Sulfur and heavy metals in biological tissue

The correlation between sulfur, metallothionein and heavy metals was investigated in biological samples from the aquatic environment. Samples of orange roughie, shark, goldfish and king crab were analysed for metals and sulfur. Results indicated that there was insufficient evidence to suggest any relationship between sulfur and total metals, but there was sufficient evidence to suggest a significant relationship existed between mercury and total sulfur in the biological tissues examined.

Molting and reproduction in portunus pelagicus

This investigation describes ovarian maturation stages in the female reproductive system, evidence for histones in sperm nuclei and novel morphological changes that occur during spermiogenesis in the male blue swimming crab, portunus pelagicus. It also identifies dual functionality of the molt inhibiting hromone on molting and vitellogenesis through RNA inteference.

Why do Gull-billed Terns Gelochelidon nilotica feed on fiddler crabs Uca tangeri in Guinea-Bissau?

Gull-billed Terns Gelochelidon nilotica wintering in Guinea Bissau mainly fed on fiddler crabs Uca tangeri and were occasionally seen feeding on fish and locusts. As fiddler crabs have a low energy content, terns need a large gross intake to meet daily energy demands. Fiddler crabs also have a low ratio of digestible flesh to exoskeleton, and therefore tern food intake may be limited by gut capacity. Activity budgets of Gullbilled Terns feeding on fiddler crabs showed that a considerable part of the time was spent resting. The duration of resting intervals increased with energy intake and was positively correlated with the metabolisable energy content of the crab eaten, suggesting that resting periods were required for a proper digestion. The poor quality of fiddler crabs was offset by high capture rates. So daily energy expenditure of the terns could easily be met by feeding on fiddler crabs. Even when resting pauses were included in foraging time, foraging for only 1.5 hours on fiddler crabs satisfied the terns’ daily energy demands. Instead, feeding on energy-rich fish would require about 2.5 hours to satisfy daily energy demands. Compared to the more specialised piscivorous Little Tern Sternula albifrons and Sandwich Tern Sterna sandvicensis, capture rate of fish was poor in Gull-billed Terns. From an energetic point of view, wintering Gull-billed Terns feeding on fiddler crabs seem to have an easy living in Guinea Bissau.

Changes in the nutritional composition of captive early-mid stage Panulirus ornatus phyllosoma over ecdysis and larval development

Elucidation of the key nutritional requirements for complete larval development of the tropical spiny rock lobster, Panulirus ornatus, presents a major challenge for the development of robust commercial aquaculture for this crustacean. As a foundation study in this area, the chemical composition of early-mid stage P. ornatus phyllosoma (Stages I-VI) receiving a novel formulated diet was analysed immediately prior and post-ecdysis to provide insight into the crude nutritional trends during the larval development cycle. From the onset of moulting, cyclical patterns were evident in the proximate composition of phyllosoma, resulting in substantial restructuring between the pre- and post-moult stages of the moult cycle. Proportions of protein, lipid and ash were high at the premoult stage, reflecting growth and nutrient accumulation over the intermoult period, and reduced at the post-moult stage, reflecting the large uptake of water to facilitate subsequent growth. Polar lipid was the dominant lipid class, accounting for >. 90% of the total lipid content. Conversely, triacylglycerol concentrations were low (<. 5%), despite being the principal lipid class available in the formulated diet. Likewise, despite receiving high concentrations of eicosapentaenoic acid (EPA, 20:5n-3) and docosahexaenoic acid (DHA, 22:6n-3) (9.2 and 7.6% of the dietary lipid source, respectively), levels of these fatty acids were comparatively low in phyllosoma (3.4 and 4.7%, respectively). In contrast, there is selective deposition of these fatty acids in wild caught phyllosoma. This finding suggests a poor assimilation of triacylglycerols by captive larvae and highlights the importance of future investigations into alternative sources of EPA and DHA. Ultimately, this study provides insight into the nutritional requirements of phyllosoma, providing valuable knowledge on diet formulation for commercially viable hatchery production of spiny rock lobsters. © 2014 Elsevier B.V.

