Saxitoxin exposure in an endangered fish: association of a shortnose sturgeon mortality event with a harmful algal bloom

Abstract

Saxitoxin (STX)-producing blooms of the toxic dinoflagellate genus Alexandrium have been responsible for devastating ecosystem-wide impacts in coastal waters of the northeastern USA. In the summer of 2009, a severe Alexandrium bloom in New England coastal waters cooccurred with a shortnose sturgeon Acipenser brevirostrum mortality event in Sagadahoc Bay, Maine, USA. Thirteen individuals of this endangered fish species were found dead on 10 July 2009, and this die-off was associated with extremely high Alexandrium cell densities, recordbreaking toxin burdens (> 80 000 ng g -1 ) in shellfish, and closures of shellfish beds affecting nearly the entire Maine coastline. STX-like activity was detected in sturgeon (n = 3) stomach contents and liver and gill tissues via neuroblastoma assay and receptor-binding assay at con centrations ranging between 37 and 2300 ng STX-eq. g -1 (STX equivalents per gram sample). Stomach content analyses of the 3 necropsied sturgeon carcasses showed a large number of amethyst gem clams Gemma gemma. Liquid chromatography-mass spectrometry confirmed the presence of STX and related congeners in sturgeon stomach contents, at concentrations between 311 and 743 ng g -1 . The present study marks the first reported detection of STXs in shortnose sturgeon, and provides evidence of trophic transfer of Alexandrium toxins as a potential cause of mortality in this event, as well as a threat to the health of this endangered population of fish.