Coral Reef Decline

Efforts to Combat Coral Reef Decline

Coral reefs offer one of the most important aquatic biomes, making up only 1% of the ocean floor they provide shelter for about a quarter of marine life. In the past 40 years it has been observed that coral reefs have been declining due to pollution, global warming, sedimentation, overfishing, and pathogens. These stressors mainly increase CO2 concentrations, or ocean acidification, which lowers the calcification rate of corals. Increased ocean temperatures and excess CO2, leaves reefs prone to algae invasion and disease. However, restoration of these important habitats is possible, one of the greatest examples of ocean conservation happened on the east coast of Mexico’s Baja California Peninsula. Where

Cabo Pulmo lies there is a small protected area that hosts a coral reef estimated to be around 20,000 years old. Conservation efforts on this specific piece of land began around twenty-one years ago, with very slow progress, during its first decade this area has seen over a 400% increase in total biomass, which is attributed to the healthy condition of the reef.
• Decades of overfishing led to the decline of the once very productive coral reef, the Castro family approached their community, which depended on the reef, with a plan to stop fishing completely in order to save their reef.

• After fourteen years of protection, every group of fish had returned to Cabo Pulmo, from the small herbivores to top predators. (Feurstein, n.d)

• Success due to community involvement, protected area size, fishing eradication. (Feurstein, n.d)

• Unclear how slow-growing top predators recovered in such a short period, research indicates that they probably didn’t grow up in Cabo Pulmo, however it does provide a sanctuary for migrating animals from other regions in search of plentiful food sources on healthy coral habitat

• Various stressors have contributed to the lessening resilience of reefs by increasing coral-algae competition; therefore reducing coral recruitment, growth and survivorship (Zaneveld et. al, 2016).

• Dark Spot Syndrome was the most prevalent disease, nutrient enrichment increased DSS Prevalence >100% in the most common coral S. sidera. (Vega, Burkepile, Fuchs, Shantz, & Zaneveld,

2014)
• (Venn, Tabutte, Lotto, Zoccola, Allemand & Tambutte, 2009)
• (Barrot, Venn, Perez, Tambutte, & Tresguerres, 2015)
• Changes in apex predator populations releases lower trophic levels from top down control, resulting in cascading effects (Rizzari, Bergseth & Frisch, 2015)

The world-wide loss of coral reefs stresses the need to understand what drives reef decline.

Most of the stressors affecting coral reefs are anthropogenic, originating from human activity. Notably, stressors such as overfishing and nutrient pollution contribute by reducing the resilience of the reefs by increasing coral-algal competition and reducing coral recruitment, growth and survival (Zaneveld et. al, 2016). A field experiment conducted over the course of three years, simulated overfishing and nutrient pollution yielded an increase in turf and macroalgal cover while destabilizing microbiomes, elevating putative pathogen loads. Together, stressors and temperature combine to alter coral microbiomes by driving bacterial blooms. Yielding an increase in disease by more than twofold and increased mortality up to eight fold. (Zaneveld et. al,

2016).
Coral reefs are largely formed from the calcium carbonate skeletons of corals. Unicellular algae living within the tissues of corals form a mutualistic relationship which provides corals organic molecules and promotes photosynthesis. Corals, a diverse group of cnidarians, are the predominant animals, but overall the animal diversity on coral reefs rivals that of tropical forests. Most corals are found on the pelagic zone where light can penetrate to promote photosynthesis.
Ocean acidification due to increased CO2 lowers the concentration of dissolved carbonate ions and therefore inhibits calcification. of the ocean due to increased CO2 will lower the concentration of dissolved carbonate ions. CO2 reacts with water yielding carbonic acid H2CO3, which then dissociates into H+ and bicarbonate ions HCO3-. Granting that the carbonic acid- bicarbonate reaction is a buffering system, accumulating CO2 drives the reaction to the right, releasing more H+ and therefore lowering the pH and making the ocean more acidic. The excess protons then combine with CO32- form bicarbonate ions, lowering the concentration of carbonate ions for the formation of calcium carbonate by corals (calcification)