Sedimentation of Crassostrea gigas and Perna perna biodeposits in the South Atlantic

This study aimed to determine the vertical sedimentation velocity of fecal and pseudofecal matter from the bivalve molluscs Crassostrea gigas and Perna perna in the Santa Catarina Island bays, focusing on two diferente locations: Caieira da Barra do Sul (CBS) and Sambaqui (SBQ). The initial phase involved collecting biodeposits using a system with twelve chambers, directing a controlled seawater flow at a rate of 500 mL.min(-1). The organisms were individually housed in these chambers, and biodeposits were collected over a three-hour period. Fourteen campaigns were conducted to collect biodeposits from the two species under study. Three types of samples were produced after each campaign: feces, pseudofeces, and a combination of both (F, PF, and F/PF, respectively). The subsequent phase involved evaluating sedimentation velocity in a controlled environment using a two-meter-long, 150 mm-diameter acrylic column filled with filtered seawater. Sedimentation tests were conducted using samples from the initial phase. The sample was inserted at the top of the column, and turbidity was measured over a specified period (up to 25 min). The sedimentation velocities for F were as follows: for C. gigas, 1.56 +/- 0.19 cm.s(-1) and 2.08 +/- 0.83 cm.s(-1) in CBS and SBQ, respectively, and for P. perna, the corresponding values were 2.36 +/- 0.70 cm.s(-1) and 3.33 +/- 0.00 cm.s(-1), respectively. For F/PF samples, the corresponding sedimentation velocities were: 2.41 +/- 0.85 cm.s(-1) and 1.15 +/- 0.61 cm.s(-1) for C. gigas and 2.36 +/- 0.70 cm.s(-1) and 2.96 +/- 0.64 cm.s(-1) for P. perna, in CBS and SBQ, respectively. The sedimentation rates of samples composed solely of pseudofeces could not be determined, as the particles in these samples did not settle within the 25-minute analysis period. The velocities determined were closely related to the characteristics of particles found in the marine water habitat of the organisms. Their filtration-based feeding mechanism significantly influences the vertical sedimentation velocity and biodeposit formation. The methodology used to determine sedimentation velocity proved to be effective and quick, offering a more cost-effective approach than other available methodologies.