Crab Populations Research Articles

Climate Change Will Fragment Florida Stone Crab Communities

Many marine species have been shown to be threatened by both ocean acidification and ocean warming which are reducing survival, altering behavior, and posing limits on physiology, especially during earlier life stages. The commercially important Florida stone crab, Menippe mercenaria, is one species that is affected by reduced seawater pH and elevated seawater temperatures. In this study, we determined the impacts of reduced pH and elevated temperature on the distribution of the stone crab larvae along the West Florida Shelf. To understand the dispersion of the larvae, we coupled the multi-scale ocean model SLIM with a larval dispersal model. We then conducted a connectivity study and evaluated the impacts of climate stressors by looking at four different scenarios which included models that represented the dispersion of stone crab larvae under: 1) present day conditions as modelled by SLIM for the temperature and NEMO-PISCES for the pH, 2) SSP1-2.6 scenario (-0.037 reduction in pH and +0.5°C compared to present-day conditions), 3) SSP2-4.5 scenario(-0.15 reduction in pH and +1.5°C) and 4) SSP5-8.5 scenario (-0.375 reduction in pH and +3.5°C). Our results show a clear impact of these climate change stressors on larval dispersal and on the subsequent stone crab distribution. Our results indicate that future climate change could result in stone crabs moving north or into deeper waters. We also observed an increase in the number of larvae settling in deeper waters (defined as the non-fishing zone in this study with depths exceeding 30 m) that are not typically part of the commercial fishing zone. The distance travelled by larvae, however, is likely to decrease, resulting in an increase of self-recruitment and decrease of the size of the sub-populations. A shift of the spawning period, to earlier in the spring, is also likely to occur. Our results suggest that habitats in the non-fishing zone cannot serve as a significant source of larvae for the habitats in the fishing zone (defined as water depth< 30 m) since there is very little exchange (< 5% of all exchanges) between the two zones. These results indicate that the stone crab populations in Florida may be susceptible to community fragmentation and that the management of the fishery should consider the potential impacts of future climate change scenarios.

Interannual fluctuations in connectivity among crab populations (Liocarcinus depurator) along the Atlantic-Mediterranean transition

An interesting evolutionary question that still remains open is the connectivity between marine populations. Marine currents can favour the dispersal of larvae or adults, but they can also produce eddies and gyres generating oceanographic fronts, thus limiting gene flow. To address this subject, we selected the Atlantic-Mediterranean transition, where several fronts are located: Gibraltar Strait (GS), Almeria-Oran Front (AOF) and Ibiza Channel (IC). Seven populations of the marine crab Liocarcinus depurator (Cadiz, West and East Alboran, Alacant, Valencia, Ebro Delta and North Catalonia) located along this transition were analysed in six consecutive years (2014–2019) using a fragment of the COI (Cytochrome Oxidase subunit I) gene. All sequences (966) belonged to two well defined haplogroups: ATL (most abundant in Atlantic waters) and MED (predominant in Mediterranean waters). Following a geographic variation, the frequency of ATL decreased significantly from Cadiz to North Catalonia. However, this variation presented steps due to the effect of oceanographic restrictions/fronts. Significant effects were recorded for GS (2015, 2017, 2018 and 2019), AOF (all years except 2018) and IC (2016). The intensity and precise location of these fronts changed over time. Multivariate analyses distinguished three main population groups: Cadiz, Alboran Sea and the remaining Mediterranean populations. These findings could be relevant to properly define Marine Protected Areas and for conservation and fisheries policies.

PCR Analysis for Genetic Distances of Two Charybdis Crab Populations.

