THE EFFECTS OF SILTATION ON RECRUITMENT OF SPINY LOBSTERS, 



PANULIRUS ARGUS 



William F Herrnkind.' Mark J. Butler IV,' and 

 Richard A. Tankersley^ 



ABSTRACT 



Several surveys in the Florida Keys indicated fewer juvenile spiny lobsters, Panulirus argus, in an 

 area where their primary habitat, stands of benthic algae Laurencia spp., was heavily silted as 

 compared with similar, less silted habitat. We tested several hypotheses explaining this relationship: 

 1) planktonic postlarval lobster abundances are lower in the silted area, 2) siltation of algae impedes 

 postlarval settlement or subsequent juvenile habitat selection, or 3) siltation increases mortality at 

 the time of metamorphosis. We also compared the time-to-metamorphosis for settling pueruli within 

 silted and nonsilted algae, analyzed the physical character of algal silt in low-silt and high-silt 

 regions and measured the abundances of epifauna constituting prey of juvenile spiny lobsters. Plank- 

 tonic postlarval abundances were substantially higher in the high-silt area thus rejecting hypothe- 

 sis 1. Likewise, results from laboratory experiments testing the effect of algal siltation on postlarval 

 time-to-metamorphosis and early postsettlement survival showed no short-term increase in mortal- 

 ity. Limited postlarval settlement and avoidance of silted algal habitats by juveniles, as determined 

 in substrate choice experiments, probably accounts for the paucity of young spiny lobsters in heavily 

 silted localities. In addition, although juvenile spiny lobsters are nonselective predators, lower prey 

 availability in silted algae probably promotes transciency which, in turn, causes increased mortality 

 by predation while juveniles are exposed. Large-scale siltation exacerbated by human activity must 

 be viewed as potentially deleterious to spiny lobster recruitment. 



The western Atlantic or Florida spiny lobster, 

 Panulirus argus, is the focus of an intense com- 

 mercial and recreational fishery in south Florida, 

 particularly the Florida Keys. Besides severe 

 fishing pressure, spiny lobster populations are 

 subject to a variety of other factors that poten- 

 tially limit population size. For example, habitat 

 degradation, like that resulting from chronic sil- 

 tation, may affect not only adult lobsters but the 

 postlarval settlement stage as well. During 1983 

 and 1984 we sampled numerous sites in a region 

 of about 40 km^ east of Big Pine Key which was 

 chronically heavily silted and held low numbers 

 of newly settled spiny lobsters despite extensive 

 benthic algal growth typical of settlement habi- 

 tat. We hypothesized that postlarval spiny lob- 

 sters either do not settle in silted habitat or settle 

 there but do not survive. In either case, we sup- 

 posed that the heavy siltation reduced the carry- 

 ing capacity of otherwise suitable habitat, poten- 

 tially reducing regional recruitment where 

 siltation is widespread. 



•Department of Biological Science, The Florida State Univer- 

 sity, Tallahassee, FL 32306-3050. 



^Department of Biological Science, The Florida State Univer- 

 sity, Tallahassee, FL; present address: Department of Biology, 

 Wake Forest University, Winston-Salem, NC 27109. 



Sediment particle size, composition, and stabil- 

 ity influence larval settlement in a variety of 

 marine benthic invertebrates (Crisp 1974, 1976; 

 Gray 1974; Rhoads 1974; Pearson and Rosenberg 

 1978). For example, heavy siltation and sediment 

 instability, created by natural biogenic rework- 

 ing of the substrate and subsequent resuspension 

 of sediments by turbulence reduces the abun- 

 dance of suspension feeding infauna (Rhoads and 

 Young 1971; Aller and Dodge 1974). In addition, 

 siltation from human activities (e.g., dredging, 

 shoreline development, boat traffic, etc.) can de- 

 grade benthic community structure via anaero- 

 biosis, direct burial, toxic poisoning, or increased 

 turbidity (Morton 1977; Allen and Hardy 1980; 

 Jones and Candy 1981; Cortes and Risk 1985). 

 Most available information concerns sessile or in- 

 faunal species, but little information exists for 

 mobile, epibenthic forms (Pearson and Rosenberg 

 1978). Although the habitat selection and bur- 

 rowing behavior of some shrimps and juvenile 

 clawed-lobsters has been investigated in relation 

 to substrate character (Ruello 1973; Howard and 

 Bennett 1979; Aziz and Greenwood 1982; Botero 

 and Atema 1982; Pottle and Elner 1982; Roach 

 1983; Herrnkind and Butler 1986), we know of no 

 research describing the effect of siltation on deca- 



Manuscnpt accepted February 1988. 

 FISHERY BULLETIN: VOL. 86, NO 2, 1988. 



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