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Atlantic Cold Water Reefs

Dec 9

Written by:
Wednesday, December 09, 2009  RssIcon

The Benguela Current, classified as a large marine ecosystem, is one of the most strongly wind driven coastal upwelling systems known.

The current extends from roughly Cape Point in the south, to Angola in the north. The current is driven by south easterly winds. Inshore of the Benguela Current proper, the south easterly winds drive coastal upwelling, forming the Benguela Upwelling System. The cold and often clear, nutrient rich waters that upwell from around 200-300 m depth in turn fuel high rates of phytoplankton growth, and sustain the productive Benguela ecosystem.
(ref: http://en.wikipedia.org/wiki/Benguela_Current).

However, once the south easterly wind drops or changes direction, the surface sea water temperature rises quickly, especially in summer. The temperature can rise from as low as 8 degrees to 16 degrees or higher. This causes the cold clear upwelled water to turn brown in a planktonic bloom. This is often associated with an increase in jellyfish. Sunfish (mola mola) move inshore to feed on the jellyfish. I have tried filming sunfish on a few occasions but found them to be very shy, swimming away from the camera at a surprisingly fast pace. So I was fortunate to get a fantastic photograph of a large Sharp Tail Sunfish swimming off Hout Bay from my friend, Jurgen Seier. Note the pilot fish beneath the sunfish, indicating that it had come from warmer water.

While nutrient rich, the reefs of the “Benguela Coast” are often quite bland from a diving point of view. However, along the Cape Point to Cape Town coat, with its impressive underwater profiles created by massive granite formations, patches of brightly coloured noble corals, seafans, sea enemonies and sponges can be found. Large sea caves and deep crevices create in ideal environment for certain reef life.

One of my favourite spots is Vulcan Rock near the fishing village of Hout Bay, close to my office. Recently we travelled by boat from Hout Bay to Cape Point. Due to planktonic blooming the water was too dirty to film underwater but we spotted the following without putting a head in the water: Humpback whales, seals, penguins, yellowtail fish (surface shoaling), sunfish, dolphins, blue sharks and various sea birds. Not bad for a morning at sea!

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A Diver Enters a Granite Cave:
A Typical Geological Feature for this Area

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Cape Rock Lobsters Shelter in a Cave

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A Large Sharp Tail Sunfish Cruises near the Surface
Photograph Copyright Jurgen Seier, Cape Town

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Colourful Noble Corals

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A Coral Garden hidden in the Kelp

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Bright Red Jellyfish are Abundant During a Planktonic
Bloom Event

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This Delicate Jellyfish is Food for Sunfish

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