Mitochondrial DNA variation and population structure in the spiny lobster Panulirus argus

Adult spiny lobsters (Panulirus argus) were collected from nine locations throughout the tropical and subtropical northwest Atlantic Ocean and examined for mitochondrial DNA (mtDNA) variation. 187 different mtDNA haplotypes were observed among the 259 lobsters sampled. Haplotype diversity was calulated to be 0.986 and mean nucleotide sequence-diversity was estimated to be 1.44%; both of these values are among the highest reported values for a marine species. Analysis of molecular variance (AMOVA) and phenetic clustering both failed to reveal any evidence of genetic structure within and among populations of P. argus. The present data are consistent with high levels of gene flow among populations of P. argus resulting from an extended planktonic larval stage and strong prevailing ocean currents.     

Disease avoidance influences shelter use and predation in Caribbean spiny lobster

Shelter competition is uncommon among social animals, as is the case among normally gregarious Caribbean spiny lobsters (Panulirus argus). However, healthy lobsters avoid sheltering with conspecifics infected by a lethal pathogenic virus, PaV1. These contradictory behaviors have implications for shelter use and survival, especially in areas where shelter is limited. In laboratory experiments, we tested shelter competition between paired healthy and diseased juvenile lobsters in shelter-limited mesocosms. Neither healthy nor diseased lobsters dominated access to shelters, but lobsters shared shelter less often when diseased lobsters were present relative to controls with two healthy lobsters. We hypothesized that exclusion of juvenile lobsters from shelter results in increased mortality from predation, especially for the more lethargic, infected individuals. Field tethering trials revealed that predation was indeed higher on infected individuals and on all tethered lobsters deprived of shelter. We then tested in mesocosm experiments how the contrasting risks of predation versus infection by a lethal pathogen influence shelter use. Lobsters were offered a choice of an empty shelter or one containing a diseased lobster in the presence of a predator (i.e., caged octopus) whose presence normally elicits shelter-seeking behavior, and these data were compared with a previous study where the predator was absent. Lobsters selected the empty shelter significantly more often despite the threat of predation, foregoing the protection of group defense in favor of reduced infection risk. These results offer striking evidence of how pathogenic diseases shape not only the behavior of social animals but also their use of shelters and risk of predation.     

Importance of rock lobster size–structure for trophic interactions: choice of soft-sediment bivalve prey

Ecologists are becoming increasingly interested in how variation in predator demographics influences prey communities. In northeastern New Zealand, the contrasting populations of previously exploited predators in highly protected marine reserves and fished areas have been used to investigate the effects of predation in soft-sediment habitats. However, these experiments have been unable to separate the role of predator size from that of density. This study provides evidence to support the model that foraging by different sizes of the rock lobster Jasus edwardsii affects soft-sediment bivalve populations in different ways. Feeding trials were conducted to investigate whether rock lobsters of different sizes vary in their choice of taxa and size of their bivalve prey. Trials with two morphologically similar species, Dosinia subrosea and Dosinia anus, indicated that lobsters of all sizes choose D. subrosea more frequently than the heavier shelled D. anus. Further results indicated that both large (>130 mm carapace length (CL)) and small (<100 mm CL) lobsters are capable of preying on a wide size range of D. subrosea (20–60 mm). However, small lobsters more frequently chose smaller shells (<30 mm) and large lobsters more frequently chose larger shells (>40 mm). Patterns in the abundance and size class distributions of these two bivalve species at protected and fished sites supported the feeding choices observed in the laboratory. These results suggest that populations of rock lobsters with large individuals inside reserves are capable of controlling the demography of bivalve populations in adjacent soft-sediment systems.     

