Crab Populations Research Articles

Is the threatened land crab Cardisoma guanhumi conquering human-dominated systems?

Land use changes are heralded as a major driver of biodiversity loss. However, recent findings show that cities, perhaps the most radical habitat transformation, sustain increasing numbers of threatened species. This emerging trend has been mostly chronicled for vertebrates from landlocked cities, although loss of biodiversity and rates or urbanization are higher in coastal marine systems. To advance our understanding on how threatened species may conquer human-dominated systems, we studied the threatened edible crab Cardisoma guanhumi and assessed how it is proliferating in croplands and urban systems at different spatial scales and whether populations show consequences of long-term exploitation. We gathered the data on crab populations covering the whole distribution range, including three countries reporting this as a threatened species. The abundance, distribution, and size structure of crab populations among different land uses at local scales were compared and published data for populations thriving in different habitats throughout their distribution range were compiled. We found that at local scale this species is able to thrive in natural and human-disturbed habitats, where food sources are heavily altered. At larger scales, the species showed no differences in abundance and size structure among natural and anthropogenic habitats. In areas near the southern distribution edge, crab populations were more abundant and composed of larger animals in urban areas and croplands than those in natural habitats, suggesting that human-disturbed systems are stepping stones to extend the geographic range. However, we found a long-term reduction in maximum body size, exacerbated by land use changes, that likely reflects exploitation regimes consistently targeting larger crabs. Despite its status as a threatened species, the long history of human exploitation combined with livestock farming practices may explain the proliferation of this crab in human-dominated systems, which emphasize the need to consider conservation in human-dominated systems.

Evaluating impacts of environmental stress and bioactive chemicals on the North Carolina blue crab population: An individual‐based model

AbstractObjectiveRecent estimates of the North Carolina blue crab Callinectes sapidus stock found that the stock is overfished and overfishing is occurring. Threats outlined in the 2018 stock assessment include climate change and estrogenic endocrine‐disrupting chemicals (EEDCs). The objective of this study was to use an individual‐based modeling approach to simulate the long‐term effects of climate change and EEDCs on the North Carolina blue crab stock.MethodsTo do this, we built an individual‐based model that simulated the life history of individual blue crabs, including but not limited to growth, reproduction, and mortality. We then tested our population of blue crabs against 30 different combinations of temperature and EEDC scenarios over 50 years to determine the long‐term effects on the population.ResultOur simulations suggested that the North Carolina blue crab population may be relatively resilient to climate change‐related temperature shifts but that there may be significant impacts at the population level as summer temperatures become more extreme. Endocrine‐disrupting chemical effects resulted in an alternative stable state of lower catch or the total extinction of the population.ConclusionThese results suggest that management strategy changes may be necessary as temperatures become more extreme in the region. In addition, more research is necessary to fully understand the effects of EEDCs on blue crabs and other crustaceans at the individual and population level.

Dispersal pathways of European green crab larvae into and throughout the eastern Salish Sea

The invasive European green crab (Carcinus maenas) was first detected on the US west coast around 1989 and has expanded its range northward from central California to southern Alaska. The eastern Salish Sea was initially thought to be protected from invasion by the dominant seaward surface current in the Strait of Juan de Fuca (SJdF). However, this “oceanographic barrier” has been breached as established green crab populations have been detected in the eastern Salish Sea in recent years. Here we carried out particle-tracking simulations to understand possible natural pathways of green crab larvae invading the eastern Salish Sea. Both diel vertical migration and temperature-dependent mortality were considered in these simulations. Our results suggest that green crab larvae from the outer coast (outside the Salish Sea) and Sooke Basin (in SJdF) could be carried into the eastern Salish Sea in a narrow time window during the later cold season (esp. in March) when frequent flow reversals in SJdF occur and the seasonally rising water temperature becomes relatively favorable for green crab larvae. The major pathway for larvae to reach the eastern Salish Sea is along the southern coast of SJdF. The probability of live larvae reaching the eastern Salish Sea is highly sensitive to water temperature. Sensitivity simulations indicate that a temperature increase of 0.5–1 °C would double or quadruple the probability of successful arrival in the eastern Salish Sea. This suggests that invading green crabs might have taken advantage of the mild winter conditions in recent warm years. Our results also suggest that the warming climate in the near future may facilitate green crab larval exchange across the Salish Sea.

