Stone Crab Menippe Research Articles

Cryptic diversity in endoparasitic isopods (Bopyroidea: Entoniscidae) from mud crabs (Panopeidae) along the Atlantic coast of North America, with the description of a new genus and new species as revealed by molecular and larval characters: the long and the short of it

AbstractAlthough intertidal crabs from the western Atlantic coast are relatively well studied for some parasite fauna, their parasitic isopods are poorly known. We document two endoparasitic entoniscids (Cancrion carolinusPearse & Walker, 1939 and Cryptocancrion brevibrachiumn. gen., n. sp.) from mud (Brachyura: Panopeidae) and stone (Brachyura: Menippidae) crabs based on molecular and morphological data, including descriptions of their epicaridium larvae. Although these species cannot be distinguished based on adult female characters, molecular data and larval and male morphologies show that two species are present, sometimes sympatrically. The only other species of CancrionGiard & Bonnier, 1887 from the Atlantic coast of North America is Cancrion needleriPearse & Walker, 1939, described from adult specimens parasitizing Dyspanopeus sayi (Smith, 1869) from Prince Edward Island, Canada. Larvae of this species were never described and we consider it a species inquirenda. Cryptocancrion brevibrachiumn. gen., n. sp. is documented to have epicaridium larvae with a “short-armed” morphology (sixth pereopod subequal in length to pereopods 1–5), and the adults parasitize at least three mud crabs: D. sayi, Panopeus herbstiiH. Milne Edwards, 1834, and Rhithropanopeus harrisii (Gould, 1841). By contrast, Cancrion carolinus (originally described from P. herbstii collected in Beaufort, NC, USA) has epicaridium larvae with a “long-armed” morphology (sixth pereopod approximately twice the length of pereopods 1–5) and is found in at least four host species: Eurypanopeus depressus (Smith, 1869), P. herbstii, and R. harrisii and the stone crab Menippe mercenaria (Say, 1818). We describe C. brevibrachiumn. gen., n. sp. and redescribe C. carolinus based on type material and fresh specimens. The cryptic nature of these entoniscids indicates that examination of epicaridium larvae and/or molecular data are needed to properly identify species.

Cyanobacterial blooms alter benthic community structure and parasite prevalence among invertebrates in Florida Bay, USA

Many marine habitats are at risk due to increasing frequency, intensity, and persistence of harmful algal blooms. Repeated cyanobacterial harmful algal blooms (cyanoHABs) in Florida Bay, USA, kill sponges, resulting in reduced filtration and loss of shelter for benthic species. The loss of these key ecosystem functions can impact disease dynamics if fewer pathogens are filtered from the water column (dilution), if shelter loss increases host density in remaining shelters and a directly transmitted disease is present (host regulation), or if shelter loss changes species distributions and foraging patterns (trophic exposure). We show persistent impacts to hard-bottom communities relative to non-impacted communities 2 yr after a significant cyanoHAB. We compared benthic structure, invertebrate epibenthic/infaunal community composition, and parasitism among macroinvertebrates, stone crab Menippe mercenaria, and Caribbean spiny lobster Panulirus argus. On sites degraded by cyanoHABs, we found more, smaller sponges, indicating regrowth. Despite this evidence of recovery, epibenthic/infaunal invertebrate communities were distinct and more diverse on unimpacted sites. Additionally, there were fewer, smaller bivalves on impacted sites. The bivalve Tucetona pectinata, prey for stone crabs, was nearly absent on impacted sites, resulting in decreased prevalence of the apicomplexan gregarine Nematopsis sp., which is trophically transmitted from T. pectinata to M. mercenaria. Panulirus argus virus 1 also appears to be affected by cyanoHABs, as it was absent on impacted sites but present in 26.5% of spiny lobster on unimpacted sites. Impacts remain evident 2 yr after significant cyanoHABs, which does not bode well for these areas considering the frequent reoccurrence of blooms.

