Threats to Reefs
Threats to Reefs
The coral reefs throughout the Florida Keys and the Caribbean have experienced unprecedented declines since the 1970’s. Local reefs were once dominated by two species of reef-building corals: staghorn (Acropora cervicornis) and elkhorn (Acropora palmata).
Both species are fast growing, branching corals that protect coastal areas and provide valuable habitat for fish and invertebrates. Without them, dramatic changes are seen with reef life and stability.
Loss Since 1970
Due to multiple stressors in the late 1970’s and early 1980’s, the population of staghorn and elkhorn coral have declined dramatically, leaving the remaining corals scattered and facing extinction.
There are a number of identified stressors that have contributed to the significant amount of loss we’ve seen over the decades.
The good news is that some of these are stressors are manageable with hard work, care, and awareness.
White Band Disease
This is characterized by a white band of denuded skeleton around the base of coral or the middle of a branch of staghorn coral. Dying tissue sloughs off the skeleton toward the branch tips and the skeleton is gradually colonized by fine algae. First documented in 1977, the causal agents and natural transmission are still poorly understood, but it affects reefs throughout the tropical western Atlantic Ocean.
Bleaching is a stress response brought on by extreme temperatures. During bleaching events, the relationship between corals and the zooxanthellae housed in their tissue fails and zooxanthellae can be expelled from the coral or die in the tissue and lose their brown pigment. With the loss of zooxanthellae or their pigment, the translucent coral tissue allows the skeleton to shine through and thus appear white or “bleached.” For many corals, the loss of the zooxanthellae is also the loss of their primary source of nutrients. The survival rate of bleached corals is severely reduced if extreme conditions persist, and the coral likely will die.
Sea Urchin Die-Off
In 1983, Caribbean reefs experienced a massive die off of of the long-spined sea urchin, Diadema antillarum, due to a disease. This drop in population allowed for increased growth in macroalgae leading to increased competition for coral larval settlement area.
White Pox Disease
Also known as “acroporid serratiosis” (APS), white pox is specific to elkhorn coral. The culprit of APS is Serratia marcescens, a bacterium commonly found in human waste and elsewhere in the environment. As a result of poor waste water treatment and perhaps other factors, acroporid serratiosis prevalence has increased throughout Caribbean reefs, causing white patches of bare skeleton to appear on elkhorn corals as the tissue is killed.
Low water temperatures for extended periods of time can cause massive stress and die off of shallow-water, inshore corals, and cold-sensitive offshore coral.
Degraded Water Quality
In developed areas, poor water quality from coastal runoff is one of the leading causes of declining health in coral reef organisms. Runoff water carries nutrients, sediments, and pollution from land-based sources and deposits them directly onto our reefs. An excess of nutrients promotes algal growth, which decreases oxygen levels leading to a condition known as eutrophication. Sedimentation limits light availability, inhibiting the corals’ ability to feed and reproduce, and in extreme cases, it can lead to death by smothering the coral. Finally, pollution from sources such as sewage and untreated wastewater carry bacteria and pathogens that can infect and kill corals.