We must address local threats to coral reefs

Coral reefs are shocking to the eye. They produce a cacophony of color and miscellany of species and life. They are the bedrock of ocean diversity. The ecosystems hold over half of all known ocean species and yet cover a mere .001% of our oceans. Their safe warm waters and complex substrate serve as the epicenters of marine life. A warmer climate is now threatening the very existence of reefs. Warming ocean temperatures make it challenging for the sensitive relationship between coral and zooxanthellae, invertebrates that live inside the hard-coral shell, to form. Rising atmospheric C)2 concentrations from fossil fuel burning also produce acidic waters. This lower pH makes it more challenging for coral to form their calcium skeletons.

Climate change is the greatest impending global threat to reefs, but not the only one. Humans, and our activities in coastal areas, also impact these near shore ecosystems. Many activities on land have consequences as the water on land mixes in the ocean. Fertilizer runoff can cause algae overgrowth in reefs. Trash and waste introduce toxics into marine food chains. Sediment suspended in water can smother corals and reduce sunlight. Waste water adds additional nutrients to ocean systems causing an ecosystem imbalance. Understanding and managing these land-based dangers may help us reduce the impact from global threats.

Off the coast of Maui lie some of the world’s most beautiful reef systems. Visitors flock to Maui by the thousands to snorkel in the ocean, climb volcanoes and lounge by the pool. The reefs support tourism, fishing and a food supply, and also protect the coasts from storms through wave attenuation. On the west coast of Maui, close to a waste water treatment facility, the reef systems show signs of deterioration. In other areas around the island the reef is much healthier. Researchers from US Geologic Survey and Woods Hole Oceanographic Institution set out to see what was causing these changes in reef health around the island.

To understand this coastal ecosystem, the marine scientists took samples of the water, coral and plant life at varying distances from the freshwater seeps. By CT scanning the specimens, the researchers were able to see the amount of erosion over time as well as the growth rate for coral. The scientists also gathered water samples over a 6-day period along the unhealthy reefs. They analyzed the water for concentrations of nitrates and phosphates, two compounds that are often polluted in excess by waste water treatment plants.   

The researchers found that coral reefs located nearest the freshwater seeps to be negatively affected by the discharge of treated waste water. The most notable differences were vast fluctuations in nitrogen levels and lower pH levels in waters close to the seeps. These water changes noticeably affected corals. The corals in an environment close to the seeps were eroding at 8 times the rate as those corals living in similar environments away from the seeps.

This research shows that local stressors can drastically affect coral reef health. By regulating land based threats to coral reefs, we can improve their condition. A healthier reef will improve tourism, food security, storm resilience and ocean biodiversity. While climate change is the most impending threat to reefs, we also must stop threats at the local level. Luckily by facing these local land-based threats to reefs head on with changes in policy and close monitoring, we can give reefs a fighting chance in our uncertain future.