Seasonal and Bathymetric Changes in Feeding Habits of the Benthic Red Crab Pleuroncodes Planipes (Decapoda, Anomura, Galatheidae) Off the Pacific Coast of Baja California Sur, Mexico

Abstract

Stomach contents of benthic red crabs (Pleuroncodes planipes) were analyzed to document number of items and composition. The crabs were captured along a series of latitudinal transects covering depths from 50 to 250 m, during March (12 stations) and September 1990 (8 stations). The number of food items decreased significantly from March to September at 150 and 200 m depth, the only strata compared since red crabs are usually absent from the coast above 100 m in summer. The particulate organic matter (POM) varied from 60 to 70% of total food items. The zooplankton fraction, mainly crustaceans, foraminiferans, and radiolarians, was second in importance. Phytoplankton was the next most important group, and was represented by 17 genera in March and 11 in September. The mean number of diatoms in stomachs per station decreased significantly (73.5 versus 7) from March to September. The number of genera/station showed the same pattern (5.36 versus 3.6). The most abundant (number of cells) and frequent (presence over number of stations) diatom genera in March were Nitzschia, Melosira and Cocconeis in that order, accounting for 74% of the relative importance index. In September, Cyclotella, Nitzschia and Melosira accounted for 42% of the importance index. The stomach contents in benthic red crabs indicate a decreasing availability of food in the area from winter-spring through the summer. This pattern correlates well with the diminishing intensity of the coastal upwelling system and weakening of the California Current. The amount of stomach contents in red crabs decreased as the density of the crustacean species increased.