Abstract
As primary producers, phytoplankton play a pivotal role in the marine environment and are central to many biogeochemical processes. Changes to phytoplankton community composition could have major consequences for wider ecosystem functioning and may occur in response to climate change. Here we describe multi-decadal variability in phytoplankton community structure using taxonomic data from the Continuous Plankton Recorder collected in the North-East Atlantic from 1969-2013, using a total of 42 diatom and dinoflagellate taxa. We considered a range of characteristics of community structure, including taxonomic diversity and community stability and disorder, and how these characteristics change in response to sea surface temperature, mixed layer depth and the North Atlantic Oscillation. We found that phytoplankton community composition was largely stable on interannual timescales. A change in community composition occurred between 1985 and 1995 due to an increased dominance of 2 diatom taxa (Rhizosolenia styliformis and Thalassiosira spp.); however, after this period, the community returned to its previous composition. Further, a community disorder analysis found that phytoplankton compositional structure became more rigid in recent years, which may lead to an eventual community shift in the future. In contrast to previous studies that revealed relationships between total phytoplankton abundance or biomass and environmental forcing, we found that community structure had, at most, a very weak relationship with the environmental parameters tested. Changes to the physical environment may therefore have less influence at interannual timescales on phytoplankton community structure than previously thought.
Highlights
IntroductionThe stability of community taxonomic composition largely depends on the capacity for individual taxa to withstand perturbation, with external forcing capable of altering a community over multiple spatio-temporalPublisher: Inter-Research · www.int-res.comMar Ecol Prog Ser 655: 43–57, 2020 tem functioning and predator−prey relationships, causing trophic mismatch (Edwards & Richardson 2004, Beaugrand et al 2008, Eggers et al 2014).In a community of taxa with similar resource needs, the community composition can be maintained through trade-offs between intrinsic population growth capacity and competitive impact through growth rates and nutrient affinity (Dakos et al 2009, Doncaster et al 2016)
The aim of this study was to evaluate the stability of phytoplankton composition in the North-East Atlantic, an environment that has changed substantially over the past half century, by testing the following hypotheses: (1) there was no significant, persistent change in the diversity and structure of the phytoplankton community in the North-East Atlantic between 1969 and 2013; and (2) there is no relationship between phytoplankton community structure and Sea surface temperature (SST), mixed layer depth (MLD) or North Atlantic Oscillation (NAO) index in the North-East Atlantic
The findings presented here suggest that the mechanisms driving long-term ecological change in phytoplankton community composition within the North-East Atlantic are highly complex and perhaps more uncertain than previously described
Summary
The stability of community taxonomic composition largely depends on the capacity for individual taxa to withstand perturbation, with external forcing capable of altering a community over multiple spatio-temporalPublisher: Inter-Research · www.int-res.comMar Ecol Prog Ser 655: 43–57, 2020 tem functioning and predator−prey relationships, causing trophic mismatch (Edwards & Richardson 2004, Beaugrand et al 2008, Eggers et al 2014).In a community of taxa with similar resource needs, the community composition can be maintained through trade-offs between intrinsic population growth capacity and competitive impact through growth rates and nutrient affinity (Dakos et al 2009, Doncaster et al 2016). Due to the diverse role that phytoplankton play in the marine environment, much research has been devoted to fluctuations in the abundance, biomass and community composition of these organisms (Dutkiewicz et al 2001, Beaugrand & Reid 2003, Sommer & Lengfellner 2008). The physical environment has been implicated as the dominant factor driving population fluctuations over interannual timescales (Beaugrand & Reid 2003, Leterme et al 2005); this remains under debate, with some studies concluding that predator−prey and other ecological interactions drive the variability (Benincà et al 2008, Dakos et al 2009, Boeing 2016). The variability of phytoplankton on longer timescales (multi-decadal, geological) is less studied, especially in regard to shifts in community composition (Cermeño et al 2008)
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