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The Comprehensive Everglades Restoration Plan (CERP) is intended to restore the Everglades ecosystem (FL, USA) by altering its hydrology, with likely consequences for “downstream” estuarine and marine communities in Florida Bay and the Florida Keys. Spiny lobsters (Panulirus argus) are among several species of special concern with respect to CERP because they are of economic and ecological importance and because their nursery habitat may be impacted. We used agent-based, spatially explicit modeling to evaluate the possible impacts of changing water quality (temperature, salinity, harmful algal blooms (HABs)) on spiny lobsters and sponges, the latter of which provide shelter for juvenile lobsters. In our simulations, lobster abundance declined 6–24% in scenarios where salinity either decreased alone or in combination with HABs that kill sponges and are associated with changing water quality. The most severe decline in lobsters occurred when salinity was lowest and HABs occurred annually. One third of this decline was attributable to decreased salinity that increased lobster mortality and movement. However, the greatest impacts on lobsters were indirect. CERP-associated changes in salinity along with HABs caused a die-off of large sponges, resulting in higher predatory mortality on lobsters that depend on sponges for shelter in hard bottom nursery habitats. Sponges declined by ∼50% in simulations with HABs, whereas decreased salinity alone led to sponge mortality of 9–18%. In contrast, higher temperatures increased juvenile lobster growth and eventual recruitment by approximately 7%. Our results suggest that returning Florida Bay to more estuarine, pre-development conditions is likely to result in an ecosystem reversal that is detrimental to stenohaline marine taxa, a scenario with significant socioeconomic implications.

Ontogenetic changes in gregariousness by pre-reproductive animals, like that observed in juvenile Caribbean spiny lobsters (Panulirus argus), may be adaptive and reflect size-specific changes in the effectiveness of aggregation in promoting survival. Alternatively, aggregation may simply result from changes in the distribution or availability of suitable habitat structure, or from other behaviors that enhance survival. There are currently two hypotheses explaining the potential benefits of gregarious behavior in juvenile spiny lobsters, both of which focus on increasing survivorship by reducing predation pressure: the group benefit hypothesis and the guide hypothesis. The group benefit hypothesis argues that aggregations of juvenile lobsters reduce individual susceptibility to predators because groups are better able to fend off attackers or benefit by dilution of risk. The guide hypothesis suggests that aggregation is a consequence of shelter seeking behavior, in which individuals searching for ...

Coastal habitats that serve as nursery grounds for numerous marine species are badly degraded, yet the traditional means of modeling populations of exploited marine species handle spatiotemporal changes in habitat characteristics and life history dynamics poorly, if at all. To explore how nursery habitat degradation impacts recruitment of a mobile, benthic species, we developed a spatially explicit, individual-based model that describes the recruitment of Caribbean spiny lobster (Panulirus argus) in the Florida Keys, where a cascade of environmental disturbances has reconfigured nursery habitat structure. In recent years, the region has experienced a series of linked perturbations, among them, seagrass die-offs, cyanobacteria blooms, and the mass mortality of sponges. Sponges are important shelters for juvenile spiny lobster, an abundant benthic predator that also sustains Florida's most valuable fishery. In the model, we simulated monthly settlement of individual lobster postlarvae and the daily growth, mortality, shelter selection, and movement of individual juvenile lobsters on a spatially explicit grid of habitat cells configured to represent the Florida Keys coastal nursery. Based on field habitat surveys, cells were designated as either seagrass or hard- bottom, and hard-bottom cells were further characterized in terms of their shelter- and size- specific lobster carrying capacities. The effect of algal blooms on sponge mortality, hence lobster habitat structure, was modeled based on the duration of exposure of each habitat cell to the blooms. Ten-year simulations of lobster recruitment with and without algal blooms suggest that the lobster population should be surprisingly resilient to massive disturbances of this type. Data not used in model development showed that predictions of large changes in lobster shelter utilization, yet small effects on recruitment in response to blooms, were realistic. The potentially severe impacts of habitat loss on recruitment were averted by compensatory changes in habitat utilization and mobility by larger individuals, coupled with periods of fortuitously high larval settlement. Our model provides an underutilized approach for assessing habitat effects on open populations with complex life histories, and our results illustrate the potential pitfalls of relying on intuition to infer the effects of habitat perturbations on upper trophic levels.

Social behavior confers numerous benefits to animals but also risks, among them an increase in the spread of pathogenic diseases. We examined the trade-off between risk of predation and disease transmission under different scenarios of host spatial structure and disease avoidance behavior using a spatially explicit, individual-based model of the host pathogen interaction between juvenile Caribbean spiny lobster (Panulirus argus) and Panulirus argus Virus 1 (PaV1). Spiny lobsters are normally social but modify their behavior to avoid diseased conspecifics, a potentially effective means of reducing transmission but one rarely observed in the wild. We found that without lobster avoidance of diseased conspecifics, viral outbreaks grew in intensity and duration in simulations until the virus was maintained continuously at unrealistically high levels. However, when we invoked disease avoidance at empirically observed levels, the intensity and duration of outbreaks was reduced and the disease extirpated within five years. Increased lobster (host) spatial aggregation mimicking that which occurs when sponge shelters for lobsters are diminished by harmful algal blooms, did not significantly increase PaV1 transmission or persistence in lobster populations. On the contrary, behavioral aversion of diseased conspecifics effectively reduced viral prevalence, even when shelters were limited, which reduced shelter availability for all lobsters but increased predation, especially of infected lobsters. Therefore, avoidance of diseased conspecifics selects against transmission by contact, promotes alternative modes of transmission, and results in a more resilient host-pathogen system.

Populations of 2 species of arvicoline rodents, the prairie vole (Microtus ochrogaster) and meadow vole (M. pennsylvanicus), were monitored monthly in alfalfa, bluegrass, and tallgrass prairie habitats in east-central Illinois from 1972 through 1997. Alfalfa provides very high-quality preferred food and poor vegetative cover for both vole species, whereas bluegrass provides intermediate food and vegetative cover. Preferred food resources were very low, especially for M. ochrogaster, and vegetative cover was very dense in tallgrass prairie. Maximum and mean population densities of M. ochrogaster were highest in alfalfa, intermediate in bluegrass, and lowest in tallgrass prairie. Populations of M. ochrogaster displayed synchronous 3- to 4-year multiannual cycles in all 3 habitats. Cycles were most pronounced in alfalfa, less pronounced in bluegrass, and barely discernible in tallgrass prairie. Food availability seems more important than vegetative cover for the success of M. ochrogaster. Densities ...

Many field studies have shown that recruitment of the Caribbean spiny lobster, Panulirus argus, is sensitive to variation in both postlarval supply and local nursery-habitat structure. We used a spatially explicit individual-based model, to investigate the effects of (i) spatio-temporal variation in postlarval supply and (ii) changes in the spatial structure of the nursery habitat on lobster recruitment to the Florida Keys, Florida (USA). By simulating eight different regional scenarios describing postlarval supply, we investigated whether differences in the spatio-temporal delivery of postlarvae to the Florida Keys alters recruitment of subadult lobsters. Our results indicate that random geographical variation in postlarval supply yields the highest predicted recruitment, whereas persistently patchy settlement yields the lowest. Field observations of postlarval supply suggest that the random model is the most realistic. In separate simulations, we determined the sensitivity of the model to changes in the geographic arrangement of nursery habitat and the spatial resolution of habitat structure. The most spatially explicit depictions of habitat structure yielded small, but marginally significant differences in lobster recruitment as compared with more generalized spatial scenarios. These differences may well be magnified when more detailed depictions of postlarval settlement are implemented in the model.