Carcinus Maenus Research Articles

Predators Induce Phenotypic Plasticity in Echinoderms across Life History Stages.

AbstractMarine invertebrates with biphasic life cycles feature life history transitions that coincide with habitat changes from benthic adults to planktonic embryos and larvae, then a return to the benthos as a juvenile at metamorphosis. The metamorphic transition exposes animals to a new suite of benthic predators, and high mortality often occurs in the hours and days following settlement. Juvenile invertebrates may produce phenotypically plastic morphological defenses when predator cues are detected. However, time lags inherent to phenotypic plasticity may delay the production of defenses until after the period of highest vulnerability. It should, therefore, be beneficial for planktonic larvae approaching settlement to detect waterborne cues from benthic predators and produce juvenile phenotypes appropriate for postmetamorphic survival. Echinoderms are useful models for testing transhabitat and trans-life history stage phenotypic plasticity because many species have larvae that construct their juvenile phenotype while still in the water column. In this study, we tested whether planktonic echinoderm larvae exposed to cues from benthic predators modified their juvenile phenotypes at settlement. Green urchin (Strongylocentrotus droebachiensis) and Pacific sand dollar (Dendraster excentricus) larvae were exposed to predatory green crab (Carcinus maenus) or red rock crab (Cancer productus) cues, respectively, from their early-stage juvenile rudiment formation through settlement. Green urchin larvae exposed to predator cues settled with significantly more juvenile spines compared to unexposed controls. Sand dollars exhibited earlier settlement, larger disk area, fewer spines, and shorter spines when exposed to benthic predator cues. Sand dollar larvae were also exposed to cues from planktonic crab larvae and in response settled sooner and larger, with even fewer and shorter spines than those exposed to benthic predator cues. These results suggest that echinoderm larvae alter their juvenile phenotype in response to predator cues, but the response varies between species, and responses to planktonic threats may be prioritized over benthic ones.

Use of Ion Exchange and Lectin Chromatograpy To Fractionate Proteins from Carcinus maenus

Across many different species of crabs, it is notable that their shells have a high abundance of protein. For instance, the snow crab is 34.2% w/w of protein within its shell (Asunchion, et al., 2011.) And while the blue crab contains about 33.4% w/w protein within its shell (Lee et al 2017), the red crab contains about 16% w/w protein (Aklog 2016). Less is known about the European green crab, Carcinus maenus, which is a species found in Europe and North Africa. This organism has also invaded the coast of Maine.We have developed an acid extraction and acetone precipitation strategy for isolating proteins from the shells of the European green crab, Carcinus maenus. Typically, roughly 5 to 10 proteins are visible when this extract is analyzed by 12% SDS‐PAGE gel. In this study, cation and anion‐exchange resins, and lectin resins, were utilized to fractionate protein species based on their charge and glycoprotein content, respectively. This work reports on the progress of these studies.This work is of value to the study of bioactive materials present in shelled marine organisms.

Optimizing Extraction of Proteins from Carcinus Maenus After Removal of Low‐Molecular Weight Chitins

Crab shells as waste products are presently of economic interest only for the value of the chitin polymer present in their shells, which may be used to formulate foods or pharmaceutical products. Other materials in the crab shells, including protein, are discarded as waste. Crab shells have a large protein content A key question to examine is if there are bioactive proteins and/or peptides that have health benefits which could be recovered and utilized as a value added fraction from the waste stream. For example proteins isolated from crab shells have been found to contain antimicrobial and moderate antitumor agents (Sawssen, 2015.)In this work, the procedures used for removal of low molecular weight (LMW) chitin were followed (Ye, 2016). After removal of LMW chitin, the acetic acid extraction of proteins from crab shells was optimized using 50%, 25% and 12% acetic acid. One of the challenges associated with the extraction of proteins from crab shells is the concomitant demineralization of the shells which results in a high calcium carbonate solution in solution. In this project, a variety of different methods for separating the protein from the acidic solution and the calcium carbonate were utilized including dialysis, polyethylene glycol precipitation strategies.These findings will be of value to the community of researchers investigating either bioactive materials in the shells of marine organisms.

Species-specific crab predation on the hydrozoan clinging jellyfish Gonionemus sp. (Cnidaria, Hydrozoa), subsequent crab mortality, and possible ecological consequences.

