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GREEN CRAB (CARCINUS MAENAS LINNAEUS) CONSUMPTION RATES ON AND PREY PREFERENCES AMONG FOUR BIVALVE PREY SPECIES
Citation:
Palacios, K. C. AND S P. Ferraro. GREEN CRAB (CARCINUS MAENAS LINNAEUS) CONSUMPTION RATES ON AND PREY PREFERENCES AMONG FOUR BIVALVE PREY SPECIES. JOURNAL OF SHELLFISH RESEARCH 22(3):865-871, (2003).
Description:
The European green crab, Carcinus maenas, is a recent invader to Pacific Northwest (PNW) estuaries with a voracious appetite, especially for bivalves. To assess their potential impact, we estimated green crab consumption rates on four PNW bivalve species, Yaquina oyster (Ostrea conchaphila Carpenter), Manila clam (Venerupis philippinarum A. Adams and Reeve), bent-nosed clam (Macoma nasuta Conrad), and Cryptomya clam (Cryptomya californica Conrad) of different sizes, and their preferences between these bivalve species in similar size classes. The bivalve size classes tested ranged in length from 10-14 mm to 33-37 mm. Replicate (n = 3-8) consumption rate and prey preference tests were conducted by allowing one previously starved (48 h) green crab (55-75 mm carapace width) to feed ad libitum on bivalve prey for 16 h. All tests were conducted in 38-l aquaria with 13 cm of sediment. In each test, a total of either 60 or 30 individuals of each prey species were offered without replacement. Mean green crab consumption rates varied depending upon the prey species and size class. For prey of similar size, Yaquina oysters were consumed at a higher rate than bent-nosed clams and Manila clams, while Yaquina oysters and Cryptomya clams were consumed at about the same rate. Green crabs preferred Yaquina oysters to both bent-nosed clams and Manila clams by ratios ranging from 2:1 to 28:1, depending upon the prey size. Small Crytomya clams were preferred to small bent-nosed clams by a ratio of 8:1. The mean total biomass of Yaquina oysters and bent-nosed clams eaten in our consumption and preference experiments was 1.54 (?0.10) g/16 h. Our results suggest that green crabs have the potential to pose a serious threat to some bivalve populations in PNW estuaries, and that Yaquina oysters are at greater risk of green crab predation than bent-nosed clams and Manila clams, and Cryptomya clams are at greater risk than bent-nosed clams.