TheBaltic Sea. Approximately 100,000 km² of the Baltic's seafloor (a quarter of its total area) is a variable dead zone. The more saline (and therefore denser) water remains on the bottom, isolating it from surface waters and the atmosphere. This leads to decreased oxygen concentrations within the zone. It is mainly bacteria that grow in it, digesting organic material and releasing hydrogen sulfide. Because of this large anaerobic zone, the seafloor ecology differs from that of the neighbouring Atlantic.

The low salinity of the Baltic sea has led to the evolution of many slightly divergent species, such as the Baltic Seaherring, which is a smaller variant of theAtlantic herring. Thebenthic fauna consists mainly ofMonoporeia affinis, which is originally a freshwater species. The lack oftides has affected the marine species as compared with the Atlantic.

TheBlack Sea.

TheCaribbean Sea is home to about 29% of the world'scoral reefs. Currently, unusually warm Caribbean waters are endangering the Caribbean coral reefs. Coral reefs support some of the most diverse habitats in the world, but are fragile ecosystems. When tropical waters exceed 85 degrees Fahrenheit for an extended period of time, microscopic plants calledzooxanthellae die off. These plant provide food for the coral and give them their color. The resultant bleaching of the coral reefs kills them, and ruins the ecosystem. Up to 42% of the coral colonies have gone completely white, while 95% have undergone at least some bleaching.^[12] The habitats supported by the reefs are critical to such tourist activities such asfishing anddiving, and provide an annual economic value to Caribbean nations of $3.1-$4.6 billion. Continued destruction of the reefs could severely damage the region's economy.^[13] AProtocol of the Convention for the Protection and Development of the Marine Environment of the Wider Caribbean Region came in effect in 1986 to protect the various endangered marine life of the Caribbean through forbidding human activities that would advance the continued destruction of such marine life in various areas. Currently this protocol has beenratified by 15 countries.^[14]

The area also generates a large fishing industry for the surrounding countries, accounting for half a million metric tons of fish a year.^[15]

TheGulf of Mexico. The outer margins of the wide continental shelves of Yucatán and Florida receive cooler,nutrient-enriched waters from the deep by a process known asupwelling, which stimulates plankton growth in theeuphotic zone. This attracts fish, shrimp, and squid.^[16] River drainage and atmospheric fallout from industrial coastal cities also provide nutrients to the coastal zone.

TheGulf Stream, a warm Atlantic Ocean current and one of the strongestocean currents known, originates in the gulf, as a continuation of theCaribbean Current-Yucatán Current-Loop Current system. Other circulation features include the anticyclonicgyres which are shed by theLoop Current and travel westward where they eventually dissipate, and a permanent cyclonicgyre in theBay of Campeche. TheBay of Campeche in Mexico constitutes a major arm of the Gulf of Mexico. Additionally, the gulf's shoreline is fringed by numerous bays and smaller inlets. A number of rivers empty into the gulf, most notably theMississippi River in the northern gulf, and theGrijalva andUsumacinta Rivers in the southern gulf. The land that forms the gulf's coast, including many long, narrow barrier islands, is almost uniformly low-lying and is characterized by marshes and swamps as well as stretches of sandy beach.

The Gulf of Mexico is an excellent example of apassive margin. Thecontinental shelf is quite wide at most points along the coast, most notably at the Florida andYucatán Peninsulas. An important commercial activity is fishing; major catches includered snapper,amberjack,tilefish,swordfish, and variousgrouper, as well asshrimp andcrabs.Oysters are also harvested on a large scale from many of the bays and sounds.

