The annual cycles of phytoplankton biomass

Abstract

Terrestrial plants are powerful climate sentinels because their annual cycles of growth, reproduction and senescence are finely tuned to the annual climate cycle having a period of one year. Consistency in the seasonal phasing of terrestrial plant activity provides a relatively low-noise background from which phenological shifts can be detected and attributed to climate change. Here, we ask whether phytoplankton biomass also fluctuates over a consistent annual cycle in lake, estuarine -coastal and ocean ecosystems and whether there is a characteristic phenology of phytoplankton as a consistent phase and amplitude of variability. We compiled 125 time series of phytoplankton biomass (chlorophyll a concentration) from temperate and subtropical zones and used wavelet analysis to extract their dominant periods of variability and the recurrence strength at those periods. Fewer than half (48%) of the series had a dominant 12-month period of variability, commonly expressed as the canonical spring-bloom pattern. About 20 per cent had a dominant six-month period of variability, commonly expressed as the spring and autumn or winter and summer blooms of temperate lakes and oceans. These annual patterns varied in recurrence strength across sites, and did not persist over the full series duration at some sites. About a third of the series had no component of variability at either the six-or 12-month period, reflecting a series of irregular pulses of biomass. These findings show that there is high variability of annual phytoplankton cycles across ecosystems, and that climate-driven annual cycles can be obscured by other drivers of population variability, including human disturbance, aperiodic weather events and strong trophic coupling between phytoplankton and their consumers. Regulation of phytoplankton biomass by multiple processes operating at multiple time scales adds complexity to the challenge of detecting climate-driven trends in aquatic ecosystems where the noise to signal ratio is high.

Long-Term Trends and Temporal Synchrony in Plankton Richness, Diversity and Biomass Driven by Re-Oligotrophication and Climate across 17 Danish Lakes

“…This suggests that either the climatic changes were not strong enough to induce a trend in lake water, except for summer, or that the effect of these variables was confounded by catchment-specific factors. An analysis of 125 freshwater and marine phytoplankton time series demonstrated that climate-driven phytoplankton biomass cycles were heavily obscured by other drivers of population variability, indicating the difficulty of detecting climate-driven trends in plankton communities [58]. However, a long-term warming trend has been documented for both North American [17,18] and European [19,20] deep lakes in investigations covering a longer time period than in our study.…”

Automated calculation of surface energy fluxes with high-frequency lake buoy data

“…Winder and Cloern, 2010;Read et al 2012). Similarly, Lake Heat Flux Analyzer can be used for global scale research by calculating the surface fluxes using the same method, which is essential for cross-site collaboration.…”

Seasonal and Inter-Annual Analysis of Chlorophyll-a and Inherent Optical Properties from Satellite Observations in the Inner and Mid-Shelves of the South of Buenos Aires Province (Argentina)

“…Phytoplankton is very sensitive to environmental changes, and shifts in cyclical behavior are reported to occur because of changes (such as ENSO events), that modify the climate and meteorological forces, at short and long time scales [74]. The decrease of rainfall in 2007-2008 (La Niña) generated a reduction in the freshwater and nutrients inputs and also an increase in the salinity, which could possibly cause deep changes in phytoplankton community composition [75,76].…”