Giant Mud Crab Scylla Serrata Research Articles

Implications of spawning migration patterns of the giant mud crab Scylla serrata (Forskål, 1775) on opportunities for larval dispersal

Connectivity is an essential driver for aquatic species distribution, genetic variability and stock structure. The giant mud crab (Scylla serrata) is a coastal portunid commonly associated with estuaries and mangrove systems. This species has been observed to undertake a seaward spawning migration, as the larval development is known to be more successful under the stable environmental conditions typically found in marine waters. The larvae return to the coastal areas through advection, where they are recruited and enter the estuaries after metamorphosing into the first instar. Here, we used numerical modelling to test hypotheses regarding probabilities of larval settlement of the giant mud crab and the effect of the distance offshore from which females release the eggs. Our scenarios considered the biological characteristics of larvae and oceanographic conditions for six locations for mud crabs along a complex coastline - the Queensland east coast, Australia. The models suggest that all locations tend to self-supply, and to exchange mud crab larvae with other regions, but in different magnitudes. The spawning distance offshore considerably affects larval distribution and settlement. The main drivers for larval advection in areas within the continental shelf are wind patterns and coastal currents, while offshore along the Australian continental slope, the main drivers are ocean currents. Self-recruitment is predominant, although we also observed a significant degree of connectivity between each location and the surrounding coastline. Short spawning migrations benefit self-recruitment in all scenarios, but long offshore migrations favour connectivity among different locations. This source/sink balance seems to depend on the local oceanographic features. Nevertheless, offshore spawning by the giant mud crab has the potential to provide for successful recruitment in a variety of environmental contexts. This study provides novel predictions of the probabilities of larval settlement for mud crab populations considering ocean advection that can be applied to different contexts.

Trial of a novel experimental design to test depuration of PFASs from the edible tissues of Giant Mud Crab following exposure under natural conditions in the wild

Poly and perfluorinated alkyl substances (PFASs) are persistent organic pollutants (POPs) that are highly resistant to environmental degradation, and have been detected in a broad range of terrestrial and aquatic species. Portunid crabs have been shown to accumulate comparatively high concentrations of PFASs, but previous work examining depuration in crabs was inconclusive. Here, we trialled a novel experimental design to study depuration of PFASs from edible tissues of portunid crabs, using paired claw samples, and trial this design with Giant Mud Crab Scylla serrata exposed to the contaminant under natural conditions. We found evidence for depuration of perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS) and perfluorooctanoic acid (PFOA), but with depuration half-lives as high as 40 days (for PFOS). We also observed substantial variability in the data, including differences in PFAS concentrations between claws from the same individuals, potentially resulting from claw loss and re-growth prior to capture. These results have broad implications for assessing and minimising exposure risk in seafood species.

Optimisation of nursery rearing for megalopa of giant mud crab Scylla serrata (Forskal, 1775)

Three nursery rearing trials were conducted to overcome the inconsistent survival of megalopa of the giant mud crab Scylla serrata (Forskal, 1775) during metamorphosis to crab instar. In the first trial, 3-4 days old megalopa (4.73 mg mean body weight) were stocked in hapas erected in outdoor brackishwater ponds and indoor fiberglass (FRP) tanks at densities of 500 nos. m-2 and 1 no. l-1 respectively and reared for 15 days using minced clam meat (Meretrix casta) as feed. Outdoor hapas were provided with seaweed, Gracilaria tenuistipitata as shelter. Mean survival rate of crab instar following three consecutive runs were significantly higher (p<0.05) for megalopa reared in outdoor hapas (57.7±2.7%) over indoor FRP tanks (24.1±2.2%). To ascertain the life stage that yields optimal survival on weaning from indoor hatchery to ponds, zoea 5 (Z5) and megalopa 1-day old (M1), 2-day old (M2), 3-day old (M3) and 4-day old (M4) were reared in hapas for15 days and fed on minced clam meat. Three day and 4-day old megalopa demonstrated significantly higher survival rates (p<0.05) of 62.3±3.08% and 69.6±2.35% respectively to crab instar stage at conclusion of the trial. Megalopa (3-4 days old, 5.05 mg mean body weight) were stocked to 100 l tanks (stocking density - 1 no. 4 l-1) and reared for a period of 8 days using different feeds viz., artemia biomass (T1), minced clam meat (T2), crab larvae (T3) and artemia nauplii (T4) in the third trial to evaluate various production parameters. Crab instar conversion rate (number of crab instars/number of megalopa stocked × 100) was significantly higher (p<0.0001) for megalopa fed using artemia biomass (T1) and minced clam meat (T2) at 74.66±5.81% and 72.00±2.30% respectively. Results of the present study indicate that, high density rearing (500 no. m-2) of megalopa (3-4 days old) in outdoor hapas provided with seaweed refuge for short periods (15 days) would yield higher survival rate to crab stage. Nursery rearing of megalopa in ponds reduces the hatchery phase in mud crab larval rearing and maximise production of crab instars.

