Western Indian Ocean Marine Science Association

Small-Scale Versus Large-Scale Coral Genetic Connectivity within Southeast African Marginal Reefs

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Project Summary:

Several marine protected areas (MPA) have been established along the east African coast to protect the coral communities from human and natural disturbances. MPAs should, firstly, preserve the genetic integrity of such marine resources. The success of such MPAs is dependent on the availability of background information describing how populations are linked, or connected. Estimates of contemporary gene flow among southeast African reefs are required to reveal the dependence of the South African coral communities on those to the north. Such a study will be especially relevant if the systems are found to be structured with high levels of self-seeding, as found on the Great Barrier Reef, since recovery from large-scale damage may be gradual. The latter is of global importance in view of increasing coral mortality from climate change-related bleaching events. Accordingly, coral population genetics will be examined in this study to assess the level of contemporary, small-scale connectivity between the reef systems and its significance to reef resilience. The objectives of the proposed research project will be to assess the population genetic structure of coral species at various spatial scales; estimate the proportion of self-seeded and non-self-seeded coral colonies within a reef; identify the potential sources of non-self-seeded coral colonies; assess whether the degree of self-recruitment/migration of species at the reefal scale limits their resilience potential; and integrate research findings into a management strategy for southeast African reefs. To accomplish these objectives, microsatellite loci will be used to assess the level of inter- and intra-population genetic connectivity of Acropora austera and Platygyra daedalea corals on reefs along the southeast African coast, from Bazaruto Island in Mozambique to Sodwana Bay in South Africa. These two coral species are common on southeast African reefs, have distinct reproductive and larval dispersal strategies, and contrasting bleaching responses. Contemporary gene flow or genetic connectivity will be estimated using both indirect and direct methods, thereby this the first study to use both methods on southeast African reefs. Comprehensive sampling will be undertaken on Two-mile Reef (TMR) which is the southernmost African reef with important hard coral communities and the most heavily-used reef in southeast Africa. Reefs to the north and south of TMR will be sampled as they are believed to constitute important sources and sinks of coral and fish larvae. The proposed project will greatly enhance our knowledge of reef connectivity on high-latitude marginal reefs by providing direct estimates of contemporary, small-scale connectivity within and between reefs. These estimates of inter- and intra-population connectivity will help assessing whether the reefs along the southeast African coast are independent and will have to rely on their own genetic diversity to adapt to environmental change which will suggest new conservation measures.

What were the problems the project intended to address?:

The proposed project will greatly enhance our knowledge of reef connectivity on high-latitude marginal reefs by providing direct estimates of contemporary, small-scale connectivity within and between reefs. These estimates of inter- and intra-population connectivity will help assessing whether the reefs along the southeast African coast are independent and will have to rely on their own genetic diversity to adapt to environmental change which will suggest new conservation measures.

Project Objectives:

The aims of this research project will be to:
a. assess the population genetic structure of two coral species at various spatial scales along the reefs of the southeast African coast
b. estimate the proportion of self-seeded and non-self-seeded coral colonies within Two-mile Reef
c. identify which northern reefs are the sources of the non-self-seeded coral colonies on Two-mile Reef and the magnitude of their contribution
d. assess whether the degree of self-recruitment/migration of species at the reefal scale limits their resilience potential, and
e. produce a revised management strategy for southeast African MPAs based on the research findings.

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