Thesis (Ph.D.) - University of Queensland, 2005. / Includes bibliography.

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Understanding the dynamics of open marine populations is difficult. Ecological processes may vary with the spatial structure of the habitat, and this variation may subsequently affect demographic rates. In a series of observational and experimental studies in the Bahamas, I examined the roles of emigration, mortality, and predation in the local population dynamics of juvenile coral-reef fishes. First, I documented mortality and emigration rates in populations of bluehead and yellowhead wrasse. Assuming that all losses were due solely to mortality would have significantly underestimated survivorship for both species on patch reefs, and for yellowheads on continuous reefs. Mortality differed between species, but emigration did not differ between species or reef types. Mortality of blueheads was density-dependent with respect to both conspecific density and total wrasse density on continuous reefs. In contrast, mortality of yellowheads varied inversely with the density of blueheads on patch reefs. Emigration rates varied inversely with distance to the nearest reef inhabited by conspecifics. In subsequent experiments, I manipulated densities of yellowhead wrasse and beaugregory damselfish, and determined that the relationship between density and mortality varied with reef spatial structure. On natural reefs, mortality rates of the wrasse were highly variable among reefs. On artificial reefs, mortality rates of both species were density-dependent on spatially isolated reefs, yet high and density-independent on aggregated reefs. Heterogeneity in the spatial structure of natural reefs likely caused variation in predation risk that resulted in high variability in mortality rates compared to artificial reefs. A final experiment demonstrated that a single resident predator caused substantial mortality of the damselfish, regardless of reef spacing. Patterns suggested that resident predators caused density-dependent mortality in their prey through a type 3 functional response on all reefs, but on aggregated reefs this density dependence was overwhelmed by high, density-independent mortality caused by transient predators. These results (1) suggest post-settlement movement should be better documented in reef-fish experiments, (2) demonstrate that the role of early post-settlement processes, such as predation, can be modified by the spatial structure of the habitat, and (3) have ramifications for the implementation of marine reserves. / Graduation date: 2004

Thesis (M.S.)--University of North Carolina at Wilmington, 2003. / Includes bibliographical references (leaves : 46-50).

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 161-170). Also available via World Wide Web.

The exceptional environment of the Red Sea has lead to high rates of endemism and biodiversity. Located at the periphery of the world’s coral reefs distribution, its relatively young reefs offer an ideal opportunity to study biogeography and underlying evolutionary and ecological triggers. Here, I provide baseline information on putative seasonal recruitment patterns of reef fishes along a cross shelf gradient at an inshore, mid-shelf, and shelf-edge reef in the central Saudi Arabian Red Sea. I propose a basic comparative model to resolve biogeographic patterns in endemic and cosmopolitan reef fishes. Therefore, I chose the genetically, biologically, and ecologically similar coral-dwelling damselfishes Dascyllus aruanus and D. marginatus as a model species-group. As a first step, basic information on the distribution, population structure, and genetic diversity is evaluated within and outside the Red Sea along most of their global distribution. Second, pelagic larval durations (PLDs) within the Red Sea environmental gradient are explored. For the aforementioned, PLDs of the only other Red Sea Dascyllus, D. trimaculatus, are included for a more comprehensive comparison. Third, to further assess ongoing pathways of connectivity and geneflow related to larval behavior and dispersal in Red Sea reef fishes, the genetic composition and kinship of a single recruitment cohort of D. aruanus arriving together at one single reef is quantified using single nuclear polymorphisms (SNPs). Genetic diversity and relatedness of the recruits are compared to that of the standing population at the settlement reef, providing insight into putative dispersal strategies and behavior of coral reef fish larvae. As a fourth component to study traits shaping biogeography, the ecology and adaptive potential of the cosmopolitan D. aruanus is described by studying morphometric-geometrics of the body structure in relation to the stomach content and prey type from specimen along the cross-shelf of the central Red Sea and at a site outside the Red Sea, in Madagascar, and approach whether foraging strategies change depending on geographic location and environment, and if differences in diet are followed by phenotypic plasticity. Jointly, results suggest that biological responses and putative adaptive strategies are correlated with different biogeographic ranges and habitat preferences.

