By Wezi Tjaronda
More than half a ton of rock lobsters were rescued while other shallow water species died as a result of blooms of algae being experienced along the Namibian coast.
Permanent Secretary of Fisheries and Marine Resources Frans Tsheehama said on Wednesday that half a ton of rock lobsters that were collected by fisheries inspectors and research staff in Swakopmund was put into the National Aquarium.
He said satellite images show that the bloom occurred all the way from south of Walvis Bay to Mowe Bay in the north, while the rock lobster walkouts were reported up to Henties Bay. Rock lobsters were washed out onto the beaches or sat in shallow rock pools where people collected them.
The deaths and walkouts started on Saturday until Monday this week.
The lobsters will be released back into the open sea once there is enough oxygen in the water.
The oxygen level needs to be between ‘four and six’ to provide the right conditions for the species to stay. As of Tuesday, the oxygen level was 2.5ml per liter, according to Senior Fisheries Biologist in the Environment Section of the ministry Deon Louw.
The ministry said since the middle of February blooms of algae, especially dinoflagellate, whose scientific name is Ceratium furca, started to develop off the central region coast. The upwelling of the cold water caused this condition from the bottom of the sea into the surface layer, due to a brief period of south-westerly winds.
However, later windless calm weather conditions prevailed allowing the water column to become stratified and sunlight to penetrate deeply, which makes favourable conditions for algae bloom.
But due to lack of sunlight and nutrients, the communities die and sink to the bottom of the sea and cause an increase in bacteria oxygen uptake and concomitant release of carbon dioxide, which depletes oxygen in the water column. The oxygen level was as low as 0.19 ml per liter.
Tsheehama said these conditions kill fish and invertebrates indiscriminately. Apart from rock lobsters, other species including rock suckers, rock fish, sole, eels, octopus, red bait and shy sharks which were trapped in the low oxygen zone close to the beach, were also affected.
The ministry said it could not quantify the mortalities because some of the areas such as south of Walvis Bay and Skeleton Coast were inaccessible.
Louw said the algae bloom was a natural phenomenon that occurs on a yearly basis on the coast although it was by different algae species. The difference between 2007 and this year’s occurrence is that this year many fish species were involved, said Louw.
Blooms of algae can occur in fresh and seawater. While the algae is not toxic to humans, it gives the seawater a characteristic red colour, thus the name red tide.