Abundance and Distribution of Blue Swimmer Crab in Response to Environmental Variation Across Two Contrasting Estuaries

Portunid crabs are an iconic, high value species in NSW, but catches are highly variable in space and time. Substantial variation in biomass is observed in both exploited and unfished populations, and environmental effects on distribution and abundance are an important factor contributing to this variability. Predicting and responding to this variability is a challenge for management and sustainability of exploited populations. We examine spatial and temporal variation in Blue Swimmer Crab (Portunus armatus) populations, over a 2.5 year trapping survey in two temperate estuaries that differ in tidal flow and riverine input. Specifically, monthly catch rates and distribution throughout the estuary are examined alongside variation in temperature and conductivity. In Wallis Lake, the shallower estuary with a restricted entrance, both water temperature and conductivity impacted abundance and distribution of crabs but there was no evidence that pulses of freshwater flow had a major impact. For a 10 °C increase in temperature the population on average shifted ~ 700 m closer to the ocean. Males were consistently located slightly further into the estuary compared to females, but there was no convincing evidence of estuarine egression in response to lower salinity. In Port Stephens, the deeper, tidal estuary, water temperature and conductivity also impacted abundance, but while males were more dispersed than females, the distribution of crabs within the estuary did not appear to be influenced by temperature, conductivity or flow. These results highlight the links between nuanced environmental relationships and estuarine geomorphology for Blue Swimmer Crab.

No place to call home: Distribution patterns of the tufted ghost crab, Ocypode cursor, populations in nature reserves, Israel, Eastern Mediterranean

Abstract The once plentiful population of the tufted ghost crab, Ocypode cursor, a legally protected species, suffered a steep decline along the densely populated Mediterranean coast of Israel. Here we assessed the effects of recreational disturbance on crab populations in three sandy shore nature reserves and adjacent bathing beaches with differing accessibility during the summers of 2020–2021, employing burrow counts and burrow opening diameter as proxies for population abundance and population size structure. A total 6270 burrows were identified, counted and their opening diameter measured during the study period. The number of burrows was greatest close by the waterline and diminished landwards; this landwards decline was notable in the smallest burrows (<20 mm), representing the youngest population fraction. Comparison of population abundance between the surveyed nature reserves and adjacent bathing beaches revealed greater numbers in the former. However, a pronounced postweekend reduction in the number of burrows was apparent in nature reserves during both survey years, across sites and months and clearly indicates elevated recreational activity. The number of burrows in the nature reserve nearest to main population centres and abutting a popular bathing beach was smaller compared with the peripheral nature reserves. We observed no postsunrise activity of adult crabs, though in strictly access‐restricted beaches, crabs were active diurnally. We thus suggest that the crabs shifted their diel activity patterns as avoidance response to chronic anthropogenic disturbance, enduring a forced curfew and a temporal habitat loss. If the sandy nature reserves are to function as true refugia for the tufted ghost crab, restorative management is to include significant conservation and mitigation intervention measurements/actions.

The impact of an abiotic variable, temperature, on larvae of the blue crab, Callinectes sapidus Rathbun, 1896 (Brachyura, Portunidae)

Abstract Reductions in the size of mature blue crabs, Callinectes sapidus, which are commercially harvested, are of concern to the aquaculture industry. Through their role in the production of viable offspring, aquaculturists focus their attention in particular on female crabs, although the phenomenon will, of course, also affect the males. Meanwhile, decreases in size at maturity throughout the crab population may be the result of temperature alterations, at present also due to global climate change. Temperature-based shifts in growth can lead to changes in reproductive efficiency, as well as in size and age at maturity. In this study, the effects of temperature on the moulting frequency of blue crabs were investigated and survival rates have been calculated. The purpose of this study was to investigate the temperature dependence of survival and of the moulting processes for blue crab larvae, and to determine the effect of increasing temperature on moulting. The stages from zoea-1 to zoea-5 were examined at 16, 22, 26 and 30°C. The results show that there is a significant difference in growth and moulting, depending on the rearing temperature. As the temperature increases, the interval between moulting days can be seen to be shortened, and increasingly so with the progress in the growth of the crabs. Moulting-interval days became less with the growth of the crabs. The effect of a rise in temperature on growth per moult is also significant, and along the temperature range tested the optimum temperature was found to be 26°C. A reduction in the length of the intermoult period was observed from the lowest to the optimum temperature, while a sudden, sharp increase in the intermoult period above 26°C was observed as well.

