Long Island Sound ecosystem

• Category: Marine and Oceanic Biomes.
• Geographic Location: North America.
• Summary: This estuary has a rich and constantly changing environment; it is under constant pressure from a high volume of human inputs.

Long Island Sound ecosystem is an estuary located on the northeast coast of the United States, where the states of Connecticut and New York meet the North Atlantic Ocean. The watershed of Long Island Sound includes nearly all of Connecticut and western Massachusetts, large parts of Vermont, New Hampshire, and Rhode Island, and a small area of New York state. Here, saltwater from the Atlantic Ocean mixes with freshwater from the Connecticut, Thames, Housatonic, and a few smaller rivers. As these waters meet and mix, varying salinity levels are created, resulting in a wide range of flora and fauna that thrive in the resulting marine and shoreline environments.

The sound supports a great spread of tidal marshes and wetlands, which play a significant role in the ecosystem, supporting both open-water and seafloor communities. The sound also supports a very large human population. In 2024, about 25 million people live within 50 miles of Long Island Sound, and about 9 million people live in its watershed. The Long Island Sound region is one of the most densely populated areas in the United States, which is why it is occasionally referred to as the Urban Sea. The heavy use of the sound and nearby coastal lands by humans for industrial, agricultural, municipal, commercial, and recreational activities has unfortunately resulted in significant levels of pollution. Both the federal government and local agencies are taking steps to reduce environmental threats and preserve the sound’s ecosystem. In 2022, areas along the Connecticut coast became a National Estuarine Research Reserve.

Long Island Sound is approximately 110 miles (177 kilometers) long and up to 21 miles (34 kilometers) wide, covering about 1,300 square miles (3,370 square kilometers). The sound has almost 600 miles (965 kilometers) of total coastline with over sixty coastal embayments. Its average depth is betwen 65 and 79 feet (20 and 24 meters), and it is 300 feet (91 meters) at its deepest point. The sound’s orientation is unique, as most estuaries along the east coast of North America have a north-south orientation, but Long Island Sound has an east-west configuration.

The eastern portion of the sound has higher saline levels than the western portion, as it is closer to the Atlantic Ocean, but, in general, salinity levels range between twenty-seven and thirty-two parts per thousand. Tides play a very important role in the sound’s ecosystem, as the incoming marine tides carry plant nutrients into the marshes to feed their inhabitants, and the outgoing tides carry excess nutrients back into the estuary. Average temperatures in the sound are about 69 degrees F (21 degrees C) in the summer and 37 degrees F (3 degrees Celsius) in the winter.

Biota

Organisms that live in the Long Island Sound biome have had to develop the ability to adapt to a rapidly changing environment, as this body of water has several ecological factors constantly in flux. The sound experiences dramatic changes in temperature from season to season. During the winter months, the temperature often drops below freezing, and in the summer it can be extremely hot. Salinity levels also experience periodic flux due to the strong tides. The biota, or all the plant and animal life of a particular region, of the intertidal zone has had to adapt for the particularly harsh contrasts in the sound. The sound is nevertheless home to more than 100 species of plants, 1,200 species of invertebrates, and 170 species of fish.

In general, coastal salt marshes are known as high-productivity environments due to the strong base of plant life within the favorable habitat of such marshes. Long Island Sound has three categories of plants: algae/phytoplankton, seaweeds, and vascular plants. Saltmarsh plants such as saltwater cordgrass grow along ditches, or slat pans, and on the seaside edges of marshes where high tides inundate daily.

Salt meadow cordgrass and amulet spikegrass grow in areas less frequently inundated by saltwater, typically closer to higher, drier land. These plants help stabilize shifting sands on beaches. Other plants found in these areas are sea lavender, saltmarsh aster, and seaside gerardia. In areas where the brackish water is more diluted with freshwater from rivers, cattail marshes replace saltmarshes. Various types of grasses, including wild rice and sedges, are found here. Eelgrass is typically found in protected bays, coves and other areas of brackish water.

All of these plants provide shelter to the mollusks, crustaceans, and other fauna breeding, hatching, feeding, and maturing here. Even as the plants decompose, the result is a rich organic soup that feeds the shellfish and smaller finfish that live within the marshes. The marshes host many types of snails, mussels, fiddler crabs, and species of minnows. Found on the sound proper’s seafloor are shrimp; multiple species of crabs; lobsters; and benthic fish species such as flounders, skates, and monkfish. These crustaceans and smaller fish act as food for the larger fish that live within the open-water community, such as bluefish and dogfish, as well as migratory types such as striped bass, Atlantic salmon, eels, and turtles. At least 50 species of fish spawn here.

Throughout the year, the sound hosts more than 280 species of migratory birds that take advantage of the shellfish and smaller fish populations, including gulls, herons, egrets, and other waterfowl and shorebirds. Long Island Sound also has a harbor-seal population and is occasionally visited by whales, porpoises, and dolphins.

