~ Sea Level Rise

Warming air and oceans cause rising sea levels due to melting glaciers and ice sheets, and increased heat uptake and thermal expansion of the oceans. Although on average the coasts of the United States have experienced approximately eight inches of sea level rise since the late 1800s, rates vary throughout the country based on topography and land subsidence and uplift (Walsh et al. 2014). Global sea levels are projected to continue rising from one to four feet by 2100 under a high-emissions scenario, and the rate of rise is expected to be faster than previously observed (Church et al. 2013). The Northeast has experienced higher rates of sea level rise than the global average over the past decades, which has led to greater coastal flooding (Horton et al. 2014).

Certain areas are more vulnerable to sea level rise because of human activities and geologic features. Land subsidence driven by groundwater withdrawals has caused the Chesapeake Bay region to experience the highest rate of sea level rise along the Atlantic Coast over the last few decades (Eggleston and Pope 2013). Over the next century, the Gulf Coast will be one of the regions most affected by rising seas due to its flat topography, subsidence rates, and shoreline urban development and with sea level rise projections as high as 20 inches (Twilley et al. 2001; Needham et al. 2012; Anderson et al. 2013). Louisiana, for instance, has been experiencing an average sea level rise rate of 0.36 inches per year, five times greater than the global average (Needham et al. 2012). Along California’s coastline, sea level rise combined with the high tides and large waves associated with large ENSO events is expected to cause the most damage through 2050 (Caldwell et al. 2013).

Rising sea level is likely to lead to changes in important habitat for fish and shellfish at various life stages (Ning et al. 2003; Daw et al. 2009; Najjar et al. 2010). Although in certain areas, such as the Gulf of Mexico, coastal inundation could initially increase coastal habitat and nursery areas (Anderson et al. 2014), sea level rise is also likely to lead to flooding, saltwater intrusion, and degradation of key breeding nursery ecosystems, such as coral reefs, mangroves, estuaries, and tidal marshes (Twilley et al. 2001; Daw et al. 2009; Najjar et al. 2010). For example, Alaskan salmon are likely to experience decreased freshwater habitat availability because of sea level rise (Johnson 2012; Chapin et al. 2014), and Atlantic and Gulf of Mexico brown (F. aztecus) and white shrimp (L. setiferus) are expected to lose critical estuarine nursery habitat from rising sea levels (Ning et al. 2003). Mangroves and seagrass habitats in the Pacific Islands that are used as key nursery and foraging habitat may also be susceptible to loss (Keener et al. 2012; Leong et al. 2014).

While it is possible for some coastal ecosystems (e.g., mangroves and marshes) to retreat landward, existing coastal infrastructure and rapid rates of rise, which may be faster than the rate at which plant species can adapt and colonize new environments, are likely to limit the ability of these ecosystems to adapt and shift landward (e.g., Twilley et al. 2001; Roessig et al. 2004; Keener et al. 2012). For example, in Northern California, Washington, and Oregon, marshes, beaches, and tidal flats that are unable to migrate inland will cause the loss of suitable habitat for finfish spawning and rearing (Glick et al. 2007); the same is true for tidal flats, wetlands, and estuaries along the Gulf Coast upon which finfish and crustacean species rely (Ning et al. 2003; Carter et al. 2014).

Additionally, rising sea levels may damage coastal and fisheries infrastructure, such as ports and fishing piers (Daw et al. 2009). Fishing communities – particularly subsistence and traditional fishing communities that are used to fishing close to home and may be less able to adapt to changing environments and potential infrastructure damages – will be economically vulnerable to rising sea levels and associated ecosystem and fisheries changes. Aquaculture operators may experience potential declines in farmed species due to inundation of coastal facilities (Anderson et al. 2013); in the Gulf of Mexico, aquaculture of small bait, food fish, and shellfish (e.g., shrimp, oysters, crawfish) is a valuable regional industry (Twilley et al. 2001) and will be vulnerable to inundation caused by sea level rise.

Table 5. Potential impacts of sea level rise on fisheries.

Observed Changes

  • Rising sea level due to melting glaciers, ice sheets, and thermal expansion of ocean
  • In United States, observed average sea level rise of ~8 inches since the late 1800s
  • Sea level rise rates faster in some regions of the country than others (e.g., Chesapeake Bay, Gulf Coast) due to flat topography and land subsidence

Projected Future Changes

  • Projected continued increase of 1 to 4 ft. by 2100 and at a faster rate than previously
  • 21st century rate of sea level rise likely to exceed rates observed to date due to continued warming and melting
  • Increased rates of sea level rise in Gulf Coast due to flat topography, shoreline subsidence, and shoreline development

Potential Impacts on Fisheries

  • Degradation of key fish and shellfish habitat (e.g., tidal marshes, mangroves, coral reefs, submerged vegetation)
  • Flooding and habitat degradation will decrease nursery habitat for fisheries
  • Increased economic vulnerability of fisheries-dependent communities (subsistence, traditional fisheries) due to damage to or disturbance of infrastructure and operations

Key Compounding Factors & Impacts

  • Natural climate variability: Studies suggest that the most damage to the California coast through 2050 will occur when rising sea levels combine with the high tides and large waves associated with large ENSO events.
  • Land subsidence: Sea level rise and land subsidence are occurring simultaneously in different areas of the United States (e.g., Maryland, Gulf Coast).