Defense mechanisms and antipredator behavior in two sympatric species of spiny lobsters, Panulirus argus and P. guttatus

The congeneric spiny lobsters Panulirus argus and P. guttatus co-occur throughout the Caribbean Sea, where they may share the coral reef habitat. Despite their phylogenetic closeness, both species have many different life-history traits that may partially explain their coexistence. However, even though both species may face the same predators, their defense mechanisms and antipredator strategies had not been compared. We compared the performance between species in 18 morphological and behavioral defense mechanisms commonly expressed by most spiny lobsters, including predator-avoidance mechanisms (activity schedule, sheltering behavior, delay to disturbance, and effect of conspecific damage-released scents on shelter choice) as well as antipredator mechanisms (body size, several parameters of the escape response and limb autospasy, clinging strength, antennal strength, and cooperative defense). As hypothesized, both species expressed all these defense mechanisms (except cooperative defense, shown only by P. argus), reflecting their phylogenetic closeness, but performed significantly differently in most, in accordance with their particular ontogenetic traits. Their comparative performance in individual defense mechanisms as well as the antipredator strategies displayed by groups of lobsters of each species in the presence of a common predator (the triggerfish Balistes vetula) showed that, in general, the defensive behavioral type of P. argus is more bold and that of P. guttatus more shy. Therefore, their distinct defensive behaviors contribute to their niche differentiation.     

Circadian shelter occupancy patterns and predator–prey interactions of juvenile Caribbean spiny lobsters in a reef lagoon

The spiny lobster, Panulirus argus, is predominantly nocturnal, remaining inside shelters during the day and foraging outside at night, presumably to minimize predation risk. Predation risk generally decreases with increasing lobster size. Therefore, this study examined the hypothesis that size would influence this basic circadian pattern. Video cameras continuously recorded the shelter occupancy of juvenile lobsters (n = 72) having a carapace length (CL) of 30–62 mm that were tethered to shelters in a shallow reef lagoon. The lobsters’ shelter occupancy was 100% during the day, but declined linearly from shortly before sunset to a minimum of 50% shortly after midnight and then increased linearly, reaching 100% by 1 h after sunrise. The percent time the lobsters spent in the shelters followed a similar trend, but there was wide variability at night (0–100%) for individual lobsters. Lobsters left their shelters 2–30 times night⁻¹, with a majority of excursions lasting <10 min. These results suggest that juvenile P. argus minimize predation risk by remaining in their shelters as long as possible but offset the energetic cost of this behavior by foraging close to their shelters for several short periods at night. This emergence pattern contrasts with those of early benthic phase lobsters (<15 mm CL), which seldom leave their shelters, and adults (>80 mm CL), which have a dusk/early evening peak in activity and leave the shelter for extended periods of time during the night. Furthermore, a minimum shelter occupancy in the middle of the night appears especially well adapted to avoid exposure to daytime predators. Videotaped observations also included interactions between lobsters and two dominant lobster predators, the triggerfish, Balistes capriscus, and the octopus Octopus cf. vulgaris. Lobsters responded differently to these predators: remaining in the shelter when attacked by a triggerfish and fleeing the shelter when attacked by an octopus. Triggerfish were nearly twice as likely to attack a lobster that was outside of the shelter than inside. Once under attack, however, a lobster had nearly the same chance of surviving if it was inside or outside. Results suggest that the patterns of shelter use and emergence change as lobsters grow, probably reflecting the interplay between perception of predation risk and the need to forage. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Temporal patterns and transport processes in recruitment of spiny lobster (Panulirus argus) postlarvae to south Florida

We used time-series analysis to identify weekly and annual patterns in the supply of spiny lobster, Panulirus argus (Latreille, 1804), postlarvae to the Florida Keys, USA, over an 8 yr period. We also investigated the relationship between postlarval influx and wind forcing as a transport mechanism using the complex vector-scalar correlation analysis. Postlarval supply had a lunar phase periodicity at 4.5 wk intervals, with postlarval abundance peaking between the new moon and first-quarter lunar phases. A distinct annual cycle of postlarval supply with two peak periods was also apparent. Cross-correlation analysis between relative postlarval abundance and a 12 mo cycle showed that the annual peak occurs in spring, centered around March. With the 12 mo periodicity removed, a smaller peak at 5 mo intervals was also well defined. Wind-forcing for 7 d prior to the time of postlarval collection was marginally correlated with postlarval abundance through the entire time-series; the association was strongest during the late fall to early spring months. The analysis indicated that postlarval supply was correlated with winds from the northeast (ca. 45°), which are associated with winter atmospheric fronts. In contrast to results reported for other spiny lobster populations, these patterns suggest that recruitment of lobster postlarvae to south Florida is predictable only at a gross level and is presumably affected by the temporally inconsistent structure of regional oceanic gyres and variability in the timing of lobster spawning in the Caribbean. Received: 24 January 1997 / Accepted: 4 March 1997     

Genetic differentiation in populations of two Palaemon prawn species at the Atlantic east coast: does gene flow prevent local adaptation?

