Temperature-dependent feeding behavior in the brown box crab

Growing fishing pressures and ocean warming are potential concerns for
populations of brown box crabs, Lopholithodes foraminatus, at the southern
end of their geographic distribution. In Southern California, brown box
crabs are thought to occupy a broad depth gradient (intertidal zone – 547
m), which exposes them to temperatures ranging from 8℃–24°C. This large
temperature span presents challenges for these ectothermic animals because
the rates of their physiological processes, and ultimately their dietary
needs, behavior, and health, vary with temperature. Here we examined how
temperature affects the feeding behavior of brown box crabs to better
understand their ecology in warmer regions of their distribution. Adult
crabs were exposed to one of three temperature treatments (8℃, 15°C, and
20℃, N=10) for 2 months. Weekly throughout the exposure period, crabs were
given two similar-sized prey items of different crushing strength (clam
and mussel). Claw pinch force, prey preference, time to consume prey, and
number of prey consumed were recorded prior to the start of the experiment
and weekly for the duration of the study, with the exception of pinch
force, which was recorded bi-weekly. We hypothesized that crabs will have
a stronger pinch force at warmer temperatures, prefer prey items that
require less breaking force at the coldest temperature, consume prey
faster at warmer temperatures, and consume more prey at warmer
temperatures. Our results confirm that pinch force is consistently greater
at 15°C compared to 8°C, however, crabs at 8°C consumed more clams (higher
strength) while those at 15°C consumed more mussels. Crabs at 8°C also
consumed prey items faster than crabs at 15°C but ate a similar number of
prey. 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.