Coastal and Marine Ecosystems & Global Climate Change: Potential Effects on U.S. Resources

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Coastal and Marine Ecosystems & Global Climate Change: Potential Effects on U.S. Resources

Prepared for the Pew Center on Global Climate Change
August 2002

Victor S. Kennedy, University of Maryland
Robert R. Twilley, University of Louisiana at Lafayette
Joan A. Kleypas, National Center for Atmospheric Research
James H. Cowan, Jr., Louisiana State University
Steven R. Hare, International Pacific Halibut Commission

Press Release

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Eileen Claussen, President, Pew Center on Global Climate Change

The world’s oceans cover approximately 70 percent of the Earth’s surface, indicating their importance to the global environment. In addition to having a large influence on global heat transport and precipitation, the oceans are comprised of diverse habitats that support a wealth of marine wildlife. They also provide humans with a wide variety of goods and services including foods, recreational opportunities, and transportation corridors. Based upon current scientific evidence, emissions of greenhouse gases from human activities are projected to cause significant global climate change during the 21st century. Such climate change will create novel challenges for coastal and marine ecosystems that are already stressed from human development, land-use change, environmental pollution, and over-fishing.

“Coastal and Marine Ecosystems & Global Climate Change” is the eighth in a series of Pew Center reports examining the potential impacts of climate change on the U.S. environment. It details the likely impacts of climate change over the next century on U.S. coastal and marine ecosystems, including estuaries, coral reefs, and the open ocean. Report authors, Drs. Victor Kennedy, Robert Twilley, Joan Klepas, James Cowan, Jr., and Steven Hare find:

Temperature changes in coastal and marine ecosystems will influence organism metabolism and alter ecological processes such as productivity and species interactions. Species are adapted to specific ranges of environmental temperature. As temperatures change, species’ geographic distributions will expand or contract, creating new combinations of species that will interact in unpredictable ways. Species that are unable to migrate or compete with other species for resources may face local or global extinction.

Changes in precipitation and sea-level rise will have important consequences for the water balance of coastal ecosystems. Increases or decreases in precipitation and runoff may respectively increase the risk of coastal flooding or drought. Meanwhile, sea-level rise will gradually inundate coastal lands. Coastal wetlands may migrate inland with rising sea levels, but only if they are not obstructed by human development.

Climate change is likely to alter patterns of wind and water circulation in the ocean environment. Such changes may influence the vertical movement of ocean waters (i.e., upwelling and downwelling), increasing or decreasing the availability of essential nutrients and oxygen to marine organisms. Changes in ocean circulation patterns can also cause substantial changes in regional ocean and land temperatures and the geographic distributions of marine species.

Critical coastal ecosystems such as wetlands, estuaries, and coral reefs are particularly vulnerable to climate change. Such ecosystems are among the most biologically productive environments in the world. Their existence at the interface between the terrestrial and marine environment exposes them to a wide variety of human and natural stressors. The added burden of climate change may further degrade these valuable ecosystems, threatening their ecological sustainability and the flow of goods and services they provide to human populations.

The authors and the Pew Center gratefully acknowledge the input of Drs. Richard Beamish, Michael Fogarty, and Nancy Rabalais on this report. The authors would also like to thank Andrea Belgrano, Jay Blundon, Lou Codispoti, Victoria Coles, Raleigh Hood, Richard Kraus, Thomas Malone, Ray Najjar, Roger Newell, Michael Pace, Frieda Taub, and Peter Vogt for comments on early drafts. The Pew Center would also like to thank Joel Smith of Stratus Consulting for his assistance in the management of this Environmental Impacts Series.

Executive Summary

Since life began on earth, changes in the global climate have affected the distribution of organisms as well as their interactions. However, human-induced increases in atmospheric concentrations of greenhouse gases are expected to cause much more rapid changes in the earth’s climate than have been experienced for millennia. If this happens, such high rates of change will probably result in local if not total extinction of some species, the alteration of species distributions in ways that may lead to major changes in their interactions with other species, and modifications in the flow of energy and cycling of materials within ecosystems.

The predicted changes may have a significant effect on coastal ecosystems, especially estuaries and coral reefs, which are relatively shallow and currently under stress because of human population growth and coastal developments. Significant environmental factors that affect the structure (e.g., plant and animal composition) and function (e.g., plant and animal production, nutrient cycling) of estuarine and marine systems and that are expected to be part of global climate change include temperature, sea-level rise, the availability of water and associated nutrients from precipitation and runoff from land, wind patterns, and storminess. Temperature, in particular, influences organism biology, affects dissolved oxygen concentrations in water, and plays a direct role in sea-level rise and in major patterns of coastal and oceanic circulation.