Genomic DNA (gDNA) set apart from two populations of Korean Charybdis crab (Charybdis japonica) was augmented by PCR experiments. The five oligonucleotides primers (ONT-primers) were spent to yield the number of unique loci shared to each crab population (ULSECP) and number of loci shared by the two crab populations (LSTCP). 305 fragments (FRAGs) were identified in the Charybdis crab population A (CCPA), and 344 in the Charybdis crab population B (CCPB): 44 number of ULSECP (14.43%) in the CCPA and 110 (31.98%) in the CCPB. 44 number of LSTCP, with an average of 8.8 per primer, were detected in the two crab populations. The bandsharing (BS) value between entity's no. 01 and no. 10 was the lowest (0.371) between the two CCPs. The average bandsharing (ABS) values of individuals in the CCPA (0.575±0.014) were lesser than in those originated from the CCPB (0.705±0.011) (p < 0.05). The polar hierarchical dendrogram (PHD) achieved by the five ONT-primers denotes three genetic clusters (GCs): cluster I (CHARYBCRAB 01, 04, 05, 06, and 08), cluster II (CHARYBCRAB 02, 03, 07, 09, 10, and 11) and cluster III (CHARYBCRAB 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, and 22). The shortest genetic distance (GD) displaying significant molecular difference (MD) was between individuals CHARYBCRAB no. 18 and CHARYBCRAB no. 17 (0.055).

Pathology and genetic connectedness of the mangrove crab (Aratus pisonii) – a foundation for understanding mangrove disease ecology

Mangrove forests are productive ecosystems, acting as a sink for CO2, a habitat for a diverse array of terrestrial and marine species, and as a natural barrier to coastline erosion. The species that reside within mangrove ecosystems have important roles to play, including litter decomposition and the recycling of nutrients. Crustacea are important detritivores in such ecosystems and understanding their limitations (i.e. disease) is an important endeavour when considering the larger ecological services provided.Histology and metagenomics were used to identify viral (Nudiviridae, Alphaflexiviridae), bacterial (Paracoccus sp., 'Candidatus Gracilibacteria sp.’, and Pseudoalteromonas sp.), protozoan, fungal, and metazoan diversity that compose the symbiome of the mangrove crab, Aratus pisonii. The symbiotic groups were observed at varying prevalence under histology: nudivirus (6.5%), putative gut epithelial virus (3.2%), ciliated protozoa (35.5%), gonad fungus (3.2%), gill ectoparasitic metazoan (6.5%). Metagenomic analysis of one specimen exhibiting a nudivirus infection provided the complete host mitochondrial genome (15,642 bp), nudivirus genome (108,981 bp), and the genome of a Cassava common mosaic virus isolate (6387 bp). Our phylogenetic analyses group the novel nudivirus with the Gammanudivirus and protein similarity searches indicate that Carcinus maenas nudivrius is the most similar to the new isolate. The mitochondrial genome were used to mine short fragments used in population genetic studies to gauge an idea of diversity in this host species across the USA, Caribbean, and central and southern America.This study report several new symbionts based on their pathology, taxonomy, and genomics (where available) and discuss what effect they may have on the crab population. The role of mangrove crabs from a OneHealth perspective were explored, since their pathobiome includes cassava-infecting viruses. Finally, given that this species is abundant in mangrove forests and now boasts a well-described pathogen profile, we posit that A. pisonii is a valuable model system for understanding mangrove disease ecology.

Occurrence of the chinese mitten crab Eriocheir sinensis (H. Milne Edwards) in South Iraq

The distribution of the invasive Chinese mitten crab Eriocheir sinensis in Shatt Al-Basrah Canal and Shatt Al-Arab River was investigated. The earlier published record of this species was in 2006 where only a single specimen was obtained from Shatt Al-Basrah Canal, but the species has long been observed in the region. The present work monitored the recent occurrence of the species where living and non living specimens were captured in large numbers. Although the species migrate to the sea for reproduction, it was not yet recorded from the North West Arabian Gulf region. Detailed description of the captured crabs is provided. Carapace width ranged from 53.4 to 56.6 mm and carapace length ranged from 56 to 62.4 mm. Recent rise in salinity or the change in water chemistry of south Iraq may play vital role in increasing the population of the mitten crab.

