Digestion of algae by red urchins leads to increased green shore crab consumption rate

Abstract

Spatial subsidies play a significant role in nearshore ecosystems. In the form of drift algae, these subsidies are not only important to larger herbivores but also smaller invertebrates as a food source. The goal of this study is to test red sea urchin (Strongylocentrotus franciscanus) feces as acceptable food items and see if there is a preference of algal type. Feeding the green shore crab (Hemigrapsus oregonensis) fecal pellets from red sea urchins that have consumed Nereocystis luetkeana, Mazzaella splendens, and Ulva spp, there was no preference of species in fecal matter. Using a control of feeding the green shore crabs blades of the algae types, there was a preference of Nereocystis, but more importantly a preference of fecal pellets over undigested algae was seen.