Meeting Abstract

52.2  Monday, Jan. 5  Low landings lead to lofty living: forces on newly settled invertebrate larvae in realistic flow environments KREFT, J.K.*; WALDROP, L.D.; KOEHL, M.A.R.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley jkreft1@berkeley.edu

Many benthic marine animals disperse via microscopic planktonic larvae. Recruitment, which begins with settlement onto substrata, affects community structure and population dynamics. Flowing water can deliver and dislodge newly settled larvae to and from surfaces. Using the nudibranch Phestilla sibogae we studied how flow microhabitats affect the hydrodynamic forces acting on settling larvae and newly-metamorphosed juveniles. Juvenile and adult P. sibogae only settle on its prey, the reef-building coral Porites compressa. The living coral tissue that juveniles and adults eat is only at the top of the reef, where ambient water velocities are much faster than they are in the interstices within the reef. Calculations (assuming spherical larvae and measured adhesion strengths for P. sibogae) indicate larvae are more likely to settle within the reef. Using dynamically-scaled physical models, we measured the effects of metamorphosis, orientation and posture on drag forces under flow conditions at the top of and within a reef. We used particle image velocimetry (PIV) to examine flow fields surrounding the models, which are interesting as our conditions span a poorly-understood intermediate range of Reynolds Numbers (Re’s of 2 to 17). Drag at the reef top was significantly lower than within the reef. Drag on juveniles was significantly lower than on larvae, enabling juveniles to withstand the high flows at the top of the reef that would dislodge larvae. PIV showed that both skin-friction drag and form drag are important, but that the drag differences between various body postures and shapes were due to form drag. Our results support hypotheses that P. sibogae larvae must first settle and metamorphose in lower, more protected regions of reefs before migrating to the top to feed.