Population dynamics of Pseudo-nitzschia species (bacillariophyceae) in the near shore waters of Dar es Salaam, Tanzania

Abstract

The genus Pseudo-nitzschia is a chain-forming diatom comprising about 30 species some of which are known to produce domoic acid (DA) that causes amnesic shellfish poisoning (ASP). The current study aimed at assessing the population dynamics of Pseudo-nitzschia in the near shore waters of Dar es Salaam. Samples were collected between August 2008 and July 2009 from two stations. The first station was located in the open waters off Mbudya Island and the second was located at a point in-between Kunduchi and Mbudya Island. Three Pseudo-nitzschia species, i.e., Pseudo-nitzschia pungens, Pseudo-nitzschia seriata and Pseudo-nitzschia cuspidata were encountered with Pseudo-nitzschia pungens being the most abundant. The concentration of Pseudo-nitzschia species ranged from none in various samples to a highest value of 16 cells/L recorded in September 2008. There was no significant difference in the abundance of Pseudonitzschia spp. between site 1 and 2 and between the northeast (NE) and southeast (SE) monsoon periods. The abundance of Pseudo-nitzschia spp. was below concentrations reported elsewhere to cause problems to shellfish  consumers implying that shellfish collected near Dar es Salaam may be ASP free. However, further studies are required to ascertain DA production in coastal waters of Tanzania.

Key words: Pseudo-nitzschia dynamics; amnesic shellfish poisoning; Tanzania