Crab Populations Research Articles

Altering river flow impacts estuarine species and catches: lessons from giant mud crabs

Abstract Anthropogenic alterations to river flow could have repercussions for flow-dependent species downstream but few studies account for these dynamic relationships or quantify impacts of altered river flow. Scylla serrata—a widely distributed portunid crab—was used as an example of a flow-dependent species to model impacts of altered flow on species abundance and catch. Crab population dynamics were modelled across a large semi-enclosed tropical sea in northern Australia. Environmental drivers, primarily river flow, but also temperature and the Southern Oscillation Index were linked to crab dynamics to explain variability in historical catches. Catch and abundance could then be predicted under altered flow scenarios. River flow significantly improved the ability to explain historical catches for some regions but not all, and the strength of this relationship varied across catchments. Altered flows had negligible effects for perennial rivers but for ephemeral and temporally variable rivers, predicted decreases in abundance and catch ranged from 36 to 46% on average. Our modelling approach showcases a way to dynamically and rigorously quantify impacts of altered river flow on a key species with potential to help inform natural resource management, including policy decisions on the timing, quantity, and method of water removed from rivers.

ANALISIS PROKSIMAT KEPITING PASIR (Ocypode Cursor) SEBAGAI SUMBER MAKANAN BERGIZI BAGI MASYARAKAT PESISIR DI KECAMATAN SALAHUTU PULAU AMBON

Background: The use of the Ocypode Cursor sand crab as a source of nutritious food for coastal communities in the Salahutu District area is because this marine animal is found living in sandy substrates along the coast and can be used as a source of nutritious food for coastal communities. Methods: Water content measurement was carried out using the oven method. Determination of ash content is carried out using the dry ashing method. Determination of fat content was carried out using the Soxhlet method. Analysis of protein levels using the Kjeldahl micro method. Results: The results of proximate analysis of sand crab for 100 grams of meat showed a water content of 79.72%, ash content of 6.82%, fat content of 7.5%, protein content of 15.7%. Conclusion: The results of the analysis show that there is a significant regression according to the regression provisions y = a + bx= 3,266 + 0.016, and the value of R2 = 0.802, even the analysis also shows that there is a significant influence according to the value of df = 24-22 = 2 with the value of F = 44,588 with a significance level of 000, < p 0.05, this means that there is a significant influence between the availability of the Ocypode cursor sand crab population in its habitat and Ocypode cursor as a source of nutritious food for the community (OcMGz).

Growth and survival rate of blue swimming crab enlargement in the south coast of Pamekasan, Madura Island

Indonesia has fishery commodities favoured by the world market, especially blue swimming crab fisheries. Fishing activities that continue to increase have caused the blue swimming crab population in nature tend to decrease. Therefore, it is necessary to develop aquaculture in ponds and coastal waters. However, blue swimming crab enlargement has technological constraints that have yet to be widely known by the wider community. The study aimed to determine the survival rate of blue swimming crabs in coastal waters using ponds conducted in Pamekasan, East Java. The parameters measured were the width of the blue swimming crab’s carapace using a ruler and the growth of the blue swimming crab’s weight using a digital scale. The experimental results on blue swimming crabs obtained an absolute growth of 9.8 cm and a survival rate of 3.96%. The high rate of cannibalism in blue swimming crabs can indicate the cause of the low survival rate of blue swimming crabs. This research is expected to increase the choice of blue swimming crab enlargement to reduce the pressure of catches and be another alternative to reduce the level of blue swimming crab fishing in nature.

Characteristics and density of the horseshoe crab (Tachypleus gigas) from gillnet fishery in Pamekasan, Madura Island

The horseshoe crab is included in the category of protected species (ETP) because of its rare existence. Therefore, it is essential to identify the characteristics and density of horseshoe crabs. This study aimed to examine horseshoe crabs’ morphometric characteristics and density (Tachypleus gigas) on the coast of Polagan Village, Pamekasan Regency, Madura. This study was conducted from November to December 2020. Results showed that 45 horseshoe crabs were found in Pamekasan waters during the study period, consisting of 30 males and 15 females. The total average length was 164.57±40.92 mm and 163.67±31.30 mm for males and females, respectively. Males than females dominated horseshoe crabs. The density was based on the size class, consisting of 9 ind of small size (73-132 mm), 31 ind of medium size (133-222 mm), and 5 ind of large size (223-282mm). The water quality was classified as good for the growth of the horseshoe crab population, with sediments dominated by sand and silt. Further study is needed regarding the seasonal variation of horseshoe crab in Pamekasan Water.