Population dynamics of mud crab, Scylla olivacea (Herbst, 1796) from the Sundarbans of Bangladesh

AbstractThe Sundarbans mangrove regions are the home of the mud crab (Scylla olivacea) business, as forest areas are potential places for random crab harvesting, trading, and exporting overseas seafood markets. Since the mud crab was being captured on a large‐scale in the wild for various purposes, estimation of population parameters were immediately done in terms of body weight and length‐frequency data collected from different locations in the forest of southwestern Bangladesh to understand the status of the stock. Recruitment pattern, growth parameters, mortality rates, and exploitation levels (E) were estimated to understand the population dynamics of S. olivacea. Asymptotic carapace widths (CW∝) were 14.70 and 14.18 cm, and growth co‐efficients (K) were 0.47 and 0.50 year–1 for male and female S. olivacea, respectively. The fishing mortalities were 2.32 and 1.13 year–1 and natural mortalities were 1.39 and 1.46 year–1 for males and females, respectively. Year‐round recruitment of this species takes place in the wild with a peak between June and November. The E for S. olivacea was found to be 0.63 for the male and 0.44 for the female. In summery, the stock of S. olivacea is found to be overexploited in the Sundarbans of Bangladesh. Therefore, mud crab resources should be taken into consideration under suitable fisheries management policies to conserve this national treasure in this delta. It is supposed that the findings will draw the attention of the scientists in the fields of aquatic biology, ecology, and management of the Sundarbans in restoring the mud crab population.

Correlation of Environmental Factors With Population of Horseshoe Crab (Tachypleus gigas) in Sedati Waters, Sidoarjo District

Horseshoe crabs (Tachypleus gigas) in local called Mimi are coastal animals belonging to the Limulidae family. The horseshoe crabs live at the bottom of calm coastal waters and river estuaries with sandy and muddy bottoms. The decrease in the population number of horseshoe crabs in nature could be caused by habitat degradation, including coastal abrasion, ecosystem damage, and the death of natural resources in the waters. This study aims to determine the correlation of environmental factors with the population of Horseshoe Crab (Tachypleus gigas) in Sedati waters, Sidoarjo District. This type of research was exploratory with data analysis using linear regression and simple correlation. Moreover, the sampling was carried out by purposive random sampling at predetermined points of the station in Sedati Waters, Sidoarjo District. The results show that the average density in October was 0.08 ind/m2, in November was 0.05 ind/m2, and in December was 0.05 ind/m2. Moreover, the correlation between the horseshoe crabs and water quality is noted in the current of 58%, transparency of 37%, and DO of 33%. Based on the results of this study, the environmental factors including transparency, currents, and DO have a strong correlation on the horseshoe crab population in Sedati waters, while pH, ammonia, carbon, and microfauna parameters have a quite influential effect on the population of horseshoe crabs.

Long-term monitoring reveals unprecedented stability of a vent mussel assemblage on the Mid-Atlantic Ridge

Understanding scales and drivers of ecological variability is essential to a full understanding of ecosystem functioning. At remote deep-sea hydrothermal vents, infra-annual dynamics remain poorly described. This study aims to characterise the factors that drive the dynamics of a vent faunal assemblage dominated by Bathymodiolus azoricus mussels from infra-daily to monthly time steps. We analysed a 7-year time series of images and environmental data collected at a depth of 1695 m at the base of the active Eiffel Tower edifice in the Lucky Strike vent field (Mid-Atlantic Ridge). Using images acquired by the TEMPO ecological module connected to the EMSO-Azores observatory, we assessed the dynamics of key species inhabiting the faunal assemblage in relation to changes in environmental conditions monitored daily.Our results show that habitat conditions were generally stable over the 7-year period, with small-scale variability related to tidal periodicity and local temperature anomalies. Likewise, the mussel and zoanthid assemblages exhibited remarkable stability. Changes in fluid exposure and substratum instability induced decimetre-scale movements of the mussel assemblage. Microbial mats displayed infra-annual changes characterised by aperiodic growth and decline. Their development patterns could not be entirely attributed to environmental conditions, because other factors, including biotic interactions, appeared to be involved. The crab population preferentially occupied the mussel habitat, but no predation was observed. Scales of variation and driving factors were compared with those governing intertidal zones. The outcomes question the assumption that vent fauna experience extreme and highly variable conditions. On the MAR, mussel assemblages appear to experience relatively stable and mild environmental conditions compared with their coastal counterparts.

