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... This expedition sampled deep-water echinoids (Mortensen, 1939), gorgonians (Cannon, 1940), bivalves (Knudsen, 1967) and fishes (Norman, 1939) amongst others. The Galathea II expedition (1950-1952 collected samples between Sri Lanka and the Kenyan coast, as well as from Mozambique to South Africa (Demopoulos et al., 2003) but did not sample Tanzanian waters. Galathea II noted Table 1. ...
The United Republic of Tanzania has jurisdiction over a large marine area (223,000 km²) of which over 92% is deeper than 200 m. These deep areas extend from, in most cases <10 km from shore, have connections to shallow and coastal marine habitats through oceanographic processes, and support important living and non-living resources, which are becoming increasingly exploited to support a valuable blue economy. Recognising the need for sustainable development, implementation of conservation and management measures in Tanzania's offshore waters has begun, with the development of coastal protected areas and marine spatial plans (e.g. the Coastal and Marine Spatial Plan for Zanzibar). As yet, the deeper areas of Tanzania have not been considered in marine spatial planning. Here we present a synthesis of available data on the habitats and biological communities of deep-water Tanzania, including new data collected in collaboration with the deep-water oil and gas industry, to provide an indication of regional-scale patterns and areas of potential importance. We also discuss the value and multiple uses of the deep ocean areas to Tanzania, and assess the ecological effects of impacts in these environments. This information is valuable to the Tanzanian government to help inform development of management measures to continue to make sustainable use of valuable deep-water resources. To facilitate uptake, we provide a series of recommendations on considering the Tanzanian deep ocean areas in marine spatial planning to boost future management of the important and sensitive offshore domain.
... As mentioned by Demopoulos et al. (2003), the seamounts of the Indian Ocean are among the least explored. As seen in Fig. 1a, the majority of seamounts are located in the western part of the basin with the South West Indian Ridge (SWIR) being particularly conspicuous. ...
Compared with other ocean basins, little is known scientifically about the seamounts in the Indian Ocean. Nonetheless, fishers have plundered these fragile ecosystems for decades, and now mining is becoming a reality. We introduce a multidisciplinary project referred to as MADRidge that recently focused on three shallow seamounts in the South West Indian Ocean between 19°S and 34°S. The larger Walters Shoal (summit at 18 m) discovered in 1963 occupies the southern part of the Madagascar Ridge and has long received attention from the fishing industry, and only recently by scientists. In contrast, nothing is known of the northern region of the ridge, which is characterised by a prominent, steep-sided seamount that has a flat circular summit at 240 m and width of ∼20 km. This seamount is some 200 km south of Madagascan and unnamed; it is referred to here as the MAD-Ridge seamount. MAD-Ridge is the shallowest of a constellation of five deeper (>1200 m) seamounts on that part of the ridge, all within the EEZ of Madagascar. It lies in a highly dynamic region at the end of the East Madagascar Current, where mesoscale eddies are produced continuously, typically as dipoles. The Madagascar Ridge appears to be an area of great productivity, as suggested by the foraging behaviour of some tropical seabirds during chick-rearing and a longline fishery that operates there. The third seamount, La Pérouse, is located between Réunion Island and Madagascar. With a summit 60 m below the sea surface, La Pérouse is distinct from MAD-Ridge and Walters Shoal; it is a solitary pinnacle surrounded by deep abyssal plains and positioned in an oligotrophic region with low mesoscale activities. The overall aim of the MADRidge project was to examine the flow structures induced by the abrupt topographies, and to evaluate whether biological responses could be detected that better explain the observed increased in fish and top predator biomasses. The MADRidge project comprised a multidisciplinary team of senior and early career scientists, along with postgraduate students from France, South Africa, Mauritius and Madagascar. The investigation was based around three cruises using the French vessels RV Antea (35 m) and RV Marion Dufresne (120 m) in September 2016 (La Pérouse),November/December 2016 (MAD-Ridge) and May 2017 (Walters Shoal). This manuscript presents the rationale for the MADRidge project, the background, a description of the research approach including the cruises, and a synopsis of the results gathered in the papers published in this Special Issue.
... The subsea topography of the South West Indian Ocean (SWIO) is rugged, formed of many banks, ridges (Mascarene Plateau, Mozambique Plateau, Madagascar Ridge, South West Indian Ridge, among others) and isolated seamounts rising from plateaus or from the deep abyssal plains (Tomczak and Godfrey, 1994;Demopoulos et al., 2003;Ingole and Koslow, 2005). The summits of these many seamounts peak at various depths, ranging from >2000 m to just a few metres below the sea surface. ...
