Factors influencing the biomass and distribution of sago pondweed, Stuckenia pectinata in a temporarily open/ closed estuary, Zandvlei, Cape Town, South Africa

Abstract

Stuckenia pectinata (Börner, 1912) offers both advantages and disadvantages to the biota and user groups of Zandvlei Estuary, Cape Town. It is therefore imperative that S. pectinata is managed so that it provides ecosystem services without growing to levels where it negatively impacts user groups. This study aimed to understand factors influencing S. pectinata biomass and distribution in Zandvlei Estuary in order to provide conservation authorities with informed S. pectinata management options. S. pectinata biomass and distribution, and system physico- chemical parameters and nutrient characteristics were assessed monthly between November 2016 and November 2017. Samples were collected in the main body of the estuary, in the Marina da Gama canals and in three influent rivers. Elevated salinity was found to negatively influence S. pectinata biomass within the lower reaches. Nutrients were thought to influence seasonal variations in S. pectinata biomass. The distribution of sediment grain size was suspected to influence variations in S. pectinata biomass within the main body of the estuary. The results add to conservation authorities’ understanding of the influence of environmental characteristics on S. pectinata biomass and distribution allowing more effective anticipation of changes in S. pectinata biomass and distribution thus preventing extremes in its growth. The knowledge acquired will assist conservation authorities in refining the S. pectinata harvesting protocol thereby allowing the macrophyte to be maintained more effectively.