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STUDYING BIODIVERSITY VIA GENETICS

Context and Objectives

For over 20 years, genetics has benefited from the huge development of powerful tools in molecular biology analyses, allowing a large range of applications. Population genetics, one component of this genetic approach, is an important issue for biodiversity management nowadays. This component has been applied to marine resource management in Reunion since 2004, and quickly developed across various scientific programmes. The latter, implemented today thanks to RUN Sea Science, are based on various biological models such as marine turtles or large pelagic fishes. Their common objectives are the management and conservation of these exploited and fragile resources. Three main actions are being developed by RUN Sea Science :

1- The study of the genetic structure of emblematic species : marine turtles in the south-west Indian Ocean. A population genetics approach has been implemented from 2005, allowing the genetic structure of the green turtle (Chelonia mydas) to be understood. This first project showed a very significant difference between the green turtles nesting in the south-west Indian Ocean, with the turtle in the south of the Mozambique Channel belonging to the Atlantic stock and the one in the north belonging to the Indo-Pacific one (Figure 1). The green turtle is classified in Annex I of the Washington Convention and is on the IUCN’s Red List, and accordingly these research results are fundamental for aiding conservation of this endangered species by establishing Management Units. Furthermore, this study showed that the south-west Indian Ocean is a mixing area between two large sub-populations of green turtle, meaning that genetic variability is high, leading to greater capability of adaptation in a context of increasing global climate changes. RUN Sea Science’s objective for the 2008-2012 period is now to work on the genetic structure of the hawksbill turtle (Eretmochelys imbricata, Photo 1) in the south-west Indian Ocean, a rare species in the region and highly impacted by fisheries and habitat change.

Figure 1 Photo 1

2- Genetic structure of exploited species : the swordfish in the Indian Ocean

Swordfish has the greatest commercial value of all billfish resources in the world. In the Indian Ocean, swordfish is a commercially important marine resource especially in the south-western region (for Reunion, Spain, Mauritius, the Seychelles and South Africa) for exports to the EU countries, as well as for domestic consumption as a valuable protein resource for most of the region’s countries. In the Indian Ocean, swordfish are caught mainly using drifting longlines (95%) and gillnets (5%). Before the early 1990s, swordfish was mainly a by-catch of industrial longline fisheries targeting tropical and temperate tunas, with catches increasing slightly from 1950 to 1990, in proportion to the increase of the catches of the target species. Swordfish catches rose markedly after 1990 to a peak of 35,000 tonnes in 1998, the year in which the maximum catch for the species was recorded. With more than 1,000 tonnes of capture, the swordfish is a key species for Reunion’s longline fleet. Due to the overall increasing level of swordfish exploitation in the Indian Ocean, management measures should be considered for sustainable exploitation ; however, the lack of data on biology, behaviour and structure of this species does not allow reliable stock assessment to be made. Under RUN Sea Science, the IOSSS project (Indian Ocean Swordfish Stock Structure) will implement the genetic tool to understand the genetic structure of this exploited species (Figure 2). Results of such a study will provide managers with important elements for reliable stock assessment.

Figure 2 Photo 2 Photo 3

3- Connectivity : assessment of the existing links between Marine Protected Areas in the south-west Indian Ocean

Marine Protected Areas (MPAs) are designed to increase ongoing efforts made to preserve marine diversity. MPAs are supposed to play an ecosystem role on a larger scale that goes beyond the boundaries of the reserve (e.g. fishery reserves where economic value depends on export of individuals into the periphery of the reserve). Although there is a consensus about the positive effects of marine reserves on the size and abundance of targeted species within the boundaries of a protected area, there is much less information available on their roles in the export of fishes at different stages of life outside the boundaries, particularly due to the difficulty of estimating it. Thus, patterns of connectivity are important in understanding the supply of adults into and out of a reserve. In general, estimates of connectivity between populations of a species are based on indirect methods : inferred from models based on oceanography and larval biology, thanks to otolith chemistry, or population genetics. Indeed, examining the genetic structure of populations provides answers to questions about the average rate of larvae exchanges and thus enables improved studying of long-term population connectivity. Under RUN Sea Science, the overall goal of the CAMP project (Connectivity between MPAs) is thus to assess the connectivity of some key reef fish species of the SWIO (Photo 3). This project aims to compare the genetic diversities and differences of some marine fish species targeted by traditional fisheries with a special focus on the relationship between MPAs from isolated islands as well as continental coastlines (Figure 3).

Figure 3

The three species of the CAMP project (from left to right) : Epinephelus merra, Myripristis berndti, Lutjanus kasmira

Epinephelus merra Myripristis berndti Lutjanus kasmira

Links with RUN Sea Science

  • Specific machines for genetic analysis
  • Appointment of a population genetician on a 17-month contract
  • Exchanges of experience and know-how in genetics

Partnership of these projects

  • Marine turtles : Kélonia, a marine turtle observatory based in Reunion.
  • IOSSS : IRD CSIRO (Australia), CAPFISH (South Africa), AFREDEC (Thailand) and SFA, IOTC (Seychelles).
  • CAMP : ARVAM, Réserve Naturelle Marine de La Réunion, SAIAB (South Africa), SFA (Seychelles) and the Marine Park of Moheli (Comoros).

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