Time and local geography determine long-term coral responses to
recurrent mass mortalities in densely populated atolls
Abstract
A quarter century after the 1998 El Niño, it is still difficult to
predict how individual reefs will respond to recurring disturbances.
Reports differ on the relative importance of anthropogenic influences,
local geography and bleaching recurrence in determining resistance and
recovery. It is assumed that coral traits largely determine winners and
losers, based on bleaching susceptibility, recruitment, survival and
growth. Whether this translates to the long-term fates of corals on
reefs is still debated. We tracked multi-decadal coral compositional
changes in reefs across the densely populated Lakshadweep Archipelago to
explore how global bleaching events and local geographical factors
(depth and wave exposure) influenced responses to repeated mass
bleaching. Coral resistance increased with recurrent bleaching,
uninfluenced by local geography. However, wave exposure regimes
positively influenced recovery rates, given sufficient time between
mortality events (>7 years). The overall trajectory though,
was of protracted decline interspersed with periods of halting recovery,
with many losers, and few resistant genera that lose less. Based on
these responses, we identified six community clusters that describe
contrasting long-term responses to local and global factors.
Interestingly, genera with different functional traits cluster together,
sharing similar fates, as a result of complex interactions between
bleaching susceptibility, local geography and inter-bleaching intervals.
These clusters provide a clear site-specific predictive framework of
long-term community change, indicating that geography, community and
time largely determine local responses to climate disturbances.