Meeting Abstract

8.4  Sunday, Jan. 4  Flow and Fertilization in Sea Urchins: A Combined Flume and Field Approach YUND, P.O.*; KREGTING, L.J.; BASS, A.L.; AVENI-DEFORGE, K.; TILBURG, C.J.; THOMAS, F.I.M.; Univ. New England; Univ. New England; Univ. Hawaii; Univ. New England; Univ. Hawaii; Univ. New England; Univ. Hawaii pyund@une.edu

Past work on the ecology of fertilization in sea urchins has tended to assume that gametes are quickly diluted upon release and immediately enter free-stream flows, with eggs either quickly fertilized in the water column, or advected out of the sperm plume. Yet the biology and physics of urchin fertilization do not appear to be consistent with these assumptions. Gametes are released in viscous fluids that resist dilution and remain on the aboral surface for hours, concentrated sperm are continuously advected downstream, and eddies that form downstream of females may entrain gametes and increase mixing and the probability of sperm:egg contact. Consequently, we have been employing a combined laboratory flume and field approach to explore how variation in flow affects where fertilization occurs and the probability that eggs are fertilized. In both unidirectional and oscillatory flows, fertilization decreased with increasing Reynolds stress, and many eggs were fertilized either on the aboral surface, in the downstream eddy, or on the substrate. At two field sites, Reynolds stress above sea urchins could be predicted with wave height data from oceanographic buoys 13-17 km away. We then used these regression equations to predict the distribution of Reynolds stress during sea urchin spawning season from the distribution of wave heights. Our results suggest that fertilization is not necessarily a water column process, and that sea urchin fertilization may be less limited by sperm availability than previously believed.