Eric Harmsen, Department of Agricultural and Biosystems Engineering, University of Puerto Rico
Azad Henareh Khalyani, Natural Resource Ecology Laboratory, Colorado State University
Eva Holupchinski, USDA Forest Service International Institute of Tropical Forestry
James P. Kossin, National Oceanic and Atmospheric Administration
Amanda J. Leinberger, Center for Climate Adaptation Science and Solutions, University of Arizona
Vanessa I. Marrero-Santiago, Department of Natural and Environmental Resources, Coastal Zone Management Program
Odalys Martínez-Sánchez, NOAA National Weather Service
Kathleen McGinley, USDA Forest Service International Institute of Tropical Forestry
Melissa Meléndez Oyola, University of New Hampshire
Pablo Méndez-Lázaro, University of Puerto Rico
Julio Morrell, University of Puerto Rico
Isabel K. Parés-Ramos, USDA Forest Service International Institute of Tropical Forestry
Roger Pulwarty, National Oceanic and Atmospheric Administration
William V. Sweet, NOAA National Ocean Service
Adam Terando, U.S. Geological Survey, Southeast Climate Adaptation Science Center
Sigfredo Torres-González, U.S. Geological Survey (Retired)
Jess K. Zimmerman, University of Puerto Rico
Mariano Argüelles, Puerto Rico Department of Agriculture
Gabriela Bernal-Vega, University of Puerto Rico
Roberto Moyano, Estudios Técnicos Inc.
Pedro Nieves, USVI Coastal Zone Management
Aurelio Mercado-Irizarry, University of Puerto Rico
Dominique Davíd-Chavez, Colorado State University
Rey Rodríguez, Puerto Rico Department of Agriculture
Allyza Lustig, Program Coordinator
Apurva Dave, International Coordinator and Senior Analyst
Christopher W. Avery, Senior Manager
<b>Gould, W.A., E.L. Díaz, (co-leads),</b> N.L. Álvarez-Berríos, F. Aponte-González, W. Archibald, J.H. Bowden, L. Carrubba, W. Crespo, S.J. Fain, G. González, A. Goulbourne, E. Harmsen, E. Holupchinski, A.H. Khalyani, J. Kossin, A.J. Leinberger, V.I. Marrero-Santiago, O. Martínez-Sánchez, K. McGinley, P. Méndez-Lázaro, J. Morell, M.M. Oyola, I.K. Parés-Ramos, R. Pulwarty, W.V. Sweet, A. Terando, and S. Torres-González, 2018: U.S. Caribbean. In <i>Impacts, Risks, and Adaptation in the United States: Fourth National Climate Assessment, Volume II</i> [Reidmiller, D.R., C.W. Avery, D.R. Easterling, K.E. Kunkel, K.L.M. Lewis, T.K. Maycock, and B.C. Stewart (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, pp. 809–871. doi: 10.7930/NCA4.2018.CH20
Marine ecological systems provide key ecosystem services such as commercial and recreational fisheries and coastal protection. These systems are threatened by changes in ocean surface temperature, ocean acidification, sea level rise, and changes in the frequency and intensity of storm events. Degradation of coral and other marine habitats can result in changes in the distribution of species that use these habitats and the loss of live coral cover, sponges, and other key species. These changes will likely disrupt valuable ecosystem services, producing subsequent effects on Caribbean island economies.
Linkage Between Climate Change and Regional Risks
Corals are a major component of the coastal protection, fisheries, and tourism economy of Caribbean islands. Key Message 3 discusses the importance of coastal systems to island economies and the potential effects of climate change on these economies. As in many tropical island systems, coral reefs anchor one end of the ridge-to-reef continuum—a concept that recognizes the linkage of social, ecological, terrestrial, and marine components associated with island systems (Ch. 27: Hawai‘i & Pacific Islands). Recognizing that the coral reef ecosystem includes mangrove and seagrass habitats, this section briefly discusses the role these habitats play in fisheries and the potential impacts climate change is likely to have on this role.
Ocean warming poses significant threats to the survival of coral species and may also cause shifts in associated habitats that compose the coral reef ecosystem (Ch. 9: Oceans, KM 1 and 3).35 The primary observable response to ocean warming is bleaching of adult coral colonies, wherein corals expel their symbiotic algae in response to stress. Severe, repeated, or prolonged periods of high temperatures leading to extended coral bleaching can result in colony death. Ocean warming can also harm hard corals that form coral reefs by decreasing successful sexual reproduction, causing abnormal development, impairing coral larvae’s attempts to attach to and grow on hard substrate, and affecting hard corals’ ability to create their calcium carbonate skeleton. Ocean warming also increases the susceptibility of corals to diseases and is expected to increase the impact of pathogens that cause disease.64 In 2005, a mass bleaching event, driven by 12 weeks of temperatures above the normal local seasonal maximum, affected the entire Caribbean region, resulting in the loss of 40%–80% of the coral cover in the region.65
Ocean acidification associated with rises in carbon dioxide (CO2) levels also is likely to diminish the structural integrity of coral habitats, affecting fisheries and other marine resources (Figure 20.9).35 One study concluded that calcification rates have decreased by about 15% based on examination of different species of calcification in planktonic foraminifera.66 Uncertainty remains about the magnitude of decreases in calcification on coral reefs and some crustaceans and mollusks (such as queen conch). However, a small decline in calcification rates has the potential to alter the growth–erosion balance of reefs if the erosion of the hard structure of reefs becomes more frequent.67 Ocean acidification effects could be further exacerbated by local processes in coastal zones, such as land-based transport of nutrients to nearshore waters.
