- Dona Paula, Goa, India.
- +91-0832- 2450327
- iiosc2020[at]nio[dot]org
Abstract Submission No. | ABS-2022-06-0395 |
Title of Abstract | Microzooplankton communities associated with diverse oceanographic environments in the South West Indian Ocean |
Authors | Jenny Huggett*, Seshnee Maduray, Margaux Noyon, Rene Brink, Sandisiwe Gwadela, Tabile Maseti |
Organisation | Department of Forestry, Fisheries and the Environment |
Address | Department of Forestry, Fisheries and the Environment, Private Bag X4390 Cape Town, Western Cape, South Africa Pincode: 8000 Mobile: 832541254 E-mail: jenny.huggett@gmail.com |
Country | South Africa |
Presentation | Oral |
Abstract | Microzooplankton play a key but largely understudied role in marine ecosystems as primary and often significant consumers of phytoplankton, important contributors to the diet of mesozooplankton, and nutrient recyclers. Image analysis was used to explore the abundance and taxonomic composition of microzooplankton communities associated with three different oceanographic environments in the South West Indian Ocean: the southern continental shelf of Madagascar, a cyclonic eddy off the southwest shelf of Madagascar, and Walters Shoals, a shallow seamount on the Madagascar Ridge. Sampling off Madagascar was conducted in July 2013 on the RV Algoa, whereas the Walters Shoals study was conducted in May 2017 on the RV Marion Dufresne. Water samples for microzooplankton analysis were collected from the surface and depth of maximum fluorescence (fmax) at 15 stations on the southern Madagascar shelf, from the surface, fmax and within the upper mixed layer (UML) at 25 stations along a transect though the cyclonic eddy, and from the surface and fmax at 24 stations surrounding Walters Shoals. Samples (5-12 L) were pre-filtered through 200-µm mesh and collected on 20-µm mesh. Samples collected off Madagascar in 2013 were processed live onboard the vessel using a FlowCam at 4x magnification, then preserved with formaldehyde, whereas those collected from Walters Shoals were preserved onboard the vessel and analysed later in the laboratory, following the same procedure. Mean abundance of microzooplankton in surface samples was significantly greater in the cyclonic eddy (157 L-1) compared to the nearby shelf (74 L-1), and abundance was greater at the surface than at the fmax. Microzooplankton communities in the eddy surface samples were dominated by dinoflagellates (53 L-1), followed by ciliates (35 L-1), radiozoans (33 L-1) and copepod nauplii (15 L-1). Dinoflagellates were significantly more abundant in the eddy core compared to the eddy periphery, likely due to enhanced primary production in the core through upwelling of nutrients from deeper layers, but there were no significant differences between eddy zones for the other groups. Microzooplankton abundance was significantly reduced over the Walters Shoals seamount compared to the Madagascar shelf and eddy, with mean values of 23 and 16 L-1 at the surface and fmax respectively. Dinoflagellates were again most abundant (13 and 6 L-1), followed by ciliates (5 and 6 L-1), with very low abundances of radiozoans and copepod nauplii (<1 L-1). |