Two Palaemon prawn species, P. adspersus Rathke and P. squilla (L.), occur along the European Atlantic coast. In areas heavily affected by tides (Netherlands and France), one species, P. squilla, inhabits the intertidal zone, and P. adspersus is found subtidally in the Zostera marina meadows. In areas with small tidal ranges (Sweden) both species occur in the Z. marina zone, and here the body size of P. squilla is reduced, something that in turn reduces reproductive output in this species. Is adaptive improvement in non-tidal P. squilla populations prevented by too extensive gene flow from tidal areas? To wanswer this, genetic differentiation was studied by horizontal starch gel electrophoresis. Each of the two species was sampled at five sites along the European Atlantic coast. Twenty-two enzymes representing 25 loci were scored. Significant genetic heterogeneity between sites was found in both species. Thus the extensive gene flow hypothesis was not supported by the results, and non-tidal populations ought to have the possibility to adapt to local conditions.     

Effects of autotomy on long-term survival and growth of painted spiny lobster (Panulirus versicolor) on the Great Barrier Reef, Australia

The effects of autotomy (shedding of appendages) on survival and growth rates of painted spiny lobster were investigated at Northwest Island (23^° 18?? S, 152^° 43?? E) during the period 2003?C2006. Adult lobsters were captured, tagged, and classified as either uninjured (n?=?68), minimally injured (n?=?39) or moderately injured (n?=?19) depending on the number and type of appendages that were autotomized during capture and handling. Six to thirty-six months after release, 86 lobsters were recaptured (mean time at large?=?305?days). Recapture rates of uninjured (64.7%), minimally injured (71.8%), and moderately injured lobsters (73.7%) were not significantly different. Similarly, mean annualized growth rates of uninjured, minimally injured, and moderately injured lobsters were not significantly different. This suggests that the energetic cost of a single episode of autotomy is either negligible or exists as a trade-off with some other life history trait, such as reduced reproductive performance. These results support the use of certain management tools (e.g., size limits) that prescribe release of non-legal lobsters, regardless of their injury status.     

Tissue distribution and excretion of 99mTc-disofenin in three marine species: Pleuronectes americanus (winter flounder), Homarus americanus (lobster), and Mya arenaria (soft-shell clam)

To determine the pharmacokinetics of a small lipophilic molecule in vivo, the distribution and accumulation of ^99mTc-radiolabelled disofenin (diisopropylacetanilide iminodiacetic acid) were traced during 1991–1992 by scintigraphy and gamma well counting in winter flounder (Pleuronectes americanus collected from Boston Harbor and Long Island Sound in 1992), lobsters (Homarus americanus collected from Massachusetts Bay in 1991), and soft-shell clams (Mya arenaria purchased in 1991). The agent was distributed throughout the bodies of lobsters within 12 s, throughout flounder within 40 s, and throughout clams within 2 min. It was concentrated most strongly by the liver of flounder, which contained 61.2±7.8% of the injected dose within 1 h of injection, and by the lobster hepatopancreas. Accumulation also occurred in the flounder kidney, lobster antennal glands, and the kidney and pericardial glands of clams. The compound was rapidly excreted from the flounder liver into the gall bladder, and from the lobster hepatopancreas into the stomach. The data suggest its excretion from the lobster antennal glands and clam kidneys. The rate of clearance of disofenin from the body varied among species: 99±2.1% of the initial dose remained in flounder sampled 16 to 24 h after injection, compared to 80.5±7% remaining in the lobster after 15 h, and 87.4±5.9% remaining in clams after 27 h. The clearance rates in flounder and lobster are considered to be minimum values because of the lack of gut activity in unfed individuals. Overall, these in vivo tracer studies establish the utility of scintigraphy for assessing the uptake and excretion of a lipid soluble compound in different taxa, and may be applicable for evaluating disease and/or environmental effects on organ function in marine animals.     

