Beach cusps and burrowing activity of crabs on a fine-grained sandy beach, southeastern Nigeria (original) (raw)
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Crabs belong to the superfamily Ocypodoidea are a significant component of benthic fauna and considered as ecosystem engineers because of their dynamic role as an active burrower in mangrove and estuarine environment. The current investigation was to evaluate the crab burrow density, diameter and total area of burrow opening along the coast of Pakistan. The variations in burrow properties and their relation to sediment characteristics were also evaluated to recognize the most influencing variables of sediments that effects on crab burrows. All crab burrow and sediment characteristics differed significantly (p b 0.05) among the monitoring sites. Regression analysis showed that crab density was significantly correlated with burrow density (P b 0.001). Moreover, burrow density was noticed significantly greater (p b 0.05) than crab density. Pearson correlation analysis reveals that moisture, porosity, organics, sand and mean grain size observed as most influencing the features of sediment to determine the ecological functioning of crab burrows in mangrove and mudflats of Pakistan.
Spatial distribution patterns of the ghost crab Ocypode quadrata were analysed using different approaches at one disturbed and two preserved reflective sandy beaches of the Mexican Caribbean. We used spatial correlation analysis to describe the across-shore distribution of O. quadrata and their patch dynamics by beach and sampling time. In addition, we analysed the across-shore variability of habitat extent of O. quadrata (habitat envelope) and its relation to human disturbance and beach features. The spatial structure of burrow density was consistent through time, showing a bimodal distribution with very low abundance in the mid distribution range and a discrete increment of burrows to landward. Nonetheless, the size of patches varied temporally for the three beaches. Burrow size increased from seaward to landward. The location of the first burrow and the habitat envelope varied among sampling times and beaches. The location of the first burrow is mostly mediated by the swash climate, while the habitat envelope is mainly controlled by the level of human disturbance. Despite the low number of disturbed and control beaches, our results suggest that the habitat envelope could be included in future studies when using ghost crabs as indicators of human disturbance. Polynomial models and variographic analysis proved to be useful tools to describe the across-shore distribution and patch dynamics of the ghost crab.
PLOS ONE
The diameter and vertical depth of sand crab tunnels in sandy beaches are usually restricted to a few centimeters scale and several tens of centimeters, respectively. We designed a study to determine what physical factors restrict tunnel diameter and predict the maximum attainable tunnel diameter and depth. We collected field data on the size and spatial distributions of ghost crab (Ocypode spp.) burrows on two sandy beaches (Kawage Beach in Tsu, Mie Prefecture, Japan and Sakieda Beach in Ishigaki, Okinawa Prefecture, Japan), where O. ceratophthalma dominants the ghost crab fauna. We measured burrow depths and distance from shoreline in concert with water content of sandy beaches. To explain our observed distributions of crab burrows in the field, we performed experiments in a lab microcosm, comprising a horizontal tunnel through wet sand. We measured the static stability of tunnel structures in relation to water content and two strengths computed from loading force exerted on the sand overlying the tunnels. By comparing field and experimental data, we found that crabs construct their burrows in appropriately wet zones (wet enough to provide sufficient cohesion of the sand grains in tunnel walls to prevent collapse) and that tunnel diameters and depths are sufficiently small to prevent deformation and collapse of their tunnels.
Momona Ethiopian Journal of Science, 2011
We applied a rapid assessment methodology to estimate the degree of human impact on exposed sandy beaches in Ghana using ghost crabs as ecological indicators. The use of ghost crab burrow density and size ranges of the burrows as ecological indicators to assess extent of anthropogenic impacts on beaches was explored in this study. For each site, three transects were laid perpendicular to the shoreline over a 100 meter distance at 50 m intervals, i.e., at reference points 0, 50 and 100 meter points. Sampling locations were randomly selected along the three transects using a 1 m x 1 m quadrat. Measurements were done twice weekly for a period of four weeks. The results showed that even though the moderately disturbed beach had higher burrow density than the disturbed beach on the average, the difference is not statistically significant (t-test; p > 0.01). However, the mean burrow diameter at the moderately disturbed site was significantly larger than for the disturbed site (t-test; p < 0.01). We conclude that ghost crab burrow sizes is a better estimator of human impacts on exposed sandy beaches and could be employed as a rapid tool for monitoring the quality of beaches.
