RECRUITMENT OF MARINE-INVERTEBRATES ONTO ARBORESCENT EPIBENTHIC STRUCTURES - ACTIVE AND PASSIVE PROCESSES ACTING AT DIFFERENT SPATIAL SCALES

The hypothesis that passive processes control larval settlement of ben thic marine invertebrates on 3-D structures was tested for several gro ups at both meso (3 cm) and small (mm, pm) scales. Flume experiments w ere carried out with inert polyvinylchloride microparticles and 5 diff erent types of silicone-coated 3-D arborescent plastic structures with 5 distal branch diameters. Microparticle attachment as a function of the distal branch diameter and the proportion of particles attached to the nodal section of each branch were used to predict the initial con tact site by living marine benthic invertebrates larvae in field exper iments using the same 3-D structures immersed for 2 mo. The flume expe riment showed that distal branch diameter had a significant effect on the density of attached particles. The proportion of particles observe d in the nodal sections (8%) was much lower than the proportion of the total surface area occupied by the nodes (20%) on each branch. Field experiments examining recruit density (6 sessile species belonging to 4 classes of marine invertebrates) on the same 3-D structures showed t he same significant effect of the distal branch diameter observed in t he flume. However, individuals were found in the nodal sections much m ore frequently (35 to 80%) than would be expected based on the results of the flume experiment (8%). Comparison of results of laboratory and field experiments suggests that passive settlement processes are suff icient to explain early recruitment patterns of the species examined o n scales ca 3 cm. However, at smaller scales (ca mm) the hypothesis of active larval exploration of the substratum could not be rejected. Th e Likelihood of post-settlement mortality processes potentially explai ning the patterns observed is discussed.