Strombus Gigas Linnaeus Research Articles

Abundancia y distribución de larvas de <i>Strombus gigas</i> (<i>Mesogastropoda: Strombidae</i>) durante el período reproductivo de la especie en el Caribe Mexicano

<span>El caracol rosa (<em>Strombus gigas</em>, Linnaeus, 1758) es una especie de importancia económica en el Mar Caribe, por lo cual, en la década de 1980 representó la segunda pesquería después de la langosta espinosa, razón por la que actualmente se encuentra en estado de sobrepesca. Con el objetivo de determinar la variación en la abundancia de larvas durante la época reproductiva, cuatro localidades del Caribe Mexicano “CM” (México: Puerto Morelos, Sian Ka’an, Mahahual; Belice: San Pedro) fueron muestreadas. Mensualmente, de mayo a octubre del 2008, se realizaron arrastres de plancton en cada localidad empleando una red cónica (300μm). Temperatura (°C), salinidad (ppm) y oxígeno disuelto (mg L-1) fueron registrados para cada sitio. Una densidad media larval de 0.34±0.87 larvas·10m-3 fue registrada entre localidades, con un pico de abundancia entre agosto y septiembre (0.82±1.00 y 0.76±1.68 larvas 10m-3, respectivamente). La densidad larval tuvo una correlación del 60% con la salinidad (r=0.6063, p<0.05). El ANOVA de una vía mostró significancia estadística en tiempo (p<0.05) y espacio (p<0.05), donde Puerto Morelos tuvo los mayores registros durante el estudio (0.54±1.49 larvas 10m-3). Fue registrada una talla media de 332.44±59.66μm. Las tallas variaron significativamente entre localidades (p<0.05), pero no entre meses (p>0.05). El 100% de las larvas capturadas corresponden al estadio I definido por Davis et al (1993), mostrando actividad reproductiva local, de esta manera, se considera que los sitios muestreados en el CM son fuente de larvas para la especie <em>S. gigas</em>.</span>

Queen Conch (Strombus Gigas) in Barbados: Density, Distribution, and Habitat Correlates

Queen conch (Strombus gigas Linnaeus, 1758) populations in Barbados support a small-scale unregulated fishery and government efforts are now underway to improve knowledge about the status of this valuable resource. In the present study, we contribute to these efforts by performing the first rigorous underwater assessment of queen conch on the shallow shelf. Between July and october of two consecutive years, we surveyed a total of 1210 10-m radius circular plots across 65 sites along the south (year 2007) and west (year 2008) coasts at depths of 2-15 m, representing the majority of conch fishing grounds in Barbados. Overall, conch density was low (south: 14.4 conch ha-1; west: 4.3 conch ha-1) and patchy, and most (approximately 90%) conch found were immature. Habitat had a significant effect on conch occurrence and conch shell characteristics over distances of several hundred meters: (1) within sites, the likelihood of finding conch increased with depth; and small, immature conch were found mainly in algal habitat, whereas larger, more mature conch were found mainly on coral habitat; (2) sites that were a few hundred meters apart tended to exhibit similar conch occurrence estimates, suggesting the existence of conch patches over such distances, and this effect was associated with habitat characteristics. Over distances of kilometers, considerable variability in conch occurrence across sites could not be accounted for by habitat alone suggesting an important role of unmeasured factors. Overall, our findings indicate that conch populations on the shallow shelf of Barbados are patchily distributed, severely depressed, and overexploited.

Negative Consequences of Allee Effect are Compounded by Fishing Pressure: Comparison of Queen Conch Reproduction in Fishing Grounds and a Marine Protected Area

Relationships between density of mature adults and mating frequency in queen conch (Strombus gigas Linnaeus, 1758) were observed at three sites in the central Bahamas including one no-take marine reserve (Exuma Cays Land and Sea Park) and two historically important fishing grounds (Berry Islands and Andros Island). No mating was observed in any one count with density < 47 adults ha-1, consistent with an earlier study suggesting a mate-finding Allee effect in queen conch. The unfished site had larger and older conch, and mating at that site increased rapidly with adult density, reaching an asymptote at 12%-14% of the population mating at highest density levels. Logistic modeling showed that a 90% probability of mating occurred at 100 adults ha-1. Mating frequencies increased more slowly with density on the fishing grounds; asymptotic mating frequencies were 6.3% in the Berry Islands and just 2.3% at Andros Island. In contrast to the marine reserve, 90% probability of mating required 350 and 570 adults ha-1 at Andros Island and the Berry Islands, respectively. Higher densities required for successful mating in the fished areas were associated with numerical dominance by small, thick-shelled adults. The small phenotype in adults appears to result from selectivity imposed by fishing pressure, and those adults had low mating frequencies, compounding the density effect on reproduction. Because releases of hatchery-reared queen conch have not been successful, preserving the integrity of spawner density and population structure will be critical for conch conservation.

