Crab Density Research Articles

Mesopredator release moderates trophic control of plant biomass in a Georgia salt marsh.

Predators regulate communities through top-down control in many ecosystems. Because most studies of top-down control last less than a year and focus on only a subset of the community, they may miss predator effects that manifest at longer timescales or across whole food webs. In southeastern US salt marshes, short-term and small-scale experiments indicate that nektonic predators (e.g., blue crab, fish, terrapins) facilitate the foundational grass, Spartina alterniflora, by consuming herbivorous snails and crabs. To test both how nekton affect marsh processes when the entire animal community is present, and how prior results scale over time, we conducted a 3-year nekton exclusion experiment in a Georgia salt marsh using replicated 19.6 m2 plots. Our nekton exclusions increased densities of plant-grazing snails and juvenile deposit-feeding fiddler crab and, in Year 2, reduced predation on tethered juvenile snails, indicating that nektonic predators control these key macroinvertebrates. However, in Year 3, densities of mesopredatory benthic mud crabs increased threefold in nekton exclusions, erasing the tethered snails' predation refuge. Nekton exclusion had no effect on Spartina biomass, likely because the observed mesopredator release suppressed grazing snail densities and elevated densities of fiddler crabs, whose burrowing alleviates soil stresses. Structural equation modeling supported the hypotheses that nektonic predators and mesopredators control invertebrate communities, with nektonic predators having stronger total effects on Spartina than mud crabs by controlling densities of species that both suppress (grazers) and facilitate (fiddler crabs) plant growth. These findings highlight that salt marshes can be resilient to multiyear reductions in nektonic predators if mesopredators are present and that multiple pathways of trophic control manifest in different ways over time to mediate community dynamics. These results highlight that larger scale and longer-term experiments can illuminate community dynamics not previously understood, even in well-studied ecosystems such as salt marshes.

No man’s land support the endemic Red Sea ghost crab (Ocypode saratan) in the Gulf of Eilat

Tourism pressure on the Red Sea ecosystem have posed significant threats to numerous endemic species, including the Ghost Crab Ocypode saratan, which is exclusively found along a small stretch of beach in the Eilat/Aqaba Red Sea Gulf. Due to the limited understanding of their ecology, we investigated how tourism impacts the behavior of this species. Employing a natural setup, we compared burrow dimensions, pyramid structures, and density across three distinct beach sections subjected to varying levels of human interference. Access to a secluded beach, referred to as “No Man’s Land,” provided a crucial control for our study. This facilitated a comparative analysis of ghost crab activity among beaches experiencing differing levels of human disturbances: (1) a tourist beach characterized by continual high disturbance, (2) a naval beach subject to moderate and sporadic disturbances, and (3) the isolated “no man’s land” beach devoid of human presence. Our observations revealed notable differences in ghost crab density among the three beaches. Furthermore, we observed that on the secluded beach, larger individuals tended to establish burrows farther from the waterline and construct taller sand pyramids. Given the significance of sexual selection processes, their conservation becomes imperative for the survival and potential expansion of the ghost crab population across the Gulf of Eilat/Aqaba. We propose a straight-forward and cost-effective strategy: the designation of short, secluded beach enclaves along this gulf. We believe that this approach will mitigate adverse impacts of tourisms while simultaneously benefiting various sandy beach species.

Ecological characteristic of hermit crabs in Lhokseumawe mangrove forest, Aceh, Indonesia

The study was conducted between August and September of 2021 in order to determine the density, ecological index, distribution pattern, geographic distribution, environmental factors, and the relationship between hermit crabs and environmental factors. Hermit crabs were gathered using a quadratic transect and sample plots, while environmental variables were measured in situ. PCA and CCA multivariate statistics were used to determine the characteristics and correlation between herm...