Here we report a unique trophic interaction between the cryptogenic and sometimes highly toxic hydrozoan clinging jellyfish Gonionemus sp. and the spider crab Libinia dubia. We assessed species–specific predation on the Gonionemus medusae by crabs found in eelgrass meadows in Massachusetts, USA. The native spider crab species L. dubia consumed Gonionemus medusae, often enthusiastically, but the invasive green crab Carcinus maenus avoided consumption in all trials. One out of two blue crabs (Callinectes sapidus) also consumed Gonionemus, but this species was too rare in our study system to evaluate further. Libinia crabs could consume up to 30 jellyfish, which was the maximum jellyfish density treatment in our experiments, over a 24-hour period. Gonionemus consumption was associated with Libinia mortality. Spider crab mortality increased with Gonionemus consumption, and 100% of spider crabs tested died within 24 h of consuming jellyfish in our maximum jellyfish density containers. As the numbers of Gonionemus medusae used in our experiments likely underestimate the number of medusae that could be encountered by spider crabs over a 24-hour period in the field, we expect that Gonionemus may be having a negative effect on natural Libinia populations. Furthermore, given that Libinia overlaps in habitat and resource use with Carcinus, which avoids Gonionemus consumption, Carcinus populations could be indirectly benefiting from this unusual crab–jellyfish trophic relationship.

Host selection by larvae of a marine insectHalocladius variabilis: nutritional dependency or escape from predation?

Larvae of the Holarctic marine chironomid,Halocladius variabilis(Staeger), have strong fidelity to the tuft-forming brown alga,Elachista fucicola(Velley) Areschoug, an abundant epiphyte on intertidal fucoids of the North Atlantic. We show that larvae are sufficiently motile to select an algal host in a Petri dish within 3–4 cm, and that larvae show differential behaviour with respect to host selection in the presence or absence of a predator. In the absence of predators 53% of larvae found an algal host within 1 hour; however, after 24 hours, there was no significant difference in host selection. When an isopod predator (Idoteasp.) was present, more larvae found a host within 1 hour (81%) andElachistawas chosen over three of the four other hosts. Furthermore, when larvae were present inElachista, predator (Carcinus maenus) success was significantly reduced relative to two other algal hosts. The adaptive significance ofElachistaas a refuge from predation was confirmed by experiments demonstrating that larval growth with other algal hosts was greater than withElachista. These experiments suggest that microhabitat selection by larvae ofH. variabilisreveals important tradeoffs for growth and predator avoidance.

Survival of European Green Crab (Carcinus maenusL.) Exposed to Simulated Overland and Boating-Vector Transport Conditions

Juveniles and adults hitch-hiking in fishing gear, recreational vessels, and fisheries and aquaculture products are believed to be important vectors of local dispersal of invasive European green crab (Carcinus maenus L.). Assessing the distance green crab might spread by hitch hiking requires an estimate of survival time under typical transport conditions. An exposure experiment (stocking density 62 crabs/m2) was conducted in fish crates containing: just crabs (no water, no cover), dry rope, damp eelgrass (Zostera marina L.), seawater (1.5 cm deep), rope seawater, or eelgrass seawater. At mean air temperature of 24°C, almost no crabs died during the first 48 h, 50% of crabs stocked alone or with dry rope survived 68 h (none survived five days), 50% of crabs in eelgrass or eelgrass seawater survived 90–100 h, and > 80% of crabs in sea water or rope seawater survived the full five days. The second experiment (just crabs, sea water, and rope seawater) used three stocking levels (84, 168, and 251 crabs/m2) and ran for seven days. Stocking density did not have a significant effect on survival. At mean air temperature of 29°C, 50% of crabs fully exposed to air survived 60 h (almost none survived seven days), whereas about 60% of crabs survived to seven days when seawater or seawater rope were present. The survival of green crab for several days out of water under severe summer conditions would allow them to be carried on boats to any point in Atlantic Canada, or almost anywhere on the eastern seaboard on trailered boats. This could result in further northward dispersal and the introduction of “northern” genetic material into previously colonized southern portions of the range, potentially increasing over wintering survival.

