To address the key research questions, this thesis incorporated a combination of observational, statistical and theoretical approaches. Though the statistical and theoretical studies cover the three major island groups within the Pacific island region (Melanesia, Micronesia, Polynesia), the field-based research was focused within Melanesia, at Fiji and Papua New Guinea. Following this general introduction (chapter 1), the thesis comprises five research-based chapters (comprising chapters 2 through 6) in the form of full manuscripts formulated for peer-reviewed journals, and are either published, in review or in preparation. The chapters fit into three broad categories (Figure 1.2); (i) the role of island communities in driving alternative benthic regimes and novel ecosystems, (ii) capturing subtle changes within the reef benthos driven by island communities, (iii) impacts of community-based fisheries management on reef benthos. The findings of all chapters are finally summarised by a general discussion (chapter 7), and future research opportunities are discussed. Additional published work associated to this project in which I am involved as a contributing author is provided in the appendix (Appendix D), and further associated manuscripts that are in preparation are summarised (Section 1.8.2).
The thesis is structured as follows, with personal contributions of the PhD candidate outlined in Table 1.2:
Chapter 2
:LOCAL SEWAGE INPUT DRIVES BENTHIC COMMUNITY SHIFTS AT OVERFISHED REEFS Ford AK, van Hoytema N, Moore B, Pandihau L, Wild C, Ferse SCA.
In Chapter 2, ‘Local sewage input drives benthic community shifts at overfished reefs in Papua New Guinea’, we carried out field research at the two small neighbouring islands Ahus and Onetah in Papua New Guinea. These two remote islands come under the same customary marine tenure system and are heavily overfished, but while Ahus is densely populated, Onetah remains uninhabited. Ahus lacks any sewage treatment, and consequently raw sewage is directly discharged onto the reef-flat. This study thus aimed to investigate the impact of untreated sewage and overfishing in driving changes within the benthic coral reef community. At sites with varying proximities to beach toilets, fore-reef herbivorous fish biomass and benthic composition were measured alongside fore- reef-flat sedimentary oxygen consumption (SOC) incubations; high SOC reflects high organic input into coastal waters, thus serving as a potential indicator of sewage input. This chapter indicated the significant influence of sewage input from small islands in driving overfished reefs from hard coral dominance towards benthic cyanobacterial mats, which led to a subsequent review into this understudied phenomenon in Chapter 3.
This manuscript, titled ‘Sedimentary oxygen consumption rates indicate that local sewage input drives distinct benthic communities at overfished reefs in Papua New Guinea’ has been published in Environmental Conservation.
GENERAL INTRODUCTION
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Chapter 3
:THE RISE, DRIVERS AND CONSEQUENCES OF BENTHIC CYANOBACTERIAL MATS Ford AK, Bejarano S, Nugues MM, Visser PM, Albert S, Ferse SCA.
Chapter 3, ‘The rise, drivers and consequences of benthic cyanobacterial mats’, comprises a thorough literature review into emerging reports of benthic cyanobacterial mats and their associated links to reef degradation. Benthic cyanobacterial mats are an increasing threat for a number of freshwater and marine ecosystems worldwide. In coral reefs, reports from around the world indicate that their prevalence and longevity are increasing with many associated ecological and social impacts. This rise in reports combined with our own field observations (in Chapter 2) prompted us to review (i) the drivers of this phenomenon, (ii) the ecosystem feedbacks and degradation that consequently arise, and (iii) priority management strategies that can be improved by outlined research gaps.
This manuscript, titled ‘Reefs under siege – the rise, putative drivers and consequences of benthic cyanobacterial mats’ is in preparation.
Chapter 4
:INCREASING LOCAL HUMAN IMPACTS MODIFY ENVIRONMENT-BENTHOS RELATIONSHIPS
Ford AK, Norström A, Jouffray JB, Nugues M, Moore B, Bejarano S, Wild C, Magron F, Ferse SCA.
