Sand Crab Research Articles

Molecular Phylogenetics of Mole Crabs (Hippidae: Emerita)

Mole crabs of the genus Emerita (Family Hippidae) inhabit many of the temperate and tropical sandy beaches of the world. The nine described species of this genus are rarely sympatric, and most are endemic to broad biogeographic regions. The phylogenetic relationships among the species have not yet been investigated. Based on presumed morphological synapomorphies, it has been suggested that the species inhabiting the New World constitute a monophyletic group, as do the species inhabiting the Old World. The relationships within the New World species were previously studied using sequence data from Cytochrome Oxidase I and 16S rRNA mitochondrial genes; the results strongly suggested that one of the species, Emerita analoga, was very divergent from the other taxa examined. This observation prompted uncertainty about monophyly of the New World species. The goal of the present study was to elucidate the relationships among the species within the genus Emerita. Partial sequences for the mitochondrial COI and 16S rRNA genes for all nine species of the genus (and several outgroups) were examined. Phylogenetic analyses suggest that E. analoga is closer to the Old World taxa than to the other New World species; thus the New World Emerita species do not constitute a monophyletic group.

Anatomy and Biology of Mysella pedroana (Mollusca: Bivalvia: Galeommatoidea), and its Commensal Relationship with Blepharipoda occidentalis (Crustacea: Anomura: Albuneidae)

The distribution, prevalence and abundance of the galeommatoidean bivalve, Mysella pedroana, on the spiny sand crab, Blepharipoda occidentalis, were studied based on newly collected material and museum specimens. Although sometimes free-living, M. pedroana occurs most often inside the branchial chamber of B. occidentalis, and appears to be a commensal associate. It is not known from outside the range of the host along the Pacific coast of California and Mexico. Approximately 60% of hosts examined contained typically 1—2 M. pedroana in their branchial chambers, but many more (maximum 22) were sometimes found. M. pedroana showed no preference for host sex, size, or branchial chamber (left vs. right) and were not more abundant in any part of the distributional range. No M. pedroana were found on specimens of the five taxa mostly closely related to B. occidentalis. M. pedroana is re-described and its systematic position discussed with special reference to difficulties of generic placement. Although the presence of the bivalves causes physical deterioration to the hosts' gill filaments, available evidence indicates that the relationship is commensal, rather than parasitic.

Synchronisation of Molting and Oogenic Cycles in a Continuously Breeding Population of the Sand Crab Emerita Asiatica on the Madras Coast, South India

Synchronisation of Molting and Oogenic Cycles in a Continuously Breeding Population of the Sand Crab Emerita Asiatica on the Madras Coast, South India

Larval dynamics of the sand crab, Emerita analoga, off the central Oregon coast during a strong El Nino period

Populations of the sand crab, Emerita analoga, are well established on the California coast. However, populations in Oregon occur sporadically and appear to be restocked by larvae drifting north from California. Due to increased northward transport in winter during El Niño events, we would expect that larval recruitment to northern populations should be higher during these periods. This hypothesis was tested by comparing larval abundances between non-El Niño and El Niño years, 1997 and 1998, respectively. In 1997, larval abundances and seasonality were similar to historical data from 1969–71. First zoeal (Z1) stage larvae were present during these summers, but in low numbers, indicating that E.analoga spawned off the coast of Oregon. In 1998, strong larval recruitment from the south occurred, demonstrated by a large number of fifth zoeal stage (Z5) larvae collected off Oregon in April and May. The large numbers of Z1 found in summer 1998 indicate that the Z5, which arrived from California earlier that spring, successfully recruited to adulthood and reproduced. These data indicate that Oregon E.analoga populations are probably dependent on larvae travelling from California in the Davidson Current. It follows that this species could be used as an indicator of coastal current fluctuations such as those seen during El Niño events.