Ontogenetic patterns in juvenile blue crab density: effects of habitat and turbidity in a Chesapeake Bay tributary

Nursery habitats are characterized by favorable conditions for juveniles, including higher food availability and lower predation risk, and disproportionately contribute more individuals per unit area to adult populations compared to other habitats. However, nursery habitat inference is complicated by changes in habitat preferences with ontogeny; individuals in early-life stages frequently inhabit different habitats than older juveniles or adults. In this field experiment, we modeled the density of 4 size classes of juvenile blue crabs Callinectes sapidus based on carapace width (CW) across multiple habitats at various locations within an estuarine seascape during the blue crab recruitment season. We examined 4 habitat types—unstructured sand, seagrass meadows, salt marsh edges (SME), and shallow detrital habitat (SDH). Results indicated that densities of small juvenile blue crabs (≤10 mm CW) were highest in seagrass, whereas densities of larger juveniles (16-25 mm CW) were highest in SME. Although densities of juveniles declined in seagrass habitat as a function of size, densities in SME remained consistently high, suggesting that secondary dispersal to SME by smaller juveniles after settlement and recruitment in seagrass may supplement losses in SME due to mortality. Turbidity was positively correlated with densities of both size classes, although our model did not address whether this was due to top-down (refuge) or bottom-up (food availability) mechanisms. Observed patterns in size-specific habitat utilization may result from changing requirements of juvenile blue crabs with size, as animals minimize mortality-to-growth ratios. Our findings emphasize the role of both seagrass and salt marsh habitat within juvenile blue crab ontogeny and emphasize the significance of structurally complex SME habitat in supporting juvenile blue crabs at sizes smaller than previously recognized, challenging past notions about the singular importance of seagrass habitat in this system. Our findings also underscore the need to quantify and preserve the complete chain of habitats used by juveniles.

Goliath is not the enemy: Fiddler crab species of similar size are stronger competitors than their larger adversaries in the climate change context

Many intertidal species are expanding their distribution limits towards the poles as a consequence of increased temperature due to climate change. At the same time, some intertidal habitats have been reduced due to rising sea levels. Fiddler crabs inhabit mangroves, and different species occupy well-established zones. Due to the restricted mangrove areas and consequent latitudinal expansion of the species, the distribution and density of fiddler crabs may be subject to change. The overlap forces several species to cohabit in a smaller territorial space. Fiddler crab species can vary in size, which could decisively affect territorial competition. Using Leptuca urguayensis as a reference, we tested how competing species of different sizes (larger size: L. thayeri and Minucapanema; similar size: L. cumulanta and L. leptodactyla) might interact in future climate change scenarios. First, we showed that within the territory of L. uruguayensis, the species L. cumulanta and L. thayeri occurred mainly in the lower mesolittoral zone, while L. leptodactyla and M.panema predominated in the upper mesolittoral zone. In a laboratory experiment, we evaluated whether the density and size of the heterospecific competitors could alter the agonistic behavior of Leptuca uruguayensis. Our results indicated that increasing the density can increase the agonistic behavior of L. uruguayensis with a greater intensity against species of a similar size. In a second field experiment, we demonstrated that the presence of a burrow enhances the intensity of agonistic interactions between L. uruguayensis and species of similar size. Therefore, in a scenario of territorial expansion of fiddler crabs due to climate change, it is expected that similarly sized species represent a greater competitive threat to populations of L. uruguayensis.

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.

The effects of Sesarma reticulatum (L.) herbivory and sea level rise on creek expansion in Cape Cod salt marshes

High densities of herbivorous purple marsh crabs (Sesarma reticulatum) have caused major vegetation loss in salt marshes across Cape Cod (Massachusetts, USA). As creekbanks are a preferred habitat for this species, much of the damage is concentrated along these edges, resulting in an elevated potential for creek widening through erosion and bank slumping. The presence and/or spatial distribution of S. reticulatum is variable across this region with impacts ranging from minor to severe, and this provides an opportunity to distinguish between background vs. S. reticulatum-enhanced widening. To accomplish this, GIS tools were used to delineate portions of tidal creek systems in 18 marshes, half of which have experienced substantial creekbank vegetation losses from crab-driven herbivory. Delineations were based on georeferenced aerial photography between 2005 and 2021. In addition, creek widths at discrete locations in the delineated systems were measured in each photo year using GIS tools to estimate rates of bank retreat. A smaller number of narrow <2.0 m mosquito ditches were analyzed in the same way to further stratify the data by initial width. Between 2010 and 2021, all tidal conduits ranging from the larger, natural creeks to mosquito ditches widened at a rate that was significantly higher in marshes with no Sesarma damage. While all marshes are under threat from SLR, creek-widening in those experiencing intense crab herbivory may have a greatly shortened lifespan.

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.