Histopathology and Phylogeny of the Dinoflagellate Hematodinium perezi and the Epibiotic Peritrich Ciliate Epistylis sp. Infecting the Blue Crab Callinectes sapidus in the Eastern Mediterranean.

Bioinvasions constitute both a direct and an indirect threat to ecosystems. Direct threats include pressures on local trophic chains, while indirect threats might take the form of an invasion of a microorganism alongside its host. The marine dinoflagellate Hematodinium perezi, parasitizing blue crabs (Callinectes sapidus), has a worldwide distribution alongside its host. In Greece, fluctuations in the blue crab population are attributed to overexploitation and the effects of climate change. The hypothesis of the present study was that blue crab population reductions cannot only be due to these factors, and that particular pathogens may also be responsible for the fluctuations. To investigate this hypothesis, both lethargic and healthy blue crab specimens were collected from three different fishing sites in order to assess the health status of this important species. Together with the lethargic responses, the hemolymph of the infested crabs presented a milky hue, indicating the first signs of parasitic infestation with H. perezi. The histopathological results and molecular identification demonstrated the effect of the presence of H. perezi in the internal organs and their important role in the mortality of blue crabs. Specifically, H. perezi, in three different tissues examined (heart, gills, hepatopancreas), affected the hemocytes of the species, resulting in alterations in tissue structure. Apart from this dinoflagellate parasite, the epibiotic peritrich ciliate Epistylis sp. was also identified, infecting the gills. This study represents the first detection of H. perezi in the eastern Mediterranean, demonstrating that this is the main causative agent of blue crab mortality on Greek coastlines.

Combined effects of norfloxacin and polystyrene nanoparticles on the oxidative stress and gut health of the juvenile horseshoe crab Tachypleus tridentatus

Pollution with anthropogenic contaminants including antibiotics and nanoplastics leads to gradual deterioration of the marine environment, which threatens endangered species such as the horseshoe crab Tachypleus tridentatus. We assessed the potential toxic mechanisms of an antibiotic (norfloxacin, 0, 0.5, 5 μg/L) and polystyrene nanoparticles (104 particles/L) in T. tridentatus using biomarkers of tissue redox status, molting, and gut microbiota. Exposure to single and combined pollutants led to disturbance of redox balance during short-term (7 days) exposure indicated by elevated level of a lipid peroxidation product, malondialdehyde (MDA). After prolonged (14–21 days) exposure, compensatory upregulation of antioxidants (catalase and glutathione but not superoxide dismutase) was observed, and MDA levels returned to the baseline in most experimental exposures. Transcript levels of molting-related genes (ecdysone receptor, retinoic acid X alpha receptor and calmodulin A) and a molecular chaperone (cognate heat shock protein 70) showed weak evidence of response to polystyrene nanoparticles and norfloxacin. The gut microbiota T. tridentatus was altered by exposures to norfloxacin and polystyrene nanoparticles shown by elevated relative abundance of Bacteroidetes. At the functional level, evidence of suppression by norfloxacin and polystyrene nanoparticles was found in multiple intestinal microbiome pathways related to the genetic information processing, metabolism, organismal systems, and environmental information processing. Future studies are needed to assess the physiological and health consequences of microbiome dysbiosis caused by norfloxacin and polystyrene nanoparticles and assist the environmental risk assessment of these pollutants in the wild populations of the horseshoe crabs.

The biometry of Cardisoma crassum (Brachyura: Gecarcinidae) from two folkloric festivals in Veraguas, Panama

This study explores the biometry of Cardisoma crassum individuals presented in two folkloric festivals within the Montijo Gulf in 2022 and 2023. Crabs in the Rio de Jesús (RJ) festival from 2022 exhibited a male biased sex ratio, contrasting Montijo's (MO) even sex ratio in 2023. Carapace widths were similar between festivals (RJ, 65.59 ± 6.56 mm; MO: 64.29 ± 5.92 mm). Sex-based size variations were consistent within years but not between years. Localities showed significant size and sex ratio differences, while transportation distance to the festival venues did not correlate with crab size. Additionally, a comparison between current data and previous studies from 2014–2015, 2021 and 2022, highlighted size differences among sites might not be related to yearly increasing crab demand; instead, site-specific extraction pressure may be an underlying factor. Festivals consumed approximately 198 crab bundles in Rio de Jesús in 2022 (≈ 2,376 individuals) and an estimated 207 bundles in Montijo in 2023 (≈ 2,484 individuals). This study unveils complex dynamics in C. crassum populations at the local level, encompassing sex ratios, size variations, and economic dimensions within festival contexts. Understanding these multifaceted dynamics is crucial for effectively managing these coastal crab populations in the future.

