Project Title : Ecological and Physiological Response of Hong Kong Coral Communities to Changing Temperature and Oxygen Level

Applicant : The City University of Hong Kong (Professor David J Randall)

Total Approved Grant : $842,845.68

Duration : 01/06/2005 to 31/10/2006

Project Status/Remarks : Completed

Scope :
The aim of the project is to study the behavioural and physiological responses of local corals and their associated reef fish communities in Hoi Ha Wan Marine Park with respect to changing environmental factors, especially dissolved oxygen, salinity and temperature. The detailed objectives of the project are as follows -

a. To investigate the relationship between the behavioural stress response of corals, i.e., bleaching and polyp swelling, to environmental factors, in particular, dissolved oxygen, salinity and temperature.

b. To investigate the changes in species diversity of coral fish in relation to changing environmental factors.

c. To integrate the results of the above studies and identify behavioural adaptations of coral and coral fish to adverse conditions. The study will create a predictive model and flow chart to identify the interaction between environmental conditions and coral community responses and thus enable appropriate predictions for park management, such as restricting access to corals during periods when they are exposed to hypoxic waters or when they are releasing gametes. The objective is to manage the marine park, based on knowledge of the biology of the corals and fish, such that the long term survival of coral communities in Hoi Ha Wan are preserved.

Summary of the Findings:
Coral communities and associated fish assemblages in Hoi Ha Wan were subjected to subtropical seasonal changes, especially to temperature variations. Two types of behavioural responses, colour changes and polyp contraction/expansion, in corals were observed. Intensity of colour in three common coral species, Platygyra sinensis, Favia rotomana and Goniopora columna was shown to be related to seasonal changes. However, Platygyra sinensis and G. columna exhibited a seasonal cycle for polyp contraction/expansion but not F. rotomana.

The two major factors in determining fish abundance were seasonal and diurnal cycles. The tide had a profound effect on fish assemblages in shallow coral communities but not on those inhabiting deeper waters. There were two migratory patterns in coral fish in Hoi Ha Wan. The first was a seasonal migratory pattern, with most species migrating to deeper waters or other places in colder months. The second was a tidal migratory pattern in shallower coral communities. Fish tended to move in and out the shallow coral communities during the tidal period, and the movement was particularly evident during neap tide. However, such a tidal migratory pattern was not detected in deeper coral communities.