Dr. Nancy Knowlton
Bacteria Associated with Scleractinian Corals. Coral reefs are valuable natural resources and major contributors to coastal and oceanic processes in the sub-tropical and tropical oceans. Scleractinian corals, by sustaining the architectural structure of these reefs, are the keystone organisms for these ecosystems. Models of coral nutrient and energy budgets have primarily focused on the coral animal and the symbiotic photosynthetic dinoflagellates (i.e., zooxanthellae), while essentially ignoring the potential influence of symbiotic bacteria. Similarly, while there has been a great deal of research to isolate and characterize microbes that cause coral diseases, very little attention has been directed towards understanding normal microbe/coral associations. Previously studies have shown that bacteria can be substantial sources of energy and nutrients for corals and it is known that the normal bacterial flora of an organism (e.g., humans) is essential for disease resistance. Overlooking the influence of bacteria on corals may seriously bias our understanding of how coral live. Here we show that specific bacteria are associated with scleractinian corals. One bacteria species, closely related to the nitrogen fixer Bradyrhizobium genus, was associated with three different coral species (Montastraea franksi, Porites porites forma divaricata, and Colpophyllia natans). This finding is especially exciting because it suggests that corals maybe production sites of organic nitrogen, an essential and limiting nutrient in the marine environment. We also found other bacteria species exclusively associated with only one of the three coral species studied. The same bacteria/coral associations were found on different reefs of the Bocas del Toro area, strongly supporting the hypothesis that corals harbor specific bacterial floras. Future research will attempt to determine the influences of coral-associated bacteria on coral health and ecology.
Coral Reproduction. Each year, about seven days after the full moon in the summer months, many corals release eggs and sperm in an event known as mass spawning. During these events, doctor Knowlton (together with a team of collaborators) collect data on the timing of spawning, the rate of fertilization of the eggs, and the distances traveled by eggs on the surface of the water. They also collect sperm samples for genetic analyses.