Occurrence of vertebrate steroids, estradiol 17β and progesterone in the reproducing females of the mud crab Scylla serrata

In crustaceans, vitellogenesis is known to be controlled by eyestalk neuropeptides, biogenic amines, ecdysteroids and a juvenile hormone-like compound, methyl farnesoate. In recent years, the occurrence of vertebrate steroid hormones, estradiol 17β (E 2) and progesterone (PG) has also been reported in a few decapods, although their precise role in female reproduction is yet to be determined. The levels of E 2 and PG in the ovary, hepatopancreas and the hemolymph of the red mud crab, Scylla serrata were analyzed in different vitellogenic stages in order to establish a correlation between hormone profile and stages of vitellogenesis. It was observed that the levels of both the steroids increased steeply in the tissues at the onset of vitellogenesis (vitellogenic stage I). Maximum levels of estradiol were present in the hepatopancreas whereas the highest concentration of progesterone was seen in the ovary, suggesting dichotomous roles for these hormones in vitellogenesis. Furthermore, levels of these hormones were estimated in different embryonic stages of the eggs of the sand crab Emerita asiatica and mud crab S. serrata. Their levels fluctuated, following a definite pattern in the different stages, suggesting a possible functional role as morphogenetic hormones. This study, in addition, also reports the presence of E 2 and PG on lipovitellin purified from ovary and eggs as well as vitellogenin purified from the hemolymph implicating a role for these lipoproteins as steroid carriers.

Testing the swash exclusion hypothesis in sandy beach populations: the mole crab Emerita brasiliensis in Uruguay

Exposed marine beaches are physically rigorous habitats in which macrofauna commu- nity patterns have been well correlated with physical factors such as grain size, beach slope and wave/swash processes. In this context, the swash exclusion hypothesis (SEH) gained wide accept- ability in explaining the control of species abundance and diversity of the sandy beach macrofauna by swash climate, determined by wave height and beach face slope. This hypothesis predicts a con- sistent increase in species richness, abundance and biomass from reflective to dissipative conditions. However, predictions of the SEH have not been adequately tested at a population level. Here, demo- graphic and life history characteristics of the intertidal mole crab Emerita brasiliensis were compared between populations of 2 microtidal exposed sandy beaches with contrasting morphodynamics dur- ing 22 consecutive months. The major prediction of the paradigm does not hold for the mole crab: total abundance, as well as that of males, females, males with spermatophores and megalops did not differ between beaches. Moreover, the reflective beach population presented higher male growth rates in size and lower natural mortality. Other population processes and life history traits gave support for the SEH: the dissipative beach population presented (1) higher abundance of ovigerous females, female growth rates, fecundity, egg production potential, size at maturity, as well as weight at size; and (2) lower female mortality and burrowing rates (for both sexes). The SEH seems to be particularly useful in explaining female somatic growth and reproductive features, which could be related to a major amount of food availability in dissipative beaches. However, other competing, but not exclusive, hypotheses are needed to explain variations in population abundance and other pro- cesses such as male growth and survivorship. The empirical evidence from several recent studies on the Uruguayan coast showed that sandy beach populations that co-occur in contrasting environments are less sensitive to variations in beach morphodynamics, which should not be considered the primary factor affecting the abundance and some life history traits. The importance of alternative population regulation processes and mechanisms are stressed.

Unusual larval abundance of Scyllarides nodifer and Albunea sp. during an intrusion of low‐salinity Mississippi flood water in the Florida Keys in September 1993: Insight into larval transport from upstream

A massive intrusion of low‐salinity water (salinity = 31–35) from the Mississippi River to the Florida Keys in September 1993 coincided with an unusual abundance of the phyllosoma larvae (stages IV–VII) of a slipper lobster, Scyllarides nodifer, and the zoeae (stages III–V) of a sand crab, Albunea sp. These species are abundant in the northeastern Gulf of Mexico, but their adults and early stage larvae are not common in the Florida Keys. The influx of S. nodifer and Albunea sp. larvae into the Florida Keys is believed to have originated on the northeastern Gulf of Mexico shelf. The southward transport of the larvae within a low‐salinity plume from the Mississippi River was apparently caused by anomalous eastward winds moving shelf waters into the Loop Current, which had extended to within ∼170 km of the Mississippi Delta. During normal‐salinity conditions (salinity > 36) the spiny lobster Panulirus argus is the most numerous species of phyllosoma larvae in the coastal waters of the Florida Keys. A wide range of stages of P. argus is present year‐round in the Florida Keys, suggesting multiple larval sources upstream possibly in the Yucatan Peninsula and the Caribbean. In contrast, the source of S. nodifer and Albunea sp. recruits for the Florida Keys may lie principally in the northeastern gulf. The recruitment success of larvae of gulf origin to the Florida Keys may depend partly on the coincidence of specific wind and Loop Current transport conditions with an availability of larvae for expatriation at the source.

