Waldman: Overview

Long Island Sound – An Ever-Evolving Ecosystem

John Waldman, Queens College, NY

Long Island Sound is a water body created recently in geological time, the product of glaciers that began their retreat approximately 15,000 years ago. It mixes with fresh waters, principally the Connecticut River, and has salinities that are on the high end for an estuary. Seasonal temperature swings of LIS are pronounced, with summer heat leading to stratification and hypoxia in its western end. Seasonal temperature changes also help drive seasonal changes in its fish community, considered a key component of the Sound’s “Restaurant for Birds.” Fish are most biodiverse and abundant in September and least so in late winter. Temperatures of LIS have been increasing at the fast rate of approximately 0.85F per decade. Changing temperatures have led to long-term changes in its ichthyofauna. Species that are rarely or no longer seen are primarily cold-water forms such as Atlantic tomcod, silver hake, squirrel hake, Atlantic mackerel, and winter flounder. Warm-water fishes that were once rare or absent include bluefish (adults), summer flounder, common searobin, and skittlefish; warm-water species that increased dramatically in abundance include scup (porgy) and black sea bass. A critical nexus exists between fish and seabirds in LIS. This includes predation by raptors such as Bald Eagles and Osprey, gulls and terns of various species, wading birds such as herons and egrets, and Double-crested Cormorants. Cormorant predation may be responsible for the great reduction of slow-swimming cunner in LIS. Menhaden, a herring species is a key species at the base of the Sound’s fish-birds food chain. One proactive measure that can provide more of herring species (alewife and blueback herring) for birds is dam removals on the fish’s spawning rivers. The future of LIS will likely include increased stratification from warming and a loss of salt marshes as a result of sea-level rise. It is also likely that both the restaurant menu (fishes) and the restaurant patrons (birds) will change due to rising temperatures, resulting in novel biotic communities for LIS. 

Note the extreme seasonal water temperature cycles in LIS, from the coldest weeks of early February to the warmest weeks around August 1st. 

These extreme water temperature cycles drive most of the fish diversity, occurrence and abundance in LIS. 

This is a photo of Northern Gannets plunge-diving into the water to catch fish.