The factors that affected zooplankton feeding by the scleractinian corals, Meandrina meandrites, Montastrea cavernosa and Madracis mirabilis were investigated. Corals feed selectively on zooplankton, but the specific factors causing the selectivity were unknown. Small-scale predator prey interactions were evaluated to determine the effects of prey behavior and water flow on capture rates. Prey avoidance and escape behaviors altered susceptibility to predation and explained previously observed selectivity patterns.
Prey contact and capture rates in still water are not representative of what occurs in flow. The effects of water flow depend on complex interactions between predators, prey, flow regime, and turbulence levels. Flow conditions (still vs. oscillatory) and speed had significant effects on prey contact with the predator, with flow affecting both encounter and escape frequencies of the prey. At low flow, zooplankton behavior is critical, while at higher flows, both coral and morphology and prey behavior are important. Higher flows decrease the ability of corals to extend feeding surfaces, and decreases the effectiveness of zooplankton behaviors.
A pump was used to sample nocturnal, near-reef zooplankton centimeters above coral tentacles. Abundances were greater than most other comparable study values. Demersal zooplankton are numerically only a small proportion of the zooplankton available to corals, so studies that exclude holoplankton from the sampling methodology may underestimate available prey. Potential zooplankton contribution to coral nutrient budgets were estimated by modeling zooplankton flux through feeding structures, zooplankton capture probabilities for each prey type, carbon and nitrogen supplied by zooplankton, and observed field coral growth rates. Based on measured abundances of zooplankton, nitrogen or carbon demands for observed tissue growth could not always be met in low (1 cm s-1) flow. However, in 5 cm s-1 flow, almost all corals would receive > 100 % of the required nitrogen and carbon.
This dissertation has done much to describe the small-scale interactions between coral predator and zooplankton prey. Much still remains to be learned about energy and nutrient acquisition by corals. Only through dedicated efforts to quantify the factors affecting zooplankton feeding will greater understanding of this mode of energy and nutrient acquisition emerge.