Environmental forcing
For the environmental forcing, we used the Sea Surface Temperature and
Mixed Layer Depth (ECCO Consortium et al., 2021) daily mean of 10 years
(2000- 2010) of an offshore region of the Mid-Atlantic Bight, a
representative North Atlantic temperate ecosystem (Figures 1, SM1, and
Supplementary Materials).
We ran the model for 50 years to allow the community to reach a
steady-state condition (hereafter pre-heatwave conditions). Our focus is
solely on examining the temperature effects on plankton communities of a
specific water mass. Thus, we didn’t change the mixed layer depth (MLD)
and nutrient input, acknowledging that this simplification reduces the
complexity typically found in natural ecosystems. For the marine
heatwave scenarios, we exposed the steady-state community to a 4 ˚C
temperature anomaly lasting for one season (three months) for either
winter (December- February), spring (March- May), summer (June- August),
or autumn (September- November). Observed heatwaves range in duration
from days to months, with no universally applicable average duration due
to variations influenced by factors like event intensity, geographic
location, and specific oceanographic conditions . For example, the
oceanic waters of the Northeastern United States Continental Shelf have
experienced long seasonal heatwaves up to 3 ˚C since 2012 . In this
context, we have opted to investigate the impact of an extended and
intense heatwave on plankton communities, portraying it as an extreme
scenario that may become increasingly common within ecosystems due to
ongoing climate change. After the heatwave event, we ran the model for
another 19 years with the pre-heatwave SST to examine the period needed
for the community to readjust to the pre-heatwave condition. To isolate
the processes responsible for the observed changes, we ran two
additional simulations. In the first, heatwaves solely affect protists’
rates, while in the second, only copepods are sensitive to the elevated
temperature. These experiments enabled us to examine whether changes in
communities are driven by direct temperature effects, indirect
temperature effects, or a combination of both.