Predictions of the effects of climate change on coastal and marine ecosystems are associated with varying degrees of confidence. There is some confidence in predictions of how increases in temperature will affect plant and animal physiology, abundances, and distributions; aquatic oxygen concentrations; and sea level. There is also some confidence in predictions of the effects of sea-level rise on shallow continental margins, including flooding of wetlands, shoreline erosion, and enhanced storm surges. There is less confidence regarding temperature’s influence on interactions among organisms, and even less as to its effects on water circulation patterns. It is also difficult to predict the effects of climate change on precipitation, wind patterns, and the frequency and intensity of storms.

Many species are sensitive to temperatures just a few degrees higher than those they usually experience in nature. A rise in temperature as small as 1oC could have important and rapid effects on mortality of some organisms and on their geographic distributions. Given that temperature increases in the coming century are predicted to exceed 1oC, the major biological change resulting from higher temperatures in U.S. coastal waters may be altered distributions of coastal organisms along the east and west coasts. The geographic ranges of heat-tolerant species such as commercial shrimp on the East Coast may expand northward, while the southern range boundaries of heat-intolerant organisms such as soft clams and winter flounder may retreat northward. The more mobile species should be able to adjust their ranges over time, but less mobile species may not. Such distributional changes would result in varying and novel mixes of organisms in a region, leaving species to adjust to new predators, prey, parasites, diseases, and competitors. Some species would flourish and others would not, and we have no way of predicting at present which species would prevail. Fisheries would also be affected as some species are lost from a region or as others arrive. Warmer conditions would support faster growth or a longer growing season for aquacultured species, but might become too warm for some species in a particular region, requiring a change in the species being cultured.

Because water expands and glaciers melt as temperatures warm, higher temperatures would raise sea levels, inundating coastal lands and eroding susceptible shores. In salt marsh and mangrove habitats, rapid sea-level rise would submerge land, waterlog soils, and cause plant death from salt stress. If sediment inputs were limited or prevented by the presence of flood-control, navigational, or other anthropogenic structures, marshes and mangroves might be starved for sediment, submerged, and lost. These plant systems can move inland on undeveloped coasts as sea levels rise on sedimentary shores with relatively gentle slopes, but seaside development by humans would prevent inland migration. Marshes and mangroves are critical contributors to the biological productivity of coastal systems and function as nurseries and as refuges from predators for many species. Thus their depletion or loss would affect nutrient flux, energy flow, essential habitat for a multitude of species, and biodiversity. Some organisms might thrive (e.g., shrimp, menhaden, dabbling ducks, some shorebirds), at least over the short term as marshes break up and release nutrients or become soft-bottom habitat. Other organisms would be lost from affected areas if their feeding or nesting grounds disappeared and they could not use alternative habitats (e.g., Black and Clapper Rails, some terns and plovers).

Climate change may decrease or increase precipitation, thereby altering coastal and estuarine ecosystems. Decreased precipitation and delivery of fresh water alters food webs in estuaries and affects the amount of time required to flush nutrients and contaminants from the system. Although reduced river flow would decrease nutrient input in estuaries with relatively uncontaminated watersheds, there could be different effects in polluted watersheds that contain point sources of nutrients and contaminants that are not a function of river flow. The combined effects of human development and reduced river flow would degrade water quality conditions, negatively affecting fisheries and human health through such changes as increased presence of harmful algal blooms and accumulation of contaminants in animals and plants. Increased rainfall and resultant freshwater runoff into an estuary would increase stratification of the water column, leading to depleted oxygen concentrations in estuaries with excess nutrients. It would also change the pattern of freshwater runoff in coastal plain watersheds, such as along the southern Atlantic coast and in the Gulf of Mexico. In those regions where water resources are managed by humans, the effects of increased flooding would depend on how managers controlled regional hydrology.

Wind speed and direction influence production of fish and invertebrate species, such as in regions of upwelling along the U.S. West Coast. If upwelling is slowed by changes in wind and temperature, phytoplankton production could be lowered. Where upwelling increases as a result of climate change, productivity should also increase. In some coastal regions, alongshore wind stress and buoyancy-driven density differences help produce water movements that transport larval fish and invertebrates to nurseries, such as in estuaries. Climate-related changes in these circulation patterns that hinder such transport might alter the species composition of coastal ecosystems.