American lobster and Jonah crab populations inside and outside the Northeast Canyons and Seamounts Marine National Monument, USA

AbstractObjectiveThere is international pressure to increase the worldwide expanse of marine protected areas (MPAs). However, MPAs often lack preexisting long‐term biological baselines, which are essential for assessing MPA effects and for refining the conservation and socioeconomic benefits they confer to society. Our study addresses this issue by establishing demographic baselines for two commercially important species prior to a proposed fishing ban inside the Northeast Canyons and Seamounts Marine National Monument, a recently established MPA on the continental shelf break approximately 200 km southeast of Cape Cod, Massachusetts.MethodsSamples were obtained by the Commercial Fisheries Research Foundation's American Lobster and Jonah Crab Research Fleet, which is an industry‐based, fishery‐dependent data collection program. Specially trained participants recorded year‐round biological data from their 2013 to 2021 commercial catches of American lobster Homarus americanus and Jonah crab Cancer borealis. Samples were taken from an area inside the MPA and from two areas outside the MPA, spanning 130 km to the east and west.ResultAmerican lobster sizes and sex ratios varied between areas, and their sizes, sex ratios, and proportion of ovigerous females differed between submarine canyons within areas. American lobster sizes, sex ratio, proportion of ovigerous females, and prevalence of shell disease were also affected by season and/or depth. Jonah crab parameters did not vary between areas, but sex ratio varied with season and depth, and the proportion of ovigerous females varied with depth.ConclusionThese demographic baselines are the only data available, at a sufficient spatial and temporal resolution, for evaluating the effects of a proposed fishing ban in the MPA, and they fill important data gaps for stock assessments. To evaluate possible future population changes, it will be necessary to continue collecting data from inside and outside the MPA using comparable methods, and to account for the preexisting sources of variation that we have identified.

Predatory impacts of invasive Blue Catfish in an Atlantic coast estuary

AbstractObjectivePredatory invasive fishes may consume species of management interest and alter food webs. Blue CatfishIctalurus furcatusis a large‐bodied, salinity‐tolerant species that exhibits broad diet breadth and preys on species of both conservation concern and fisheries management interest. To better understand the ecological consequences of the establishment of Blue Catfish fisheries, estimates of predatory impacts are needed.MethodsUsing a Monte Carlo simulation, we integrated abundance estimates, diet information, and consumption‐to‐biomass ratios to estimate population‐level Blue Catfish predation for a large Chesapeake Bay tributary along the mid‐Atlantic coast of the United States, the James River.ResultPopulation‐level annual predation estimates by Blue Catfish exceeded 100 metric tons for several species or taxa of interest, including an estimated 400.7 metric tons (95% CI = 272.6–613.2) of blue crabCallinectes sapidus. Prey species abundances were unknown and thus limited opportunities to evaluate prey population responses. For instance, effects of Blue Catfish on blue crab populations remain unknown without tributary‐specific estimates of blue crab abundance, but comparisons to landings data suggests that Blue Catfish predation on blue crab in the James River may be low compared with harvest.ConclusionEstimation of Blue Catfish predatory effects may inform development of management goals and objectives that balance diverse stakeholder interests. This work provides beneficial information to assess trade‐offs of Blue Catfish fisheries and their effects on coastal aquatic resources.

Redox-active metals and oxidative stress-mediated myopathies in Callinectes amnicola, blue crab populations from impacted sites of the Lagos Lagoon: inferences for adverse ecological outcomes.

