Organic polymer consumption facilitates domoic acid entry into the marine food web without direct ingestion of Pseudo-nitzschia

Abstract

Domoic acid (DA) is a neurotoxin produced by diatoms from the genera Pseudo-nitzschia and Nitzschia. DA is transferred through the food web when consumed by organisms such as copepods (e.g., Acartia tonsa). DA bioaccumulates in higher trophic levels and poses a threat to human health through amnesic shellfish poisoning. Laboratory experiments using a DA reference standard demonstrated that mild turbulence facilitates formation of organic polymer aggregates >0.6 µm in-vivo that can scavenge dissolved DA (dDA). Using A. tonsa, we demonstrate that DA can be assimilated through consumption of these organic polymers which scavenged dDA —a pathway which does not require direct ingestion of the toxin-producer Pseudo-nitzschia. In filtered seawater with spiked DA, copepods accumulated 24.8 ± 4.7 pg DA copepod−1 (2.1 ppm) on average by consuming organic polymers. This was validated in one out of five experiments using ambient DA concentrations. Copepods were suspended in particle-free seawater and accumulated 14.4 ± 3.8 pg DA copepod−1 (1.20 ppm), and in particle-concentrated seawater they accumulated 40.9 ± 3.8 pg DA copepod−1 (3.42 ppm). Data from this experiment suggests that ~34% of the total assimilated DA entered via an organic polymer-bound DA pathway. This experiment had the highest Pseudo-nitzschia spp. abundance (~225,000 cells L − 1) and cellular toxin quota, up to 0.88 pg DA cell−1, relative to the other four ambient DA experiments. These results demonstrate the potential for DA to enter the marine food web through an alternate pathway and may have considerable implications to understanding the flow of DA through marine food webs, and how we monitor DA and its potential vectors into the food web.