A new species of micro-mangrove crab of the genus Haberma Ng & Schubart, 2002 (Crustacea, Brachyura, Sesarmidae) from Hong Kong

The sesarmid genus Haberma Ng & Schubart, 2002, currently contains two species of small mangrove crabs with the first two pairs of the male ambulatory legs possessing characteristic subchelate dactyli and propodi. A new species, H. tingkok, is here described from Hong Kong. It can be separated from H. nanum Ng & Schubart, 2002 (from Singapore), and H. kamora Rahayu & Ng, 2005 (from Indonesian Papua) by its carapace shape, proportions of the ambulatory legs, and structures of the male pleon and male first gonopod.published_or_final_versio

Feeding specialization and activity in certain mangrove crabs

Decapoda is surely one of the most important taxa, both regarding the number of species and individuals, in the macrofauna of the mangrove ecosystem (Macnae, 1968; Macintosh, 1988). For this reason, knowledge about their feeding habits and diet is of primary importance for understanding the energy flow typical of this ecosystem.In Mida Creek and Gazi Bay (Kenya) we collected and then analysed the stomach contents of about 350 crabs belonging to the most common mangrove crab species (excluding the Uca species whose micro-algal feeding habits were already known): Cardisoma carnifex, Epixanthus dentatus, Eurycarcinus natalensis, Metopograpsus oceanicus, M. thukuhar, Sesarma elongatum, S. guttatum, S. leptosoma, S. meinerti, S. ortmanni, Thalamita crenata.Species were divided into classes according to the animal/vegetable matter ratio of their stomach contents.The average stomach fullness proved to be correlated with the degree of vegetable content, being lower in the carnivorous species.Stomach analysis showed that only a few species were strictly herbivorous (mostly feeding on leaf litter) or strictly carnivorous (ambush predators of molluscs or crabs). Instead, magrove crabs seemed to be generally omnivorous, probably due to the low energy and protein content of the food commonly found and to the difficulties in catching suitable prey.For Thalamita crenata, a predator inhabiting the intertidal platform in front of the mangroves, it was also possible to analyse the feeding activity in relation to the different conditions of tide and light. Its feeding activity was higher during the day than at night, and it also seems to feed during low tide, probably catching prey during ebb tides and consuming them when it hides in its shelter

Demographic history and reproductive output correlates with intraspecific genetic variation in seven species of Indo-Pacific mangrove crabs

The spatial distribution and the amount of intraspecific genetic variation of marine organisms are strongly influenced by many biotic and abiotic factors. Comparing biological and genetic data characterizing species living in the same habitat can help to elucidate the processes driving these variation patterns. Here, we present a comparative multispecies population genetic study on seven mangrove crabs co-occurring in the West Indian Ocean characterized by planktotrophic larvae with similar pelagic larval duration. Our main aim was to investigate whether a suite of biological, behavioural and ecological traits could affect genetic diversities of the study species in combination with historical demographic parameters. As possible current explanatory factors, we used the intertidal micro-habitat colonised by adult populations, various parameters of individual and population fecundity, and the timing of larval release. As the genetic marker, we used partial sequences of cytochrome oxidase subunit I gene. Genetic and ecological data were collected by the authors and/or gathered from primary literature. Permutational multiple regression models and ANOVA tests showed that species density and their reproductive output in combination with historical demographic parameters could explain the intraspecific genetic variation indexes across the seven species. In particular, species producing consistently less eggs per spawning event showed higher values of haplotype diversity. Moreover, Tajima's D parameters well explained the recorded values for haplotype diversity and average γst. We concluded that current intraspecific gene diversities in crabs inhabiting mangrove forests were affected by population fecundity as well as past demographic history. The results were also discussed in terms of management and conservation of fauna in the Western Indian Ocean mangroves

Environmental domains and range-limiting mechanisms: testing the Abundant Centre Hypothesis using southern African sandhoppers

