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Ecological Functions of Submersed Plant Beds

Lead Scientist(s): Dr. Stuart E.G. Findlay, David Fischer, Dr. David L. Strayer

It has become apparent that these beds of submersed aquatic vegetation ("SAV") may play important roles in the river's ecosystem. A team of scientists (Stuart Findlay and Dave Strayer at Cary; Eugenia Barnaba, Susan Hoskins, Mark Bain, and Geof Eckerlin at Cornell University, Betsy Blair and Chuck Nieder at the New York State Department of Environmental Conservation) is now engaged in an intensive effort to map the extent and composition of the SAV beds and assess their ecological functions.

About 13% of the area of the freshwater tidal Hudson River is occupied by rooted vegetation. Beds of the native Vallisneria americana (mixed with small amounts of other submersed species) cover 3/4 of this area and beds of the alien water-chestnut (Trapa natans) cover the remaining 1/4. These plant beds are choice habitats for invertebrates. Invertebrate densities rise with increasing plant cover (see figure), and are much higher among plants than on unvegetated sediments. Many kinds of invertebrates (damselflies, the cladoceran Sida crystallina, several kinds of snails, many kinds of chironomid midges) live only among plants. Very different invertebrates live in the native Vallisneria than in the alien Trapa (Strayer et al. Freshwater Biology 48:1938-1949). When the alien zebra mussel recently invaded the Hudson River and destroyed much of the planktonic food web, the plant beds apparently increased in importance, buffering the ecosystem from the full effects of this invader.