Weak meiofaunal trophic linkages in Crangon crangon and Carcinus maenus

To document the relative importance of meiofauna as prey for juvenile Crangon crangon and Carcinus maenus, short interval (1.5–2 h) collections were made in the muddy Lynher Estuary (Plymouth, Great Britain) and in the sandy-bottom Ythan Estuary (Aberdeenshire, Scotland) in 1990. Gut passage times of Crangon fed flaked fish food and fluorescent tracer in the laboratory at 13 °C ranged from 4 to 20 h. Wild shrimp exhibited feeding periodicity, with guts fullest during high tide in both locations. Visual and immunological gut contents analyses revealed that meiofaunal nematodes and harpacticoid copepods were present only in recently settled shrimp from 8 to 12 mm total length on muddy bottoms. Larger shrimp collectively consumed up to 33 different macrobenthic prey types. Shrimp were fullest at night (mean gut contents weight = 8% wet body weight, Lynher) or at dawn (6%, Ythan). The Lynher Carcinus gut contents—from animals 8 to 30 mm carapace width, examined visually only—contained mostly fluids, green benthic algae, sediment particles, and masses of unidentifiable prey remains plus digestion-resistant hard parts visually identifiable as macrobenthic in origin. None of the 203 crabs examined from the 24-h collection contained meiofaunal prey. Crangon shrimp probably eat meiofaunal prey for only a brief period of time after their initial settlement to the bottom. Evidence for significant top–down impacts on meiofauna from these two abundant shallow-water predators was weak. More trophic studies are needed on newly settled epibenthic predators to test the hypothesis that biological control of shallow-water meiofauna is important.

Assessing the potential benthic–pelagic coupling in episodic blue mussel ( Mytilus edulis) settlement events within eelgrass ( Zostera marina) communities

Coastal marine seagrass ecosystems are important nursery grounds for commercially and recreationally important species, and they serve as key settlement and recruitment sites for other species. We investigated several years (2001–2003) where episodic settlement events of blue mussels ( Mytilus edulis) occurred in Barnegat Bay, NJ, USA. Population assessment indicated that blue mussels settled in eelgrass beds ( Zostera marina) in late spring with peak densities exceeding 170,000 m −2. Based on calculated filtration rates of M. edulis, we determined that for at least 53 days in 2001, the density and size distribution of M. edulis were sufficient to filter the water column volume in excess of twice a day, with maximum calculated filtration rates exceeding 8 m 3 water m −2 day −1. While the settlement event in 2001 was very localized, in 2003, the settlement event was considerably more widespread throughout the bay, with maximum settling densities exceeding 175,000 individuals m −2. Associated with these high densities, maximum calculated filtration rates exceeded 15 m 3 water m −2 day −1. This filtration potential may have impeded the localized development of a brown-tide ( Aureococcus anophagefferens) bloom in 2001, which occurred in other regions of the bay, but the widespread settlement event seen in 2003 may have impeded the development of any brown-tide blooms in Barnegat Bay during that summer. The decline in mussel densities throughout the summer may be a result of elevated water temperatures in this back bay, but at one site, the high settlement of M. edulis was followed by a substantial migration (>40 individuals m −2) of small sea stars ( Asterias forbesii). In 2001, A. forbesii was a significant factor in reducing M. edulis density by the end of the summer at the Barnegat Inlet site and a community level assessment showed significant positive correlations between mussel aggregations and sea star densities ( r=0.68–0.73, P<0.001). At this same site in 2003, the sea stars were again present in high densities (26 m −2) and were a potential mechanism for mussel decline. In other regions of the bay, sea star densities are very low, but numerous other predatory species exist, including blue crabs ( Callinectes sapidus), green crabs ( Carcinus maenus), spider crabs ( Libinia spp.), and several Xanthid crabs. Given the high mussel densities seen in this study and the considerable predation by sea stars and other benthic predators, the benthic–pelagic coupling which these mussels provide in this system contributes to the high secondary production in these grass beds.

