Coastal Habitat Extent

The Coastal Habitat Extent indicator reflects progress on the Partnership’s efforts to protect the extent, or area, of coastal habitats for the Coastal Habitat Objective.

Coastal habitats are critical environments that provide essential ecosystem services, that benefit plants, animals, and humans around the Sound. The Partnership works hard to protect important coastal habitats within the Long Island Sound coastal boundary. However,  coastal habitats across the United States in general are being lost.

Two of the biggest causes of coastal habitat loss are:

• Development. Human development, including cities, homes, and factories built on and near coastal habitats, reduces the amount of coastal habitat and impacts coastal habitat health.
• Sea level rise. Rising sea levels flood coastal habitats with more saltwater than would otherwise occur naturally.

Tracking the extent of eelgrass and tidal wetlands, two of the 12 priority habitat types for the Partnership to protect and restore, gives insight on how two vulnerable yet critical coastal habitats are faring in the face of multiple stressors with restoration support from the Partnership.

Eelgrass Extent

Eelgrass (Zostera marina), a type of submerged aquatic plant, is the dominant seagrass species found in Long Island Sound. Eelgrass primarily grows in embayments that have specific water clarity, depth, substrate (like the sandy embayment floor), temperature, and salinity. Eelgrass meadows provide important ecosystem services that benefit plants, animals, and humans around the Sound, such as supporting biodiversity, improving water quality, and reducing wave energy.

The total acreage for eelgrass in the Sound for 2024 was 2,041 acres based on this 2024 eelgrass mapping report. From 2017 to 2024, eelgrass extent increased by 473 acres. Furthermore, a change analysis between 2017 and 2024 resulted in 1,057 acres of change between the two years, indicating the dynamic nature eelgrass abundance in eastern Long Island Sound over this time span (765 acre increase and a 292-acre decrease). The result of the change analysis is a net gain of 473 acres between the two years. Increases in the eelgrass extent can be attributed to improvements in water and sediment quality. As indicated by Save the Sound’s Unified Waters Study, water quality (e.g., water clarity, macroalgae abundance, etc.) has improved in areas where eelgrass is typically present (Stonington Harbor, Mystic Harbor, Alewife Cove, and Niantic River). On the other hand, eelgrass losses may be due to other water quality factors, such as warmer water temperatures. Some eelgrass meadows are experiencing annual die-offs earlier than usual. In the Niantic River, eelgrass meadows typically experience senescence, or die-off, in early fall after the field surveying occurs. However, in 2024, this die-off occurred in late August and therefore no eelgrass was observed during the field surveys in September. While this annual senescence is normal, losing eelgrass meadows earlier in the season can impact their services, such as, capturing suspended particles in the water column, nutrient recycling, and habitat provisioning for important fish species.

All surveys of eelgrass abundance focus on the Eastern Basin of Long Island Sound (east of the Connecticut River) since eelgrass experts believe that 95 percent of eelgrass beds occur in this portion of Long Island Sound.  While there are some small patches of eelgrass west of the Connecticut River, these beds do not contribute significantly to the total area. However, more reconnaissance of this area will be conducted during the summer of 2025.

The recent increase in eelgrass extent indicates that the Partnership is well positioned to achieve the goal stated in the Coastal Habitat Objective to restore 10 additional acres of eelgrass meadows by 2035. To continue restoring eelgrass beds, everyone dedicated to helping Long Island Sound’s eelgrass must collaborate to improve water quality and substrate issues in embayments. Learn more about the Eelgrass Management and Restoration Strategy and Partnership projects to protect eelgrass.

Tidal Wetlands

Tidal wetlands are transitional zones between the land and submerged systems. These areas are dominated by rooted plants that are flooded by the tide. Healthy tidal wetlands help trap sediments, store floodwater, and reduce wave energy during storms. Two-thirds of all marine species depend on tidal wetlands for a portion of their life cycle.

In 1995, the estimated acreage for tidal wetlands along the Sound’s shoreline was 20,895 acres (Bulletin No. 34: Tidal Marshes of Long Island Sound: Ecology, History and Restoration). A 2015 study of tidal wetlands from the 1880s to the 2000s indicated a 31 percent overall loss of tidal wetlands, with a 27 percent loss in Connecticut and a 48 percent loss in New York (Status and Trends of Wetlands in the Long Island Sound Area: 130 Year Assessment). The study cited a 2009 regional model which predicted a 20-45 percent loss in tidal wetland acreage over the current century. This loss can be attributed to a number of complex issues facing the tidal wetlands. Major stressors generally include excess nutrients, invasive species, sediment deprivation, hydraulic modification, pollution, sea level rise, and extreme weather events.

The Coastal Habitat Objective calls for the restoration of 250 additional acres of tidal wetlands by 2035. The Partnership plans to develop a method to measure tidal wetlands extent in Long Island Sound because understanding the extent of tidal wetlands informs the Partnership about the effectiveness of tidal wetlands restoration efforts.