• The study assessed the response of ghost crabs to human stressors. • Beaches were categorized into high use, medium use and low use beaches. • Burrow sizes and densities were significantly higher at the low use beaches. • Several human uses are attributed to low crab numbers recorded on impacted beaches. • There is the need to pursue direct ecological beach management policy in Ghana. a b s t r a c t The increasing urbanization of much of the world's coasts threatens irreversible damages to beach ecosystems, if unchecked. Unfortunately, beach monitoring programmes for remediation actions are uncommon, especially for less developed nations where infrastructural development and socioeconomic goals are regarded more important than environmental goals. This study aimed at obtaining information about the effects of the modification and use of beaches and dunes on beach biota using ghost crab burrow density and size as variables. The study tested a hypothesis that the mean densities and sizes of ghost crab burrows on six beaches under three categories of human use in the Central Region of Ghana are different. Results indicated that low use beaches had significantly higher numbers of burrows and larger burrow sizes compared to medium use and high use beaches. Since physical and environmental parameters were consistently the same amongst the six surveyed beaches, the paper concluded that the differences in the observed beach use and dune modifications were responsible for the observed differences in ghost crab abundance and sizes. Major beach use such as intense trampling levels and clearing of dune vegetation for infrastructural developments are most likely responsible for the observed differences. On account of ecological considerations, it is recommended that beach land use reforms by coastal municipal authorities in Ghana should ensure that infrastructure development along undeveloped sections of the coast is limited to a safe distance from the shoreline. There should also be consideration of natural vegetation barriers between development and the beach to enhance natural beach–dune ecosystem interaction.
Ghost crab populations respond to changing morphodynamic and habitat properties on sandy beaches
Acta Oecologica, 2015
The morphodynamic state and habitat properties of microtidal sandy beaches largely account for variations in macrofauna structure. In ecological theory, the habitat harshness hypothesis and the habitat safety hypothesis explain variations in macrofauna populations of the intertidal and supratidal zones of sandy beaches. The former hypothesis states that intertidal macrofauna should increase from reflective to dissipative beaches. The latter hypothesis supports the idea that supratidal species are more successful on reflective beaches, given their relative independence from the swash. However, trends in abundance of supratidal species, particularly crustaceans, have been unclear and further investigation is therefore needed. This study tested the two hypotheses on the largest invertebrate intertidal-to-supratidal crustacean on sandy beaches, namely the ghost crab (genus Ocypode). Variations in ghost crab burrow density, abundance, size and across-shore distribution were measured on four warm-temperate microtidal sandy beaches in KwaZulu-Natal, South Africa. Burrow numbers increased with beach morphodynamic state, while average burrow size decreased. The steepest, narrowest and most inundationprone beach represented the least hospitable environment for the ghost crabs. The results that are reported here tend to support the habitat harshness hypothesis. However, the relevance of i) individual physical variables, ii) tidal action, and iii) the ecology of various species, in shaping ghost crab population dynamics, is also discussed. The results contribute to the knowledge regarding population dynamics of intertidal and supratidal crustaceans across beach types.
2018
Mangrove crabs are active burrowers in intertidal sediments of wetland, living beneath drifts and high-tide marks in lagoon shores in many parts of the world. The occurrence, distribution and burrow depths and diameters of the mangrove crabs, Cardisoma armatum and Goniopsis pelii collected from a mangrove wetland of the Lagos Lagoon were investigated between February and July, 2017. Burrows were counted biweekly on permanent square plots marked out in the six stations, while the appearance of new burrows as well as disappearance of old burrows, depths and diameters were recorded. C. armatum was present in all the study sites with a total of 848 specimens and occurred throughout the study period, while G. pelli with a total of 115 specimens occurred in two study sites and during the wet season only. Species ratio was 1: 0.37 while the Chi- squared value at 1 d.f and 5 % significant level was 557.93. The depth of the crab burrows across the stations ranged from 16.65 – 33.47 cm with d...
地質学雑誌, 2008
Burrow morphologies of the ghost crabs Ocypode ceratophthalma and O. sinensis were observed in foreshore, backshore, and dune subenvironments on the Irino Coast, southwestern Japan, with the aim of clarifying their paleoenvironmental significance. The observed diameter of the main shaft, burrow depth, and total burrow length varied from 14 to 40mm, 12 to 89cm, and 8 to 143cm, respectively. Although the burrow diameters are largely similar among the three subenvironments, the burrows increased in length and complexity from the foreshore to dune subenvironments. These findings indicate that burrow morphology can be used as an indicator of ancient sandy beach subenvironments.