Species Specific Stable Isotope Fractionation Baseline between Oysters and Algae

Project Description

Stable isotopes are commonly used understand predator-prey interactions and food web dynamics. Stable isotope ¹⁵N is enriched with increasing trophic levels while stable isotope ¹³C remains relatively consistent across trophic levels. When these two isotopes are considered together, they can indicate predator-prey interactions in a food web. The common assumption for all species across trophic levels is that fractionation values for stable isotope ¹⁵N are about 3.4 permil and about 0.8 permil for stable isotope ¹³C. Although a helpful rule-of-thumb for fish interactions, there is skepticism in the literature as to whether it holds true for lower trophic level interactions, such as phytoplankton and bivalves. This assumption was tested to see if it is accurate or if a species-specific fractionation value should be established for different organisms in food webs. The goal was to see the trophic-step fractionation values between commercially important bivalve species and a known food source, phytoplankton, and to gain a better understanding of how these species relate to each other and their trophic levels. This research was directly applicable to shellfish aquaculture in understanding how filter feeding shellfish incorporate nutrition for growth and to help quantify carrying capacity for site selection.

Results and Accomplishments

To establish a baseline, phytoplankton samples from three locations as well as mussel tissue were analyzed for stable isotopes. For the mussel tissue, all of the samples had approximately the same ¹³C and ¹⁵N values. The phytoplankton samples from the oyster and mussel bins had approximately the same ¹³C and ¹⁵N values. Researchers observed that trophic fractionation between algae and shellfish is similar to reported literature values, although it takes 15-30 days for the bivalves to incorporate the algae stable isotope signal into their tissues.

Summary of Data Being Collected

Data	Type	Quantity	Location
Enrichment of nitrogen between primary producers and consumers	Stable isotope d13C and d15N on phytoplantkon and oysters and mussels	Lab experiments over 90-day period; 200+ samples	UNE Marine Science Center