  Seed formation is part of the reproductive cycle, leading to the accumulation
of resistance stages that can withstand harsh environmental conditions for long
periods of time. At the community level, multiple species with such
long-lasting life stages can be more likely to coexist. While the implications
of this process for biodiversity have been studied in terrestrial plants, seed
banks are usually neglected in phytoplankton multispecies dynamic models, in
spite of widespread empirical evidence for such seed banks. In this study, we
build a metacommunity model of interacting phytoplankton species, including a
resting stage supplying the seed bank. The model is parameterized with
empirically-driven growth rate functions and field-based interaction estimates,
which include both facilitative and competitive interactions. Exchanges between
compartments (coastal pelagic cells, coastal resting cells on the seabed, and
open ocean pelagic cells) are controlled by hydrodynamical parameters to which
the sensitivity of the model is assessed. We consider two models, i.e., with
and without a saturating effect of the interactions on the growth rates. Our
results are consistent between models, and show that a seed bank allows to
maintain all species in the community over 30 years. Indeed, a fraction of the
species are vulnerable to extinction at specific times within the year, but
this process is buffered by their survival in their resting stage. We thus
highlight the potential role of the seed bank in the recurrent re-invasion of
the coastal community, and of coastal environments in re-seeding oceanic
regions. Moreover, the seed bank enables populations to tolerate stronger
interactions within the community as well as more severe changes to the
environment, such as those predicted in a climate change context. Our study
therefore shows how resting stages may help phytoplanktonic diversity
maintenance.
