PhD Studentship: Fish Ecology of Mesophotic Coral Reef Ecosystems

Dominic Andradi-Brown

University of Oxford

Supervisor(s): Alex Rogers (Oxford) and Dan Exton (Operation Wallacea)

Mesophotic coral reef ecosystems (MCE) occur in tropical regions extending from 30 m to the limit of the photic zone, c. 150 m.  These reefs are often connected to shallow coral reef ecosystems, where it is suggested they provide an important reservoir of recruits for coral and fish populations. Existing reef fish studies are highly depth biased mostly < 30 m, making the importance of mesophotic reefs to overall reef resilience in the face of human disturbances such as overfishing largely unknown, with a lack of evidence for whether fish populations on shallow reefs and adjacent MCEs are connected.

This study addresses this important information gap by using advanced diving technologies coupled with a newly developed stereo-video system and molecular ecology techniques to better understand fish communities by examining fish biomass distributions and community structure down depth gradients from shallow reefs to MCEs and by exploring the connectivity of MCE fish populations down depth gradients with shallow reefs and between mesophotic reefs.

This project is being conducted in partnership with Operation Wallacea with fieldwork principally based at their field site on Utila, Honduras where MCEs connected to shallow reefs have been identified but are unstudied.

The aims of the project are twofold, first to Investigate biomass and community structure. Fisheries value and ecological service provision requires biomass to be quantified as it provides a better indication of functional pressure exerted by a fish-feeding guild than richness or abundance. Fish biomass along transects will be assessed by stereo-video surveys capturing the shallow reef to MCE gradient at various fished and protected sites. Biomass will be standardised using fish length-weight relationships, through data from local fisheries monitoring programmes to obtain local length to weight ratios, but for any fish species not caught locally, through available datasets (e.g. Fishbase). To allow patterns in fish biomass and community structure to be explained, benthic composition will be quantified using point intercept video transects, quantifying coral (genera and morphology), algal and other coverage. Physical parameters will also be recorded including temperature, light and turbidity and HOBO loggers for detailed year-round temperature and light readings.

The second aim is to Investigate connectivity in MCE fish populations. Levels of population connectivity between populations of depth-generalist fish species with residents found on both shallow reefs and MCEs are not known. This has major implications for conservation and sustainable management of MCE fisheries, as well as the design and location of marine protected area networks. Many studies have demonstrated the ability of molecular techniques such as microsatellites to identify population structure; these protocols can be applied to assess connectivity down depth gradients and between MCE specialist species on small spatial scales. Non-lethal fin clippings will be collected from fish using a hand net and a clove oil anaesthetic mix. Care will be taken to return individuals to the reef where they were caught. To assess connectivity along depth gradients, samples of depth-generalist reef associated fish will be collected at different depths at several sites. To assess population connectivity between MCEs, an MCE specialist fish species will be identified samples collected at several sites.


Ocean Research and Conservation Group
Department of Zoology
University of Oxford
The Tinbergen Building
South Parks Road

Twitter: @dandradibrown