Anthropogenic Factors Causing Harm to Coral Reefs
Coral reefs are known to be home to most of the world’s fish species, with these being known as hotspots of biodiversity. On top of that, both reef-living fish and most pelagic, open-ocean fish spawn in coral reefs, becoming the prime source of the fishing industry. Coral reefs also fixate dissolved nitrogen, making it accessible in the marine food chain, and ultimately contributed to fish biomass that the fishing industry hungrily seeks. However, not all of human efforts contribute to the benefit if the coral reefs, despite it being a vital aspect of our economy and biology. Besides the obvious effects of pollution, here are some of the anthropogenic activities that directly and indirectly detriment the world’s coral reefs.
Destructive Fishing Practices
These are the anthropogenic acts that directly cause physical damage to coral reefs as a means for a greater catch. These include, but are not limited to, bottom trawling and the use of explosives.
Bottom trawling involves the dragging of heavily weighted nets on the ocean floor, indiscriminately raking benthic organisms, including age-old and slow-growing corals. Larger fishing vessels employ this method to efficiently and effectively catch large amounts of fish in as little time and concern for the environment as possible. Naturally, this method is unsustainable, as fish would lose their spawning sites and habitat faster than it would regrow, effectively inhibiting the repopulation of the fish of the area.
Usage of Explosives
Explosives are used in small to medium-scale fishing, as these methods are less efficient than bottom trawling, but does not require the use of large fishing vessels. Explosives are primarily used to cause shockwaves aimed at destroying the calcareous structure of corals, and secondarily to destroy the fishes’ swim bladders. These two added results would then give these reckless fishermen an easy catch.
Side-Effects of Industry
Does the term “agricultural runoff” sound familiar? Chemical compounds used in agriculture, such as fertilizers and pesticides, are “run off” to sea, as an accident or an intentional endeavor to use the world’s oceans as a waste pond. These chemical compounds foreign to the coral reef ecosystem cause disruption by either the killing off or causing the uncontrollable growth of certain organisms. As such, the natural nutrient cycle is disrupted, or the overriding of algae causes the stifling of resources for other organisms.
Introduction of Chemical Compounds that Directly Cause Mortality
Let us first provide examples of the effects of introducing large amounts of foreign chemical compounds to the coral reefs that immediately lead to death of certain organisms. For example, a farmer’s waste pond full of herbicide overflowed due to excessive torrential rains, and drained to a nearby river, which eventually led to the ocean. The large amounts of would immediately cause the death of phytoplankton and sea grass communities. Oil spills will cause the reduction of light reaching the benthos, stifling the corals’ zooxanthellae of their and their host’s means to survive, grow, and reproduce.
Now, we illustrate the effects of the introduction of large amounts of nutrients to coral reef waters, which is also known as “nutrient loading”. First, we consider that algae are competitors of corals in substrate and light. Also, algae grow and multiply at a much faster rate than corals. Why don’t algae naturally dominate coral reefs? It is because coral reefs are low-nutrient environments. Now, the introduction of nutrients to these coral reefs would then cause the rise of the biomass of algae in the area, which is also known as “algal bloom”, which subsequently stifles the resources needed by corals, leading to the reduction in the population of corals and all other organisms depending on them, and ultimately leading to the phase shift of the community.
The increase in the amount of sediments suspended in the water column will trigger corals to secrete mucus in order to rid themselves of sediment. However, the corals will use up valuable energy in doing so, making them more vulnerable to disease and would slow their growth. Also, in the even of the coral not secrete enough mucus to get the sediment off fast enough, then the light going down the water column will be again restricted, yet another stress for the corals. Lastly, sediment will smother the coral, and will prevent the entry of the suspended particles corals do need to survive; food.
The increased amount of suspended sediment in the water column may be attributed to natural causes, wherein sediment upwelled by water currents as a natural part of reef ecology and healthily adds optimal amounts of nutrients to the reef, and by anthropological activities, which usually leads to the negative effects mentioned above. This may include the activities that, as a side-effect, causes nearby land to be more vulnerable to erosion, such as deforestation and mangrove-cutting and the activities that directly add sediment to the waters, such as the dumping of land from construction projects.