Compositional characteristics of green crab ( Carcinus maenas)

The invasive European green crab ( Carcinus maenus) was harvested at four sites in Nova Scotia. Crabs were individually weighed and measured for carapace width. A composite of claw and leg meats was sampled from raw green crabs and the meat was subjected to proximate (moisture, protein [N × 6.25], and total lipids), carotenoids, fatty acid distribution, and amino acids composition analyses. In addition, the shell discards were analyzed for their contents of chitin, total lipids, total nitrogen, and total carotenoids. The total protein (N × 6.25) content, lipids, and carotenoids in crab meat, on a dry weight basis (db), were 80.6–83.5, 3.6–4.8%, and 5.1–19.2 mg%, respectively. The shell discards, db, contained 12.6–14.5% of chitin, 2.6–3.11% of total nitrogen, 0.37–0.65% of total lipids, and 4.4–9.3 mg% of total carotenoids. The saturated and n−3 fatty acids accounted for 19–20.7% and 37.4–40% of total fatty acids, respectively. The polyunsaturated fatty acids (PUFA) were dominated by eicosapentaenoic acid (EPA: 20:5 n−3) and docosahexaenoic acid (DHA: 22:6 n−3). The ratio of EPA:DHA varied from 1.6 to 2.8. Green crab meat was well balanced in its composition of essential amino acids, except for tryptophan.

Nutrient composition of green crab ( Carcinus maenus) leg meat and claw meat

Research is underway in New England to examine the potential for initiating a commercial fishery for the invasive European green crab ( Carcinus maenus). Information on the nutrient composition is needed to facilitate the processing, utilization, and marketing of value-added green crab products. Green crabs were harvested and individually weighed and measured for carapace width. Claw meat and leg meat samples were picked from steamed crabs, and raw crabs were sampled for claw meat only. Samples were subjected to proximate, mineral (calcium, phosphorus, magnesium, sodium, potassium, aluminium, iron, zinc, copper), cholesterol, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) analyses. Moisture, protein, and total mineral contents of the crab meat averaged 78.7, 17.1, and 2.2 g/100 g, respectively. Leg meat had higher lipid concentrations (1.16 g/100 g) than either steamed (0.62 g/100 g) or raw (0.54 g/100 g) claw meat. Average n-3 fatty acid concentrations ranged from 115 to 336 mg/100 g and 154 to 344 mg/100 g for DHA and EPA, respectively, and were significantly higher in leg meat than in claw meat.

Epizootiology of the parasitic dinoflagellate Hematodinium sp. in the American blue crab Callinectes sapidus.

Hematodinium sp. is a parasitic dinoflagellate that infects and kills blue crabs Callinectes sapidus. Periodic outbreaks of dinoflagellate infections with subsequent high host mortalities prompted a study of the epizootiology and distribution of the crab pathogen. Hemolymph samples from over 13000 crabs were assessed for infections over 8 yr. Moderate to high prevalences were found at several locations along the Atlantic and Gulf coasts of the United States. In the coastal bays of Maryland and Virginia, prevalence followed a seasonal pattern, with a sharp peak in late autumn. Infections were significantly more prevalent in crabs measuring less than 30 mm carapace width; host sex did not influence prevalence. Prevalences were highest in crabs collected from salinities of 26 to 30%o; no infected crabs were found in salinities below 11%o. Intensity of infection did not vary among crab sizes, molt stages, or sexes. Naturally and experimentally infected crabs died over 35 and 55 d in captivity, with a mean time to death of approximately 13 and 42 d, respectively. Several other crustaceans, including gammaridean amphipods, xanthid (mud) crabs, and the green crab Carcinus maenus, were found with Hematodinium-like infections. Considering its widespread distribution and high pathogenicity, we suggest that Hematodinium sp. represents a significant threat to blue crab populations in high salinity estuaries along the Atlantic and Gulf coasts of the USA.

Factors affecting prey handling in lesser octopus (Eledone cirrhosa) feeding on crabs (Carcinus maenas)

Octopuses (Eledone cirrhosa) feeding on crabs (Carcinus maenus) may penetrate the crab by a carapace borehole or puncture of the eye. In ad libitum feeding trials (632 crabs eaten), 31% of the predated crabs had a punctured eye, 57% had a borehole in the dorsal carapace. Eye puncture and boring occurred together in 6% of cases but 18% were neither punctured nor bored.Feeding trials in which size of prey and size of octopus were controlled showed that the incidence of boreholes was greatest (&gt;70%) in small crabs (&lt;50 mm carapace width). Incidence of eye puncture (10% in small crabs) rose to 25% in crabs of over 50 mm carapace width and to over 40% in the largest crabs used (65–80 mm carapace width).Large octopuses used eye puncture less frequently than small octopuses. Increasing the proportion of small crabs in the diet increased the subsequent incidence of carapace boring at all crab sizes. The results are discussed in relation to differences in prey handling efficiency at different prey sizes.

