| dc.description.abstract | Several factors can influence fertilization success, and for marine broadcast spawners, the main
constraint is rapid dilution of gametes. Because the measurement of fertilization success in the
field is logistically difficult, theoretical models have been used as an alternative method of
estimation. We tested the predictive ability of the existing models (time-averaged diffusion model
in conjunction with a fertilization kinetics model) by making direct comparisons between empirical
and corresponding predicted rates of fertilization in the tropical sea star Oreaster reticulatus.
Using induced spawnings, we measured in situ fertilization in field experiments at 4 sites on sand
bottoms and seagrass beds in the Bahamas. Rate of fertilization decreased exponentially with
increasing distance downstream (x) from a spawning male for all experimental runs at all sites, and
when averaged across all sites, it ranged from 74% at x = 1 m to 31% at x = 32 m. For each
experimental run, we parameterized the 2 models by quantifying the flow field, and thus obtained
predicted estimates of fertilization success. The shape of the fitted exponentially-decaying curves
was similar between the observed and predicted data for sites on sand bottoms, but not in seagrass
beds. There was a highly significant correlation between the observed and predicted data at each
distance directly downstream for each run, but the predicted values were 1 to 10 orders of magnitude
lower than the observed values for distances off the main axis of advection. We also used dye
dilution runs to test the validity of the diffusion model and, in agreement with the observed
values, the predicted concentrations of dye decreased as a power function of distance downstream
from the point of release. Turbulent diffusivity was quantified in 2 ways: by measuring the standard
deviation of dye concentration across-stream and vertically (sigmay and sigmaz), and by calculating
coefficients of diffusivity (alphay and alphaz). Using alphay and alphaz, the values predicted with
the model of diffusion were up to 24 orders of magnitude lower than the observed values at heights
>0.2 m above the bottom, but this inconsistency was alleviated when sigmay and sigmaz were
used. Thus, the combination of the 2 models currently used can predict fertilization rate reliably
for a particular parameter space, which can be increased by quantifying turbulent diffusivity more
accurately. These modified models can substitute field experiments to estimate fertilization success
in species of marine benthic invertebrates that are fragile, such as O. reticulatus, or are
relatively inaccessible, such as inhabitants of the deep sea. | en_US |
