Spatial and Temporal Distribution of Echinoderms in Rocky Nearshore Areas of Alaska

Abstract

Among near shore invertebrates, echinoderms play an important role in the structure (specifically in food web structure) and function of rocky intertidal and shallow subtidal communities because of their high densities, biomass, and versatile ecological functions. Alaska has a variety of near shore echinoderm species, but little is known about their spatial and temporal distribution. Rocky habitats were surveyed following Natural Geography in Shore Areas (NaGISA) protocols in three areas of the Gulf of Alaska (Prince William Sound, Kachemak Bay, and Kodiak Island) in 2003 and 2004. Within each area, two to three sites were destructively sampled. The abundance of echinoderms within five 25×25cm quadrats was recorded in the high, mid, and low intertidal heights and 1m, 5m, and 10m depths. We attempted to detect interannual variability in the distribution of echinoderms and to evaluate whether distribution was different along horizontal scales between regions 100’s of kilometers apart and, within each region, between sites 10’s of kilometers apart. We also looked at tidal height as a factor of variation and tried to determine if any vertical patterns were consistently observed over time and over regional and local areas. The diversity and abundance of echinoderms were greatly variable between our two sampling events and over all spatial scales. No clear patterns were identified over time and over (regional and local) horizontal gradients. However, different echinoderm groups showed distinctive distribution patterns over the vertical immersion gradient, with asteroids and holothuroids being more abundant in the intertidal and shallow subtidal zone and ophiuroids being more abundant at deeper depths.