Oxygen and the Trade-off between Egg Ventilation and Brood Protection in the Common Goby

Abstract1. We examined compromises between defence of nests against predation and ventilation of eggs in the common goby (Pomatoschistus microps). Females are known to prefer nests with small entrances, which are less vulnerable to predatory shore crabs, Carcinus maenus. However, small nest entrances may hamper egg ventilation by males. This may be especially detrimental under conditions of low dissolved oxygen. 2. Males did not make smaller entrances to their nests when in the presence of predatory crabs, but they had larger entrances under low oxygen than in normal oxygen levels. 3. Males diverted time from ventilating nests to attacking crabs. 4. Thus, males exchanged direct care of the eggs for protection against predators by reducing their fanning activity, but not according to needs of their eggs for oxygenation. This trade-off may therefore impose a greater cost to egg survival for males in low oxygen.

CRAB PREDATION, WATERBORNE CUES, AND INDUCIBLE DEFENSES IN THE BLUE MUSSEL,MYTILUS EDULIS

Inducible defenses are found in both terrestrial and aquatic organisms and appear to be a common defensive strategy of both sessile and mobile species. Here we report the presence of previously undescribed inducible defenses in marine mussels, a dominant member of temperate rocky intertidal communities. In the Gulf of Maine, estuarine shorelines with low water flow are characterized by high crab predation on the common blue mussel, Mytilus edulis, compared to nearby shore- lines with high water flow. Mussels at these high predation sites had thicker shells, relatively more shell mass, and were more tightly attached to the substrate than mussels at low predation sites. Field and laboratory experiments were used to test whether the between- site differences in these traits were the result of phenotypic plasticity. Mussels outplanted to high predation sites produced more byssal threads and attached more firmly to the substrate than did mussels outplanted to low predation sites. In the laboratory, thicker shells were induced by waterborne cues from both the common predator, Carcinus maenus, and damaged conspecifics, and these thicker shells were mechanically stronger than thinner, noninduced ones. Our results contribute to growing evidence that inducible defenses are a pervasive feature of intertidal assemblages. In addition to the bivalve example presented here, gastropods, barnacles, bryozoans, and seaweeds are also known to have inducible defenses. Phenotypic plasticity for defensive traits has likely evolved repeatedly in intertidal organisms and appears to play a major role in the dynamics of rocky intertidal communities.

Mesanophrys chesapeakensis n. sp., a Histophagous Ciliate in the Blue Crab, Callinectes sapidus, and Associated Histopathology

