Harmful Algal Blooms (HAB’s) in Marine Mammals – Part 2.

Saxitoxins, Brevetoxins, Cyanobacteria toxins and Okadaic Acid. HAB diagnostic sampling.

Dr Rick Last – Specialist Veterinary Pathologist.

As a recap on Part 1. Biotoxins that pose the greatest real or potential threat to marine mammal health include:

• Domoic acid (produced by diatoms of Pseudo-nitzschia )
• Saxitoxins (produced mainly by dinoflagellates Gymnodinium catenatum, Pyrodinium bahamense, and Alexandrium tamarense)
• Brevetoxins (produced by the dinoflagellate Karenia brevis)
• Cyanobacteria algal toxins.
• Okadaic acid (produced by dinoflagellates of Prorocentrum and Dinophysis )

Saxitoxin.

Saxitoxin (STX) is a carbamate alkaloid neurotoxin isolated from marine dinoflagellates and freshwater cyanobacteria. Dinoflagellates of the genera Alexandrium are the major producers of STX, which are considered among the most toxic of the biotoxins. STX blocks neurotransmission by binding directly to the voltage-dependent sodium channels in nerve and muscle cell membranes, interrupting nerve signal transmission and leading to paralysis.

In the marine environment toxin is found in plaktonic algae (Alexandrium tamarense, Gymnodinium catenatum and Pyrodinium bahamense) and has been detected in filter-feeding molluscs, clams and pelagic fishes that consume this plakton, as well as birds and marine mammals that feed on these shellfish and pelagic fish. In freshwaters, saxitoxins are produced cyanobacteria (Anabaena, Aphanizomenon, Planktothrix Cylindrospermopsis

Lyngbya, and Scytonema) and STX also accumulate in freshwater fish such as tilapia.

STX has been implicated in mass mortalities in multiple taxa of marine mammals including whales, porpoises, dolphins, seals and sea otters. As prey species can accumulate STX over a period of weeks and offshore blooms are possible, marine mammal strandings with detection of high levels of STX in tissues of stranded animals, often do not match a specific bloom period.

Acute onset incoordination, paralysis and sudden death characterise the clinical syndrome. Pulmonary congestion and oedema, although non-specific, is a common and consistent feature at post-mortem and on histopathology.

Read full article in HooHoo

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