Ecologically or Biologically Significant Areas (EBSAs)
published: 12 Jun 2015
The Mozambique Channel and southward extension of its associated water flow into the Agulhas Current can be characterized in its entirety as an area meeting EBSA criteria, or can be broken down into sub-regions, each with their own particular significance. The ecology of the area is driven by the oceanography of currents, strong eddies and mixing, producing a highly productive ecosystem that attracts a wide range of species, many of them threatened and endangered.
The Mozambique Channel is bounded by the oldest coastlines and seabed of the Indian Ocean and marks the first stages in the tectonic movements that created the ocean. The eddy and gyre dynamics in the channel are globally unique, contributing to the Agulhas Current, a major western boundary current in the Indian Ocean that plays a role in the global conveyor belt of ocean circulation and regulation of the climate system. Upwelling eddies form on the Madagascar Plateau, flowing into the southern Mozambique Channel, which joins the East Madagascar Current and forms the Agulhas Current system. The geology and oceanography of the channel thus 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, and the spatial and temporal activity of faunal groups, including large fish, marine turtles, seabirds and marine mammals.
Southern Indian Ocean
The area runs across the Mozambique Channel from Mtwara in southern Tanzania to the north-eastern corner of Madagascar, southwards to the south-eastern tip of Madagascar and St Lucia Lighthouse in South Africa
DISCLAIMER: The designations employed and the presentation of material in this map do not imply the expression of any opinion whatsoever on the part of the Secretariat concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.
The oceanography of the Mozambique Channel was unknown until ten years ago, when the existence of highly variable eddies several hundreds of kilometres 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 six to eight 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 function. 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 centres 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 are 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 contribute a substantial proportion of the water transported into the Agulhas Current, forming a link in the chain of water transport 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 East Madagascar Current water flowing southwards and over the Madagascar Plateau results in highly dynamic and productive coastal and offshore upwelling. Due to the continuity of the Madagascar Plateau with Madagascar, 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. Turbulent currents and upwelled water from the Madagascar Plateau derived largely from the East Madagascar Current flow into the southern part of the Mozambique Channel, interacting with the waters here (and hence also influencing channel dynamics farther north within eddies), and merging with the Mozambique eddies 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 and the island’s south-eastern tip. 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 centre second in absolute numbers to the Coral Triangle, but with a unique evolutionary history and genetic diversity. Genetic connectivity in the Mozambique Channel shows several overlapping patterns – one of high mixing from north to south but distinct from points farther north (coelacanths), 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. Further south, there is evidence of a genetic disjunction north and south of the point where the Agulhas Current first impinges on the African coast. Oceanographic and genetic connectivity between southern Madagascar and South Africa is thus soon to be investigated in ACEP III. Fish: the area has highest fish diversity in the WIO, with a high abundance in deeper waters, such as the St Lazarus bank. Turtles: notable nesting sites for greens, hawksbills and leatherbacks, and foraging ground for olive ridleys and loggerheads. Marine mammals: important humpback whale mother/calf nursing zone. Sharks and Rays: a superlative reef shark site between Vamizi/Metundo islands shows the influence of variable currents in aggregating the sharks, and in protecting them from use. Birds: the oceanic islands in the Mozambique channel, most notably Europa and Juan de Nova, are host to globally or regionally significant populations of several seabird species. Around 10% of the world’s sooty terns Sterna fuscata breed at Juan de Nova (2 million pairs) and Europa Island (1 million pairs) (Le Corre and Jaquemet 2005; Wanless 2012). The second-largest regional colony of frigatebirds Fregatta ariel and F. minor (seven thousand) and the largest colony of red-tailed tropicbirds Phaethon rubricauda (five thousand pairs) breed at Europa Island. The waters surrounding these islands are critical to these species during the breeding season.
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, South Africa in an MPA and World Heritage Site) requiring additional instruments relevant to integrated coastal zone management, EEZ and fisheries instruments to regulate threats sufficiently to meet World Heritage designation for individual sites, or the channel as a whole. The Nairobi Convention is the prime convention relevant to marine and coastal management, and all countries bordering the channel are party to it.
