A Historical and Integrative Taxonomic Account of Mangrove Oyster Species Native to the Atlantic American Coast: A Re-Evaluation of Brazilian Crassostrea Species

The identification of native mangrove oyster species of the genus Crassostrea in Brazil is a recurring issue for specialists. Studies have recognized the presence of two species in the littoral zone: C. rhizophorae and C. gasar. However, other names may be used, such as C. mangle for C. rhizophorae and C. brasiliana or C. tulipa for C.gasar. As in most oyster taxonomic studies, their identification requires genetic evaluation for the precise determination of taxa. Moreover, previous revisions have proposed some morphological traits by which each species could be precisely identified, leading to a series of debates about the best model for species identity. The aim of this study was to apply an integrative taxonomic approach to native Crassostrea mangrove oyster species on the Brazilian coast to assert the correct species names, delimitations, and concise descriptions. Molecular tracing of cultivated specimens, along with wild specimens of Crassostrea collected from the Brazilian coast, was used to confirm the morphological identity of the taxa. The wild specimens were tentatively identified as either C. gasar or C. rhizophorae based on previous morphological revisions. PCR-RFLP and DNA analyses of the mitochondrial 16S gene mitochondrial rDNA from wild specimens were used to confirm taxa and re-evaluate morphological boundaries and descriptions of the species. We confirmed two patterns in the RFLP and sequence analyses: C. gasar and C. rhizophorae. Conchological and anatomical evaluations of 1006 identified Crassostrea specimens confirmed the inherent polymorphism between the native species, preventing reliable identification of the species by morphology alone. A clear exception, however, is found for specimens whose shell height is greater than 110 mm with internal view of white-colored valves and without an umbonal cavity, fitting the description of C. paraibanensis, which belongs to C. gasar. C. brasiliana and C. mangle are synonyms of C. gasar and C. rhizophorae, respectively. C. tulipa represents a species disconnected from any described mangrove oyster species from Atlantic seas. Conchological and anatomical descriptions of both species were improved to include the variability encountered.