Colony development and formation in halysitid corals

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Abstract
Modes of colony formation and their relationship with colony morphology, size and substrate characteristics in species of halysitid corals have been studied. Two distinctive modes of colony formation in halysitids are proposed. In the monoplanulate mode, represented by Catenipora simplex, the colony is developed from a single protocorallite and colony formation is achieved by a combination of asexual increase and intracolony fusions. In contrast, the polyplanulate mode is demonstrated by C. escharoides, in which the early colony formation is achieved primarily by fusions of many ''incipient colonies'' of more than a single planulate origin and of different generations. The latter mode has not previously been described in tabulates and has significant implications for coloniality, reproductive and life history characteristics, histo-compatibility and adaptative ecology. The colony size and morphology, and the distribution of halysitid species were primarily determined by the modes of colony formation and the substrate characteristics. Colonies of the monoplanulate mode, when developed on soft substrates, exhibit a small and spherical morphology with isolated distribution patterns, while those developed on hard substrates are tabular and variable in size, depending on the availability of substrate. In colonies of the polyplanulate mode, on the other hand, the size of the colony is largely dependent on the frequency and timing of allograft fusion. They are characteristically found on soft substrates, often as dense monospecific thickets. The mode of colony formation in halysitids is probably species-specific and results in the adaptation to substrates.