The role of recruitment in coral community regeneration

Fisk, David Anthony (1997) The role of recruitment in coral community regeneration. PhD thesis, James Cook University.

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Abstract

Green Island reef has been subjected to at least two severe outbreaks of crown of thorns starfish (Acanthaster planci) in the last thirty years. The most recent outbreak occurred in the early 1980's. This study commenced in 1985 with the aim of investigating coral recovery following this outbreak, with an emphasis on the recruitment process. The study of Green Island coral communities produced conclusions on coral regeneration based on approximately nine years data on recruitment and of other influential events. These events included two cyclone impacts, minor outbreaks of Drupella spp, and the effects of small increases in A.planci numbers.

The main characteristic of the recovery process was one of rapid and significant increase in coral (ranging from 15% to 50% cover) between the fourth to the ninth year post-A.planci. The observed rapid increase was due to the dominance of fast growing Acropora spp. Diversity at Green Island in 1990 was moderate with approximately 25-30% (or 80-100 species) of the total species recorded from the Great Barrier Reef.

Recruitment was investigated during two phases: an early recruitment phase where microscopic (<2 mm diameter) recruits were studied on artificial settlement substratum; and a visible recruitment phase, where annual recruits (>2 mm diameter) were followed on natural substrata on the reef slope. Spatial and temporal variability in both annual early and visible recruitment was evident from this study. However, longer term patterns were detected as follows: (1) three reefs separated by several kilometers showed consistently different early recruit abundance and composition of major families; (2) specific zones on these different reefs showed consistent relative abundance of early recruits; (3) at a smaller spatial scale, specific positions within an individual reef had comparatively different early recruit densities and composition to other positions on the same reef; (4) relatively different densities of early recruits occurred along a depth gradient, which on Green Island ranged from 3 m to 6 m depth. Visible recruit abundance and composition generally reflected early recruitment variations at several spatial and temporal scales, with the exception of massive species. Massive species were very abundant in the visible recruitment community but not in the early recruitment pool. Either the settlement plate technique was under sampling this component, or the relative abundance estimates of the early recruit taxa reflect substantially higher survival rates for the massive corals.

This study covered a period where a change in successional phases took place. An inhibition model via overtopping of arborescent and plate Acropora spp could explain the observed pattern. A significant decrease in visible recruitment occurred during a relatively brief time when there was a rapid expansion in overtopping colony morphologies, despite the continuing high abundance in early recruits at the same sites. Relatively minor disturbance events also occurred during the study (especially in the latter period) which created a more complex and less predictable mosaic of reef patches with different conditions and therefore at different successional stages.

Item ID: 27398
Item Type: Thesis (PhD)
Keywords: coral recovery; recruitment process; patterns of recruitment; Green Island
Date Deposited: 25 Jun 2013 01:06
FoR Codes: 06 BIOLOGICAL SCIENCES > 0602 Ecology > 060205 Marine and Estuarine Ecology (incl Marine Ichthyology) @ 90%
06 BIOLOGICAL SCIENCES > 0603 Evolutionary Biology > 060303 Biological Adaptation @ 10%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960808 Marine Flora, Fauna and Biodiversity @ 51%
97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 49%
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