Larval Dispersal Modelling of the Blue Swimming Crab Portunus pelagicus (Linnaeus, 1758) from the Crab Banks along the Coast of Trang Province, Southern Thailand

In Thailand, the populations of a commercially important crab Portunus pelagicus (Linnaeus, 1758) have been decreasing due to overfishing, raising concerns about the conservation efforts of this crab species. The Crab Bank Project has recently been established to restore crab populations by releasing crab larvae from each crab bank station. However, the fate of crab larvae after the release is poorly understood. Here, we assessed the dispersal and settlement patterns of the larvae P. pelagicus released from crab banks along the coast of Trang Province, Southern Thailand. The Lagrangian particle tracking model was employed to simulate the larval dispersal and settlement patterns after release from the crab banks during the inter-monsoon, southwest monsoon, and northeast monsoon. Our simulation revealed that virtual larvae were predominantly retained within inshore areas after the release for 14 days, regulated by tidal-driven currents, wind-induced currents, and local coastal topography. Monsoon periods affected the larval dispersal, with some larvae being transported into estuaries due to the SW monsoonal effects. After the 14-day release period, our modelled simulations suggested that the crab larvae arrived at numerous seagrass meadows along the coast, indicating potential settlement and growth. This result highlights the connectivity of sources and sinks for crab larvae after release from crab banks. Moreover, significant implications for conservation efforts and the fishery management of P. pelagicus were also discussed based on our modelled simulations.

Reproductive phenology of the Chesapeake Bay blue crab population in a changing climate

Global temperatures are rising across marine ecosystems in response to climate change. Marine and estuarine-dependent species including the blue crab, Callinectes sapidus, may adapt to warming temperatures phenologically, by shifting the seasonal timing of biological events, such as reproduction. In Chesapeake Bay, average water temperatures have risen by an average 0.02°C per year since the 1980s. Extension of the blue crab spawning season, through earlier onset and later conclusion, may augment annual brood production and alter the efficacy of management strategies. The duration of the potential spawning season from 1985 to 2019 was assessed using degree days, and the observed spawning season from 1995 to 2019 was assessed using the occurrence of ovigerous crabs from the Virginia Institute of Marine Science Trawl Survey in the James River and in the mainstem of lower Chesapeake Bay. Spawning degree days (SDD) and reproductive degree days (RDD) were defined using minimum temperatures of 19°C and 12°C, respectively. The mean duration of the potential spawning season increased by 25% in SDD and 10% in RDD between 1985 and 2019 in the James River and lower Chesapeake Bay, respectively. This progressive expansion of the potential spawning season was not, however, reflected in the observed spawning season. Rather, the onset, conclusion, and duration of the observed spawning season were variable over the time series. The observed month of onset was driven by RDD in spring, whereby spawning began earlier during warmer springs. The spawning conclusion date was driven by the onset of spawning, rather than Fall temperature, such that the duration of the observed spawning season and, therefore, annual brood production did not change over time. In Chesapeake Bay, the spawning stock is protected by a sanctuary that is closed to fishing from mid-May to mid-September during the putative spawning season. An earlier start to the spawning season during warmer springs, as seen in recent years, is expected to reduce the efficacy of the spawning sanctuary and intensify exploitation of the spawning stock, without enhancing brood production, thereby reducing reproductive output of the blue crab population in Chesapeake Bay.

Invasive European green crab (Carcinus maenas) predation in a Washington State estuary revealed with DNA metabarcoding.

