. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FERTILIZATION AND SPERM MODELS 27. 0 6 20 40 60 80 95 Fertilization Zone Figure 7. Number of zygotes formed at varying distances from sperm source. Values are those predicted for the case of a single male Acanthaster planci spawning in a field of uniformly distributed female starfish. Density of female starfish is taken to be half the mean density of starfish on our study transect at Davies Reef during 1990-92, or female star- fish -nr. Based on our gonad index data (Babcock and Mundy, 1992; and unpublished data) each
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. FERTILIZATION AND SPERM MODELS 27. 0 6 20 40 60 80 95 Fertilization Zone Figure 7. Number of zygotes formed at varying distances from sperm source. Values are those predicted for the case of a single male Acanthaster planci spawning in a field of uniformly distributed female starfish. Density of female starfish is taken to be half the mean density of starfish on our study transect at Davies Reef during 1990-92, or female star- fish -nr. Based on our gonad index data (Babcock and Mundy, 1992; and unpublished data) each of these females could spawn an average of 220 g of eggs during a natural spawning event. At approximately 9 X 10" eggs-g"1 (Conand. 1985), this gives an egg release of x 107 per female or X 105 eggs • m2. The area defined by each fertilization zone (cf. Fig. 4) was then multiplied by this value to provide a total egg production value in each zone. The number of zygotes produced in each zone was calculated as the product of the total egg production and the median value for fertilization rate in each zone. Zygote production was not calculated for the area in which fertilization rates were predicted to be less than 5%. spawning, and similar behaviors (, rearing) are seen in holothurians (McEuen. 1988). We frequently observed such behaviors in spawning Acanthaster. as have many other authors (Pearson and Endean, 1969). This activity is commonly associated with spawning in various benthic marine animals (McEuen, 1988). In some situations, ga- metes can actually pile up on the substratum adjacent to spawning animals (Minchin, 1987). Such situations are unlikely to result in high levels of fertilization, and their consequences would be reduced by arching behavior that would raise the gonopores further into the flow field. The results of field experiments on the fertilization suc- cess of A. planci spawnings indicate a high level of success at separations as
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