Carbohydrate components of lipovitellin of the sand crab Emerita asiatica.

Lipovitellin II (Lv II), the major yolk protein of the anomuran crab Emerita asiatica, was purified using heparin-sepharose affinity column chromatography. The purified Lv II was a glycoprotein as it was stainable with periodic acid-Schiff's reagent. Quantitative analysis of sugars showed the presence of fucose, mannose, galactosamine, N-linked oligosaccharides, as well as O-linked oligosaccharides containing N-acetyl hexosamine as the terminal residue. The amount of N-linked oligosaccharides is higher than that of the O-linked oligosaccharides. Biogel P-4 column chromatographic separation of the radiolabeled oligosaccharides of Lv II showed the presence of five different O-linked oligosaccharides and four different N-linked oligosaccharide species. HPTLC separation of the neoglycolipids prepared from the O-linked oligosaccharides also showed the presence of five different O-linked oligosaccharide species. N-linked oligosaccharides contain significant quantities of mannose. Unisil column chromatographic purification in conjunction with HPTLC separation revealed three neutral glycolipid species such as monoglycosylceramide, diglycosylceramide, and triglycosylceramide in the Lv II. The functional significance of these carbohydrate components of the major yolk protein during embryogenesis of the sand crab is discussed.

The Gender of Grace: Impotence, Servitude, and Manliness in the Fifth-Century West

This essay attempts to stage an encounter between post-Foucauldian approaches to masculinity in the ancient world on the one hand, and the reading of Augustine of Hippo's idea of Original Sin as a disjunction of the will, put forward in Robert Markus's Saeculum: History and Society in the Theology of Saint Augustine. Emphasis is placed on Book XIV of the City of God, where Augustine emblematises the result of Original Sin not –pace Foucault – through an image of irrepressible lust, but rather through that of the impotent male, humiliated by his inability to embody his desire.

Longshore patterns of distribution of macroinfauna on a Uruguayan sandy beach:an analysis at different spatial scales and of their potential causes

Spatial distribution of macrofaunaalong the longshore axis was studied on an exposed (Uruguayan) sandybeach in order to assess (1) its dependence on beach topography,and (2) the validity to extrapolate local distribution patterns to largerspatial scales (i.e. km). The distribution of the isopods Excirolanaarmata and Excirolana braziliensis, the sand crab Emeritabrasiliensis and several species of insects was analyzed at 3spatial scales. A grid sampling was used at small scale(intersample distance: 4 m; extension sampled: 30 to 40 m), atransect design at meso scale (intersample distance 4 to 20 m;extension sampled: 100 to 120 m), and random sampling at largescale (intersample distance: 100 m; extension sampled: 3000 m).Spatial distribution at small and meso scales were describedusing autocorrelation functions, and tested for effects oftopography at meso and large scales using ANOVA and pairedt-tests. We found that at small and meso scales the distribution ofE. armata and E. brasiliensis was patchy and affected by cusptopography. At large scales, the effect of cusp topography wasrestricted to E. armata. E. armata and E. brasiliensis showedlarge-scale aggregations, and E. braziliensis and insects showedlarge-scale patchiness associated with longshore variability insediment water content and dune characteristics. We conclude thatcusp topography affects longshore distribution patterns, and that itis not valid to extrapolate local longshore distribution to largerscales for every species. We suggest that different processesaffecting spatial distribution must be operating at different scales.At small scales, patterns of distribution may be affected by swashtransport of food and/or organisms, involving factors such as beachtopography, swash and animal movements. At larger scales, inaddition to larval and food supply, sediment transport by the windwould play an important role. Spatial patterns of sand transport bythe wind may be affected by longshore changes in vegetationcover on the dune field. We further suggest that there may be a linkbetween the beach and the dune habitats operating at large spatialscales.

