Abstract
Reductions in calcification in reef-building corals occur when thermal conditions are suboptimal, but it is unclear how they vary between genera in response to the same thermal stress event. Using densitometry techniques, we investigate reductions in the calcification rate of massive Porites spp. from the Great Barrier Reef (GBR), and P. astreoides, Montastraea faveolata, and M. franksi from the Mesoamerican Barrier Reef (MBR), and correlate them to thermal stress associated with ocean warming. Results show that Porites spp. are more sensitive to increasing temperature than Montastraea, with calcification rates decreasing by 0.40 g cm−2 year−1 in Porites spp. and 0.12 g cm−2 year−1 in Montastraea spp. for each 1°C increase. Under similar warming trends, the predicted calcification rates at 2100 are close to zero in Porites spp. and reduced by 40% in Montastraea spp. However, these predictions do not account for ocean acidification. Although yearly mean aragonite saturation (Ωar) at MBR sites has recently decreased, only P. astreoides at Chinchorro showed a reduction in calcification. In corals at the other sites calcification did not change, indicating there was no widespread effect of Ωar changes on coral calcification rate in the MBR. Even in the absence of ocean acidification, differential reductions in calcification between Porites spp. and Montastraea spp. associated with warming might be expected to have significant ecological repercussions. For instance, Porites spp. invest increased calcification in extension, and under warming scenarios it may reduce their ability to compete for space. As a consequence, shifts in taxonomic composition would be expected in Indo-Pacific reefs with uncertain repercussions for biodiversity. By contrast, Montastraea spp. use their increased calcification resources to construct denser skeletons. Reductions in calcification would therefore make them more susceptible to both physical and biological breakdown, seriously affecting ecosystem function in Atlantic reefs.
Highlights
Skeletal calcification in scleractinian corals generates large amounts of calcium carbonate substrate and offsets the physical and biological erosion of reefs [1,2]
The same is true for Montastraea species in the Mesoamerican Barrier Reef (MBR) (F-test, P.0.05), mean calcification rate in M. franksi was significantly lower in Mahahual (0.83 g cm22 year21) than in M. faveolata in Mahahual and Chinchorro Bank (0.96 g cm22 year21 and 0.97 g cm22 year21, respectively) (One-way ANOVA, Tukey’s HSD, P,0.0001, F = 48.24)
Intercepts indicate calcification would cease at 30.0uC in Porites ssp., whereas for Montastraea spp. zero calcification is projected to occur at 35.0uC
Summary
Skeletal calcification in scleractinian corals generates large amounts of calcium carbonate substrate and offsets the physical and biological erosion of reefs [1,2]. During the annual seasonal cycle, the calcification rate increases as temperature increases, until it reaches a maximum in midsummer, after which it declines as temperature decreases [4,16]. This produces the density-banding pattern in massive corals (somewhat analogous to tree-rings) that was first observed by Kuntson and coworkers [17]. Shortand long-term experiments on corals adapted to a specific SST regime have shown that as temperature increases, coral calcification rate increases to a maximum and declines thereafter [20,21,22,23]
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