COS 309-1 - A novel copepod egg predator infesting commercially important rock crabs

Abstract: A novel copepod egg predator (Nicothoidae cf. Choniosphaera sp.) infestation has been discovered in the egg masses and gills of three commercially important crabs (Cancer anthonyi, C. antennarium, and C. productus). We document high copepod prevalence and host egg mortality in ovigerous crabs along the Santa Barbara coast. Nicothoid egg predator infestations have never been observed in crabs along the Pacific coast of the Americas, a notable extension of the geographical range of these copepods. Extensive work on cancrid crab brood mortality caused by nemertean egg predators in the 1990s found no evidence of nicothoids, indicating that this outbreak is a recent and possibly unique event. Female copepods appear highly modified, mimicking the coloration and globular shape of crab eggs. Unlike nemertean crab egg predators, these are partial egg feeders. The copepods feed by puncturing a small hole in the shell of the crab egg, stunting the development of the embryo and subsequently facilitating entry of microbial agents. We have been conducting studies into the impacts of these egg predators on their hosts and have documented entire host egg masses being overtaken by these egg predators and their progeny, with unknown impacts on total crab reproductive success. Rock crabs are common nearshore consumers and are prey to otters, octopi, and several species of rockfish and also commercially fished without consideration of the impacts of this novel egg predator. The geographical extent and host specificity of this new consumer warrants further investigation.