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Recognised as 'Essential Fish Habitat', red mangrove (Rhizophora mangle) has received much attention in recent years to assess its nursery function. Research suggests that mangrove habitat contributes significantly to coral reef fish populations. Not all mangrove is utilised to its full capacity by juvenile fish, and it may be that, in terms of fisheries sustainability and enhancement, the use of management resources for mangrove habitat protection could be more judiciously targeted on the basis of preferred habitat use. In order to establish the factors influencing fish distribution in Rhizophora mangle, fish populations were studied in a Bahamian tidal lagoon. Biotopic, hydrophysical, structural and biological influences were investigated in natural red mangrove habitat, and by experimental manipulation of artificial mangrove units (AMUs). Reef fish were distributed unevenly over various spatial scales, indicating preferences in some species for particular lagoon biotopes, and various physical and biological characteristics inmangrove prop root habitat. With the exception of tidal flow, other physical attributes such as salinity, pH, dissolved oxygen and water depth had limited influence on fish distribution. In natural mangrove habitat the degree of shade appeared to be the most important factor in attracting fish to mangrove habitat followed by habitat complexity and epiphytic algae biomass. Variations in preference for these attributes between species and size classes suggested that no single attribute was exclusively responsible for a particular locational preference. Experimental manipulations of AMUs indicated a preference for greater shade and root density up to a certain level after which no preference was shown. Preferences varied between species and size classes and also with increased vulnerability to predation. Red mangrove trees perform a number of important functions on tropical and sub-tropical coastlines. They stabilise and protect: the coastline against erosion. supply nutrients to other coastal habitats, and provide habitat for many avian and terrestrial species. Prioritising management in mangrove habitat must be done with care, taking into account all of the habitat's functions.

The present thesis deals with the related themes of mortality and growth in coral reef fishes. In the first chapter, a nine-year dataset from Bermuda is used to quantify how reef fish populations respond to the introduction of a trap-fishing ban, finding that herbivores exhibit extremely strong recovery, but that stock-recruitment relationships may be decoupled by a numerical response in a meso-predator. In the second chapter, a dataset from Bonaire is used to test the efficacy of the widely-used coefficient of natural mortality, M, in modelling a population of stoplight parrotfish (Sparisoma viride). As determined from simulation models, this statistical coefficient performs considerably less well than a novel mechanistic function that partitions mortality into size- and age-based processes and achieves extremely good fits to the field data. The third chapter presents a new approach to estimating growth parameters of reef fish from tagging data that exploits the disproportionate response of certain parameters to misestimates in the true age of the tagged individuals. The method works considerably better than the most widely used method when sample sizes are small, as is commonly the case in reef fish tagging studies where recapture rates tend to be low. The fourth and final chapter uses non-lethal stable isotope techniques to tease apart the invasion dynamics of Indo Pacific lionfish (Pterois spp.) that are currently colonising the wider Caribbean. The results show that lionfish exhibit habitat-specific ontogenetic shifts in prey selection, inflicting elevated mortality on small, bommie-dwelling fishes on forereefs but switching to seagrass-foraging invertivores as they grow. Lionfish also display ontogenetically shifting competition with native Nassau grouper (Epinephelus striatus), which may provide a greater barrier to invasion success on patch reefs than on fore reefs, where competitive overlap is diminished. The thesis concludes with a discussion of some lines of enquiry that could not be undertaken owing to time or data limitations, but which may hold as much interest for the reader as they do for the author.