Marine trophic levels balance
LOSS OF LARGE PREDATORY FISH CAUSES CASCADING EFFECT THROUGH REEF -
A cascade effect throughout the reef ecosystem is produced when the major predatory fish are no longer present. Loss of these important predators causes their prey populations to explode. As the prey populations expand, what they feed upon is also decimated. Wildlife Conservation Society and UC Santa Cruz researchers in Kenya have uncovered some of these far-reaching effects.
Conditions of reefs under three different management conditions were compared; closed, gear-restricted, and open access. Prior research has shown that when predators are removed from reefs, sea urchins are one type of prey population that expands drastically. Sea urchins graze upon coralline algae, a very critical yet poorly studied component of the reef ecosystem. Coralline algae deposit calcium carbonate; this hardens the substrate and improves reef stability and growth. Some types of coralline algae even produce a chemical to induce coral settlement. This type of settlement is required for a reef to recover after disturbances.
This study found that closed reefs had a significantly higher percent cover of coralline algae and juvenile coral than that of the gear-restricted and open access zoned reefs. As expected, the closed reefs also had much lower sea urchin populations, as the predators were still there to prey upon them. This indicates that overfishing of important predatory fish indirectly reduces coral settlement and juvenile coral success rates.
No difference in coral percent cover was found between gear-restricted and open access zones. One of the scientists, Dr. Daniel Potts, stated “most managers and conservationists, and even many scientists, are unaware of the existence, abundance, and importance of coralline algae, so management regimes intended to enhance the health of reefs may actually be detrimental.” Researchers hope that this study will lead to a better understanding of the importance of coral reefs and the predators that help to maintain their populations.