While oxidative stress pathways are associated with a wide variety of tissue pathologies, its applications for evaluating and discerning ecological risks are limited. This study seeks to associate trends of lipid peroxidation and oxidative stress to risks of muscle pathologies in blue crabs inhabiting regions of the Lagos Lagoon. Crab samples (n = 520) were selected from pollution-impacted sites of the lagoon at Iddo, Ajah, Okobaba, Makoko, and the mid-lagoon area (control site). Antioxidant enzyme capacity, i.e., superoxide dismutase, catalase, glutathione peroxidase (GPx), and glutathione-S-transferase, and lipid peroxidation were evaluated in the muscle tissue of the blue crabs. The study findings showed distinct patterns of metal uptake in muscle, with redox-active metals (Cu and Zn) and redox-inactive metals (Pb and Cd) exhibiting site-specific differences. Additionally, there were changes in antioxidant modulation, lipid peroxidation, and the presence of associated myopathies. Blue crabs from sites (Makoko and Ajah) with greater uptake of redox-active metals (Cu and Zn) in muscle tissue showed higher trends of lipid peroxidation and the most prevalence of severe regression-type myopathies. Sites with lower uptake of redox-active metals showed the predominance of circulatory-type myopathies. This study also provides evidence of severe necrosis and myositis associated with digenean parasite cysts in crab muscle. Pathological evidence of severe skeletal muscle deterioration in the presence of greater lipid peroxidation could have implications for motor-neuron activity and reduced force-generating capacity necessary for adaptive responses in the wild. We conclude that elevated uptake of redox metals could aggravate the onset of myopathies in wild populations.

The effects of moderate concentrations of Karenia brevis on stone crab reproduction

The stone crab, Menippe mercenaria, supports a commercial fishery along Florida's Gulf coast where harmful algae blooms, known as red tides (Karenia brevis) develop. Red tides occur nearly annually and can overlap with the stone crab reproductive season. We determined the impact of moderate red tide (K. brevis) concentrations (∼105 cells L−1) on stone crab embryo development, hatching success, female stress, hatch duration, and larval survival. Crabs and larvae were exposed to a control (no K. brevis) or moderate concentrations of K. brevis. No difference in embryo development or hatching success was observed. Stress was elevated in the K. brevis treatment, resulting in prolonged hatching relative to the control. Larval survival was reduced in K. brevis relative to the control. Moderate concentrations of K. brevis results in sublethal effects on stone crabs and reduces larval survival, suggesting that mitigation that reduces bloom concentrations could provide relief to stone crab populations.

Population and spatial ecology of horseshoe crabs (Limulidae) in a nursery ground at Pulau Bedukang, Brunei Bay, Borneo

Abstract. Rozaini AF, Laurie KH, Marshall DJ. 2023. Population and spatial ecology of horseshoe crabs (Limulidae) in a nursery ground at Pulau Bedukang, Brunei Bay, Borneo. Biodiversitas 24: 4485-4492. Suitable nursery habitat to support populations of juvenile horseshoe crabs is becoming threatened globally. There are currently no formal studies on juvenile populations of the horseshoe crabs (Limulidae) for Brunei Darussalam (Brunei, Borneo). We investigated body size structure, population cohort and ecological distribution of juvenile horseshoe crabs associated with a mudflat on Pulau Bedukang, in Brunei Bay. Seventy juveniles were retrieved during four sampling days covering two seasons and four study sites. Carcinoscorpius rotundicauda and Tachypleus gigas were common, whereas only two individuals of Tachypleus tridentatus were found. Carapace width (size) was similar in the common species and there was no difference in juvenile size between the seasons and study sites. Body weight to carapace width relationships showed that the species grew at similar rates, although C. rotundicauda developed faster, producing 14 compared to the eight pre-migration mudflat instars produced by T. gigas. Species densities were similar, and there was no spatial separation of species or juvenile size across the mudflat or in relation to the mangrove forest edge. Nearest-neighbor (NN) analysis showed that individual crabs were generally dispersed. Their mudflat cohabitation suggests physiological and behavioral plesiomorphies for common optimal developmental salinity and temperature conditions. This study provides baseline information for comparison with other regional studies and for local conservation planning.

