In recent years, bleaching events have grown from local curiosities to global phenomena, and in some cases are so severe and long-lasting that the corals cannot recover.
Conserving coral populations is a lot harder than restoring fish: the primary threats to corals cannot be managed locally and fish can't stop climate change or disease outbreaks from happening.
While the loss of symbionts may be adaptive in the short-term, once bleaching occurs, if a coral colony continues to experience stressful conditions, it will rapidly succumb--scleractinian corals cannot persist indefinitely as heterotrophs.
While small numbers of hybrid embryos can be produced in a few species in vitro, the evidence for hybrids in the field is often equivocal because the genetic techniques used for corals cannot distinguish between hybridization and incomplete lineage sorting.
At the corallite level, these corals cannot be reconciled within the same taxon, since Favia stelligera corallites have single centers with separate walls (plocoid), Goniastrea spp. have fused walls (cerioid) and may form valleys (meandroid), while Merulina and Scapophyllia are composed predominantly of elongated valleys (see Additional file 1).
Mules are sterile, of course, and first-generation coral hybrids cannot reproduce sexually, either.
While Acropora spp. coral cover cannot be detected through remote sensing, the threshold of ≥30% provided guidance in identifying reefs for which this system could be expected to perform properly.
Although it is evident that epizoic flatworms are able to impair zooplanktivory and thus nutrient acquisition by their host coral, we cannot exclude translocation of refractory organic material from the flatworm to the coral.
Hence, the orthology and substrate specificity of coral CYP enzymes cannot be predicted solely on homology to CYPs of known function assigned to higher metazoans.
Thus, the evolutionary potential of the two coral-algal populations cannot be directly compared.
