February 27, 2011 – Ascension Island – Over the last few weeks we have been recording high numbers of dead fish washing up onto the beaches around the Island. The same thing happened, at the same time of year, in 2008. A report was published recently, called ‘Reef fish mass mortality event in an isolated island off Brazil, with notes on recent similar events at Ascension, St Helena and Maldives’ by Hudson Pinheiro, Joao Gasparini and Jean-Christophe Joyeux. The report states that ‘it is possible that blooms of toxic algae, under certain conditions, caused cascading intoxication along the trophic web. Toxic algae occur in other Atlantic oceanic islands and there are reports of algal blooms occurring in remote areas that suffer low human impact. A second hypothesis is that seasonal upwelling events of anoxic or hypoxic waters may be involved (the low oxygen content would be due to the resuspension of sediment and organic matter deposited at geological scales) often heavily loaded with hydrogen sulphide. Oxygen-poor waters of the Benguela upwelling have been reported to affect the southeastern Atlantic continental shelf and these waters, in years of strong Benguela upwelling, can even reach the Mid-Atlantic Ridge island of St Helena.’ The full report is available to download from our website. We are currently consulting with contacts in the UK and Falklands. I have sent them as much information as I have, including species affected, numbers, symptoms and photographs. They will be able to offer advice on the best course of action. I have also been in touch with one of the authors of 2010 report, this was his response. -The Islander
Ascension Island and Tristan da Cunha both lie along the Mid-Atlantic Ridge and volcanism is one of the culprits contributing to conditions which create hypoxic zones.