Global warming reshuffling marine plankton communities

Forming the basis of the ocean's food web, marine plankton are essential to a number of ecosystem services including carbon sequestration. Increasing sea temperatures may promote speciation and diversity, but also force species to shift their ranges to more suitable climates.

In this paper, researchers built an ensemble of species distribution models for more than 800 species of phyto- and zooplankton based on occurrence records mediated by GBIF and other sources, coupled with environmental variables such as surface temperature, oxygen concentration, solar irradiance and macronutrient levels.

For the present time, the constructed models predicted strong latitudinal richness gradients with overall annual means decreasing from the equator towards the poles. Phytoplankton displayed richness peaks in tropical upwellings, whereas zooplankton peaked in the subtropics.

Projecting the models into a future climatic scenario of high greenhouse gas emissions, the researchers found an overall global increase in mean species richness by the end of the century, driven primarily by changes in ocean surface temperature. The models, however, also predicted poleward shifts of species' distributions at a velocity of 35 km/decade, leading to net increases in species diversity in temperate latitudes and decreases in the tropics.

As the ranges of species shift, the composition of plankton communities would be restructured with novel species interactions. The authors suggest that the combined changes could weaken the biological carbon pump effect of plankton carbon sequestration with the risk of functional ecosystem collapse in particularly sensitive regions.