Habitat selection by post-settlement juvenile stone crabs (Menippe mercenaria) and predation risk in shallow near-shore habitats

Characterizing habitat selection of the stone crab Menippe mercenaria (Say) provides crucial information for the successful management of this commercially important fishery in Florida. The post-settlement juvenile stage of the stone crab lifecycle faces unique environmental, physiological, and survival challenges prior to becoming sexually mature, yet little is known about their preferred habitat. Our study focuses on post-settlement juvenile (< 1 year, 2–20 mm carapace width) habitat selection between structured artificial seagrass, structured oyster shell rubble, and non-structured sand habitats in the laboratory. Our laboratory experiments provided a unique opportunity to uncouple chemical and environmental cues from the structure of habitats, allowing the study to focus predominantly on the effect of structure on habitat selection. In the controlled laboratory environments, post-settlement juvenile stone crabs preferred structured habitats (artificial seagrass and oyster shell rubble) over non-structured habitats (sand). Survivorship across all trials was high (97%). The laboratory experimental results were complemented with a field predation risk experiment in comparable shallow, near-shore habitats. During the field experiments, predation risk was highest in structured oyster shell rubble and lowest in structured vegetated seagrass. In the seagrass habitat, post-settlement juvenile stone crabs experienced 33% mortality. The sand and oyster shell rubble habitats experienced 69.3% and 83.3% mortality respectively. The data presented here indicate that stone crab juveniles prefer structurally complex habitats and have higher survival in comparable natural habitats. Our results suggest that structurally complex habitats (i.e., seagrass beds) may provide better nurseries for post-settlement juvenile stone crabs and that seagrass restoration or preservation efforts may improve stone crab post-settlement survivorship possibly allowing new recruits to enter the stone crab fishery.

Estimating and Applying Fish and Invertebrate Density and Production Enhancement from Seagrass, Salt Marsh Edge, and Oyster Reef Nursery Habitats in the Gulf of Mexico

Seagrasses, oyster reefs, and salt marshes are critical coastal habitats that support high densities of juvenile fish and invertebrates. Yet which species are enhanced through these nursery habitats, and to what degree, remains largely unquantified. Densities of young-of-year fish and invertebrates in seagrasses, oyster reefs, and salt marsh edges as well as in paired adjacent unstructured habitats of the northern Gulf of Mexico were compiled. Species consistently found at higher densities in the structured habitats were identified, and species-specific growth and mortality models were applied to derive production enhancement estimates arising from this enhanced density. Enhancement levels for fish and invertebrate production were similar for seagrass (1370 [SD 317] g m–2 y–1for 25 enhanced species) and salt marsh edge habitats (1222 [SD 190] g m–2 y–1, 25 spp.), whereas oyster reefs produced ~650 [SD 114] g m–2 y–1(20 spp). This difference was partly due to lower densities of juvenile blue crab (Callinectes sapidus) on oyster reefs, although only oyster reefs enhanced commercially valuable stone crabs (Menippe spp.). The production estimates were applied to Galveston Bay, Texas, and Pensacola Bay, Florida, for species known to recruit consistently in those embayments. These case studies illustrated variability in production enhancement by coastal habitats within the northern Gulf of Mexico. Quantitative estimates of production enhancement within specific embayments can be used to quantify the role of essential fish habitat, inform management decisions, and communicate the value of habitat protection and restoration.

Trophic Ecology of Sheepshead and Stone Crabs at Oil and Gas Platforms in the Northern Gulf of Mexico's Hypoxic Zone

