Saxitoxin δ 15N as a species-specific tracer of the source of nitrogen used by the toxin-producing dinoflagellate Alexandrium tamarense

Abstract

Alexandrium tamarense Balech is a harmful, bloom-forming dinoflagellate which can produce saxitoxins (STXs), a suite of powerful neurotoxins that bioaccumulate up the food chain and can have severe economic and health impacts. Being nitrogen-rich, STX is ideal for studying the relationship between its producer and the nitrogen used for growth. In this study, we measured the δ 15N of medium nitrate, algal cells and toxin in batch cultures of A. tamarense. In nitrate-replete conditions, cells were 1.5 depleted relative to the source, and STX was 1.5 depleted relative to the cells. In nitrogen-limiting cultures the isotopic difference between cells and STX changed as nitrate in the growth medium was depleted, indicating uncoupled toxin synthesis and cell growth under changing external nutrient conditions. Our results show that toxinspecific nitrogen stable isotope analysis may provide a tool that can help to identify the nitrogen sources supporting toxic Alexandrium blooms. © 2011 Inter-Research.