Application of a catch multiple survey analysis for Atlantic horseshoe crab Limulus polyphemus in the Delaware Bay

AbstractObjectiveThis paper applies a catch multiple survey analysis (CMSA) to Atlantic horseshoe crabs Limulus polyphemus in the Delaware Bay to generate robust population estimates for harvest management. Currently, horseshoe crabs along the U.S. Atlantic coast are harvested as bait for other fisheries and collected for their blood, which is used in a biomedical industry. The Delaware Bay is home to the largest population of horseshoe crabs and is a significant stopover for shorebirds to rebuild energy by consuming horseshoe crab eggs prior to completing their northward migration. To address this interrelationship, the Adaptive Resource Management (ARM) Framework has been used since 2013 to ensure that horseshoe crab harvest within the region takes into account the forage needs of migratory birds. Since its inception, the ARM Framework has used a single trawl survey's swept area‐based population estimates of horseshoe crab relative abundance and a theoretical population model developed primarily from literature‐derived values. With more data collected in the region in recent years and other sources of mortality that can now be quantified, a catch survey model can provide horseshoe crab population estimates going forward.MethodsA CMSA was used to estimate male and female horseshoe crab population size for 2003–2021 using all quantifiable sources of mortality and three fishery‐independent indices of abundance.ResultThe CMSA results indicated that adult abundance of male and female horseshoe crabs was stable from 2003 to 2013 and then began to increase through 2017, a result that is consistent with stock rebuilding following a period of harvest restrictions as recommended by the ARM Framework. Population estimates were lower in recent years but remained above the levels estimated before implementation of the ARM Framework. In 2021, the CMSA estimated that there were over 6 million mature females and nearly 16 million mature male horseshoe crabs in the region.ConclusionThe CMSA provides the best and most comprehensive population estimates of horseshoe crabs in Delaware Bay and will improve modeling efforts within the ARM Framework going forward.

Temperature-dependent feeding behavior in the brown box crab, Lopholithodes foraminatus

IntroductionGrowing fishing pressures and ocean warming are potential concerns for populations of brown box crabs, Lopholithodes foraminatus, at the southern end of their geographic distribution. In Southern California, brown box crabs are thought to occupy a broad depth gradient (intertidal zone - 547 m), which exposes them to temperatures ranging from 8°C - 24°C. This large temperature span presents challenges for these ectothermic animals because the rates of their physiological processes, and ultimately their dietary needs, behavior, and health, vary with temperature. Here we examined how temperature affects the feeding behavior of brown box crabs to better understand their ecology in warmer regions of their distribution.MethodsAdult crabs were exposed to one of three temperature treatments (8°C, 15°C, and 20°C, N=10) for 2 months. Weekly throughout the exposure period, crabs were given two similar-sized prey items of different crushing strength (clam and mussel). Claw pinch force, prey preference, time to consume prey, and number of prey consumed were recorded prior to the start of the experiment and weekly for the duration of the study, with the exception of pinch force, which was recorded bi-weekly. We hypothesized that crabs will have a stronger pinch force at warmer temperatures, prefer prey items that require less breaking force at the coldest temperature, consume prey faster at warmer temperatures, and consume more prey at warmer temperatures.ResultsOur results confirm that pinch force is consistently greater at 15°C compared to 8°C, however, crabs at 8°C consumed more clams (higher strength) while those at 15°C consumed more mussels. Crabs at 8°C also consumed prey items faster than crabs at 15°C but ate a similar number of prey. Furthermore, there was 100% mortality at 20°C within 8 days of exposure, indicating their proximity to lethal limits within Southern California.DiscussionThese results show that brown box crab feeding behavior exhibits temperature thresholds, which may alter their nutritional state, community interactions, and distribution under both short-term and long-term changes in ocean temperature.