Simple Modeling to Inform Harvest Strategy Policy for a Data‐Moderate Crab Fishery

AbstractAttempts to model the giant mud crab Scylla serrata fishery in the Northern Territory (Australia), have often been complex and the results difficult to interpret, leading to divergent estimates of fishing mortality. This has hindered the development of meaningful management policy. Additionally, analyses based on the entire Northern Territory fishery have masked the extreme variation in catches observed along the Gulf of Carpentaria coast. We applied a structurally simple model to visualize the historical patterns in stock size, recruitment, fishing mortality, and fishing mortality at maximum sustainable yield in the western Gulf of Carpentaria mud crab fishery (WGOCMCF) from 1983 to 2017. We also projected future catch and female spawning stock biomass (FSSB) under positive, neutral, and negative recruitment scenarios for three closure periods contained in the fishery harvest strategy (which start in October, if triggered) and compared these with the results of equivalent closures beginning in September. This exercise was undertaken because of known and significant changes in the proportion of fishing effort across different months as well as large variations in the proportion of females harvested each month (with both factors being particularly low in December). These differences were annualized and incorporated into the yearly time step of the model. Predicted catch and FSSB were similar for shorter closure periods (3 or 6 weeks), irrespective of the starting month. However, initiating a 3‐month closure in September rather than October could lead to a 16–17% increase in FSSB under negative and average recruitment anomalies, imposing a 9–10% reduction in predicted catch. Based on our experience applying a simple model to the WGOCMCF, we also describe processes and practices that could improve the quality of assessment data for this and other data‐moderate crab fisheries.

Muddy waters: An assessment of the suitability of zygocardiac ossicles for direct age estimation in the Giant mud crab Scylla serrata

AbstractA fundamental characteristic of calcified structures commonly used for direct age estimation in animals is that new material is accreted cumulatively and preserved across ontogeny, thus allowing growth marks to be reliably observed and counted. Direct age estimation in crustaceans has been problematic due to molting of calcified structures across ontogeny; however, recent studies suggest that gastric ossicle tissue is retained through molts and can be used for age estimation. We evaluate the use of sectioned gastric ossicles for direct aging of the Giant mud crab Scylla serrata. Sectioned zygocardiac ossicles from crabs collected in northern Australia are analyzed to determine: (1) whether putative annual age estimates can be reliably reproduced; (2) if age estimates are compatible with previous information; and (3) if ossicle growth is cumulative across ontogeny. Our analyses show that readability of putative annual increments in sectioned ossicles is poor and age estimates imprecise in comparison to fish otolith studies. Age‐at‐size estimates are broadly compatible with previous mark‐recapture data from the same regions. However, analyses of ossicle growth morphology suggest that the zygocardiac ossicles are either shed or extensively reworked during ontogeny, thus casting doubt on the utility of gastric ossicles for direct age estimation in this species. We conclude that the ontogenetic growth morphology of structures used for crustacean aging needs to be carefully considered and that detailed information on the timing and frequency of increment formation—and at least some understanding of the underlying processes—is required before this method is widely adopted.