AbstractOil and gas platforms (platforms) may provide important habitat for reef‐associated organisms in the Gulf of Mexico's hypoxic zone. While summer hypoxia typically affects the bottom 3.0 m of the water column, platforms span from the bottom to above the surface and provide hard substrate in oxygenated waters overlaying hypoxia. However, little is known about the effects of hypoxia on organisms living at these platforms. We compared diets of Sheepshead Archosargus probatocephalus and Gulf stone crabs Menippe adina during early and late summer at platforms with mild (shoal platforms) and intense hypoxia (seaward platforms) using a combination of stable isotopes (δ13C and δ15N) and gut contents analyses. We hypothesized that diets at seaward platforms would shift from bottom to platform‐dwelling prey during late summer when hypoxia had fully developed and decimated benthic communities, but no such effect was found. Barnacles (Balanidae) were the most common prey found in Sheepshead guts for all samples collected (64.1% of gut contents). Sheepshead gut contents showed high predation of mantis shrimp (Squillidae; 35.2% of gut contents) soon after the formation of hypoxia at seaward platforms, likely reflecting Sheepshead exploiting benthic prey that were vulnerable because of hypoxia. These findings indicate that hypoxia affected the behavior of mantis shrimp in a way that altered their availability for Sheepshead associated with platforms. Comparisons of Sheepshead and stone crab isotope values (δ13C and δ15N) to those of their potential prey and basal sources suggested a high dependence on barnacles (proxy for water column particulate organic matter) and filamentous algae throughout the summer. However, comparisons of isotope values in early and late summer indicated no apparent effect of hypoxia. High contributions of barnacles to Sheepshead diet showed that platform‐dwelling prey were an important resource for Sheepshead.

Increasing the Selectivity of the Stone Crab Menippe mercenaria Trap by the Addition of a Cull Ring

AbstractThe fishery for stone crab Menippe mercenaria in Florida is dominated by plastic traps that do not require a cull ring or device that limits retention of prerecruits and bycatch. An experiment was conducted to determine what size of cull ring would reduce the catch of prerecruit stone crabs and bycatch while maintaining legal catch. Catch compositions of crabs from unmodified plastic commercial stone crab traps and traps fitted with a 54.0‐, 55.6‐, or 57.2‐mm cull ring were compared in the stone crab fishery across Florida's west coast. Traps outfitted with cull rings retained bigger crabs, less bycatch, and fewer prerecruit stone crabs and, for most cull ring sizes tested, yielded the same number of legal‐size claws. Retention of prerecruit crabs in traps with cull rings varied among regions because of the sexual dimorphism in carapace length (males, 58.2 mm; females, 64.6 mm) observed when an original crusher claw has reached legal size (&gt;70 mm). We recommend that a minimum size cull ring of 55.6‐mm (23∕16 in) be used in stone crab traps fished in state and federal waters off Florida.

Assessment of Maturity in the Eastern Gulf of Mexico Florida Stone Crab Menippe mercenaria Fishery

AbstractThe Florida stone crab Menippe mercenaria supports one of Florida's most valuable commercial fisheries. Sustained fishing pressure and overexploitation, despite negative trends in landings, have facilitated the need to transition from stock assessments based on effort and landings toward more sophisticated methods. This requires accurate knowledge of life history parameters, such as size at sexual maturity. The physiological, behavioral, and functional maturity of female Florida stone crabs and the physiological maturity of male crabs were assessed in individuals collected throughout the geographically fished range of the population between 2013 and 2014. Morphological maturity of both sexes was assessed in individuals collected from the same locations in 2005–2016. Histology was used to determine oocyte maturity, presence of spermatophores, and presence of postovulatory follicles in females and the production of spermatophores (present in the anterior vas deferens) in males. Decision tree analysis determined that 50% of females were mature at 43 mm carapace width (CW) based on an indicator of physiological and behavioral sexual maturity. In males, physiological maturity occurred at a CW of 34.75 mm. Sexual maturity estimated using morphological maturity occurred at 66.3 mm CW in females and 63.1 mm CW in males. Differences in estimated size at sexual maturity between morphological maturity and physiological, behavioral, and functional maturity indicate that the relative growth of body parts is not reliable for estimating sexual maturity in Florida stone crabs. Smaller females may be contributing more to the spawning population than had been previously estimated. Large, morphometrically mature males may be more successful in mating encounters, but during times of flux in population size structure (i.e., fewer large males), morphologically immature but physiologically mature males have increased mating opportunities. Results indicate that male and female Florida stone crabs can contribute to the reproductive population multiple times before they become vulnerable to the fishery.

