Idotea wosnesenskii distribution and spatial preference in the intertidal areas of the south and east side of San Juan Island

Abstract

Idotea wosnesenskii is one of the common isopod species observed on the rocky shores of San Juan Island. This highly mobile isopod is known to have a wide geographical distribution from intertidal to subtidal areas. It feeds on macroalgae along the shoreline as an herbivore and tends to live on algae like Fucus spp. and under rocks for shelter. While its range of occupation along the intertidal zone is vast, its specific spatial preference remains unclear. We did quadrat sampling of I. wosnesenskii at different intertidal heights, recorded the types of the substrate it occupies, and measured the width of the rock we found I. wosnesenskii under. We hypothesized that I. wosnesenskii would be abundant at high tide areas with large boulders, under a rock with bigger width, and absent of shore crabs. Our findings show that I. wosnesenskii prefers seaweed compared to rocky habitats and tends to be in aggregate under bigger rock width. However, the results of this study do not suggest that intertidal heights and the presence of shore crabs affect I. wosnesenskii distribution.