Molt cycle alterations in behavior,feeding and diel rhythms of a decapod crustacean,the spiny lobster Panulirus argus

The crustacean molt cycle manifests extensive behavioral changes in addition to physiological and integumentary modifications. The paucity of quantitative studies led us to characterize molt stage dependent alterations in rhythmic locomotor, feeding, and agonistic behavior of subadult spiny lobster Panulirus argus held grouped and solitarily in simulated natural conditions. Non-disruptively determined molt stages were defined as proportions of intermolt duration. Significant nocturnal rhythmicity persisted through the full molt cycle, though daily form varied as a function of activity level and molt stage. A distinct early evening peak signaled initiation of foraging and walking behavior. Thereafter, rhythm amplitude either declined progressively (low activity: unimodal pattern), remained high (high activity: nocturnal plateau), or exhibited a secondary early morning peak (intermediate activity: bimodal and polymodal patterns). Activity ceased at or immediately prior to sunrise. Ecdysis was predominantly nocturnal, probably reflecting species specific spatiotemporal movement patterns and social behavior. A selective advantage of nocturnal ecdysis was postulated concerning avoidance of cannibalism and diurnal predators. Locomotor activity and feeding rates were not equivalent through the molt cycle, though both peaked in stages B₂-C₁. Locomotor activity remained high in metecdysis, decreased sharply at proecdysis initiation (D₀), reaching lowest levels in D₁-D₃, then increased in D₃ through B₁. Activity dropped steeply at ecdysis, though lobsters were capable of intense and coordinated activity. Feeding decreased slowly through metecdysis after the B₂-C₁ maximum, then increased temporarily in C₄ and D₀, indicating heightened feeding motivation. This contrasts with the locomotor activity decrease at proecdysis. Food consumption declined rapidly in D₁ and D₂ and ceased at the D₂-D₃ transition. Feeding resumed in B₁ or B₂, intensifying to maximum in late B₂. Feeding remained relatively constant within stages, whereas locomotor activity varied greatly, though both correlated with metabolic needs. Grouped and solitary lobsters displayed similar patterns of foraging and walking, equivalent to those of locomotor activity and feeding of solitary individuals. Frequency of agonistic interactions (not aggression per se) remained relatively constant through the cycle, peaking in metecdysis, though the highest relative proportion occurred near ecdysis. Lobsters then were submissive and avoided physical contact with conspecifics. Clearly, locomotor activity, feeding, and social behavior of P. argus are not simply determined. Indeed, behavior is distinctly phase coordinated with varying metabolic requirements dependent on the proximity to ecdysis and ecological pressures.     

Shelter selection of the spiny lobster <Emphasis Type="Italic">Palinurus elephas</Emphasis> under different levels of <Emphasis Type="Italic">Octopus vulgaris</Emphasis> predation threat

The skill of recognizing and reacting to predators is often based on a learned component. Few studies have examined the role of learning in spiny lobster anti-predator behavior. We investigated whether European spiny lobster (Palinurus elephas) shelter selection is influenced by olfactory stimuli released by one of the most common lobster predators, the common octopus (Octopus vulgaris), and whether the behavioral response to octopus chemical stimuli is innate or influenced by experience. In experimental arenas, we conditioned wild-caught lobsters with three levels of predation threat: no threat, with no predator–prey interaction; medium threat, with odor and visual predator cues only; high threat, active predation risk. We subsequently tested the shelter choice of the conditioned lobster under different experimental conditions: (1) shelter plus seawater; (2) shelter plus seawater plus chemical octopus cue. Our results showed significant differences in mean shelter occupancy with conditioning level. We conclude that P. elephas individuals use chemosensory systems in predator-avoidance mechanisms. Moreover, lobsters subject to a training period of high-level predation threat were able to learn the octopus chemical stimuli and treat its odor as a cue related to predation risk. The findings relative to the spiny lobster learning abilities could be an important tool for future management of lobster populations, e.g., by re-introduction of reared juveniles, which have not yet experienced predation.     

