Distribution and density of the bivalve Tivela mactroides (Born, 1778) in the tropical estuarine region of semiarid Northeast Brazil
2014
Eudilena Laurindo Medeiros | Gabryelle Fernandes Viégas | Gustavo Gonzaga Henry-Silva
The present study evaluated the distribution (spatial and temporal) and density of the mollusc Tivela mactroides on beaches in a tropical estuarine region of the Brazilian semiarid region and their relationship with temperature, salinity, organic matter and sediment grain size. Semiannually (April 2009 to October 2011), 20 transects were arranged perpendicular to the line of the beach towards the sea, 300 m long in the intertidal zone. Seven sampling points, 50 m apart, were established in each transect, and samples of molluscs and sediment were collected. The highest average densities of T. mactroides were observed in April 2009 (43 individuals/m2) and October 2009 (45 individuals/m²), while the lowest values were found in April 2010 and October 2010 (11 and 7 individuals/m², respectively). The lower density in these months was probably related to the intense rainfall that caused a decrease in salinity in the region. The correlation between density of T. mactroides and distance from the estuary of the Apodi-Mossoró River was positive, indicating an increase in the number of individuals of this species with distance from the estuarine region. The density of T. mactroides was negatively correlated with the percentage of organic matter. It was also found that this species has an aggregated distribution pattern.
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