A step towards the integration of spatial dynamics in population dynamics models: Eastern Bering Sea snow crab as a case study

Considering spatial processes in population dynamics models can be difficult because of data limitations and computational costs. We adapted a high-resolution spatiotemporal assessment framework to better address fine-scale spatial heterogeneities based on theories of fish population dynamics and spatiotemporal statistics. Specifically, we developed a size-based state-space model for the snow crab (Chionoecetes opilio) population in the Eastern Bering Sea (EBS) to refine the representation of spatial processes in integrated population models, facilitate understanding of the drivers of spatiotemporal population dynamics, and provide new insights for management advice. The model fits to spatial survey and fishery-dependent catch data. It implicitly accounts for seasonal movement between the time of the survey and that of fishery to estimate fine-scale spatial population dynamic and fishing impacts, including potential environmental drivers. We quantify, for the first time, spatiotemporal variation in exploitable abundance, fishing mortality, recruitment, and mature and immature abundance. The model estimated declines in exploitable abundance and in fishing mortality with variable spatial distributions, and sporadic recruitment, spatially concentrated in the northeast EBS. Few spatial assessments have been used as the basis for management advice and we consider this study as a step towards the integration of spatial dynamics in stock assessment.

Investigating conspecific CsRV1 transmission in Callinectes sapidus

A reo-like virus, CsRV1, is found in blue crabs, Callinectes sapidus, from every North American location assessed, including Chesapeake Bay and the Atlantic and Gulf coasts, USA and associated with blue crabs in softshell production. CsRV1-associated crab mortality is prevalent in captive crabs, but it is still unknown how CsRV1 is transmitted. The purpose of this study was to examine the role that conspecific predation or scavenging may play in per os transmission in single exposure and repeated exposure experiments. For viruses without cell culture propagation, repeated exposure experiments have the challenge of presenting the virus consistently during the experiment and across time replicates. In a single-exposure experiment, none of the crabs fed muscle tissue of crabs carrying intense infections of CsRV1 developed CsRV1 infections. In a repeated-exposure trial, using infected muscle tissue prepared in alginate blocks, CsRV1 was detected in 11% of the crabs fed infected tissue but was not significantly different from the control group fed alginate lacking CsRV1. For repeated per os exposure experiments, the study demonstrated the utility of using alginate to present the same homogenous sample of virus, both injected and per os, over time for oral challenge experiments. Conspecific predation and scavenging could be a transmission route, but future work into this and other possible routes of transmission for CsRV1 is important to better understand the role this virus plays in wild crab populations and the soft-shell crab industry.

Exposure of blue crab (Callinectes sapidus) to modified clay treatment of Karenia brevis as a bloom control strategy

Harmful algal blooms (HABs) of the toxic marine dinoflagellate Karenia brevis, commonly called red tides, are an ongoing threat to human health and marine ecosystems in Florida. Clay flocculation is a standard control strategy for marine HABs in China and Korea and is currently being assessed for use in the United States. We evaluated the effects of a PAC-modified clay called Modified Clay II on mortality, eyestalk reflexes, and righting reflexes of 48 adult blue crabs (Callinectes sapidus). Crabs were exposed to clay alone (0.5 g L − 1), untreated K. brevis (1 × 106 cells L − 1), or a combination of K. brevis and clay for eight days. Clay treatment reduced cell concentrations in the water column by 95% after 24 h. We detected no significant differences in mortality, righting reflexes, or eyestalk reflexes between treatments. Our results indicate that the clay alone is not harmful to adult crabs at typical treatment concentrations within the measured time frame, and that treatment of K. brevis with this clay appears to have a negligible impact on crab mortality and the reflex variables we measured. These results suggest that Modified Clay II may be a viable option to treat K. brevis blooms without impacting adult blue crab populations. Additional controlled experiments and field tests are needed to further evaluate the impact of clay on natural benthic communities.

