Conservation of the endangered blue land crab Cardisoma guanhumi Latreille in Latreille, Le Peletier, Serville & Guérin, 1828 (Decapoda: Brachyura: Gecarcinidae) in Brazil: optimal habitats and environmental factors

Cardisoma guanhumi Latreille in Latreille, Le Peletier, Serville & Guérin, 1828, the blue land crab, is a marine semi-terrestrial crab that builds burrows in different habitats along estuaries, an ecosystem severely modified and fundamental to this endangered species in Brazil. The presence of adequate habitats and physical, chemical, and biological conditions often determine the spatial distribution of populations. We aimed to characterize the most relevant environmental conditions among the main environments present in southern Bahia state, Brazil, and evaluate their influence on the spatial distributions of C. guanhumi to define which habitats are most critical for the conservation of the species. Our results showed that there is no relationship between spatial distributions and any particular habitat, but instead to the physical and other environmental parameters studied. Low-elevation areas along the river shore, shading, a supply of leaf litter, and bare sandy substrate are highlighted as priority for the conservation of C. guanhumi. These physical factors limit the distribution of juveniles, which form dense groups on river shores without significant differences between habitats. The preservation of the native forest and restinga shrubs that border rivers appear as fundamental for the conservation of the species.

Genetic diversity of the blue land crab Cardisoma guanhumi (Latreille 1825) in the Alvarado Lagoon System in Veracruz, gulf coast of Mexico

In the Alvarado Lagoon System (ALS) in south-central Veracruz on Mexico's gulf coast, the blue land crab, Cardisoma guanhumi, a semi-terrestrial crustacean species, represents an important fishery resource, but one that is subject to overexploitation and habitat destruction. Identifying genetic diversity and the genetic unit are required to establish efficient conservation strategies. The present study's goal was to assess the genetic structure and degree of genetic diversity of C. guanhumi populations along the ALS. A fragment of the D-loop region of the mtDNA (750 bp) and a partial sequence of the COI gene (580 pb) was sequenced for 120 specimens collected at four sites in the ALS. Genetic diversity indices were estimated for each marker. The study sites' gene flow was estimated, as was the effective population size and the mutational rate for each locality. A haplotype network was built to estimate the gene genealogies of the populations. A Tajima's neutrality test, Fu tests, and mismatch analysis were performed to detect demographic expansion. Results show that this C. guanhumi population has high genetic diversity with a large gene flow among the localities studied and expanded during the recent evolutionary past. All haplotypes from both markers are novel for the species, according to the NCBI GenBank. The high genetic diversity and genetic connectivity among sites suggests that the size of blue crab populations in the ALS has not been drastically affected by past exploitation. Finally, management strategies are proposed to protect the species.

MORPHOMETRY OF BLUE LAND CRAB (CARDISOMA GUANHUMI) BURROWS: ICHNOLOGICAL CONTEXT AND PALEOENVIRONMENTAL IMPLICATIONS

ABSTRACT A large brachyuran, the blue land crab (Cardisoma guanhumiLatreille, 1825) is a keystone species and a prolific burrower in a variety of low-latitude supratidal habitats; however, few studies have addressed its ichnological aspects. Here we present a detailed morphological assessment of C. guanhumi burrows and make comparisons to Macanopsis plataniformis, a trace fossil thought to be constructed by a similar brachyuran. Using nine burrow casts from a mangrove wetland on San Salvador Island, Bahamas, 29 dimensionless morphometric parameters were compared. Results of Bray-Curtis tests show high overall similarity index (0.85) between casts, with complexity, tortuosity, and opening inclination angle having moderate to high similarity (> 0.8). End chamber angle of the blue land crab has highest similarity both within the modern morphometric parameter dataset (> 0.9) and to that of M. plataniformis (0.88). The large terminal chamber is particularly important because of its high preservation potential, as a repository for organic remains, and as a reliable water table (∼ sea-level) indicator. Cluster analysis suggests size-independent Macanopsis-resembling burrow morphology among different extant taxa can be discriminated via quantitative neoichnological methods. Our findings demonstrate how a quantitative assessment of modern burrows and their likely counterparts from the sedimentary record can help constrain tracemaker identity and aid paleoenvironmental reconstruction of low-energy microtidal settings.

Estimation of density and abundance of the blue land crab, Cardisoma guanhumi Latreille, 1828, in the Imburana peninsula, northern Brazil

The blue land crab (Cardisoma guanhumi Latreille, 1828) supports extensive small-scale artisanal fisheries in the tropical western Atlantic, including Brazil. Land surveys were conducted on a peninsula in a northeastern Brazilian estuary in 2014-2015 in order to evaluate density and abundance. The study area (26 700 m2) was dividied into three subareas with a total of 30 sampling points. In all, 529 burrows were registered of which 71.7% were open (indicating activity), 22.1% were closed (indicating moulting) and 6.2% were empty (fishermen catch). Burrow diameter ranged from 12 to 174 mm (mean: 62.05 ± 3.01 mm; 95% confidence interval). The highly significant correlation between mean burrow diameter and mean carapace length (n = 7; R2 = 0.8968, ) shows that one is a good proxy for the other. The estimated total population size in the study area was 10 362 individuals, with a mean density of 0.39 individuals/m2 (stock of 7347 kg).