Oceans occupy almost 72% of the Earth's surface, which play an important role in the climatic conditions of the adjacent land regions. Ocean is playing an important role by generating oxygen, absorbing carbon dioxide, providing food and creates new jobs options. Ocean has diversification to add new resources for energy, drugs, chemicals, food and minerals for human. It is estimated that three-quarters of the world's mega-cities are by the sea and currently 80 percent of people live within 62 miles of the coast, with about 40 percent living within 37 miles of a coastline and two-thirds of all the population lives within 100 kilometers of a coastline. Thus, the economic activities in the ocean are mainly concentrated in the coast and based on the rapid expansions of ocean industries like maritime and coastal tourism, offshore oil and gas, ship building and maritime equipment transportations. It is estimated that ocean-based businesses contribute more than 500 billion USD to the world's economy (Ocean, 2017). According to the OECD's Ocean Economy Database (OECD, 2016), the economic value of the ocean outputs in 2010 was 1.5 trillion USD, or in other words, approximately 2.5% of world's gross economic value.

Similar to the other coast of the world, Bangladesh coast also tells the story of development. This area is located at the north-eastern part of the Bay of Bengal. Following the international verdicts on the disputed maritime areas with the neighboring countries India and Myanmar, the permanent coverage of Bangladesh's maritime areas is estimated to about 119,000 sq km, with an extended continental shelf of about 37,000 sq km with a depth up to 50m depth (MoFA, 2016). The coastal and marine ecosystem of Bangladesh is divided into three zones i.e. south east zone, central zone and south west zone. The south-western coast of Bangladesh contains part of the world's largest area of mangrove swamps, the Sundarbans, that continues westward into India. The central coast contains the estuaries of the combined drainages of the Ganges-Padma, Maghna and Brahmaputra Rivers. The southeastern-most coastline contains muddy flats and sandy beaches.

The maritime ecosystem of Bangladesh is rich in biodiversity, they play an important role in maintaining the life cycles of economically important resources such as shrimp, crabs and fish. Coastal and marine resources of Bangladesh are generally categorized into living, non-living and renewable resources. In addition, trade and commerce related to sea and coast, and protection from the natural disasters also offer economic returns. Marine living resources in the maritime zone of Bangladesh include fisheries, mangrove forests, coral ecosystems, plankton, seagrass and seaweeds. About 475 bony fish species belonging to 133 families, 50 cartilaginous fishes, 50 crab species (11 purely marine and 3 commercially important species), 7 turtles species of 6 genera (of which 3 are commercially important), 36 shrimp and 5 lobster species, 3 star fish and 11 dolphin species have been reported from the coastal and marine water of Bangladesh. A total 301 species of marine mollusks (i.e. bivalves, snails and slugs, cuttlefish, squids and octopuses) are reported from the marine water of Bangladesh. Among the mollusks, oyster has great economic value and 3 types of oysters (i.e. edible, pearl and windowpane) occur in the coastal waters of the Bangladesh. The most important species of edible oyster is Crassostrea sp. About 7 species of squids and 2 species of cuttlefish are reported from the Bay of Bengal. Total marine fish production accounted 0.6 million MT during 2013-2014 (Fig. 2, 17% of the total fish production) (DoF, 2016). River and estuarine ecosystems cover an area of 850,000 ha and contribute about 175,000 MT of fish (FRSS, 2016). Over 0.5 million people are directly and indirectly engaged with marine fisheries sector for their livelihood options (DoF, 2013). Currently, 225 industrial trawlers of which 24 are mid-water and around 68 thousand mechanized and non-mechanized boats are in operation in the marine waters of Bangladesh (DoF, 2013).

The Bangladesh coast supports comparatively higher mangrove biomass than any other coastal regions of the Bay of Bengal (Fig. 2). The coastal region of Bangladesh supports about 530,000 ha of mangrove forests of which 99,000 ha are planted mangrove forests (FAO, 2015). The major continuous natural block of mangrove forest, known as 'the Sunderban', lies in the south-west coastal zone of Bangladesh and covers an area of about 6, 00,000 ha (Department of Forest, 2017). Planted mangrove forests are located along the central and south-east coast of Bangladesh. The entire mangrove forest ecosystem supports 345 plant species of 245 genera which are economically important. In addition, 53 species of pelagic fish belonging to 27 families, 124 species under 49 families of demersal fish, 24 shrimp species, 58 wildlife and 270 bird species are also reported from the mangrove ecosystem of Bangladesh. Data suggest that in recent years revenues from this forest are comparatively less than the revenues from the 1980s and the 1990s. On average total annual mean revenue from this forest is about 400000 USD where timber, fisheries, honey, wax and tourism contribute 3500000, 290000, 10000, 3700 and 267000 USD, respectively.

