Abstract: Habitat structure is an important driver of fish community structure, but its quantification can be problematic because it comprises of components at different spatial scales and may also be influenced by biotic processes. I will present work from a Caribbean reef examining the relationship between fishes and both habitat quality at two spatial scales and biotic factors. The findings demonstrate the potential impacts of coral mortality on reef-associated species that are inferior competitors to territorial damselfishes. Work on the same reef examined the effect of meso-scale rugosity (within 25 square meter plots), and demonstrated that intra-habitat variability of different fish families is significantly influenced by different meso-scale metrics. We suggest that meso-scale rugosity should be explicitly considered when investigating fish-habitat relationships. Finally, I will describe a study aimed at understanding the influence of abiotic and biotic variables on crypto-benthic fishes. Cryptic fishes are much less frequently studied on reefs, but are an abundant component of fish communities and have a range of ecological functions.

The physical environment of reef flats represents an unusual ecological scenario for many reef fishes. On reef flats such as at Heron Island, the daily tidal changes alter water depths from <50cm to over 2m. In addition to altering temperature and flow speed, this change in water depth drives profound changes in fish assemblages. Fishes that remain on the reef-flat through tidal cycles are subject to significant changes in the abundance and identity of predators. Food availability may also vary with water depth, providing an opportunity to examine how ecological trade-offs and small-scale population dynamics for reef-flat individuals differs from those of conspecifics in deeper water. The identity and movement patterns of fishes that leave the reef flat at low water are also poorly known. I will present some initial data on the changes in reef fish assemblages over tidal cycles, and how water depth interacts with time of day. Finally, I will discuss future work to integrate the ecological data into food web models that will demonstrate the significant spatial and temporal changes in food web dynamics over tidal cycles and with position in the reef-flat seascape. Future sea-level rise will potentially lead to greater water depths at low tide, fewer changes in fish assemblages with tidal state, and less temporal variation in food webs. Consequently, the food web models will provide the first insights into the implications of this ‘permanent high tide’ on the food webs and fishing of reef flats.

Biography:  Alastair is from the UK, and obtained a degree in marine biology from the University of Southampton, where he first became interested in coral reef fishes. He then spent 8 years working for Coral Cay Conservation, managing  volunteer reef surveys in the Caribbean and Pacific. He then worked with Peter Mumby to complete his PhD at the University of Exeter, studying reef ecology and conservation in The Bahamas. This work continued through a NERC Research Fellowship at Exeter, focusing on reef fishes. He is now an ARC DECRA Fellow, studying the ecology of fishes on reef flat habitats along the Great Barrier Reef, while maintaining a research programme on fish ecology in The Bahamas.