Impacts of the cryptic macroalgal invader, Nitellopsis obtusa, on macrophyte communities

Early detection of aquatic invasive species, such as Nitellopsis obtusa, is often critical to reduce their longterm negative effects. This macroalga resembles native taxa and can invade deep locations in littoral zones of lakes in North America. Studies in which effects of Nitellopsis on macrophyte communities were quantified are rare. We surveyed 4 lakes in central New York where Nitellopsis is present to document whether macrophyte communities are negatively affected by this invasive macroalgae and to test whether Nitellopsis was found more frequently in deeper-than in shallow -water habitats. We found lower macrophyte species richness when Nitellopsis was abundant. This pattern was consistent at 3 water depths (shallow [>1 m], intermediate [1-2 m], and deep [>2 m]). Macrophyte biomasses (total, including native and other nonnative species, and only native species) were significantly lower in quadrats with greater abundance of Nitellopsis. Nitellopsis biomass exceeded the combined biomass of macrophytes in some lakes. Nitellopsis was present more frequently in deeper than in shallow water in 2 of the study lakes. Our results suggest that Nitellopsis can have negative effects on macrophyte communities and indicate that this taxon can become dominant in littoral zones of invaded lakes. It is more likely to be present in deeper water, which may prevent casual observation, so personnel responsible for monitoring programs should establish protocols and methods tailored to detect this spreading, cryptic invasive species.