Caraguatatuba Bay Research Articles

New species of Macoma (Bivalvia: Tellinoidea: Tellinidae) from southeastern Brazil, and with description of its gross anatomy

Macoma biota n. sp. is described from material collected in the intertidal zone of Praia da Cidade, Caraguatatuba Bay on the northern coast of the state of São Paulo, Brazil. The species is characterized by its shell features and gross anatomy. The western Atlantic M. constricta (Bruguière, 1792) is the most similar species to M. biota, both hardly distinguishing by their shell characteristics. The main shell feature distinguishing M. biota from M. constricta is the ventral limb of the pallial sinus that is shorter, steeper and confluent with the pallial line along the first quarter of this scar in M. biota, and long, closely parallel to and confluent with the pallial line far posteriorly in M. constricta. Anatomical characters distinguishing M. biota are: ventral channel formed by asymmetrical left and right additional mantle folds; paired, asymmetrical siphonal organs; all four labial palps provided of short conical papillae on their outer surface and simple, acute terminal tip; both demibranchs equally long; and presence of a single short, stout “accessory adductor muscle” adjacent to the cruciform muscle. Macoma constricta has ventral channel formed by the right additional mantle fold only; unpaired, left siphonal organ; all four labial palps lacking papillae on their outer surface and terminal tip of the left inner labial palp produced into a thin sheath with undulated plicae; inner demibranch longer and extending beyond the antero-dorsal limit of the outer demibranch; and “accessory adductor muscle” absent.

Mollusc feeding guilds on sandy beaches in S�o Paulo State, Brazil

The feeding guilds of four communities of molluscs living in the intertidal zone of Enseada in Caraguatatuba Bay and Barra Velha and Araca beaches along the Sao Sebastiao Channel were identified. Three-letter codes were assigned to each feeding guild, identifying the feeding habit, mobility patterns related to feeding, and food-capturing structures. Data were obtained from qualitative analyses of the digestive tract contents and from observations on the feeding behaviour of the gastropod Olivella minuta and the bivalves Tagelus plebeius, Macoma constricta, Tellina lineata, and T. versicolor. These data were complemented by published information on the feeding of congeneric or confamilial species. Six feeding guilds were identified. The SDS (suspension-feeder, discreetly motile, inhalant siphon and ctenidia) and DDS (deposit-feeder, discreetly motile, inhalant siphon and ctenidia) groups were more abundant. Suspension-feeding bivalves showed higher Trophic Importance Index (TI) values in all the study areas. Deposit-feeders showed high TI values only at Barra Velha beach. The species in the SDS feeding guild tended to occur in areas with lower salinity and moderately to well-sorted sediments with very fine sand predominating. The distribution of the feeding guilds correlated best with salinity, particle size distribution, and the contents of silt-clay and organic matter in the sediment.

Minerais Pesados dos Sedimentos do Fundo da Enseada de Caraguatatuba, São Paulo, Brasil

The bottom sediments of the Caraguatatuba bay, localized in the coast of São Paulo State, were collected for a qualitative study of the heavy minerals in the sandy fraction between 0,125 and 0,062 mm. The mineralogical study allowed the recognition of three groups of heavy minerals: group I – opaque minerals, with magnetite, ilmenite and pyrite; group II – transparent minerals, with amphibole, pyroxene, epidote, biotite, muscovite, zircon, tourmaline, titanite, rutile and apatite; and group III – carbonates, represented by bioclasts and aragonite needles. The source areas of these heavy detritic minerals are related with rocks of the coastal complex, of syntectonic granites and of the alkaline rocks from São Sebastião island. The average content of heavy detritic minerals in the Caraguatatuba bay is 0,77%. Besides biotite and bioclast material, magnetite and ilmenite, are the most abundant phases with an average percentage of 12,9% in the 0,125/0,062 mm fraction.

Influence of marine and continental processes on the dynamics of a sand-ridge at the mouth of the Maçaguaçu river (Caraguatabuba - SP): preliminary conditions

This paper deals with the sedimentation and erosion dynamics of a sand-ridge on the Maçaguaçu River mouth on the São Paulo coastal plain, north of Caraguatatuba Bay. Sedimentological, climatic and hydrodynamic data were analysed from an integrative point of view, considering relationships between continental and marine antagonic forces. Even if incomplete these preliminary observation show that erosion only occurs when more intense rains and higher tidal cycles coincide and that even the intense occurrence of one of these phenomena is not enough to trigger the destructive processes.