Effect of Depth on Sponge Assemblage Structure at Palmyra Atoll, Central Pacific

We examined the influence of depth on sponge assemblages across three lagoons at Palmyra; a remote atoll situated in the Central Pacific. The atoll is unusual in that it was heavily altered during WWII resulting in an atypical lagoon system. We conducted surveys at both 6-8m and 12-14m at 3 sites at the atoll and recorded sponge densities, area cover and available substrate for the 29 species found at these sites. Multivariate analysis of sponge densities and area cover revealed significant variability in sponge assemblages between both site and depth. Univariate analysis also showed significant differences in area cover between depths, but not between sites. Diversity indices and the average number of species at each site showed an increase in diversity across lagoons from West to East. This study indicates that despite the small size of the atoll, depth is a factor that shapes sponge assemblages at Palmyra Atoll. The heavy alterations to the lagoon, particularly the area near the channel entrance may be influencing the sponge assemblage structure, however, other environmental variables still need to be investigated.