The red tide

Katrina Brevis

MONDAY 6 November. The bemused tourists were gathered around the Hobart docks staring and pointing at the water — but they weren’t admiring Tasmanian’s maritime heritage or clean-green image. The water surface along much of the wharf front from Parliament House to the Marine Building was covered in a thick bright-orange/red scum.

The most probable cause was a “red tide” — an occurrence of dinoflagellates causing an ugly bloom on the water surface. The significance of this occurrence is that whilst the bloom is “natural” in composition, it is generally believed that such blooms are generated by a combination of increases in water temperature, declined rainfall and water current and an increase in nutrient levels (such as sewerage). In summary the occurrence of a red tide is not a good sign for either the health of the river or sea temperatures in this era of climate change dynamics.

The impact of a red tide is variable, depending on the species present. In most cases the species is benign, but the presence of some species can have serious impacts on the health of filter-feeders such as shellfish. In Argentina documented poisoning and death of humans has occurred where shell fish were consumed after a poisonous red tide — leading to Toxic Shellfish Paralysis and death.

Whilst the red tide was of great interest to the State’s tourists, there seemed to be little interest from the officers of DPIWE and Hobart Ports housed in the Marine Building directly opposite the bloom. There was no sign of officers rushing about to collect samples for analysis and neither was there any sign of Mr. Gay, glass in hand, desperate to sample the delicious solution.