Human disturbance affects behavioural time allocation in a fiddler crab (&lt;em&gt;Austruca annulipes&lt;/em&gt;) in Southern Thailand

Human disturbances affect the macroinvertebrate populations in coastal regions. They respond to disturbances by altering their density and behaviour. Therefore, many of them are used as bioindicator species of human disturbance. Here, we pioneer the use of fiddler crabs to examine whether they alter their behaviour under human disturbance. Male fiddler crabs possess one large claw used for courting (waving) and fighting, and one small feeding claw, whereas females have two feeding claws. They show several surface activities. This study investigates (1) the effects of human disturbance on density and sex-ratio, and (2) the effects of human disturbance, and sex on behavioural time allocations in Austruca annulipes. Their density, sex-ratio, and time allocations were investigated in human-disturbed area (DA) and nondisturbed area (NDA). They showed feeding, feeding and walking, walking, running, standing/vigilance, inside burrows, burrowing, grooming, fighting, and waving. The results showed that crab density was higher and the sex ratio was more male biased in NDA than in DA. Human disturbance and sex affected time allocations but their interaction had no effect. Crabs in DA spent more time running, standing, and inside burrows but less time walking, burrowing, fighting, and waving than crabs in NDA. Between sexes, males spent more time standing, burrowing, grooming, and fighting but less time feeding, and walking than females. This indicates that human disturbances force the crabs to spend more time on anti-predator and escape behavior (standing/vigilance, running, inside burrows) rather than courting (waving) and constructing burrows (mating/breeding sites), which are important for breeding.

Burrowing crabs' influence on tidal marsh vegetation species composition and abundance in a temperate back-barrier marsh, Cape Cod, Massachusetts, USA

Emergent vegetation in coastal marshes across the Northeastern United States have been declining and changing in relative species composition due to abiotic factors such as accelerated sea level rise, storm intensity, excess nutrients, and other anthropogenic disturbances. A possible biotic factor in marsh decline is increased perturbation from burrowing crabs. Uca pugilator and Minuca pugnax (fiddler crabs) whose populations are increasing in many marshes in the eastern US, likely due to disruptions in food webs and expanding habitat from sea level rise. High densities of crab burrows contribute to creek bank erosion and possibly in other factors of marsh peat degradation. When burrowing crabs were excluded from large scale (9 m2) plots in a Cape Cod, MA, marsh for five months, vegetation species richness increased significantly, as did abundance of woody shrubs and the forb, Suaeda maritima (L.). Conversely, burrowing crab exclusion resulted in less Spartina alterniflora (Loisel) and less bare ground - indicating that the other types of vegetation were able to occupy more space in the absence of crab burrowing and sediment sorting activity. The experimental enclosure results were compared with vegetation and burrow density monitoring data taken from nearby long-term monitoring plots. Of the sixteen analyses, we found only one similar result between the 5 month exclusions and monitoring plots; high burrow densities were associated with higher density of S. alterniflora. In contrast to the exclusions, high burrow densities were positively correlated with abundance of Iva frutescens and Suaeda maritima. Six other species (or groupings of rare plants) were negatively associated with burrow densities, four of these are sensitive to inundation and are considered characteristic of the high marsh zone. Different interpretations of the effects of burrowing crabs will result depending on whether correlations are observed from monitoring plots or longer term, large-scale exclusions are conducted; both are needed to assess the rapid vegetation and faunal shifts that are occurring in temperate salt marshes. We suggest that Uca pugilator and Minuca sp. will benefit from sea level rise induced habitat expansion at the expense of the abundance and species richness of flooding-sensitive plants. The erosion and vegetation disturbance that high burrowing crab densities lead to will further exacerbate the decline of these species that are receding at the seaward edge of their distributions.

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.

Association between Mangrove Types and Some Mangrove Crab Species in West Lombok Sheet Mangrove Ecosystem

