Tuesday, 3 July 2012

What’s in a Name… Red Tide or HABs?

The first hint of the creeping threat was a lacy trace of dirty foam along the high-tide mark. Then the seabirds disappeared...

Red Tide Bio Luminescence, California Coast 2005
That was the start of red tide; in the beginning stretching from Eland’s Bay to Doringbaai (Thorn Bay), about 80km long. This began in February; by mid-March, red tide was just north of Cape Columbine.  This bit of coastline is well known for its sea life, and local delicacies like West Coast Rock Lobster, abalone, mussels and oysters, etc. The fact that the shellfish was off limits because of toxicity might have had something to do with the quieter Easter Holidays this year.

Beach in St Helena Bay
Red tide is the common name for an incidence known as an algal bloom. The algae (phytoplankton) are tiny micro-organisms. When conditions are favorable, they grow in huge masses, forming visible clouds on the water's surface. Red tides can be a natural phenomenon or may be triggered by other factors; their origins are controversial. Not all red tides are harmful but some are deadly; to humans as well as marine life.

Rock Lobster Remains with Car Keys
Occasionally, a red tide will produce swathes of bio-luminescence when the surface is disturbed (for example; a breaking wave). Anyone who has been on a cruise will probably be familiar with the enchanting spectacle as the ship cuts through patches of luminescent phytoplankton, far from any shore.

Scientists and researchers aren’t happy with the imprecise name Red Tide, preferring the term Harmful Algal Blooms or HABs. One of the reasons cited is that, depending on the species of phytoplankton, the masses forming the huge patches could be brown, purple or pink, even green or red while some species don’t form dense enough groups to have a color. There is also no relationship between the tides and red tide. 

Of course, it’s not only shellfish that are affected. Low oxygen levels in the water cause the Rock Lobster to literally walkout of the sea, straight into the cruel beaks of thousands of greedy seabirds. By the end of March, the Department of Agriculture, Forestry and Fisheries (DAFF), working with 100 recruits from the South African Navy, collected over 2-tons of West Coast Rock Lobster after a walkout was reported at Eland’s Bay. With the majority still alive, these rock lobsters were returned to the sea; further down the coast in areas unaffected by the red tide. This was done to alleviate the negative impact on population numbers as the stranded creatures were mostly egg-bearing females.

Many Eels
Down on our beach, the walkout was minimal, comparatively speaking. Sure, we saw crayfish but also dead eels, rays and a few smaller fish. Sea urchins seemed to be the biggest casualty – piles of urchins lay at the high tide mark. Blue black mussels, clams and oysters along with many smaller shellfish made up the remainder of the scraps littering the beach.

Towards Lamberts Bay

Then the winds changed, storms blew in and the tides dispersed. Now the only reminders of the red tide are the drying shells of sea urchins, mussels and limpets scattered on the beach.

Image of  Bio-luminescence, courtesy of Wikipedia

All other images by Wildmoz.com


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