Mozambique Channel

Description / The oceanography of the Mozambique channel / Jurisdiction / Features of Potential Outstanding Universal Values / Threats / Management status / Geographic scale and integrity issues / Other sites in the region / Key References

The Mozambique channel.
© David Obura

Depth in the Mozambique channel, showing the major transitions from 2000 m in the mid-point of the channel down to >4,000m towards the basins to the north and south.
© David Obura

Connectivity patterns in the northern Mozambique channel, showing drifter paths that move across the entire channel, and both north and south out of the northern channel region.
© Raymond Roman


– The Mozambique channel extends from about 12°N, where the Glorioso Front marks the transition from the South Equatorial Current to the waters of the channel, slightly N of Glorieuses island, to about 25°S at a line stretching from the southern tip of Madagascar to Mozambique. It varies from approximately 800-900 km wide at its northern and southern ends, to a minimum of 400 km wide at about 16°S.
The channel started to form about 180 mya as the ancient continent Gondwana rifted and Madagascar (then joined with India, Australia and Antarctica) split off from the African coast. Since about 140 mya its configuration has remained relatively constant though during the Cenozoic the Africa-Madagascar complex has migrated northwards about 15° of latitude, and tectonic and volcanic activity has occurred in the central and northern parts of the channel. The floor of the channel ranges from about 3500 to < 2000 m, being shallowest at the narrowest point at about 16°S. Within the northern part of the channel, tectonic and volcanic activity has resulted in the formation of the Davie Ridge (13-18°S) which peaks at 300 m. A hotspot has created the Comoros islands, starting with Mayotte (5.4 mya) and ending with Grande Comore, which is estimated at 130,000 y, and still active today, and a source of earthquakes and volcanic eruptions.

The oceanography of the Mozambique channel was unknown until ten years ago, when the existence of highly variable eddies several 100 km across, often in dipoles (an anticyclonic and cyclonic eddy pair) that formed in the region around the Comoros were discovered. As a result of vorticity imparted into the flow of the SEC as it flows around the tip of northern Madagascar, both cyclonic (clockwise) and anticyclonic (anticlockwise) eddies are generated. At times, a larger gyre is also formed that circulates around the Comoro islands. Further dynamism in these features is imparted by Rossby waves that cross the Indian Ocean, interacting with the narrow constriction of the channel at 16°S. Often eddies are generated in pairs that move southwards through the channel, and 6-8 pairs may be formed through the course of a year.
The consequences of eddy formation ramify throughout the channel, and at all levels of biological functions. Because water flows in all directions as a result of the eddies, genetic connectivity throughout the Mozambique channel is likely very high, particularly in the north, resulting in high retention and recruitment of larvae in pelagic and shallow marine ecosystems, and thereby high resilience of communities and populations. Due to the rotation of the eddies, they also result in down- and up-welling of water, and warmer and cooler temperatures in the centers of the eddies, and this transfers nutrients across the thermocline. Further, the eddies reach throughout the water column to at least 1000 m depth, and as these touch the continental shelves they draw nutrients off the slopes and into the water column. These eddy dynamics profoundly affect pelagic biological communities including phytoplankton, zooplankton, larger invertebrates, fish and marine mammals, and birds. While the full biological consequences of the eddy dynamics are not yet known these count as a unique oceanic system and likely to be critically important not only for the biology of species and ecosystem processes in the Mozambique channel, but also for fisheries and other economic uses.
Finally, the highly dynamic eddies and net current in the channel contributes about 50% of the water transported in the Agulhas current, forming a link in the chain of transport of water masses from the Pacific back to the Atlantic. This contribution of water from the Indian to the Atlantic oceans may be a significant factor in climate regulation on a planetary scale, and a justification for new research to address this question.
The interaction of waters of the East Madagascar Current flowing southwards and over the Madagascar Plateau results in highly dynamic and productive coastal and offshore upwellings. Due to the continuity of the Madagascar Plateau with Madagascar island, and similar turbulent interactions between the geology and ocean currents at northern and southern tips of the island, this Plateau is used here to extend what is normally considered as the Mozambique channel boundary farther south, beyond the tip of Madagascar. Turbullent currents and upwelling waters from the Madagascar Plateau flow into the southern part of the Mozambique Channel, interact with the waters here (and hence may also influence channel dynamics farther north when carried north in eddies), and the two merge to form the Agulhas Current off South Africa. To capture these interactions, the Mozambique Channel as described here, includes features of the oceanography of the Madagascar Plateau.

Jurisdiction – the Mozambique channel is entirely within the EEZs of the neighbouring countries, which include Mozambique, Madagascar, the Comoros, Tanzania and France.

