Efficiency of Strongylocentrotus franciscanus in extracting calories from algal foods: implications for benthic communities.

Abstract

Algal subsidies are extremely important to the success of the deep benthos where there is little to no primary productivity. Little research has been done on the nutritional value of detritus, such as pieces of kelp, sinking into deep habitats. Sea urchin feces, in the form of detritus, may provide an energetic link to benthic communities with no primary productivity. Urchins are known to have an inefficient digestive system which leaves the potential for high food value in feces. I conducted a series of tests on the relative caloric contents of algae and urchin feces. First, I measured the biomass consumed and egested by urchins. Secondly, I quantified the caloric content of aged and fresh feces of 10 urchins fed diets of either Nereocystis luetkeana or Saccharina latissima. For both kelp diets, the caloric content of algal material increased after being consumed by urchins, and the longer the urchin feces aged, the higher the caloric value became. This could be significant in considering the importance of urchins as a link to benthic communities that rely heavily on detritus for their success.