Marine planktonic diatoms consist of about 250 genera with more than 100 000 species that produce approx. 20-25% of world wide fixed carbon (1.4 x 1014 kg). Within the diatoms the genus Pseudo-nitzschia has gained lively interest since 1987 when P. multiseries caused an Amnesic Shellfish Poisoning (ASP) event along Prince Edward Island, Canada; three people died and 105 showed acute signs of poisoning. Since then several ASP events have been reported from Canada, the USA, and New Zealand while domoic acid producing species were also detected in the coastal waters of Japan, Scotland, Denmark, Spain, Portugal, France and Italy. Under specific conditions Pseudo-nitzschia spp. can form blooms, characterized by dense, local aggregations of algae in which high cell numbers are reached, leading to dramatic increase in toxin production. These toxin loaded algae might then reach the sea food market via the absorption by shellfish considered for human consumption.
P. multistriata occurs regularly in the Gulf of Naples where it blooms in early spring at temperatures around 15 °C with cell numbers up to 2.2 x105 per liter. The species is easily identified because of its typical sigmoid form (see Figure). Toxicity has been demonstrated by the Marine Botany group of the Stazione Zoologica "Anton Dohrn" in Naples.
The poison has little or no effect on the herbivorous zooplankton, that is, the organisms that graze the phytoplankton. Nevertheless, the domoic acid is absorbed into the body of these tiny organisms and transmitted up in the food chain where it accumulates, for instance, in filter-feeding mussels and oysters. These shellfish are eaten in their turn by fish, birds, sea-mammals and, of course, people and it is in all these so-called top predators that things go awry. Domoic acid affects the neural pathways and inhibits the neuro-chemical processes of these vertebrate organisms. In other words, they go crazy.
Symptoms in Humans
Mild cases: after three to five hours, nausea, vomiting, diarrhea and abdominal cramps.
Extreme cases: decreased sensitivity to deep pain, dizziness, hallucinations, confusion, short-term memory loss and seizures.
For detailed information see:
Orsini, L., Sarno, D., Pocaccini, G., Poletti, R., Dahlmann, J., and Montresor, M. (2002). Toxic Pseudo-nitzschia multistriata (Bacillariophyceae) from the Gulf of Naples: morphology, toxin production and phylogenetic relationship with other Pseudo-nitzschia species. European Journal of Phycology 37: 247-257