Sea level rise in response to global warming is a major concern to all coastal wetlands and tidal flats. Current estimates predict sea levels to rise between 12 inches to 8 feet by 2100. Though estuaries are thought of as ephemeral, most present-day estuaries have been relatively stable for approximately 6,000 years. Past changes in sea level have greatly affected estuarine outlines and could have rapid and significant present-day effects. Rising sea levels could render intertidal flats into subtidal habitat and inundate adjoining mangrove and salt marsh areas, diminishing their protective and ecological benefits.
Much attention has been given to the effects of rising sea level on coastal ecosystems throughout the world. As intertidal communities, salt marshes and mangroves are at risk from both the amplitude and rate of this rise. For the ecosystems to thrive, they must occur at the appropriate elevation and slope. In fact, one of the most common reasons for restoration failure in salt marshes is choosing an improper site based on these parameters (Crewz & Lewis 1991). As sea level rises, it is possible for marshes and mangroves to shift in a landward direction if the rate of rise is slow enough for sediment accretion to occur (Montague & Wiegert 1990). However, coastal development and steep terrain may inhibit plant migration, changing zonation in these habitats or flooding them completely. In addition, compression of the intertidal zone can lead to increased interspecific competition and loss of biodiversity.
Surrounded by the Atlantic Ocean and Gulf of Mexico and also inundated by waters from the Everglades, low-lying Florida is particularly prone to climate change and rising sea levels. Further, most of Florida sits on porous bedrock, which allows for the infiltration of saltwater.
Rising sea levels can also erode beaches, submerge estuaries and low-lying wetlands, enhance coastal flooding and increase the salinity of estuaries.
Mangrove communities, occurring along the fringes of intertidal regions throughout most of the IRL, stabilize shorelines and also provide habitat and nursery area for IRL's many ecologically and recreationally important finfish and invertebrates. These mangrove communities have adapted to occupy and maintain their position along the fringes of the lagoon by accreting sediment at a rate in tune with sea level rise when it was occurring at a relatively slow pace. Accelerated sea level rise could pose threat to these vital communities by outpacing their ability to accumulate sediments at appropriate rates.
Seagrass beds are indispensible to the overall health and water quality of the IRL. They also provide sediment stabilization and complex habitat. In addition, seagrasses oxygenate the water column, provide substratum for epiphytes and are a food source utilized by manatees, urchins, conchs, some fish and sea turtles. Deeper waters associated with accelerated sea level rise could diminish sunlight levels and adversely impact the photosynthetic capacities of seagrasses leading to substantial decreases in seagrass acreage.
Larval stages of some estuarine invertebrate organisms have a narrow range of salinity tolerance. Increased salinity in the lagoon accompanying sea level rise could negatively impact their life histories with consequences affecting their abundance and diversity.
Threats to biodiversity: Sea level rise and warmer water temperatures could decrease the number of temperate species that co-occur in the IRL alongside subtropical species; invasive and other opportunistic organisms could more easily establish themselves under stressful conditions resulting from sea level rise, displacing native flora and fauna.
Wetlands and maritime hammocks are at risk of drowning and being inundated by salt water. These habitats have nowhere to retreat due to development along much of the lagoon’s shoreline. In the northern sections of the lagoon, losses of mud flats and salt marshes would impact the many bird, mammal and invertebrate species that live and feed there.
The ability of barrier islands and dune communities to buffer storm effects of wind and water would be compromised, directly affecting the region’s flora and fauna, but also its many humans and their infrastructure systems.