Predation by invasive species can threaten local ecosystems and economies. The European green crab (Carcinus maenas), one of the most widespread marine invasive species, is an effective predator associated with clam and crab population declines outside of its native range. In the U.S. Pacific Northwest, green crab has recently increased in abundance and expanded its distribution, generating concern for estuarine ecosystems and associated aquaculture production. However, regionally-specific information on the trophic impacts of invasive green crab is very limited. We compared the stomach contents of green crabs collected on clam aquaculture beds versus intertidal sloughs in Willapa Bay, Washington, to provide the first in-depth description of European green crab diet at a particularly crucial time for regional management. We first identified putative prey items using DNA metabarcoding of stomach content samples. We compared diet composition across sites using prey presence/absence and an index of species-specific relative abundance. For eight prey species, we also calibrated metabarcoding data to quantitatively compare DNA abundance between prey taxa, and to describe an 'average' green crab diet at an intertidal slough versus a clam aquaculture bed. From the stomach contents of 61 green crabs, we identified 54 unique taxa belonging to nine phyla. The stomach contents of crabs collected from clam aquaculture beds were significantly different from the stomach contents of crabs collected at intertidal sloughs. Across all sites, arthropods were the most frequently detected prey, with the native hairy shore crab (Hemigrapsus oregonensis) the single most common prey item. Of the eight species calibrated with a quantitative model, two ecologically-important native species-the sand shrimp (Crangon franciscorum) and the Pacific staghorn sculpin (Leptocottus armatus)-had the highest average DNA abundance when detected in a stomach content sample. In addition to providing timely information on green crab diet, our research demonstrates the novel application of a recently developed model for more quantitative DNA metabarcoding. This represents another step in the ongoing evolution of DNA-based diet analysis towards producing the quantitative data necessary for modeling invasive species impacts.

Evidence for a male bias in Atlantic blue crab pot‐based sampling

AbstractObjectiveThe Atlantic blue crab Callinectes sapidus (hereafter, “blue crab”) is an ecologically and economically important species that supports one of the highest valued commercial fisheries in coastal South Carolina, USA. Researchers at the South Carolina Department of Natural Resources conduct multiple surveys to monitor the status of the blue crab by using a variety of gear configurations. Demographic characterizations can often be influenced by sampling gear‐related biases.MethodsWe compared blue crab sex ratios between passive, pot‐based sampling and active, trawl‐based sampling in the fall across three estuaries and for year‐round sampling in a single estuary (Ashley River, South Carolina).ResultDuring the fall, there was a difference of 20.1% between the percentage of males collected in pot‐based sampling (73.5%) and the percentage of males in trawl‐based sampling (53.4%). Furthermore, an overall male bias of 23.0% was observed for year‐round sampling in the Ashley River; however, this bias was only significant in certain months.ConclusionOur findings suggest that although particular sampling gears may have specific advantages, such as greater suitability to effectively sample certain habitats, the resulting characterizations of blue crab population demographics can differ among gear types. Recognizing gear‐related biases is important for ensuring that field surveys are representative of population demographics, particularly when sex‐specific modeling approaches are used as part of stock assessments to determine population status.

Identification of Food Types of Ghost Crabs (Ocypode kuhlii L.) in The Intertidal Zone of Peudawa Beach, East Aceh

Ghost crabs are one of the arthropod animals that live in coastal ecosystems and are one of the key species that have a very important role in maintaining ecological balance. Here the author refers to the abundance of ghost crabs and the types of food eaten by ghost crabs, this is because there are still many who do not know about the types of ghost crab hands and the abundance of ghost crab hands and the abundance of ghost crabs on an east aceh beach. The type of research used was quantitative research with a random sampling method which was carried out on November 25 2023. From the results of this crab density research, there were 100 individuals with a translation size of 254M and a density index of 1,96 D at 40 54’’ 9’ N 970 51’’ 2’ T. Aceh Regency Timur, the types of food for ghost crabs are Zooplankton, Phytoplankton and Bacterioplankton. The conclusion of this research is that the existence of this crab population is greatly influenced by the condition of the beach which is its habitat. Natural beaches usually find many ghost crabs because the food chain process is still maintained.