Erratum to: Hepatopancreatic cells of a stone crab Menippe frontalis from Perú: separation, viability study, and evaluation of lipoperoxidation against cadmium contamination.

Crustaceans are frequently used as bioindicators, and changes in their metabolism at the hepatopancreas (HP) level are often followed in these studies. The HP is the site of digestion, absorption, nutrient storage, and toxic metal detoxification, enabling crabs to survive in metal contaminated regions. Cellular damage and high lipid peroxidation (LPO) levels have been found in crab populations under high cadmium (Cd) concentrations. The aim of this work was to separate and characterize the HP cells of the stone crab Menippe frontalis from the Pacific Ocean, Peru (5° 5′ 21″ S–81° 6′ 51″ W) and to measure the cellular viability and LPO after exposure to the non-essential metal Cd. The HP cells were dissociated by magnetic stirring, with posterior separation by sucrose gradient at concentrations of 10, 20, 30, and 40%. We found the same cell types that were described for other species (e.g., Ucides cordatus, Atlantic Ocean, Brazil). High cellular viability against 1 mmol L−1 of Cd was observed for resorptive (R) cells in 20% sucrose layer (88 ± 8%, *P < 0.05, ANOVA), and blister (B) cells in the 40% sucrose layers (92 ± 7%, *P < 0.05, ANOVA). Cd (1 mmol L−1) caused an increase in LPO levels, suggesting that crabs from polluted areas can be affected by toxic metals, generating a physiological stress. The gradient sucrose methodology can be used for different species and results in a similar separation, viability, and cellular identification. The results are a starting point for toxic metal studies for species distributed across different geographic coordinates.

Hepatopancreatic cells of a stone crab Menippe frontalis from Perú: separation, viability study, and evaluation of lipoperoxidation against cadmium contamination

Crustaceans are frequently used as bioindicators, and changes in their metabolism at the hepatopancreas (HP) level are often followed in these studies. The HP is the site of digestion, absorption, nutrient storage, and toxic metal detoxification, enabling crabs to survive in metal contaminated regions. Cellular damage and high lipid peroxidation (LPO) levels have been found in crab populations under high cadmium (Cd) concentrations. The aim of this work was to separate and characterize the HP cells of the stone crab Menippe frontalis from the Pacific Ocean, Perú (5° 5' 21″ S-81° 6' 51″ W) and to measure the cellular viability and LPO after exposure to the non-essential metal Cd. The HP cells were dissociated by magnetic stirring, with posterior separation by sucrose gradient at concentrations of 10, 20, 30, and 40%. We found the same cell types that were described for other species (e.g., Ucides cordatus, Atlantic Ocean, Brazil). High cellular viability against 1mmolL-1 of Cd was observed for resorptive (R) cells in 20% sucrose layer (88±8%, *P<0.05, ANOVA), and blister (B) cells in the 40% sucrose layers (92±7%, *P<0.05, ANOVA). Cd (1mmolL-1) caused an increase in LPO levels, suggesting that crabs from polluted areas can be affected by toxic metals, generating a physiological stress. The gradient sucrose methodology can be used for different species and results in a similar separation, viability, and cellular identification. The results are a starting point for toxic metal studies for species distributed across different geographic coordinates.

A field assessment of claw removal impacts on the movement and survival of stone crabs Menippe spp.

