Modelling Toxin-Producing Algae in the Coastal Waters of Nigeria

Abstract

This research describes the development and application of an empirical model for toxin-producing algae developed from time series of cell abundance coupled with concurrent measurements of environmental variables in Nigerian coast, Gulf of Guinea. A Generalized Linear Model was formulated to predict the population size of Cyanophyta, Oscillatoria, Dinophyta, total phytoplankton abundance and toxic algae, for four different months in a year, namely March (dry-wet period), July (wet period), October (wet-dry period) and January (dry period), using 12 input variables, namely pH, salinity, PO4, NO3, Fe, water temperature, DO, turbidity, Si, SO4 and location determined by Latitude and Longitude coordinates, with data collected from 53 locations. The interactive effects of silicate and iron were also modeled to elicit effect of these nutrients on the density and occurrence of toxic algae/phytoplankton and total phytoplankton abundance. The model gives a very good fit for the data and the results reveal the influence of season, location and nutrients on the variation in the abundance of total phytoplankton abundance and the toxic form abundance. In the wet season and dry seasons, surface and stem plots for total phytoplankton abundance and toxic algae abundance were noticeably dissimilar, with the Lagos axis of the Atlantic Ocean having significantly high total phytoplankton abundance in the wet season and abundant toxic algae in the south-south locations of Cross River and Akwa Ibom. Ondo and Ogun axes of the Atlantic Ocean had significantly high abundance of the toxic algae in the dry season. In the dry-wet and wet-dry seasons, the surface and stem plots for total phytoplankton abundance and toxic algae abundance were similar. There was significant abundance of toxic algae in the south-west locations. Specifically, Ondo and Ogun in the south-west had significantly high total phytoplankton and toxic algae abundance in the dry-wet season.