Classification of estuaries in the Ciskei and Transkei regions based on physical and botanical characteristics

For the first time a comprehensive botanical survey has taken place in the Ciskei and Transkei estuaries, Eastern Cape Province, South Africa. In total 54 plant species were found in the 92 estuaries surveyed. These plants could be divided into the following five habitat complexes; reed and sedge beds (23 species), salt marsh (20 species), mangrove forest (4 species), macroalgal assemblages (3 species) and swamp forest (4 species). Ordination showed that salinity and depth were important in influencing the distribution of species. Salinity separated salt marsh from reed and sedge species and depth separated mangrove and associated species (e.g. Zostera capensis, Halophila ovalis and Acrostichum aureum) from reed and sedge species.Based on the plant species composition the estuaries could be divided into those that were permanently open versus those that were temporarily open/closed. The characteristic habitat complexes for the permanently open estuaries were intertidal salt marsh and mangrove forest. This region is a transition between the warm temperate and subtropical biogeographic zones and both permanently open and temporarily open/closed estuaries showed divisions at the Great Kei and Mngazana estuaries. In permanently open estuaries mangrove forest occurred north of the Great Kei Estuary and swamp forest north of the Mngazana Estuary. In temporarily open/closed estuaries reed and sedge beds occurred north of the Great Kei River and swamp forest, reed and sedge beds occurred north of the Mngazana Estuary where they replaced the salt marsh. The temporarily open/closed estuaries in the Ciskei were characterised by salt marsh and macroalgae. Submerged macrophytes such as Ruppia cirrhosa and Potamogeton pectinatus were also common. Salt marsh occurred because of high water column salinity and wide intertidal and supratidal zones. These estuaries were characterised by seawater washing into the estuary over the berm at the mouth and thus had high salinity. The variation in physical environment, changes in climate and transition between biogeographic regions has resulted in regions of high biodiversity. Mangrove, salt marsh and swamp forest species are found in the same region

Multivariate analysis of the dominant and sub-dominant epipelic diatoms and water quality data from South African rivers

Data are presented on the distribution of the dominant and sub-dominant epipelic diatoms found in South African rivers from different regions of the country. A multivariate analysis identified 36 diatom species that were associated with different levels of TDS, PO4, NH4 and SiO2. Three groups of rivers were identified. Group I consisted of sites with high PO4 and SiO2, which corresponded to Durban Metropolitan Area sites, Kruger National Park rivers, the rivers in the Johannesburg Metropolitan Area and the Orange River. In these rivers 12 diatom species were identified that might  indicate those water quality characteristics. Group II included stations where the water quality had high TDS and NH4 values which were associated with most stations in the Swartkops River in the Eastern Cape. The indicators in this group comprised 12 diatom species. Group III were from sampling stations where the water had low levels of minerals, i.e. the upper reaches of the Gamtoos River and the Swartkops River in the Eastern Cape, the Olifants River in the Northern Cape, rivers sampled in KwaZulu-Natal and the Northern Cape. At these sites, 13 diatom species were found as dominants in this better water quality. Water quality data collected during this study showed that over 50% of the river systems display some degree of eutrophication and thus efforts should be made to reduce inputs of nutrients and pollutants to those rivers.Keywords: ammonium, diatoms, phosphate, rivers, South Africa, total dissolved solid

The Physics of Star Cluster Formation and Evolution

© 2020 Springer-Verlag. The final publication is available at Springer via https://doi.org/10.1007/s11214-020-00689-4.Star clusters form in dense, hierarchically collapsing gas clouds. Bulk kinetic energy is transformed to turbulence with stars forming from cores fed by filaments. In the most compact regions, stellar feedback is least effective in removing the gas and stars may form very efficiently. These are also the regions where, in high-mass clusters, ejecta from some kind of high-mass stars are effectively captured during the formation phase of some of the low mass stars and effectively channeled into the latter to form multiple populations. Star formation epochs in star clusters are generally set by gas flows that determine the abundance of gas in the cluster. We argue that there is likely only one star formation epoch after which clusters remain essentially clear of gas by cluster winds. Collisional dynamics is important in this phase leading to core collapse, expansion and eventual dispersion of every cluster. We review recent developments in the field with a focus on theoretical work.Peer reviewe

Overview and status of estuarine microphytobenthos ecological research in South Africa

This article presents a historical overview of estuarine microphytobenthos (MPB) research in South Africa published over the period 1950 to the present, highlighting major milestones, challenges and estuarine management problems, as well as future research needs within the South African context. The studies that were covered comprise peer-reviewed books and journal articles on relevant research conducted in any estuarine environment during the period reviewed. There was a general increase in MPB research outputs over the decades, from only two publications in the 1950s, to over 20 outputs between 2010 and the present. Whereas the MPB studies in South Africa cover a broad spectrum of themes, the research priorities in these works have changed from taxonomically biased studies to those of ecologically based research. Research in the 1950s and 1960s was exclusively taxonomic in nature, with the first ecological investigation incorporating MPB being produced in the 1970s. By the 1980s, ecological studies dominated the research outputs and this trend has persisted to the present. The 1990s and 2000s saw the rise of research into the role of fresh water as a driver of MPB dynamics, whereas the period 2010 to the present saw an increase in more diverse ecological themes, ranging from an autecological investigation to food-web studies and the assessment of multiple drivers of MPB dynamics. However, the majority of studies have focused on either diatoms or estimates of overall MPB biomass. Moreover, there is a regional underrepresentation that runs broadly along biogeographic lines, with the bulk of the work having been conducted in the warm-temperate and subtropical zones of South Africa. Challenges and future research needs for the region are outlined, as is the need to expand MPB research to include other aspects of the biology and ecology of this flor

Overview and status of estuarine microphytobenthos ecological research in South Africa

This article presents a historical overview of estuarine microphytobenthos (MPB) research in South Africa published over the period 1950 to the present, highlighting major milestones, challenges and estuarine management problems, as well as future research needs within the South African context. The studies that were covered comprise peer-reviewed books and journal articles on relevant research conducted in any estuarine environment during the period reviewed. There was a general increase in MPB research outputs over the decades, from only two publications in the 1950s, to over 20 outputs between 2010 and the present. Whereas the MPB studies in South Africa cover a broad spectrum of themes, the research priorities in these works have changed from taxonomically biased studies to those of ecologically based research. Research in the 1950s and 1960s was exclusively taxonomic in nature, with the first ecological investigation incorporating MPB being produced in the 1970s. By the 1980s, ecological studies dominated the research outputs and this trend has persisted to the present. The 1990s and 2000s saw the rise of research into the role of fresh water as a driver of MPB dynamics, whereas the period 2010 to the present saw an increase in more diverse ecological themes, ranging from an autecological investigation to food-web studies and the assessment of multiple drivers of MPB dynamics. However, the majority of studies have focused on either diatoms or estimates of overall MPB biomass. Moreover, there is a regional underrepresentation that runs broadly along biogeographic lines, with the bulk of the work having been conducted in the warm-temperate and subtropical zones of South Africa. Challenges and future research needs for the region are outlined, as is the need to expand MPB research to include other aspects of the biology and ecology of this flora.Keywords: biomass, diatoms, estuaries, literature review, microalgae, sediment stability, taxonom