Claw-only crab fisheries are often marketed as renewable because crabs are returned to the water after declawing to regenerate claws and re-enter the fishery. The challenge of managing a claw-only fishery for stone crabs (Menippe spp.) is compounded by varying regulations throughout their range that include the number of claws harvested from a crab and use of a seasonal closure to protect spawning females. We conducted mark-recapture studies to examine crab responses to claw removal in the field and compared claw handedness and type (crusher, intermediate, pincer) in a wild population to commercial landings to examine compliance with fishery regulations in a one-claw fishery with no seasonal closure. Declawed crabs were recaptured less frequently than control crabs, particularly if claw removal created large wounds. Control crabs were more commonly recaptured within one month of tagging and declawed crabs recaptured one to three months after tagging, suggesting that declawed crabs were less mobile or less motivated to feed initially after claws were harvested and that, over time, intact crabs left the study area. Crabs with fishery-related, regenerated claws comprised 3% of crabs with legal claws. Claw type ratios in a limited assessment of the commercial catch most closely reflected expected ratios consistent with a two-claw fishery, indicating that voluntary adherence to current one-claw fishing regulations is not universal. In fisheries needing better protection of spawning stock, a seasonal closure on fishing could be instituted to ensure better protection of spawning.

Anatomy of a cline: dissecting anti‐predatory adaptations in a marine gastropod along the U.S. Atlantic coast

The scope of anti‐predatory adaptation is expected to be greater in warm than in cold environments. High temperatures lower the costs associated with the production and maintenance of energetically expensive traits and enable ecological interactions to intensify. We tested this hypothesis by characterizing the expression of anti‐predatory morphology within a marine gastropod species (the knobbed whelk Busycon carica) over a large (&gt; 1400 km) geographic area that spans more than 10°C annual temperature variation. We also conducted experimental predation studies with a powerful durophagous predator, the stone crab Menippe, to verify the anti‐predatory advantages of a heavily ornamented shell morphology (e.g. increased thickness, pronounced spines), and we used repair scar data to assess clinal variation in selective pressure from predators. We predicted that repair scar rates would be greatest in warm southernmost latitudes, and that expression of energetically costly anti‐predatory morphology would peak in concert with elevated predation pressures.Experiments confirmed that whelks with energetically costly, heavily ornamented shells had higher survivorship rates than those with weakly ornamented shells. As predicted, we also found that the expression of anti‐predatory traits was greatest in the southern part of B. carica's range. After standardizing shells for size, shape, and exposure time to enemies, repair scar rates also peaked to the south. Taken together, these results suggest that the expression of anti‐predatory traits along the geographic cline is governed by the interaction of two selective factors: temperature and predation, with the former acting as the ultimate control on the scope of adaptation both by escalating predation pressure in the southern part of B. carica's range and by physically limiting (to the north) and facilitating (to the south) the production of anti‐predatory traits. Feedbacks between temperature and predation thus causally interact to enable and drive, respectively, the observed geographic cline in energy‐intensive anti‐predatory shell traits.

Competition with stone crabs drives juvenile spiny lobster abundance and distribution.

Interspecific competition is assumed to have a strong influence on the population dynamics of competing species, but is not easily demonstrated for mobile species in the wild. In the Florida Keys (USA), anecdotal observations have long pointed to an inverse relationship in abundance of two large decapod crustaceans found co-occurring in hard-bottom habitat, the stone crab Menippe mercenaria and the Caribbean spiny lobster Panulirus argus. We used them to explicitly test whether competition for a renewable resource (shelter) can drive the abundance and distribution of the inferior competitor. We first explored this relationship in shelter competition mesocosm experiments to determine the competitively dominant species. Results showed that stone crabs are clearly the dominant competitors regardless of the number of lobsters present, the presence of co-sheltering species such as the spider crab, Damithrax spinosissimus, or the order of introduction of competitors into the mesocosm. We also found that lobsters use chemical cues from stone crabs to detect and avoid them. We then tested the ramifications of this competitive dominance in the field by manipulating stone crab abundance and then tracking the abundance and distribution of spiny lobsters through time. Increased stone crab abundance immediately resulted in decreased lobster abundance and increased aggregation. The opposite occurred on sites where stone crabs were removed. When we stopped removing stone crabs from these sites, they soon returned and lobster abundance decreased. This study explicitly demonstrated that interspecific competition can drive population dynamics between these species, and ultimately, community composition in these shallow water habitats.

