Starvation intensifies the impacts of interspecific interactions on foraging behavior of swimming crab (Portunus trituberculatus)

Although local species usually suffer from starvation during the early stage of marine ranching construction, few studies focus on the effects of starvation on predation and competition among benthic economic species. A multitrophic species foraging system was established in the laboratory to investigate how starvation and a rapa whelk (Rapana venosa) affect the behavior of swimming crab (Portunus trituberculatus) preying on Manila clams (Ruditapes philippinarum). We calculated the predation rate and quantified the foraging behavior and encounter behavior between predators. Under no starvation (0 d) and short-term starvation (3 d), the interactions between crab and whelk, including intraguild predation and kleptoparasitism, were relatively weak, which did not have the significant impacts on crab. However, the interspecific interactions were intensified by the long-term starvation (6-12 d). Specifically, the probability of intraguild predation was increased, but crab did not obtain revenue from preying on whelk. These made crab reduces the investments for foraging on clams, such as the decreasing of handling time and probability of capture upon encounter. Additionally, the active foraging of whelk stimulated the occurrence of kleptoparasitism under long-term starvation, promoting the foraging of crab partly, included the increasing of encounter rate with clam and probability of consumption upon capture. In long-term starvation treatments, the positive effects provided by whelk perhaps were swamped by the negative effects of intraguild predation, which impeded the foraging behaviors of crab, resulting in the decline of predation rate of crab eventually.