Meeting Abstract
Nearshore kelp forests and seagrass meadows create complex 3-D habitats that house high species diversity within the Salish Sea. Bull kelp (Nereocystis luetkeana) is one of the main annual canopy-forming kelp in these coastal waters. Eelgrass (Zostera marina) is a native seagrass that forms underwater meadows and provides habitat for many fish and invertebrates. Wireweed (Sargassum muticum) is an invasive perennial species from the Western Pacific Ocean that is potentially detrimental to the growth and distribution of native kelp and seagrass species. One native species of kelp crab (Pugettia producta, the Northern Kelp crab) has a voracious appetite for bull kelp, and may exert some level of top-down control of the habitat. Less is known about the diet by another local species of kelp crab, Pugettia gracilis (graceful kelp crab). We analyzed fresh foregut contents of P. producta and P. gracilis collected near San Juan Island, WA using SCUBA and snorkeling. We hoped to gain insight into whether kelp crabs are eating the kelp and seagrass on which they are found. We visually quantified the percentage of each food type found in a crab’s foregut and used a chi-square contingency table to test whether the crabs were eating the kelp or seagrass they were found on. P. gracilis had a non-significant interaction (Χ2 = 2.213, p = 0.136) indicating that they are not preferentially eating or avoiding the seaweed species on which they were found. P. producta did have a significant interaction (Χ2 = 10.693, p = 0.005) indicating that they are preferentially eating (S. muticum and eelgrass) or avoiding (bull kelp) the species they were found on. These results indicate that kelp crabs exhibit a wide variety of diet preferences and move around a fair amount to access the different food types.