One of the ecosystems found in coastal areas is the mangrove ecosystem. Mangroves have many functions including as a shelter, a place to find food, a breeding ground for aquatic biota. Damage to mangrove areas can cause a decrease in the quality of mangrove ecosystems, especially for the life of mangrove crabs. Mud crab is one of the aquatic biota associated with mangroves and its life is influenced by the presence of mangrove forests. Therefore, the purpose of this study was to determine the diversity of mud crabs that live in mangrove ecosystems and the association of mangrove species with several species of mud crabs in the coastal mangrove ecosystem of Lembar, West Lombok. Mud crab samples were taken using purposive sampling by looking at the density of mangroves in each observation plot. The collected data were analyzed by diversity index, ecological index, association and Pearson's correlation coefficient. Then a simple linear regression analysis was performed with the variable (x) density of mangroves and (y) density of mangrove crabs. The results of this study were found to be 10 species of mud crabs consisting of 2 families of Ovalipidae and 8 families of Portunidae which belong to the moderate diversity index. There were 2 species of mud crabs that were positively associated with 2 species of mangroves out of 10 species of mud crabs found. Linear regression equation y = 0.2482x + 0.0004 with a pearson correlation coefficient (r²) (0.58). The conclusion of this study is that there is a relationship between mangrove density and mangrove crab densityOne of the ecosystems found in coastal areas is the mangrove ecosystem. Mangroves have many functions including as a shelter, a place to find food, a breeding ground for aquatic biota. Damage to mangrove areas can cause a decrease in the quality of mangrove ecosystems, especially for the life of mangrove crabs. Mud crab is one of the aquatic biota associated with mangroves and its life is influenced by the presence of mangrove forests. Therefore, the purpose of this study was to determine the diversity of mud crabs that live in mangrove ecosystems and the association of mangrove species with several species of mud crabs in the coastal mangrove ecosystem of Lembar, West Lombok. Mud crab samples were taken using purposive sampling by looking at the density of mangroves in each observation plot. The collected data were analyzed by diversity index, ecological index, association and Pearson's correlation coefficient. Then a simple linear regression analysis was performed with the variable (x) density of mangroves and (y) density of mangrove crabs. The results of this study were found to be 10 species of mud crabs consisting of 2 families of Ovalipidae and 8 families of Portunidae which belong to the moderate diversity index. There were 2 species of mud crabs that were positively associated with 2 species of mangroves out of 10 species of mud crabs found. Linear regression equation y = 0.2482x + 0.0004 with a pearson correlation coefficient (r²) (0.58). The conclusion of this study is that there is a relationship between mangrove density and mangrove crab density

Density and extractive potential of “uçá”-crab, Ucides cordatus (Linnaeus, 1763), in mangroves of the “Todos os Santos” Bay, Bahia, Brazil

Ucides cordatus is one of the main fishery resources of the “Todos os Santos” Bay (BTS), State of Bahia, Brazil. Population parameters (structure, density, and fishery potential) of this crab species were analyzed in the dry and rainy seasons in nine mangrove areas of BTS. Five sample quadrats (5 × 5 m) were used to record the number and diameter of active open burrows (with biogenic activity) and closed burrows of U. cordatus, tree variables (composition, density, and diameter), and flood level. Crab density (ind.m−2) was indirectly estimated by counting galleries. The diameter of open galleries was converted into carapace width (CW) using a regression model to later characterize the U. cordatus population structure. There were more galleries in the dry season than in the rainy season. Crab density ranged from 0.32 to 2.63 ind.m−2 (1.32 ± 0.90 ind.m−2), and the mean density was higher during the dry period (t = 0.02; p < 0.05). Crab density differed among sampling areas regardless of seasonal period. Crab size (CW) in BTS was 52.4 ± 16.7 mm, with specimens significantly larger during the dry period (t = 0.01; p < 0.05), and there was a significant difference (F = 4.57; p = 000.1) among mangrove areas. Non-commercial size animals (CW < 60.0 mm) were more abundant (65.2%) than those with commercial size (34.8%) in BTS. Crab density and flood level showed significant negative correlation (p = −0.51; p < 0.05), while there was a positive correlation between CW and flooding level (p = 0.40; p < 0.05). U. cordatus population parameters differed significantly among BTS sampling sites due to their heterogeneity. This study is the first assessment of “uçá”-crab populations in BTS mangroves and reveals a need for a sustainable management in the area. Furthermore, this study could be a model for monitoring other large brachyuran species inhabiting estuarine systems, which are economically and biologically relevant.

Intertidal habitat complexity influences the density of the non-native crab Hemigrapsus sanguineus.

Habitat structural complexity can provide protection from predators, potentially affecting population density of native and non-native prey. The invasive Asian shore crab, Hemigrapsus sanguineus, occurs in variable densities in the rocky intertidal zone of eastern North America and northern Europe, often in densities greater than in its native range. The present study examined the influence of habitat complexity on the density of H. sanguineus. Artificial shelters of concrete pavers with stones arranged in increasing complexity were deployed in the intertidal zone along a rocky shore in southeastern Massachusetts, USA, for 21 consecutive weekly intervals in 2020. Crabs consistently reached the highest densities in the most complex shelters despite their lower internal surface area. In addition, crabs exhibited shelter selectivity based on body size, with large crabs occupying artificial shelters in greater numbers than adjacent natural substrate. In a subsequent lab study, crab activity over 1 h was observed in the presence of the same artificial shelters, under simulated tidal conditions. Shelter complexity had little influence on the number of crabs under the pavers although crabs were more active when submerged in water than exposed to air. These results show that crab density increases as habitat complexity increases, and complexity may serve as a predictor of H. sanguineus density but not short-term behavior.

