Awards Human interactions Marine & freshwater Poster

★ Hamilton, Mark // Implications of coral reef degradation for fisheries


This poster introduces my PhD project and highlights the research questions I plan to investigate regarding tropical coral reef degradation and small-scale fisheries. My poster is aimed at early-career scientists who are thinking about doing a PhD (e.g. undergraduate/masters students) and I hope that it illustrates the process of defining different research questions within the main research topic of a PhD, which has been an interesting learning curve for me.


Coral reef degradation

One of the major causes of coral reef degradation is coral bleaching, caused by unfavourably high sea temperatures, which can result in mass coral mortality. Bleaching occurs when corals succumb to heat stress and eject the symbiotic algae within their tissues that they rely upon to produce food via photosynthesis, giving the corals a bleached white appearance. Corals can recover if environmental conditions quickly improve, otherwise the coral colonies die, leaving behind a calcium carbonate skeleton. The central diagram on this poster focuses on coral bleaching as the cause of degradation, however other causes include storm damage, coral disease and destructive fishing practices. Even dead coral reefs can still have relatively high structural complexity, which provides shelter for many fish species. If the recruitment of juvenile corals is sufficiently high, as well as the abundance of herbivorous fish that graze on the algae which compete for space with corals, then the reef may recover and return to a coral-dominated state. However, if new corals are not recruited to the reef and the reef structure continues to degrade, the habitat becomes less suitable for many coral and fish species alike and may undergo a regime-shift to a state dominated by fleshy macroalgae. It is difficult for juvenile corals to recruit to macroalgal reefs, therefore transitioning back to a coral-dominated state is unlikely. Macroalgae-dominated reefs are typically less structurally complex compared to coral-dominated reefs, have reduced biodiversity and provide fewer ecosystem services to humans.

My research focuses on how coral reef degradation can affect small-scale tropical fisheries and the implications it may have for fishing communities.

1) Fisheries productivity

Different types of fish respond to reef degradation differently. For example, species that rely heavily on live coral for food (corallivores) or shelter (e.g. small planktivorous fish) are particularly negatively affected by reef degradation, whereas herbivorous fish may appear to benefit from an increase in algae abundance on degraded reefs. I plan to use newly developed methods to calculate the productivity (growth rates) and turnover of fish groups from Seychelles reef survey data. I will compare these metrics between recovering coral reefs and regime-shifted reefs, considering what the implications might be for species that are commonly targeted in Seychelles fisheries.

2) Catches

As fish populations change on reefs, so do the fish present in fishers’ catches. I will gather catch data from reef fishers to assess how fishing yields are affected across a gradient of reef condition. Catch per unit of fishing effort (CPUE) and catch composition (what species, in what quantities and what sizes) will be measured across different types of fishing gears to give an indication of how different fishing methods are affected by reef degradation. The value per unit effort (VPUE) may also be investigated to see how variation in catches by weight compares to that by value, so that the effects of reef condition on the income for fishers as well as on the quantity of fish landed can be investigated.

3) Fishing patterns

As fishing yields change in response to the varying quality of fishable habitats, the fishing habits of local fishers are also likely to alter. For example, fishers may travel further on fishing trips to reach more desirable fishing grounds, although this may be dependent on factors such as boat size, fishing gears used, level of fishing experience and fuel affordability. By interviewing local fishers and gathering information on their usage and perceptions of fishing grounds in their area using habitat maps, I aim to show how reef degradation has altered fishing behaviour throughout the fishing community.

4) Fishing communities

With reef degradation altering fish assemblages, fishery yields and fishing habits, the relationships coastal communities have with reefs may also be changing as degradation progresses. Reef degradation has the potential to change the types and quantities of fish available to fishing communities, in a nutritional sense and as a source of income. By incorporating interview data from fishing communities and production estimates of targeted fish species, in this chapter I plan to assess how reef degradation can affect lifestyle in small-scale fishing communities and also how people’s lifestyles and fishing habits can impact on degraded reef ecosystems.


My PhD research will take a multidisciplinary approach to answering some key questions regarding how small-scale fisheries are affected by coral reef degradation. As reef degradation progresses – as a result of more frequent coral bleaching events for example – a better understanding of the effects on fisheries, and those who depend on them, becomes increasingly important.

Fish silhouette graphics from Morais et al. (2020). Human exploitation shapes productivity-biomass relationships on coral reefs. Global Change Biology, 2020;00:1–11. DOI: 10.1111/gcb.14941

REEFS – Reef Environments: Ecosystem, Function & Society

Mark Hamilton

Mark Hamilton

Mark is in the first year of his PhD at Lancaster Environment Centre. He has an interest in tropical coral reef ecosystems and fisheries. Mark has previously been involved in coral reef research in Tobago, Cambodia and the Philippines, and has also worked in inshore fisheries research in the North Sea.

Mark’s Envision profile


Twitter: @Mark_H_22

Organisation: Lancaster University