Incidence of highly genetically diversified Vibrio parahaemolyticus in seafood imported from Asian countries

Vibrio parahaemolyticus is an important pathogen of humans and aquacultured animals, especially in Asian countries. In this study, we examined 686 samples of seafood imported from Hong Kong, Indonesia, Thailand and Vietnam for V. parahaemolyticus. V. parahaemolyticus was recovered from 315 (45.9%) samples. The incidence of V. parahaemolyticus in products from Hong Kong and Thailand was markedly higher than the incidence in products from Indonesia and Vietnam. The incidence rates in shrimp, crab, snail, lobster, sand crab, fish and crawfish were 75.8, 73.3, 44.3, 44.1, 32.5, 29.3 and 21.1%, respectively. None of the isolates possessed the hemolysin genes ( tdh, trh). The chromosomal DNA of 121 randomly selected imported isolates and three local environmental strains was digested with SfiI and analyzed by pulsed-field gel electrophoresis (PFGE). These isolates were then grouped into 96 different but mostly unique PFGE patterns. After hierarchical cluster analysis, these patterns could be arbitrarily grouped into twenty-two PFGE types (type A to V). A wide range of PFGE types were identified in isolates from different origin. Moreover, the PFGE types were not specifically associated with the origin or kind of seafood. These results reveal the high genetic diversity in V. parahaemolyticus isolated from seafood.

Effects of Freshwater Discharge in Sandy Beach Populations: The Mole Crab Emerita brasiliensis in Uruguay

Sandy beaches are ecosystems which are heavily affected by human activities. An example of this is freshwater discharges, which are known to change salinity, temperature and nutrient regimes and degrade nearshore environments. However, the effects of this kind of disturbance on sandy beach fauna have been little studied. This paper reports the spatial effects of a man-made freshwater canal discharge on the population structure, abundance and reproductive characteristics of the sandy beach mole crab Emerita brasiliensis. Along the 22km of sandy beach sampled, the mole crab showed a marked longshore variability in population structure and abundance. Abundance of different population components (juveniles, males, females and ovigerous females) significantly decreased towards the canal. Population structure by sex and size, individual weight, fecundity and female maturity patterns at size also displayed a non-linear response to the distance from the freshwater discharge. Only the size structure of males did not follow this pattern. For males, spatial heterogeneity enhanced the detection of density-dependence at less disturbed sites. The authors conclude that artificial freshwater discharges could significantly influence the distribution, abundance and life-history traits of the biota of sandy beaches, and that further study of these ecosystems should include human activities as important factors affecting spatial and temporal trends. The need to consider different spatial and temporal scales in order to detect the effect of anthropogenically-driven impacts in sandy beach populations is stressed.

Receptor potentials and electrical properties of nonspiking stretch-receptive neurons in the sand crab Emerita analoga (Anomura, Hippidae).

Receptor potentials and electrical properties of nonspiking stretch-receptive neurons in the sand crab Emerita analoga (Anomura, Hippidae). Four nonspiking, monopolar neurons with central somata and large peripheral dendrites constitute the sole innervation of the telson-uropod elastic strand stretch receptor in Emerita analoga. We characterized their responses to stretch and current injection, using two-electrode current clamp, in intact cells and in two types of isolated peripheral dendritic segments, one that included and one that excluded the dendritic termini (mechanosensory membrane). The membrane potentials of intact cells at rest (mean +/- SD: -57 +/- 4. 4 mV, n = 30), recorded in peripheral or neuropil processes, are similar to the membrane potentials of isolated dendritic segments and always less negative than membrane potentials of motoneurons and interneurons recorded in the same preparations. Ion substitution experiments indicate that the membrane potential is influenced strongly by Na+ conductance, probably localized in the mechanotransducing terminals within the elastic strand. The form of the receptor potential in response to ramp-hold-release stretch remains the same as stretch amplitude is varied and is not dependent on initial membrane potential (-70 to -30 mV) or recording site: initial depolarization (slope follows ramp of applied stretch), terminated by rapid, partial repolarization to a plateau (delayed depolarization) that is intermediate between the peak depolarization and the initial potential and sustained for the duration of the stretch. Responses to depolarizing current pulses are similar to stretch-evoked receptor potentials, except for small amplitude stimuli: an initial peak occurs only in response to stretch and probably reflects elastic recoil of the extracellular matrix surrounding the dendritic terminals. The rapid, partial repolarization depends on holding potential and is abolished by 4-aminopyridine (4-AP; 10 mM), implicating a fast-activating, fast-inactivating K+ conductance; TEA (60 mM) abolishes the remaining slow repolarization to the plateau. In intact cells, but not dendritic segments, regenerative depolarizations can arise in response to stretch or depolarizing current pulses; they are reduced by CdCl2 (10 microM) in the saline containing TEA and 4-AP and probably reflect current spread from Ca2+ influx at presynaptic terminals in the ganglion. We found no evidence for other voltage-activated conductances. Unlike morphologically similar "nonspiking" thoracic receptors of other species, E. analoga's nonspiking neurons are electrically compact and do not boost the analogue afferent signal by voltage-activated inward currents. The most prominent (only?) voltage-activated extra-ganglionic conductances are for potassium; by reducing the slope of the stretch-plateau depolarization curve, they extend each neuron's functional range to the full range of sensitivity of the receptor.

