Comparative dynamics of paralytic shellfish toxins (PST) in a tolerant and susceptible population of the copepod Acartia hudsonica

In common-environment experiments, we measured the uptake, accumulation, retention, transformation and depuration of paralytic shellfish toxins (PSTs) of the dinoflagellate Alexandrium fundyense in adult females of two geographically separated populations (Maine and New Jersey, USA) of the copepod Acartia hudsonica. These populations were previously shown to differ in their history of exposure to Alexandrium blooms, and in their degree of adaptation to this dinoflagellate. Toxin accumulation was measured at several times in incubations lasting up to 72 h. Toxin depuration was assessed after a 60 h incubation of females with toxic A. fundyense and subsequent 60 h incubation in a sole diet of the non-toxic green flagellate Tetraselmis sp. As previously observed, the Maine population had significantly higher toxin ingestion rates. By contrast, both toxin accumulation (up to ∼2.5 ng STX eq. female−1) and the depuration rate (∼0.73 d−1) were not significantly different between populations. Hence, faster depuration is ruled out as a tolerance mechanism in the Maine population. Some toxin transformation during both accumulation and depuration was evident in both populations. However, differential toxin transformation does not appear to be a tolerance mechanism either. In contrast to these results, toxin retention (ratio of accumulation/cumulative ingestion) was significantly lower in the Maine population. The retentions of gonyautoxin 3 (GTX3) and of two of the most potent toxins, neosaxitoxin (NEO) and saxitoxin (STX), were also significantly lower in that population. At steady state, toxin absorption efficiency was estimated to be 6% for the Maine population and 9% for the New Jersey population. These results suggest that lower toxin absorption is a possible tolerance mechanism for the Maine population. The results of the present study also suggest that copepod adaptation to toxic dinoflagellates does not necessarily lead to higher toxin transfer up the food web.

Research highlights▶ Tolerant copepods have higher ingestion rate of toxic Alexandrium than non-tolerant copepods. ▶ Tolerant and non-tolerant accumulate similar levels of PSTs. ▶ Toxin retention was lower in tolerant copepods. ▶ Toxin depuration did not differ between tolerant and non-tolerant copepods.