Diet and distribution of green sea urchins (Strongylocentrotus droebachiensis) on the northeast Newfoundland coast: the influence of spawning capelin (Mallotus villosus)

Abstract

Spawning capelin (Mallotus villosus) provide a pulse resource of fish eggs and dead fish on the northeast Newfoundland coast, bringing an abundance of nutrients into the system that can be relied upon by numerous predatory and scavenging species. I investigated how this annual resource pulse influenced the diet and distribution of green sea urchins (Strongylocentrotus droebachiensis) at capelin spawning sites and the potential for urchins to impact capelin recruitment through egg predation. Urchin density was monitored using a remotely operated vehicle (ROV) during the summers of 2013 and 2014, and urchins were collected from capelin spawning sites in 2014 to assess diet using nitrogen and carbon stable isotopes. Urchins were distributed in higher densities in areas with dead capelin and were often clumped directly on dead fish. Conversely, the presence of capelin eggs negatively influenced urchin density. Stable isotope analysis revealed an increase in 15N when capelin resources became available, suggesting urchins were consuming capelin resources. Diet preference experiments also indicated that dead capelin were preferentially consumed over eggs. Overall, urchins appear to prefer and seek out dead capelin on spawning sites suggesting urchins may be important recyclers of capelin detritus and have little impact on capelin recruitment.