Diminishing potential for tropical reefs to function as coral diversity strongholds under climate change conditions

Aim: Forecasting the influence of climate change on coral biodiversity and
reef functioning is important for informing policy decisions. Dominance
shifts, tropicalisation and local extinctions are common responses of
climate change, but uncertainty surrounds the reliability of predicted
coral community transformations. Here, we use species distribution models
(SDMs) to assess changes in suitable coral habitat and associated patterns
in biodiversity across Western Australia (WA) under present-day and future
climate scenarios (RCP 2.6 and RCP 8.5). Location: Coral reef systems in
WA. Methods: We developed SDMs with model prediction uncertainty analyses,
using specimen-based occurrence records of 188 hermatypic scleractinian
coral species and seven variables to estimate present-day and future
changes to coral species distribution and biodiversity patterns in WA
under climate change conditions. Results: We found that suitable habitat
is predicted to increase across all regions in WA under RCP2.6 2050,
RCP8.5 2050 and RCP2.6 2100 scenarios with all tropical and subtropical
regions remaining coral biodiversity strongholds. Under the extreme RCP8.5
2100 scenario however, a clear tropicalisation trend could be observed
with coral species expanding their range to mid-higher latitude regions,
while a substantial drop in coral species richness was predicted at low
latitude tropical coral reefs, such as the inshore Kimberley and offshore
NW reefs. Despite the predicted expansion south, we identified a net
decline in biodiversity across the WA coastline. Main Conclusions: Results
from the models predicted higher net biodiversity loss at low latitude
tropical regions compared to net gains at mid-high latitude regions under
RCP8.5 2100. These results are likely to be representative of latitudinal
trends across the southern hemisphere and highlight that increases in
habitat suitability at higher latitudes may not lead to equivalent
biodiversity benefits. Urgent action is needed to limit climate change to
prevent spatial erosion of tropical coral communities, extinction events
and loss of tropical ecosystem services.