north-east monsoon rainy season (December–February), when there are also strong westerly (onshore) winds and waves. Ecology Flora Along the northern littoral of East Timor, including the strait, the shallow coastal waters are dominated by a seagrass bed about in total area. Seagrass beds protect coral reefs from sedimentation and are feeding grounds for dugong (Dugong dugon), an endangered species. Seven genera of seagrass are known to exist off East Timor's coastline as a whole. East Timor's coastal waters have also traditionally hosted mangrove forests. Together with seagrasses and coral reefs, they are the primary breeding grounds for many species of fish and shellfish. However, the country's mangrove cover has very substantially declined since 1940, and in Ombai Strait is now confined to the coastline and hinterland between and the Bay of Dili. A survey of Tibar Bay carried out in 2016 found three mangrove species, namely Sonneratia alba, which was the dominant species, Avicennia marina and Rhizophora stylosa. The report of another survey, carried out in 2017, stated that the dominant species in the area was Sonneratia albia, and that there were some clusters of Rhizophora apiculata, Ceriops tagal, and Lumnitzera. The 2016 survey report estimated the total area of mangrove in the bay to be ; the 2017 survey report's estimate was . According to the latter report, tree density was relatively low, at around 100–400 trees per hectare, and the mangrove cluster was heavily degraded, due to direct and indirect human activities. The former activities included fish pond and salt pan development, mangrove cutting, and cattle grazing. The latter activities were sea level rise, and siltation due to erosion in the hills on the landward side of the mangroves. In parts of Ombai Strait, and especially close to the coast of Alor Island, elevated phytoplankton blooms or concentrations (and therefore availability of food for other species) have been observed, particularly during the dry south-east monsoon. The physical structure of the strait makes it likely that such concentrations are driven by fronts and vertical flows caused by some combination of tidal currents or topographic effects. A study published in 2002 noted persistent flow-induced upwelling and frontal features in the strait, together with subjective evidence of extremely strong tides. The study concluded that the upwelling and frontal features coincided with large phytoplankton blooms and significantly affected the concentration and distribution of chlorophyll in the Savu Sea. According to the study