Increases in the severity of coastal storms and storm surges would have serious implications for the well-being of fishery and aquaculture industries, as has been demonstrated by the effects of recent intense hurricanes along the U.S. East Coast. Most ecosystems can recover rapidly from hurricanes, but the anthropogenic alteration of coastal habitats may increase the ecological damage associated with more severe storms.

The immense area and the modest extent of our knowledge of the open ocean hamper predictions of how ocean systems will respond to climate change. Nevertheless, it is clear that increased temperature or freshwater input to the upper layers of the ocean results in increased density stratification, which affects ocean productivity. Coupled physical/biogeochemical models predict a net decrease (~5 percent) in global productivity if atmospheric concentrations of carbon dioxide (CO2) reach a doubling of pre-industrial levels, increasing oceanic thermal stratification and reducing nutrient upwelling. Because productivity varies regionally, simple extrapolation to particular U.S. marine waters is difficult, although some high-latitude areas might benefit from warmer temperatures that lengthen the growing season. Open ocean productivity is also affected by natural interannual climate variability associated with large-scale climate phenomena such as the El Niño-Southern Oscillation. Climate-driven changes in the intensity or timing of any of these phenomena could lead to marked changes in water column mixing and stratification and, ultimately, a reorganization of the ecosystems involved, for better or worse.

Increased CO2 concentrations lower ocean pH, which in turn changes ocean carbonate chemistry. This may have negative effects on the myriad planktonic organisms that use calcium carbonate to build their skeletons. Some of these organisms appear to play important roles in ocean-atmosphere interactions, but we cannot yet predict any effects that might arise from their diminishment.

Finally, coral reefs, which are already threatened by multiple stressors such as abusive fishing practices, pollution, increased disease outbreaks, and invasive species, would also be at risk from changes in seawater chemistry, temperature increase, and sea-level rise. Lower ocean pH and changed carbonate chemistry would decrease the calcification necessary for building coral reef material. Increased warming would lead to coral bleaching, the breakdown in the symbiotic relationship between the coral animal and the unicellular algae (zooxanthellae) that live within coral tissues and allow corals to thrive in nutrient-poor waters and to secrete massive calcium carbonate accumulations. If sea levels were to rise at a pace faster than corals could build their reefs upward, eventually light conditions would be too low for the zooxanthellae to continue photosynthesis. On reefs near low-lying coastal areas, sea-level rise would likely increase coastal erosion rates, thus degrading water quality and reducing light penetration necessary for photosynthesis and increasing sedimentation that smothers and stresses coral animals. Losses of coral reefs would mean losses in the high biodiversity of these systems as well as the fisheries and recreational opportunities they provide.

About the Authors

Dr. Victor S. Kennedy
University of Maryland Center for Environmental Science

Dr. Kennedy is a marine ecologist who has spent over 30 years working as a research scientist on the ecology and physiology of aquatic animals. His early training included studying the effects of temperature on survival and physiology of estuarine species. His research in the 1960s helped convince the State of Maryland to revise its regulations governing discharge of heated water from power plants and other industrial facilities into Chesapeake Bay. Beginning in 1989, he used his experience with the effects of temperature on aquatic organisms to write papers and make presentations at scientific meetings on the possible effects of climate change. He is a co-author of the recent assessment for the mid-Atlantic coastal region that appeared in Climate Research and is the lead author of the Center's report, "Coastal and Marine Systems and Global Climate Change."

Dr. Kennedy is a Professor at the Horn Point Laboratory of the University of Maryland Center for Environmental Science, where he performs research, directs the Multiscale Experimental Ecosystem Research Center, and teaches graduate students. In addition to his research activities in Chesapeake Bay, he has worked as a marine ecologist in the coastal waters of New Zealand and in the coastal and offshore waters of Newfoundland, Canada. He has had extensive experience as a science editor, spending five years as the Editor of the Transactions of the American Fisheries Society, as well as editing or co-editing six technical books. He served as president of two scientific organizations.