Hydrobiological studies on the shelf of the southeastern part of the Barents Sea in the summer of 2022

The purpose of this work is to assess the state of the red king crab population, as well as to collect related information about other types of invertebrates found in the study area. Materials and methods: a total of 114 trawl stations were made onboard the R/V Professor Boyko at depths from 42 to 185 m, which made it possible to cover a water area of 46.6 thousand square meters. km. Calculations of population density and biomass of organisms are given. Also, for the densest concentrations of invertebrates, the temperature and distribution depths were determined. Results of the study: the basis of trawl catches on the shelf of the south-eastern part of the Barents Sea was 8 species of commercial and by-catch of 34 species of non-commercial invertebrates, assigned to 6 groups of different taxa. The paper provides information on the biological state, distribution and biomass. The practical significance lies in the provision of annual forecasting materials on the total allowable catches of bottom commercial aquatic species for the Barents Sea.

Response of moulting genes and gut microbiome to nano-plastics and copper in juvenile horseshoe crab Tachypleus tridentatus

Nanoplastics (NPs) and heavy metals are typical marine pollutants, affecting the gut microbiota composition and molting rate of marine organisms. Currently, there is a lack of research on the toxicological effects of combined exposure to horseshoe crabs. In this study, we investigated the effects of NPs and copper on the expression of molt-related genes and gut microbiome in juvenile tri-spine horseshoe crabs Tachypleus tridentatus by exposing them to NPs (100 nm, 104 particles L−1) and/or Cu2+ (10 μgL−1) in seawater for 21 days. Compared with the control group, the relative mRNA expression of ecdysone receptor (EcR), retinoid x receptor (RXR), calmodulin-A-like isoform X1 (CaM X1), and heat shock 70 kDa protein (Hsp70) were significantly increased under the combined stress of NPs and Cu2+. There were no significant differences in the diversity and abundance indices of the gut microbial population of horseshoe crabs between the NPs and/or Cu2+ groups and the control group. According to linear discriminant analysis, Oleobacillus was the most abundant microorganism in the NPs and Cu2+ stress groups. These results indicate that exposure to either NPs stress alone or combined NPs and Cu2+ stress can promote the expression levels of juvenile molting genes. NPs exposure has a greater impact on the gut microbial community structure of juvenile horseshoe crabs compared to Cu2+ exposure. This study is helpful for predicting the growth and development of horseshoe crabs under complex environmental pollution.

Microsatellite and mitochondrial DNA based evidence reveals a single horseshoe crab (Limulus polyphemus) population on the northern Yucatan Peninsula, Mexico

In Mexico, the American horseshoe crab, Limulus polyphemus, is regarded as in danger of extinction, with a distribution range limited to the Yucatan Peninsula. Population genetics knowledge of this species in Mexico is incipient. We conducted a base-line genetic survey of eight localities on the northern coast of the Yucatan Peninsula to assess patterns of genetic structure, genetic variation, and gene flow among these localities. We analyzed DNA samples from 190 L. polyphemus specimens using 14 nuclear-encoded microsatellites and a region of the mitochondrial Cytochrome Oxidase I (COI) gene. Total allelic richness was 5.432, similar to previous figures for populations at the northern and southern extremes of the species’ global distribution. Observed heterozygosities (Ho) were 0.540–0.590, while expected heterozygosities (He) were 0.479–0.532, and there was no evidence of population bottlenecks. We found 129 mtDNA haplotypes (121 of which were found in single individuals) and 275 polymorphic sites, and the mean haplotype diversity among sites was high (0.852 ± 0.027 SD). AMOVAs based on both microsatellite and mtDNA data revealed that L. polyphemus from the northern Yucatan Peninsula show low genetic structure (Fst < 0.05, p > 0.05) and high gene flow (Nm = 10.967) favored by the absence of geographic barriers between coastal lagoons, suggesting that they constitute a single population. This was further confirmed by discriminant analyses of principal components using microsatellite data. This information is useful in establishing coordinated conservation efforts among federal and state protected areas.

