Above the sea

Of course, the marine realm includes more than just what lies under the waves. What happens within the reefs, flats and lagoon of D’Arros and St Joseph are inextricably linked to what occurs above sea level on each tiny coralline island and sand cay in the group. The SOSF-DRC understands that to undertake the best research, a holistic approach to tropical island ecosystems must incorporate studies above the sea as well as below it.

While the heavy rain of coconuts from unmanaged former plantations continues to fall on D’Arros and the largest islands within St Joseph Atoll, forest rehabilitation efforts have expanded relic stands of indigenous broadleaf trees. Thus a new rain of nutrient-rich guano from returning seabirds enhances efforts to restore parts of the islands to their former ecological state. Because all islands in the group have been rat-free for more than a decade, these rehabilitated indigenous forests provide potential areas for the introduction of endangered endemic land birds – and a possible stronghold for Seychelles bird species under threat. Indeed, forest rehabilitation is likely to increase biodiversity within the whole system.

In 2017, the SOSF-DRC plans to initiate a terrestrial biodiversity assessment of the area by partnering with the University of Seychelles. This project aims to contribute to the broader national biodiversity database, such as the National Environmental Data and Information portal, as outlined in the most recent Seychelles National Biodiversity Strategy Action Plan. The opportunity for the SOSF-DRC to work closely with the University of Seychelles promotes capacity building for the Seychellois people and adds to the vision of a knowledge-based society.

Birds, including 15 breeding species, make up a large part of the biodiversity of St Joseph and D’Arros. Accordingly, the SOSF-DRC currently supports a research project on the most abundant seabird found in the area, the wedge-tailed shearwater Ardenna pacifica. Soaring in after foraging at sea for days at a time, the shearwaters, or fouquet in Seychellois Creole, gather in their tens of thousands as night falls on St Joseph and D’Arros. The colony is estimated to be the third largest in the Western Indian Ocean and the sheer numbers of these nesting seabirds provide an opportunity to uncover significant feeding areas for the species. As shearwaters frequently associate with tuna, studying this popu-lation may help the government of the Seychelles, a major tuna-fishing nation in the Western Indian Ocean, to better understand and manage its tuna stocks.

Beneath the waves

Under the sea exists a kaleidoscope of colour, a treasure trove of life. But because overexploitation, pollution and damage aren’t as visible beneath the waves as they are on land and beaches, extra precautions and special reserves are required to safeguard marine ecosystems. From the study of oceanographic systems to coral reef monitoring and manta ray ecology, the dedication of the SOSF-DRC to marine research is unmistakable.

Understanding oceanographic trends is the backbone for recognising broad drivers of animal movements and ecology. For this reason, the SOSF-DRC monitors relevant ambient environmental data such as tidal movements, light intensity and temperature. Every five minutes since 2011, no fewer than 100 temperature loggers have recorded the sea temperature in the waters surrounding the island and atoll. Early analysis of data from loggers at five metres highlights a significant annual temperature change of nearly 7 °C, which probably affects animal movements and foraging around both St Joseph and D’Arros. These results may ultimately help to predict the severity of bleaching events and estimate the mortality or recovery of corals after the events.

By monitoring the marine environment around St Joseph and D’Arros, researchers are able to detect changes in good time. The earlier they perceive these changes, the sooner they can try to understand them, answer questions about why they are happening and put measures in place that could help to reverse or mitigate them or encourage adaption to them.

Monitoring oceanographic conditions feeds directly into the uninterrupted five-year coral and reef fish monitoring programme run by the SOSF-DRC. In the coral aspect of the programme, the most detailed such programme in the Seychelles, the data collected include benthic cover and composition, growth rate and recruitment of corals and both broad- and fine-scale bleaching surveys. These surveys were particularly relevant during the bleaching event in mid-2016, as without prior monitoring of composition, recruitment and growth prior to the bleaching, there would be little to compare for recovery. Without baseline data such as these, it is difficult to pinpoint what constitutes a healthy reef. In the second part of the monitoring programme, data from reef fish surveys have shown abundant and diverse fish populations that have the potential to act as replenishing stock for the wider Seychelles.

A healthy coral reef system with abundant reef fishes provides support for larger top predators such as giant trevally Caranx ignobilis. Although this species is commercially and recreationally important throughout the Indian Ocean, virtually nothing is known about its life history. In 2016 the SOSF-DRC set out to use behavioural ecology and genetic analysis to investigate the population connectivity of this large species. For the Seychelles, a better understanding of the giant trevally could lead to improved management of the species and the prioritisation of exploiting it sustainably, which would benefit both the tourism economy and local food security.

Finally, another ocean giant, the reef manta Manta alfredi, is a popular resident in the waters surrounding St Joseph and D’Arros and it too has an established research project associated with it. With a local population exceeding 120 identified individuals, the mantas studied by the SOSF-DRC make up the largest and densest aggregation known in the Seychelles. Because the reef manta faces population declines throughout its range, understanding its ecology and movements is crucial to its survival as a species and its participation in the tourism industry. The conservation needs of the reef manta in the wider Seychelles are generally not known, but the species’ global ecotourism value of roughly $50-million makes finding out how best to protect it worthwhile in terms of both conservation and the economy.