Plankton dynamics associated with the convergence zone of a shear front in the permanently open Kowie Estuary, South Africa

Abstract

Estuarine frontal systems are thought to play an important role in plankton accumulations in estuaries. However, knowledge surrounding these estuarine circulation patterns is not clear, and consensus regarding the importance of fronts has yet to be reached. A full appraisal of the plankton in frontal systems in the estuary was undertaken. Ichthyoplankton, zooplankton and phytoplankton were collected from in and out of the frontal systems in the Kowie Estuary, using two WP2 plankton nets. Plankton was identified and abundance calculated. Various water quality parameters were also recorded in and out of the front and make up an important part of determining the physical difference between the separated water masses. Values for in and out of the frontal region were determined in order to make comparisons between the different areas. All data was tested for normality and homogeneity of variance. Differences between in and out of the frontal region were determined using ANOVA or Kruskal-Wallis tests. Multiple linear regression was used to determine the relationships between water quality variables and plankton abundances. Community analysis was also run on the data in order to determine community dynamics associated with frontal system convergence and downwelling.

Key words:

• ichthyoplankton
• phytoplankton
• zooplankton
• estuarine fronts
• water quality