Assimilation efficiency of Idotea wosnesenskii on different algal diets

Abstract

Drift algae are an important resource in marine food webs and undergo a vital change in chemical composition during the degrading (or aging) process. I investigated the effects of aging algae and different species of algae on the Assimilation Efficiency (AE) of Idotea wosnesenskii, a grazing isopod found on San Juan Island. One week feeding (3 days) and starving (4 days) treatments were run with daily fecal matter collection. Weights of algae fed to isopods over 3 days and fecal matter subsequently produced were used to determine AE. The data show that in an alga with high levels of secondary metabolites, AE increased with algal age. This was not the case with another alga with few defensive chemicals, suggesting that aging causes a change in chemical composition, which increases AEs. Food preference was correlated with AE, as the preferred fresh algal species also had a higher AE. This study provides further support for why drift algae is important in food webs.