Habitat-related phenotypic variation in adult Western Atlantic stone crabs (Menippe mercenaria Say, 1818) (Decapoda: Brachyura)

Habitat partitioning by different life stages or phenotypes in a heterogeneous marine environment could confer fitness advantages. Two distinct phenotypes of the Western Atlantic stone crab ( Menippe mercenaria Say, 1818), spotted and brown, are easily distinguishable and occupy different habitats in allopatry. Intermediate phenotypes occur in two geographic zones, the northeastern Gulf of Mexico and the southern Atlantic coast of the USA from South Carolina to northern Florida. We examined stone crab phenotypic variation and demography in two adjacent rivers near Charleston, SC, USA, the Kiawah and Stono rivers. The intertidal oyster habitat (quantified as reef per meter shoreline) in the Kiawah River is more than twice as dense as the oyster habitat in the Stono River. Significantly more brown than spotted crabs, a higher proportion of males, and larger individuals were collected in the Kiawah River in a year-long trapping study. Brown coloration for stone crabs on oyster reefs could confer a fitness advantage if these crabs are more cryptic than spotted crabs. The timing of ovigery and egg development did not differ between crabs in the Kiawah and Stono rivers or between brown and spotted stone crabs regardless of capture location. Males exhibited greater cheliped wear than females, but wear was unrelated to proximity to an oyster-reef habitat. Demographic patterns related to habitat use presented here are consistent with habitat use in the northeastern Gulf of Mexico zone of phenotypic variation. The differences in stone crab demographics in these two coastal rivers in South Carolina indicate that further studies are needed to determine whether this habitat-related phenotypic variation is representative of stone crab distributions throughout the South Atlantic Bight.

The Consequences of Claw Removal on Stone Crabs Menippe spp. and the Ecological and Fishery Implications

AbstractThe practice of claw removal in the fishery for stone crab Menippe spp. can affect fished populations in an atypical way because harvested individuals are not necessarily killed. In all stone crab fisheries, crabs are returned to the water after their claws are harvested with the expectation that claws may be regenerated, thus “renewing” the fishery. The number of legal‐sized claws that can be removed from an individual differs (with local regulations) throughout the stone crabs' range. We examined the direct and indirect consequences of removing one and two claws by monitoring mortality and prey consumption in the short term (14 d) and mortality and growth over the long term (11 months). Claw removal induced mortality within days when wound widths were greater than 7 mm, regardless of the number of claws removed. Wound widths created by autotomy were similar to those created by a clean, forced break along the natural fracture plane. These results suggest that direct mortality following claw removal may be low in a two‐claw fishery for stone crabs that do not incur large wounds; however, indirect effects that result from altered feeding abilities may be substantial. Stone crabs with one claw removed (the crusher) consumed fewer bivalves than control (intact) crabs, whereas stone crabs with two claws removed did not consume any bivalves but ate fish flesh. Consequently, bivalves, an important prey resource throughout the stone crabs' geographical range, are eliminated from a clawless crab's diet until its claws are regenerated. No stone crabs regenerated a legal‐sized claw on the first molt after claw removal, and no stone crabs larger than 104 mm carapace width molted within 11 months. Thus, the long intermolt duration of legal‐sized stone crabs and the reduced prey consumption for stone crabs that lost claws indicate that the return to the fishery of previously harvested stone crabs is probably an uncommon occurrence.Received December 17, 2014; accepted June 15, 2015

Predator-induced edge-drilling behaviour of Chicoreus dilectus (Gastropoda: Muricidae)

The duration of drilling attacks on bivalve prey by muricid gastropods is largely a function of shell thickness at the drilling site selected by the predator. Attacks initiated at the thin valve edges (edge drilling) take significantly less time than drilling through the thicker shell wall (wall drilling). Here, we demonstrate experimentally that the muricid Chicoreus dilectus (Adams, 1885) employs the edge-drilling mode of attack nearly three times more often than wall drilling when exposed to chemical cues from the shell-crushing stone crab Menippe mercenaria, one of its natural enemies, than when foraging in isolation. Chicoreus dilectus is also known to edge drill more frequently in the presence of conspecific snails, which represent competitors for food as well as potential cannibals. Together, these findings suggest that edge drilling by C. dilectus should be considered as a general behavioural response to enemies instead of a specialized response to conspecific enemies. Although all snails exposed to stone crabs expressed the edge-drilling behaviour at least once, wall drilling was still more commonly used by each of these snails, suggesting that there are constraints on behavioural plasticity in the expression of edge drilling.

