Competition between Macro Algae and The Coral Reefs of The Thousand Islands, Indonesia

Competitive interactions between corals and macro algae has been recorded in several waters, and it affects the community structure of coral reefs. Human activities that lead to nutrient enrichment and overfishing of algae... [ view full abstract ]

Competitive interactions between corals and macro algae has been recorded in several waters, and it affects the community structure of coral reefs. Human activities that lead to nutrient enrichment and overfishing of algae grazers contributes to this shifting community. To determine the competitive interaction between macro algae and corals, and if the coral reef community was shifting into a macro algae state in the waters of the Thousand Islands, we recorded the occurrence and effects of the macro algae and coral interactions on different coral lifeforms. The data was collected from the southeast and northwest of Pramuka Island, and northwest of Air Island. Methods used in this research are the line intercept transect and belt transect. The northwest of Pramuka Island has the most abundant macro algae on the coral reef among all sites. The first transect is dominated by branching corals, a fast growing lifeform, whereas the second transect is dominated by algae assemblage, and gradually changing into mostly slow growing lifeforms, such as encrusting on the third transect. The lifeform that has the most interaction with macro algae is the submassive. However, the interaction is most likely that macro algae outcompeted submassive corals. We also found that the encrusting corals have more resistance and ‘wins’ against algae while the submassive is the opposite. Moreover, the condition of the corals at the northwest of Pramuka Island is more severe than the other two sites, which indicates the impact of sedimentation to the health of the coral reefs.