No description available.

Several studies have shown that corals are associated with diverse, host speciesspecific bacterial communities and these have been proposed to be of primary importance for their health. Various factors have been suggested to influence the structure of these communities, including production of antimicrobial chemicals, the supply of microorganisms from the surrounding environment (e.g. sediments and water column), mucus composition and production rates by the coral. However, few studies have investigated the factors that control the development and maintenance of these communities. Describing the microbial communities of healthy corals and how they interact with their surrounding environment is imperative to understanding how environmental stress and health problems in corals are related. This study utilised a culture-independent 16S rRNA gene approach to investigate the structure of the bacterial community on corals, the factors that might control the development of these microbial communities and their organisation within the coral host. In addition, the study identified the role of cytophagous ciliates as a potential cause of White Syndrome in the GBR. Study of the bacterial (16S rRNA gene) community of the surrounding water column (the potential supply to the surface mucus layer of corals) revealed that changes in productivity and/or vertical diurnal migrations of plankton might have greater effects than large scale water movements effected by tidal flows. Results also showed that waterborne bacterial communities and their underlying benthos were not strongly linked, suggesting either that there is little benthic-pelagic coupling or that large-scale (island wide) water column mixing is rapid and highly efficient, resulting in homogeneous bacterial communities in the water column, independent of the underlying benthos. The bacterial communities forming on artificial surfaces and those associated with the mucus layer of corals were different from the water column as well as each other, with a variety of ribotypes of - proteobacteria favouring both the biofilms and those of the surface mucus layer, compared to a high dominance of -proteobacetria within the water column. This suggests that the coral actively controls the microbial community on its surface, rather than it being a result of passive settlement from the water column. Results also show that bacterial communities within the coral are highly compartmentalized with distinct assemblages inhabiting the mucus layer, tissue and skeleton, which indicates high levels of complexity in the coral-microbial associations. The use of a broad spectrum antibiotic treatment further allowed investigation of turnover rates of the microbiota associated with healthy corals. Re-establishment of the corals’ normal microflora was slower than anticipated, taking over 96 h to return to that of its original bacterial community once disturbed, however the fact that the community returned towards its original state indicates a high degree of resilience and strong controls on the microbial community structure Despite the undisputed importance the bacteria associated with corals have on the overall coral holobiont, other microorganisms such as ciliates were also important for coral health, particularly during thermal stress. Results indicated that coral White Syndromes, previously attributed to pathogenic bacteria such as Vibrio spp., may have different etiologies, with cytophagous ciliates playing an important role. These findings further complicate correct disease identification in the field and appropriate treatment and/or prevention methods for diseased corals.

Wildlife-based tourism, which is Kenya’s second largest economic sector, is threatened by the risk of extinction of many wildlife species in the country. The endemic roan antelope (Hippotragus equinus langheldi) now only survives in Ruma National Park (RNP) where its population has been declining continuously since 1976. This thesis investigates the roan’s habitat use and selection, causes of population decline and population viability in RNP with the aim of recommending scientifically-based management interventions for population recovery and sustainable conservation. Roan movement patterns and habitat use were investigated using 4 home range estimation techniques. Habitat selection was studied at multi-spatial scales using compositional analysis, logistic regression, and information-theoretic (IT) and multi-model inference (MMI) techniques. Data for this study consisted of population estimates for roans and other grazers, Landsat images, soil maps, digital terrain data, rainfall records, snare distribution records, and roan ground tracking data. Identification of causes of population decline was carried out using both multivariate and univariate techniques. A generic population viability analysis (PVA) package was used to (i) estimate the likelihood of roan extinction under various management options; and (2) rank the management alternatives for roan population recovery. All 4 home range estimators are useful in characterizing different aspects of the roan home range, but overall the local convex hull method produced the most realistic home ranges. The three habitat selection methods yielded similar results but the IT techniques demonstrated superior qualities as they identified important habitat variables and produced the most accurate model predictions. MMI averaged models coupled with GIS data developed very informative habitat suitability and poaching risk maps. Analysis of habitat selection indicated different usage in seasons and spatial scales depending on water availability, habitat composition and burned status, and distribution of eco-geographical features. High adult mortality due to poaching with snares was identified as the main cause of roan population decline. Other important factors included habitat change and rainfall variability with its associated droughts and floods. PVA showed that under the current conditions, the roan population cannot persist more than 3 decades. Several anti-poaching and prioritized management interventions to curb poaching and promote population recovery are described.