Did shell-crushing crabs trigger an escalatory arms race in the aftermath of a Late Neogene regional mass extinction event? An experimental test

A regional mass extinction event in the late Neogene western Atlantic is widely thought to have generated evolutionary opportunities for survivors, including enemy-related adaptation (escalation). The Strombus alatus species complex is one potential example of this phenomenon. Strombid gastropods are abundant in the Plio-Pleistocene fossil record and Recent in subtropical Florida, and the percentage of these shells bearing a row of short spines on the last whorl increased from nearly zero to almost 100% over this time. As shell ornamentation is one of the most frequently cited defenses against both peeling and crushing predators, we exposed live spined and spineless S. alatus to the stone crab Menippe, one of its natural enemies and the predator responsible for shells scars commonly found on modern and fossil S. alatus shells, to test whether the increase in expression of shell spines in this species complex is consistent with an adaptive or induced response to intensifying predation pressure from durophagous crabs. We also utilize random variation in prey shell length, diameter, and lip thickness to quantify the relative importance of additional shell parameters thought to deter attacks from durophagous crabs. The central finding of this study is that neither thicker shell lips nor the modern configuration of spines determine whether S. alatus will be more likely to survive Menippe attacks or have less severe shell damage. In our experiments, the only shell trait associated with reduced damage and increased probability of survival was whorl diameter. We conclude that menippid crabs, at least those crabs within the range of large, adult sizes used in this experiment, probably did not play a primary role in the changing expression of Strombus spines on the last whorl in the post-Pliocene of Florida or elsewhere in tropical America. This conclusion is consistent with the position that faunal-scale increases in expression of defensive shell traits in the post-Pliocene of Florida were driven more by differential extinction of lightly armored species than escalatory responses to increasing crab predation pressure. However this conclusion is tentative and additional data are needed to explore this hypothesis fully.

Characterization of the Bycatch in the Commercial Blue Crab Pot Fishery in Georgia, November 2003– December 2006

AbstractBycatch studies have been conducted in many fisheries in Georgia, but none has focused on the commercial pot fishery for blue crab Callinectes sapidus. The purpose of this study was to identify abundance and seasonality of finfish and invertebrate bycatch species in the commercial blue crab fishery in Georgia. Between November 2003 and December 2006, observers accompanied volunteer commercial blue crab fishers randomly selected from a list of willing participants. A total of 91 trips were observed, with 5,707 commercial blue crab pots sampled. Soak times, or fishing effort, ranged from 24 to 168 h, averaging 55.8 h/trap for each trip. The number of traps sampled each trip ranged from 5 to 163, with a mean of 62.7 traps per trip. We collected 306 finfish and 4,972 invertebrates in this study period. The most numerous finfish were Southern Flounder Paralichthys lethostigma (n = 52), Atlantic Spadefish Chaetodipterus faber (n = 50), Oyster Toadfish Opsanus tau (n = 50), Hardhead Catfish Ariopsis felis (n = 46), and Southern Kingfish Menticirrhus americanus (n = 37). The most numerous invertebrates species were hermit crabs Pagurus spp. (n = 2,341), spider crabs Libinia spp. (n = 532), stone crabs Menippe mercenaria (n = 438), channeled whelk Busycon canaliculatum (n = 1,570), and knobbed whelk Busycon carica (n = 25). The similarity of bycatch by season was compared using a Morisita similarity index, and results were that Southern Flounder, Atlantic Spadefish, Oyster Toadfish, spider crabs, channeled whelk, and stone crabs varied seasonally. Of all species observed, we conclude that channeled whelk populations may be impacted by this fishery.Received October 22, 2012; accepted June 17, 2013

