Exposure provides refuge from a rootless invasive macrophyte

Free-floating Utricularia inflata Walt. has the potential to alter native isoetid communities as it expands its range from the Atlantic coastal plain into northeastern New York lakes. This field study assessed (1) in situ growth potential for U. inflata at varying depths (1.0-3.0 m), (2) displacement of U. inflata from sites with different exposures to wind and water movement, and (3) U. inflata's relative abundance over a depth range (0.5 m, 1.0 m, 1.5 m, 2.0 m, and 2.5 m) at each of nine Adirondack Mountain lake sites varying in exposure. Plants grew well in shallow water (RGR: 0.014-0.039 day−1) at depths from 1.0 m to 2.5 m, but lost mass at 3.0 m. Significantly fewer U. inflata plants remained at sites and depths with greater exposure to wave action, as well as those with greater water current. Vegetation sampling confirmed greater relative frequency of U. inflata at sheltered sites and along deeper contours. Despite its potential to grow well in shallow water, water movement can prevent the accumulation of U. inflata there, and thus provide a refuge for native species able to withstand wave exposure.