Observations on the distribution and abundance of a green tide along an intertidal shore, Knysna Estuary

Abstract

Observations on an unexpected bloom of Ulvales taxa in the Knysna River Estuary, South Africa, were made between summer 2014/15 and through the winter and early spring of 2015. Assessments of the diversity and abundance of macroalgae were obtained from a number of transects across the intertidal zone in the marine dominated lower estuary basin. The maximum ‘dosage’ of macroalgal wet weight at 2040gm−2 (2kgm−2) fell well below the highest dosage (10kgm−2 wet weight) reported in the literature. In the Knysna Estuary patches of Ulva lactuca L. vary in abundance and frequency of appearance as they are disseminated by wind and flooding tide. The literature cited stresses the importance of nitrogen and phosphorus nutrients in initiating and maintaining blooms in shallow well lit coastal waters. The estuary possesses these features and through upwelling and drainage from the immediate catchments offer support for this hypothesis.