Shell repair as a reliable indicator of bivalve predation by shell-wedging gastropods in the fossil record

Shells of the tulip snail Fasciolaria (Cinctura) lilium hunteria often exhibit small (< 1 cm), scallop-shaped repair scars positioned at the convex edge of the apertural lip. When attacking bivalves, Fasciolaria inserts its shell between the prey's valves, wedging them apart, which may cause the attacking predator's apertural lip to break. Here, we evaluate whether wedging behavior causes repair scars that are distinct from breakage due to predators such as crabs. Feeding experiments, in which Fasciolaria were offered the oyster Crassostrea virginica, confirmed a wedging-induced origin for the conspicuous band of scars located at the convex apertural lip. These scars occurred regardless of whether the attacks by Fasciolaria on oysters were successful, and they are readily differentiated from scars induced by predatory crabs. Fasciolaria offered to the stone crab Menippe mercenaria and the blue crab Callinectes sapidus suffered extensive damage (embayed breaks typically with a jagged outline). Fasciolaria collected from four localities in southeastern North Carolina exhibited high frequencies of wedging-induced shell repairs, with nearly all shells experiencing evidence of feeding-induced injury. The ability to identify wedging predation traces in the fossil record holds promise for addressing a host of questions related to the role of the behavior in evolution.

Prey size selection and bottom type influence multiple predator effects in a crab–bivalve system

Consumption by multiple conspecific or interspecific predators on shared prey is not always predicted when data from isolated predators are combined. Predator interactions can result in non-independent predator effects on prey, and may be influenced by prey size selection and bottom type. We examined stone crab Menippe mercenaria and blue crab Callinectes sapidus predation of hard clams Mercenaria mercenaria. Interactions between these predators may become common in mid-Atlantic estuaries as stone crab abundance increases with a poleward range shift driven by climate change. Crabs in isolation, in conspecific pairs and in the interspecific pair were offered clams in 5 size classes simultaneously (10–60 mm shell length [SL]) or 1 size class (10–20 mm SL). Trials were on sand and hard bottom. On sand, all predator pairs had independent effects on prey, regardless of the presence or absence of multiple prey sizes. On hard bottom, when multiple prey sizes were present, blue crab conspecific and the interspecific pairs consumed less than predicted from isolated crabs. Strong selection of small clams by blue crabs led to conspecific interactions that reduced foraging compared to isolated crabs. Because stone crabs consumed all clam sizes, behaviours other than prey size selection caused the non-independent effect on prey by the interspecific pair. When multiple prey sizes were absent on hard bottom, most predator pairs had independent effects on prey. Thus, an expected poleward range shift of stone crabs may not increase interactions with blue crabs when foraging on sand. However, on hard bottom, increased predator interactions could reduce overall predation risk for prey, especially when consuming multiple prey sizes. In a climate-changed midAtlantic estuary, stone crabs will consume a wide range of clam sizes, and the size refuge large clams usually have from blue crab predation will be lost.

Growth of Juvenile Stone Crabs, Menippe mercenaria, Reared in the Laboratory

Abstract In this study we determined the rate of growth of juvenile Florida stone crabs (Menippe mercenaria Say, 1818) reared in the laboratory. We monitored carapace width and intermolt duration through the first 12 juvenile molts. Because all experimental crabs had been reared from eggs in the laboratory, we knew the exact age and molt dates for each individual. Mean carapace width of 1st stage juveniles was 2.0 ± 0.2 mm. Juveniles reached the 13th juvenile stage (15.9 ± 2.1 mm) in a mean of 297.6 ± 32.7 d. The rate of growth in carapace width fit a linear model and was similar in pattern to that reported for juveniles of other brachyuran species.