Early growth of a pioneer recruited coral Oulastrea crispata (Scleractinia, Faviidae) on PFA-concrete blocks in a marine park in Hong Kong, China

Abstract

In December 1993, an experimental artificial reef made of pulverised fuel ash (PFA) and concrete was deployed at Hoi Ha Wan Marine Park, Hong Kong. Oulastrea crispata was the pioneer coral recruited on the structure. The initial growth of juveniles on the retrieved PFA-concrete blocks was analysed in an attempt to explain why and how this, and only this, scleractinian was able to col- onize such a new marine habitat. Growth occurred through extra- and intra-tentacular budding. Juvenile growth, expressed as geometric diameter extension rate, of O. crispata was assessed by 2 methods. First, growth was estimated by the repeated measurement of the same colonies for a period of 12 mo. Mean growth rate was 1.04 ± 0.05 mm mo -1 (n = 105). Second, growth was estimated from the size of new recruits at an age of 3 mo on the PFA-concrete blocks. Mean growth rate was 0.9 ± 0.51 mm mo -1 (n = 10). The first approach also showed that the growth rate of O. crispata was higher in winter and spring (from December to April) than summer and autumn (from April to December). With an opportunist life history trait, a wide range of reproductive strategies and surface- orientation independent growth, O. crispata is able to colonize a variety of substrata and to flourish as a pioneer colonizer of newly immersed structures.