EVALUATING THE POTENTIAL OF DETRITUS AS A SUPPLEMENTAL DIET FOR BIVALVE AQUACULTURE USING STABLE ISOTOPES AND FATTY ACID BIOMARKERS  

There has been increasing evidence that bivalves are not solely herbivorous and are indeed omnivores. One of the many alternative food resources available to bivalves besides phytoplankton is detritus. Detritus has been found to be important for cultured bivalves which have been shown to be able to incorporate detrital material into their diets. For example, Mytilus edulis cultured off the shores of Ireland have been found to utilize a mix of phytoplankton and detritus in their diet.

As a commercially important aquaculture species Mytilus edulis is generally reared in areas selected for high phytoplankton abundance with little consideration of other potential food sources such as detritus. With increasing evidence that bivalves do utilize detritus understanding which detrital source is utilized and to what degree by bivalves becomes an important question for aquaculture.

This study will characterize the biochemical composition of detritus along the coast of Maine using stable isotope, lipid and fatty acid analysis. Samples were collected from six locations throughout Saco Bay, ME, from April until Nov. 2016. Stable isotopes and fatty acid biomarkers will be used to trace detrital material back to its source while nutritional quality will be determined by the percent organic content and C:N of detritus as well as its lipid and fatty acid composition. Comparison of the stable isotope and fatty acid signature of bivalves in the field with that of local detritus will inform if ingestion of the material occurs and what proportion of the diet it comprises. Areas suspected to be dominated by a single type of detritus, i.e. salt marsh, macroalgae or phytoplankton, will be selected in order to ascertain if there is any effect of detrital source on nutritional quality and contribution to bivalve diets. Nutritional quality, likelihood of ingestion, presence in the environment as well as bioavailability will be used to evaluate detrital types for their potential to be used as bivalve diets for aquaculture.

The goal of evaluating the potential of detritus to be used as a supplemental diet for bivalve aquaculture is to create another criterion that could be used for site selection. Better site selection criteria will allow more informed aquaculture placement as well as help avoid use conflicts by allowing aquaculture to move out of crowded estuarine systems. By using stable isotopes and fatty acid biomarkers to evaluate detritus as a supplemental diet for bivalve aquaculture we will also be informing the role detritus plays within coastal foodwebs.

It is anticipated that preliminary results from the stable isotope analysis from the collected bivalves will be available for presentation.