No abstract

Overall growth rates of sublegal-sized (50–75 mm carapace length (CL)) and large ([Formula: see text] CL) spiny lobsters, Panulirus argus, in the Florida Keys were 0.46 and 0.15 mm CL/wk; growth rates were 48 and 67% less, respectively, in winter than in summer. Injuries caused a significant 39% growth reduction in small (≤60 mm CL) lobsters. Growth decreased dramatically between 74 mm CL (0.46 mm CL/wk) and 76 mm CL (0.23 CL/wk). Between 71–75 and 76–80 mm CL size classes, intermolt periods of females increased 58% and molt increments decreased 16%; male intermolt periods increased 33% but molt increments did not change until 85 mm CL. Consequently, large ([Formula: see text] CL) males grew 33% faster than females. Changes in growth rates signified a shift in energy use at onset of maturation.

During night dives along randomly selected transects across sand, seagrass, and rubble on the reef flat of Looe Key, a spur-and-groove coral reef, spiny lobsters (Panulirus argus) from dens on the forereef were observed foraging on the reef flat, particularly on the extensive rubble ridge and also relatively frequently in Thalassia. Subsequent sampling of the rubble revealed hundreds of taxa of appropriate prey items, many at high densities; the density of Cerithium litteratum, a favoured food item, was as high as 180 individuals m-2. Arthropods, especially spider crabs (Pitho spp.), were common in seagrass. Gut contents of 75 intermoult lobsters caught on offshore reefs at Biscayne National Park and Dry Tortugas National Park included a myriad of prey items, predominantly molluscs—especially gastropods (49%), chitons (15%), and bivalves (11%)—and arthropods (12%); many of the species in lobster guts were rubble dwellers, but some guts contained multiple prey peculiar to seagrass and sand. It is concluded that Panulirus argus can forage successfully wherever suitable prey items, especially molluscs, are abundant. However, where a wide range of substrata, including rubble, is available, rubble is preferred because of its abundant, accessible prey.

Population dynamics of the spotted spiny lobster, Panulirus guttatus, were examined at Looe Key Reef, Florida, USA, from April 1987 to August 1989. The 347 lobsters captured (including recaptures), ranged from 9 mm (puerulus) to 75 mm carapace length (X = 54 mm CL). Pueruli settled all year round into small holes along the underside of the reef. All lobsters recaptured were found at the site of their initial capture; one was captured four times, all on the same reef spur, over 762 days. Adults sheltered within the reef during the day and foraged on top of the reef at night. Males and females were captured in equal proportions (1.2 M:1 F) from den entrances during the day; females were numerically dominant on foraging grounds at night (3 F:1 M). Reproduction occurred all year round but peaked between March and June; minimum size at maturity was 38 mm CL for females and 48 mm CL for males. The sheltering behaviour of P. guttatus, typically found on the ceiling of dens, contrasted markedly with that of the sympatric P. argus, typically found on the floor; both species used many of the same dens, but simultaneous co-occupancy was rare.