Prey profitability and consumption tactics of the red rock crab, <i>Cancer productus</i> Randall, 1840 (Decapoda: Brachyura: Cancridae) based on laboratory studies

Abstract The red rock crab Cancer productus Randall, 1840 (Decapoda: Brachyura: Cancridae) is a common durophagous predator along the Pacific coast of North America that can influence the structure of rocky intertidal ecosystems. Many predation experiments have documented the ability of these crabs to prey successfully upon multiple species and a range of prey sizes. Even though the crabs are capable of preying upon many species and size classes, not all are likely to be profitable when considering energy gained versus time spent attacking. We reanalyzed prey profitability and hunting strategies of red rock crabs on ten unique prey taxa from six previously reported laboratory predation experiments. We found that grappling time was significantly affected by the identity of the prey taxon. An analysis of benefit-cost ratios (internal volume multiplied by success probability, all divided by average grappling time) identified the Pacific blue mussel Mytilus trossulus A. Gould, 1850 as the most profitable prey item, whereas the other prey species had similar benefit-cost ratios. Predator attack behavior, which influences grappling time, depends on both predator and prey size. Outright crushing attacks are typically employed as the primary attack strategy, while secondary strategies, such as perimeter and peeling tactics, are generally used after crushing attacks fail. Outright crushing attacks are typically faster than secondary strategies; thus, a prey item successfully subdued using a crushing attack may result in a more profitable outcome for the red rock crab. Understanding prey profitability in controlled, laboratory settings can provide a working hypothesis for future studies investigating prey selection in natural settings.