Resilience and Recovery: Science for Future Reefs

Science Center Objects

Understanding the variability in mechanisms underlying reef resilience is critical for reef management under climate change.

Illustration showing islands and the channels in the ocean in between them with path lines of instruments with little flags.

Map showing the paths that ocean current-following surface drifters deployed in coral larval slicks off west Maui traveled in 24 hours following their release during a coral spawning event. Such data suggests that the coral reefs off west-central Maui may provide coral larvae to the reefs off northeastern Lānaʻi.

This study is part of the USGS Coral Reef Project.

The Problem

Coral reefs are facing increasing stress from climate change (elevated sea-surface temperatures and acidification), combined with local stresses from over-fishing and sedimentation and other sources of land-based pollution. In light of the potential for these stressors to increase the rate of coral reef degradation to epidemic levels, coral reef scientists and managers world-wide are shifting emphasis towards identifying the key mechanisms controlling reef resiliency. There is a compelling need for information that will help managers identify processes and specific areas, at the jurisdictional level, where coral reefs will be the most viable in the future and where, given the unpredictability of stresses, reefs might be best suited for recovery. For example, some coral reefs that had been decimated by bleaching in 1997–1998 subsequently made rapid recoveries; clearly, identifying reefs having such potential will be powerful management tool in this era of increasing stress agents. This shift by the scientific community from identifying the processes of decline to identifying solutions for the future is highlighted in many recent publications, workshops, and international meetings.

Underwater photo with light-colored corals in foreground and green and dark corals in background, with tiny round orbs floating.

Underwater photograph of coral (Montipora capitata) egg-sperm bundles floating to the surface during a coral spawning experiment off west-central Maui.

Much of the thinking thus far by the scientific community has focused on the biologic indicators of resiliency, such as coral cover, species diversity, and fish populations. The parameters that influence the health and sustainability of coral reefs are diverse and include changes in watersheds, coastal development, stream discharge, coastal circulation, and larval pathways and natural causes of stress (for example, large wave events in Hawaiʻi). They also include potential natural processes that reduce stress (for example, upwelling, internal-wave mixing, submarine groundwater discharge). Identifying areas of coral reefs that have the highest potential for survival requires a cross-cutting assessment of all of the salient geographic, geologic, and oceanographic factors as well.

Very little effort thus far has addressed potential reef managed/protected areas using a comprehensive evaluation of all the important processes that affect the health and long-term viability of a reef. Understanding the variability in mechanisms underlying resilience is critical for reef management under climate change, for reefs able to rapidly recover due to a combination of resiliency factors may serve as key refugia, or sources of larvae, for reef recovery at larger scales.

Map shows Hawaiian islands and outlines some small, offshore areas near each island and names each area.

Map showing the location of existing marine managed/protected areas in the Maui Nui complex in the Hawaiian islands, which encompasses the islands of Molokaʻi, Maui, Lānaʻi, and Kahoʻolawe.

The Approach

This effort represents a new level of research and coordination, and we will have a two-fold approach. 

  1. Focused research studies on natural processes that have the potential to offset deleterious effects due to climate change. Improved understanding of the natural processes that reduce water temperature to selected reefs is a key objective. Upwelling of cool oceanic seawater along reef fronts, mixing by breaking internal waves, and discharge of submarine groundwater onto shallow reef flats are three such processes. 
  2. A comprehensive evaluation of coral reefs and all important geologic and oceanographic factors for identification of those reefs, at a regional scale, that are potentially the most resilient and the most likely to recover from an extreme event. Marine protected areas in Hawaiʻi are very small, and as noted in Status of Coral Reefs in Hawaiʻi and U.S. Pacific Remote Island Areas, Chapter 15, (2008): “MPAs [in Hawaiʻi] are too small to have significant effects outside their boundaries.”

The approach to these interdisciplinary studies will rely on a combination of laboratory efforts, field measurements and physics-based numerical monitoring. We use a wide range of tools to try to answer these questions, including: oceanographic instruments (for example, acoustic Doppler current profilers, wave/tide gauges, temperature sensors, salinity sensors, turbidity sensors, chemical sensors) mounted on the seabed or on moorings, water-column profilers with similar suites of sensors, GPS-equipped Lagrangian surface drifters, drop and towed underwater video mapping systems, swath acoustic mapping systems, airborne and space-based remote sensing imagery, and physics-based numerical models.