Abstract
Estimates of heritability inform evolutionary potential and the likely outcome of many management actions, but such estimates remain scarce for marine organisms. Here, we report high heritability of calcification rate among the eight most dominant Hawaiian coral species under reduced pH simulating future ocean conditions. Coral colonies were sampled from up to six locations across a natural mosaic in seawater chemistry throughout Hawaiʻi and fragmented into clonal replicates maintained under both ambient and high pCO2 conditions. Broad sense heritability of calcification rates was high among all eight species, ranging from a low of 0.32 in Porites evermanni to a high of 0.61 in Porites compressa. The overall results were inconsistent with short-term acclimatization to the local environment or adaptation to the mean or ideal conditions. Similarly, in ‘local vs. foreign’ and ‘home vs. away’ tests there was no clear signature of local adaptation. Instead, the data are most consistent with a protected polymorphism as the mechanism which maintains differential pH tolerance within the populations. Substantial individual variation, coupled with high heritability and large population sizes, imply considerable scope for natural selection and adaptive capacity, which has major implications for evolutionary potential and management of corals in response to climate change.
Highlights
We show that coral calcification rates varied significantly among species, conspecific colonies and pH treatments, with significant interactions between colony and pH treatment in only 2 of 8 species (Pocillopora meandrina and Porites evermanni)
Broad sense heritability of calcification rates was high among all eight species, ranging from 0.32 in Porites evermanni to 0.61 in Porites compressa
Future studies that incorporate multifactorial stressors, and consider interactions and trade-offs among them, should be performed to better predict how scleractinian corals might respond under global change scenarios
Summary
Sample collection.Samples of each of the most common reef-building corals in Hawaii (Pocillopora acuta, P. meandrina, Montipora capitata, M. patula, M. flabellata, Porites compressa, P. evermanni, and P. lobata) were collected from six locations around the island of Oahu, Hawaii (Table 1), spanning a natural mosaic in carbonate chemistry (Fig. 1). Species were only sampled at sites where colonies were relatively abundant, but every species was collected at a minimum of two sites with differing typical conditions (Fig. 1). Coral genets were sampled with a hammer and chisel on snorkel from a depth of 0.5–5 m and returned to the Hawaii Institute of Marine Biology where they were allowed to recover. Six replicate clonal ramets (~3 cm nubbins) were cut from each sampled coral genet using a band saw prior to being mounted on a labeled plaster plug using cyanoacrylate gel. Experimental fragments were allowed to recover in flow-through aquaria for ~6 months to standardize the short-term history for all colonies prior to starting the experiment (Fig. S1)
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