The Suitcase Project: Eddies as Potential Vectors of Connectivity between Madagascar and South Africa
Mesoscale eddies are prominent at the ends of the western boundary currents (WBC). The Agulhas is the only WBC that has frequent mesoscale eddy activity in its source region, largely induced by the Madagascar landmass splitting the South Equatorial Current (SEC) into northward & southward flows at 20o S. The source & cause of mesoscale eddies travelling westward from southern Madagascar remains unresolved as few studies have focused here. Indications are that the westward drift of eddies is influenced by the Mozambique Ridge, protruding southwards from Africa at 35o E. While it’s plausible that eddies act as transport vectors given their ability to entrain & sustain biological material, it’s unclear how they unpack their biological passengers onto the KZN shelf & coast. Insights gained from theoretical & simplified numerical models have highlighted important principals relevant to the Madagascan eddies impinging on the KZN shelf. The KZN marine fauna comprises species from adjacent tropical & warm temperate climes. The tropical fauna are evidence of connectivity with East African countries to the north via prevailing southward water movement. Less easily explained is the co-occurrence of subtropical fauna in KZN & Madagascar ─ notably species thought to be endemic to southern Africa, but also non endemic, co-occurring invertebrate species. The questions to be answered are: Are these organisms conspecific? If so, do their origins date to pre-separation of Madagascar with genetic links being maintained by Madagascar to South Africa flow? Species dispersal over long distances is aided by lengthy planktonic larval phases. Genetic population analyses combined with ocean current system information & life-history characteristics are used to infer connectivity pathways. In species lacking pelagic larvae, long-distance dispersal could involve rafting of adults. ORI scientists working on fishes, corals and macrobenthos will collaborate with scientists from the South African Institute for Aquatic Biodiversity, the South African National Biodiversity Institute, the University of Cape Town and the Department of Environmental Affairs in solving this mystery.
Sean Fennessy and Fiona Mackay will be undertaking a reconnaissance trip to Fort Dauphin/Tolagnano in October 2012 to meet with Malagasy collaborators. They will be looking at habitats for suitable sampling and gathering of information to help plan this logistically challenging project.