Personality and plasticity: consistent responses within-, but not across-temperature situations in crabs

Recent research suggests that repeated assays of behaviour, conducted both within and across situations, could reveal important insights into two traditionally distinct areas of study: animal personality and individual differences in behavioural plasticity. However, at present relatively few studies present such data, and few consider how changing abiotic conditions affect behavioural plasticity. Individual differences in metabolic rate have been suggested as a proximate mechanism promoting personality, leading one to speculate that individual differences in metabolic sensitivity to temperature may affect behavioural responses in ectotherms. At present, only one study (out of two) has tested for and shown individual differences in behavioural responses to temperature. Here, we repeatedly assayed the behaviour of a marine crab across a narrow range of temperatures to test for individual differences in responses to temperature. We observed large inter-individual differences in behaviour that were consistent over time at a given temperature (evidence for personality), and individual differences in responses to temperature (evidence for plasticity). This study adds to the very scant literature on ectotherm behavioural sensitivity to temperature, and suggests the phenomenon might be widespread. We speculate about the role of metabolism as a proximate mechanism that might explain these individual differences in plasticity and make suggestions for future research to test this hypothesis. © Koninklijke Brill NV, Leiden, The Netherlands.

A glycosyl hydrolase family 16 gene is responsible for the endogenous production of β-1,3-glucanases within decapod crustaceans

To identify the gene responsible for the production of a β-1,3-glucanase (laminarinase) within crustacea, a glycosyl hydrolase family 16 (GHF16) gene was sequenced from the midgut glands of the gecarcinid land crab, Gecarcoidea natalis and the freshwater crayfish, Cherax destructor. An open reading frame of 1098bp for G. natalis and 1095bp for C. destructor was sequenced from cDNA. For G. natalis and C. destructor respectively, this encoded putative proteins of 365 and 364 amino acids with molecular masses of 41.4 and 41.5kDa. mRNA for an identical GHF16 protein was also expressed in the haemolymph of C. destructor. These putative proteins contained binding and catalytic domains that are characteristic of a β-1,3-glucanase from glycosyl hydrolase family 16. The amino acid sequences of two short 8-9 amino acid residue peptides from a previously purified β-1,3-glucanase from G. natalis matched exactly that of the putative protein sequence. This plus the molecular masses of the putative proteins matching that of the purified proteins strongly suggests that the sequences obtained encode for a catalytically active β-1,3-glucanase. A glycosyl hydrolase family 16 cDNA was also partially sequenced from the midgut glands of other amphibious (Mictyrisplatycheles and Paragrapsus laevis) and terrestrial decapod species (Coenobita rugosus, Coenobita perlatus, Coenobita brevimanus and Birgus latro) to confirm that the gene is widely expressed within this group. There are three possible hypothesised functions and thus evolutionary routes for the β-1,3-glucanase: 1) a digestive enzyme which hydrolyses β-1,3-glucans, 2) an enzyme which cleaves β-1,3-glycosidic bonds within cell walls to release cell contents or 3) an immune protein which can hydrolyse the cell walls of potentially pathogenic micro-organisms.

Restricting prey dispersal can overestimate the importance of predation in trophic cascades

