FACTORS REGULATING MICROHABITAT USE BY YOUNG JUVENILE SPINY LOBSTERS, PANULIRUS ARGUS: FOOD AND SHELTER

Habitation patterns ofalgal-dwellingjuvenile spiny lobsters, Panulirus argus, are apparently regulated by a) the availability of epifaunal prey, and/or b) limited sheltering qualities provided by algal branching. Predictions derived from each hypothesis were tested by monitoring emigration from normal (prey abundant), rinsed (prey reduced), and rinsed but structurally enhanced clumps of red algae, Laurencia spp. Density dependent emigration from untreated clumps containing natural prey, and markedly increased emigration from clumps nearly void of potential prey, suggest that trophic pressures play an important role in regulating algal habitation. Solitary dwelling induced by agonistic behavior may function to reduce required foraging area, thus minimizing both exposure to predators and energetic expenditures. The young benthic stages of the spiny lobster Panulirus argus inhabit intricately branched clumps of red algae, Laurencia spp. , in shallow habitats of Florida Bay and the Florida Keys (Marx and Herrnkind, in press). Small size, cryptic behavior, camouflaged pigmentation, and disruptive markings (light-dark banding of appendages and dorsal stripe), seemingly adapt the early stages to residency within algal clumps. Moreover, algae provide abundant prey in the form of diverse epifaunal invertebrates including small gastropod mollusks, isopods, amphipods, and ostracods, all of which are commonly found in the gut contents of young lobsters (Marx and Herrnkind, in press). Young benthic stages are typically solitary in small algal clumps, or occupy widely spaced portions of large clumps, and exhibit aggressively maintained isolation in aquaria. Solitary dwelling behaviorally distinguishes postsettlement stages from older juveniles which are gregarious (Kanciruk, 1980). These collective observations suggest that macroalgal habitation functions to protect the otherwise susceptible young stages from predators and physical stresses while simultaneously providing access to food, thus enhancing the value of algae as a refugium. We examined this relationship by experimentally testing the effects of food and physical sheltering factors on residency patterns of young benthic stages within algal clumps. Assuming trophic regulation, we reasoned that a young lobster should remain within a clump so long as sufficient food is available, but emigrate when prey abundance is low. Increased food searching when prey is scarce conceivably exacerbates agonism by causing frequent contact between residents, or food scarcity might induce increased individual aggressiveness. One predicts increased emigration as a result in either case. Assuming that refuge quality is a regulating factor, we propose that macroalgal clumps are selected as habitat because of physical features independent of prey availability. Alternatively, early benthic stages may occupy algae only in the absence of rock crevices, which constitute the typical shelter for slightly older juveniles in other habitats (Andree, 1981). Below, we report on experimental tests of each prediction and discuss the implications with respect to the behavioral ecology and population dynamics of young juvenile lobsters. Specifying the nature of the biological relationship between spiny lobsters and their settlement habitat is essential to management of the multimillion dollar spiny lobster fishery and will contribute to our understanding of life history tactics.