Meta‐ and subpopulation estimation with disparate data: coconut crabs in the Western Indian Ocean

AbstractWidely dispersed fragmented populations are a challenge to monitor because subpopulation sizes may be very small, difficult to access and time consuming to sample regularly. We use the coconut crab (Birgus latro) on Pemba, United Republic of Zanzibar as a case study for estimating highly fragmented populations and metapopulation sizes. The species is a very large terrestrial decapod threatened by exploitation and habitat alteration and now classified as vulnerable. We developed an integrated model to analyse capture‐mark‐recapture (CMR) data from five sites jointly with count data from 24 sites to estimate site‐level densities and population sizes, predicted total population size across the Pemba archipelago, and investigated the effect of six predictors of human influence on density. We fitted separate models to test the effect of the same predictors on raw counts and individual body mass. We estimate the total population of coconut crabs on the Pemba archipelago to be c. 6700 terrestrial individuals. We show that government protection generally affects crabs positively, whereas presence of agriculture negatively affects their densities. This study highlights that time‐consuming CMR data can be leveraged to estimate densities on less visited sites, and that fully protected islands are critical for maintaining relatively high population densities. Our overall population estimate suggests that Pemba still hosts a viable coconut crab population in a part of its range where the species is otherwise in steep decline.

Beach morphodynamics modulate the effects of multidirectional habitat loss on population density and size structure of the Atlantic ghost crab Ocypode quadrata

Sandy beaches are land-sea transitional habitats experiencing ‘multidirectional’ habitat loss due to coastal developments (e.g. armoring and/or conversion of natural vegetation into manmade structures) and beach erosion. This ‘coastal squeeze’ is a chronic and progressive process; however, its impacts on beach biodiversity across morphodynamic gradients are still to be unveiled. We hypothesized that the effects of multidirectional habitat loss would be more severe on dissipative than on reflective beaches, due to the higher elevation, amount of built up sediment, and width of the backshore compartment of the latter. We, thus, examined the effects of coastal developments and erosion on density and size structure of the Atlantic ghost crab, Ocypode quadrata, on beaches with different morphodynamics. Given that the living area of ghost crabs spans all cross-shore compartments and the whole dissipative-to-reflective morphodynamic gradient, they are appropriate organisms to access the synergic effects of coastal developments and beach erosion under different morphodynamic regimes. On dissipative beaches, density and mean crab size increased with moderate erosion, attributed to the effects of space loss, which might increase territorial competition, favoring the remaining larger individuals. However, mean size and density decreased with high erosion given the more intense reduction in the abundance of large-sized crabs living in up-shore habitats. Mean crab size also decreased in the presence of coastal development while crab density did not vary with loss of backshore habitats occupied by larger individuals. On reflective beaches, both density and crab size decreased with coastal development; the crab size decrease recorded under moderate erosion was more evident in the presence of coastal development. Under high erosion, mean crab sizes declined, reflecting those under low erosion conditions. Overall, populations on reflective beaches appeared more resilient to extreme erosion. Notwithstanding, coastal developments affected population structure across all beach types, and especially in areas subjected to high erosion, exhibiting a synergic effect. We predict that, in combination, these stressors may lead to functionally extinct populations where conditions necessary for individuals to reach sexual maturity (i.e. occurrence of only small-sized and immature individuals) are not met. Thus, the connectivity between water, beach compartments and dunes/coastal plain, on both local and regional scales, may be essential to maintain viable and connected populations of ghost crabs. Further, our results strongly suggest that both size and density (complemented with crab abundance) must be considered equally important and in combination in future efforts to assess anthropogenic stressors on ghost crab populations and when guiding conservation strategies and policies to prevent their local and regional extinctions.

Orange mud crab (Scylla olivacea) exploitation at Sorong waters

Mangrove forests along the vast coast of West Papua serve as the habitat for mud crabs, which are high-value economic resources marketed to various regions in Indonesia. However, intensive utilization impacts the sustainability of mangrove crab populations, especially orange mud crabs (Scylla olivacea). Exploitation studies need to be conducted for further use to manage crab resources. This study was conducted for six months, from April to September 2021, with a sample of 2,971 orange mud crabs. Data analysis was carried out using crab carapace width (CW) data to predict resource exploitation and sustainability. The caught orange mud crab size was 80-190 mm, with natural mortality (M) lower than fishing mortality (F). The exploitation of this crab has attained E = 0.72, which proves that overfishing. We can do the management of orange mud crabs by observing the size of mature gonads and spawning areas to provide an opportunity to increase the population in the waters.