Autotomy induced effects on the locomotor performance of the ghost crab, Ocypode quadrata

The voluntary amputation of an appendage, or autotomy, is an effective defensive mechanism that allows an animal to escape aggressive interactions. However, animals may suffer long-term costs that can reduce their overall fitness. Atlantic ghost crabs (Ocypode quadrata) are one of the fastest terrestrial invertebrates, and regularly lose one or more limbs in response to an antagonist encounter. When running laterally at fast speeds, they adopt a quadrupedal gait using their 1st and 2nd pair of legs while raising their 4th, and sometimes the 3rd, pair of legs off the ground. This suggests that some limbs may be more important for achieving maximal locomotor performance than others. The goal of this study was to determine whether the loss of certain limbs would affect running performance more than others, and what compensatory strategies were used. Crabs were assigned to four different paired limb removal treatments or the control group and run on an enclosed trackway in their natural habitat. Ghost crabs were found to adjust stride kinematics in response to limb loss. Loss of the 2nd or 3rd limb pairs caused a reduction in running speed by about 25%, suggesting that the remaining intact limbs were unable to compensate for the loss of either limb, either due to lack of propulsive forces produced by these limbs or issues stemming from re-coupling limb arrangements. Loss of any of the other limbs had no detectable effect on running speed. We conclude that compensatory ability varies depending on the limb that is lost.

Low Densities of the Ghost Crab Ocypode quadrata Related to Large Scale Human Modification of Sandy Shores

Sandy beaches are the most common ecosystems of coastal regions and provide direct and indirect essential services for millions of people, such as coastal protection, fishing, tourism, and recreational activities. However, the natural habitats of sandy shores are being modified at rates never experienced before, making beaches key monitoring sites of marine ecosystems worldwide. The ghost crab species Ocypode quadrata is the most conspicuous crustacean of sandy beaches along the Western Atlantic coast and has been successfully used as an indicator of anthropogenic disturbance and environmental variability. To investigate the potential role of a “triple whammy” [(1) urbanization; (2) use of resources; (3) decreasing resilience] on the most common bioindicator of sandy shores, we compiled a dataset including 214 records of burrows density from 94 microtidal sandy beach sectors covering a range of over 65° of latitude. The response of burrows density to synergetic effects of human modification of natural systems and environmental changes was investigated using linear models. We used the cumulative Human Modification (HMc) index, a standardized geographic projection of changes of natural systems, as a predictor of urbanization, industrialization and use of resources. The predictor wave energy, tidal range and temperature (sea surface and air) were included as potential effects of climate changes. Literature review showed records mainly concentrated at sub-tropical and temperate regions. HMc values were clearly negatively related to burrows density, thereby supporting an effect of modification of natural habitat at large spatial scale. Sea surface temperature and air temperature were positive related with density and the lack of a general pattern of the relationship between burrows density, interactions between wave energy and tide range, supported unclear patterns reported at regional scales. Finally, we argue that ghost crabs are valuable targets for protection actions on sandy beaches that can benefit coexisting species and provide natural habitat conservation.

THE ANALYSIS OF OIL CONTENT IN SEDIMENT AND COMMUNITY STRUCTURE OF MACROZOOBENTHOS IN BELAWAN WATERS OF MEDAN CITY, NORTH SUMATERA PROVINCE

This research was conducted in March 2019 to determine the oil content in sediment, it’s community structure of macrozoobenthos and it’s a relationship in Belawan Waters of Medan City, North Sumatera. Four sampling stations with five replications in each station were surveyed. The results showed that the average oil content in sediments exceeded the threshold had set by the National Academy of Science. Macrozoobenthos found consists of Ocypode quadrata, Scyla serrate, Rotun dicauda, Penaeus sp, Murex tribulus, and Nassarius olivaccus. The highest abundance was in Station 3 and the lowest was in Station 2. The diversity index in each station was generally very low. Dominance Index in Station 4 was medium, whilst the other stations were high. Evenness index showed in Station 3 and 4 were in high population, Station 1 was in medium population and Station 2 was in low population. Simple linear regression analyses between oil content in sediment with community structure of macrozoobenthos indicated negative correlation ( Y = 10,5-0,0001x , R2 = 0,0004 and r = 0,02 ) which indicated that the higher the oil content, the lower the macrozoobenthos abundance in sediment.

WHICH MOON PHASE DO WE FIND MORE GHOSTS? EFFECTS OF THE LUNAR CYCLE ON THE GHOST CRAB Ocypode quadrata (FABRICIUS, 1787)

The ghost crab Ocypode quadrata is commonly found in the middle and supralittoral areas of sandy beaches along the Brazilian coast. It is a known and important species in the ecology of beaches, which inhabit semi-permanent burrows excavated, maintained, and protected by them. This study evaluated the density and diameter of O. quadrata burrows, considering three lunar cycles in a Conservation Unit on the coast of Ceará state, Northeastern Brazil. Quarterly samplings were performed between 2014 and 2015 during the early morning in the four phases of the moon over three lunar cycles. The tidal range (high tide and low tide) and nocturnal luminosity were used to evaluate the effects of the lunar phases on crab behavior. The lunar cycles influence the activity of the O. quadrata, varying the density, diameter, and distribution of the burrows along the beach, due to changes in the tide conditions and nocturnal luminosity. The construction of burrows by the crabs was higher in the moons that provided more bright nights.Keywords: ghost crab, burrows, Canto Verde beach, phases of the moon.

Natural diet of Ocypode quadrata (Fabricius, 1787) (Crustacea, Decapoda, Brachyura) from the Northern Coast of São Paulo, Brazil

Decapod crustaceans have a wide variety of feeding habits, alternating among herbivory, predation, saprophagy, and filtration. The occupation of various trophic positions in the food web is a key feature in the evolution of the group. Thus, we analyzed the natural diet of the crab Ocypode quadrata (Fabricius, 1787), commonly known as the ghost crab and typically found on sandy beaches. The crabs were collected in the region of Ubatuba, between July 2016 and May 2017. The individuals were dissected in a laboratory, and each stomach was weighed and visually assessed in relation to the degree of repletion. After identification and classification, the items found were grouped for the analysis. In analyzing the stomach contents of Ocypode quadrata, 12 items were found: sand, Insecta, Hymenoptera, Hemiptera, Coleoptera, Crustacea, and other unidentified Arthropoda. We also found poriferans, Actnopterygii bones, plant pieces, non-organic material (plastic), and other non-identified materials. In the statistical analyzes, we observed seasonal differences in the composition of the diet, mostly related to the frequency of items consumed between dry and rainy seasons; the rainy season provided a greater diversity of items. Due to the great trophic spectrum of this species and tendency to feed on a wide range of items, O. quadrata is considered a generalist species, adapting according to the availability of prey in the wild.