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Red Tide in Algoa Bay

This has been a very interesting year in Algoa Bay. Firstly the strong Easterly winds did not blow through December and early January like normal. It is these onshore winds that send the visitors from up country packing. Instead we had great weather and extremely warm seas. It is the first time I have recorded 25 degree Celsius water here in Algoa Bay for such an extended period. These led to extremely humid conditions in Port Elizabeth. At sea we saw hundreds of Hammerhead sharks (not so unusual) and thousands of flying fish. If that was not enough, we had a family of Orcas (Killer whales) gracing the Wild Side coast in mid-January and giving us a real show.


Now we have had the whole of Algoa Bay turning red, why is this? Upwelling of water occurs in Algoa Bay due to two reasons, strong easterly winds (causing water temperatures to plummet in the middle of summer) and the shearing effect of the Agulhas current. Either way dormant phytoplankton (plant plankton) spores are brought to the surface and trapped in the confines of Algoa Bay. After getting exposed to sunlight they can bloom so densely that they colour the water red. Very often these blooms can cause mass mortalities of marine animals although this is limited to the West Coast of South Africa. These unicellular organisms are quite unusual as they can grow to about one millimetre in size which is huge for an organism that has only one cell. The red colour is due to red pigment spots which shield the light sensors in these organisms and allows them to detect the direction of the light source. The most common one is called “Noctiluca” which will produce phosphorescence at night, look out for it.


Although the one in Algoa Bay is harmless, as with all red tides its blooms may consume all available nutrients and then die leaving masses of decaying phytoplankton. This may further deplete the water of oxygen, killing various forms of marine life. Remember when thousands of crayfish on the west coast left the water due to oxygen depletion only to die on the beach.


Luckily for us and the marine life in Algoa Bay this bloom in phytoplankton supported a similar bloom in zooplankton (animal plankton). This is what has been feeding the vast shoals of saury that are now present in Algoa Bay. On Thursday Dr Lorien Pichegru and I were busy conducting a fish survey in Algoa Bay to determine the biomass of bait fish. This is all to answer questions on her ground breaking research about the effect of marine protected areas on the survival of penguins here. As you may know we have lost 60% of our penguin population in the last seven years. We were presently surprised to find a massive feeding frenzy just south of St Croix Island in the early hours of Thursday morning. We witnessed 600 penguins, 400 cape gannets and various other seabirds tucking into a feast of note. The saury being consumed were huge, about 15cm long, the largest we have ever seen as we have been taking penguin diet samples for the last five years. It is vital that penguin parents fatten up as they are just about to enter the new breeding season. Being a fat healthy parent will ensure that we have a good breeding season this year.


So while other areas may suffer from the scourge of Red Tide it looks like it may be doing many organisms and especially the penguins and gannets in Algoa Bay a good turn!

 

Lloyd Edwards, Seaview, Port Elizabeth, 19th February, 2013

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