Human Impact

The Long Island Sound ecosystem supports the third-largest lobster fishery in the United States; oysters, clams, mussels, and many of the larger fish species are harvested by humans as well. At the same time, the sound has more than forty sewage-treatment plants that empty about 1 billion gallons (3.8 billion liters) of treated sewage into its waters every day. Unfortunately, this activity has resulted in high levels of pollution, which has not only contaminated organisms that live in the sound, but also greatly depleted oxygen levels in its waters. The low oxygen levels have sometimes resulted in mass lobster and fish casualties, with one of the largest die-offs occurring in 1999.

Fortunately, in 1987, the Clean Water Act created the National Estuary Program, which eventually led Congress to pass the Long Island Sound Restoration Act of 2000. Millions of dollars per year are being used to clean up the sound and save the plant, animal, and human populations that depend on the sound to survive. The portion of the sound that is considered a "dead zone" due to low oxygen has decreased from a total area of 200 square miles in 1997 to ninety-five square miles in 2017, in part due to a 61 percent decrease in nitrogen released into the sound between 2001 and 2017. Efforts to further reduce nitrogen continue to take place in the twenty-first century. In 2024, scientists from the Long Island Sound Study (LISS) report the third-smallest area of hypoxia, zones with low dissolved oxygen, since monitoring efforts began in 1987. During the annual summer hypoxia monitoring season, the affected area measured 43.4 square miles, roughly the size of the Bronx. While this is an encouraging statistic, scientists associated with the study want to continue to raise "awareness of hypoxia and other nutrient-related issues in the Sound. While substantial progress has been made in reducing hypoxia in recent decades, there’s more work to do."

Studies are being carried out and data is being collected on the potential effects of climate change for this biome into the twenty-first century. As yet, scientists feel a higher level of confidence in observed and predicted changes in global average temperature, while sea-level rise projections are more uncertain. Observations indicate that global sea-level rise is occurring and will continue to occur; indeed, the impact in the Long Island Sound biome is expected to occur faster than the global average. However, the magnitude of impact on coastal areas is complex, and will depend on rates of Arctic ice sheet melt, changes in ocean circulation due to additional freshwater inflow from melting ice, accompanying temperature fluctuations, altered salinity differentials, and naturally-cyclic climate patterns. Global warming may cause significant changes in Long Island Sound, primarily through rising water temperatures, sea level rise, and ocean acidification. These changes would impact marine life by favoring warm-water species, displacing cold-water species like lobsters, and potentially affecting shellfish populations due to decreased pH levels, leading to changes in fish distribution and a potential decline in biodiversity within the sound.

Bibliography

Andersen, Tom. This Fine Piece of Water: An Environmental History of Long Island Sound. Yale University Press, 2002.

Dreyer, Glenn D. and William A. Niering, eds. Tidal Marshes of Long Island Sound: Ecology, History and Restoration. Connecticut College Arboretum, 1995.

Grondalski, Anya. "Long Island Sound Records Third Smallest 'Dead Zone' Since Monitoring Begain in 1987." Long Island Sound Study, 21 Oct. 2024, longislandsoundstudy.net/2024/10/third-smallest-dead-zone-long-island-sound/. Accessed 27 Dec. 2024.

Kaufmann, Carol. "Where Rivers Meet the Sea." Pew Trusts, 27 May 2022, https://www.pewtrusts.org/en/trust/archive/spring-2022/where-rivers-meet-the-sea. Accessed 24 Aug. 2022.

Murphy, Jarrett. "Defenders of Long Island Sound Hail Its Recovery, Push for More Progress." CityLimits.org, 15 Nov. 2017, citylimits.org/2017/11/15/defenders-of-long-island-sound-hail-its-recovery-push-for-more-progress/. Accessed 27 July 2018.

"Population Within 50-Mile Buffer of Long Island Sound." Long Island Sound Study, longislandsoundstudy.net/ecosystem-target-indicators/population-within-50-mile-buffer-of-long-island-sound/#:~:text=The%20Long%20Island%20Sound%20region,within%20the%2050%2Dmile%20radius. Acessed 27 Dec. 2024.

"Respect Wildlife While Boating." Connecticut Department of Energy & Environmental Protection, portal.ct.gov/deep/boating/clean-marina/respect-wildlife#:~:text=Long%20Island%20Sound%20is%20home,marine%20mammals%20and%20sea%20turtles. Accessed 27 Dec. 2024.

Wahle, Lisa, and Nancy Balcom. Living Treasures: The Plants and Animals of Long Island Sound, 4th ed., Connecticut Sea Grant College Program, 2020.

Weigold, Marilyn E. The Long Island Sound: A History of Its People, Places, and Environment. New York University Press, 2004.