APPARENT OCEANOGRAPHIC TRIGGERS TO THE SPAWNING OF THE LIMPET LOTTIA-DIGITALIS (RATHKE)

At South Cove, Cape Arago, Oregon, spawning by Lottia digitalis was mo nitored daily during the winters of 1995 and 1996. Sharp drops in a Go nad Index indicated that there was one spawning in February of 1995 an d two in April of 1996. Each of the spawnings occurred when (1) the se as were relatively rough as indicated by total wave energy and signifi cant wave height, (2) seawater temperatures were > 11 degrees C, and ( 3) salinity was relatively low (less than or equal to 32.5). Periods o f high temperature and low salinity tended to occur after strong winds from the south that, due to Ekman transport, generated downwelling. T hese results suggest that spawning occurred during rough seas associat ed with downwelling. Spawning in archaeogastropods during rough seas a nd downwelling has been reported a number of times in the literature. The consequences of spawning at these times may be that larvae are rap idly swept out of the surf zone by the stronger rip currents generated by large waves, but coastal currents and density structure associated with downwelling may maintain larvae relatively close to shore. The t iming of spawning and the brief larval duration characteristic of spec ies that spawn during rough seas and downwelling may have evolved to e xploit oceanographic conditions that enhance the survival and settleme nt of their larvae. (C) 1998 Elsevier Science B.V.