Charles A. Acosta

Is seagrass an important nursery habitat for the Caribbean spiny lobster, panulirus argus, in Florida?

Abstract Caribbean spiny lobster (Panulirus argus) settle preferentially in macroalgal‐covered hard‐bottom habitat, but seagrass is more prevalent in Florida (United States) and the Caribbean, so even low settlement of lobsters within seagrass could contribute substantially to recruitment if post‐settlement survival and growth were high. We tested the role of seagrass and hard‐bottom habitats for P. argus recruitment in three ways. We first explored possible density‐dependent regulation of early benthic juvenile lobster survival within cages deployed in seagrass and hard‐bottom habitats. Second, we compared settlement and survival of P. argus in both habitats, by comparing the recovery of microwire‐tagged early benthic juveniles from patches of seagrass and hard‐bottom. Finally, we assessed the relative abundance of juvenile lobsters in each habitat by deploying artificial structures in seagrass sites and compared these data with data from similar deployments of artificial structures in hard‐bottom habitat in other years. More early benthic juvenile lobsters were recovered from cages placed in hard‐bottom than in seagrass, but mortality of the early benthic life stage was high in both habitats. In regional surveys, the mean number of lobsters recovered from artificial shelters deployed within seagrass was lower than in any year that we sampled hard‐bottom, indicating that fewer lobsters reside naturally in seagrass, particularly large juveniles >40 mm carapace length. The greater abundance (and likely survival) of juvenile P. argus that we observed in hard‐bottom habitat as opposed to seagrass, combined with previous studies demonstrating that postlarval P. argus are attracted to, settle in, and metamorphose more quickly in red macroalgae, confirm that macroalgae‐dominated hard‐bottom habitat appears to be the preferred and more optimal nursery for Caribbean spiny lobster.

Differential growth of crayfish Procambarus alleni in relation to hydrological conditions in marl prairie wetlands of Everglades National Park, USA

Environmental conditions influence crustacean growth by affecting molt intervals and incremental increases in length and weight. In the seasonally-flooded marl prairie wetlands of eastern Everglades National Park, U.S.A., hydropattern exerts considerable influence on aquatic primary productivity, and so may influence the availability of food resources for higher trophic levels. The seasonal hydroperiod has been drastically altered by anthropogenic factors, but the impacts on the aquatic community are not well known. We studied whether differences in growth of crayfish Procambarus alleni could be detected in habitats with different hydroperiods. We first described growth patterns based on incremental increases in length and weight of crayfish on a high protein diet in the laboratory. Regression analyses indicated that growth patterns in males and females were similar. Although the intermolt period increased with age, the proportional increases in length and weight were similar through successive molts. The relationship between length and weight of crayfish was best described by a power equation for allometric growth. We then compared growth curves for crayfish subpopulations from different areas of the marl prairie. In habitats with the longest hydroperiods, crayfish weight-at-size was not significantly different from that in laboratory crayfish on the high protein diet. However, weight gain per unit increase in length in short hydroperiod sites was significantly less than in long hydroperiod sites or in the laboratory. These results indicate that crayfish productivity may be associated with hydroperiod in these stressed wetlands, and this may contribute to observed source-sink population regulation.

Impending Trade Suspensions of Caribbean Queen Conch under CITES

Abstract The Convention on International Trade in Endangered Species (CITES) Authority issued injunctions in 2003 and 2004 to halt export trade of Caribbean queen conch (Strombus gigas) from several countries and initiated reviews of a number of other conch-producing countries. The current regulatory framework for regional conch fisheries has obviously failed to protect stocks. I present a case study of the Belize conch fishery to examine fishing impacts, effectiveness of existing regulations, and potential for population recovery. Fishery-independent data from a no-take marine reserve indicated that unfished density and biomass were nearly an order of magnitude greater than in comparable fished areas. Size structure of the protected population showed that an average of 38% of the legal catch may consist of juvenile conch. The spawning potential ratio indicated that the fished stock is severely overexploited, and furthermore, the protected population has not compensated to make the local fishery sustainab...

Spatially explicit population responses of crayfish Procambarus alleni to potential shifts in vegetation distribution in the marl marshes of Everglades National Park, USA

Hydropattern disturbance has had wide-ranging impacts on wetland communities of the Florida Everglades, especially on the habitats and the aquatic biota of the seasonally flooded marl marshes. We used the Everglades crayfish Procambarus alleni as a model to study the associations among hydrology, vegetation distribution, and population dynamics to assess the potential impacts of hydrological changes on the aquatic faunal community in Everglades National Park. To classify benthic habitats as sources or sinks for the crayfish population, we quantified vegetation community structure using GIS maps in which dominant vegetation types were weighted by local hydroperiod (length of inundation). Regression analysis showed that this habitat classification was associated with crayfish density distribution. We then used a spatially explicit, stage-structured population model to describe crayfish population fluctuations under current environmental conditions and to simulate the potential population-level responses to habitat changes that might occur following hydrological restoration. In habitat that was initially saturated with crayfish, the crayfish population size declined under current environmental conditions and then stabilized at about 13% of the initial density over a 50-year period. A 4-month increase in hydroperiod was then simulated by converting shorter-hydroperiod Muhlenbergia-dominated marsh habitat to longer-hydroperiod Cladium-dominated marshes. The model predicted a rapid 7-fold increase in crayfish density following the simulated habitat restoration. This indicated that several functional effects may result from the restoration of historical hydropatterns in marl marshes: (1) the areal extent of habitat sinks will be reduced to isolated patches, whereas the spatial distribution of aquatic source habitats will expand; (2) crayfish population size will increase and persist over time; (3) the minimum threshold needed to increase secondary aquatic productivity may be a 7-month hydroperiod over 90% of the marl marsh landscape. Restoration of historical hydropatterns could thus have cascading positive effects throughout the Everglades aquatic food web.

Spatio-Temporal Variation in Crayfish Production in Disturbed Marl Prairie Marshes of the Florida Everglades

ABSTRACT We used the burrowing crayfish Procambarus alleni as a model organism to compare spatial and temporal patterns of density, standing crop biomass, and size-structured productivity in the seasonal wetlands of the Florida Everglades where environmental stress has been exacerbated by hydropattern disturbance. Crayfish density was not linked to fluctuations in water temperature or dissolved oxygen and was only artifactually associated with water depth. Density and biomass within sites were similar over time but increased significantly in habitats with longer hydroperiods (duration of flooding). The effect of hydroperiod-associated habitat quality on annual crayfish production, in terms of size-structured growth and recruit production, was even more pronounced. Crayfish production in the long-hydroperiod sites was approximately two times greater than in medium-hydroperiod sites and five times greater than in short-hydroperiod sites. Turnover ratios (productivity:biomass) showed that the spatial trend in productivity consistently lagged density and biomass trends in the shorter hydroperiod habitat, indicative of population sink conditions. The long-hydroperiod sites were characterized by high productivity and appeared to function as population sources from which crayfish dispersed to nearby, often marginal, habitats. Therefore, the spatial extent and distribution of short-hydroperiod sink habitats significantly impacted crayfish density, population size structure, and productivity. Simple estimates of density or biomass that do not account for the influence of hydropattern on habitat quality may be misleading indicators of productivity because survival, growth, and reproductive output may vary substantially across disturbed landscapes.