Predators can affect prey populations and, via trophic cascades, predators can indirectly impact resource populations (2 trophic levels below the predator) through consumption of prey (density-mediated indirect effects; DMIEs) and by inducing predator-avoidance behavior in prey (trait-mediated indirect effects; TMIEs). Prey often employ multiple predator-avoidance behaviors, such as dispersal or reduced foraging activity, but estimates of TMIEs are usually on individual behaviors. We assessed direct and indirect predator effects in a mesocosm experiment using a marine food chain consisting of a predator (toadfish--Opsanus tau), prey (mud crab--Panopeus herbstii) and resource (ribbed musse--Geukensia demissa). We measured dispersal and foraging activity of prey separately by manipulating both the presence and absence of the predator, and whether prey could or could not disperse into a predator-free area. Consumption of prey was 9 times greater when prey could not disperse, probably because mesocosm boundaries increased predator capture success. Although predator presence did not significantly affect the number of crabs that emigrated, the presence of a predator decreased resource consumption by prey, which resulted in fewer resources consumed for each prey that emigrated in the presence of a predator, and reduced the overall TMIE. When prey were unable to disperse, TMIEs on mussel survival were 3 times higher than the DMIEs. When prey were allowed to disperse, the TMIEs on resource survival increased to 11-times the DMIEs. We found that restricting the ability of prey to disperse, or focusing on only one predator-avoidance behavior, may be underestimating TMIEs. Our results indicate that the relative contribution of behavior and consumption in food chain dynamics will depend on which predator-avoidance behaviors are allowed to occur and measured.

Preference for feeding at habitat edges declines among juvenile blue crabs as oyster reef patchiness increases and predation risk grows

Both habitat patchiness and behaviorally-mediated indirect effects (BMIEs; predator- induced changes in prey behavior that affect the prey's resources) are important in many food webs, but the relationships between these 2 factors have yet to be investigated. To explore effects of habitat patchiness and variation in perceived risk of predation on food-web dynamics, we conducted a factorial experiment in a model aquatic food chain of predator-prey-resource using 2 contrasting predators (adult blue crab Callinectes sapidus and toad fish Opsanus tau), juvenile blue crab as prey, and mussel Geukensia demissa as resource. Both predator presence and habitat patchiness influenced the prey's preference for consuming resources at patch edges instead of interiors. The preference of prey for consuming resources at habitat edges was 4 times stronger in continuous oyster reef habitat than in smaller habitat patches. This suggests that interior resources in continuous habitat experience a refuge from consumption, but this refuge is largely lost in patchy habitat. The mere presence of predators reduced the prey's preference for consuming resources at habitat edges. This BMIE was significant for the ambush predator (toadfish) and the treatment containing both predators, but not for the actively hunting predator (adult blue crab). We conclude that habitat patchiness and predator presence can jointly affect resource distribution by inducing shifts in prey foraging behavior, revealing a need to incorporate BMIEs into habitat fragmentation studies. This conclusion has broad and growing relevance as anthropogenic factors increasingly modify predator abundances and fragment coastal habitats. © Inter-Research 2012.

Feeding ecology of King George whiting Sillaginodes punctatus (Perciformes) recruits in seagrass and unvegetated habitats. Does diet reflect habitat utilization?

This study investigated the feeding ecology of King George whiting Sillaginodes punctatus recruits to determine how diet composition varies between habitat types (seagrass and unvegetated habitats), and between sites separated by distance. Broad-scale sampling of seagrass and unvegetated habitats at nine sites in Port Phillip Bay (Australia) indicated the diet composition varied more by distance into the bay than by habitat. Near the entrance to the bay the diet was dominated by harpacticoids and gammarid amphipods, in the middle reaches of the bay the diet was completely dominated by harpacticoids, while at sites furthest into the bay, mysids and crab zoea were also important. Abundances of prey in guts was significantly higher between 1000 and 2200 hours compared with other times, indicating diurnal feeding. Laboratory determined gut evacuation rate (based on an exponential model) was estimated to be -0·54. Daily rations were highly variable among sites and habitat types. Sillaginodes punctatus recruits consumed much higher quantities of prey on unvegetated habitat than seagrass habitat at some middle reach sites; with prey consumption of harpacticoid copepods on unvegetated habitat approaching 3000 individuals per day at one site. The results of this study provide insight into why habitat associations of S. punctatus recruits within mosaics of seagrass and unvegetated habitat show high spatial variation.

