Master's Thesis (Open Access)
Master of Science (M.S.)
Science & Environmental Policy
Comprehensive high-resolution seafloor mapping of California's state waters have revealed rippled scour depressions (RSD) to be one of the most abundant and widespread habitats of the inner continental shelf. These sharply delineated elongate features range in size from 1 OO's to 1000's of m2 in aerial extent and are characterized by 30 to 50 cm deep depressions of coarser sediments and longer period bedforms than found on the surrounding seabed. Although RSDs have been identified on many of the world's continental margins, previous stUdies focused on their geomorphology and dynamics, leaving the ecological influence and associated biological communities of RSDs unexplored. Here we test the hypothesis that there are ecologically important differences in the density and richness of benthic fish and invertebrate groups inside and outside RSDs. A small remotely operated vehicle (ROV) was used to survey twenty RSDs in three depth zones (shallow [<15 m], intermediate [15 to 30 m], deep [>30 m]) within Monterey Bay, California. Sediment grab samples taken inside and outside of RSDs confirmed the mean grain size was significantly larger inside RSDs (0.5 to 0.9 mm) than outside (0.15 to 0.4 mm). As predicted from known species/grain size relationships, mean density of combined trophic groups was lower inside RSDs in the shallow, intermediate, and deep zones 2 (0.03,0.16,0.21 ind m-2 respectively) than outside (0.04, 0.31,0.45 ind mrespectively). Richness of trophic groups was also lower inside RSDs in each depth zone (0.03, 0.10, 0.14 taxa m-2 respectively) than outside RSDs (0.03, 0.17,0.25 taxa m-2 respectively). Surprisingly, RSDs did contain significantly more young of the year (YOY) rockfish (especially ESA threatened canary rockfish, Sebastes pinniger) and small flatfish than adjacent fine sediments, suggesting a possible nursery function for these otherwise depauperate coarsegrained habitats. This study illustrates the utility of high-resolution habitat mapping data in refining our understanding of seafloor landscape heterogeneity and species habitat relationships specifically in the context of adaptive management in marine spatial planning.
Hallenbeck, Todd Russell, "Rippled Scour Depressions Add Ecologically Significant Heterogeneity to Soft Sediment Habitats on the Continental Shelf" (2011). SNS Master's Theses. 29.