(full paper is archived in the Miller Library)
Title: Changes in diet composition of Pisaster giganteus in response to changes in prey availability
Student Author(s): Lu, Jimmy
Faculty Advisor(s): Watanabe, James
Location: Final Papers Biology 175H
Date: June 1996
Abstract: This study examined the diet of the generalized predatory sea star Pisaster giganteus, comparing proportions of various species in the diet to abundance in the habitat. Comparisons to assess temporal variation were made to similar data collected in the same site in 1981 (Harrold 1981). Relative frequences of prey species in the diet and in the habitat were tabulated. The past and present diets of sea stars overlap considerably, with a Morista overlap index of 0.667 and nearly identical Shannon-weiner diversity indices (2.035 in 1981 compared to 2.029 now). However, a Chi-square analysis reveals several major differences: (1) the absence of the vermetid gastropod Petaloconchus montereyensis, and (2) an increase in the frequency of two other sessile prey species, the barnacle Balanus spp. and another vermetid, Serpulorbis squamigerus. The absence of Petaloconchus in the diet was due to its low abundance in the habitat. The increased feeding on Balanus and Serpulorbis cannot be explained by changes in abundance, which were not statistically significant. Rather, I hypothesize that the absence of Petaloconchus, previously a reliable, easily obtainable source of energy, led to increased feeding on these other sessile prey species. Further study is needed to explore the impact of other factors, such as individual sea star variation.