The La Pérouse seamount (60 m depth) has so far been poorly studied despite it being a short distance (160 km) from Réunion Island. As part of the MADRidge project, a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology. Current measurements, temperature and chlorophyll-a profiles, and mesozooplankton and micronekton samples were collected between the summit and 35 km away. Micronekton data were supplemented with stomach content of pelagic top predators as well as fisheries statistics from the domestic longline fleet operating from Réunion. Vertical current profiles revealed distinct patterns between the offshore and seamount-flanked stations, giving evidence of topographical induced flow instabilities, notably on its leeward side (west) relative to the east flank. Distinct patterns in temperature and chlorophyll-a vertical profiles suggest the formation of convergent and divergent circulation cells as a result of the irregular and crescent-like summit topography. Spatial differences in zooplankton abundance were detected with higher biovolumes on the leeward flank. The overall acoustic backscatter for micronekton over the summit was weaker than offshore, but highly concentrated in the upper layer. Albacore tuna and swordfish dominate the longline catch west of Réunion, seemingly in association with a deep (900 m) topographic feature. Yet the largest catch is not directly associated with La Pérouse which would be too shallow for top predators to aggregate around in the long term. Enhanced levels of phytoplankton or zooplankton enrichment at La Pérouse were not demonstrated in this study, nor was there notable diversity of micronekton species. This might explain the relatively limited importance of this seamount to the tuna fisheries in this region.
... There is seasonality as a consequence of the reversing monsoonal wind system, which is strongly active to the north of 20 � S (Schott et al., 2009). Furthermore, a complex dynamic pattern emerges due to the northern termination of the Indian Ocean in the subtropics, which is a consequence of the presence of the Asian continental land-mass (Demopoulos et al., 2003;Tomczack and Godfrey, 1994). ...
Published information from the Western Indian Ocean (WIO) and new data from the South West Indian Ocean Ridge, are consolidated and combined to generate an updated biogeography of calanoid copepods. The WIO was divided into 75 5° grid squares, and a similarity matrix between grids was generated on the basis of presence:absence data for more than 172 species. Distinct assemblages are identified that correspond to the 1) coastal waters of Somalia, Kenya, Tanzania and northern Mozambique, 2) coastal and offshore waters of southern Mozambique and NE South Africa, 3) coastal and offshore waters of South Africa, 4) waters of the central WIO. The patterns observed are in agreement with surface circulation patterns in the region, and the influence of gyres and eddies on the distribution of some taxa is hypothesised. The coarse and qualitative nature of the data prevents us from identifying transitional faunas, as well as those associated with mesoscale features.
... In spite of a series of intensive efforts in the 1960s (Zeitzschel, 1973), the basin-scale ecology and the fauna inhabiting seamounts of the Indian Ocean and the SWIR are poorly known, in part because of the ocean's remoteness to nations with large-scale historical oceanographic research programmes. However, there is now an urgent need to explore these ecosystems to complete the picture of the biodiversity and productivity associated with the Indian Ocean (Demopoulos et al., 2003). ...
... Malgré des efforts déployés dans les années 1960 (Zeitzschel, 1973), l'écologie à l'échelle du bassin et la faune peuplant les monts sous-marins de l'océan Indien et de la ride SWIR sont méconnues, en partie du fait de l'éloignement de l'océan pour les nations disposant de programmes de recherche océanographiques notoires et à grande échelle. Cependant, il est urgent maintenant d'explorer ces écosystèmes pour disposer d'une vision complète de la biodiversité et de la productivité associées à l'océan Indien (Demopoulos et al., 2003). ...
... In spite of a series of intensive efforts in the 1960s (Zeitzschel, 1973), the basin-scale ecology and the fauna inhabiting seamounts of the Indian Ocean and the SWIR are poorly known, in part because of the ocean's remoteness to nations with large-scale historical oceanographic research programmes. However, there is now an urgent need to explore these ecosystems to complete the picture of the biodiversity and productivity associated with the Indian Ocean (Demopoulos et al., 2003). ...
... Malgré des efforts déployés dans les années 1960 (Zeitzschel, 1973), l'écologie à l'échelle du bassin et la faune peuplant les monts sous-marins de l'océan Indien et de la ride SWIR sont méconnues, en partie du fait de l'éloignement de l'océan pour les nations disposant de programmes de recherche océanographiques notoires et à grande échelle. Cependant, il est urgent maintenant d'explorer ces écosystèmes pour disposer d'une vision complète de la biodiversité et de la productivité associées à l'océan Indien (Demopoulos et al., 2003). ...
... The OMZ of sea facilitate large-scale degradation of organic matter sinking from highly productive surface water and thus provides abundant food supply for the dwelling organisms 7 . E. armstrongi is a highly mobile crab and possibly plays its role in the ecosystem by resuspending fine organic material from the sea surface and helping in the process of decomposition by burying the deposited organic matter 8 . The long legs and rostrum could be attributed to the above-mentioned functionality of the crab. ...
