Diversity of zooplankton and aquatic macroinvertebrates in the Ntsikeni Nature Reserve

Abstract

The Ntsikeni Nature Reserve is one of 23 wetlands in South Africa that is designated as a Ramsar Wetland of International Importance. The Ntsikeni wetland complex comprises an area of 1070 ha, located within a provincial nature reserve of 9200 ha. This reserve has an altitude in excess of 1800 m, thus making the Ntsikeni wetland complex one of the largest high-altitude wetlands to have obtained protective status under the Ramsar Convention. However, the available aquatic biodiversity information is scanty with very little known apart from the bird diversity of the wetland complex. Therefore, the aim of this research project was to establish the diversity, community structure, and distribution of zooplankton and aquatic macroinvertebrates at the Ntsikeni Nature Reserve. Samples were collected from 10 selected sites located throughout the Ntsikeni Nature Reserve during three seasonal surveys in the winter month of July 2015, the summer month of December 2015, and the autumn month of April 2016. Water and sediment samples were collected in situ and transported back to the laboratory for further analyses. Water samples were analysed to determine nutrient and metal concentrations using the Spectroquant® Pharo 300 and an Agilent 7500ce inductively coupled plasma mass spectrophotometer (ICP-MS) respectively. Sediment analyses were conducted to determine grain size percentages and metal concentrations using accepted techniques. Zooplankton were sampled using a plankton net with a mesh size of 50 μm, while aquatic macroinvertebrates were sampled using standard sweep nets measuring 30 cm x 30 cm with a mesh size of 1 mm. All collected zooplankton and macroinvertebrates were identified to the lowest taxonomic level possible. Water quality variables such as dissolved oxygen, electrical conductivity (EC), and temperature were found to be responsible for macroinvertebrate variation. However, water quality variables had no significant influence on zooplankton community structure. Arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), mercury (Hg), nickel (Ni), silver (Ag) and zinc (Zn) concentrations in the sediment were compared to the Sediment Quality Guidelines (SQG) as provided by the US Environmental Protection Agency (USEPA). The metal concentrations fell within accepted guidelines, however, these sediment quality variables were located in areas with the least macroinvertebrates. Seasonality originally appeared to have an effect on both zooplankton and macroinvertebrate community structures. During the winter survey in July 13 zooplankton taxa and 84 macroinvertebrate taxa were found. During the summer survey in December 18 zooplankton taxa and 95 macroinvertebrate taxa were found. During the autumn survey in April 20 zooplankton taxa and 94 macroinvertebrate taxa were found. However, an analysis of similarities (ANOSIM) revealed that seasonality had no significant influence on zooplankton or aquatic macroinvertebrate community structures of the Ntsikeni Nature Reserve. In total, 25 zooplankton taxa and 129 macroinvertebrate taxa were identified. When the Ntsikeni wetland complex was compared to other water bodies, both nationally and internationally, it was established that the Ntsikeni Nature Reserve contained a high variety of aquatic organisms. Statistical analyses of the combined data revealed the area’s biodiversity, dominant genera, and overall connection between abiotic and biotic factors. Overall, the Ntsikeni wetland complex contains a rich biodiversity of both zooplankton and aquatic macroinvertebrates. The research of this project has assisted in updating the available aquatic biodiversity information for the Ntsikeni Nature Reserve