Corals Reefs in the Pacific
Providing scientific information to support ecosystem approaches to management and conservation of coral reefs
Coral reefs are considered rainforests of the sea. They are the most biologically diverse marine ecosystems, yet they only cover a small portion of the ocean floor and many of their inhabitants remain a mystery. The number of invertebrate species that live in coral reefs is estimated to range from 1 to 10 million, many still unidentified and undiscovered.
Compounding our lack of knowledge on reef inhabitants, coral reefs are among the most threatened ecosystems in the world. Corals are highly susceptible to local stressors (overfishing, pollution, and habitat destruction) and global stressors (climate change, coral bleaching, and ocean acidification).
In the Pacific Islands, we monitor coral reef health at nearly 40 islands and atolls using a suite of interdisciplinary monitoring and research activities, including habitat mapping, oceanographic and climate studies, and long-term monitoring of coral reef ecosystems. As part of the Pacific Reef Assessment and Monitoring Program (Pacific RAMP), we use standardized survey methods to assess corals, algae, other invertebrates, fishes, and microbes in among their benthic habitats and oceanographic environments.
These methods are used consistently across the Pacific Islands region to enable comparative ecosystem analyses across diverse biogeographic, environmental, oceanographic, and socioeconomic (human use) gradients. Since 2000, we have been collecting data on corals, reef fishes, algae, invertebrates, microbes, and ocean chemistry. This long-term monitoring program helps us assess the status and health of coral reef ecosystems throughout the U.S. Pacific. Our Pacific RAMP surveys align with the National Coral Reef Monitoring Plan and contribute scientific information that is essential to protect, conserve, and restore coral reef resources by maintaining healthy ecosystem function.
Coral Health and Threats
Coral cover—and the balance between corals versus algal dominance on reefs—can indicate the overall health of the reef ecosystem. Tracking trends in coral cover over time can be used to assess the resistance (ecological stability) and resilience (ability to recover) to disturbances, a critical indicator for long-term survival of coral reef ecosystems. Divers survey shallow reefs using rapid ecological assessment methods to measure coral cover, mortality, demography, bleaching, and disease.
The numbers and size of reef fishes are also indicators of overall ecosystem health. Fish communities can reveal insights into natural oceanographic processes such as nutrient upwelling, and disturbances such as overfishing, pollution, and climate impacts. We use two main types of underwater surveys to count and study reef fishes, scuba diver surveys and remote camera surveys.
Coral reef ecosystems are influenced by changing weather and oceanographic factors including temperature, currents, carbonate chemistry, nutrients, and productivity. Ocean temperatures and ocean acidification are fundamentally changing the condition and chemistry of the world’s oceans and threatening marine resources, especially coral reefs and their inhabitants. We document and assess ocean conditions around coral reefs with a combination of water samples, climate station installations, and satellite imagery.
- Rapid ecological assessments: Scuba divers swim along transects and stop at specific sites above reefs to photograph and document coral condition and fish species.
- Remote camera surveys: Underwater video cameras capture footage of benthic habitat and reef fish populations.
- Water chemistry: We samples ocean water to monitor changes in temperature, salinity, nutrients, and ocean acidification over time.
- Coral growth rates: Coral “cores” show growth of the coral’s skeleton through time, similar to how rings in a tree trunk show the tree’s age and growth.
- Calcium carbonate: Corals make their skeletons with calcium carbonate. We install “calcification accretion units,” or small plates, on reefs to measure levels of calcium carbonate and coral reef growth.
- Bioerosion rates: Ocean acidification can also cause coral reefs to erode or break down. If a reef is eroding faster than it is growing, its coral skeleton will weaken and, eventually, massive reef structures will convert to rubble, sand, and silt—altering the entire ecosystem.
- Reef biodiversity: Autonomous reef monitoring structures are used to examine the biodiversity and community structure of the coral reef.