A whole-animal bioassay for the determination of the food attractants of the lobster Homarus gammarus

A semi-quantitative assay is described for assessing the effectiveness of bait extracts for the lobster Homarus gammarus (L.), using an extract of the squid Loligo vulgaris Lamarck as a standard. Fractionation of this extract indicated that, while no single component was as attractive to lobsters as the whole, the recombination of the various components yielded a solution which was as attractive as the original extract. It appears likely that several different classes of chemosensory cell must be simultaneously stimulated for the initiation of feeding behaviour in the lobster.     

Assessment of the aquatic biodiversity of a threatened coastal lagoon at Bimini, Bahamas

Coastal biodiversity is threatened worldwide by both direct and indirect anthropogenic activities. To more effectively manage and protect coastal biodiversity, accurate assessments of genetic, species, and ecosystem level diversity are required. We present the results from an assessment of the aquatic species diversity of a small (3?km²), shallow, mangrove-fringed Bahamian lagoon (the North Sound) subject to ongoing anthropogenic development. The assessment was conducted through a collation of field observations and data in published literature. We found that eight angiosperm species, 30 macroalgal species, and 370 animal species (including 95 fishes, 69 arthropods, 56 birds, and 45 mollusks) were documented within the lagoon. At least 11 of these species are of conservation concern, such as the critically endangered smalltooth sawfish (Pristis pectinata) and hawksbill turtle (Eretmochelys imbricata). Comparisons of community similarity indicated that the North Sound has a relatively distinct fauna and flora, but available data suggest that the species found there are most similar to those found in nearby habitats in Cuba. The lagoon forms a key nursery habitat for many species, including lemon sharks (Negaprion brevirostris), Caribbean spiny lobsters (Panulirus argus), and queen conch (Strombas gigas). Recently, the lagoon was included as part of a new marine protected area (MPA), but much of the habitat has already experienced considerable anthropogenic disturbance and the MPA boundaries have yet to be established. We have therefore analyzed the lagoon biodiversity and expect the data presented here to serve as a baseline for future comparisons.     

Conserving spawning stocks through harvest slot limits and no-take protected areas

The key to the conservation of harvested species is the maintenance of reproductive success. Yet for many marine species large, old, individuals are targeted despite their disproportionate contribution to reproduction. We hypothesized that a combination of no-take marine protected areas (MPAs) and harvest slot limits (maximum and minimum size limits) would result in the conservation of large spawning individuals under heavy harvest. We tested this approach under different harvest intensities with a 2-sex, stage-structured metapopulation model for the Caribbean spiny lobster (Panulirus argus). P. argus is intensively harvested in the Caribbean, and in many localities large, mature individuals no longer exist. No-take MPAs and harvest slot limits combined, rebuilt and maintained large mature individuals even under high harvest pressure. The most conservative model (a 30% MPA and harvest slot limit of 75–105 mm) increased spawner abundance by 5.53E¹² compared with the fishing status quo at the end of 30 years. Spawning stock abundance also increased by 2.76–9.56E¹² individuals at a high harvest intensity over 30 years with MPAs alone. Our results demonstrate the potential of MPAs and harvest slot limits for the conservation of large breeding individuals in some marine and freshwater environments. Decisions on which management strategy best suits a fishery, however, requires balancing what is ecologically desirable with what is economically and socially feasible.     

Genetic diversity and relatedness of the mangrove Rhizophora mangle L. (Rhizophoraceae) using amplified fragment polymorphism (AFLP) among locations in Florida, USA and the Caribbean

Rhizophora mangle L. is a widespread mangrove species in the Western Hemisphere. Mangrove habitat loss and their importance to coastal and reef ecosystems make greater understanding of their genetic structure useful for conservation and management. An amplified fragment polymorphism (AFLP) analysis was performed on samples from Florida and the Caribbean to discover the genetic structure present. R. mangle had variable genetic diversity not related to latitude; P ranged 7 %–92 %. Some other factor, perhaps human impact, has caused low genetic diversity in some populations. Across Florida R. mangle populations varied in genetic diversity with less diversity (G_st?=?0.195) and greater gene flow on the Atlantic coast (Nm =2.07) than on the Gulf coast (G_st?=?0.717, Nm?=?0.197). Gene flow between Caribbean islands was low (Nm?=?0.386) compared to continental populations (Nm?=?1.40), indicating that long distance dispersal is not common between islands. Analysis of molecular variance (AMOVA) analysis showed significant deviations from Hardy-Weinberg expectations at the level of region among subpopulations and overall genetic difference among subpopulations for R. mangle. One implication for management is that small continental populations and island populations may be genetically isolated and distinct from each other.     

