Although some red tides form a healthy part of phytoplankton production,
recurrent harmful or toxic blooms also occur, with results depending upon the
type of plankton and on atmospheric and oceanic conditions. At Elands Bay in
South Africas Western Cape province, about 1000 tons of rock lobsters beached
themselves during February 2002, when the decay of dense blooms of phytoplankton
caused a rapid reduction in the oxygen concentration of nearshore waters. The
lobsters (or crayfish, as they are known locally) moved toward the breaking surf
in search of oxygen, but were stranded by the retreating tide.
The Multi-angle Imaging SpectroRadiometers nadir camera acquired these red,
green, blue composites on February 2 and 18, 2002, during Terra orbits 11315 and
11548. The colors have been accentuated to highlight the bloom, and land and
water have been enhanced separately. The two views show the shoreward migration
of the algal bloom. Each image represents an area of about 205 kilometers x 330
kilometers. Elands Bay is situated near the mouth of the Doring River, about 75
kilometers northeast of the jutting Cape Columbine.
The term red tide is used to refer to a number of different types of
phytoplankton blooms of various hues. The wine color of certain parts of this
bloom are consistent with the ciliate species Mesodinium rubrum, which has been
associated with recurring harmful algal blooms along the Western Cape coast.
Under these conditions, the lobsters are not poisoned. During the recent event,
government and military staff transported as many of the living lobsters as
possible to areas that were less affected by the red tide. At the same time,
people came from across South Africa to gather the undersized creatures for
food. The effects of the losses on the maritime economy are expected to be felt
over the next few years.