Cesium chloride gradient centrifugation improves the quality of total RNA preparations from the gastropod Strombus gigas and the coral Montastraea faveolata

RNA preparation from marine invertebrate samples including gastropods and cnidarians is often difficult, producing low-purity RNA samples that perform poorly in downstream procedures. This is increasingly problematic given the current interest in transcriptional studies of marine invertebrates. We report an RNA preparation method using a phenol/chloroform extraction followed by CsCl gradient centrifugation, modified from previous reports and adapted for a modern benchtop ultracentrifuge. This method produced improved spectrophotometric indicators of RNA quality (A 260/A 280 and A 260/A 230) for Strombus gigas Linnaeus, 1758, testis samples and improved RNA integrity number (RIN) for Montastraea faveolata Ellis, 1786, samples, relative to a preparation procedure that relies solely on chemical extraction of RNA. Rate of success in microarray labeling reactions was slightly, but not significantly, improved following CsCl gradient centrifugation. A real-time RT-PCR assay performed using CsCl-prepared samples was efficient (92.5%) and produced consistent and reproducible results.

Discarded queen conch (Strombus gigas) shells as shelter sites for fish

Within the Caribbean millions of queen conch (Strombus gigas Linnaeus) are harvested each year and shells discarded randomly or as middens. Fish use of discarded conch shells was investigated in four different habitat types: sand, seagrass beds, mangrove forests, and coral reefs. The study was carried out in the waters off South Caicos, Turks and Caicos Islands (TCI), between October 2003 and January 2004. The density of discarded shells was greatest near coral reefs; however, the percentage of shells occupied by adult fish was higher in isolated shells on sand and in mangrove habitats. Juvenile fish also showed a preference for sheltering in conch shells relative to other microhabitat types on sandy plains and in mangrove and seagrass habitats. Differences in use of single shells by fish in different habitats were attributed to differences in piscivore abundance and habitat complexity. Although not all isolated shells were occupied by fish, all conch middens deposited by fishermen had fish inhabitants. Examination of fish use of conch middens in three habitat types and conch piles of one, three, and five shells constructed on sand found both fish diversity and abundance increased on conch middens of increasing size. This study suggests that disposal of conch shells as large middens in habitats of low complexity will increase the amount of shelter present and may enhance fish populations in these habitats.

The queen conch fishery on Pedro Bank, Jamaica: discovery, development, management

The history, methods, problems and regulation of fishing of the last remaining large queen conch resource in the world, located on a Jamaican fishing bank, are examined. The fishery activities for the queen conch, Strombus gigas Linnaeus are briefly described with the main activities in the industrial sector which produce the bulk of the harvest, which is exported. There are a few large producers harvesting the single major fishing ground of Pedro Bank, southwest of Kingston. These fishers harvested at least 1500 t annually between 1992 and 1998. Management is by licensing, individual quotas and a close season from July to October. Regulations related to CITES are thought to greatly assist in making licensed harvesters provide catch data to the Fisheries Division. The industrial operators have provided funding to undertake stock assessment studies in 1994 and again in 1997. We highlight the focus on management on a participatory consensual approach with meetings with all players in the industry. The conch fishery is thought to be one of the few areas of the Jamaica fishery where there is close and successful collaboration between fishers and the Fisheries Division. It provides an example of how rapid, precautionary, participatory action can provide an adequate basis for management until more definitive scientific information becomes available. The status of the conch fishery is thought to be sustainable at present, once reductions are made to the annual quota.

