MEPS 186:137-148 (1999)  -  doi:10.3354/meps186137

ABSTRACT: Submarine canyons can provide large quantities of food in aggregated form on the deep-sea floor by acting as conduits for marine macrophyte production produced in the intertidal and shallow subtidal zone. Longshore transport delivers substantial quantities of macrophyte detritus from surfgrass Phyllospadix torreyi, kelps Macrocystis pyrifera and Egregia menziesii, and other macroalgae to the heads of Scripps and La Jolla Submarine Canyons. Strong tidal and gravity currents distribute this material throughout much of the canyon system, where it is utilized as food and habitat by benthic fauna. Video data taken from remotely operated vehicles and submarines were used to evaluate differences in detrital cover and megafaunal abundance in the canyons, and at nearby reference stations. Within the canyons dense mats of detritus were common down to 550 m, and M. pyrifera holdfasts were observed at 700 and 900 m. Virtually no drift material was observed out of the canyons. Comparisons of megafaunal invertebrates in and out of the canyons revealed generally higher densities at non-canyon sites due to large numbers of urchins. Species richness of all megafauna and abundance of non-urchin megafauna were greater in the canyons than out. It is likely that urchin abundance in canyons is reduced through disturbance by currents and detrital flows in the canyons. Species richness and abundance of fishes were greater in the canyons at all depths for which comparative data were available (100 to 500 m). From 150 to 200 m in Scripps Canyon, juvenile Pacific hake Merluccius productus were so abundant at times that their bodies obscured visibility. Turbot Pleuronichthys sp. and zoarcids Lycodes pacifica were also abundant in Scripps Canyon from 100 to 300 m. Data from this study support the hypotheses that macrophyte detritus covers large areas of the La Jolla and Scripps Canyon axis, and that megafaunal abundance is associated with detritus at both large and small spatial scales.

KEY WORDS: Submarine canyon · Detritus · Megafauna · Organic enrichment · Community · Physical disturbance · Surfgrass · Kelp