Recurrent vernal presence of the toxic Alexandrium tamarense/Alexandrium fundyense (Dinoflagellata) species complex in Narragansett Bay, USA

• Alexandrium tamarense and Alexandrium fundyense from Narragansett Bay, RI, USA are identified via thecal plate morphology and molecular analysis.
• A suite of toxins (C1/2, B1 (GTX-5), STX, GTX-2/3. Neo, and GTX-1/4) are identified in both A. tamarense (6.31 fmol cell−1 STX equivalent) and A. fundyense (9.56 fmol cell−1 STX equivalent) isolated from Narragansett Bay.
• First report of regular appearance of the A. fundyense/A. tamarense species complex in Narragansett Bay.

The vernal occurrence of toxic dinoflagellates in the Alexandrium tamarense/Alexandrium fundyense species complex in an enclosed embayment of Narragansett Bay (Wickford Cove, Rhode Island) was documented during 2005 and 2009–2012. This is the first report of regular appearance of the Alexandrium fundyense/Alexandrium tamarense species complex in Narragansett Bay. Thecal plate analysis of clonal isolates using SEM revealed cells morphologically consistent with both Alexandrium tamarense Lebour (Balech) and Alexandrium fundyense Balech. Additionally, molecular analyses confirmed that the partial sequences for 18S through the D1–D2 region of 28S were consistent with the identity of the two Alexandrium species. Toxin analyses revealed the presence of a suite of toxins (C1/2, B1 (GTX-5), STX, GTX-2/3. Neo, and GTX-1/4) in both Alexandrium tamarense (6.31 fmol cell−1 STX equiv.) and Alexandrium fundyense (9.56 fmol cell−1 STX equiv.) isolated from Wickford Cove; the toxicity of a Narragansett Bay Alexandrium peruvianum isolate (1.79 fmol cell−1 STX equiv.) was also determined. Combined Alexandrium tamarense/Alexandrium fundyense abundance in Wickford Cove reached a peak abundance of 1280 cells L−1 (May of 2010), with the combined abundance routinely exceeding levels leading to shellfishing closures in other systems. The toxic Alexandrium tamarense/Alexandrium fundyense species complex appears to be a regular component of the lower Narragansett Bay phytoplankton community, either newly emergent or previously overlooked by extant monitoring programs.