Phytoplankton taxonomic and functional diversity patterns across a coastal tidal front

Type Article
Date 2021-01
Language English
Author(s) Ramond Pierre1, 2, 3, Siano Raffaele2, Schmitt Sophie2, de Vargas Colomban1, 4, Marié Louis5, Memery Laurent6, Sourisseau Marc2
Affiliation(s) 1 : Sorbonne Université, CNRS-UMR7144-Station Biologique de Roscoff, Place Georges Teissier, 29688, Roscoff, France
2 : Ifremer-Centre de Brest, DYNECO/Pelagos, Technopôle Brest Iroise, 29280, Plouzané, France
3 : Department of Marine Microbiology and Biogeochemistry, NIOZ-Royal Netherlands Institute for Sea Research and Utrecht University, Den Burg, The Netherlands
4 : Research Federation for the Study of Global Ocean Systems Ecology and Evolution, FR2022/GOSEE, 3 rue Michel-Ange, 75016, Paris, France
5 : Laboratoire d’Océanographie Physique et Spatiale (LOPS), UMR 6523 Univ. Brest, CNRS, IFREMER, IRD, Plouzané, France
6 : Laboratoire des Sciences de l’Environnement MARin (LEMAR), UMR 6539 Univ. Brest, CNRS, IFREMER, IRD, Plouzané, France
Source Scientific Reports (2045-2322) (Springer Science and Business Media LLC), 2021-01 , Vol. 11 , N. 1 , P. 2682 (15p.)
DOI 10.1038/s41598-021-82071-0
Abstract

Oceanic physics at fine scale; e.g. eddies, fronts, filaments; are notoriously difficult to sample. However, an increasing number of theoretical approaches hypothesize that these processes affect phytoplankton diversity which have cascading effects on regional ecosystems. In 2015, we targeted the Iroise Sea (France) and evidenced the setting up of the Ushant tidal front from the beginning of spring to late summer. Seawater samples were taken during three sampling cruises and DNA-barcoding allowed us to investigate patterns of eukaryotic phytoplankton diversity across this front. First focusing on patterns of taxonomic richness, we evidenced that the front harbored a hotspot of eukaryotic phytoplankton diversity sustained throughout summer. We then detail the ecological processes leading to the formation of this hotspot by studying shifts in community composition across the Iroise Sea. Physical mixing mingled the communities surrounding the front, allowing the formation of a local ecotone, but it was cycles of disturbances and nutrient inputs over the front that allowed a decrease in competitive exclusion, which maintained a higher diversity of rare phytoplankton taxa. These processes did not select a specific ecological strategy as inferred by a trait approach coupled to our taxonomic approach. Instead the front favored higher richness within widespread strategies, resulting in functional redundancy. We detail how fine-scale ocean physics affect phytoplankton diversity and suppose that this interplay is a major control on regional ecosystems.

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