Future phytoplankton diversity in a changing climate

Abstract

The future response of marine ecosystem diversity to continued anthropogenic forcing is poorly constrained. Phytoplankton are a diverse set of organisms that form the base of the marine ecosystem. Currently, ocean biogeochemistry and ecosystem models used for climate change projections typically include only 2-3 phytoplankton types and are, therefore, too simple to adequately assess the potential for changes in plankton community structure. Here, we analyse a complex ecosystem model with 35 phytoplankton types to evaluate the changes in phytoplankton community composition, turnover and size structure over the 21st century. We find that the rate of turnover in the phytoplankton community becomes faster during this century, that is, the community structure becomes increasingly unstable in response to climate change. Combined with alterations to phytoplankton diversity, our results imply a loss of ecological resilience with likely knock-on effects on the productivity and functioning of the marine environment.

Fig. 1. Change in phytoplankton community structure by the end of the century.

For subplots a–d, f the change between the baseline period (mean of 2005−2024) and end of the century (mean of 2081−2100) is shown. a Percent change in total phytoplankton biomass; b percent change in richness; c percent change in evenness; d community turnover; e change in community turnover rate (turnover between the mean of 2061−2080 and 2081−2100 minus mean of 2011−2030 and 2031−2040); f change in slope of the phytoplankton community size structure, where negative values indicate a greater abundance of small phytoplankton types.

Fig. 2. Appearance and disappearance of phytoplankton types by the end of the century.

The number of phytoplankton types appearing (a–d) and disappearing (e–h) between the baseline period (mean of 2005−2024) and end of century period (mean of 2081−2100) in each of six groups: coccolithophores (a, e), of which there are five types; diazotrophs (b, f), of which there are five types; diatoms (c, g), of which there are 11 types; mixotrophic dinoflagellates (d, h), of which there are 10 types. Prokaryotes and picoeukaryotes (of which there are two types of each) do not show any significant changes. Appearance (disappearance) is defined as a type contributing >0.1% (<0.1%) to total biomass.