SPATIO-TEMPORAL DYNAMICS OF PHYTOPLANKTON OF A TIDAL COASTAL CREEK, LAGOS, NIGERIA

An annual study of the phytoplankton and physical and chemical variables of Five Cowries Creek (FCC), a tropical tidal creek, in Lagos, in the coastal region of Nigeria, was undertaken from July 2002 to June 2003, at monthly intervals, to investigate spatial and temporal variations of phytoplankton flora. The phytoplankton flora comprised a moderately diverse taxa of 75, of the divisions Bacillariophyta (76%), Chlorophyta (12%), Cyanobacteria (10.6%) and Dinophyta (1.33%). The diatoms or Bacillariophyta was the most representative division or group, both qualitatively and quantitatively, represented by both Pennales (60%) and Centrales (40%). The Chlorophytes were chiefly Zygnematales (5 Zygnemataceae-Mougeotia (1) and Spirogyra (2); and Desmidiaceae (Closterium-1) Cosmarium-1). Cyanobacteria were mainly non-heterocystousNostocales (Oscillatorialceae-Oscillatoria (3), Trichodesmium(1), Spirulina major, and Lyngbyamajuscula and a few Chroococcales (Chroococaceae-Merismopediaglauca, Microcystis wassenbergii). The only member of Dinophyta (dinoflagellates) was a freshwater species-Ceratiumhirundinella. Four assemblages could be discerned on the basis of season and these were rainy season assemblage, dry season assemblage, season-indifferent assemblage and transitional assemblage. Phytoplankton of FCC was subjected to both spatial and temporal distribution, though the former was qualitatively less evident. Phytoplankton with large spatio-temporal distribution were Coscinodiscus centralis (69%) occurrence, followed by Pleurosigmaangulatum(47%) occurrence and Thalassiosirarotula(42%) occurrence. Phytoplankton density was generally low in the rainy season and high during the dry season. The seasonal variation of the consistently quantitatively dominant species reveals peak densities in December (Coscinodiscus centralis) and February (Aulacoseira granulata and Thalassiosirarotula). The Creek is brackish, essentially circum-neutral pH (7.04-7.78), with high conductivities ranging from 2.025 to 37.6 mS/cm, total dissolved solids, 1.013-18.95g/l and salinities, 1. 03 – 23.9‰. Regular and continuous monitoring of the creek is essential to ascertain the possible onset of phytoplankton bloom and occurrence of harmful algae, to enable formulation of good management practices important or critical for fisheries, navigation, recreation and ecosystem health.