Circulation of water through a mussel raft: clearance area vs. idealized linear flows

This study suggests revision of ecological concepts as food depletions and/or water flow reductions based on idealized linear flows through mussel rafts. We offer an alternative based on the extension of the clearance area, defined as the area affected by the nonlinear effects produced by each raft and surroundings ones. These conclusions are supported by our results, which indicate that (i) the preferential entry of water through a mussel raft does not occur through the bow, contrary to previously thought, and (ii) the intraraft circulation is strongly influenced by the orientation of the raft relative to the background current direction and does not follow a defined pattern. Intraraft circulation is assessed by means of four current metres installed at each side of the raft and the dimensions of the clearance area using long-term data provided by GPS and compass. While both intraraft circulation and clearance area dimensions are mainly controlled by tide, the net water exchange through the raft is reasonably explained by wind (velocity and direction) and river discharges.