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The diversity, abundance and spatial distribution of macro-epibionts colonizing the graceful crab. Cancer gracilis, the red rock crab, Cancer productus, and the Dungeness crab Cancer magister were examined. These three crab species were common in Barkley Sound, British Columbia, occurring sympatrically across much of their range. Twenty nine epibiont species, representing ten different phyla were found. Thirty three percent of Cancer gracilis, 49% of Cancer magister and 68% of Cancer productus possessed one or more epibiont species. Cancer gracilis was the least speciose, while Cancer productus exhibited the greatest diversity of epibiont species. Male crabs were larger than females and had a greater species richness and diversity of epibionts. Epibionts were largely absent on juvenile crabs; in adult crabs, occurrence increased with crab size. Barnacles were the most common epibiont; the majority were Balanus crenatus, which predominated on the dorsal surfaces of the cephalothorax of each crab species. Green, red and brown algae were also common, the majority of which (>80%) were found on the antennae of the crabs. Tube-dwelling polychaete worms were less abundant, showing a preference for the ventral surfaces of the crabs. Hydrozoan colonies were found on only 7% of all the crabs examined, mostly settling on the ventral surfaces and limbs. Bryozoans were only found on Cancer productus and Cancer magister. The majority were the encrusting Membranipora membranacea. Unlike the above taxa, bryozoans showed no clear preference for a specific area of the carapace. Organisms in the phyla Urochordata, Mollusca and Porifera were only found on a few individual Cancer magister and Cancer productus. The distribution of each epibiont species is discussed in relation to larval settlement patterns and ecological, morphological and behavioural differences among the three host species.
Journal of Crustacean Biology © 2006 Brill