Cascading effects of climate change on plankton community structure

Plankton communities account for at least half of global primary
production and play a key role in the global carbon cycle. Warming and
acidification may alter the interaction chains in these communities from
the bottom and top of the food web. Yet, the relative importance of these
potentially complex interactions has not yet been quantified. Here we
examine the isolated and combined effects of warming, acidification, and
reductions in phytoplankton and predator abundances in a series of
factorial experiments. We find that warming directly impacts the top of
the food web, but that the intermediate trophic groups are more strongly
influenced by indirect effects mediated by altered top-down interactions.
Direct manipulations of predator and phytoplankton abundance reveal
similar strong top-down interactions following top predator decline. A
meta-analysis of published experiments further support the conclusion that
warming has stronger direct impacts on the top and bottom of the food web
rather than the intermediate trophic groups, with important differences
between freshwater and marine plankton communities. Our results reveal
that the trophic effect of warming cascading down from the top of the
plankton food web is a powerful agent of global change.