Trophic interactions, toxicokinetics, and detoxification processes in a domoic acid‐producing diatom and two copepod species

Abstract

In costal ecosystems, copepods coexist with toxin-producing phytoplankton. The presence of copepods can amplify the phytoplankton toxin production and thereby increase the overall toxicity of a bloom. Copepods are not always affected by the toxins and can vector the toxins to higher trophic levels. To investigate the interactions between toxin producers and their grazers, we determined the kinetics of grazer-induced increases in toxin production and the subsequent toxin reduction in a domoic acid (DA)-producing diatom, Pseudo-nitzschia seriata. The cellular DA level of the diatom was within the range of in situ measurements. Ten days after removal of the copepods, 28% AE 8% of the cellular DA still remained in the cells. Simultaneously, we monitored the toxicokinetics of DA in two grazers; Calanus finmarchicus and Calanus glacialis. After 144 h of grazing on the toxic diet, the copepods accumulated and retained high concentrations of DA. Nine hours after exposure to the toxic diet was terminated, the copepods had depurated 70% AE 10% of the DA. The depuration lasted 4 AE 2 d and was independent of Calanus species and treatment. We explored the possible physiological responses in copepods after feeding on a purely toxic diet from gene expression profiles of C. finmarchicus. Expression of genes regulating several major metabolic and cellular processes was reduced in copepods feeding on DA-containing diatoms, and we hypothesize that this is because of exposure to DA.

Transcriptomic responses to grazing reveal the metabolic pathway leading to the biosynthesis of domoic acid and highlight different defense strategies in diatoms

“…Thus, mortality has been detected in copepods after feeding on toxic Pseudonitzschia [8], and reduced escape response has been seen in copepods having fed on toxic Pseudo-nitzschia [33]. No cost of DA production is detected in this study in terms of reduction in the growth rate of Pseudo-nitzschia and the same has been seen in [6,7,32]. Reduction of growth rate correlated, however, with high DA production in [8].…”

Ocean acidification increases domoic acid contents during a spring to summer succession of coastal phytoplankton

“…Such increased frequencies and grazing impacts of copepods may exert a strong effect on the biosynthesis of domoic acid in Pseudo-nitzschia spp. (Harðardóttir et al, 2019;Harðardóttir et al, 2015;Tammilehto et al, 2015). Therefore, the here presented potential cause of the observed increased particulate domoic acid contents is not mutually exclusive for other possible scenarios and may be rooted in a more complex context.…”

Costs and benefits of predator-induced defence in a toxic diatom

“…Phytoplankton exposed to predators up-or downregulate thousands of genes, e.g. genes related to signal transduction pathways, stress responses, and lipid and nitrogen metabolism [48,49]. Such associated responses may be energetically costly and may account for the growth reduction.…”