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Neus CampanyĆ -Llovet, Memorial University, Newfoundland, Canada
Paul V.R. Snelgrove, Memorial University, Newfoundland, Canada
Food quantity and quality available for benthic communities within Pacific and Atlantic submarine canyons

Benthic communities respond to food availability, among other environmental variables. Higher food quantities usually support higher benthic biomasses and/or abundances. Although usually neglected, food quality can also play a role in structuring benthic communities based on nutritional value and food preferences of different species. Submarine canyons provide traps and conduits of organic matter from shallow to deeper waters depending on topography and circulation patterns. In this study we compare the quantity and quality of food within submarine canyons from the Gulf of Maine in the Atlantic (North East Channel, Corsair and Heezen Canyons) and Pacific (Barkley Canyon) at different depths. Total sedimentary organic carbon and nitrogen were low at the head of the canyons and increased with depth. These results correlate with sediment grain size, which was coarser at the head of the canyon, suggesting strong currents transporting organic matter and sediments down the canyon to ~1000 m where major deposition occurs. The increased total lipids and chlorophyll/phaeoforbides ratio, a metric of food quality, at about 400-600 m, suggests higher nutritional value at that depth.  Complex circulation in submarine canyons likely contributes to this result.  Similarly, phospholipids (indicative of live or recently deceased organisms) in bottom water particulate organic matter increased at about 400 m. Despite generally lower food quantities in Barkley Canyon than in the Atlantic canyons, low amounts of high-quality food characterize all canyon heads of this study and contrast more abundant but lower quality food below 1000 m depth. Other characteristics of organic matter differ in each of the canyons. For example, high levels of wax esters occurred in bottom water samples from 800 and 1500 m, coinciding with zooplankton migration depths in Barkley Canyon. Abundant hydrocarbons in Barkley canyon at 900 m coincided with methane hydrates in sediments; we also observed abundant hydrocarbons at Heezen Canyon, although we did not observe hydrates or seeps. Therefore, the physical, geological, and biological characteristics of submarine canyons complicate any simple linear decrease in degradation of organic matter with depth contrary to expectation. These results suggest food availability (amounts and quality) change along submarine canyons with depth in unusual ways, and such changes should be considered when trying to understand patterns in benthic communities and food webs.

Theme 3: Biological patterns in submarine canyons: role of scale and heterogeneity
Oral Presentation
food availability, food quality, benthic communities, food web