Abstract
AbstractAimPhytoplankton form the basis of the marine food web and are responsible for approximately 50% of the world's photosynthesis. Changes to their ecology are, therefore, important: here, we examined seasonal patterns in ocean phytoplankton abundance for 45 taxa over 59 years collected from circa 410,000 km of line‐transect sampling at temperate latitudes.LocationThe North Sea.MethodsFor our analysis we used plankton abundance data from the Continuous Plankton Recorder (CPR) survey, sea surface temperature measurements from the Hadley Centre, UK Meteorological Office and wind speed data from the International Comprehensive Ocean–Atmosphere Data Set, NOAA.ResultsWe found large differences in changes in the timing of peak abundance between the major phytoplankton groups. Late‐summer blooming dinoflagellates (n = 10 taxa) tended to show a large seasonal advancement, the timing of peak abundance for dinoflagellates as group advancing 39 days over these six decades. By contrast diatoms (n = 35) did not show any change as a group in their timing of peak abundance over the time series. Granger causality testing suggested a major driver of these phenological changes has been ocean warming in general but more specifically the rate of spring temperature rise as the most important factor. We also found differences in the timing of peak abundance of harmful algal bloom taxa, with some showing peak abundance earlier while others have moved later.Main conclusionsThere has been a fundamental transformation of the classic seasonal progression from blooms of diatoms to dinoflagellates, which lies at the heart of temperate marine food chains, as the classic bimodal diatom and dinoflagellate seasonal peaks are eroded to a more continuous, single, longer‐lasting phytoplankton peak. This phenological shuffling within and between major taxonomic groups is likely to have profound implications for the transfer of energy to higher trophic levels.
Highlights
It is widely accepted that climate change may impact the seasonal timing of biological events such as breeding, migration and seasonal peaks in abundance (Bedford, Johns, Greenstreet, & McQuatters-Gollop, 2018; Boyce, Petrie, Frank, Worm, & Leggett, 2017; Hunter-Cevera et al, 2016; Pecl et al, 2017; Root et al, 2003; Stenseth & Mysterud, 2002; Thackeray et al, 2016)
We found no relationship between the sea surface temperature (SST) and the seasonal peak of the diatoms, either spring or autumn bloomers, nor did we find any correlation between wind speed and the seasonal peaks of any group (Figures S2, S3; Tables S4, S5, S6)
We looked for interactions between aspects of the SST and annual mean wind speed (WSPD) in a regression model predicting the seasonal peaks of the phytoplankton groups—such an interaction may indicate a collective effect of these factors on seasonal peaks
Summary
It is widely accepted that climate change may impact the seasonal timing (phenology) of biological events such as breeding, migration and seasonal peaks in abundance (Bedford, Johns, Greenstreet, & McQuatters-Gollop, 2018; Boyce, Petrie, Frank, Worm, & Leggett, 2017; Hunter-Cevera et al, 2016; Pecl et al, 2017; Root et al, 2003; Stenseth & Mysterud, 2002; Thackeray et al, 2016). The CPR data were used to identify major phenological changes in seasonal abundance of ocean plankton (Edwards & Richardson, 2004), leading to a series of studies that examined plankton phenology across the ocean basins (Atkinson et al, 2015; Chiba, Batten, Sasaoka, Sasai, & Sugisaki, 2012; Schlüter, Kraberg, & Wiltshire, 2012) Often these studies have tended to focus on phytoplankton as one group or to focus only on one or a few taxa; for example, in a recent study, a 13-year time series was used to show how cell division rates for an important picophytoplankter, Synechococcus, was impacted by temperature so that ocean warming caused earlier blooming (HunterCevera et al, 2016). By examining a data set that is unique in terms of its length, spatial coverage and multi-taxa composition, we considered how life history and environment change may interact to impact observed patterns of plankton phenological change
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