Abstract

Harmful algae are phytoplankton that produce toxins at certain times in their life cycle. These toxins are well recognized to have a potential impact on humans and animals. Among marine mammals, domoic acid (DA), a neurotoxin produced by the diatom Pseudo-nitzschia spp., has caused mortality events since 1998 particularly in California sea lions (Zalophus californianus).³ In addition saxitoxin (STX) has been implicated in the mass mortality of Mediterranean monk seals (Monachus monachus).²

Since the late 1990s there has been a decline in harbor seal (Phoca vitulina) abundance around Scotland. A recent study found Scottish harbor seals are exposed to biotoxins from harmful algae, especially DA.¹ This finding has led to the hypothesis that DA and potentially other biotoxins found in Scottish waters, such as saxitoxin and okadaic acid (OA), may be involved in the observed population decline. An objective of this study is to determine the extent of harbor seal exposure to multiple biotoxins. There are regional differences in their exposure to DA, as estimated from levels in their feces and urine. The highest levels of DA are found in the Eden Estuary on the east coast of Scotland with DA in feces ranging from 99–1141 ng/g and urine 24–12912 ng/ml. A foodchain study is being carried out to look into the role and uptake of these three main biotoxins in two coastal environments. Preliminary results show that there are higher concentrations of biotoxin on the east coast and that demersal benthivores like plaice and dab contain more DA than other prey species such as whiting and cod.

The clearance rate of DA and other biotoxins from harbor seals is important for determining their half-life and therefore how long they might remain in samples collected from the wild. This study will examine how quickly DA clears from the animals by looking at urine and faeces collected from captive harbour seals and test how long DA is detectable in their excreta. Preliminary results show that when a harbour seal was fed flatfish from a batch naturally contaminated with DA with concentrations ranging from 50–3200 ng/g, DA was detectable in the faeces of the seal at 37.25 ng/g. Ten days later a faecal sample contained 1.22 ng/g. This indicates that DA is still present at low concentrations 10 days after DA exposure and seems to be cleared to levels below the limit of detection within two weeks. The outcome of this research will be critical to our understanding of the role of biotoxins in harbour seal health and survival.

* Presenting author
+ Student presenter

Literature Cited

1.  Hall AJ, Frame E. 2010. Evidence of domoic acid exposure in harbour seals from Scotland: A potential factor in the decline in abundance? Harmful Algae 9:489–93.

2.  Hernández M, Robinson I, Aguilar A, González LM, López-Jurado LF, Reyero MI, Cacho E, Franco J, López-Rodas V, Costas E. Did algal toxins cause monk seal mortality? Nature 393:28–29.

3.  Scholin CA, Gulland F, Doucette GJ, Benson S, Busman M, Chavez FP, Cordaro J, DeLong R, De Vogelaere A, Harvey J. 2000. Mortality of sea lions along the central California coast linked to a toxic diatom bloom. Nature 403:80–84.