Larval settlement in turbulent pipe flows

In two experiments, larval settlement was studied within a series of pipes, each containing steady, turbulent, flowing seawater. The study was designe d to determine effects of flow (speed, turbulence intensity and wall shear stress) and surface orientation on rates of settlement of larvae of various taxa, and to relate variability in patterns of settlement among orientatio ns and flows to the concomitant variability expected in rates of larval sup ply or delivery to the pipe walls. Patterns of settlement of all five taxa (the barnacle Balanus spp., the mussel Mytilus trossulus, the serpulid poly chaete Pseudochitinopoma occidentalis, the cyclostome bryozoan Tubulipora s p., and the terebellid polychaete Eupolymnia heterobranchia) generally conf ormed to predicted patterns of larval supply to pipe walls (the larval tran sport flux). Within each taxon results were consistent in the two experimen ts. For these taxa, the transport fluxes that most closely matched observed settlement fluxes were predicted by assuming that larvae exhibited average speeds of advection (by swimming or sinking) of comparatively low magnitud e. These best-fit larval speeds are consistent with results from previous s tudies of larval swimming. However, some results indicate that settlement p atterns also were affected significantly by processes operating after larva l contact with pipe walls. In several instances settlement patterns exhibit ed a strong and significant effect of wall orientation that varied in inten sity with flow speed in a manner not predictable from expected patterns of larval supply. The probable causes for this effect and statistical interact ion vary among taxa, but in all cases involve consideration of the habitat, behavior or success of the post-settlement, benthic individual.