Conflict of interest

Overall, the evaluation of the life history of M. cf. platyphylla suggests a competitive strategy, based on few locally produced sexual recruits and their ability of reaching large sizes (fusion [235] and stolonal spreading [59]), which allows them to pre-empt space on coral reefs, but also brought evidence of high susceptibility to fragmentation. This life strategy is well suited for population persistence in the absence of sexual recruitment, but can be risky in unstable environments [247]. Yet M. cf. platyphylla populations in Moorea have withstood severe disturbances, e.g. Acanthaster outbreaks, cyclones and mass bleaching events. Their recovery is foremost sustained by the rapid growth of remnant colonies, mostly those encrusting, and the subsequent local recruitment via both sexual and asexual reproduction. There is evidence that under pressure from environmental changes fire corals might be among the reef coral 'winners', joining some scleractinian species that have already been described as such [32, 85, 140]. Yet more information on how they respond to bleaching events is needed, as Millepora species have been reported to be highly vulnerable to thermal stress in other reefs [4, 130, 133]. Nevertheless, the life history of M. cf. platyphylla is most likely contributing to its colonization success in various reef environments in French Polynesia. Although M. cf. platyphylla is the only fire coral species reported in this geographic region [50], this species is also characterized by one of the widest ranges of distribution in the entire Indo-Pacific region within the Millepora genus [248], but similar to the branching species M. intricata. Evaluating the life history of other Millepora species with different growth forms will enable to determine whether these strategies are

Invertebrates - Ecophysiology and Management

unique to M. cf. platyphylla or spread within the Millepora genus.

In recent decades, declines in scleractinian coral cover have challenged their role as key ecosystem engineers of coral reefs [25–27, 249–251]. Assuming rising sea temperatures and increased ocean acidification, climate change can interfere with a range of key processes in the life history of reef corals, including growth, calcification, development, reproduction and behavior [162, 252]. Despite the acclimatization and genetic adaptation of reef corals [2], such persistent physical and chemical conditions can lead to shifts in reef community composition. This phenomenon has already been reported in many reefs, where alternative organisms are dominating reef assemblages (reviewed in [253]). Only few studies have considered hydrocorals

in ecological monitoring of coral reefs [130, 254, 255]. For instance, M. cf. platyphylla can dominate some reefs in the Indo-Pacific region [89] and also contribute to the survival of corals during Acanthaster outbreaks [106]. Therefore, it is crucial to gain insights into how populations of this keystone species can adapt and survive in the face of climate change, and other natural or anthropogenic disturbances. In this chapter, we established that fire corals possess a great variety of life history strategies that favor a high degree of genetic diversity and plasticity enabling these organisms to persist throughout environmental variations. Consequently, these Millepora species may become one of the major components in some

modern reefs and requires more consideration in ecological monitoring.

Much of the information in this review has come from expeditions and field work we have made in the Indian and Pacific Oceans, courtesy of grants from the LabEx 'CORAIL', Regional Council of Reunion Island, ANR French funds, French

8. Conclusions

Acknowledgements

34

The authors declare no conflict of interest.