Hybrid Model of the Collapse of the Commercial Crab Paralithodes camtschaticus (Decapoda, Lithodidae) Population of the Kodiak Archipelago.

Degradation of commercial populations remains a frequent phenomenon even with the use of methods of stocktaking and control of production volume. In fish farming, the concept of “overfishing” is used with and the signs of this condition are well known. However, the processes leading to the degradation of reserves develope in various ways. According to the theory of nonlinear dynamical systems, several types of crisis development can be classified. Of particular interest are the phenomena of collapse, that is, variants of a rapid decline in numbers, which are unexpected for the organizations controlling the fishery. Immediately before the collapse, the state of the stock can be assessed as relatively stable and it may experience fluctuations. Contrary to expectations, there was no rapid recovery after a rapid reduction in cod, whitefish Coregonus clupeaformis of the Great Lakes, halibut and other valuable species. This paper considers a hybrid model for the collapse of red king crab Paralithodes camtschaticus stocks of the Kodiak archipelago of Alaska with unusual distinctive oscillating dynamics. The computational scenario in a hybrid system with survival and growth equations considers the logic of decision-making in operation management. The scenario differs in that after the fall of catches, the crab population goes into the sporadic fluctuations that do not have a regular character and are not characteristic of the population. The collapse itself occurs after a long interval of fishing while the population is in an unstable mode. The analysis shows that a long species life cycle is not a decisive factor for eliminating the risk of a collapse scenario. The presence of reserve generations does not change the situation qualitatively, the efficiency of their reproduction in crab and cod off the coast of Labrador turned out to be unexpectedly low. The status of stocks of large predators that require seasonal moratoriums on fishing must be regularly checked.

Studies on freshwater crab population as influencedby physico-chemical attributes in Gho-Manhasanstream, a tributary of river Chenab

Crustaceans are distributed world-wide and are found in a variety of habitats. Freshwater crabs constitute one-fifth of the brachyurans all over the world. Freshwater crabs are the eminent indicators of good water quality. The present study was carried out with an aim to assess the influence of various physico-chemical parameters such as temperature, pH, depth, dissolved oxygen, free carbon dioxide, calcium, magnesium, bicarbonates and chlorides on the population of crabs in the Gho-Manhasan stream, a tributary of river Chenab. A comprehensive study of these parameters and a comparative analysis with those recorded in last eight years span gave a clear picture of the pollution stress due to anthropogenic activities in the water body that has led to a considerable decline in the population of crabs in this stream. This emphasizes the need to spotlight and improve measures of conservation before there is decline in the crab population to the levels from which they cannot recuperate.

ACUTE TOXICITY, OXIDATIVE STRESS AND DAMAGES TO GILLS OF CARDIOSOMA ARMATUM (RAINBOW CRAB) INDUCED BY EXPOSURE TO PESTICIDES (DICHLORVOS AND CYPERMETHRIN)

The relative acute toxicity of Dichlorvos and Cypermethrin acting singly against Rainbow crab, Cardiosoma armatum was evaluated. The effects of sub lethal concentrations of the pesticides on the oxidative responses and histopathological effects in the gills of the crab were also investigated over a 30 days period. On the basis of 96 hrs LC50 value, Dichlorvos with 96 hr LC50 of 8.86 ?g/L was 2 times more toxic to the crabs than Cypermethrin with 96 hr LC50 of 17.80 ?g/L. The exposures to sub lethal concentrations (1/10th and 1/100th 96 hr LC50) of both pesticides each resulted in increase in the levels of lipid peroxidation product, malondialdehyde (MDA) in the gills compared to the control group at both day 15 and 30 of the bioassay . Super oxide dismutase (SOD) activity was inhibited by day 30 relative to control for both pesticides but the activities of Catalase (CAT) did not show a significant trend (P &gt; 0.05). Exposure to sub lethal concentration (1/10th and 1/100th LC50) of both pesticides resulted in various histopathological effects such as curved filaments, fused filaments, epithelial lifting, congestion and odema. The damages to the gills were more severe in those exposed to Dichlorvous. The findings from this study indicates that both pesticides are potential threats to non- target rainbow crab populations and there is a risk of bioaccumulation and transport in the food chain under sub lethal exposures

Carbapenem-Resistant Acinetobacter baumannii in U.S. Hospitals: Diversification of Circulating Lineages and Antimicrobial Resistance.

