Coral reefs that are located in remote offshore places are healthier than those that are found near the coastline, as the latter tend to be subject to nutrient runoff and sedimentation.
Researchers from the Woods Hole Oceanographic Institution (WHOI) and the Centro de Investigaciones Marinas—Universidad de La Habana (CIM-UH) have discovered that offshore coral reefs that are also protected tend to be healthier than nearshore ones.
In the study, seawater from 25 reefs in Cuba and the Florida Keys in the US were tested for nutrients and other parameters that would give researchers a glimpse into the microbial community present.
They discovered a marked difference between the reefs that experienced a large amount of human activity compared to those that did not.
Many of the Cuban reefs studied did not experience a lot of nutrient runoff or sedimentation flowing into the sea, since there was not large-scale industrial agriculture or extensive development along most of the Cuban coastline.
For instance, at the Jardines de la Reina, a reef system about 50 miles off Cuba’s southern coast, sees minimal human activity due to its remote location. In addition, most of the archipelago lies within a marine natural park, enabling it to enjoy further protection from maritime traffic, fishing and recreational diving.
Here, researchers detected low nutrient concentrations and a high abundance of Prochlorococcus, a photosynthetic bacterium that thrives in low nutrient waters.
In contrast, at the more accessible reefs of Los Canarreos in Cuba (which experiences relatively more human activity in the form of illegal fishing, tourism and recreational diving as a result), there were higher concentrations of nitrogen and organic carbon.
The same was true for the nearshore reefs in the Florida Keys, where the condition of the reefs had been declining as the study progressed.
In addition, the healthier Cuban reefs saw more diverse microbial communities with abundant photosynthetic microbes, compared to those at the reefs in Florida.
The findings of the study was published in the Environmental Microbiology journal.
According to lead author WHOI graduate student Laura Weber, human impact like overfishing and pollution lead to changes in the reef structure. She added that “removal of algae grazers such as herbivorous fish and sea urchins leads to increases in macroalgae, which then leads to increased organic carbon, contributing to the degradation of coral reefs."
The study concluded that reefs that were offshore and enjoy protection status tended to be healthier, as they were subject to lower nutrient runoff and carbon from industrial activities.
The team hopes that the findings can help resource managers in their decision making to protect and restore coral reefs in the Caribbean in light of habitat and climate-based change.