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Following the first description of living marine stromatolites along the South African east coast, new investigations along the south coast have revealed the occurrence of extensive fields of actively calcifying stromatolites. These stromatolites have been recorded at regular distances along a 200-km stretch of coastline, from Cape Recife in the east to the Storms River mouth in the west, with the highest density found between Schoenmakerskop and the Maitland River mouth. All active stromatolites are associated with freshwater seepage streams flowing from the dune cordon, which form rimstone dams and other accretions capable of retaining water in the supratidal platform. Resulting pools can reach a maximum depth of about 1 m and constitute a unique ecosystem in which freshwater and marine organisms alternate their dominance in response to vertical mixing and the balance between freshwater versus marine inflow. Although the factors controlling stromatolite growth are yet to be determined, nitrogen appears to be supplied mainly via the dune seeps. The epibenthic algal community within stromatolite pools is generally co-dominated by cyanobacteria and chlorophytes, with minimal diatom contribution.

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Calcifying tufa stromatolites are forming on a high energy coast of the South African Indian Ocean. The tufa stromatolites form in upper intertidal to supra tidal rock pools, encrust bedrock and are linked both laterally and vertically to physico-chemical properties of their pool water. Calcification only occurs in pools where dissolved carbonate-rich, spring-fed groundwater is routed, and d18O values are consistent with calcification in a mixture of freshwater and seawater. Increasing pH and less negative isotope values away from the spring are consistent with CO2 degassing and in-stream calcification, albeit with some in-mixing of seawater. The rocky shore setting of these active tufa stromatolites is new and invites serious comparison with some Archaean rocky substrate peritidal stromatolites (e.g. the c. 3.45 Ga Strelley Pool sequences, Pilbara Craton). This new association shows that initial encrustation of rocky intertidal substrates can begin with freshwater influence in the intertidal zone, a facies detail that should be sought in ancient peritidal stromatolites

ABSTRACT-The composibon, distribution, abundance, biomass and size-structure of macroplankton/ mcronekton communities at the Subtropical Convergence (STC) and the Antarctic Polar Front (APF) regions were investigated dunng the South African Antarctic Manne Ecosystem Study (SAAMES 11, January-February 1993; SAAMES 111, June-July 1993) A total of 115 and 32 macroplankton/micronekton species were found in the epipelagic zones of the STC and APF, respectively. Cluster analysis based on species composition indicated the occurrence of 3 different plankton communities: one in the STC region, another to the north of the APF and the third to the south of the APF Although the APF and the STC were investigated in dfferent seasons, average abundance and biomass were sirmlar in both regions. Tunicates, euphausiids, decapods and myctophiid fishes dominated the total stock of the 2 frontal regions, in terms of both abundance and biomass Both fronts exhibited considerable fluctuations in the abundance and biomass levels which appeared to covary with the spatial distribution of the phytoplankton stock in the area. The dominant sue-classes were composed of a small group of 5 to 30 rnnl siphonophores, tunicates and euphauslids and a larger group of 40 to 80 mm euphausiids, chaetognaths, vertically-migrating decapods and myctophiid flshes.