Experimental interbreeding between geographically separated populations of the marine wood-boring isopod Limnoria tripunctata with preliminary indications of hybrid vigor

Populations of the marine wood-boring isopod Limnoria tripunctata Menzies were cultivated and interbred in the laboratory in order to determine whether geographically separated populations would interbreed. Two series of interbreeding studies were conducted. In the first, field populations from 11 Atlantic and Caribbean sites and 3 Pacific sites were interbred with a North Western Atlantic population from Beaufort, North Carolina (USA). Viable crossings, to at least F ₁, occurred in all but one case—that of a BeaufortxChatham (Massachusetts, USA) cross. In the second series of experiments, field populations from 9 Atlantic and Caribbean sites were crossed with populations from St. Teresa, Florida, Gulf of Mexico. In this case also, all crosses except one produced viable offspring, not only to the F ₁, but to the F ₂ generations as well. The St. Teresa x Chatham cross was not successful. Geographic distance was not a factor in the success of crossbreeding between disjunct populations. Chatham populations (mainly) are now believed to represent a valid but previously obscure species, Limnoria tuberculata Sowinski, and not a variant of L. tripunctata Menzies. Enhanced viality or vigor, as determined from rate of wood destruction, population growth rate and survival, was indicated in several crossings, but this was not necessarily correlated with distance between populations. Observations were made on the manner in which the species has achieved a worldwide distribution, and a hypothesis is put forward to explain the evolution of species related to L. tripunctata.Contribution from Zoology Department, Duke University, Durham, North Carolina, and Duke University Marine Laboratory, Beaufort, North Carolina, and the Department of Oceanography, No. 289, Florida State University, Tallahassee, Florida. Support in part from NSF Grant No. GB-6898.     

Astaxanthin deposition in the cuticle of juvenile American lobster (<Emphasis Type="Italic">Homarus americanus</Emphasis>): implications for phenotypic and genotypic coloration

The phenotypic brownish-green color of an American lobster (Homarus americanus Milne-Edwards, 1837) is determined by genetic and dietary mechanisms. Diet influences color through the carotenoid astaxanthin. This pigment can appear red or blue depending if it is bound to protein, and the relative amounts of each form influence lobster color. Carotenoprotein formation was examined in sibling American lobsters rendered white by a diet low in astaxanthin, by feeding a diet containing 0, 55, 110, or 220 g astaxanthin g^–1 for 110 days beginning on 7 February 2004. The relative levels of red and blue in these lobsters were assessed through the analysis of digital photographs of the lobsters, which were taken monthly. The red/blue ratio was used to assess if free (red) or protein-bound astaxanthin (blue) was the dominant form in the lobsters, or if the two forms occurred in ratios allowing for natural coloration. Naturally colored lobsters developed only in the highest astaxanthin diet group, while lobsters fed the 55-g diet were blue. Differences were observed among different parts of the body, and were presumed to be a function of cuticle thickness. However, within each diet treatment, some lobsters initially became red, suggesting an accumulation of free astaxanthin, while other lobsters initially became blue, suggesting an accumulation of protein-bound astaxanthin. This variation may be a result of differences in the uptake of astaxanthin, the rate of carotenoid-protein complexing, or in the total amount of protein available for binding. This variability is likely to be the key to understanding the underlying basis of genetically determined color in American lobsters.Communicated by J.P. Grassle, New Brunswick     

Long-term trends in invertebrate–habitat relationships under protected and fished conditions

