Effect of Benthic Microhabitat Cues on the Metamorphosis of Pueruli of the Spiny Lobster Panulirus Argus

To determine whether settlement microhabitat induces metamorphosis in the puerulus stage of the Caribbean spiny lobster (Panulirus argus) and to identify the specific features of the habitat that might elicit the response, we monitored the metamorphic progress of more than 200 pueruli exposed to 6 different settlement substrates: sea water alone (no substrate), red algae, sea grass, artificial algae, algae-treated sea water, and artificial algae plus algae-treated sea water. Initial pigmentation followed settlement by approximately 1 day and began 3-6 days (mean = 5 days) after the swimming pueruli were intercepted entering the Florida Bay nursery. Presence of red algae, Laurencia spp. , a preferred settlement substrate, accelerated the rate of pigmentation, but by < 1 day. Metamorphosis to the first benthic juvenile stage occurred 7-9 days (mean = 8 days) after pueruli entered the bay and was unaffected by any of the substrates tested. Rates of both pigmentation and metamorphosis varied by as much as 2 days among replicate experiments conducted during the summers of 1986-1988. These results suggest that metamorphosis of pueruli of P. argus is essentially determinant; thus, physiological constraints may limit the distance that pueruli can disperse into the nursery and may force many pueruli to settle in inappropriate habitats where survival is improbable. Settlement and metamorphosis of planktonic larvae of many marine invertebrates can be induced by physical or chemical cues associated with settlement habitat (see Chia and Rice, 1978; Burke, 1983, for reviews). Specific environmental cues are thought to stimulate neural or hormonal processes that trigger larval settlement and metamorphosis in habitats that offer greater survival for subsequent life stages (Burke, 1983). Larvae that can retard development until favorable conditions are encountered are capable of increased dispersal, which is a function of both transport processes and length of larval life (Sulkin and Van Heukelem, 1986). Such physiological plasticity in the onset of metamorphosis may be a desirable trait for widely dispersing larvae or larvae with ecological requirements that differ from adults, because the probability of encountering suitable settlement habitat within a specific locality or period of time may be low. Alternatively, marine animals living in regions where currents are seasonally predictable and can reliably transport larvae to appropriate nursery grounds may evolve more canalized larval development with physiologically constrained metamorphic rates (Lipcius et al., 1990). For-sessile or sedentary invertebrates (e.g., hydroids, ascidians, echinoids, molluscs, barnacles), on which most research on this topic has focused, selection of a settlement site ultimately reflects the habitat requirements of the adult stage (Meadows and Campbell, 1972; Highsmith, 1982; Morse et al., 1988; and many ot ers). But for invertebrates such as decapod crustaceans, with more complex life cycles and mobile adult s ages, habitat choice by larvae or postlarvae should be influenced by factors that affect juvenile survival, factors that may be unrelated to adult habitat requirements. Despite their widespread abundance and distribution in the marine environment, little information is available concerning metam rphic induction in decapod crustaceans (Felder et al., 1985). Induction or inhibition of metamorphosis from the larval or puerulus stage to he first benthic stage in resp nse to the presence/absence of natural substrates has been recorded for a brachyuran crab (Castro, 1978), a homarid lobster (Botero and Atema, 1982), and a palinurid lobster (Serfling and Ford, 1975). The absence of metamorphic induction for a pagurid crab was reported by Roberts (1971). In contrast to observations made by Serfling and Ford (1975), who reported that the pueruli of the California spiny lobster Panulirus interruptus apparently required surf