Coral reefs have emerged as one of the ecosystems most vulnerable to climate variation and change. While the contribution of climate warming to the loss of live coral cover has been well documented, the associated effects on fish have not. Such information is important as coral reef fish assemblages provide critical contributions to ecosystem function and services. This thesis assesses the medium to long term impacts of coral loss on fish assemblages in the western Indian Ocean. Feeding observations of corallivorous butterflyfish demonstrates that considerable feeding plasticity occurs among habitat types, but strong relationships exist between degree of specialisation and declines in abundance following coral loss. Furthermore, obligate corallivores are lost fairly rapidly following decline in coral cover, whereas facultative corallivores are sustained until the structure of the dead coral begins to erode. Surveys of benthic and fish assemblages in Mauritius spanning 11 years highlight small changes in both benthos and fish through time, but strong spatial trends associated with dredging and inter-specific competition. In Seychelles, although there was little change in biomass of fishery target species above size of first capture, size spectra analysis of the entire assemblage revealed a loss of smaller individuals (<30cm) and an increase in the larger individuals (>45cm). This represents a lag effect where fishery production cannot be assured for the long term. A targeted before (mid-1990s) – after (2005) sampling program of coral reef benthos and fish assemblages in 7 countries across the Indian Ocean demonstrated changes in size structure, diversity and trophic composition of the reef fish community have followed coral declines in both fished and protected areas. The thesis highlights the pivotal role that loss of reef structural complexity plays in the effects of bleaching on fish assemblages and that coral reef management needs to radically adapt to address climate change issues.

No description available.

Estuaries are the interface between freshwater systems and the sea, with clearly recognizable changes in the distribution of organisms along various environmental gradients from riverine to fully marine conditions. This thesis studied ecological processes affecting the distribution of marine species along estuarine gradients using both field and laboratory experiments with barnacles as a tractable model system. Elminius modestus Darwin, Semibalanus balanoides Linneaus, Chthamalus montagui Southward are the most common barnacle species found in the intertidal of British estuaries. Surveys performed in the Plym and the Yealm Estuaries revealed that E. modestus occurred furthest up estuaries and was dominant along most of their length, with the exception of sites closest to the sea; C. montagui had the most restricted degree of penetration up-estuary; and S. balanoides occurred at low abundances, with limits of penetration located between those of C. montagui and E. modestus. Transplants of adult specimens to sites along the marine-to-freshwater gradient revealed that E. modestus was better adapted to environmental conditions found in inner areas of the estuaries than C. montagui and S. balanoides. Survival of the latter two species was negatively correlated with deposition of silt and decreasing salinity. Laboratory experiments showed that, in contrast to the other two species, E. modestus was highly tolerant to burial by silt. A comparison of observed distributions along the gradients with survivability showed that C. montagui was able to survive in areas where adults were absent, indicating that early life cycle stages were a potential limiting factor to the distribution of this species. Examination of patterns of cyprid settlement and recruitment to the benthic phase reinforced the suggestion that pre-settlement processes contribute to restrictions in the distribution of both C. montagui and S. balanoides. The abundance of these species, post-settlement, was also affected by physico-chemical conditions in the upper estuary. Pre-settlement processes did not limit the distribution of E. modestus and post-settlement processes appeared to be more important in limiting its abundance at sites closest to the sea.

The hunting of the black iguana (Ctenosaura pectinata) in some regions of Mexico constitutes an acute problem because mature, gravid females arc killed and eaten just before they lay their eggs. This practice thus impacts both the survival of adults and the otherwise imminent recruitment of new individuals to the population. The objective of this project was to compare the demographic behaviour and the genetic variability of two population of the black iguana, one protected and one subject to hunting. This information allowed us to project their population dynamics and investigate the likely population-level consequences of hunting. A clear difference in age structure was observed between the two populations, with younger reproductive individuals and shorter lifespan in the hunted population. Body size was also different and reproductive individuals tended to be bigger and produce bigger clutch sizes in the hunted population than in the protected one. Survival rate of hatchlings and yearlings was estimated in both populations using soap moulds. A clear difference in survival was observed. This difference is related to the absence of natural predators in the more disturbed (hunted) area. Genetic diversity was estimated using mitochondrial DNA and differences in haplotype and nucleotide diversity between the two populations were found. It was therefore concluded that the hunted population (Nizanda) is at higher risk of suffering genetic bottlenecks. Age-based matrix projections and population viability analysis revealed that under the present conditions both populations can persist. They, however, show that current hunting levels in a closed population would cause local extinction in the short term. The study makes it possible to infer that although black iguanas are resilient to a substantial amount or disturbance and modification or their population parameters, the gradual loss of numbers and genetic variability will increase their risk of extinction in the near future. Management actions to diminish this risk are suggested.