Impact of Mangrove Deforestation on Fiddler Crab Distribution and Soil Physico-chemistry at Eagle Island, Rivers State

Mangrove forest in the Niger Delta and its associated biotic and abiotic has been greatly impacted by several factors, some natural and others anthropogenic in nature. Anthropogenic activities have negatively affected the organisms that inhabit the forest resulting in the decrease in size of population of fiddler crabs (Uca tangeri). To investigate the influence of anthropogenic activities on the mangrove habitat, burrow distribution and population of fiddler crabs and soil physico-chemistry were determined in forested and deforested sites. Burrows and number of crabs outside burrows were counted while samples of soil were retrieved and moved to the laboratory for the determination of cadmium (Cd), lead (Pb), total hydrocarbon content (THC) and Zinc (Zn) using atomic absorption spectrophotometer. The conclusions show a lack of significant difference in burrow distribution between forested and deforested areas (P>0.05). Contrastingly there is significance in the difference in crab population in forested and deforested sites. (P<0.05), which showed that there were more crabs in deforested areas than forested areas. There was also a significant difference in chemical and microbial population (P<0.05). There was higher THC in deforested areas, which was probably impacted by the heavy-duty vehicles used to cut down the trees. The result implies that human activities of deforestation and pollution influence crab population and soil physicochemistry in mangrove forest.

Stock Analysis of Kroyo Crab in Cirebon Waters, Gebang Mekar Village, Gebang District, Cirebon Regency

The development of crabs in Cirebon Regency is one of the important indicators in increasing fisheries production, the increase is based on the high market demand for crab commodities, especially kroyo crabs, causing an impact on the crab population. This research was carried out from February 2022 to March 2023 in 3 sub-districts, namely Suranenggala, Mundu and Gebang. This study aims to determine the stock of kroyo crabs which include carapace width and weight, growth, condition factors, mortality, and exploitation rate. The method used is direct observation of special fishermen catching kroyo crabs. The key crabs measured during the study amounted to 360 individuals with a carapace width range of male crabs of 27-44 mm and female crabs of 28-51 mm, with a frequency distribution of 8 class intervals from December 2022 to February 2023. Tools used to analyze stock conditions using the help of FISAT II and Microsoft Excel software. The first size results were caught in males (L50%=34,18mm) with more than half the asymptotic length (½L∞=23,75mm), while in females (L50%=41,08mm) greater than half the asymptotic length (½L∞=25,75mm). The carapace-weight width relationship of the male crab is W = 1,227L0,510 and the female crab W = 0,371L0,896. Conditions factors in male crabs (1,007) and females (1,008) have the same level of mon-decency. Growth equation of Von Bertalanffy male crab Lt=47,25[1- e(-0,79(t+0,179))] and female crabs Lt=51,45[1- e(-0,99(t+0,138))], So it can be stated that the growth of female crabs is faster than that of male crabs. In male crabs, the Total Mortality Rate (Z) was obtained at 2.99 per year, natural mortality (M) of 1.39 per year, and arrest mortality (F) of 1.60 per year. While in female crabs Z = 2.44 per year, M = 1.57 per year, F = 1.60 per year. The exploitation rate (E) of male crabs was obtained at 0.54 per year and females at 0.35 which means that the capture of Charybdis anisodon waters is still a tendency of underfishing. The pattern of adding new male crabs in Cirebon waters has two peaks, namely in April and August, with female crabs in July. Based on the results of this study, it can be concluded that the stock condition in Cirebon waters is still in the category of suitable for fishing for fishermen.

Morphometric Study of Swimming Crab (Portunus pelagicus) Using Truss Network Analysis for Determination of Stock Structure in FMA 711

The crab of Portunus pelagicus is a fishery resource with a wide distribution area and quite diverse environmental conditions in Indonesia, giving rise to morphometric diversity. The study aims to analyze differences in morphometric diversity of crab populations (P. pelagicus) in the waters of Indonesian Fisheries Management Area (FMA) 711, landed in Bintan, Bangka, and Ketapang, which can describe the condition of the crab stock units. A total of 300 individuals were collected from all locations using random sampling. The crab morphometric characters were analyzed using Truss Network body shape method (TNA). The Kruskal Wallis results analysis showed distinguishing in some morphometric characters for both carapace and abdomen. Cluster analysis shows that there were two population groups: The Bintan group, and the Bangka-Ketapang groups. The discriminant analysis on the carapace characters resulting that the crabs from three locations have the potential for more than one stock unit, so different management is needed.

On the rebound: removal programs yield local-scale benefits but do not sustainably suppress populations of invasive European green crabs (Carcinus maenas)

On the rebound: removal programs yield local-scale benefits but do not sustainably suppress populations of invasive European green crabs (Carcinus maenas)

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).