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Aquatic Biology

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AB 23:71-86 (2014)  -  DOI:

Detrital kelp subsidy supports high reproductive condition of deep-living sea urchins in a sedimentary basin

K. Filbee-Dexter*, R. E. Scheibling

Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
*Corresponding author:

ABSTRACT: Highly productive kelp beds off Nova Scotia, Canada export detrital material to adjacent sedimentary habitats in deeper waters. We evaluated the importance of this subsidy to sea urchins Strongylocentrotus droebachiensis in less productive habitats. Gonad index and gut content of urchins on sediments at 60 m depth were measured monthly from September 2010 to May 2013 in a large semi-protected bay, and compared to concurrent measurements of sea urchins at 8 m depth off a nearby headland. Detrital algal cover in the bay was measured using a towed camera system. Seasonal patterns in algal deposition and gut contents of deep-living urchins indicated that detritus was the predominant food source from March to October. We observed lower gonad indices in deep-living sea urchins compared to those at 8 m, but deep-living urchins spawned outside of the main spring season, suggesting periodic detrital subsidy enhances their reproductive condition. Food availability and temperature appear to control the timing of gametogenesis, and phytodetritus may cue gamete release in these deep habitats. To evaluate the response of deep-living urchins to detrital subsidy, and turnover time of this material, we deployed lines baited with kelp thalli at 45 and 60 m depth and measured rates of encounter and consumption of kelp detritus by sea urchins, using the towed camera. Sea urchins aggregated on kelp within hours of deployment, and consumed it after 3 to 5 mo. Our findings suggest kelp detritus represents an important energy source that can support a high reproductive capacity in deep-living urchins.

KEY WORDS: Kelp · Strongylocentrotus droebachiensis · Reproduction · Spawning · Kelp detritus · Sea urchin · Resource subsidy

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Cite this article as: Filbee-Dexter K, Scheibling RE (2014) Detrital kelp subsidy supports high reproductive condition of deep-living sea urchins in a sedimentary basin. Aquat Biol 23:71-86.

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