Figure 20.9: Climate Change Effects on Coral Reefs
Figure 20.9: The diagram demonstrates how coral reef ecosystems in the U.S. Caribbean are likely to change in potentially warmer and more acidic waters caused by climate change, including elevated sea surface temperatures and elevated carbon dioxide (CO2) levels. The severity of these impacts increases as CO2 levels and sea surface temperatures rise. If conditions stabilized with concentrations of atmospheric CO2 at 380 ppm (parts per million), coral would continue to be carbonate accreting, meaning reefs would still form and have corals. At 450–500 ppm, reef erosion could exceed calcification, meaning that reef structure is likely to erode and coral cover is likely to decline dramatically. Beyond 500 ppm, corals are not expected to survive.77 Sources: NOAA and USFS.
The compounded risk of climate change with human-caused stressors increases vulnerability and accelerates habitat loss and degradation.68 Where fringing (nearshore) and barrier reef systems have eroded, mangroves and seagrass may also decline due to the loss of protection from wave action afforded by reefs. The potential decline in seagrass and mangrove habitats would be compounded by the effects of coastal and in-water development on these habitats and on coral reefs, resulting in overall declines in nursery habitat for important fishery species like spiny lobster, queen conch, snappers, and groupers. The impacts of climate change, in general, on seagrass in the Caribbean is uncertain, but some studies suggest that photosynthesis could be inhibited at high temperatures.69 Sea level rise may lead to a reduction in the area occupied by seagrass if waters become too deep for the plants to obtain enough light to photosynthesize. Sea level rise is also projected to result in a loss of mangrove habitat if low-lying coastal areas are not present or have already been developed on islands such that mangroves cannot colonize these areas as coastal waters get deeper.70 Additionally, increases in the magnitude and frequency of storms result in impacts caused not only by waves and surge but also by increased rainfall and the associated transport of sediment and other land-based pollutants into nearshore waters. Mangrove and seagrass habitats filter storm water runoff, but large volumes of sediment transported downstream can overwhelm these systems, leading to burial of seagrass beds and partial burial of mangrove roots, thus affecting the ability of these habitats to reduce pollutant transport to coral reefs.
Caribbean reefs have experienced declines in important fishery species—such as the Caribbean spiny lobster and queen conch; predatory species, such as snappers and groupers; and important herbivores, like parrotfish—due to overexploitation.71,72 Overexploitation is demonstrated by the exceedance of commercial annual catch limits (established by the Caribbean Fishery Management Council to protect depleted stocks) in 2013 in Puerto Rico and the USVI and in 2014 in Puerto Rico, leading to the establishment of additional regulatory measures.73 In terms of annual economies, commercial fishing of reef fish provides an average of $9 million to Puerto Rico, $2.4 million to St. Thomas and St. John, and $3 million to St. Croix (in 2014 dollars).73
Studies show that major shifts in fisheries distribution, coupled with structural and compositional changes in marine habitats such as coral reefs due to climate change, adversely affect food security, shoreline protection, and economies throughout the Caribbean.5,69,74,75,76 In the U.S. Caribbean region, where fishery resources are shared with other Caribbean islands, competition for fisheries resources are likely to increase as stock distribution changes due to climate change (Ch. 16: International, KM 4). Figure 20.10 shows the connections between climate change, marine habitats and species, and human communities. In the case of Puerto Rico, the coral reef ecosystems off the east coast of the main island (Fajardo area) and the islands of Culebra and Vieques were estimated as generating $192 million per year for recreation and tourism and $1 million in coastal protection services annually (in 2007 dollars, or $217 million and $1 million in 2015 dollars, respectively).68 For the territory of USVI, reef-related tourism was estimated as generating $96 million per year, and coastal protection was estimated as providing $6 million annually to the local economy (in 2007 dollars, or $108 million and $7 million in 2015 dollars, respectively).68
Figure 20.10: Climate Change Impacts on Coral Reef Ecosystems and Societal Implications
Figure 20.10: The figure shows the connections between climate-related impacts (ocean acidification and warming as well as severe storms), responses of marine habitats and species to these impacts, and, ultimately, the effects to ecosystem services (such as fisheries and shoreline protection) and, in turn, the human community. Specifically, the figure depicts how degradation of coral reefs due to climate change is expected to affect fisheries and the economies that depend on them as habitat is lost. The figure also shows how reef degradation decreases shoreline protection for local communities, which affects the economy and human populations more generally. Source: adapted from Pendleton et al. 2016.78. Photo credits: NOAA.
