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OCEANS AND ATMOSPHERE Bioregions of the Indian Oceans Piers K Dunstan, Donna Hayes, Skipton N C Woolley, Lamona Bernawis, Scott D Foster, Emmanuel Chassot, Eugenie Khani, Rowana Walton , Laura Blamey, Uvicka Bristol, Sean Porter, Arul Ananthan Kanapatipillai, Natasha Karenyi, Babin Ingole, Widodo Pranowo, RA Sreepada, Mohamed Shimal, Natalie Bodin, Shihan Mohamed, Will White, Peter Last, Nic Bax, Mat Vanderklift, Rudy Kloser, Rudy Kloser, Leo Dutra and Brett Molony Bioregions of the Indian Oceans | i Citation Dunstan et al. 2020. Bioregions of the Indian Ocean. CSIRO, Australia. Copyright © Commonwealth Scientific and Industrial Research Organisation 20XX. To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. 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If you are having difficulties with accessing this document please contact [email protected]. ii | Bioregions of the Indian Oceans Contents Acknowledgments ........................................................................................................................... iv Bioregions of the Indian Ocean 6 1 Pelagic Bioregions ............................................................................................................... 7 1.1 Western Tropical Indian Ocean ............................................................................. 9 1.2 Northern Central Indian Ocean ........................................................................... 12 1.3 Mozambique Channel Region ............................................................................. 19 1.4 Indian Ocean Subtropical Gyre Region ................................................................ 22 1.5 Western Australian Coastal Region ..................................................................... 32 1.6 Indian Ocean Subtropical Convergence Region .................................................. 33 1.7 Indian Ocean Sub Antarctic Region ..................................................................... 34 2 Benthic Bioregions ............................................................................................................ 36 2.1 Southern Indian Ocean ........................................................................................ 38 2.2 Subpolar Indian Ocean ........................................................................................ 59 2.3 Eastern Indian Ocean ........................................................................................... 64 2.4 Western Indian Ocean ....................................................................................... 110 Appendix 1: Statistical Bioregions ............................................................................................... 193 Appendix 1: Qualitative Models ................................................................................................. 204 References 206 Bioregions of the Indian Oceans | iii Acknowledgments This work was carried out as part of the Global Ocean Biodiversity Initiative (GOBI), which is supported by the International Climate Initiative (IKI). The German Federal Ministry for the Environment, Nature Conservation Nuclear Safety (BMU) supports this initiative on the basis of a decision adopted by the German Bundestag. iv | Bioregions of the Indian Oceans Bioregions of the Indian Ocean This project has developed sub-regional bioregionalisations for the Indian Ocean. This combines approaches CSIRO developed in Australia, used in the Bay of Bengal (in collaboration with BOBLME) with similar approaches that have been used throughout the Indian and Pacific Oceans to derive a single combined bioregionalisation. The project has developed an expert derived bioregionalisation in the Indian and Pacific Oceans through expert workshops and novel statistical analysis of physical and biological data. The project draws on experience in CSIRO, GOBI partners, and other collaborators, using approaches currently being trialled in Australia and around the Antarctic margins, and has collaborated with regional and national stakeholders to ensure a consistent approach. This Appendix contains the descriptions of each marine region and each province with the region. Where sufficient information exists it includes a description, a qualitative ecosystem model of the system and the pressures on it and a scenario analysis that explores the way the ecosystem changes with different pressures. 6 | Bioregions of the Indian Oceans 1 Pelagic Bioregions The distribution of the Large Marine Areas – the highest level of classification for the Indian Ocean is shown below. Map 1 Indian Ocean Epipelagic Regions The distribution of the provinces within the Large Regions is shown below. More detailed descriptions of each of the provinces to given below. Bioregions of the Indian Oceans | 7 Map 2 Indian Ocean Epipelagic Provinces. 8 | Bioregions of the Indian Oceans 1.1 Western Tropical Indian Ocean One of the most biologically productive ecoregions of the world oceans characterized by a dominant seasonal cycle manifested as a unique western-boundary upwelling system supporting major pelagic fisheries. The region is bounded to the north by the northern limit of the North Equatorial Current (NEC) and the Southwest Monsoon Current (SMC), to the west by the east African coasts of Somalia and Kenya, in the south west by the Seychelles-Chagos thermocline ridge (SCTR), in the central and east South by the northern limit of South Equatorial Current (SEC) tipping towards 18°S of Australian Coast and to the east by the thermo-haline front of the western limit of the Indo-Pacific warm pool. Main characteristics - Strong seasonal upwelling of cold (22-26°C) and nutrient-rich waters (nitrate ~ 10-15 mmol), high Salinity (35.5-36 psu) linked to Arabian Sea high salinity water mass and high chlorophyll concentration (5-15 mg/mg3) - Enrichment of surface waters results in high primary and secondary production with increased abundance of calanoid copepods species and occurrence of high density of myctophyds in the mesopelagic region (200-1000 m deep) (Catul et al. 2011, Vipin et al. 2012) - Major fishing grounds for tropical tuna purse seine fisheries during July-Oct, medium-size pelagic fishes (e.g. horse-mackerel, small pelagics), and neritic tunas, and important grounds for skipjack fisheries in the Maldives. Bioregions of the Indian Oceans | 9 Figure 1: Qualitative model for the prominent ecosystem Western Tropical Indian Ocean and the associated pressures impact chart (PRESSURES :- PF – Pelagic Fisheries, Temp - Temperature ,; FUNCTIONAL GROUPS:- SQ – Squid, Pred – Predatory Fish, Tu – Turtle, WS – Whale Shark , BW – Blue Whale, ZP - Zooplankton, MSP – Medium Size Predator, UP – Upwelling, SB – Sea birds ) 10 | Bioregions of the Indian Oceans Figure 2: Ecosystem scenario responses to combinations of pressures. Red indicates a negative change and blue indicates a positive change. Labels are described above. Bioregions of the Indian Oceans | 11 1.2 Northern Central Indian Ocean The Central Eastern Tropical Indian Ocean region is influenced by the Indonesian Throughflow (ITF) and climate-mode Indian Ocean Dipole (IOD) described by strong inter-annual and seasonal signals that result in strong coastal upwellings and influence the productivity of the central and eastern equatorial Indian Ocean, supporting important pelagic fisheries. The region extends from southern Indian south to approximately 15 °Sand eastwards to the coasts of Indonesia and the core of the Indonesian Throughflow at approximately 115°E. Within this region are the Central Tropical and North eastern Indian Ocean Provinces. 1.2.1 Northern Central Indian Ocean Province Within the Central Tropical Indian Ocean there are two sub regions defined. The western portion is defined by the western limit of the Indo-Pacific warm pool to the west (68°-80°E) and the most western region of influence of IOD-ITF (from tip of Sumatra peninsula bounded by 90°E south around 12°S) to the east. This sub region is characterised by the Indo-Sri Lankan seasonal upwelling region during June-September (de Vos et al, 2014), high temperature (>30°C) all through the year except during upwelling season, and low salinity waters (34-34.4 psu) influenced by the low-salinity water from the Bay of Bengal. The region supports important fisheries along the coasts of Indian and Sri Lanka (e.g. mackerel; BOBLME 2015). 12 | Bioregions of the Indian Oceans Figure 3: Ecosystem components in the qualitative model are: Seabirds ( SB ), Micro Nekton ( MN ), Predatory Fish ( Pred ), Squid ( SQ ), Copepods ( COP ), Regenerated