Distribution, habitat and food preferences of sympatric high intertidal isopod species Ligia occidentalis and Ligia pallasii (Ligiidae: Oniscidea)

Abstract

The distribution, habitat and food preferences of two partially sympatric high intertidal isopods, Ligia pallasii and Ligia occidentalis, were investigated. A survey along the Eastern Pacific coast indicated species-specific site preferences as evidenced by a mosaic pattern of distribution with few sites of co-occurrence. Ligia pallasii preferred sites with rocky cliffs and caves that may provide a thermal refuge for the northern species, whereas L. occidentalis apparently is a habitat generalist of rocky shores. Differences in reproductive patterns exist: L. occidentalis reproduced once annually in spring and summer, but gravid females of L. pallasii were observed throughout the year. Feeding experiments did not indicate any significant differences in diets; both isopod species fed mainly on seaweed and diatoms but preferred rare protein sources when available.

Keywords:

• Isopod
• Ligia
• sympatry
• microhabitat
• diet

Acknowledgements

T. Grosholz and D.R. Strong provided helpful suggestions for improvement of this manuscript. Thanks to A. Newsom for help with isopod collection and maintenance of mesocosms. The Bodega Marine Laboratory provided wet lab. space and outdoor tank facilities. Thanks to J. Sones for help with site selection at the Bodega Marine Reserve and for supplying Ligia photos used in Figure 1. Funding for this research was provided through UC Davis internal grants, Explorer's Club Diversa Research Fund and through NSF DGE grant 0841297 to S.L. Williams. This is a contribution of the Bodega Marine Laboratory, University of California Davis.