Pacific Coastal & Marine Science Center
Integrated Geologic Studies of Coral Reefs: Impacts from Land-Based Pollution and Sea Level Rise
United States coral reefs are in peril for a variety of known and yet-to-be-discovered causes. It is now well accepted that reefs are declining from poorly understood impacts of land-based pollution, including sedimentation and nutrification, over-fishing, and global change. Two of these major impacts, land-based pollution to coral reefs and sea-level rise due to global change, are topics that the USGS, and CMG in particular, can provide scientific expertise for improved understanding and guidance for resource managers. During past five years here have been significant changes in the over-all goals of the coral reef research community as new threats have evolved or grown in importance. Within the US, there are numerous locations where coral reefs are highly impacted or threatened by watershed alteration and climate change. Global change, including the effects of a warming ocean and a rising sea level, have are being increasingly recognized as crucial topics. The importance of altering and monitoring the impact of land-based pollution has become a major issue within the US, as evidenced by priorities set by the US Task Force on Coral Reefs. One of the key topics in the April 2004 Report of the U.S. Commission on Ocean Policy includes the need for "an ecosystem and watershed-based management" approach to ocean pollution, and highlights "the astounding decline of coral reef ecosystems" and "an urgent need to address the identified, major factors causing coral declines." There is a strong consensus in the scientific community that greenhouseinduced warming is occurring, and that one result of such warming is an acceleration of sea-level rise. The Intergovernmental Panel on Climate Change (IPCC) projects that sea level will rise 48 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 5m 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 that are available for exhumation by increased energy in back reef environments. The global rise is modulated by significant variations in relative sea level rate due to variations in uplift or subsidence of coastal lands. For example, in Hawaii, there is substantial subsidence on Maui and particularly the Big Island, the result of which is rates of sea-level rise of 3.5 to 5 mm/y. Recognition of these processes have lead to a series of questions to be addressed through objective research: How will reefs respond to rapid sea-level rise? Will increased wave energy and circulation across the reef flat lead to damage? Or will coralalgal ecosystems be able to respond to these shifts and experience renewed growth? Do thresholds exist in the rate of sea level rise that would push a reef ecosystem from a state of stability to one of net loss?
This Project addresses two broad objectives both derived from a series of workshops and publications: understanding the fate and impact of land-based pollution on coral reefs; and understanding and predicting the response of reefs to accelerated sea-level rise. The activities are a response to findings from many sources, including the National Plan to guide the Coastal and Marine Geology Program following the DOI theme: Protecting the Nation’s Reefs (March, 1999), and USGS Coral Reef Planning Meeting in Santa Cruz CA in May, 2004. Research objectives for the project are strongly guided by and coordinated with the Local Action Strategy of the US Coral Reef Task Force. The first objective is to better understand the behavior of sediment on coral reefs, including its delivery pathways, residence time, processes of transport on the reef, and effect on corals and other organisms. By understanding the driving forces that control particle behavior and residence time on reefs, information can be provided to managers and planners so that the effects of particular land management practices can be forecast. The quantity of terrigenous sediment delivered from high islands to adjacent reefs has increased in many areas due to alteration of the watersheds and drainage systems. Particles transported onto the reef block light, interfere with coral feeding, and carry nutrients that support growth of competing algae, decrease larval recruitment sites, and in extreme cases, bury living coral. Improved understanding of the transport patterns, residence time, and over-all fate of particles on the reef is critical to understanding the over-all impact of sediment and other land-based pollutants. Key ancillary studies focus on sediment delivery from the watershed and studies with university cooperators that examine the effects of sediment on coral health. A second objective is to evaluate the effect of the projected rapid sea-level rise on coral reef communities. The over-arching question is “How will sea-level increases of 50 to 100 cm, and possibly more, affect the health, diversity, and longevity of coral reefs?” At present there is almost no information on this topic. Accelerated growth may lead to increased sediment production and improved shoreline stability. Other impacts may be inconsequential, or alternately, they may be highly negative. Importantly, climate change impacts (warming, increased storm impacts) and the associated effects of sea-level rise on adjacent coastal ecosystems and shorelines may change local circulation and sedimentation and negatively impact reefs. This objective is linked to the first (sediment on reefs): rising sea level may substantially increase the amount of finegrained sediment eroded from coastal plains and stream deltas onto reef areas, thus decreasing available light and larval recruitment sites, and increasing stress levels in coral and other reef organisms. Plans for the next several years are as follows:
Land-Based Pollution on Coral Reefs: Research on this topic will proceed through field studies that incorporate and seek to identify the role of key environmental processes; through monitoring efforts coordinated with local action strategy groups, with development of new in situ technologies; and through modeling to identify likely behavior of sediment particles under typical and extreme events. Our strategy to accomplish the objectives include field research, field monitoring office analysis and modeling. Because of the complexity of the topic, we our strategy depends on cooperation and collaboration from other Bureau disciplines, other agencies within and without DOI, local action groups, and university colleagues. Many of the research activities undertaken over the next five years will be coordinated so as 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. 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. Impact of Rapid Sea Level Rise: The effect of forecasted, higher-than-present sea levels and accelerating rates of rise on framework reefs has largely been ignored by the scientific community. Our strategy for achieving the stated objectives will focus on three components:
The first approach proposes that analysis of reef history from drill samples from different islands will provide an understanding of how reefs have responded to rapid sea-level rise in the recent geologic past in terms of their over-all structure and key reef-building organisms and associations. Steps 2 and 3 will be addressed through extrapolation and modeling of sediment processes under different sea level rise scenarios, which would be useful for understanding the likely impacts from turbidity and new circulation patterns and help reef managers plan for possible changes that will take place over the next 20 to 50 years. Part of this work will involve the application of three-dimensional numerical models to predict energy changes across the reef environment under various likely scenarios of wave and water level changes. USGS research on this topic will be formulated to address the following questions:
web site: http://coralreefs.wr.usgs.gov/