Highly mobile predators are known to have an important influence on shallow-water habitats. There is, however, little information about the role of crabs on the ecology of rocky shores. Here I examine the extent and consequences of predation by crabs on shores in the North-East Atlantic. The specific aims of this thesis are to: investigate spatial variation in use of the intertidal by crabs along a horizontal gradient of exposure to wave action and a vertical gradient of tidal elevation; assess their use of the intertidal as a feeding area by examining stomach content composition; examine the extent of connectivity between the subtidal and intertidal habitats as a consequence of predation by crabs, investigate the ecological role of crabs as predators in the intertidal, and to assess the importance of behavioral and morphological factors in determining the outcomes of these predator-prey interactions. Field sampling showed that on shores in southwest Britain, the abundance of Carcinus maenas, Necora puber and Cancer pagurus varied between high and low-tide, with the vertical gradient of tidal height and horizontal gradient of exposure to wave action. Crabs were typically more abundant on the lower shore than on the upper shore. C. maenas and N. puber were more abundant on sheltered shores than on exposed shores, while C. pagurus showed the opposite pattern. Individuals captured at high-tide were on average larger than those captured at low-tide. Stomach content analysis of individuals captured with traps at high-tide showed that all three crabs feed on intertidal prey including limpets, chitons and algae. In a mark-recapture field experiment, I demonstrate the migration of sublittoral crabs into the intertidal during high-tide. Subsequent manipulative field experiments showed that predation by crabs can have a considerable effect on abundance of limpets. Laboratory experiments showed that Necora puber has a preference for smaller limpets, indicating that the population structure of these grazers may also be modulated by predation. On shores of differing exposure in Portugal I examine cheliped morphological variation of Eriphia verrucosa in response to variation in prey abundance. Chelipeds were typically larger on exposed shores, where hard shelled prey such as mussels were more abundant than they were on sheltered shores, which were dominated by chitons and algae. Predation by crabs therefore appears to have an important ecological role in shallow-water habitats by influencing intertidal prey populations and establishing an important trophic link between intertidal and subtidal habitats. The implication of predation by crabs on the ecology of rocky shores is discussed.

No description available.

In the current climate of biodiversity loss how species diversity and ecosystem process are linked is, arguably, one of the most pressing issues and greatest challenges currently facing the scientific community. Previous studies suggest that there is no universal trajectory for the relationship between diversity and ecosystem processes, the pattern depends largely on species identity and their interactions. Furthermore, the effect of reduced diversity on ecosystem process in multi-trophic assemblages is both understudied and poorly understood. Consequently, the overall aim of the present study was to investigate the role of species identity, diversity and interactions in determining ecosystem processes using the strandline as a model system. Appropriate strandline species, three species of kelp fly larvae, an amphipod and four rove beetles were selected for use in laboratory manipulative experiments that measured decomposition as an ecosystem process. This study is one of the few to consider the affect of species interactions on ecosystem processes. The use of metabolic theory to make predictions of trophic interactions and ecosystem processes, using tractable surrogate measures of interaction strength, was also investigated. Finally, the importance of trophic interactions in affecting the connection between ecosystem processes and consumer species identity, diversity and interactions was examined. Species identity combination explained the variability in decomposition when strandline decomposer diversity and identity were manipulated. Positive and negative interactions were identified, and the effect of diversity on decomposition was dependent on the balance of these negative and positive species interactions. A mechanism of microbial facilitation and inhibition was proposed to explain the outcome as no previously proposed single mechanism adequately described the observed effect of species identity, diversity and interactions on ecosystem process found in this study. It was not possible to accurately predict observed predator-prey interaction strengths and ecosystem processes between strandline predators and prey and decomposition using body size as a surrogate measure of interaction strength and ecosystem processes. Although body size was an important factor explaining the variability in predator-prey interactions and decomposition, so too was species identity. The absence of a consistent relationship between size and interaction strength and decomposition was attributed to species-specific differences. The presence of trophic interactions subtly affected decomposition of wrack by strandline detritivores. However, in the presence and absence of a predator the overall effect of detritivore diversity and interactions on decomposition remained constant. The results of this study have implications for the fields of biodiversity ecology, metabolic theory of ecology and food web ecology. Firstly, the identification of positive detritivore-resource interactions adds to a growing body of evidence that some detritivore species may interact positively, with respect to ecosystem processes. The loss of species within a trophic group may result in a greater reduction in ecosystem processes than previously thought. If positive species interactions are prevalent, ecosystem process will decrease to a greater extent as species are lost, than that predicted from single species processing rates. By considering species interactions, future biodiversity ecosystem processing studies may better understand the effects of species diversity and identity on ecosystem process. It is also suggested that patterns and relationships uncovered in previous studies investigating the effects of species from a single trophic level on ecosystem process may still be valid in more realistic multi-trophic systems. If future biodiversity-ecosystem process studies are to make predictions concerning actual species-ecosystem process interactions in real assemblages the size of constituent species should be considered, as predator and prey size was shown to effect predator-prey interactions and ecosystem processes. The results of this study also suggest that allometry and metabolic theory have limited capacity for making predictions of predator-prey interactions and ecosystem processes, at least at the scale investigated here. Species specific factors are more likely to explain the patterns of predator-prey interactions and ecosystem processes at smaller scales. Unless food web models consider, or allocate, non-trophic interactions correctly, erroneous predictions of energy How and ecosystem process may result. Finally, the use of body size and allometric scaling laws to quantify food web models and energy fiow through an assemblage must be treated with caution if these models are used to make predictions on interactions between species and ecosystem processes occurring at the scale investigated in this study.