Shifted dynamics of plankton communities in a restored lake: exploring the effects of climate change on phenology through four decades

Sj Moe,B Skjelbred,A Hobæk,Je Løvik,J Persson

doi:10.3354/cr01654

Sj Moe, B Skjelbred + Show 3 more

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https://doi.org/10.3354/cr01654

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Journal: Climate research	Publication Date: Apr 19, 2021
Citations: 5	License type: CC BY 4.0

Affiliation: Norwegian Institute for Water Research

Abstract

Lake surface temperatures have increased globally in recent decades. Climate change can affect lake biota directly via enhanced water temperatures, shorter ice cover duration and prolonged stratification, and indirectly via changes in species interactions. Changes in the seasonal dynamics of phytoplankton and zooplankton can further affect whole lake ecosystems. However, separating the effects of climate change from the more direct and dominating effects of nutrients is a challenge. Our aim was to explore the ecological effects of climate change while accounting for the effects of re-oligotrophication in Lake Mjøsa, the largest lake in Norway. While restoration measures since the 1970s have resulted in strongly reduced nutrient levels, the surface water temperature has increased by almost 0.4°C decade-1 during the same period. We analysed long-term trends and abrupt changes in environmental and biological time series as well as changes in the seasonal dynamics of individual plankton taxa. The general long-term trends in phenology were diverging for phytoplankton (later peaks) vs. zooplankton (earlier peaks). However, individual taxa of both phytoplankton and zooplankton displayed earlier peaks. Earlier peaks of the phytoplankton group Cryptophyceae can be explained by increased spring temperature or other climate-related changes. Earlier onset of population growth of certain zooplankton species (Limnocalanus macrurus and Holopedium gibberum) can also be explained by climatic change, either directly (earlier temperature increase) or more indirectly (earlier availability of Cryptophyceae as a food source). In the long run, climate-related changes in both phytoplankton and zooplankton phenology may have implications for the fish communities of this lake.

Highlights

Lake ecosystems can be considered as sentinels of climate change (Adrian et al 2009)
The lake temperature has continued to increase in the years following our study period, with the highest maximum temperature recorded in 2018 (Lyche Solheim et al 2020)
The timing of the central tendency has shifted to later in the season, while the timing of the peak values is unchanged according to the MK trend analysis (Table 1)

Summary

Introduction

Lake ecosystems can be considered as sentinels of climate change (Adrian et al 2009). Lake summer surface temperatures have increased on average by 0.32°C decade−1 in recent decades (O’Reilly et al 2015). In Lake Mjøsa, the largest lake in Norway, the surface water temperature has increased by almost 0.4°C decade−1 during the last 40 yr Besides the general warming trends, changes in precipitation and episodic events such as extreme heat have been observed and are forecast to increase further (IPCC 2014). Both warming and extreme events affect the biota of lakes — directly via enhanced water temperatures that influence phenology (i.e. timing), biomass production and metabolic processes, and indirectly via a suite of effects Ecological responses to climate change in lakes show site-specific patterns, influenced by local conditions such as community structure and species interactions (Flaim et al 2016)

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