This study conducted the first high-resolution investigation of the ichthyofaunal assemblages on a high-latitude coral reef in the Western Indian Ocean (WIO). Two-Mile reef, in South Africa, is a large, accessible patch-reef, and was selected as a candidate study area. Although the effect of season in structuring coral reef fish communities is most-often overlooked, the relationship between these fish communities and their habitat structure has been investigated. In South Africa, however, neither of these potential community-level drivers has been explored. As coral reefs worldwide are faced with high levels of usage pressure, nondestructive underwater visual census (UVC) techniques were identified as the most appropriate survey methods. This study had two primary aims that were; (1) to identify the most suitable technique for the UVC of coral reef fishes, and to test variations of the selected technique for appropriateness to implementation in long-term monitoring programs, and (2) to determine if possible changes to ichthyofaunal community structure could be related to trends in season and/or habitat characteristics. A review of the literature indicated that the most appropriate UVC method for surveying epibenthic coral reef fishes is underwater transecting. To compare the traditional slate-based transects to variations that implement digital image technology, slate transects were compared to a first-attempt digital photographic transect technique, and digital videographic transects. Videographic transects produced the most favourable species richness, abundance, and standard deviations of the three techniques. Diversity was not significantly different between transect techniques. The minimum required sample size was lowest for videographic transects (17 replicates), intermediate for photographic transects (27 replicates) and highest for slate transects (37 replicates). Videographic and photographic transects required greater analysis time to generate counts, but required lower observer training time. While videographic transects produced the lowest proportion of species considered unidentifiable, all three transect techniques showed similar functionality to surveying epibenthic coral reef fishes. Videographic transects were therefore identified as the most appropriate UVC technique for this study. Videographic transects at shallow (6 – 14 m), intermediate (14 – 22 m) and deep (22 – 30 m) depths in mid-winter and mid-summer, sampled a total of 41 families consisting of 209 species and 18172 individuals, dominated by pomacentrids in abundance and labrids in richness. The fish assemblages on Two-Mile Reef were found to be similar in composition to lower-latitude WIO reefs. Overall ichthyofaunal abundance and richness was significantly higher in summer than in winter, and was higher at shallow sites than at intermediate and deep sites. A multivariate approach confirmed differences between seasons at shallow depths but not between seasons at intermediate and deep depths. The fish assemblages on Two-Mile Reef can therefore be described as being comprised of four relatively distinct communities: a shallow, winter community; a shallow, summer community; a year-round intermediate community; and a year-round deep community. The distributions of discriminating species indicated that high abundances of the algal-feeding pomacentrids are observed only at shallow and intermediate sites while high abundances of the zooplanktivorous serranid subfamily, the Anthiinae, are observed predominantly at deep sites. Assessment of all measured supplementary variables indicated that of all factor combinations, observed patterns could be ascribed most strongly to depth. Quantification of reef characteristics indicated that as depth increases, habitat complexity decreases, benthic communities shift from dense coral domination to sparse sponge domination, and algal biomass and cover decreases. The ability of the videographic transect technique to detect changes in community structure with season and depth indicates that season and depth should be accounted for in future high-latitude ichtyofaunal surveys, and that the videographic transect technique is suitable for implementation in long-term monitoring programs on coral reefs. The similarity in fish assemblages between Two-Mile Reef and lower latitude regions suggests that the protocol for surveying epibenthic coral reef fishes, resulting from this study, is relevant throughout the continental WIO.

published_or_final_version / Biological Sciences / Master / Master of Philosophy

Coral reef fish larvae take an active role in selecting their settlement site and sensory cues may help them to orientate during this process. As settlement is a period of transition through which the majority of individuals do not survive, it is often a focal point for the management of coral reef populations, which are of high conservation concern. In this thesis, I used choice tests and in situ techniques to assess the response of settlement-stage larvae to a range of odour, light and acoustic cues and I found that larvae are more selective in their response to sensory stimuli than previously thought. Micro-habitat odours are not likely to be used during settlement orientation, and odour cues may be used to avoid inappropriate settlement sites. The photopositive behaviour of larval fish is likely to match their spectral sensitivity but this proved difficult to assess in situ because of the high amount of spatial and temporal variation in larval distribution. The positive response of settlement-stage fish to played back reef noise is location specific as well as being highly specific to the reef sound recording. To understand whether it might be the composition of reef sound that drives the selective response of larvae to acoustic cues, I took sound recordings while collecting visual data on fish diversity and the behavioural activity of a sound producing, or soniferous, fish species. I found that the variation in intensity of reef noise matches the activity patterns of a soniferous species, and when reef noise is most intense is when visual estimates on the diversity of the reef fish assemblage are decreased. This information provides the basis for understanding how changes in the reef soundscape may effect larval recruitment and has exciting implications for using sound recordings as a method to monitor coral reefs. Finally, I tested the viability of releasing reared larvae to boost depleted populations and found that collecting and holding settlement-stage fish for a week can increase survival, relative to natural settlement. These data demonstrate that applying our knowledge of the settlement behaviour of coral reef fish will make a significant contribution to developing tools for management.

This study examined whether movements of fishes across reserve boundaries reduced the difference in density and size of fish between reserve and non-reserve areas. Visual censuses, experimental trapping, habitat measurements and tagging were performed at 10 sites on two nearly contiguous fringing coral reefs at the northern edge of the Barbados Marine Reserve and at 10 sites on the two fringing reefs closest to the boundary in the non-reserve. The visual censuses showed that overall density and size of fishes large enough to be caught in Antillean fish traps were higher on reserve reefs than on non-reserve reefs. The differences in density and size varied considerably among species and were not statistically significant for individual species. In contrast to a previous study, experimental trap catches were not higher in the reserve than in the non-reserve. Visual censuses, trap catches, and their ratio (trappability) were affected by habitat variables. Species mobility, estimated by the maximum distance between locations at which an individual was captured, corrected for the sampling effort at that distance, was highly variable among species (medians 0--116m). For the more mobile species, movements within fringing reefs and between the nearly contiguous reserve reefs was high but extremely rare among reefs separated by expanses of sand and rubble. For this discrete fringing reef system, there is no evidence that movement across the reserve boundary influences the relative density or size of fish between the reserve and non-reserve.