I thought I knew about plankton blooms, and was fairly sure that I had dived in the worst that they have to offer. I was wrong, however, and that is the reason that all the photos in this post that were taken horizontally are the colour of Appletiser. After a week of strong southeasterly winds, during which the water turned beautiful clear blue, we booked ourselves onto Grant’s boat to go and visit a granite pinnacle off Sea Point that has been named Sea Point Ridge Pinnacles. It’s marked on the hydrographic chart for Table Bay, with a maximum depth of 16 metres. The pinnacle is located close to the slipway at Oceana Power Boat Club and we think we were the first group of people to dive it.
It was a beautiful, windless day in contrast to the howling gale we’d experienced the day(s) before. As we approached the location of the pinnacle, the water had an odd tinge to it. Hoping it was localised, Grant took the boat further south towards North and South Paw, but the colour stayed the same. Since we were out there anyway and sweating in our wetsuits, it was decided to go ahead with the dive back at the Sea Point pinnacle, and hope that the water was cleaner further down.
It was cleaner further down: nearly 20 metres further down. We descended through thick, green, soupy plankton bloom for what seemed like an eternity, and then through a 7 degree thermocline (yes, the surface temperature was 17 degrees) which looked like a solid black barrier. Forcing myself to keep descending through the thermocline, when it looked like a solid object, was one of the hardest things I’ve done since I started diving. We reached the bottom at about 24 metres. Having breathed a quarter of my air already, it wasn’t going to be a long dive.
The bottom layer of water, 4-5 metres’ worth, was crystal clear and freezing cold. The dive had the quality of a night dive, since the massive plankton layer above us let very little light through. It didn’t look that way at the time, but when I took pictures through the water column the camera recorded everything in shades of green, filtered by the green water that was between me and the sun.
The pinnacle is part of a longish ridge that extends out to sea. It is home to some small kelp plants, lots of fish (mostly hottentot by the looks of things), and a very large number of mussels. In between the mussels, which cover almost every available surface, are beautiful anemones in all colours, many of them squeezed into very small spaces. We also saw a lot of West coast rock lobster, who had never seen a diver before and looked at us impassively. A seal visited us, his eyes glowing oddly in the dim light. There are a couple more pictures from this dive in Tony’s newsletter of that week.
We also saw lots of tubeworms, and the largest strawberry anemones I have ever seen. This site is one of the rare granite outcrops on an otherwise almost featureless ocean floor along this part of the coast (apart from wrecks – the SS Cape Matapan being a case in point). It’s a lovely location to dive, with a beautiful boat ride featuring views of the mountain and Cape Town Stadium. It’s far enough out of the shipping lanes that you can relax about being run over by a tanker, but you must dive with an SMB because small boats do ply this part of the coast.
Lesson learned: the sea can change in a day. All that beautiful clean, clear upwelled water from the deep ocean is teeming with life just waiting for the sun’s rays to give it enough energy to multiply prolifically. There’s a small window to enjoy the Atlantic visibility after – or during – a southeaster, and then plankton will probably spoil the party. Diving in that sort of muck is extremely challenging (we lost Maurice at the safety stop, for example, and my air consumption was horrible because I was not relaxed), and is best avoided, specially if you’re paying for the dive! For training in low visibility diving, however, this was better than a night dive. The picture of Tony at the safety stop, below, was taken while I was holding onto his cummerbund.
On the other hand, I was reminded how privileged we are to live on such a fecund stretch of coastline. The upwelling along South Africa’s west coast is among the strongest in the world, occuring at a rate of up to 30 metres per day (compared to 1-3 metres per day elsewhere). It supports incredibly productive fisheries as well as countless other marine organisms and seabirds (phytoplankton included) – all of which we are able to enjoy as scuba divers, consumers of seafood, and bird watchers.
Dive date: 19 November 2011
Air temperature: 28 degrees
Water temperature: 10 degrees
Maximum depth: 23.8 metres
Visibility: 1-12 metres
Dive duration: 30 minutes
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