The Suitcase Project

Principal Investigators: Sean Fennessy and Michael Roberts

Project summary:

Mesoscale eddies are prominent at the ends of the western boundary currents (WBCs). 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 and southward flows at 20o S. The source and 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 35°E. While it’s plausible that eddies act as transport vectors given their ability to entrain and sustain biological material, it’s unclear how they unpack their biological passengers onto the KZN shelf and coast. Insights gained from theoretical and 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 and 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 and Madagascar ─ notably species thought to be endemic to southern Africa, but also nonendemic, 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 and life-history characteristics are used to infer connectivity pathways. In species lacking pelagic larvae, long-distance dispersal could involve rafting of adults.

Major aims:

  1. Establish whether marine species which co-occur in south-east Madagascar and in KZN are conspecific, and if so, establish to what extent there is mixing between the populations.
  2. Establish what mechanisms and processes could have maintained connectivity between, or which have isolated, populations of these species.