Role of particle wettability in capture by a suspension-feeding crab ( Emerita talpoida )

Suspension feeders sometimes depend on adhesion between particle and collector to capture food. If food particles have different adhesive properties than other particles, food could be passively selected by adhesive mechanisms. In this regard, the effect of particle wettability on adhesion to artificial and natural collectors was studied. First, the adhesion of glass particles to artificial collectors, both varying in wettability, was assessed to determine if wettability influenced adhesion in seawater. The adhesive force between glass particles and artificial collectors was measured by increasing the force pulling particles away from the collector until 50% of the particles fell off the collector. Adhesion increased as particle wettability decreased. Next, glass particles were used to determine if the antennal collector of the suspension-feeding mole crab Emerita talpoida captured particles based on particle wettability. 0.5 to 10 and 15 to 25 μm particles were suspended in a recirculating flow tank filled with seawater, and ablated antennae were exposed to this flow, after which the captured particles were counted. Results for the 0.5 to 10 μm particles confirmed predictions based on results from artificial collectors; particle capture increased as particle wettability decreased. The 15 to 25 μm particles may have been captured by sieving, and consequently did not follow predictions based on adhesion. Passive selection of particles based upon wettability differences can occur.

Sensitivity of the sand crab Emerita analoga to a weathered oil.

Sensitivity of the sand crab Emerita analoga to a weathered oil.

Embryonic ecdysteroids in a mole crab,Emerita asiatica (Milne-Edwards)

Using radioimmunoassay (RIA) and high performance liquid chromatography (HPLC), the presence of a complex mixture of free and conjugated ecdysteroids is reported in the embryonated eggs of a mole crab,Emerita asiatica. From an initial low value of 6.5 ng/g egg wet weight in stage I, the total ecdysteroids increased in concentration to 15.2 ng/g egg wet weight in stage III. This was followed by a sharp fall in stage IV, but again increased to 15.0 ng/g egg wet weight in stage VI. After a further decline in stage VII, the total ecdysteroids registered the highest value of 36.2 ng/g egg wet weight in stage VIII. This value, however, declined to a low level in the prehatching stage (IX). The concentration of the free ecdysteroids always predominated over the conjugated ones. The HPLC analysis of free ecdysteroids demonstrated the presence of 20-hydroxyecdysone and ecdysone in the ratio of 2.5. Purified lipovitellin II also contained free and conjugated ecdysteroids. The functional significance of the embryonic ecdysteroids as well as their nature of synthesis and storage within the eggs is discussed in the light of the information available on insect embryogenesis.