ABSTRACTCarbapenem-resistant Acinetobacter baumannii (CRAb) is a major cause of health care-associated infections. CRAb is typically multidrug resistant, and infection is difficult to treat. Despite the urgent threat that CRAb poses, few systematic studies of CRAb clinical and molecular epidemiology have been conducted. The Study Network of Acinetobacter as a Carbapenem-Resistant Pathogen (SNAP) is designed to investigate the clinical characteristics and contemporary population structure of CRAb circulating in U.S. hospital systems using whole-genome sequencing (WGS). Analysis of the initial 120 SNAP patients from four U.S. centers revealed that CRAb remains a significant threat to hospitalized patients, affecting the most vulnerable patients and resulting in 24% all-cause 30-day mortality. The majority of currently circulating isolates belonged to ST2Pas, a part of clonal complex 2 (CC2), which is the dominant drug-resistant lineage in the United States and Europe. We identified three distinct sublineages within CC2, which differed in their antibiotic resistance phenotypes and geographic distribution. Most concerning, colistin resistance (38%) and cefiderocol resistance (10%) were common within CC2 sublineage C (CC2C), where the majority of isolates belonged to ST2Pas/ST281Ox. Additionally, we identified ST499Pas as the most common non-CC2 lineage in our study. Our findings suggest a shift within the CRAb population in the United States during the past 10 years and emphasize the importance of real-time surveillance and molecular epidemiology in studying CRAb dissemination and clinical impact.

Hematodinium sp. infection does not drive collateral disease contraction in a crustacean host.

Host, pathogen, and environment are determinants of the disease triangle, the latter being a key driver of disease outcomes and persistence within a community. The dinoflagellate genus Hematodinium is detrimental to crustaceans globally - considered to suppress the innate defences of hosts, making them more susceptible to co-infections. Evidence supporting immune suppression is largely anecdotal and sourced from diffuse accounts of compromised decapods. We used a population of shore crabs (Carcinus maenas), where Hematodinium sp. is endemic, to determine the extent of collateral infections across two distinct environments (open-water, semi-closed dock). Using a multi-resource approach (PCR, histology, haematology, population genetics, eDNA), we identified 162 Hematodinium-positive crabs and size/sex-matched these to 162 Hematodinium-free crabs out of 1191 analysed. Crabs were interrogated for known additional disease-causing agents; haplosporidians, microsporidians, mikrocytids, Vibrio spp., fungi, Sacculina, trematodes, and haemolymph bacterial loads. We found no significant differences in occurrence, severity, or composition of collateral infections between Hematodinium-positive and Hematodinium-free crabs at either site, but crucially, we recorded site-restricted blends of pathogens. We found no gross signs of host cell immune reactivity towards Hematodinium in the presence or absence of other pathogens. We contend Hematodinium sp. is not the proximal driver of co-infections in shore crabs, which suggests an evolutionary drive towards latency in this environmentally plastic host.

Predation Scars Reveal Declines in Crab Populations Since the Pleistocene

Despite growing concerns over global fisheries, the stock status of most commercially exploited species are poorly understood. Fossil data provide pre-anthropogenic baselines for data-poor fisheries, yet are underutilized in fisheries management. Here, we provide the first use of predation traces to assess the status of fisheries (crab). We compared crab predation traces on living individuals of the crab prey gastropod, Tegula funebralis, to Pleistocene individuals from the same regions in southern California. There were fewer crab predation traces on modern gastropods than their Pleistocene counterparts, revealing reductions in crab abundances today compared to the Pleistocene. We conclude that: (1) regardless of the cause, immediate actions are required to avoid further population reductions of commercially exploited crabs in southern California, (2) predation traces are a rapid, cost-effective method to assess otherwise data-poor fisheries, and (3) the inclusion of fossil data provides key new insights for modern resource and fisheries management.

