Updated: Oct 21, 2019
The overall health of coral reef ecosystems are steadily declining due to problems associated with pollution, overfishing, deforestation, sedimentation, and other anthropogenic factors. These already sensitive ecosystems are becoming more susceptible to disease outbreak and bleaching. The reef-building organisms (hard corals) that are responsible for creating carbonate structures that reef ecosystems rely on, are being detrimentally impacted. Algal species are outcompeting hard corals and thus altering the community and ecological structure of reef systems. When algae are the dominant species over reef-building corals, the calcium carbonate reef structure becomes depleted, leaving a harder to inhabitant environment. Anthropogenic effects are directly causing a large amount of coral death; however they are also leading to indirect effects by promoting conditions more favorable for coral competitors such as algae.
*Photos from Pelican Pouch Island, Belize with a GoPro3 by me.
It is unknown what coral reef systems looked like before humans began influencing them. Thus Smith et al. used uninhabited islands to serve as an idea of what reefs would function like without anthropogenic factors influencing their ecosystems. Between 2002 and 2009, Smith et al. used SCUBA to survey 56 islands with benthic coral habitats at depths of 10-12 meters. Standard photoquadrat surveys were taken to identify taxa of coral, macroalgae, and macroinvertebrates. Islands were used as replicates and defined as uninhabited or inhabited based on densities of human population at each individual island.
Differences in species between islands was examined. Further analysis suggested a negative correlation where a decrease in coral species results in an increase in macroalgae abundance. Results showed that human population densities had significant effects on coral community structures. Islands with high human densities had significantly more algal growth than coral growth. Thus anthropogenic activities are altering coral communities directly and indirectly.
Read the article for yourself here:
Smith, JE., Brainard, R., Carter, A., Grillo, S., Edwards, C., Harris, J., Lewis, L., Obura, D., Rohwer, F., Sala, E., Vroom, PS, & Sandin, S. 2016. Re-evaluating the health of coral reef communities: baselines and evidence for human impacts across the central Pacific. In Proceedings B of The Royal Society, 283:20151985