UC San Diego

Growing fishing pressures and ocean warming are potential concerns for populations of brown box crabs, Lopholithodes foramanitus, at the southern end of their geographic distribution. Brown box crabs are though to occupy a broad depth gradient (intertidal zone - 547 m), exposing them to temperatures ranging from 8℃ - 24℃. Here we examined how temperature affects the feeding behavior of brown box crabs to better understand their thermal ecology. Adult crabs were exposed to one of three temperature treatments (8℃, 15 ℃, and 20℃, N=10) for 2 months. Crabs were given two similar-sized prey items of different crushing strength (clam and mussel) weekly. Prey preference, time to consume prey, and number of prey items consumed were recorded weekly, and pinch force was recorded bi-weekly. We hypothesized that crabs would have a stronger pinch force, consume prey faster, and consume more prey at warmer temperatures, while crabs would prefer prey items that require less breaking force at the coldest temperature. Our results confirm that pinch force is consistentlygreater at 15℃ compared to 8℃, however, crabs at 8℃ consumed more clams (higher strength). Crabs at 8℃ also consumed prey items faster than crabs at 15℃. Furthermore, there was 100% mortality at 20 ℃ within 8 days of exposure, indicating their proximity to lethal limits within Southern California. These results show that brown box crab feeding behavior exhibits temperature thresholds, which may alter their nutritional state, community interactions, and distribution under both short-term and long-term changes in ocean temperature.