Pacific Coastal & Marine Science Center
Pacific Coral Reef Geology and Oceanography
United States coral reefs are in peril for a variety of causes, most of which are well known but not well understood. It is now well accepted that reefs are declining from poorly understood impacts of land-based pollution, including:
Every evaluation and workshop report published in the past decade has identified these three factors as the most significant causes of coral reef degradation. The importance of these factors was very recently underscored when the U.S. Coral Reef Task Force (USCRTF) developed a set of nationally established guidelines to address efforts for understanding and addressing the same three issues as the top global threats to coral reef ecosystems.
This project addresses the sources and processes of pollution and nutrient transport by surface run-off and groundwater discharge. It also addresses the ultimate fate and impact of pollutants and nutrients, particularly during the present-day rise in sea level, and assesses the key scientific parameters needed to establish marine protected areas.
Sedimentation, including higher levels of suspended sediment in overlying waters, is commonly acknowledged to be one of the primary causes of reef degradation (Pandolfi and others, 2003; Wilkinson, 2004; Fabricius, 2005; Richmond and others, 2007). The combination of suspended sediment and deposited sediment act to limit coral growth, feeding patterns, photosynthesis, recruitment, and more, as shown by numerous studies by in a variety of settings (e.g. Dodge and others, 1974; Rogers, 1983; Fabricius and Wolanski, 2000; Dollar and Grigg, 2004). Although some corals can flourish in turbid water (Woolfe and Larcombe, 1999) such reefs are typically less diverse and are more restricted in depth range than those in clear water (Fabricious, 2005).
In Hawaii and Guam, fringing coral reef habitats are presently at risk from elevated sediment runoff due to anthropogenic changes in adjacent watersheds (USCRTF Hawaii and Guam Local Action Strategies [LAS]; Grigg and Dollar, 1997; Field and others, 2008). Frequent resuspension of fine-grain sediment by waves is particularly harmful to reef habitats. Increases in the amount of sediment currently reaching the reef, or increases in the frequency, duration, and intensity of sediment resuspension on the reef are likely to increase coral degradation. Even small quantities of deposited mud magnify the deleterious effects of terrigenous runoff by several orders of magnitude, as individual particles are repeatedly resuspended, commonly on a daily basis (Field and others, 2008).
Coral reef ecosystems are also widely recognized to be at risk from climate change due to anthropogenic-driven increases in atmospheric concentrations of greenhouse gases. Not only do higher-than-normal sea surface temperatures lead to bleaching and consequentially to coral death, they also cause increased susceptibility to other stressors (Hughes and others, 2003; McClanahan, 2002; Jokiel and Brown, 2004).
It is becoming increasingly evident that a prime mechanism for preservation of coral reefs against these threats is establishment of marine protected areas, but guidelines for such are extremely limited. Another impact of climate change on atoll and fringing coral reef ecosystems will be changes in hydrodynamics due to sea-level rise that result in increased turbidity and nutrient pathways.
The Intergovernmental Panel on Climate Change (IPCC) projects that sea level will rise 30 to 50 cm by 2100, which is about double the rate of the past century. Future sea-level rise is particularly significant for low-lying coral atolls, many of which have maximum elevations of less than 5 m above present sea level. Even in high-island settings, such as Hawaii, Guam, and the US Virgin Islands, large volumes of muddy sediment are stored at or near sea level and are available for exhumation by increased wave energy in back reef environments.
The overarching goal of research conducted for this project is to provide scientific understanding of the natural physical processes and anthropogenic impacts that critically influence the development and sustainability of U.S. coral reefs. This goal is achieved through field, laboratory, and modeling studies involving USGS staff, partners, and stakeholders in many diverse disciplines. Our results are made available to partners and resource mangers through peer-reviewed publications, USGS reports, briefings, presentations, and web sites.Research studies are conducted through four linked and overlapping Tasks:
These research studies will lead to understanding of the highly complex nature of flow and particle retention on coral reefs, the first step in predicting the fate on reefs of fine-grained sediment and nutrients, contaminants, and larvae. Such information is essential for effective management of coral reef resources. Complementary research will characterize the relationship between precipitation, recharge, storage, and discharge of submarine groundwater (SGD) through the coastal zone and develop metrics of coral reef response to variations in SGD with climate change and land use. This information will help guide management of coastal water supplies, aquifers, and critical marine resources that sustain ecologic, cultural and economic functions for human livelihood. Research will also address how reefs will respond to rapid sea-level rise at a decadal time-scale, and how increased wave energy and altered circulation across the reef flat will affect sediment transport. Lastly, this research will identify the key factors that determine a coral reef's ability to withstand multiple stresses and recover from periodic disturbances, and to provide GIS-based maps of the reefs in Hawaii critical for protection.
Coral reef research, by its nature, cuts across many complex science issues and a host of disciplines, including toxicology, ecology, sedimentology, oceanography, phycology, geochemistry, parasitology, geology, biology, geochronology, paleontology, geophysics, and many, many more. In this maze it has been important for the USGS/CMG to identify the critical scientific questions that it, along with partners, can address with expertise and leadership.
This project will conduct cutting-edge research on coral reefs, employing diverse expertise in sediment dynamics, sedimentology, geochemistry, numerical modeling, high-resolution benthic habitat mapping, coastal circulation, remote sensing and paleohistory (facies and geochemical proxies). Our Coastal and Marine Geology Program in-house expertise is coupled with strong partnerships in the Bureau (ESP, Water, Biology, Geography), and with partnerships with other experts in biology (University of Hawaii, NPS, NOAA), oceanography (University of Washington), and reef geology (University of Hawaii).
Research on all tasks will be conducted through field studies that incorporate and seek to identify the role of key environmental processes; through monitoring efforts coordinated with local action strategy groups; development of new in situ technologies; and through modeling. These studies will identify likely behavior of sediment particles under typical and extreme events to develop a predictive capability.
Because of the complexity of the topic, our strategy depends on cooperation and collaboration from other Bureau disciplines, other Federal agencies within and outside of DOI, State agencies, local action groups, and university colleagues. Many of the research activities undertaken over the next five years will be coordinated to integrate as many of the questions as possible. We envision that CMG scientists will play a leadership role in both conducting and coordinating research on this topic.
There exists at present an excellent opportunity to collaborate with working groups in Hawaii that are addressing land-based sources of pollution to reefs. This collaboration will take place in each task:
Our already-existing cooperation with EPA, Hawaii's Dept Lands and Natural Resources, The Nature Conservancy, and others will expand as other groups join the local action strategy plans. In particular, research on this topic will lead to increased collaborative studies with colleagues in BRD, WRD, and NMD. Those groups have identified the "ridge-to-reef" as a topic that is important for them to pursue, and they are planning on doing such, with CMG leading the "on-the-reef' phase.
Our strategy for determining the likely effect of the present-day sea-level rise on coral ecosystems has three components:
Part of this work will involve the application of two- and three-dimensional numerical models to predict energy changes across the reef environment under various likely scenarios of wave and water level changes.
See web site: http://coralreefs.wr.usgs.gov/