Genetic diversity and connectivity in the East African giant mud crab Scylla serrata: Implications for fisheries management.

The giant mud crab Scylla serrata provides an important source of income and food to coastal communities in East Africa. However, increasing demand and exploitation due to the growing coastal population, export trade, and tourism industry are threatening the sustainability of the wild stock of this species. Because effective management requires a clear understanding of the connectivity among populations, this study was conducted to assess the genetic diversity and connectivity in the East African mangrove crab S. serrata. A section of 535 base pairs of the cytochrome oxidase subunit I (COI) gene and eight microsatellite loci were analysed from 230 tissue samples of giant mud crabs collected from Kenya, Tanzania, Mozambique, Madagascar, and South Africa. Microsatellite genetic diversity (He) ranged between 0.56 and 0.6. The COI sequences showed 57 different haplotypes associated with low nucleotide diversity (current nucleotide diversity = 0.29%). In addition, the current nucleotide diversity was lower than the historical nucleotide diversity, indicating overexploitation or historical bottlenecks in the recent history of the studied population. Considering that the coastal population is growing rapidly, East African countries should promote sustainable fishing practices and sustainable use of mangrove resources to protect mud crabs and other marine fauna from the increasing pressure of exploitation. While microsatellite loci did not show significant genetic differentiation (p > 0.05), COI sequences revealed significant genetic divergence between sites on the East coast of Madagascar (ECM) and sites on the West coast of Madagascar, mainland East Africa, as well as the Seychelles. Since East African countries agreed to achieve the Convention on Biological Diversity (CBD) target to protect over 10% of their marine areas by 2020, the observed pattern of connectivity and the measured genetic diversity can serve to provide useful information for designing networks of marine protected areas.

Serotonin induces ecdysteroidogenesis and methyl farnesoate synthesis in the mud crab, Scylla serrata

In the current study, we have examined the role of serotonin in regulating the levels of methyl farnesoate and ecdysteroids in the giant mud crab Scylla serrata and validated that serotonin indeed is a reproductive hormone. Administration of serotonin elevated circulatory levels of methyl farnesoate and ecdysteroids in crabs. Since methyl farnesoate and ecdysteroid act through retinoid X receptor (RXR) and ecdysteroid receptor (EcR) respectively and these receptors are involved in the regulation of reproduction in crustaceans, we have determined the mRNA levels of RXR and EcR in hepatopancreas and ovary after serotonin administration. The expression levels of both RXR and EcR increased significantly in the hepatopancreas and ovary of serotonin injected crabs when compared to the controls. In vitro organ culture studies revealed that incubation of Y-orgas and mandibular organ explants in the presence of serotonin resulted in a significant increase in the secretion of ecdysteroids by Y-organs, but without alterations in MF synthesis in mandibular organs. From the above studies it is evident that serotonin stimulates Y organs resulting in increased ecdysteroidogenesis. Though the circulatory levels methyl farnesoate elevated after serotonin administration, organ culture studies revealed serotonin mediated methyl farnesaote synthesis is indirect probably by inhibiting release of mandibular organ inhibiting hormone from eyestalks.

Induction of ecdysteroidogenesis, methyl farnesoate synthesis and expression of ecdysteroid receptor and retinoid X receptor in the hepatopancreas and ovary of the giant mud crab, Scylla serrata by melatonin