Histophagous ciliate infections were infrequently detected in blue crabs, Callinectes sapidus, from Chesapeake Bay, Delaware Bay, and a coastal bay of Maryland. Associated pathology included hemocyte aggregations in various tissues and nodule formation. Protargol silver staining of cultured ciliates revealed an oral apparatus morphologically similar to that of other hemolymph-infecting ciliates of the genus Mesanophrys. The oral apparatus included three distinct oral polykinetids and an oral dikinetid consisting predominantly of a b segment and a smaller c segment. Morphologic comparison to other histophagous ciliates infecting crustaceans showed that the ciliate in blue crabs is a distinct species, Mesanophrys chesapeakensis n. sp., family Orchitophryidae. Additional key words: protargol, Orchitophryidae Histophagous ciliates from wild and captive crustaceans have been reported sporadically from various locations since 1888. The ciliate Mesanophrys (Anophrys COHN 1866) maggii CATTANEO 1888 was first reported parasitizing the hemolymph of a European shore crab, Carcinus maenus LINNAEUS 1758, from Italy. Incomplete or poor morphological descriptions of several crustacean-infecting ciliates have caused considerable confusion and elicited much discussion on systematics (Armstrong et al. 1981). Based on the morphology of oral structures of protargol-stained specimens, a new genus, Mesanophrys, was erected by Small & Lynn (1985) to include ciliates with only a short oral dikinetid and other features now found in the genera of the family Orchitophryidae. Two species, Mesanophrys (Paranophrys) maggii CATTANEO 1888, and Mesanophrys (Anophrys) carcini GROLIERE & LEGLISE 1977 (Small & Lynn 1985), were transferred into this newly erected genus; a third species, Mesanophrys pugettensis MORADO & SMALL 1994, was recently reported. However, incorrect generic placements of histophagous ciliates from crustaceans have continued, as discussed by Morado & Small (1994). Recently, the family Paranophryidae (JANOWSKI, in Small & Lynn 1985) was determined to be a junior synonym a To whom correspondence should be addressed: Gretchen Messick 410-226-5193 FAX: 410-226-5925 e-mail gmessick @ hatteras.bea.nmfs.gov. of Orchitophryidae CEPEDE 1907, due to rule of priority (Morado & Small 1994). Orchitophrya stellarum CEPEDE 1907 was recently reinvestigated using protargol staining and was determined to be a scuticociliate rather than an astome (Bouland et al. 1986). Thus, Paranophryidae falls as a junior synonym to Orchitophryidae (Morado & Small 1994). Most reports of ciliates in crustacean hemolymph involve captive hosts (Cattaneo 1888; Bang et al. 1972; Aiken et al. 1973; Groliere & Leglise 1977; Armstrong et al. 1981; Sparks et al. 1982). Reports of histophagous ciliates in wild crustacean populations are rare, and infection prevalence has typically been low. Poisson (1930) found only 0.2% (7 of 3000) shore crabs, C. maenus, infected with histophagous ciliates. Infections in wild stocks of the American lobster, Homarus americanus H. MILNE EDWARDS 1837, were found only three times in 14 years (Aiken & Waddy 1986). In contrast to these reported low prevalence levels in hemolymph of wild lobsters, a ciliate was present in smears of hepatopancreas tissue of all freshly caught Maine lobsters, H. americanus (n=89), although the ciliate was often undetected in hemolymph preparations (Sherburne & Bean 1991). Mesanophrys pugettensis was found in fewer than 0.4% (n=1916) of wild and captive Dungeness crabs, Cancer magister DANA 1852, although it was reported in 3% (n=87) of wild rock crabs, C. productus RANDALL 1839, and 29% (n 7) of wild kelp crabs, Pugettia producta RANDALL This content downloaded from 157.55.39.153 on Mon, 19 Sep 2016 04:45:06 UTC All use subject to http://about.jstor.org/terms

High-affinity binding of putative moult-inhibiting hormone (MIH) and crustacean hyperglycaemic hormone (CHH) to membrane-bound receptors on the Y-organ of the shore crab Carcinus maenus

Receptor-binding assays for putative moult-inhibiting hormone (MIH) and crustacean hyperglycaemic hormone (CHH) were developed to determine the distribution and characteristics of their receptors on crude membrane preparations of Carcinus maenus tissues. High-affinity, specific, displaceable and saturable binding of [$^{125}$I]MIH indicative of receptor-ligand interaction was observed on Y-organ preparations. All tissues examined including the Y-organ specifically bound [$^{125}$I]CHH, and, for this tissue, high-affinity binding characteristics were determined by Scatchard analysis. As previous studies had shown that CHH is active in repressing ecdysteroid biosynthesis by Y-organs in vitro, it is argued that this neuropeptide has a physiological role in moult control, further strengthening the emerging scenario of a complex, multihormonal control of moulting. Receptor binding experiments using heterologous MIHs from Necora and Cancer revealed that all these MIHs were similarly effective at displacing homologous (Carcinus) radioligand, a feature reflected in their somewhat similar biological activities. Nevertheless, all three MIHs could be distinguished in terms of chromatographic and immunochemical behaviour and in terms of amino acid analysis in a manner correlated with evolutionary relationships within the Brachyura. It is therefore suggested that binding domains of MIHs have been highly conserved.

Factors affecting diet selection in the shore crab, Carcinus maenus (L.)

Abstract. Model prey were used to examine the olfactory and tactile basis of prey selection when crabs feed on resistant items such as bivalves. Shape was an important determinant of handling time which increased with height and hence cross-sectional area of the model. The additional stimulus of odour prolonged persistence time with inedible models and crabs preferred those incorporating the highest concentration of mussel, Mytilus edulis, filtrate. When presented with a sequence of edible models, crabs improved their handling skills during a foraging bout. When models were presented alternately with real mussels, however, the handling skills associated with the mussels were learned more slowly, particularly if a model was encountered first in a sequence. Crabs never rejected edible models that were encountered individually in a sequence, but frequently did so when they were encountered simultaneously in groups. During simultaneous encounters, handling time was shorter than for individual encounters. It appears that chemical cues are important attractants, and may be correlated with the probable yield and vulnerability of the prey. However, whereas olfaction is particularly important early in the attack, shape, which is the main determinant of handling time, becomes important later. Olfactory cues remain potent reinforcers throughout an attack.

