Re ECF Project: 2011-08

Project Title: Erosion and growth of massive corals in Hong Kong

Applicant: Dr. Jian-wen Qiu, Department of Biology, The Hong Kong Baptist University

Total Approved Grant: $981,000

Duration: 15/10/2012 to 31/5/2015

Project Status/Remarks: Completed

This study aims to quantify the erosion and growth of massive corals in local waters though:

  1. field surveys to examine the general pattern of bioerosion by quantifying boreholes on live massive corals and sedimentation rate from 33 sites across Hong Kong;
  2. collection of coral samples from 10 sites to determine the patterns of coral growth and internal bioerosion along the estuarine to oceanic and sheltered-exposed gradients;
  3. exposure of dead coral skeleton to the two environmental gradients in the field to quantify changes in calcium carbonate (accretion vs. erosion); and
  4. field experiments to quantify coral mortality and external bioerosion caused by the sea urchin Diadema setosum, and effects of predatory crabs.

Summary of the Findings/Outcomes:
This project aimed to conduct: 1) Field surveys to determine coral coverage and pattern of bioerosion by quantifying boreholes on coral surface and sedimentation analysis on 33 sites in Hong Kong along two environmental gradients; 2) Collection of coral samples from 10 sites to determine the growth and erosion of massive coral colonies along two environmental gradient: shelter to exposed and estuarine to oceanic; 3) Exposure of dead coral skeleton under the two environmental gradients stated above to quantify changes in calcium carbonate. We have completed all of the proposed work. The results showed that boreholes are abundant in two genera of dominant massive corals (i.e. Porites and Platygyra), and sedimentation rate is positively correlated with the density of boreholes in these corals. The growth rates of Porites and Platygyra in Hong Kong are slower than those in tropical regions, and are negatively correlated with sedimentation rate, as well as borehole density. The one-year deployment of dead coral skeleton showed that external erosion as well as the development of internal bioeroders are quick in local waters.