Potentially Harmful Algae along the Kenyan Coast: A Norm or Threat.

Abstract

Harmful algal blooms are known to cause mortalities of aquatic organisms when in high biomass through formation of anoxic conditions or production of marine biotoxins (that ultimately reach humans through food web transfer). Only a few studies of phytoplankton communities have been carried out along the Kenyan coast. Of these studies, very few have focused on potentially harmful algae. Due to the increasing economic importance of harmful algal blooms, there is need to carry out an inventory of potentially harmful algal species that are present in the Kenyan coastal waters. Phytoplankton samples were collected along the Kenya Coast from 2009-2010 and analyzed for species abundance. A total of 39 taxa of potentially harmful algae were encountered over the study period. Potentially harmful algal taxa with high abundance were Chaetoceros sp., Nitzschia sp., Coscinodiscus sp., Pseudo-nitzschia sp., Rhizosolenia sp., Anabaena sp., Protoperidinium sp., Oscillatoria sp. and Trichodesnium sp. whereas the taxa with lowest abundances were Fibrocapsa sp., Chrysochromulina sp., Umezakia sp., Dinophysis sp. and Aphanizomenom sp. Taxa such as Dinophysis sp. that is generally known to be toxic at low cell densities occurred in most sampling stations. Highest cell densities of potentially harmful algae (39.51x102cells/L) were recorded in the estuarine systems as compared to the creeks (22.83x102cells/L) and near-shore (2.86x102cells/L) ecosystems. Compared to previous studies, this study registered increased number of potentially harmful algae species, an indication of potential threat of future bloom occurrences with the risks of phycotoxins contamination in the expected scenarios of increased eutrophication and climate change.