Development of epipods and gills in some pagurids and brachyurans

The development of gills is described in zoea and megalopa stages of the following 16 species of decapods, and the patterns of gill development are discussed in terms of phylogenetic relationships of the larvae: Pagurus prideaux Leach, Pagurus bernhardus (Linnaeus), Inachus dorsettensis (Pennant), Hyas araneus (Linnaeus), Eurynome aspera (Pennant), Pisa armata (Latreille), Carcinus maenus (Linnaeus), Liocarcinus corrugatus (Pennant), Liocarcinus holsatus (Fabricius), Pilumnus hirtellus (Linnaeus), Monodaeus couchi (Couch), Pinnotheres pinnotheres (Linnaeus), Pinnotheres pisum (Linnaeus), Pinnaxodes mutuensis Sakai, Pinnixa rathbuni Sakai and Pinnixa (?)chaetopterana Stimpson. The gills of most of the species investigated migrate during development, not only dorsally but, in some cases, also posteriorly. The Pinnotheridae provide the only known example in which rudiments of ‘lost’ gills appear within larval stages only to disappear by the first crab stage.

Biological consequences of ice rafting in a New England salt marsh community

Ice rafting of salt marsh peat is a recurrent phenomenon in north temperate regions. This process was simulated in a northern New England salt marsh to test several hypotheses concerning the effects of peat transport from high to low intertidal heights on the growth and mortality of key sessile organisms: the ribbed mussel Geukensia demissa (Dillwyn), the fucoid alga Fucus vesiculosus L. var. spiralis (Farlow) and the cordgrass Spartina alterniflora (Loisel.). Growth rates increased when Geukensia and Fucus were transported to the lower intertidal; however, Spartina died when similarly transported. Predation pressure (primarily from Carcinus maenus L.) on Geukensia was greater when it was rafted to the lower intertidal zone than in the upper intertidal habitat and was size specific; mussels >3.5cm reached a size-escape from crab predation. A winter survey of dislodged mussels revealed that 72% of the mussels collected were dead and 86% had been overgrown by large Fucus plants, >2.5 × the natural frequency of Fucus overgrowth (32%). In marsh habitats where hard substratum is rare, 91% of the Fucus were growing on Geukensia. A dislodgement experiment showed that a significantly greater percentage of Geukensia was dislodged after ice-out when Fucus was attached to the shell than those mussels without Fucus overgrowth. In the spring, a population survey conducted in the salt marsh examined densities, biomass and population structure of Geukensia, as well as densities, percent cover and biomass of Fucus. Values obtained in the foremarsh were compared to those from the peat islands recently rafted to the tidal flats. Both biomass and densities of Geukensia were similar in the two areas; however, the size-frequency distributions of the mussels were different. Since fewer large mussels, Fucus and Fucus-overgrown mussels were found on the newly transported peat islands, this pattern appears to reflect dislodgement of larger Geukensia by attached algae during ice transport. Two ice-related sources of mortality were identified for Geukensia: (1) Fucus overgrowth acted as a vector for mussel dislodgement and was an indirect source of mortality; and (2) ice crushing was a direct source of mortality for non-overgrown mussels.

The lipid composition of the foregut wall of Carcinus maenas and its relationship to observed permeability

Abstract 1. 1. The detailed biochemical composition of the epidermis and cuticle from the foregut in Carcinus maenus has been examined. 2. 2. The cuticle was composed mainly of protein and chitin with a relatively small lipid component whilst the epidermis was rich in both protein and lipid. 3. 3. The sterol fractions of both tissues were composed almost entirely of cholesterol but the component phospholipids were quite distinct. 4. 4. The phospholipids of the epidermis were composed mainly of long chain, highly unsaturated fatty acids, whilst those of the cuticle were dominated by short-chain saturated fatty acids. 5. 5. These compositional differences are discussed in relation to the likely permeabilities of the tissues.