TheLabrador Sea

TheMediterranean Sea. Being nearly landlocked affects the Mediterranean Sea's properties; for instance,tides are very limited as a result of the narrow connection with the AtlanticOcean.Evaporation greatly exceedsprecipitation and river runoff in the Mediterranean, a fact that is central to the water circulation within the basin.^[17] Evaporation is especially high in its eastern half, causing the water level to decrease andsalinity to increase eastward.^[18] This pressure gradient pushes relatively cool, low-salinity water from the Atlantic across the basin; it warms and becomes saltier as it travels east, then sinks in the region of theLevant and circulates westward, to spill over the Strait of Gibraltar.^[19] Thus, seawater flow is eastward in the Strait's surface waters, and westward below; once in the Atlantic, this chemically-distinct "Mediterranean Intermediate Water" can persist thousands of kilometers away from its source.^[20]

The Mediterranean Sea has an average depth of 1,500 metres (4,920 ft) and the deepest recorded point is 5,267 meters (about 3.27 miles). The coastline extends for 46,000 kilometres (29,000 mi).

Invasive species originating from the Red Sea andintroduced into the Mediterranean by the construction of theSuez Canal have become a major component of the Mediterranean ecosystem and have serious impacts on the Mediterranean ecology, endangering many local andendemic Mediterranean species. Up to this day, about 300 species native to the Red Sea have already been identified in the Mediterranean Sea, and there are probably others yet unidentified. In recent years, the Egyptian government's announcement of its intentions to deepen and widen the canal have raised concerns frommarine biologists, fearing that such an act will only worsen the invasion of Red Sea species into the Mediterranean, facilitating the crossing of the canal for yet additional species.^[21]

Pollution in this region has been extremely high in recent years. TheUnited Nations Environment Programme has estimated that 650 million tons ofsewage, 129,000 tons ofmineral oil, 60,000 tons of mercury, 3,800 tons of lead and 36,000 tons of phosphates are dumped into the Mediterranean each year.^[22] TheBarcelona Convention aims to 'reduce pollution in the Mediterranean Sea and protect and improve the marine environment in the area, thereby contributing to its sustainable development.'^[23]

Many marine species have been almost wiped out because of the sea's pollution. TheMediterranean monk seal is considered to be among the world's mostendangeredmarine mammals.^[24]

The Mediterranean is also plagued bymarine debris. A 1994 study of theseabed using trawl nets around the coasts of Spain, France and Italy reported a particularly high mean concentration of debris; an average of 1,935 items per square kilometre. Plastic debris accounted for 76%, of which 94% was plastic bags.^[25]

TheNorth Sea. A large part of the Europeandrainage basin empties into the North Sea including water from theBaltic Sea. Fishing in the North Sea is concentrated in the southern part of the coastal waters. The main method of fishing istrawling. Annual catches grew each year until the 1980s, when a high point of more than 3 million metric tons (3.3 million S/T) was reached. Since then, the numbers have fallen back to around 2.3 million tons (2.5 million S/T) annually with considerable differences between years. Besides the fish caught, it is estimated that 150,000 metric tons (165,000 S/T) of unmarketableby-catch are caught and around 85,000 metric tons (94,000 S/T) of dead and injuredinvertebrates.^[26]

TheNorwegian Sea. In the Norwegian Sea and Greenland Sea, surface water descends two to three kilometres down to the bottom of the ocean, forming cold, oxygen-rich groundwater. As a result, there is a warm surfacecurrent and a cold depth current running along the west coast of Norway. The so-calledEast Iceland Current transports cold water south from the Norwegian Sea towards Iceland and then east, along theArctic Circle. In theNorwegian Current, a branch of theGulf Stream carries warm water masses northward and contributes to the mild and moist climate in Norway. The Norwegian Sea is the source of much of theNorth Atlantic Deep Water. The region remains ice-free due to the warm andsaline Norwegian Atlantic Current. It provides richfishing grounds, with catches mostly consisting of cod, herrings, sardines and anchovies. Nowadays, shifts and fluctuations in these currents are closely monitored, as they are thought to be indicators for an ongoingclimate change.

TheScotia Sea. Habitually stormy and cold, about half of the sea falls above thecontinental shelf.

