Abstract
To identify the environmental factors that drive plankton community composition and structure in coastal waters, a shallow northwestern Mediterranean lagoon was monitored from winter to spring in two contrasting years. The campaign was based on high-frequency recordings of hydrological and meteorological parameters and weekly samplings of nutrients and the plankton community. The collected data allowed the construction of correlation networks, which revealed that water temperature was the most important factor governing community composition, structure and succession at different trophic levels, suggesting its ubiquitous food web control. Temperature favoured phytoplanktonic flagellates (Cryptophyceae, Chrysophyceae, and Chlorophyceae) and ciliates during winter and early spring. In contrast, it favoured Bacillariophyceae, dinoflagellates, phytoplankton < 6 µm and aloricate Choreotrichida during spring. The secondary factors were light, which influenced phytoplankton, and wind, which may regulate turbidity and the nutrient supply from land or sediment, thus affecting benthic species such as Nitzschia sp. and Uronema sp. or salinity-tolerant species such as Prorocentrum sp. The central role of temperature in structuring the co-occurrence network suggests that future global warming could deeply modify plankton communities in shallow coastal zones, affecting whole-food web functioning.
Highlights
Environmental forcing factors play a central role in driving plankton community composition and dynamics in marine and freshwater ecosystems
The present study’s objective was to investigate environmental factors associated with changes in plankton community composition and structure in a highly dynamic system, Thau Lagoon, a shallow coastal lagoon along the northwestern Mediterranean coast
No studies were made on the role of water temperature, and other environmental factors, on the structure and succession of the entire plankton community
Summary
Environmental forcing factors play a central role in driving plankton community composition and dynamics in marine and freshwater ecosystems. Few studies have investigated the environmental forcing factors structuring the plankton community composition and structure in shallow coastal waters, preventing a deep understanding of plankton food web functioning. In addition to being routinely applied to model planktonic food webs, network analysis is a powerful tool for studying the effects of abiotic forcing factors on plankton food webs[23,24] It can, for example, shed light on the role of complex physico-chemical changes responsible for shifts in planktonic food webs triggered by environmental forcing, for example, anthropogenic hydrology alterations in natural coastal lagoons[24]. The present study follows two previous works that focused on the environmental forcing factors triggering phytoplankton blooms initiation[19] and on the microbial food web interactions in Thau L agoon[22] These studies found that the particular climatic characteristics of 2016 led to a the dominance of small size phytoplankton in the community[19]. The present study will, for the first time, quantitatively link multiple environmental variables to plankton community composition and structure in a characteristic shallow coastal lagoon
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