Coral reefs are one of the ocean's most colorful and complex creations. I'm sure you have read about how they are in peril. Climate change, acidification, human development - all are having an impact, most often represented by coral bleaching which is the result of the loss of the symbiotic algae that lives within the coral.
I was reviewing several scientific papers and found that there are many studies going on to determine more specifically what is happening to the reefs. As it turns out, the external factors of temperature, pollutants, and others can trigger a variety of eco-systemic or internal components that adversely affect the coral. Oh, if it were only simple, then the solutions might be simpler too.
One study examined the impact on several species of reef fish and their aerobic scope, or ability to breath, in elevated temperatures. Ever felt your breathing was a bit more labored on a really hot day? Well, according to this study, reef fish can have a similar reaction when water temperatures rise. This causes a reduced capacity to absorb oxygen which weakens the health of the fish, its level of immunity, and overall lifespan.
Water quality was found, in another study, to impact the sensitivity of corals to coral bleaching. "Terrestrially-sourced dissolved inorganic nitrogen" or DIN was found to make coral more sensitive to the temperature threshold that triggers coral bleaching. Higher levels of DIN are often found in areas of human development in the form of runoff from urban development or construction.
The levels of nutrients within a coral reef system can also effect the balance between hard corals, anemones, and algae. All three live in relative harmony, with hard corals as the dominant species. But in the typically low-nutrient world of a healthy coral ecosystem, warmer temperatures can increase nutrient levels and, at various levels, the anemones become more aggressive towards the coral and at the highest levels, the algae becomes dominant.
Coral reef ecosystems are tremendously complicated and we are continually learning more about the inter-relationships of species and the environment. And not everything falls into perfect agreement. One study that reviewed the relationship between temperature and salinity at a mass bleaching in Thailand, found that salinity did not seem to play a critical role in triggering the event. Whereas, another study concluded that higher salinity levels can impact both the coral host and its symbiotic algae, effecting its long-term health.
We still have much to learn but the research must continue so that we have a clear understanding as to what is happening to the earth's coral reefs so that we can both potentially treat and prevent the abuses that are impacting these critical marine ecosystems.