Seascape genomics identify adaptive barriers correlated to tidal amplitude in the shore crab Carcinus maenas.

Most marine invertebrates disperse during a planktonic larval stage that may drift for weeks with ocean currents. A challenge for larvae of coastal species is to return to coastal nursery habitats. Shore crab (Carcinus maenas L.) larvae are known to show tidal rhythmicity in vertical migration in tidal areas and circadian rhythmicity in microtidal areas, which seems to increase successful coastal settlement. We studied genome‐wide differentiation based on 24,000 single nucleotide polymorphisms of 12 native populations of shore crab sampled from a large tidal amplitude gradient from macrotidal (~8 m) to microtidal (~0.2 m). Dispersal and recruitment success of larvae was assessed with a Lagrangian biophysical model, which showed a strong effect of larval behaviour on long‐term connectivity, and dispersal barriers that partly coincided with different tidal environments. The genetic population structure showed a subdivision of the samples into three clusters, which represent micro‐, meso‐ and macrotidal areas. The genetic differentiation was mostly driven by 0.5% outlier loci, which showed strong allelic clines located at the limits between the three tidal areas. Demographic modelling suggested that the two genetic barriers have different origins. Differential gene expression of two clock genes (cyc and pdp1) further highlighted phenotypic differences among genetic clusters that are potentially linked to the differences in larval behaviour. Taken together, our seascape genomic study suggests that tidal regime acts as a strong selection force on shore crab population structure, consistent with larval behaviour affecting dispersal and recruitment success.

COI gene‐based mitochondrial DNA variation of horseshoe crab (Tachypleus gigas) reveals high genetic variation and occurrence of distinct populations in the Bay of Bengal, India, and its comparison with other populations

AbstractHorseshoe crab (Tachypleus gigas) is an archaic group of marine species which plays a vital role in the saline ecosystem. We attempted to develop a baseline database about the ecology, phylogeography, and genetic variation among the horseshoe crab population from Odisha, India. We collected 152 samples of horseshoe crab from the coastal area of the Bay of Bengal. The generated cytochrome c oxidase subunit I gene (COI) sequences of T. gigas were compared with the GenBank sequences of five populations from Bangladesh, Thailand, Singapore, South China, and Malaysia. A total of 33 unique haplotypes were observed in six populations of T. gigas. Pairwise F‐statistic distance (FST) between South China‐India, Malaysia‐India, Singapore‐India, Thailand‐India, and Bangladesh‐India were 0.021, 0.020, 0.017, 0.015, and 0.008, respectively. It indicated that the Indian and Bangladesh populations were genetically close and distinct from the other four populations. Furthermore, the migrant per generation (Nm) was 0.16, which indicated a low gene flow among T. gigas populations. The haplotype diversity (Hd) and nucleotide diversity (π) were 0.7482 and 0.00313, respectively. It signifies the ecological importance of the Indian population that would help in formulating the future strategy for the conservation of horseshoe crab.

Differential gene expression and chemical patterns of an intertidal crab inhabiting a polluted port and an adjacent marine protected area

The acquisition of data to safeguard marine protected areas located close to ports is important in order to develop plans that allow effective protection from pollution as well as sustainable development of the port. The area Secche della Meloria is a Marine Protected Area (MPA-MEL) three miles from Livorno Harbour (LH), which is characterized by a long history of pollution. Here we studied the bioaccumulation and transcriptomic patterns of the marbled crab, Pachygrapsus marmoratus (Fabricius, 1787) (Crustacea; Brachyura, Grapsidae), inhabiting the two selected sites. Results showed that the two crab populations are significantly different in their chemical composition of trace elements and Polyciclic Aromatic Hydrocarbons (PAHs), and gene expression patterns (1280 DEGs). Enrichment analysis indicated that crabs at LH had the highest stress response genes, and they were associated with higher levels of bioaccumulation detected in body tissues. We are confident that the significant differential gene expression profiles observed between crabs, characterized by significant chemical differences, is associated with responses to contaminant exposure.

