MEPS 549:125-135 (2016)  -  DOI: https://doi.org/10.3354/meps11699

ABSTRACT: Spawning capelin Mallotus villosus provide an abundance of nutrients in the form of fish eggs and dead fish that can be relied upon by numerous predatory and scavenging species. We investigated whether the annual resource pulse of spawning capelin influenced the distribution of green sea urchins Strongylocentrotus droebachiensis at capelin spawning sites on the northeast coast of Newfoundland, Canada. Sea urchin densities at capelin spawning sites were monitored using a remotely operated vehicle during the summers of 2013 and 2014 and were modeled against the presence or absence of substrate types (bedrock, cobble, and sediment waves) and food resources (capelin eggs, dead capelin, and drift algae). Mean (±SE) sea urchin densities associated with each predictor variable were highest on bedrock substrate (7.2 ± 0.6 urchins m^-2), dead capelin (3.7 ± 0.2 urchins m^-2), and drift algae (3.1 ± 0.2 urchins m^-2) and were <1.5 urchins m^-2 on all other predictors. In accordance, transect segments containing bedrock, dead capelin, and drift algae were 3-20, 6-20, and 2-7 times more likely to have sea urchins, respectively. Contrary to what was predicted, transect intervals containing capelin eggs were 5-10 times more likely to have no sea urchins and had the lowest mean sea urchin densities out of all predictors (0.91 ± 0.1 urchins m^-2). In addition, sea urchins were more likely to be clumped in areas with patchily distributed food, with urchin clumps being 15-18 times more likely in areas with dead capelin and 4-9 times more likely in areas with drift algae. Overall, results suggest that capelin spawning provides an important food source for sea urchins in an otherwise nutrient-poor environment, and, additionally, that sea urchins may be important recyclers of capelin detritus.

KEY WORDS: Sea urchin · Capelin · Remotely operated vehicle · ROV · Transect · Density