Meeting Abstract
Bull kelp (Nereocystis luetkeana) is ecologically important to primary production, supply of detrital material, and creation of 3D habitat in Salish Sea nearshore subtidal ecosystems. Crustaceans are found in kelp bed food webs but feeding electivities and trophic impacts can be challenging to quantify. To assess the potential for Pugettia producta (the Northern Kelp Crab) to exert top-down control on kelp bed species, we first quantified feeding electivities and preferences in laboratory feeding trials on a range of prey items. In all trials, kelp crabs consumed more bull kelp than any other macroalga tested and elected to eat fresh kelp over aged; they showed no significant preference between kelp and snails (p=0.363). To determine if morphology influenced this feeding electivity, we compared claw morphology of P. producta with three other crab species: Glebocarcinus oregonensis, Oregonia gracilis, and Chionoecetes bairdi. Morphological measurements included number of denticles, radius of curvature of denticles and the distance that denticles extend along the claw. Foods tested in choice and no-choice feeding trials were bull kelp, snails, and non-kelp detritus (shelled shrimp). Kelp crabs (P. producta) have multiple denticles and frequently elect to eat bull kelp but also consumed snails and detritus in much smaller quantities. Decorator crabs (O. gracilis), another “spider” crab, have fewer denticles and rarely elect to eat kelp, eating mostly detritus. G. oregonensis had multiple denticles and consumed the widest variety of food. C. bairdii had the largest number of denticles and consumed detrital material almost exclusively. These results indicate that the serrated, multi-denticulate claws of P. producta may confer an advantage in handling both kelp and detrital matter, suggesting generalist, not strictly herbivorous, feeding patterns.