A single specimen of the male crab (3.0 cm carapace length and 3.8 g body weight) was collected from the incidental catch sample of a multiday trawler operating at a depth range of 107-132 m off Gujarat coast of India. The detailed morphometric measurements and diagnostic features with updated systematics have been presented in this paper. The crab has well devolved branchial region and thrive in the oxygen minimum zone of the sea. © 2017, National Institute of Science Communication and Information Resources (NISCAIR). All rights reserved.
... The Arabian Sea has an intense Oxygen Minimum Zone (OMZ) with oxygen concentrations between 0.1 and 0.5 mL/L (Demopoulos et al., 2003) at intermediate depths that range from 200 to 1200 m (Wyrtki, 1973;Hermelin and Shimmield, 1990). There is a strong influence of the Indian monsoon system on the sedimentation processes, surface water productivity and intensity of the Arabian Sea OMZ. ...
... At present, the study area is located in the core of the OMZ in the northwestern Arabian Sea at a water depth of~800 m where oxygen concentrations are b 0.5 mL/L (Demopoulos et al., 2003). The combination of high surface productivity driven by upwelling or lateral advection of nutrient rich water, and inflow of oxygen poor waters at intermediate depths result into intensification of the OMZ. ...
A high resolution 14,000 year old record of benthic foraminifera from ODP Hole 723A was produced to understand changing intensity of the NW Arabian Sea Oxygen Minimum Zone (OMZ) and its links with intermediate water circulation and Indian Monsoon Intensity. During the latest Pleistocene, the OMZ was very weak marked by the abundance of oxic species. From early to mid Holocene period (up to 6500 years BP), intense SW monsoon-related high surface productivity led to the development of an OMZ in the Arabian Sea; however, presence of oxic and suboxic species indicate that OMZ intensification was minimized by cyclic incursions of oxygen-rich intermediate waters from the South. The middle Holocene was a transitional period to intense OMZ conditions. The intensification of the OMZ could be due to replacement of oxygen-rich southern source Sub-Antarctic Mode and Antarctic Intermediate Waters (SAMW-AAIW), with oxygen poor Red Sea Water (RSW)from the north during the middle Holocene. As the intensity of the summer monsoon weakened during the late Holocene (~ 4200 years BP onwards) the Arabian Sea OMZ intensified, suggesting total cut off from the oxygenated SAMW-AAIW. Spectral analysis of Information Function (H), benthic foraminifer Bolivina spp. and oxic species of benthic foraminifera indicate that the intensity of the OMZ and deep water conditions respond closely to solar cycles.
... The region around the Southwest Indian Ocean Ridge is relatively poorly known; that of the Madagascar Ridge, including Walter's Shoals, was investigated by RV Vityaz in December 1988 using six different trawls (Nesis, 1994). In general, all deep-sea ecosystems of the Indian Ocean apart from the Arabian Sea are also largely unknown, with seamounts being a particular gap in knowledge within this region (Banse, 1994;Demopoulos et al., 2003;Ingole and Koslow, 2005). ...
... The region around the Southwest Indian Ocean Ridge is relatively poorly known; that of the Madagascar Ridge, including Walter's Shoals, was investigated by RV Vityaz in December 1988 using six different trawls (Nesis, 1994). In general, all deep-sea ecosystems of the Indian Ocean apart from the Arabian Sea are also largely unknown, with seamounts being a particular gap in knowledge within this region (Banse, 1994;Demopoulos et al., 2003;Ingole and Koslow, 2005). ...
A total of 68 cephalopod species belonging to 26 families (10–11% of the total known cephalopod diversity) were collected onboard R/V Fridtjof Nansen during a research survey on Southwest Indian Ocean Ridge in November–December 2009. This relatively small area extends from the Tropical front to the Subantarctic front with four distinctive cephalopod faunas and represents one of the most outstanding hotspots of cephalopod diversity reported to date. However, most of the species caught there were characterised by circumglobal distribution in the Southern Hemisphere, and no endemic species were unambiguously found, although a number of taxa could not be confidently attributed to known species. Most of the studied area was dominated by squid species reproducing in epipelagic layers (mostly Enoploteuthidae and Pyroteuthidae). Species reproducing in meso-bathypelagial whose juveniles ascend to surface water (Cranchiidae, Histioteuthidae, etc.) became gradually more and more important southward from the Tropical Zone to the Southern Peripheral Ecotone. In the latter region they were joined by near-bottom dwellers of the order Sepiolida. The epipelagic strategy of reproduction disappears completely at the Subpolar Front, where epipelagic waters were inhabited by young members of the Cranchiidae and Gonatidae hatched in deep-seas. This study demonstrated the importance of conservation and management of this high-seas area, with its unique biodiversity and ecological resources, in line with recommendations by the IUCN Seamount project and Global Ocean Biodiversity Initiative.
