Effects of thermal input and climate change on growth of Ascophyllum nodosum (Fucales, Phaeophyceae) in eastern Long Island Sound (USA)

Growth of Ascophyllum nodosum (L.) Le Jolis was monitored monthly from 1979 to 2002 at four locations in eastern Long Island Sound near Millstone Power Station (MPS), Waterford, Connecticut, USA. At the two sites unaffected by the MPS thermal discharge, annual growth estimates were positively correlated with mean annual ambient seawater temperatures, which increased by approximately 1 °C during the 24-y study period. This increase was most pronounced during the first quarter of the year (Jan.–Mar.), when a temperature rise of 1.6 °C was observed. In the MPS thermal plume area, enhanced Ascophyllum growth related to thermal input was observed until temperatures reached 25 °C. Above 25 °C, growth rates decreased rapidly, and mortality was observed as temperatures exceeded 27–28 °C. At present, peak ambient seawater temperatures in eastern Long Island Sound reach 22–23 °C. Research on climate change suggests that seawater temperatures in the North Atlantic Ocean could increase by an additional 3 °C during the 21st century. This level of warming could lead to demise of Ascophyllum populations in Long Island Sound, which is currently the southern distributional limit for this species in the western Atlantic Ocean. Loss of Ascophyllum, a major primary producer and habitat former, would significantly impact the Long Island Sound coastal ecosystem.