Urchin Feces: a Possibly Vital Nutritional Link to Benthic Organisms

Abstract

Detritus is a vital source of nutrients for many benthic organisms, but its composition and dynamics in the ocean are relatively unstudied. Sea urchin feces may provide an important link from the relatively shallow benthic areas to other benthic communities, such as those in the deep-sea, as urchin “mobs” are capable of mowing down entire forests of algae and, of that algae, their digestive systems absorb on average only 60% of the calories available. Through these relatively unprocessed feces, a large amount of material could be available to benthic communities, making the feces a potentially vitally important nutrient conveyer to benthic organisms. To gain insight into the composition of urchin feces, and more insight into their digestive system, I conducted a series of tests on the caloric content of algae and urchin feces. First, I tested two species of algae at various stages of decay for caloric content. Then, I tested aged and fresh feces of 12 urchins on diets of either Nereocystis luetkeana (Nereocystis), or Agarum fimbriatum, for caloric content using a modified version of a micro assay technique. I found that aging dramatically increases the caloric values of both Nereocystis feces and tissue samples, however in agarum feces and tissue samples aging has little effect. This could have significant implications in considering where benthic organisms acquire their nutrients, as well as the importance of sea urchins in providing a link to those organisms.