Dr. Robert R. Twilley
University of Louisiana at Lafayette

Dr. Twilley is the Director for Ecology and Environmental Technology at the University of Louisiana at Lafayette. Dr. Twilley received his B.S. and M.S. (Biology) from East Carolina University, and his Ph.D. (Botany/Systems Ecology) from the University of Florida, after which he completed a postdoctoral fellowship in coastal oceanography at the University of Maryland. His research interests include ecosystem ecology, estuarine and coastal ecosystems; biogeochemistry of mangroves and tropical estuarine ecosystems; and ecosystem management and restoration of coastal regions. Among his various professional activities, Dr. Twilley currently serves on the editorial boards for Mangroves and Salt Marches and Environmental Science and Policy, and he previously served as a guest editor for Ecology and as an associate editor for Estuaries. Dr. Twilley is an active member in several professional societies including the Ecological Society of America, Estuarine Research Federation, Society of Wetland Science, and the American Association for the Advancement of Science. In addition to serving on the Board of Directors for the Society of Wetland Scientists (1993-97), Dr. Twilley has contributed to 71 publications and received a Distinguished Professor award for the 1999-00 academic year at the University of Louisiana at Lafayette.

Joan A. Kleypas
National Center for Atmospheric Research

Joan Kleypas specializes in examining how environmental factors control coral reef development at the global scale. She has a bachelor's degree in Marine Biology (Lamar Univ., Texas), and a master's in Marine Ecology (Univ. of South Carolina). She obtained a Ph.D. from James Cook University, as a Fulbright scholar to Australia, where she conducted a reef coring program to examine the causes for differences in coral reef development in the southern Great Barrier Reef. From there she moved to the National Center for Atmospheric Research (NCAR) Boulder, Colorado, to examine not only how climate affects coral reefs, but also how coral reefs affect climate. Much of this work entailed modeling reef response to sea level and temperature changes since the last ice age. She is currently involved with issues relating to the direct effects of increasing atmospheric CO2 on coral reefs; i.e., how CO2-induced changes in seawater chemistry affect the rates at which reef-building coral and algae secrete their calcium carbonate skeletons. She continues to work at NCAR as an Associate Scientist with Scott Doney, in the broad field of ocean biogeochemistry and its role in the global carbon cycle. Dr. Kleypas has also taught numerous courses in geology, oceanography, and global change as a visiting professor at Colorado College.

Dr. James H. Cowan, Jr.
Louisiana State University

James H. Cowan, Jr. is a Professor in the Department of Oceanography and Coastal Sciences and the Coastal Fisheries Institute at the Louisiana State University. He received B.Sc. (Biology) and M.Sc. (Biological Oceanography) degrees from Old Dominion University, and M.Sc. (Experimental Statistics) and Ph.D. (Marine Sciences) degrees from the Louisiana State University. Among many other professional activities, he has thrice served on National Research Council study committees and technical review panels concerning fisheries issues, has twice served on the Ocean Sciences Division, Biological Oceanography Review Panel for the National Science Foundation, and has served as a U.S. delegate both to the International Council for the Exploration of the Sea (ICES) and the Pacific Marine Sciences Organization (PICES). He currently is Chairman of the Reef Fish Stock Assessment Panel and a member of the Standing Scientific and Statistical Committee for the Gulf of Mexico Fishery Management Council. He has served as President of the Early Life History Section, and on the Outstanding Chapter Award and Distinguished Service Award committees for the American Fisheries Society. He has almost 20 years of experience conducting fisheries research in marine and estuarine ecosystems, has authored more than 75 refereed publications in the primary fisheries literature, served four years as an associate editor for Estuaries, the journal of the Estuarine Research Federation, for 6 years as an associate editor for Gulf of Mexico Science, and currently is an associate editor for Transactions of the American Fisheries Society.

Dr. Steven R. Hare
International Pacific Halibut Commission

Dr. Steven Hare is a quantitative biologist with the International Pacific Halibut Commission in Seattle, Washington. His principal duties are to assess the status of the Pacific halibut resource, determine a sustainable harvest level and conduct life history investigations. Dr. Hare obtained his B.S. in Engineering at the University of Michigan and both his M.S. and Ph.D. at the University of Washington in Fisheries Science. His main area of research is fisheries oceanography, in particular the organizing influence of climate on marine resources of the North Pacific. Dr. Hare is a co-discoverer, and was responsible for naming, the Pacific Decadal Oscillation, an important mode of Pacific climate variability. In his 20 years as a fisheries biologist, Dr. Hare has worked for the University of Washington and National Marine Fisheries Service. He has also spent considerable time working overseas with stints in Oman and Guinea-Bissau and a tour of duty in the Peace Corps in the Solomon Islands.