Crabs and sea stars are known to preferentially select mussels with morphological traits that diminish the predators' searching or handling times. I compared two distinct morphotype of mussels (Mytilus trossulus; Gould, 1850) from Howe Sound, British Columbia, Canada, by dissection and measurement. Then, I experimentally offered mussels of the two morphotypes on the same patch to crabs (Cancer productus; Randall, 1839) and sea stars (Pisaster ochraceus; Brandt, 1835) to quantify the extent to which these predators select prey based on morphological features. Sea stars preferentially consumed mussels with gaps in shell closures, although these mussels also had larger adductor muscles compared with mussels rejected. Gaps at the shell margin presumably allowed sea stars easier access between shell valves to insert their stomachs and begin digestion. Small crabs preferentially consumed mussels with thin shells, which are easier to crush, whereas, large crabs consumed more thick-shelled mussels, possibly because these mussels were larger and offered greater energetic return. However, overall, crabs and sea stars did not exhibit strong preferences for smaller or larger mussel prey. These findings indicate that morphological features of mussels are important in prey selection by crab and sea star predators. Predator selectivity could cause a trade-off in defense strategies in mussels, and ultimately mediate indirect effects between these predators in the rocky intertidal community.
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Vol. 28 • No. 2