Calcification of coral assemblages in the eastern Pacific: Reshuffling calcification scenarios under climate change

Abstract

The rearrangement of coral assemblages may produce significant changes in coral community calcification, yet it is not understood how the modification of community structure in depauperate areas under climate change scenarios may affect reef functionality. Observed coral community calcification (OCC) was calculated using coral cover data from 126 sites across the eastern tropical Pacific (ETP). To assess the effect that species assemblages exert on potential coral community calcification (PCC) of ETP reefs, we implemented a novel permutation approach for this purpose. We contrasted OCC across the ETP against the PCC of hypothetical monospecific and maximum ecological evenness (ME) ETP reefs and monogeneric Indo-Pacific (IP) and Caribbean (C) reefs. Average coral cover (21 ± 23%; mean ± SD) and OCC (8.23 ± 11.32 kg m−2 yr−1; mean ± SD) in the ETP were not related to species richness but to Pocillopora abundance and calcification. For any level of coral abundance or species richness, the permutation model indicates that PCC depends on community structure: the PCC of Pocillopora monospecific reefs reaches its maximum; PCC drops to half of its potential when ME is attained; and PCC reaches its minimum when slow-growing species turn dominant. A dynamic model with changing community structure based on the differential species tolerance to climate change showed a similar pattern as the permutation model. ETP Pocillopora reefs have lower PCC than IP Acropora, IP Pocillopora and C Acropora. Massive taxa are more tolerant to climate change and could replace branching taxa if environmental pressure trends in the ETP continue, meaning an ∼85% drop in PCC.