A Comparison of Species Composition and Diversity Between Urchin Rocks and Northwest Island, WA

A class Project by the Summer 2002 Walla Walla College Marine Station Marine Invertebrates Class:

Anna Dyer, Brandon White, Brian Catelli, Christina Smith, Heidee Leno, Janisse Maxwell, Kelly Williams,

Melissa McFadden, Nathaniel Charbonneau, Robbie Wheeling, and Ryan Lunsford.

Coordinated and Final Writeup by David L. Cowles, Ph.D., Walla Walla College Associate Professor of Biology


1 m2 quadrats were examined along transects which spanned the intertidal zone at Urchin Rocks, a site which is frequently visited by people, and at Northwest Island, a nearby site with similar characteristics but which is seldom visited. Both sites were composed of gradually sloping gray bedrock with a northerly exposure. Overall animal species richness and diversity did not differ significantly between the sites. Many species, however, most notably the macroalgae, large barnacles, and motile and colorful species such as large seastars and urchins, Calliostoma and Ceratostoma snails, and Tonicella lineata chitons were scarce or absent in the lower intertidal of Urchin Rocks. The expected increase in algal and animal diversity in the lower intertidal was muted or absent there as well but was clearly seen at Northwest Island. On the other hand, cryptic species such as Leptasterias and some snails seem to be doing well at Urchin Rocks. Another group which is doing well includes species such as barnacles and some chitons which are armored and can cling tightly to the rocks, though the lack of large barnacles suggests that they may be impacted at later life stages. The lower intertidal of Urchin Rocks had a striking deficit of macroalgae combined with an extensive diatom mat in the same areas. These trends could be due to local competition but may well be due to species displacement due to repeated trampling in the lower intertidal zone.