Predation by xanthid crabs on early post-settlement gastropods: the role of prey size, prey density, and habitat complexity

Abstract Small predators in marine benthic communities create a hazardous environment for newly settled invertebrates, especially for the smallest individuals. To explore the effects of predation on a newly settled gastropod, queen conch ( Strombus gigas Linnaeus), by a xanthid crab ( Micropanope sp.), prey size, prey density, and habitat complexity were manipulated in five laboratory experiments. All crabs >3.1 mm CW killed all conch 5.0 mm CW, however, killed conch that were >5.0 mm SL, suggesting that conch may reach a size refuge from xanthid crabs at 5 mm SL. Furthermore, when given a choice, crabs (4.8 mm CW) preferred smaller conch (2.0 mm SL) to larger (3.7 mm SL), suggesting that 1 week of additional growth in shell length is advantageous to survivorship. Proportional mortality decreased as conch density increased when crabs were offered conch at seven different densities (two to 96 individuals). Crabs proved to be effective predators regardless of the amount of seagrass structure provided in a microcosm experiment, and could consume two conch in 10 s. The high densities of xanthid crabs that occur in the wild, their effectiveness as predators, and their large appetites point to the important role that small predators may potentially play in structuring the population dynamics of their small prey immediately after settlement.

Role of Chemical Inducers in Larval Metamorphosis of Queen Conch, Strombus gigas Linnaeus: Relationship to Other Marine Invertebrate Systems.

Chemical cues are important in the exogenous and endogenous control of metamorphosis in many marine invertebrate larvae. In the queen conch, Strombus gigas Linnaeus, larval metamorphosis is induced by low molecular weight compounds associated with dominant species of red algae found in conch nursery grounds; these species include the foliose rhodophyte Laurencia poitei (Lamouroux). The responses of conch larvae to the algal-associated cues are dependent on concentration and length of exposure, with the initial events of metamorphosis occurring within 10 min of treatment with an aqueous extract of L. poitei. The free amino acids valine and isoleutine mimic the effects of the natural inducer, and they may bind to and be recognized by the same sites on the larvae as the algal cues. Hydrogen peroxide, vanadate, and {gamma}-aminobutyric acid (GABA), as well as elevated K+ concentrations (i.e., above ambient seawater levels), also induce larval metamorphosis. Acetylsalicylic acid decreases the responses of conch larvae to the algal-associated cues and to the free amino acids, but it has no effect on the induction triggered by hydrogen peroxide. The chemical induction of metamorphosis in conch larvae shares many general features with chemoreception in aquatic invertebrates. The natural inducers of metamorphosis, like the cues involved in olfactory responses in other marine organisms, are of low molecular weight and water soluble. In addition, the results of the experiments with hydrogen peroxide, vanadate, and GABA suggest that second messenger pathways are involved in conch metamorphosis.

Induction of metamorphosis in queen conch, Strombus gigas Linnaeus, larvae by cues associated with red algae from their nursery grounds

Strombus gigas Linnaeus larvae are induced to metamorphose by a selection of substrata from their nursery grounds. The most effective inducers are cues associated with red algae, specifically Laurencia poitei (Lamouroux) Howe and the epiphyte Fosliella sp. (Foslie) found on Thalassia testudinum Köenig detritus. Larvae metamorphose in response to these intact rhodophytes and to aqueous extracts of these species. The cues associated with Laurencia poitei and Fosliella sp. are water soluble and of low molecular size (<1 kDa). They are stable over time (≈ 12 months) and their activity is not altered by heat treatment (10 min of boiling). Although the larvae respond to aqueous extracts of the red algae, their response in the presence of whole plants appears to be contact or near surface dependent. Unlike many invertebrate larvae that are induced to metamorphose by red algal species, Strombus gigas do not respond to the neurotransmitter γ-aminobutyric acid (GABA). The responses of the larvae to the various nursery ground substrata and to cues isolated from their extracts is discussed in relation to temporal and spatial variability in the suitability of seagrass beds as sites for conch metamorphosis.

Determination of calcite: aragonite ratios in mollusc shells by infrared spectra1

Calcium carbonate structure in mollusc shells can be determined by infrared spectroscopy. Infrared analysis is easier and less expensive than most other current methods for macroscopic analysis of the structures in gross calcium carbonate.Shell specimens from 22 river species were shown to be entirely aragonite; the composition of two shells of Strombus gigas Linnaeus was primarily aragonite with a thin surface layer of calcite and that of a fossil oyster shell (Ostrea sp.) was entirely calcite.