With high levels of greenhouse gas emissions (in other words, business as usual), mass coral bleaching in the Caribbean may occur at least twice a year within the next decade.79 The increasing frequency of extreme heat events is highly likely to preclude reef recovery, considering that the region’s reefs have yet to fully recover from the 2005 event. Moreover, the increase in average temperature will make corals more susceptible to extreme heat events and to coral disease, further contributing to declines in live coral cover in marine habitats.64 One study suggests that coral reefs in Puerto Rico are expected to pass a critical ecosystem threshold in the first several decades of the century with coral cover loss of 95% by 2090 under a higher scenario (RCP8.5).80
Sea level rise is another climate-related stressor in the Caribbean. The rate of sea level rise in the region is expected to follow or exceed global projections. Sea level rise will likely have effects not only on marine communities by diminishing the amount of sunlight they receive but also on low-lying cays, which provide important habitat for seabirds and sea turtles. Coastlines on the larger islands and mainlands of the U.S. Caribbean will be submerged or greatly reduced in extent as sea levels rise. Coastal mangroves, squeezed between rising seas and coastal development, may be reduced in extent, diminishing the natural protection they provide against the action of waves and storm surge and limiting their role as wildlife habitat. Sea level rise is also expected to lead to a loss of seagrass if waters become too deep for them to photosynthesize. Photosynthesis will also be inhibited as sea surface temperatures continue to rise, which is likely to affect both seagrass and mangroves in addition to corals, as noted above.
The combined stress of sea level rise, increases in sea surface temperatures, and ocean acidification, along with increases in the severity and frequency of storms and associated transport of land-based pollutants into coastal and marine habitats, will likely lead to loss and degradation of these habitats. Future climate change effects on marine habitats will likely impact island economies due to changes in the availability of key fishery species such as queen conch, Caribbean spiny lobster, and species in the snapper and grouper complexes; declines in natural shoreline protection and associated impacts to coastal infrastructure and communities, as well as wildlife habitat; and loss of tourism associated with habitats such as coral reefs. Fisheries productivity is projected to decline while catch-per-unit effort increases as fishers travel longer distances and spend more time on the water.75 Potential losses of up to 90% of the coral reef recreation value in Puerto Rico are projected under most scenarios considered by the end of the century, due to the expected loss of coral reef habitat associated with climate change impacts.80
Challenges, Opportunities, and Success Stories for Reducing Risk
Climate change directly influences marine species’ physiology, behavior, growth, reproductive capacity, mortality, and distribution, while indirectly influencing marine ecosystem productivity, structure, and composition.74 As a result, fishery resources and essential habitats for commercially, recreationally, and ecologically important species are likely to be less resilient.
Several strategies meant to increase ecosystem resilience to local stressors (such as declines in water quality, overexploitation of fisheries, recreational use, and coastal and marine development) are being implemented in the Caribbean to lessen the potential impacts of climate change on marine resources. One such strategy is the establishment of protected areas in coastal and marine areas. Management of these areas may include limiting or prohibiting extractive uses, implementing conservation and restoration of coastal and marine habitats, and designating usage zones to minimize the impacts of recreational use on ecosystems. Another strategy is watershed planning to minimize the transport of land-based pollutants to nearshore waters, thus protecting marine habitats from declines in water quality caused by influxes of sediment, nutrients, and other contaminants. The NOAA Coral Reef Conservation Program, in partnership with federal and local agencies and local nongovernmental organizations, has sponsored the development and implementation of several watershed management plans in Puerto Rico and the USVI.81
Coral Farming Can Increase the Extent and Diversity of Coral Reefs
Figure 20.11: Examples of coral farming in the U.S. Caribbean and Florida demonstrate different types of …
Building the resilience of marine organisms, such as corals, is another strategy aimed at lessening the potential impacts of climate change on the marine ecosystem. Coral population enhancement through propagation (or coral farming) is a strategy meant to improve the reef community and ecosystem function, including for fish species that use this ecosystem (Figure 20.11). The selection and propagation of fragments and samples from coral colonies that have survived stressors such as bleaching events are emphasized as part of these efforts in an attempt to accelerate the otherwise uncertain recovery of these species.82 This strategy has been used in the U.S. Caribbean and South Florida to recover species such as elkhorn and staghorn corals and species from the star coral complex—all of which are listed as threatened under the Endangered Species Act—without negatively affecting native populations of corals.
Integrating international monitoring networks of marine species and environmental conditions is critical to understanding the status and trends of wide-ranging marine resources. Areas like the Caribbean and the Pacific (Ch. 27: Hawai‘i & Pacific Islands), where marine resources are key to socioeconomic well-being, benefit from monitoring programs that assess threats to reef health, ecosystem services, and reef-dependent communities. Research into the linkages between climate change and marine ecosystems is critical to enhancing the ability to predict future ecosystem responses to climate change and the associated socioeconomic consequences, as well as finding ways to mitigate those consequences.