An assessment of temporal, spatial and taxonomic trends in harmful algal toxin exposure in stranded marine mammals from the U.S. New England coast

Abstract

Despite a long-documented history of severe harmful algal blooms (HABs) in New England coastal waters, corresponding HAB-associated marine mammal mortality events in this region are far less frequent or severe relative to other regions where HABs are common. This long-term survey of the HAB toxins saxitoxin (STX) and domoic acid (DA) demonstrates significant and widespread exposure of these toxins in New England marine mammals, across multiple geographic, temporal and taxonomic groups. Overall, 19% of the 458 animals tested positive for one or more toxins, with 15% and 7% testing positive for STX and DA, respectively. 74% of the 23 different species analyzed demonstrated evidence of toxin exposure. STX was most prevalent in Maine coastal waters, most frequently detected in common dolphins (Delphinus delphis), and most often detected during July and October. DA was most prevalent in animals sampled in offshore locations and in bycaught animals, and most frequently detected in mysticetes, with humpback whales (Megaptera novaeangliae) testing positive at the highest rates. Feces and urine appeared to be the sample matrices most useful for determining the presence of toxins in an exposed animal, with feces samples having the highest concentrations of STX or DA. No relationship was found between the bloom season of toxin-producing phytoplankton and toxin detection rates, however STX was more likely to be present in July and October. No relationship between marine mammal dietary preference and frequency of toxin detection was observed. These findings are an important part of a framework for assessing future marine mammal morbidity and mortality events, as well as monitoring ecosystem health using marine mammals as sentinel organisms for predicting coastal ocean changes.

Fig 1. Animal collection/sampling locations and detections of saxitoxin (presence/absence in at least one sample).

Fig 2. Animal collection/sampling locations and detections of domoic acid (presence/absence in at least one sample).

Fig 3. Correspondence analysis ordination for sub-region comparisons.

Positive values for dimension 1 correlate with larger proportion of positive domoic acid samples and negative values correlate with larger proportion of negative domoic acid samples. Positive values for dimension 2 correlate with larger proportion of positive saxitoxin samples and negative values correlate with larger proportion of negative saxitoxin samples. MA = Massachusetts, ME = Maine, NH = New Hampshire, OB = offshore/bycatch.

Fig 4. Correspondence analysis ordination for taxonomic group comparisons.

Positive values for dimension 1 correlate with larger proportion of positive domoic acid samples and negative values correlate with larger proportion of negative domoic acidsamples. Positive values for dimension 2 correlate with larger proportion of positive saxitoxin samples and negative values correlate with larger proportion of negative saxitoxin samples.

Fig 5. Correspondence analysis ordination for species comparisons.

Positive values for dimension 1 correlate with larger proportion of positive domoic acid samples and negative values correlate with larger proportion of negative domoic acid samples. Positive values for dimension 2 correlated with larger proportion of positive saxitoxin samples and negative values correlate with larger proportion of negative saxitoxin samples.

Fig 6. Frequency of animals testing positive for saxitoxin, domoic acid or either toxin, by month.

Fig 7. Correspondence analysis ordination for frequency comparisons by month of sampling.

Positive values for dimension 1 correlate with larger proportion of positive saxitoxin samples and negative values correlate with larger proportion of negative saxitoxin samples. Positive values for dimension 2 correlated with larger proportion of positive domoic acid samples and negative values correlate with larger proportion of negative domoic acid samples.

Fig 8. Animals testing positive for saxitoxin, domoic acid, or either toxin, by year.

Fig 9. Domoic acid and saxitoxin fecal concentrations (ng/g) detected in this study vs. previously reported values in Pacific U.S. marine mammals.

Box lines correspond to 25%, 50% and 75% quartiles, whisker lines correspond to 1.5 times the interquartile range, circle markers represent outliers beyond 1.5 times the interquartile range.