Effects of cyclone waves on massive coral assemblages on the Great Barrier Reef: meteorology,hydrodynamics and demography

Cyclone waves directly affect the density, structure and local distribution of coral assemblages by acting as agents of mortality and colony transport. Using the meteorological record, hydrodynamic formulations and risk analysis, we predict some demographic consequences of cyclones for massive corals growing in different regions of the Great Barrier Reef. Analysis of shear, compression and tension forces generated by waves indicate that corals firmly attached to solid substratum, even if only over a small proportion of their base, can resist all waves, regardless of colony size or shape, cyclone intensity or region. Waves are thus directly important as controls on colony-size frequency distributions only for weakly attached or unattached colonies. At 3 m depth, these colonies have a higher probability of escaping dislodgement in their first 10 years of life, the further north or south they are from 21°S, which is the latitude where severe cyclones are most frequent. At 21°S, corals at depths as great as 12m are exposed to the greatest likelihood of dislodgement. Possible implications of predicted increased storminess associated with global warming are briefly discussed.