Plankton spatial variability within the Marquesas archipelago, South Pacific

Type Article
Date 2020-12
Language English
Author(s) Martinez Elodie1, 2, Rodier Martine2, 3, Pagano M.3, Sauzede R.2, 4
Affiliation(s) 1 : Institut de Recherche pour le Développement (IRD), University of Bretagne Occidentale (UBO), Centre National de la Recherche Scientifique (CNRS), Ifremer, Laboratoire d'Océanographie Physique et Spatiale (LOPS), IUEM, Brest 29280, France
2 : IRD, University of French Polynesia (UPF), Institut Louis Malardé (ILM), Ifremer, Écosystèmes Insulaires Océaniens (EIO), Tahiti, French Polynesia
3 : Aix Marseille Université, Université de Toulon, CNRS, IRD, Mediterranean Institute of Oceanography (MIO), 13288 Marseille, France
4 : Sorbonne Université, CNRS-INSU, Institut de la Mer de Villefranche, 06230 Villefranche-Sur-Mer, France
Source Journal Of Marine Systems (0924-7963) (Elsevier BV), 2020-12 , Vol. 212 , P. 103432 (13p.)
DOI 10.1016/j.jmarsys.2020.103432
Keyword(s) Island mass effect, Marquesas Islands, South Pacific, Oceanographic cruise, Plankton distribution

The Marquesas Islands, in the central South Pacific, are a place of an outstanding phytoplankton enrichment visible from space and is a hotspot of endemism and biodiversity; however, it has been poorly studied. In situ physical-chemical-biological concomitant observations are almost non-existent and all located close to the main northern island, while ocean dynamics based on satellite observations and numerical modeling show contrasting north/south patterns within the archipelago. Thus, we took the opportunity of the Pakahi I te Moana cruise conducted in 2012 to collect hydrological and plankton samples and investigate biogeochemical spatial patterns, especially north/south, over the archipelago. These data provide the first description of the spatial and vertical distribution of physical, chemical and plankton characteristics over the entire Marquesas archipelago, and gave a first hint to improve our understanding of this planktonic enrichment. The whole archipelago appeared to be a macronutrient-rich environment. Different patterns in the physical, chemical and biological vertical distributions were observed between the northern vs. southern part of the archipelago, and offshore vs. nearshore stations. Phytoplankton biomasses were higher in the north where stratification was weaker, compared to the south and higher close to the islands than offshore. Phytoplankton all over the archipelago was largely dominated by picophytoplankton; specifically, Prochlorococcus presented a more widespread distribution than previously thought and were present over a large range of nutrient concentrations. Copepods were always the most abundant taxa in the archipelago but showed higher mean relative abundances near the islands. The importance of suspension-feeding zooplankton in the northern islands coincided with the highest biomasses of phytoplankton with a predominance of nano- and micro-phytoplankton. This was consistent with a young community responding to nutrient enrichment by an increase of suspension-feeders animals and bottom-up effect on zooplankton. Opposite to this, small copepods were significantly less abundant in the northern offshore region and the dominance of carnivorous forms coincided with low phytoplankton biomass and strong dominance of picoplankton, suggesting a microbial grazing pathway and more mature communities.

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