Population structure and dynamics of Petrolisthes armatus (Gibbes, 1850) (Anomura: Porcellanidae) in an Amazon estuary

The aim of this study was to assess the environmental factors that modulate the spatiotemporal distribution of Petrolisthes armatus and analyze their population structure, dynamics and secondary production in an Amazon estuary. Monthly samplings were carried out over one year in the intertidal rocky outcrop considering the following environmental features; season (dry and rainy), areas (middle and lower estuary), banks (east and west), substrate with different rock sizes, and the upper and lower intertidal zones. Crab density was positively correlated with salinity and negatively correlated with temperature. Higher densities occurred during dry season, on the eastern bank, in the lower estuary, in the lower intertidal zone, and in the larger rock substrate. The high abundance of P. armatus indicates that this estuary is a suitable habitat for the development of this anomuran, and salinity and substrate were the most important factors driving population structure. High production reflects high density and biomass and the fast growth of this crab indicated that this filter feeder generates substantial production to the benthos. This study corroborated the hypothesis that the high metabolism of P. armatus combined with the high temperature in the Amazon region results in short life span (∼one year), high mortality rate (∼6 year −1), and high P/B ratio (∼4 year −1).

Carbon stocks and sequestration rate in mangroves and its major influencing factors from highly urbanised port city, southern India

This study estimated the total ecosystem carbon stock (TECS) and sediment carbon sequestration rate through burial for fragmented mangrove habitats of Kochi, south-west coast of India. The mean TECS of Kochi mangroves was estimated at 335.33 ± 184.47 t C ha−1, with above ground biomass of 171.68 ± 104.42 t C ha−1, belowground biomass of 83.30 ± 41.98 t C ha−1, litterfall carbon as dead biomass of 7.12 ± 2.81 t C ha−1 and soil carbon stock of 73.22 ± 39.40 t C ha−1. The average historical soil carbon sequestration rate of Kochi mangroves was also estimated as 2.95 t C ha−1 yr−1. The study revealed that there was significant variability in TECS and sediment carbon burial rate among riverine, estuarine and marine mangrove habitats and it appears that, the biological factors especially mangrove plant structure, species, age, litterfall production, crab density, mangrove conversion to aquaculture ponds and other urban pressure played major roles in driving the variability in carbon stocks and storage. While the sediment particle size, bulk density and the environmental settings played a secondary role. Very low TECS and soil carbon sequestration rate was found in aquaculture converted mangrove habitat. The CO2e of ecosystem carbon stock (496311.20 t CO2 e) and soil CO2 burial (10.62 t CO2 e ha−1 yr−1 respectively) of mangroves of Kochi, revealed that even with high urban pressure and anthropogenic activities which resulted in fragmented distribution, they are still potent in long term carbon sequestration unless it is not further disturbed. Therefore, conservation and restoration of mangrove habitats based on understanding of the regional controlling factors of carbon stock and carbon burial is a need for scientific climate change mitigation efforts. The study will also contribute to fill the gaps in global mangrove carbon stock assessments for avoiding uncertainties.

Intertidal Green Crab Survey Over a Ten-Year Period on a Maine Cobble Beach

Here we report on the long-term monitoring of Carcinus maenas (European Green Crab) populations on an intertidal region of a cobble beach in Maine conducted from 2011 to 2021. The number of Green Crabs collected fluctuated between 129 and 474 individuals per sample event. We collected crabs twice each year, with a total number collected of 389 to 798 per year. In addition, we collected Hemigrapsus sanguineus (Asian Shore Crab) in 2 sample years (2019 and 2021), accounting for only 7 individuals. No compelling relationships between Green Crab densities and sea-water temperature, average carapace width, or year of the collection were revealed.

