Functional divergence from ecological baselines on Caribbean coral reefs

Understanding how emergent ecological assemblages have diverged from
natural states is fundamental in predicting future functioning and
services of ecosystems. Coral reefs are of particular concern due to their
high susceptibility to anthropogenic stressors. Yet, little is known about
their pre-disturbance ranges of natural states, and most reports of
decline are based on a limited number of sites and high levels of
uncertainty. Here, we used a novel approach to estimate the physical
functionality of reefs across marine ecoregions based on habitat
suitability and morpho-functional traits for coral species. We calibrated
ecological niche models for 49 reef-building corals of the Greater
Caribbean based on occurrence records and environmental predictors, which
we combined with species-specific functional coefficients derived from
morpho-functional traits reflecting their contribution to the reef
three-dimensional structure to estimate the reef functional potential
(RFP). We then assessed the degree of divergence of western Caribbean
reefs by comparing our physical functionality estimates against recent
field data evaluations. We found spatial variability in RFP across the
Caribbean, with the highest mean value in the western Caribbean and the
lowest in areas with marginal environmental conditions. Hotspots of RFP
exist along the coast of Belize and the southeast of Cuba. Overall, 84% of
sites along the western Caribbean showed a substantial reduction in their
physical functioning, with the highest reductions occurring within
hotspots, implying that reefs displaying the greatest changes have high
initial RFP. We conclude that combining niche models with species
morpho-functional traits is a valuable and promising approach to estimate
the large-scale functional potential of communities and the degree of
change in the absence of ecological baselines. These findings have
important implications and could be used to guide efforts to preserve
coral reefs functionality and define priority conservation areas in the
Caribbean.