AN OPTIMIZATION STUDY ON THE FEEDING BEHAVIOR OF LUIDIA CLATHRATA (SAY) (ECHINODERMATA: ASTEROIDEA) (BENTHIC, MARINE, ECOLOGY)

The feeding and foraging behaviors of the soft-bottom inhibiting asteroid Luidia clathrata are generally consistent with the predictions of optimization models. Luidia clathrata show a strong preference for the infaunal bivalve Mulinia lateralis in Tampa Bay. Quantitative and qualitative changes in diet occur over time with detrital material dominating the gut contents during periods of low macrofaunal availability. Luidia clathrata may feed on detrital material intraorally, through ingestion, or extraorally, by eversion of the cardiac stomach. This is the first report of extraoral feeding in any paxillosid asteroid. Luidia clathrata show size-selection feeding behavior for both artificial and natural foods. Selection by L. clathrata for small prey is related to maximization of prey intake per unit foraging time as large prey, although ingestible, require extensive manipulation. Starved individuals also select small prey but ingest prey at higher rates. Juveniles (R < 25 mm) show no size-preference for prey. Those compounds most stimulatory to L. clathrata (L-isoleucine, L-glutamic acid, L-cysteine and betaine) are closely aligned with its macroinvertebrate diet. Feeding responses to amino-acids are dose-dependent, increasing in intensity with increasing concentration to a plateau. Associative learning occurs as individuals show an ability to associate an aphotic stimulus (darknes) with a food stimulus (the bivalve, Donax variabilis). This may be related to increased availability of infauna occurring at dusk. Luidia clathrata show ingestive conditioning. Individuals offered different densities of two food types feed disproportionately on the more abundant food. Luidia clathrata show a functional response to changes in prey availability. Starvation increases the slope of the functional response curve. Luidia clathrata show directional movement in the absence of prey but non-directional movement in the presence of prey. Luidia clathrata appear to have evolved an ability to exploit prey efficiently, responding to changes in food availability and quality in a predictable manner. However, past experience, nutritive condition and age may significantly modify foraging behaviors and thus should be considered in models of optimal foraging strategies.