Zooplankton abundance biovolume and composition in the uThukela pelagic zone, KwaZulu-Natal (KZN).

Abstract

The uThukela Banks is one of the three new (2019) Marine Protected Areas (MPAs) in KwaZulu-Natal (KZN) established through Operation Phakisa; a national initiative which set out to achieve 5% protection of South Africa’s waters by 2018 through a representative MPA network. As part of the African Coelacanth Ecosystem Programme (ACEP) Spatial Solutions project, this study aimed to provide baseline data on zooplankton communities in the uThukela Banks pelagic zone and to assess zooplankton community structure in waters overlying reef and sand substrates as well as within and outside of the MPA. Due to their rapid turnover rates, zooplankton are essential in marine food webs and can be used as bioindicators in the pelagic region. Zooplankton samples were collected in 2016 at 18 sites in the KZN Bight area, including the uThukela Banks MPA. Zooplankton community structure was compared between locations (inside/outside the MPA) and underlying substrate types (reef/sand). The samples were analysed in terms of overall zooplankton abundance and composition as well as a more detailed analysis of meroplankton community structure. Zooplankton abundance was significantly higher over sand substrate than over reef substrate, potentially because reef substrates support a higher abundance of zooplanktivorous fish. Higher abundance was also found over sand substrates located outside the MPA, possibly because sand substrate dominated the stations outside the MPA. These sites were also usually located downstream of the Agulhas Current, suggesting the southward transportation of zooplankton. Copepoda contributed over 65% of the total zooplankton abundance inside and outside the MPA, with Appendicularia contributing 14% inside and 6% outside the MPA. Chaetognatha, Hydrozoa, and Decapoda were also among the dominant groups. Fifty-one meroplankton taxa were recorded, with Caridea being the most abundant across all stations. Inside the MPA, Portunidae, Alpheidae, and Paguridae followed in abundance, while Callianassidae dominated sand stations outside the MPA, contributing over 20% to total abundance. pH was the only environmental factor that significantly influenced both zooplankton and meroplankton abundance. Although not included in this study, currents also play an essential role due to the drifting nature of zooplankton. This study provides baseline data on the zooplankton communities in the uThukela Banks pelagic zone, contributing to systematic conservation planning for the KZN coastal waters.