Trophic ecology of an abundant kelp forest echinoderm, the bat star Patiria miniata

Abstract

Echinoderms often play key roles in structuring marine ecosystems. The bat star Patiria miniata is an abundant echinoderm in the kelp forests of the northeastern Pacific coast whose trophic ecology has been understudied. Understanding the trophic role of P. miniata is important given the recent declines of many sea star populations due to wasting disease. Patiria miniata was largely unaffected by these outbreaks and could potentially fill the trophic niches left by other ecologically important sea star species. In this study, we used a combination of feeding experiments and stable isotope analysis to provide new insights into the trophic ecology of P. miniata. Given that P. miniata is considered an omnivorous generalist, we conducted a series of feeding experiments in which we quantified consumption rates for a wide range of reported prey items. Consumption rates were highest for different types of carrion, lower for sessile invertebrates, and negligible for all species of macrophytes. In a series of follow-up experiments, we found that food deprivation did not lead to demonstrable consumption of macrophytes by P. miniata, but that the presence of epiphytes significantly increased consumption rates (presumably of the epiphytes plus incidental consumption of macrophytes). Finally, we compared the isotopic niche of P. miniata with that of a carnivore (the giant sea star Pisaster giganteus), an herbivore (the purple sea urchin Strongylocentrotus purpuratus), and a detritivore (the warty sea cucumber Parastichopus parvimensis) and found that P. miniata occupied the highest relative trophic level and was isotopically most similar to P. giganteus. Altogether, our results suggest that the diet of P. miniata is narrower and more carnivorous than previously expected.