Developing protocols and methods to predictably induce ex situ broadcast coral spawning and increase post settlement survivorship

The production of broadcast spawning gamete material ex situ has great potential in developing areas for coral research and/or to support initiatives aimed at rebuilding damaged reefs utilising sexually produced spat. Current effectiveness of such restoration practises are limited due to the high mortality rates post settlement and therefore methods aimed at increasing survival, and therefore productivity, are required and vital in order to further support upscaling of such practices. Therefore, this thesis focuses on developing methodology to predictably induce broadcast reef building corals to spawn ex situ and investigate ways to maximise post settlement survivorship. Acquisition of broodstock for any ex situ breeding project is essential. Chapter two describes the methodology designed and implemented in order for me to carry out long distance transportation (a journey time of ~34 hrs) of large (16-37 cm) gravid Acropora hyacinthus (Dana, 1846) colonies from fringing reefs south of Singapore to the Horniman Museum and Gardens, London. Collection was purposefully timed to occur just before the predicted annual mass spawning event and on the day of transportation 12 of the 14 genotypes contained large visible oocytes, which spawned ex situ within the same lunar month as those in the wild. A closed system mesocosm aquarium was designed at the same time, as described in chapter 3 that utilises microprocessor technology to accurately replicate environmental conditions associated with stimulating broadcast spawning events (photoperiod, seasonal solar irradiance, lunar cycles and seasonal temperature) from two synchronous spawning locations, Singapore and the Great Barrier Reef, Australia. Coupled with appropriate coral husbandry, four species (A. hyacinthus, Acropora millepora (Ehrenberg 1834), Acropora tenuis (Dana 1846) and Acropora microclados (Ehrenberg 1834)) completed full gametogenic cycles and spawned in a fully closed artificial ex situ environment (in synchrony with the wild). The effects of spawning broadcast corals ex situ is currently unknown, therefore following gamete release embryological development stages of three acroporids (A. millepora, A. tenuis and Acropora anthocercis (Brook 1893)) was assessed utilising scanning electron microscopy and confocal laser scanning microscopy techniques (Chapter 4). No abnormal developmental effects (as result of the ex situ environment) were observed, but the study built on previous works to provide increased detail of fertilisation and early cell stages. Reef building corals typically undergo a type III survival curve in their early life stages, with high mortality rates during early ontogeny. Increased post settlement survival can occur due to size mediated multi-genotype settlement aggregations and species hybridisation. These two factors were empirically tested (Chapter 5) in pure and interspecific hybrid crosses of A. millepora and Acropora anthocercis. Increased survival, and to a lesser extent growth, were observed in post settlement entities with >2 genotypes compared with single genotype primary polyps and in interspecific hybrid crosses compared to pure species crosses, highlighting the role of hybridisation vigour. Reef herbivory may enhance coral settlement and recruitment success however the influence of herbivory size classes on survival benefits are not ubiquitous. In order to assess the positive role that microherbivory may contribute to maximising coral survival and growth ex situ two species, the Tuxedo sea urchin, Mespilia globulus (Linnaeus, 1758) and the reef building coral, A. millepora, were co-cultured at varying densities. Increasing density of microherbivory significantly enhanced coral survival and growth, highlighting this as a potentially beneficial practise in improving productivity of coral produced via sexual reproduction. Finally closing the life cycle of a target organism marks an important milestone in any ex situ breeding programme or aquaculture method. Chapter 7 describes the production of the first F2 generation of A. millepora in a fully closed aquarium environment. In summary, it is therefore hoped this thesis will, in part, make a contribution to coral sexual reproductive research and the important work of reef restoration, particularly in light of the global decline in coral reef ecosystems.