Melatonin, a chronobiotic molecule, is known to modulate several physiological functions in crustaceans including reproduction, molting and glucose homeostasis. In our earlier studies (Sainath and Reddy, 2010a), we observed hyperglycemia in crabs after melatonin administration and concluded that melatonin is another crustacean hyperglycemic hormone. In the current study, we have further examined the role of melatonin in regulating the levels of methyl farnesoate and ecdysteroid in the giant mud crab Scylla serrata and determined that melatonin indeed is a reproductive hormone. Further, we have determined partial nucleotide sequences of retinoid X receptor (RXR) and ecdysone receptor (EcR) in S. serrata and also studied the effect of melatonin on expression of these genes. Cloned RXR and EcR possess high sequence similarity with other Brachyuran genes. Administration of melatonin elevated circulatory methyl farnesoate (MF) and ecdysteroid levels in crabs. Since MF and ecdysteroid act through RXR and EcR respectively and these receptors are involved in the regulation of reproduction in crustaceans, we measured the expression levels of RXR and EcR in hepatopancreas and ovary after melatonin administration. The expression levels of both RXR and EcR increased significantly in the hepatopancreas and ovary of melatonin injected crabs when compared to the controls. In vitro culture of mandibular organ (MO) and Y-organ (YO) in the presence of melatonin resulted in a significant increase in the secretion of methyl farnesoate and ecdysteroid respectively. From the above studies it is clear that melatonin stimulates YO and MO, resulting in increased synthesis of ecdysteroids and methyl farnesoate, and thereby inducing reproduction in S. serrata.

Long-term effects of marine park zoning on giant mud crab Scylla serrata populations in three Australian estuaries

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 508:163-176 (2014) - DOI: https://doi.org/10.3354/meps10865 Long-term effects of marine park zoning on giant mud crab Scylla serrata populations in three Australian estuaries Paul A. Butcher1,4,*, Andrew J. Boulton1, William G. Macbeth2, Hamish A. Malcolm3 1School of Rural and Environmental Science and the National Marine Science Centre, University of New England, Coffs Harbour, New South Wales 2450, Australia 2Cardno Ecology Lab, Cardno NSW/ACT, PO Box 19, St Leonards, New South Wales 1590, Australia 3New South Wales Department of Primary Industries, PO Box 4297, Coffs Harbour, New South Wales 2450, Australia 4Present address: New South Wales Department of Primary Industries, National Marine Science Centre, PO Box 4321, Coffs Harbour, New South Wales 2450, Australia *Corresponding author: paul.butcher@dpi.nsw.gov.au ABSTRACT: Multiple-use marine parks are a powerful management tool to help protect marine biodiversity and sustain wild fisheries while allowing some access to recreational and commercial activities using zoning arrangements. Research has focused on fish but far less is known about the effectiveness of zoning for other groups, such as exploited crustaceans, especially in estuaries. In this 8 yr study, we tested the hypotheses that unfished zones, which had been closed to fishing since 1991, would have higher abundances (catch per unit effort) of the giant mud crab Scylla serrata in 3 estuaries (Wooli, Corindi and Sandon) of the Solitary Islands Marine Park (SIMP) in New South Wales, Australia, and that recovery after fishing closure would be rapid. Replicate fished and unfished zones were sampled from December 1998 (Wooli) and July 2000 (Corindi and Sandon) until April 2007. In August 2002, re-zoning occurred with some estuarine sections re-opened to trapping, some newly closed and others either remaining closed or open. This enabled Before-After-Control-Impact analyses to test our hypotheses. Crab numbers increased rapidly after zone closure and unfished zones protected giant mud crabs from exploitation with catches 2 to 3 times greater than in fished zones. Although there was substantial temporal variation in crab abundance within and among the 3 estuaries, responses to zoning were consistent and spatial protection in estuaries in the SIMP proved effective for sustaining giant mud crab populations. This type of management shows promise for protecting or replenishing stocks of other species of crabs worldwide. KEY WORDS: Marine parks · Giant mud crab · Scylla serrata · No-take zones · CPUE Full text in pdf format PreviousNextCite this article as: Butcher PA, Boulton AJ, Macbeth WG, Malcolm HA (2014) Long-term effects of marine park zoning on giant mud crab Scylla serrata populations in three Australian estuaries. Mar Ecol Prog Ser 508:163-176. https://doi.org/10.3354/meps10865 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 508. Online publication date: August 04, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.