In Chapter 4, ‘Increasing local human impacts modify environment-benthos relationships’
we analyse an extensive data-set from the Pacific Island region. The data encompasses benthic and fish community data from 182 reefs close to coastal communities and spanning 63 Pacific islands. We extracted additional data on thermal stress and storm exposure from public repositories, and subsequently investigated whether different levels of local anthropogenic impacts (a) directly influence benthic regimes, and (b) shift the importance of drivers in structuring benthic assemblages. Recent work in the Pacific region indicated that reefs close to humans exhibit decoupled relationships with natural biophysical predictors compared with remote reefs. Thus our approach allowed us to develop on this work by asking how different levels of local impacts directly affect benthic communities, as well as investigating which specific predictors (e.g. biomass of herbivorous fish, reef depth, storm exposure, local human density) become most important in shaping benthic assemblages under increasing local impacts. This approach gives us insight into how reefs exposed to increasing levels of human impacts will respond to future climate change-related stressors.
This manuscript, titled ‘Local human impacts influence predictability of global stressors on Pacific Island coral reef assemblages’, is in preparation.
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Chapter 5
:DISCREPANCIES BETWEEN DIFFERENT METRICS FOR CORAL REEF MONITORING
Ford AK, McAndrews R, Eich A, Mangubhai S, Bejarano S, Nugues MN, Moore B, Rico C, Wild C, Ferse SCA
In Chapter 5, ‘Discrepancies between different metrics for coral reef monitoring’, we use a combination of conventional and newly development monitoring tools to evaluate differences in reef ecosystems under local management. Considering the increasingly stressful environment for coral reefs, it is critical to define tools that enable us to evaluate their dynamics and resilience under various scenarios. In this context, surveys must go beyond conventional monitoring approaches focusing on abundance and biomass of key groups and quantify metrics that better reflect longer-term ecological functions and processes. Such a novel approach to monitoring can identify ecosystem trajectories and provide early warnings of reef degradation. We measured a suite of conventional metrics (e.g. biomass of herbivorous fish, cover of broad benthic groups) alongside complementary status and ecological function- and process-based metrics (e.g. turf height, grazing rates, coral recruitment, juvenile coral density) at locally managed and adjacent fished reefs in Fiji, where locally managed marine areas are well-established. By comparing discrepancies between the different metrics, we investigate whether conventional metrics may overlook benefits within managed reefs in terms of superior ecological functions and processes that have important implications for the ability for the system to sustain itself and recover from future perturbations.
This manuscript, titled ‘Evaluation of coral reef management effectiveness using conventional versus newly developed monitoring metrics’ is in revision.
Chapter 6
:BIOLOGY, ECOLOGY AND MANAGEMENT OF KEY HERBIVOROUS UNICORNFISH IN THE PACIFIC
Ford AK, Bejarano S, Marshell A, Mumby PJ
In Chapter 6, ‘Biology, ecology and management of key herbivorous unicornfish in the Pacific’, we evaluate the regional ecological role and fisheries status of Naso lituratus (orangespine unicornfish) and Naso unicornis (bluespine unicornfish). These species are widespread and fulfil critical ecological functions in the top-down control of coral reef macroalgae; particularly fleshy brown algae (e.g. Sargassum spp.) which can out-compete and smother corals. However, they are heavily targeted by nearshore fisheries, and their continued exploitation could thus have serious consequences on reef ecosystems. We summarise current management throughout the region and provide recommendations based on their biological features.
This manuscript, titled ‘Linking the biology and ecology of key herbivorous unicornfish to management in the Pacific’ has been published in Aquatic Conservation: Marine and Freshwater Systems.
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Figure 1.2. Thesis structure and approach for each of the five research-based chapters.
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Table 1.2. Contributions of PhD candidate to tasks within each research-based chapter. For each chapter, each listed contributing author was involved in the development of the final manuscript following the first draft.