SOME ASPECTS OF THE WATER-FLOW THROUGH MUSSEL RAFTS

All studies on particle retention by mussel rafts have assumed a lamin ar or nearly laminar water flow, directed from the front to the rear o f the raft. We have studied such a flow in five rafts in the Ria de Ar ousa, Our results show that, in most cases, the current velocity at th e centre of the raft is slower than at the rear. This situation can on ly be achieved by means of lateral inputs. The current velocity showed great variation with depth and the differences depended on raft and t ime. The current direction also varied with depth and, in some cases, all currents entered the rafts from the same side. These findings have two important repercussions: a) it is necessary to change the samplin g strategy to measure the retention of suspended material and the envi ronmental impact by rafts; and b) the structure of the rafts can be mo dified to optimize their adaptation to the water flow.