Features of Potential Outstanding Universal Values

Criterion viii - Geology and oceanography
The Mozambique channel is bounded by the oldest coastlines and seabed of the Indian Ocean, and marks the 1st stages in the tectonic movements that created the ocean.
The eddy and gyre generation dynamics of the channel are unique globally, contributing to the western boundary currents in the Indian Ocean that play a role in the global conveyor belt of ocean circulation, and regulation of the climate system.
Similar upwelling and turbulence features are produced on the Madagascar plateau, that feed into the southern Mozambique channel and thence into the Agulhas Current system

Criterion x - Habitats and conservation
The geology and oceanography of the channel profoundly affect the ecosystem dynamics and habitats of the channel. The unique eddy dynamics of the channel and upwelling on the Madagascar Plateau contribute to the highly connected and highly productive shallow benthic and pelagic marine communities, affecting the productivity of coral reefs, planktonic and pelagic communities alike, and the behavior, spatial and temporal activities of species groups including large fish, marine turtles, seabirds and marine mammals.
Seabirds – half of the breeding seabirds of the WIO breed in the Mozambique Channel, and it and the Madagascar Plateau are the two most productive of the five main foraging grounds for seabirds in the WIO.
Turtles – Europa has the most significant green turtle nesting site in the Indian Ocean, and migration patterns criss-cross the channel due to oceanographic conditions and high mixing.
Cetaceans – use the Mozambique channel as prime wintering, feeding and nursing grounds.

Criterion ix - Ecology, species and evolution
Over an evolutionary timescale, the geology and oceanography of the Mozambique channel may have played a key role in driving the evolutionary dynamics of the Western Indian Ocean, maintaining and accumulating species in the northern Mozambique channel in a biodiversity center second in absolute numbers to the Coral Triangle region, but with a unique evolutionary history and genetic diversity.
Genetic connectivity in the Mozambique channel show several overlapping patterns – one of high mixing from north to south and distinct from points farther north (coelacanth), and one showing a barrier at the narrow constriction of the channel, showing southern and northern populations (green turtle). Corals show highest diversity, and indications of high connectivity in the northern Mozambique Channel.

Threats – The Mozambique channel is bordered by long coastlines and nations with growing and active fishing fleets, and the increased understanding of productivity in the channel will undoubtedly lead to increased and targeted exploitation of fisheries and other living resources. Extraction for genetic resources is growing, reflecting the high genetic diversity in the channel, as are threats of mineral, oil and gas extraction, and climate change.

Management status – At the level of the channel, and with respect to oceanographic processes, management within the channel is nascent. Individual countries have taken steps towards site-based management in MPAs (Mozambique and Madagascar in coastal MPAs, France in whole-EEZ MPAs in Mayotte and Glorieuses) requiring additional instruments relevant to ICZM, EEZ and fisheries instruments to regulate threats sufficiently to meet WH designation for individual sites, or the channel as a whole. The Nairobi Convention is the prime convention relevant to marine and coastal management, that all countries bordering the channel are party to.

Geographic scale and integrity issues – The channel covers 13° of latitude and varies between 400-900 km wide, equivalent to almost 1 million km2 of ocean. Whole-site designation as a World Heritage site is unlikely, offering the possibilities of designating key sites or regions within the channel that may reflect different properties. Further, different portions of the channel contain different components of the geological and oceanographic features of Outstanding Universal Value, that support different classes of biological systems (species and ecosystems) that themselves have potential OUV. Thus, the report proposes an approach at two levels:

  1. Regional/trans-boundary - recognition of the geological and oceanographic features of Outstanding Universal Value at the level of the Mozambique Channel as a whole. These will serve to provide the integrity and governance context among the countries that share the channel to frame a consistent set of sites that can be part of an overarching trans-boundary serial sites that extends across the entire channel,
  2. National - within individual countries, the designation of the specific locations with potential Outstanding Universal Value that would be the individual sites in the channel-wide serial site. Based on current knowledge, the following individual sites are proposed:
    • Northern Mozambique to southern Tanzania – Nacala – Quirimbas – Mtwara
    • Northern Madagascar – the bays and islets of northern Madagascar, from Nosy Ankao/Loky Bay in the east to Sahamalaza/Radama in the west.
    • The Comoros – Glorieuses crescent, including the Comoros, Mayotte, Glorieuses and the Zélée and Geyser banks.
    • The Scattered Islands (Iles Éparses) in the central and southern Mozambique Channel
    • Southern Mozambique – the Bazaruto-Tofo complex
    • Southern Madagascar – the ‘deep south’ of Madagascar, including the coast and Madagascar plateau.
    In considering these individual sites, their hydrodynamic, geological and biological integrity must be sufficiently assessed to meet the stringent criteria for World Heritage designation, so that each site on its own, as well as as part of the serial site, has Outstanding Universal Value.

Site type – A serial (potentially transboundary) nomination would likely best address the OUV of the Mozambique channel, comprising individual sites also expressing OUV of what they contain.

Other sites in the region – No other part of the WIO is comparable to the Mozambique Channel.

Key References – Ali & Huber (2006); Beal et al. (2010); de Ruijter et al. (2005); Obura (2012); Obura (in review); Ternon et al. (2012). --> References