How small-scale variation in oyster reef patchiness influences predation on bivalves

As oyster fishing continues to degrade reef habitat along the US Atlantic coast, oyster reefs appear increasingly fragmented on small spatial scales. In outdoor mesocosms, experiments tested how consumption of representatives of 4 different bivalve guilds by each of 3 mesopredators varies between continuous and fine-scale patches of oyster reef habitat. The mesopredator that fed least (stone crab) exhibited no detectable change in consumption on any bivalve (ribbed mussel, bay scallop, hard clam, and 3 size classes of eastern oyster). Consumption of bay scallops by both blue crabs and sheepshead fish was greater in small patches than in continuous oyster reef habitat. Of the bivalve guilds tested, only the scallop possesses swimming motility sufficient to reduce predation, an escape response that would likely leave the bivalve protected within structured habitat in larger continuous oyster reefs. Sheepshead consumed more small oysters in the continuous habitat than in the fine patches, while no other predator-prey interaction exhibited differential feeding as a function of habitat patchiness. Consequently, predation by mesopredators on bivalves can vary with the scale of oyster reef patchiness, but this process may depend upon the bivalve guild. Understanding the role of habitat patchiness on fine scales may be increasingly important in view of the declines in apex predatory sharks leading to mesopredator release, and global climate change directly and indirectly enhancing stone crab abundances, thereby increasing potential predation on bivalves.

Development of drug-loaded chitosan-vanillin nanoparticles and its cytotoxicity against HT-29 cells

Chitosan as a natural polysaccharide derived from chitin of arthropods like shrimp and crab, attracts much interest due to its inherent properties, especially for application in biomedical materials. Presently, biodegradable and biocompatible chitosan nanoparticles are attractive for drug delivery. However, some physicochemical characteristics of chitosan nanoparticles still need to be further improved in practice. In this work, chitosan nanoparticles were produced by crosslinking chitosan with 3-methoxy-4-hydroxybenzaldehyde (vanillin) through a Schiff reaction. Chitosan nanoparticles were 200-250 nm in diameter with smooth surface and were negatively charged with a zeta potential of - 17.4 mV in neutral solution. Efficient drug loading and drug encapsulation were achieved using 5-fluorouracil as a model of hydrophilic drug. Drug release from the nanoparticles was constant and controllable. The in vitro cytotoxicity against HT-29 cells and cellular uptake of the chitosan nanoparticles were evaluated by methyl thiazolyl tetrazolium method, confocal laser scanning microscope and flow cytometer, respectively. The results indicate that the chitosan nanoparticles crosslinked with vanillin are a promising vehicle for the delivery of anticancer drugs.

A single panmictic population of endemic red crabs, Gecarcoidea natalis, on Christmas Island with high levels of genetic diversity

The red crab, Gecarcoidea natalis, is endemic to Christmas Island in the Indian Ocean and largely responsible for shaping the unique ecosystem found throughout the island's rainforests. However, the introduction and establishment of supercolonies of the highly invasive yellow crazy ant, Anoplolepis gracilipes, has decimated red crab numbers over the last several decades. This poses a significant risk to the future conservation of G. natalis and consequently threatens the integrity of the unique island ecosystem. Here we undertook a population genetic analysis of G. natalis using a combination of 11 microsatellite markers and sequencing of the mitochondrial cytochrome oxidase subunit I gene from samples collected on Christmas Island as well as a single location from North Keeling Island (located approximately 900 km west of Christmas Island). The genetic results indicate that G. natalis is a single panmictic population on Christmas Island, with no spatial genetic structure or restricted gene flow apparent between sampled locations. Further, G. natalis from North Keeling Island are not genetically distinct and are recent immigrants from Christmas Island. The effective population size of G. natalis has likely remained large and stable on Christmas Island throughout its evolutionary history with relatively moderate to high levels of genetic diversity in microsatellite loci and mitochondrial haplotypes assessed in this study. For management purposes G. natalis can be considered a single panmictic population, which should simplify conservation efforts for the genetic management of this iconic island species. © 2014 Springer Science+Business Media Dordrecht.