The growth of five species of Acropora, A. tenuis, A. hyacinthus, A. digitifera, A. donei, A. valenciennesi, transplanted on the reef of Maeganeku, Okinawa, Japan, was monitored during a coral restoration program implemented by the Okinawa Prefectural Government. The major/minor axis length and projected area of identified coral transplants were measured using photographs taken every six months period between 2014 and 2016. The geometrically estimated area of each transplant species, which was calculated by major/minor axis length, was strongly correlated with the projected area, although the former was overestimated (8.1±1.1% for A. tenuis, 5.4±0.9% for A. hyacinthus, 9.2±1.0% for A. digitifera, 18.5±2.1% for A. donei, and 16.9±1.9% for A. valenciennesi, mean±SE). It was found from the growth equations that the growth of A. tenuis, A. digitifera and A. donei seemed to reach a determinate phase in 2 to 3 years after transplantation, while A. hyacinthus and A. valenciennesi continued their growth. Information regarding the growth of transplanted corals obtained in this study enables various entities assisting the design of a coral transplantation project, including a period required for human intervention, as well as the transplant densities and projected coral cover.
Although the need for predicting coral responses to future environmental changes at the reef scale is increasing, it remains a difficult task to achieve. This is because: (1) multiple environmental factors are affecting corals, (2) biological responses to such factors are usually nonlinear, and (3) these environmental factors are changing over time. Using numerical models can be highly effective in evaluating the effects of multiple environmental factors if the dynamic responses of corals to each environmental parameter are properly incorporated into the model and the underlying mechanisms are well-understood and reproduced. To help attain this goal, we developed a “coral polyp model” which simulates the internal physical, chemical, and physiological processes within an individual coral polyp. Furthermore, to evaluate the responses of corals under a spatiotemporally varying environment at the reef-scale, we coupled a hydrodynamic-biogeochemical model to the coral polyp model. The coupled model was able to accurately reproduce the main characteristics of both the reef environment and the coral metabolic responses, and can be set up to predict the coral responses under various future climate change scenarios. To obtain more accurate predictions of the impact of multiple environmental factors on coral reef ecosystems, ongoing work includes incorporating the responses to temperature, red soil, and nutrients into the coupled model.