Abstract
Brittlestars Amphiodia (Amphispina) spp., particularly Amphiodia <br /><br />(Amphispina) urtica (Lyman 1860), are of interest in southern California because <br /><br />they are rare or absent adjacent to municipal wastewater outfalls even where they <br /><br />are expected to be the community dominant. In the monitoring programs for the <br /><br />outfalls, impacts to benthic communities are determined by comparing abun- <br /><br />dances near the outfall to the abundance in "reference" areas. In order help define <br /><br />reference conditions, data from a survey conducted between 1956 and 1959 were <br /><br />used to determine the effect of latitude, depth and sediment grain size on the <br /><br />distribution and abundance of Amphiodia {Amphispina) spp. <br /><br /><br /><br />Brittlestars Amphiodia {Amphispina) spp. were most abundant in water depths <br /><br />of 48 to 102 m in sediments with median grain size between 0.035 and 0.093 <br /><br />mm, a diameter classified as coarse silt to very fine sand. Amphiodia {Amphispina) <br /><br />spp. were rarely collected in less than 15 or more than 85 m of water. <br /><br /><br /><br />The abundance of Amphiodia {Amphispina) spp. was generally lower north of <br /><br />Ventura than elsewhere in the Bight. The difference in abundance can, in part, <br /><br />be attributed to the character of the sediment. However, even in areas with suitable <br /><br />sediment, the abundance of Amphiodia {Amphispina) spp. north of Ventura was <br /><br />relatively low. The reason for this difference is unknown. It is also not known if <br /><br />Amphiodia {Amphispina) spp. are, at the present time, less abundant north of <br /><br />Ventura than elsewhere in the Bight.