Ali JR & Huber M (2006) Mammalian biodiversity on Madagascar controlled by ocean currents. Nature doi:10.1038/nature08706 Beal LM, De Ruijter WPM, Biastoch A, Zahn R & SCOR/WCRP/IAPSO Working Group 136 (2010) On the role of the Agulhas system in ocean circulation and climate. Nature 472: 429-36. doi:10.1038/nature09983 deRuijter, W. P. M., Ridderinkhof, H. & Schouten, M. W. 2005. Variability of the southwest Indian Ocean. Phil. Trans. R. Soc. A 363, 63–76 Le Corre, M., Pinet, P., Kappes, M., Weimerskirch, H., Catry, T., Ramos, J., Russel, J.G., Shah, N., Jaquemet, S., 2012.Tracking seabirds to identify potential Marine Protected Areas in the tropical Indian Ocean. Biological Conservation. Available Early Online. Le Corre, M., Jaquemet, S., 2005. Assessment of the seabird community of the Mozambique Channel and its potential use as an indicator of tuna abundance. Estuarine, Coastal and Shelf Science 63, 421-428. Obura, DO (2012) Evolutionary mechanisms and diversity in a western Indian Ocean center of diversity. Proceedings of the 12th International Coral Reef Symposium, Cairns, Australia, 9-13 July 2012. Session 3A Evolution, biogeography and taxonomy Obura DO (2012/in review). The diversity and biogeography of Western Indian Ocean reef-building corals.PLoS ONE. Schleyer, M.H. &BenayahuY. 2009. Soft coral biodiversity and distribution in East Africa: Gradients, function and significance. Proceedings of the 11th International Coral Reef Symposium, Ft. Lauderdale, Florida, 7-11 July 2008. Ternon, J.F., Barlow,R., Huggett, J., Kaehler, S., Marsac, F., Ménard, F., Potier, M. and Roberts, M. (2012) An overview of recent field experiments on the ecosystem's mesoscale signature in the Mozambique Channel: from physics to upper trophic levels. in prep. for Deep Sea Research 2: The Mozambique Channel: Mesoscale dynamics and biological production) Wanless, RM 2012.Seabirds of the Western Indian Ocean. In: van der Elst, R (Ed) Mainstreaming biodiversity in fisheries management: a retrospective analysis of existing data on vulnerable organisms in the South West Indian Ocean.Specialist Report for the South West Indian Ocean Fisheries Project (SWIOFP), 206 pp.
Areas described as meeting EBSA criteria that were considered by the Conference of the Parties
C1: Uniqueness or rarity High
The area encompasses the East African Coral Triangle, second in biodiversity to the Coral Triangle centred around Indonesia, Malaysia and Papua New Guinea (Obura 2012). A biodiversity gradient as one moves south introduces other unique components in areas of high productivity and the migration routes of diverse biota. See Schleyer & Benayahu (2009) regarding soft corals.
C2: Special importance for life-history stages of species High
Many threatened and endangered species (turtles, mammals, birds) use the area for nesting and breeding. The most important example is that of the dugong, the Bazaruto region having the last viable population of this marine mammal in the WIO.
C3: Importance for threatened, endangered or declining species and/or habitats High
Fish: the highest fish diversity in the WIO, with high abundance found in deeper waters such as the St Lazarus bank. Turtles: notable nesting site for greens and hawksbills and foraging ground for olive ridleys, loggerheads and leatherbacks. Marine mammals: important humpback whale mother/calf nursing zone. Sharks and Rays: a superlative reef shark site between Vamizi/Metundo islands shows the influence of variable currents in aggregating the sharks, and in protecting them from use. Corals: a rich biodiversity gradient that includes regional endemics. Birds: Globally significant colonies of Sooty terns Sterna fuscata breed at Juan de Nova (2 million pairs) and Europa Island (1 million pairs) (Le Corre and Jaquemet 2005). The second-largest regional colony of frigatebirds Fregattaariel and F. minor (seven thousand) and the largest colony of red-tailed tropicbirds Phaethon rubricauda (five thousand pairs) breed at Europa Island (BirdLife South Africa unpubl. data, Wanless 2012). The waters surrounding these islands are critical to these species during the breeding season. The Endangered Barau’s petrel Pterodro mabarauiforages extensively in the southern portion of the proposed area (Le Corre et al. 2012).
C4: Vulnerability, fragility, sensitivity, or slow recovery High
Coral reefs, including regional endemics, highly susceptible and fragile to global warming.
C5: Biological productivity High
Mesoscale dynamics of the Mozambique Channel drive highly productive pelagic communities, mobile within eddies as they move through the channel (Beal et al., 2010). Linkages with habitats such as mangroves and seagrass beds provide crucial nursery areas for many species (www.transmap.fc.ul.pt).
C6: Biological diversity High
Highest diversity of coral reef species and coral habitats, and probably the highest diversity in the WIO of different marine (benthic and pelagic) habitats, with high genetic diversity and some important discontinuities.
C7: Naturalness Medium
Some areas are remote and have suffered less impact from human-induced disturbance, but as a whole, region-scale vulnerability is high.
The area is under consideration for WHS status and has been identified as important in the WWF WIO marine eco-region process. Rights and permissions Text is from a UNESCO World Heritage report: Assessing Marine World Heritage from an Ecosystem Perspective: The Western Indian Ocean, by David Obura, Julie Church, Catherine Gabrié.