PARENT SESSION
Contributed Oral Session 9: Marine Ecology: Disturbance; Dispersal; Recruitment
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 519 A, Level 5, Palais des congrès de Montréal
Spawning events in small and large populations of the green sea urchin Strongylocentotus droebachiensis as recorded using fertilization assays.
Gaudette, Julien*,1, Wahle, Rick2, Himmelman, John2, 1 Gulf of Maine Research Institute, Porltand, ME, USA2 Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME, USA
ABSTRACT- Recent experimental studies of marine free-spawning organisms indicate that fertilization success may be particularly sensitive to changes both in density and the size of the spawning aggregation. However, the degree to which sperm limitation occurs is debated because it is difficult to measure fertilization rates in natural populations and our understanding of fertilization ecology is mainly based on small-scale experiments. During the winter and spring of 2002 and 2003, we used time-integrated fertilization assays to monitor sperm availability and gonad mass in three populations of the green sea urchin Strongylocentrotus droebachiensis in Maine, USA: a naturally occurring population of >40,000 urchins, and two smaller groups (<1000) of transplanted urchins isolated from other aggregations. Episodes of sperm release coincided in two populations 10 km apart, suggesting urchins were responding to a widespread environmental signal. We observed a significant lunar periodicity in sperm release events for both of these populations. Near the onset of thermal stratification and the spring phytoplankton bloom, we observed evidence of mass spawning only in the large natural population, as revealed by fertilization rates near 100 % and a dramatic drop in gonad mass. By contrast, in the two small populations, we observed low fertilization rates and little or no change in gonad mass. We speculate that a subset of males in these populations responded to a common external spawning signal, but that mass spawning is more likely to occur in large, dense populations where sperm concentrations reach high enough levels to trigger spawning in less responsive urchins. Our results suggest that the negative reproductive consequences of small population size may extend beyond fertilization to the spawning process itself.
Key words: fertilization ecology, allee effect, spawning synchrony, environmental cue