The biology of the coral Porites astreoides: Reproduction, larval settlement behavior and responses to ammonium enrichment

Date of Award




Degree Name

Doctor of Philosophy (Ph.D.)


Marine Biology and Fisheries

First Committee Member

Alina M. Szmant, Committee Chair


Several aspects of the biology and physiology of the common Atlantic coral, Porites astreoides, were studied. Nightly larval release was quantified for each of 146 P. astreoides colonies collected over 3.5 years. Planulae were released each month over several nights centered on the new moon. The majority of larval release occurred in April and May, although smaller numbers of larvae were observed from June through as late as September. P. astreoides larvae showed no preference for texture or orientation of the surface (upper, side or lower) on which they attached. The presence of calcareous red algae increased attachment. Colonies grew from a single polyp to a maximum of 25 polyps in eight months. Planula larvae contained about four times as much lipid and had higher zooxanthellae densities per mg protein as adult tissues. About 60% of the photosynthetically-produced carbon was translocated from zooxanthellae to host tissues in both adults and larvae.It has been proposed that zooxanthellae in vivo are nitrogen-limited and that N-enrichment results in a decrease in translocation to the host and a subsequent decrease in coral calcification. This hypothesis was tested for 3 levels of ammonium enrichment (2, 5 and 10 $\mu$M) by maintaining replicate subsamples from individual colonies of Porites astreoides in unenriched (controls) and ammonium chloride-enriched seawater for up to 4 weeks. Translocation was estimated by incubating the corals in seawater containing $\sp{14}$C-labeled bicarbonate. Zooxanthellae and animal fractions were separated and radioactivity was assessed in each fraction. There were no significant differences between enriched and control corals in the 2$\mu$M experiment. At the two higher levels of enrichment, zooxanthellae densities in enriched corals were 25-30% higher than those in controls. Enriched zooxanthellae had lower C:N ratios and translocated significantly less radiolabeled carbon than controls from the same colonies. However, translocation per cm$\sp2$ was not different between enriched and control treatments. It was hypothesized that responses of planula larvae and juvenile corals to ammonium enrichment would include changes in protein content, zooxanthellae density, translocation and calcification. Unlike adult colonies, there were no measurable effects of ammonium enrichment on either larvae or recruits of P. astreoides.


Biology, Ecology; Biology, Oceanography

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