Deposition of mimics of planktonic invertebrate larvae on simple and complex substrata in flume flows

Abstract

The purpose of this study was to compare the distribution of inert particles on polyvinylchloride (PVC) panels with earlier results from field studies. The panels were prepared in order to test heterogeneity (crevices similar in shape, but differing in size) and complexity (combination of crevices of different sizes) effects. The experiments were carried out using PVC particles and preserved Placopecten magellanicus larvae in a flume under controlled flow conditions (mean velocities of 3, 5 and 10 cm s-1) and using silicon-coated panels. The heterogeneous panels had different combinations of flat surfaces and 1, 10 and 100 mm crevices. The density of particles per unit surface area adhering to the panels was higher at 3 and 5 cm s-1 than at 10 cm s-1 for all experiments. The density of adhering particles decreased with increasing panel complexity. Within panels with only 1 mm crevices, the density of particles was significantly higher inside the crevices than on smooth surfaces. However the density of particles was significantly lower in 10 and 100 mm crevices than on adjacent flat surfaces within panels with only 10 and 100 mm crevices, respectively. Furthermore, the 1 and 10 mm crevices nested inside 100 mm crevices collected fewer particles than those outside 100 mm crevices within panels with many scales of crevices. The patterns of distribution for dead larvae on heterogeneous panels in the flume corresponded to those of the inert PVC particles. However, the distribution patterns of inert particles in the flume did not correspond to those of living bivalve spat observed in an earlier field study. This suggests that larval behaviour contributed to the selection of settlement location lot these bivalve larvae, though flume hydrodynamical conditions may differ from those in the field. The results also indicate that the hydrodynamic processes affecting settlement on heterogeneous substrates are scale-dependent and that processes occurring at scales of 10 and 100 mm influence processes occurring at smaller, 1 mm, scales.