A resilient brooding coral in the broadcast spawning Porites lobata species complex: a new endemic, introduced species, mutant, or new adaptive potential?

Abstract

With increasing exposure to local and global stressors associated with a rapidly changing climate, corals adapted to thrive within stressful environments are of particular interest to researchers and managers. A bleaching resilient Porites coral with an unusual appearance was discovered dominating shallow waters (1–2 m) within Honolulu Harbor, Hawai‘i, a heavily sedimented and polluted habitat with high levels of anthropogenic influence. Continuous monitoring of this ‘Harbor Porites’ revealed prolific year-round brooding and release of planula larvae, with no clear seasonal pattern. Furthermore, recruitment and rapid growth were observed in seawater tanks followed by fusing of various sized colonies, indicating brooding of clonal larvae. Genetic markers placed this coral with high similarity (histone and ITS sequences are 99.9% and 99.4% similar, respectively) to corals in the P. lobata species complex which are gonochoric broadcast spawning corals. Fixed differences were observed, and FST values were high and significant, which could either be explained by reproductive isolation or from clonal sampling over a limited area (this coral has not yet been found in other locations). Observations of skeletal microstructure also showed similarity to corals in the P. lobata complex, although with a higher proportion of corallites with excavated columella resulting in a cavity similar in size to the brooded larvae. These observations suggest that bleaching resilience and reproductive mode may be more plastic than previously assumed for Porites corals. Additional work is needed to determine if these corals represent a very recent endemic species, an introduced coral, the result of reproductive disruption from pollution (e.g., endocrine disruption), or extreme phenotypic variation within the P. lobata complex. Prolific growth and production of larvae, combined with observations of resilience to anthropogenic impacts such as bleaching, sedimentation, and pollution, make this coral a good candidate model for the study of adaptation and acclimatization to climate change and other anthropogenic stressors.