Evaluating environmental controls on the exoskeleton density of larval Dungeness crab via micro computed tomography

Dungeness crab (Metacarcinus magister) have significant socioeconomic value, but are threatened by ocean acidification (OA) and other environmental stressors that are driven by climate change. Despite evidence that adult harvests are sensitive to the abundance of larval populations, relatively little is known about how Dungeness megalopae will respond to these stressors. Here we evaluate the ability to use micro-computed tomography (μCT) to detect variations in megalope exoskeleton density and how these measurements reflect environmental variables and calcification mechanisms. We use a combination of field data, culture experiments, and model simulations to suggest resolvable differences in density are best explained by minimum pH at the time zoeae molt into megalopae. We suggest that this occurs because more energy must be expended on active ion pumping to reach a given degree of calcite supersaturation at lower pH. Energy availability may also be reduced due to its diversion to other coping mechanisms. Alternate models based on minimum temperature at the time of the zoea-megalope molt are nearly as strong and complicate the ability to conclusively disentangle pH and temperature influences. Despite this, our results suggest that carryover effects between life stages and short-lived extreme events may be particularly important controls on exoskeleton integrity. μCT-based estimates of exoskeleton density are a promising tool for evaluating the health of Dungeness crab populations that will likely provide more nuanced information than presence-absence observations, but future in situ field sampling and culture experiments are needed to refine and validate our results.

Population density and distribution patterns of Austruca annulipes (Ring-legged fiddler crab) in the mangrove of Bogowonto Estuary, Kulon Progo, Yogyakarta, Indonesia

Abstract. Fadilah RN, Yulia IT, Alfitra ZS, Armadhan WS, Widyaningtyas R, Rahmayani D, Permatasari DP, Igustita, Kusuma D, Prambudi SA, Berlin GE, Triyanto A, Sutarno, Indrawan M, Dadiono MS, Rahim KABA, Setyawan AD. 2023. Population density and distribution patterns of Austruca annulipes (Ring-legged fiddler crab) in the mangrove of Bogowonto Estuary, Kulon Progo, Yogyakarta, Indonesia. Intl J Bonorowo Wetlands 13: 1-8. The mangrove forest ecosystem is a forest with coastal plant characteristics that are influenced by tides and tolerate high salt levels. Mangrove forests in Indonesia contain about 89 species of flora, and around 18% of their fauna are keystone species. Keystone species are species that play an important role in maintaining the balance of the ecosystem. Austruca annulipes (H. Milne-Edwards, 1837), or Ring-legged fiddler crab is one of the fauna species in the mangrove ecosystem, which has an important role in maintaining the balance of the food chain and nitrogen cycle, so the study of this species is very important for the sustainability of the ecosystem in mangrove area. This study aimed to determine the population density and distribution patterns of A. annulipes in the Mangrove Bogowonto Estuary Area, Kulon Progo, Yogyakarta, Indonesia. The research method was purposive random sampling using a 10m x 10m square plot. Furthermore, the identification of morphology and documentation of the activities of A. annulipes was carried out, and data were examined using calculations of crab density. Based on the research finding, the population density of A. annulipes is 0.9975 individuals/m2. Calculating the Morisita Index of A. annulipes obtained a value of 1.38 with the category of clumped distribution patterns. Various factors influence this distribution, including abiotic factors such as soil moisture, temperature, air, salinity, and pH. In addition, the presence of vegetation has also affected the density of A. annulipes because it is used as a shelter and foraging among its roots.

Delayed response of hermit crabs carrying anemones to a benthic impact experiment at the deep-sea nodule fields of the Peru Basin?

The deep Peru Basin is characterised by a unique abyssal scavenging community featuring large numbers of hermit crabs (Probeebei mirabilis, Decapoda, Crustacea). These are atypical hermit crabs, not carrying a shell, but on some occasions carrying an anemone (Actiniaria). The reason why some hermit crabs carry or not carry anemones is thought to be indicative of a changed environment, outweighing the cost/benefit of their relationship. Here we present the temporal variation of abundances of P. mirabilis with and without anemones, spanning more than two decades, following a benthic impact experiment. An overall decrease in hermit crab densities was observed, most noticeable and significant after 26 years and characterised by a loss of Actiniaria on the Probeebei mirabilis' pleon. Whether this is a delayed response to the benthic impact experiment carried out 26 years’ prior or a natural variation in the population remains to be corroborated by an extension of the time-series. Attention is drawn to the limitations of our knowledge over time and space of the abyssal community dynamics and the urgent necessity to fill in these gaps prior to any type of deep-sea exploitation.