Omnivory in the diet of juvenile dungeness crab, Cancer magister Dana

Juvenile Dungeness crab ( Cancer magister Dana) have always been considered strict carnivores; however, early instars have been observed ingesting filamentous, epiphytic diatoms in the field. To investigate the potential importance of diatoms in the diet of this species, wild-caught megalopae were raised to the third juvenile instar on a variety of dietary treatments. Although the animals that were fed only filamentous diatoms ( Melosira sp. and Grammatophora sp.) had intermolt periods 20–25% longer than those raised on mussel ( Mytilus sp.) flesh or a mix of diatoms and mussels, there was no difference in molt size increment between the treatments. This ability to utilize such alternative food resources at a lower trophic level may be especially important in years of high settlement into coastal estuaries, when large numbers of juvenile crab are known to cause dramatic reductions in prey densities.