Wezi Tjaronda
22 October 2008
Algae blooms that sometimes occur off the Namibian coast have been named as one of the deadly dozen diseases that could spread into new regions as a result of climate change.
Commonly known as red tide, the occurrence kills fish, causes marine mammal strandings, sea bird mortalities and sometimes human illnesses and death. These occurrences, says a report The Deadly Dozen Wildlife Diseases in the Age of Climate Change, could spread due to the advent of climate change.
The report released early October by the Wildlife Conservation Society, named algae blooms, bird flu, babesia, cholera, ebola, intestinal and external parasites, plague, lyme disease, Rift Valley fever, sleeping sickness, tuberculosis and yellow fever as diseases that could spread as a result of climate induced changes in the temperature and precipitation level.
The report said in addition to health threats that the diseases pose to humans and wildlife populations, the pathogens that affect wildlife have destabilised trade and caused significant economic damage.
It also says altered temperatures or food web dynamics resulting from climate change in the case of red tides would have unprecedented impact on the occurrences of these worldwide phenomena.
This year, oyster farmers lost millions due to algae blooms that caused damage to 75 percent of their production in Walvis Bay. The red tide this year was the third since 2005, with previous red tides occurring in June 2006 and December 2005.
The Namibia Coast Conservation and Management project (Nacoma) website said the series of algal blooms that occurred along the central Namibian coast developed during warm and windless conditions. Although it usually occurs during summer-autumn (February to April), the tide can also develop in winter when similar conditions occur for longer periods.
"Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful impacts, and are generally described as harmful algal blooms," said Nacoma.
The most visible effects of red tides are wildlife mortalities among marine and coastal species of fish, birds, marine mammals and other organisms.
The species responsible for the blooms experienced along the Namibian coast in March were non-toxic but the eventual die-off and bacterial decomposition of the bloom reduced oxygen concentrations in the water column, which caused the rock lobster walk-outs and other fish mortalities, said the organisation.
Fish and rock lobsters are usually safe to eat even in the event of a toxic bloom. "However, oysters and other shellfish such as clams and mussels are filter feeders and can accumulate red tide toxins in their tissues. People that would eat these shellfish containing red tide toxins may become ill with stomach upsets, breathing difficulties and even death in very rare cases," it added.
According to Nacoma, the effects of global warning through climate change are already seen on the Namibian coast and will be more visible shortly with the rise of sea levels, more aggressive coastal erosion, the increase of air and water temperatures and the occurrence of harsh droughts, which will seriously impact Namibia's environment and her economy.
The Deadly Dozen report said although many pathogens have been the focus of monitoring efforts, little information existed on the diseases would spread in response to climate change. The report said monitoring efforts for the diseases should be examined concurrently with meteorological data to uncover climate related trends.
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