EXPERIMENTAL-EVIDENCE OF PASSIVE ACCUMULATION OF MARINE BIVALVE LARVAE ON FILAMENTOUS EPIBENTHIC STRUCTURES

A series of multifactorial experiments were carried out, in the field and in a flume, to test the hypothesis that early recruitment of semim obile bivalve spat on an epibenthic filamentous substratum is directly related to the heterogeneity (branching pattern) and the diameter of their individual branches or filaments and to evaluate the likelihood that passive settlement processes influence bivalve larval early recru itment on filamentous natural epibenthic substrata. The experiments we re carried out with three-dimensional plastic structures similar in sh ape to hydroids and filamentous benthic algae-the preferred larval set tlement substrata of several bivalve species in the held. Field experi ments showed a highly significant effect for both branch heterogeneity and diameter. The 3-D structures collecting the highest number of spa t per unit area were those offering smallest diameter and heterogeneit y. Flume experiments that used inert particles and the same silicone-c oated, 3-D structures reproduced early recruitment abundance patterns observed on heterogeneous structures in the field. Comparison of resul ts from the field to those from the laboratory suggests that passive s ettlement processes are sufficient to explain early recruitment patter ns of some bivalve species on scales of order 10 cm, although alternat ive, biological hypotheses were not tested in this study.