Predicting shifts of species geographical ranges is a fundamental challenge for conservation ecologists given the great complexity of factors involved in setting range limits. Distributional patterns are frequently modelled to “simplify” species responses to the environment, yet the central mechanisms that drive a particular pattern are rarely understood. We evaluated the distributions of two sandhopper species (Crustacea, Amphipoda, Talitridae), Talorchestia capensis and Africorchestia quadrispinosa along the Namibian and South African coasts, encompassing three biogeographic regions influenced by two different oceanographic systems, the Benguela and Agulhas currents. We aimed to test whether the Abundant Centre Hypothesis (ACH) can explain the distributions of these species’ abundances, sizes and sex ratios and examined which environmental parameters influence/drive these distributions. Animals were collected during a once-off survey at 29 sites over c.3500 km of coastline. The ACH was tested using a non-parametric constraint space analysis of the goodness of fit of five hypothetical models. Distance Based Linear Modelling (DistLM) was performed to evaluate which environmental traits influenced the distribution data. Abundance, size and sex ratio showed different patterns of distribution. A ramped model fitted the abundance (Ramped North) and size (Ramped South) distribution for A. quadrispinosa. The Inverse Quadratic model fitted the size distribution of T. capensis. Beach slope, salinity, sand temperature and percentage of detritus found on the shore at the time of collection played important roles in driving the abundance of A. quadrispinosa. T. capensis was mainly affected by salinity and the morphodynamic state of the beach. Our results provided only some support for the ACH predictions. The DistLM confirmed that the physical state of the beach is an important factor for sandy beach organisms. The effect of salinity and temperature suggest metabolic responses to local conditions and a role in small to mesoscale shifts in the range of these populations

Homing in the mangrove swimming crab <i>Thalamita crenata</i> (Decapoda: Portunidae)

Thalamita crenata is a swimming crab which commonly lives in the shallow waters of sheltered shores of the whole Indo-Pacific region. On the Kenyan coast, this species colonises the intertidal plateau in front of the mangrove. This crab proved to be faithful to a familiar area in which it visited a small number of known holes where it hides during low tide (Vezzosi et al., in prep.). The aim of this study was to test the homing ability of T. crenata after being passively displaced both within the supposed familiar range (internal homing) and outside it (external homing)

Investigation of mechanisms underlying chaotic genetic patchiness in the intertidal marbled crab Pachygrapsus marmoratus (Brachyura: Grapsidae) across the Ligurian Sea

Abstract Background Studies on marine community dynamics and population structures are limited by the lack of exhaustive knowledge on the larval dispersal component of connectivity. Genetic data represents a powerful tool in understanding such processes in the marine realm. When dealing with dispersion and connectivity in marine ecosystems, many evidences show patterns of genetic structure that cannot be explained by any clear geographic trend and may show temporal instability. This scenario is usually referred to as chaotic genetic patchiness, whose driving mechanisms are recognized to be selection, temporal shifts in local population dynamics, sweepstakes reproductive success and collective dispersal. In this study we focused on the marbled crab Pachygrapsus marmoratus that inhabits the rocky shores of the Mediterranean Sea, Black Sea and East Atlantic Ocean, and disperses through planktonic larvae for about 1 month. P. marmoratus exhibits unexpectedly low connectivity levels at local scale, although well-defined phylogeographic patterns across the species’ distribution range were described. This has been explained as an effect of subtle geographic barriers or due to sweepstake reproductive success. In order to verify a chaotic genetic patchiness scenario, and to explore mechanisms underlying it, we planned our investigation within the Ligurian Sea, an isolated basin of the western Mediterranean Sea, and we genotyped 321 individuals at 11 microsatellite loci. Results We recorded genetic heterogeneity among our Ligurian Sea samples with the occurrence of genetic clusters not matching the original populations and a slight inter-population divergence, with the geographically most distant populations being the genetically most similar ones. Moreover, individuals from each site were assigned to all the genetic clusters. We also recorded evidences of self-recruitment and a higher than expected within-site kinship. Conclusions Overall, our results suggest that the chaotic genetic patchiness we found in P. marmoratus Ligurian Sea populations is the result of a combination of differences in reproductive success, en masse larval dispersion and local larval retention. This study defines P. marmoratus as an example of marine spawner whose genetic pool is not homogenous at population level, but rather split in a chaotic mosaic of slightly differentiated genetic patches derived from complex and dynamic ecological processes