Infaunal Macroinvertebrate Diversity of East and West Sound Orcas Island: use of Multibeam and In-Situ sampling to characterize soft-sediment communities

Abstract

Marine soft-sediments comprise the largest and oldest habitat types on earth (Gray 1974). Species and communities within these habitats vary spatially and temporally; controlled by sediment composition, disturbance, primary production, and biotic interactions (Lenihan and Micheli, 2001). These variations can occur over a matter of meters and result in highly patchy sea floors (Snelgrove and Butman, 1994). A relationship between grain-size and faunal diversity was first identified by Peterson (1913) and further investigated by Johnson (1957) becoming a widely accepted supposition until the 90's (Snelgrove and Butman, 1994). Snelgrove and Butman’s (1994) review of animal-sediment relationships noted no consistent relationship in the literature between fauna and grain size and questioned if other mechanisms are driving the apparent relationship.

Gray (2002) maintains the animal-sediment relationship and argues that many results cannot be considered characteristic of soft-sediment communities as a whole because most studies are small in spatial and temporal scale and lack extensive sampling. Regional scale diversity controls local species richness and environmental factors in turn determine regional richness. Environmental factors are grain-size diversity, temperature, and productivity. Gray (2002) further postulates that reduced richness may be the result of geologic history such as the Pleistocene glaciation of high latitudes. Benthic animals may not have had the time needed to fully colonize or establish stable communities in environs bound up or scraped clean by ice. Both reviews agree that further sampling controlling for a number of biologically relevant physical factors, including sediment grain size, need to be performed over larger temporal and spatial scales (Snelgrove and Butman, 1994; Lenihan and Micheli, 2001; Gray 2002).