Modes of regeneration and adaptation to soft‐bottom substrates of the free‐living solitary scleractinianDeltocyathoides orientalis

Abstract

2018: Modes of regeneration and adaptation to soft-bottom substrates of the free-living solitary scleractinian Deltocyathoides orientalis. Lethaia, Vol. 51, Scleractinian corals adapt to various substrate conditions with a variety of growth morphologies and modes of life. The azooxanthellate solitary scleractinian Deltocyathoides orientalis exhibits slightly flattened, bowl-shaped corallites. This study describes in detail the modes of skeletal regeneration after fragmentation in association with exquisitely adaptive strategies of the corals for life on soft substrates. Larger fragments of individuals retaining almost two-thirds to five-sixths of the original skeletal area inherit the densely dilated, lower central skeleton, so as to keep a stable life position on soft substrates and regenerate the lost parts promptly. Even highly fragmented individuals preserving less than 10% of the original skeleton still regenerate and repair.Fragmented individuals with almost one-sixth to one-third original skeleton actively maintain a posture with the oral disc upward using movements of remaining tentacles. Damaged and missing soft tissues are then efficiently regenerated to form a mouth and gastrovascular cavity near the new centre of the corallum. Every regenerated individual reuses skeleton and soft tissues, and is capable of burrowing before the completion of growth morphology. The mode of regeneration characteristic of D. orientalis is thus effective and adaptive for maintenance of a stable life position on soft substrates for this solitary scleractinian. As fragmentation in deeper-water, soft-bottom settings is likely due to predation rather than turbulence, the rapid corallum regeneration and burrowing strategy may both represent adaptive strategies for life on soft substrates and exploitation of new niches, such as an infaunal mode of life, in a predator-rich environment. □ Azooxanthellate coral, burrowing, fragmentation, predation, regeneration.Asuka Sentoku ✉ [a.sentoku@gmail.com], and Gregory E. Webb [g.webb@uq.edu.au],

Selective consumption of sacoglossan sea slugs (Mollusca: Gastropoda) by scleractinian corals (Cnidaria: Anthozoa)

“…(Flabellidae) and Deltocyathoides spp. (Turbinoliidae) [39–41]. Little is known about the ecology of these low-cover, soft-bottom communities near reefs, which have been considered to play a limited role in reef-building [35].…”

“…Free-living corals of the species Heteropsammia cochlea and Pleuractis paumotensis were recently observed to ingest salps and a sea slug at Koh Tao, Gulf of Thailand [5,26]. The 19-km 2 island is surrounded by a fringing coral reef, with many of the locations around the island supporting large populations of free-living mushroom corals [41–43]. Beyond the reef slope there is a soft-sediment ecosystem that supports mixed aggregations of free-living scleractinian corals such as Heteropsammia cochlea and Heterocyathus aequicostatus [26,31].…”

Dimorphic life cycle through transverse division in burrowing hard corals

“…3, Table S2). In addition, Sentoku et al [6] showed that D. orientalis is capable of self-repair if 10% of the skeleton remains after physical damage, in which the basal discoloration can potentially be lost. Therefore, discoloration restricted to the basal part of D. orientalis is inferred to be generated by decalci cation, and almost all D. orientalis may inherently have a discolored basal part.…”

“…Although many azooxanthellate corals have been found in the seas around Japan, small and free-living species are di cult to collect and only a few detailed studies of their populations and ecology have been conducted [5][6][7] .…”

“…Although little is known about the predators, predation pressure, or predation frequency of this coral, damage repairs have been well recorded in the skeletons of Deltocyathoides orientalis. Even highly fragmented individuals preserving less than 10% of their original skeleton are able to regenerate and repair [6] . D. orientalis exhibits slightly attened bowl-shaped corallites, with an average diameter of 10 mm.…”