Information on Tanzania's marine algae environment has been researched and documented by Professor K. Mshigeni and others from the Department of Botany, University of Dar-es-Salaam and the Institute of Marine Sciences, Zanzibar. For further, more comprehensive material, a list of references is attached as Appendix 4.
The environmental factors which appear to be most influential in the distribution of marine algae in Tanzania are seawater temperature, salinity, illuminance, tides, ocean currents and substratum type.
Seawater temperature
The surface seawater temperature falls within the range 24.3 – 29.7 Celsius, with the highest temperatures during January to March and lowest temperatures occurring during the months of June and July.
Salinity
The average open surface seawater salinity lies within the range of 34.5 – 35.5 % salinity, with the exception of localized areas such as big river mouths and tide pool habitats.
Illuminance
Illuminance is intense all year round, although cloud cover reduces the scorching effects of the sun on inter-tidal organisms during the rainy seasons between February to May. Since clouds attain maximum development during the afternoons, the slope of the sea bottom in relation to morning insolation may be important in affecting local distribution patterns of certain intertidal algal species.
Tides
The time of low tide, when intertidal organisms are exposed to the air and associated stresses (eg. desiccation, salinity fluctuations, lethal temperatures and light intensities) are a very important factor affecting the distribution of marine algae. The tides in Tanzania are of the ‘mixed’ type characterised by two successive high and low tides, with the two high and low tides being of unequal magnitude. Between October to March, the lowest tides occur during the day when effects of algal exposure can be devastating. However, during May to August the lowest tides occur at night.
Winds and Currents
Both northwest monsoon winds during October to March and southwest monsoon winds during April to September are experienced. These winds are associated with ocean currents which can tear off large quantities of benthic marine algae from their substrata and cast them ashore during high tides.
Sea bottom types
Many habitats along the Tanzanian shoreline are rocky although near river mouths the shore is generally muddy and sandy and usually poor in benthic marine algal resources.
Coral reefs are also common and serve to break the force of waves giving the optimum level of water movement suitable for many algal species in the lagoons between coral ridges and the shoreline.
The main species of marine algae found in Tanzania by type of product extracted are described in this section. A brief explanation of the uses of these products is provided in Appendix 5.
Carrageenan Sources
The genus Eucheuma and Laurencia are both found in Tanzania, the most commonly occurring species being E.spinosum, E.striatum and L. papillosa. To a lesser extent, E.platycladum and E. okamurai are also found. At present Eucheuma species are the only commercially exploited species in Tanzania. Large populations are found around the islands of Zanzibar, Pemba, Mafia and on the sea facing sides of reefs around Tanga, Lindi/Mtwara and Dar-es-Salaam.
Agar sources
Gracilaria, Gelidium, Pterocladia, and Gelidiella are found in Tanzania. Gracilaria are in greater abundance with G. corticata, G. crassa and G. fergusonii being the most widespread. In addition, large populations of G. verrucosa are found near river estuaries.
Algin sources
Species of Sargassum, Turbinaria, Hormophysa and Cystoseira reach the largest size in Tanzania with Sargassum attaining the largest size and densest strands. The distribution of Sargassum is mainly confined to large lagoons which are permanently immersed at low tide.