Trophic Niche Dynamics and Diet Partitioning of King Crab Lithodes santolla in Chile’s Sub-Antarctic Water

The southern king crab Lithodes santolla is one of the most economically important fishery species in the southern waters of the Atlantic and Pacific Oceans. A combination of stomach content and stable isotope analyses was used to reveal the potential dietary characteristics, isotopic niche, overlap among maturity stages and sexes, and trophic relationships of an L. santolla population in the Nassau Bay, Cape Horn region. Stable isotope analyses indicated that L. santolla assimilated energy from a basal carbon source, the giant kelp Macrocystis pyrifera, forming the trophic baseline of the benthic food web. Moreover, the trophic position of L. santolla varied among late juveniles and adults, suggesting that the southern king crab does undergo an ontogenetic diet shift. L. santolla exhibited intraspecific isotopic niche variation, reflecting niche differentiation which allows the species to partition resources. The trophic relationships of L. santolla with the associated fauna suggested some potential interactions for food resources/habitat use when they are limited. This study is the first attempt to characterize the trophic dynamics of the southern king crab in the Cape Horn area and, by generating more data, contributes to the conservation of the king crab population and the long-term management of local fisheries that rely on this resource.

Short-term effects of hurricane events on the bioindicator species Ocypode quadrata inhabiting an island in essence free of anthropogenic disturbances

The effects of high-energy weather events may be most dramatic on coast dominated by sandy beaches, characteristic habitat of the Atlantic ghost crab. This study evaluates the impact of two hurricanes over Ocypode quadrata populations based on the hypothesis that natural disturbances may bring on a decrease in crab burrow size (population structure) and/or a significant decline in the burrow density (relative abundance). Densities of crabs, estimated via burrow counts and their size, evaluated according to burrow opening diameter, were quantified at six sites around Isla de Aves, before (July) and after (November) two major hurricanes (Irma and Maria) that hit the coastal areas on islands of the Caribbean Sea in 2017. Six 2 × 2 m areas were sampled at each site. The results reveal an effect on the size structure, while the population density did not present any evident change between the pre and post-hurricane moments. The decrease in the diameter of the burrows after the passage of the hurricanes, suggests that the larger crabs could have been removed during this event followed by an arrival of new recruits into the ghost crab population. The results suggest a short-term resilience to the impact of extreme climatic events in terms of population density, a scenario that could had been favored by several conditions. Isla de Aves has sandy beaches exposed to ocean currents, which favor the transport of larvae and the recruitment of juveniles. The availability and quality of food, due to its characteristics of being a main nesting site for sea turtles (mainly green turtle); therefore, it offers various resources in abundance (e.g., turtle eggs). As well as the characteristic of being an island practically free of anthropogenic disturbances.

Evaluation of a novel research trap for surveys of blue swimmer crab populations

Surveying free-ranging crab populations is important for monitoring the health of exploited stocks and predicting future productivity. Here, we present a novel research trap design for use in fisheries-independent surveys of blue swimmer crab (Portunus armatus) populations, and evaluate the trap against some existing approaches within an independent survey framework. Specifically, the trap design aimed to improve efficiency for capturing smaller crabs, without adversely affecting catches of larger crabs. We quantify and report the abundance and selectivity of these traps, relative to co-located samples obtained using beam trawls and standard commercial round traps, to establish whether these small-mesh traps may offer any improvements over existing survey methods. Comparison and evaluation of these small-mesh traps against other existing survey gear, in different places and at different times, showed that the traps are more effective at catching smaller crabs when they are present, and equally or more effective at catching larger size classes of crabs. The beam trawl appeared to be effective at capturing a reasonable size range of crabs; however, the number of crabs caught (using a similar investment of time) was substantially lower than that caught in traps. This novel small-mesh research trap appears suitable for fisheries-independent surveys of portunid crab species.