Saint Martin's Island from the south-east coastal zone with a total area of about 7.5 km2 is the only coral bearing island of Bangladesh. It is recorded that about 66 coral species are available in this island. In addition this Saint Martin's Island represent 20-22 species of seaweed. The river and estuarine ecosystems of Bangladesh cover an area of 850,000 ha. Saltmarshes or tidal marshes are distributed over an area of more than 110,000 ha along the low-energy coasts and estuaries of Bangladesh. The Encyclopedia of Flora and Fauna of Bangladesh reported a total of 156 algal species and 50 of them are brown algae, 82 species are red algae, and 26 species are green algae. Around 34 species of phytoplankton are recorded along the coastal regions of Bangladesh. Due to the presence of diverse phytoplankton groups, the coastal waters of Bangladesh are highly productive.

Non-living resources of the Bay of Bengal include crude oil, gas and sea salt. Of 26 gas fields discovered in the country so far, only 2 are located in the offshore areas. The Kutubdia gas field is located about 92 km south-west of Chittagong Port and Sangu gas field is located about 50 km south-west of Chittagong city and stands at a depth of 10 m of water in the Bay of Bengal. About 6000 ha area is cultivated for sea salt production in the coastal area of Bangladesh. This sector creates over 5 million employments (and contributes about 35.5 million to 41.2 million USD each year to the national economy.

Bangladesh has a distinctive attraction with many popular coastal tourist destinations, including one of the world's longest sea beaches (i.e. Cox's Bazar), the largest compact mangrove forest of the world (the Sundarbans) as well as different national parks and islands. The tourism sector in Bangladesh is now employing over 1 million people and this sector generates a total value of 8.4 million USD. Apart from these, commercial use of the marine water of Bangladesh includes international ports development (i.e. Chittagong and Mongla sea port), as well as the newly established Payra seaport. Local transportation, small and large scale industries in the coastal cities, shipbuilding and shipbreaking industries also provide important for economic returns for Bangladesh. At present 10,000 inland and coastal ships, and 36 sea-going ships are plying all over the country. The Mercantile Marine Department (MMD) of Bangladesh earned 1.2 million USD in the fiscal year of 2012-13.

While coastal area of Bangladesh has a huge economic potentiality, climate change extreme events and their impact on human are often considered as the regular social fabric here.

Disaster-related records of Bangladesh show that the number of cyclones tripled over the last 50 years. Climate change extreme events include warming trend, cyclone, sea level rise, droughts, erosion, tidal surge, saline water intrusion, flood, change in precipitation trend and ocean acidification. Bangladesh is ranked among the most affected countries in the South Asia in the scenario of 2 °C rise in the world's average temperatures in the next decades. Rising sea levels, more extreme heat and more intense cyclones will threaten the food production, livelihoods and infrastructure as well as will slow down the poverty reduction.

International Disaster Database showed that the frequency of storm, flood and extreme temperature are higher than any other climate related extreme events in Bangladesh from 1990 to 2014. Maximum mortality of human occurred from cyclonic storm. Maximum economic loss occurred due to flood and cyclonic storm and flood contributed most in average annual hazard loss (AAHL). Records of the last 200 years show that at least 70 major cyclones have hit the coastal belt region of our country. At least 12 major tropical cyclones hit the country since 1965, leaving 479,490 people dead. The devastating cyclone of April 1991 caused a damage of around 1.5 billion USD. Cyclone Sidr in 2007 caused a damage of 1355 million USD. Cyclone Aila in 2009 losses in Bangladesh estimated at 269 million USD. In Bangladesh, 40% of productive land is projected to be lost in the southern region of In addition, the impacts of a slowly-rising sea-level are currently much less than those generated by rapidly increasing population pressure on Bangladesh's available land and water resources and by exposure to existing environmental hazards, and the latter problems need priority attention (Brammer, 2014). About 20 million people in the coastal areas of Bangladesh are already affected by saline water intrusion. This created the scarcity of pure drinking water supply (Rasheed et al., 2016). Approximately 1 million hectares of land in southern in coastal areas of Bangladesh are at risk from saline water intrusion (Baten, Seal, and Lisa, 2015). Saline water intrusion (Fig. 3) into the upstream region will lead to negative socio-economic impacts through disrupting agriculture, fisheries, forestry and navigation. The largest mangrove forest in the world, The Sundarbans, could face severe impacts in the coming years due to increasing salinity and rising sea level.

Rapid industrialization without having any proper waste treatment plant is responsible for dumping polluting materials in rivers, estuaries and coastal waters. This poses threats to aquatic life and the ecosystem. Ship breaking activities in Chittagong discharge a considerable amount of heavy metals, waste oil and other pollutants during dismantling operations. Oil spills from ships have drastic effect on biotic communities. Mangroves are highly susceptible to oil exposure; oiling may kill them within a few weeks to several months. Oil-impacted mangroves suffer from yellowed leaves, defoliation, and also lead to the death of the tree.

Though Bangladesh coast is rich in vast economic potentiality, the coast is under the risk of many vulnerabilities. However, through proper strategies, it is possible to develop the coast as a driver for the national economy of Bangladesh. For that, special focus is required on energy efficiency, marine and coastal biodiversity, ecosystem based adaptation, environmental resilience building in the coastal areas, ecosystem restoration, building economic resilience and policy formulation for climate change.

Subrata Sarker, Department of Oceanography, Shahjalal University of Science and Technology, Sylhet-3114, Bangladesh, Email: subratasrk-ocg@sust.edu