Document Type

Thesis

Publication details

dela Cruz, DW 2019, 'Coral reef restoration using mass coral larval enhancement', PhD thesis, Southern Cross University, Lismore, NSW.

Copyright DW dela Cruz 2019

Abstract

Coral reef communities are rapidly declining worldwide due to increasing direct anthropogenic disturbances, including global climate change. Active management approaches are needed for effectively slowing and reversing coral loss on degraded reef systems to promote recovery. Research presented in this thesis includes fertilization experiments to optimize embryo and larval culture and testing three tiles types to determine suitable larval recruitment surfaces. Two successful coral restoration experiments, using many thousands of ex situ cultured larvae of two Acropora species, resulted in increased coral settlement and recruitment and re-establishing breeding corals on degraded reef sites in the northern Philippines.

Spawned eggs and sperm of Acropora millepora, A. tenuis and Favites colemani were collected and optimal ranges of sperm concentrations and temporal response patterns for egg-sperm crosses were measured. High fertilization rates were achieved for all three species when sperm density ranged from 104-107 mL-1 and when eggs and sperm were combined after 30 minutes up to 2 hours. Following successful fertilization and larval development, coral settlement and recruitment are essential key drivers of coral reef recovery and resilience. The influence of different settlement surfaces (dead Acropora skeletons, terracotta and fibre-cement tiles) on the spatial and temporal patterns of recruitment in three reef locations in the Bolinao-Anda Reef Complex (BARC), Philippines were examined. Density and composition of coral recruits were consistent among tile types and the spatial density of recruits varied among reefs, possibly influenced by existing coral cover and distance from the major eutrophication source.

Larval enhancement experiments involved collecting gravid colonies of A. tenuis in 2013 and A. cf. loripes in 2014 for spawning and larval culture in the hatchery. Hundreds of thousands of larvae were released onto replicated degraded reef patches (4 x 6 m) enclosed in a low-cost mesh matting system. High settlement rates (>25 spat per tile) were recorded in larval enhancement treatments, versus none in control sites. After 35 months, there were an average of 2.3 colonies per m2 of A. tenuis and 1.8 colonies per m2 of A. cf. loripes. Most A. tenuis colonies grew rapidly and spawned successfully at three years quickly re-establishing a breeding population on degraded reef areas for the first time. The results of these experiments show that mass larval enhancement is a viable option for restoring coral populations on larval-limited, degraded reef areas, where the immediate threats of blast-fishing and other direct human impacts are being managed.

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