Few studies examine the long-term effects of changing predator size and abundance on the habitat associations of resident organisms despite that this knowledge is critical to understand the ecosystem effects of fishing. Marine reserves offer the opportunity to determine ecosystem-level effects of manipulated predator densities, while parallel monitoring of adjacent fished areas allows separating these effects from regional-scale change. Relationships between two measures of benthic habitat structure (reef architecture and topographic complexity) and key invertebrate species were followed over 17 years at fished and protected subtidal rocky reefs associated with two southern Australian marine reserves. Two commercially harvested species, the southern rock lobster (Jasus edwardsii) and blacklip abalone (Haliotis rubra) were initially weakly associated with habitat structure across all fished and protected sites. The strength of association with habitat for both species increased markedly at protected sites 2 years after marine reserve declaration, and then gradually weakened over subsequent years. The increasing size of rock lobster within reserves apparently reduced their dependency on reef shelters as refuges from predation. Rising predation by fish and rock lobster in the reserves corresponded with weakening invertebrate–habitat relationships for H. rubra and sea urchins (Heliocidaris erythrogramma). These results emphasise that animal–habitat relationships are not necessarily stable through time and highlight the value of marine reserves as reference sites. Our work shows that fishery closures to enhance populations of commercially important and keystone species should be in areas with a range of habitat features to accommodate shifting ecological requirements with ontogenesis.     

Control of larval release in the Caribbean spiny lobster, <Emphasis Type="Italic">Panulirus argus</Emphasis>: role of chemical cues

The current model for larval release in subtidal crustaceans suggests that hatching time is controlled by the embryos, which release a pheromone that stimulates the parent female to undergo behaviors that synchronize larval release. Alternatively, hatching could be controlled by the females. Ovigerous spiny lobsters Panulirus argus (Latreille) exhibit stereotypic behaviors during larval release, including rapid abdominal extensions and pleopod-pumping activity. Ovigerous P. argus were collected from coral reefs in the Florida Keys, USA during the summers of 2005 and 2006. Pleopod-pumping activity was quantified to determine if a female’s pumping activity correlates with the developmental state of the embryos. The role of pheromones released by developing and hatching embryos in controlling pumping behaviors was tested by measuring the pumping response of ovigerous lobsters to (1) hatch water, (2) homogenized embryo water, (3) embryo-conditioned water (unhatched late-stage embryos soaked for 20 h), and (4) water containing homogenized post-hatch embryo cases. Bioassays were conducted under constant conditions (dim-red light) in the laboratory at random times during the day to control for any possible rhythm in pumping activity. Spontaneous pleopod-pumping activity increased significantly with increasing embryo development. Upon exposure to hatch water, ovigerous lobsters with late-stage embryos displayed increased pleopod pumping with increased treatment concentration. Water individually conditioned with homogenized late-stage embryos, intact late-stage embryos, and homogenized post-hatch embryo cases all induced larval release behaviors in females with late-stage embryos. Ovigerous females with early-stage embryos did not respond to water conditioned with homogenized early- or late-stage embryos. These results suggest that active substances are released by embryos at the time of hatching and induce the stereotypical pumping behaviors of the female that synchronizes larval release. The results support the model that larval release in subtidal crustaceans is controlled by pheromones released from hatching embryos.     

Mitochondrial DNA variation in the European lobster (<Emphasis Type="Italic">Homarus gammarus</Emphasis>) throughout the range

The genetic differentiation of the European lobster (Homarus gammarus) was investigated in 3,283 individuals from 44 population samples throughout its geographical distribution (Norway to Greece) by means of polymerase chain reaction restriction fragment length polymorphism analysis of a 3-kb mitochondrial DNA segment. Ninety composite haplotypes were revealed with the number of haplotypes in each population sample ranging from 4 to 31. Private haplotypes were found at very low frequencies. The global exact test of sample differentiation based on composite haplotype frequencies was statistically significant. F_ST analyses also showed significant heterogeneity among the European lobster population samples (F_ST=0.078, P<0.001). This differentiation was mainly due to the population samples from northern Norway, the Netherlands, and the Mediterranean Sea. These samples differentiated from the rest due to reduced gene diversity rather than to unique haplotypes. The relationships among these samples were illustrated with cluster analyses; four major distinct groups were evident: Mediterranean, northern Norway, Netherlands, and the remaining Atlantic samples. Based on the low degree of differentiation revealed in the European lobster and its limited capacity for dispersal, the most probable hypothesis is that all populations have been established from a common refuge after the end of the last Ice Age, that is, within the past 15,000 years. The results of this study show that mitochondrial DNA is a powerful tool for the determination of the genetic structure among lobster samples, which is important for a proper management policy designed to protect and to cultivate this species.Communicated by O. Kinne, Oldendorf/Luhe