The Gulf of Mannar (GoM), located between India and Sri Lanka, has astonishing faunal richness and diversity. Two oceanographic data sets supplemented with satellite remote sensing observations are discussed here to show the unique ecological setting in the GoM sustaining a rich and diverse fauna. We tested the hypothesis that a specific stretch of a large marine environment behaves differently from the rest of the region due to its peculiar geographical position. Primarily, unlike the adjacent Indian southwestern shelf in the Southeastern Arabian Sea, oxygen deficiency associated with coastal upwelling imparting physiological stress to marine fauna does not occur in the GoM. Secondly, the GoM along the Indian coastline receives an adequate amount of primary (plankton) food from the Arabian Sea and the Bay of Bengal through the advected water associated with the seasonally reversing surface currents. Thirdly, the GoM water has high transparency, aerated sandy seafloor conducive for the growth of diverse corals and much sensitive fauna. All these indicate that an astonishingly rich and diverse aquatic fauna in the GoM is a biological manifestation of a conducive geographical setting and propose that similar other environments worldwide, protected from oxygen deficiency, might also be functioning as a refuge for marine life.