Distributional Ecology of Selected Megaepifauna on Abyssal Plains Adjacent to Gorda Ridge, Northeast Pacific Ocean
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Patterns of distribution and abundance of benthic megaepifauna demonstrate mesoscale zoogeographic trends across the nearshore Cascadia Abyssal Plain and offshore Tufts Abyssal Plain. Species composition analysis of Holothuroidea and Ophiuroidea (Echinodermata) and Galatheidae (Crustacea: Decapoda) separates the fauna into sediment fan, slope-base, Cascadia Plain, Tufts Plain, Gorda Ridge, and northern California abyssal elements. Faunal distribution and abundance are correlated with distance from the continent and depth of the water column. Gradients in rates of sedimentation and food flux to the seafloor are probable causes. Unlike macrofaunal distribution and abundance patterns, the species composition, abundance, and diversity of megafauna (e.g., Holothuroidea) appear to be more controlled by depth than by distance from the continent.
Megafaunal species that live on the surrounding plains have been identified from Gorda Ridge axial valley, particularly the sediment-filled Escanaba Trough at the southern end of the ridge system. Deposit-feeding holothuroids and ophiuroids, and omnivorous galatheid crabs have been collected and observed from sedimented areas along the length of the axial valley; three species have been positively identified. Further sampling in the valley should demonstrate that many of the abundant deposit feeding species associated with abyssal plains also live in association with sediment cover in Gorda Ridge axial valley. Data suggest that the valley deposit-feeding mega-epifauna is derived from the surrounding abyssal plains from a broad range of depths.
KeywordsAbyssal Plain Otter Trawl Beam Trawl Columbia River Estuary Slope Base
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