOAA News Releases 2003
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Researchers from the National Oceanic and Atmospheric Administration’s (NOAA) National Centers for Coastal Ocean Science’s Center for Coastal Fisheries and Habitat Research have found that littleneck clams, an important commercial and recreational fishery in Alaska, rely heavily on microscopic algae growing on tidal flats for growth rather than phytoplankton in the water column. NOAA is part of the U.S. Department of Commerce.

This finding could potentially affect shellfish aquaculture operations. It also could help scientists predict the consequences of oil spills and climate change on food webs in Alaskan coastal ecosystems. Littleneck clams and other intertidal bivalves are important prey species for many Alaskan animals, including salmon, juvenile cod, sea otters and shorebirds.

The NOAA research team examined the extensive intertidal flats of Kachemak Bay in Alaska looking for the extent of benthic microalgae, a group of microscopic plants that are an important food source in many estuarine ecosystems. They measured the biomass of the algae in sediments around the bay and found it equaled or exceeded any amount previously reported for similar environments. They also collected animal samples from the same environment.

After analyzing both the plant and animals’ chemical “signatures,” the researchers found that the signature of the clams, and several other filter-feeding bivalves, most closely resembled that of the benthic, or sediment-dwelling level, microalgae as opposed to phytoplankton found in upper levels of the water column. The finding indicated that bottom-dwelling microalgae were significant food sources for the clams, more so than previously believed.

This conclusion is based on the results of stable carbon and nitrogen isotope analysis, and is further supported by the measurements of abundant benthic microalgal biomass found in the tidal flats and sand bars in Kachemak Bay, where the NOAA Kasitsna Bay Laboratory is located.

Algae are resuspended in bottom-level waters by wave action, making this nutrient-rich food source available to bivalves and similar bay organisms located near the gravel or rocky beaches and shoreline areas.

“The results from these studies reveal a significant role for benthic microalgae in the food webs we sampled,” stated Carolyn Currin, head of the NOAA research team. “The Pacific littleneck clam, is an abundant member of tidal communities in the Pacific Northwest, and in addition to being harvested by humans, it is particularly used by sea otters and diving ducks as a food source.”

Currin continued the study explanation by noting, “Another smaller clam (Macoma baltica), which is important prey for juvenile salmon, was also found to rely almost entirely on benthic microalgae production. As these organisms are important links in the food chain of the bay, the availability of microscopic algae living in the sediment may be more significant than phytoplankton production (higher up) in the water column in supporting the total carrying capacity of these estuarine ecosystems.”

Currin presented these results recently at an International Colloquium hosted by the Royal Netherlands Academy of Science.

NOAA is dedicated to enhancing economic security and national safety through the prediction and research of weather and climate-related events and providing environmental stewardship of the nation’s coastal and marine resources.

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