Biologia populacional de Emerita brasiliensis Schmitt (Crustacea, Hippidae) na Praia Vermelha do Norte, Ubatuba (São Paulo, Brasil)

Emerita brasiliensis Schmitt, 1935 is a common mole crab called tatuira in Brazil, with distribution from Espirito-Santo State (Brazil) to Buenos Aires Province (Argentina). Specimens were collected bimonthly from May/1992 through March/1993 with 4mm siffers mesh, in the intertidal region at Vermelha do Norte Beach, Ubatuba, Sao Paulo, Brazil. The animals were sexed and measured with a precision caliper of 0.1 mm (Cl = carapace length). Males presented cl amplitude from 3.4-17.3mm (13.2±2.1mm), and females from 13.8-26.3mm (20.5±1.8mm), showing a well-defined sexual dimorfism for this variable. The population presented a smaller incidence of males in relation to females (0.54:1.00), however in May/1992 an inverse pattern occurred (1.84:1.00). Ovigerous females were present in all samples with exception of May and September/1992 with greater frequencies in July/1992 and January/1993. It is probable that female maturity occurs is reached with 17mm CL, the smallest size in wich ovigerous females were found.

Timing of larval release in the mole crab Emerita talpoida

The timing of larval release by the mole crab Emerita talpoida was followed for more than 2 mo at a beach near Duck, North Carolina, USA. The time series of the frequency of females carrying gray-stage eggs (i.e. fully developed eggs) was compared statistically to the time series of along- and cross-shore wind stress, salinity, water temperature, tidal range, and average significant wave height. The coastal oceanography was dominated by the wind. Winds from the northeast caused downwelling events and large waves in the surf zone while winds from the southwest caused upwelling and small surf. Drops in the frequency of females with gray-stage eggs (an indication of larval release) tended to occur a day after large wave events (cross-correlation, r = -0.304, lag = -1 d, p < 0.05, n = 53). Large wave events cause rapid flushing of the water in the surf zone. Larvae released during large wave events would experience a short residence time in the surf zone that may decrease mortality due to benthic and surf zone predators.

Population structure and dynamics of two scopimerine sand crabsScopimera crabricaudaAlcock 1900 andDotilla sulcata(Forskåll 1775) in an estuarine habitat in Oman

Monthly samples of the scopimerine sand crabs, Scopimera crabricauda Alcock 1900 and Dotilla sulcata (Forskall 1775), were collected from November 1992 to January 1994 from a marine inlet, Khawr Suwadi (23°45′N 57°47′E), in the Gulf of Oman. The crabs inhabited mobile sand banks and flats. S. crabricauda occurred at mean densities of 79 m−2, between low high water neap and mean low water neap, and D. sulcata occurred at mean densities of 39 m−2, below this and down to near mean low water spring. The largest individuals were males, but in general the adult crabs were small, ranging from 2.2–5.9 mm CW in S. crabricauda and 2.1–10.3 mm CW in D. sulcata. Juveniles of both species were present throughout the year, but seasonal recruitment varied between years and did not show a clear temporal relationship to the cycles of breeding as indicated by the percentage of ovigerous females in the population. In comparison with other members of the genera, female egg loads of both species were low. This can be accounte...

A new pressure sensory mechanism for prey detection in birds: the use of principles of seabed dynamics?

We demonstrate a novel mechanism for prey detection in birds. Red knots (Calidris canutus), sandpipers that occur worldwide in coastal intertidal areas, are able to detect their favourite hard-shelled prey even when buried in sand beyond the reach of their bills. In operant conditioning experiments designed to find out whether the birds could tell buckets containing only wet sand from buckets containing hard objects in wet sand, we show that they detect the presence not only of deeply buried live bivalves but also of stones. The latter finding virtually excludes, under experimental conditions, prey-detection mechanisms based on vision, acoustics, smell, taste, vibrational signals emitted by prey, temperature gradients and electromagnetic fields. A failure to discriminate between food and non-food trays with dry sand indicates that pore water is involved. Based on the presence of large arrays of Herbst corpuscles (sensory organs that can measure the acceleration due to changes in pressure), the specifics of foraging technique and the characteristics of sediments on which red knots feed, we deduce that the sensory mechanism involves the perception of pressure gradients that are formed when bills probe in soft sediments in which inanimate objects block pore water flow. To our knowledge, this mechanism has not been described before. It is argued that repeated probing in soft, wet sediments allows red knots to induce a residual pressure build-up of sufficient strength to detect the pressure disturbance caused by a nearby object. The cyclic process of shaking loosely packed sand grains followed by gravitational settling into a closer packing, leads, owing to insufficient drainage of the sediment, to a locally increased pressure disturbance that is 'pumped up' at each shake.