Recovery of native zooplankton associated with increased mortality of an invasive mussel

• Published in: Ecosphere (Washington, D.C) D.C), 2010-07, Vol.1 (1), p.art3-10
• Main Authors: PACE, M. L, STRAYER, D. L, FISCHER, D, MALCOM, H. M
• Format: Article
• Language: English
• Subjects: alien species; Biogeochemistry; Biomass; Dreissena polymorpha; Ecosystems; Estuaries; Hudson River; invasion; long-term studies; Mollusks; Mortality; Phytoplankton; Plankton; population size structure; River ecology; Rivers; Sediments; Studies; zebra mussels; Zooplankton
• ISSN: 2150-8925; 2150-8925
• DOI: 10.1890/ES10-00002.1

Impacts of alien species may change with time but there are few long-term studies of invasions. Here, we present an example of a substantial change in the impact of an alien species that appeared more than a decade after initial invasion. We studied an invasion of zebra mussels ( Dreissena polymorpha ) into the Hudson River (New York, USA) over a 22 year period (1987-2008) including five years of pre-invasion observations. Zebra mussels caused a substantial and sustained decline in phytoplankton, and until recently, zooplankton. However from 2005-2008, the abundance of copepods, copepod nauplii, and rotifers recovered while tintinnid ciliates partially recovered. These changes are consistent with an increased mortality of larger (> 20 mm) zebra mussels that has altered the filter-feeding impact of the population. Large mussels had a threshold relationship with the abundance of nauplii, rotifers, and zebra mussel veligers suppressing these microzooplankton when filtration by large mussels was > 0.5 m 3 m −2 d −1 . Zooplankton biomass declined approximately 50% after the zebra mussel invasion but has recovered to pre-invasion levels. Overall, while zebra mussels are still present and abundant in the Hudson River, their impact on zooplankton has significantly diminished.