Plankton production and trophic dynamics in the waters surrounding the Subantarctic Prince Edward Islands archipelago

Abstract

The Southern Ocean is defined as a High Nutrient-Low Chlorophyll (HNLC. region owing to the combined iron and light limitation of phytoplankton that leaves major nutrients unconsumed in surface waters. Nonetheless, the region supports a complex food web shaped by the many interactions that occur between the plankton system and the physico-chemical conditions of the marine environment. An essential source of energy for marine ecosystems is plankton production (a combination of primary and secondary production., which may be particularly important in the vicinity of islands where it can be high due to terrestrial inputs of fundamental nutrients – the so-called Island Mass Effect (IME.. Marine ecosystems are currently experiencing rapid change, particularly at high latitudes, yet little is known about the ’baseline’ state of trophic carbon fluxes in these systems, which is key to understanding their potential response(s. to ongoing and future perturbations. We investigated plankton production and trophic dynamics in the waters surrounding the Subantarctic Prince Edward Islands archipelago during two expeditions to the Southern Ocean – the Antarctic Circumnavigation Expedition in December 2016 (summer. and the South African National Antarctic Programme (SANAP. cruise to Marion Island in April/May 2017 (autumn.. We collected biological (e.g., phyto- and zooplankton abundance, biomass, diversity. and chemical (e.g., dissolved organic carbon, nutrients, carbon and nitrogen isotopes. samples, and conducted experiments to determine important biogeochemical rates (e.g., primary and secondary production, nutrient regeneration. in the open Subantarctic Ocean and in the vicinity of the islands. Our results on planktonic trophic structure, rates of production, nutrient biogeochemistry and their interactions will be discussed in the context of Subantarctic ecosystem carbon cycling and the IME. - Abstract as displayed in the - Abstract booklet. The presentation on the day may differ from the - Abstract.