Seasonal Variations in the Biodiversity, Ecological Strategy, and Specialization of Diatoms and Copepods in a Coastal System With Phaeocystis Blooms: The Key Role of Trait Trade-Offs

Elsa Breton,Oscar Demonio,Christophe Salmeron,Loïck Kléparski,Gregory Beaugrand,Sophie Ferreira,Dimitra-Ioli Skouroliakou,Antoine Nowaczyk,Muriel Crouvoisier,Laurent Seuront,Eric Goberville,Jean-Michel Brylinski,David Pecqueur,Benoit Sautour,Urania Christaki,Adrien Poquet,Arnaud Lheureux

doi:10.3389/fmars.2021.656300

Abstract

Although eutrophication induced by anthropogenic nutrient enrichment is a driver of shifts in community composition and eventually a threat to marine biodiversity, the causes and consequences on ecosystem functioning remain greatly unknown. In this study, by applying a trait-based approach and measuring niche breadth of diatoms and copepods, the drivers and underlying mechanisms of the seasonal species succession of these ecological communities in a coastal system dominated in spring by Phaeocystis blooms were explored. It is suggested that the seasonal succession of diatoms and copepods is the result of several trade-offs among functional traits that are controlled by the seasonal abiotic and biotic pressure encountered by the plankton communities. The results of this study highlight that a trade-off between competition and predator, i.e., weak competitors are better protected against predation, plays an important role in promoting plankton species richness and triggers the Phaeocystis bloom. As often observed in eutrophicated ecosystems, only the biotic homogenization of the copepod community and the shift in the diet of copepods toward Phaeocystis detrital materials have been detected during the Phaeocystis bloom. The diatom and copepod communities respond synchronously to fluctuating resources and biotic conditions by successively selecting species with specific traits. This study confirms the key role of competition and predation in controlling annual plankton succession.

Highlights

Coastal eutrophication induced by anthropogenic nutrient enrichment is one of the major threats to biodiversity (Vitousek et al, 1997; Halpern et al, 2008; Howarth, 2008)
Zooplankton biomass was mainly composed of copepods, except during the seasonal outburst of the meroplankton that was mainly composed of Echinodermata
While a slight decrease was observed during the peak of Phaeocystis, the biomass of diatoms followed the same seasonal dynamics as protozooplankton and copepods (Figures 3A–D)

Summary

Introduction

Coastal eutrophication induced by anthropogenic nutrient enrichment is one of the major threats to biodiversity (Vitousek et al, 1997; Halpern et al, 2008; Howarth, 2008). Eutrophication may cause excessive blooms of opportunistic species, species loss (Smith and Schindler, 2009) and, subtle changes in functional trait composition; and may even lead to a loss of functional diversity (FD) caused by a biotic homogenization by favoring generalist (species with broad environmental tolerances) over specialist (species well adapted to particular habitats) species: the latter showed narrower niche breadth and a lower tolerance to high nutrient levels (e.g., Clavel et al, 2011; Nelson et al, 2013; Villéger et al, 2014; Wengrat et al, 2018; Chihoub et al, 2020). Biotic changes may alter biodiversity by selecting species that possess functional traits that confer to them a selecting advantage. Understanding how functional traits relate to associated ecological strategies (i.e., a combination of functional attributes reflecting how species cope with their environment) and ecological specialization across productivity gradients, which defines the degree of tolerance to changing environmental conditions, is, important to better measure ecosystem functioning and health

Methods

Results

Discussion

Conclusion