TheAndaman Sea is a body of water to the southeast of theBay of Bengal, south ofMyanmar, west ofThailand and east of theAndaman Islands; it is part of theIndian Ocean. It is roughly 1,200 kilometres (750 mi) long (north-south) and 650 kilometres (400 mi) wide (east-west), with an area of 797,700 square kilometres (308,000 sq mi). Its average depth is 870 meters (2,854 ft), and the maximum depth is 3,777 meters (12,392 ft).

TheArabian Sea is a region of theIndian Ocean bounded on the east byIndia, on the north byPakistan andIran, on the west byArabian Peninsula, on the south, approximately, by a line betweenCape Guardafui, the north-east point ofSomalia,Socotra andKanyakumari (Cape Comorin) inIndia.

The maximum width of the Arabian Sea is approximately 2,400 km (1,490 mi), and its maximum depth is 4,652 metres (15,262 ft),

TheBay of Bengal occupies an area of 2,172,000 km². A number of large rivers –Ganges,Brahmaputra,Ayeyarwady,Godavari,Mahanadi,Krishna andKaveri – flow into the Bay of Bengal. The islands in the bay are very numerous, including the Andaman,Nicobar andMergui groups.

The Bay of Bengal is full of biological diversity, diverging amongstcoral reefs,estuaries, fish spawning and nursery areas, andmangroves. The Bay of Bengal is one of the World's 64largest marineecosystems.

Kerilia jerdonii is a sea snake of the Bay of Bengal. Glory of Bengal cone (Conus bengalensis) is just one of the seashells which can be photographed along beaches of the Bay of Bengal.^[27]

Anendangered species, theolive ridleysea turtle can survive because of the nesting grounds made available at the Gahirmatha Marine Wildlife Sanctuary,Gahirmatha Beach,Orissa, India.

Bryde's whale which can be seen in the Bay of Bengal is the 10thheaviest animal of the world, weighing in at 22,000 kg (48,000 lb).

Marlin,barracuda,skipjack tuna (Katsuwonus pelamis),yellowfin tuna,Indo-Pacific hump-backed dolphin (Sousa chinensis), andBryde's whale (Balaenoptera edeni) are a few of the marine animals. Bay of Bengal hogfish (Bodianus neilli) is a type ofwrasse which lives in turbid lagoon reefs or shallow coastal reefs. Schools ofdolphins can be seen, whether they are thebottle nose (Tursiops truncatus),pantropical spotted (Stenella attenuata) or thespinner (Stenella longirostris) .Tuna anddolphins are usually residing in the same waters. In shallower and warmer coastal waters theIrrawaddy dolphin (Orcaella brevirostris) can be found.^[28][29]

TheGreat Australian Bight is a largebight, or open bay located off the central and western portions of the southern coastline of mainlandAustralia.

The coast line of the Great Australian Bight is characterised by stunning cliff faces (up to 60 m high), surfing beaches and rock platforms, ideal for whale-watching. The waters of the Great Australian Bight, despite being relatively shallow, are not fertile. While mostcontinental shelves are rich in sea life and make popularfishing areas, the barrendeserts north of the bight have very little rainfall, and what there is mostly flows inland, to dissipate underground or insalt lakes. In consequence, the Great Australian Bight receives very little of the runoff that fertilises most continental shelves and is essentially a marine desert. It is probably best noted for the large number ofsharks that frequent its coastal waters, as well as the increasing numbers ofsouthern right whales that migrate within the region.

Economically, the Bight has been exploited over many years as part of the fishing, whaling and shellfish industries.Bluefin tuna have been a favoured target of fishing in the Bight.

TheGulf of Aden. The temperature of the gulf varies between 15 °C (59 °F) and 28 °C (82 °F), depending on the season and the appearance ofmonsoons. The salinity of the Gulf at 10 metres (33 ft) depth varies from 35.3‰ along the eastern Somali coast to as high as 37.3 ‰ in the Gulf's center,^[30] while the oxygen content in the Gulf of Aden at the same depth is typically between 4.0 and 5.0 mL/L.^[30]

A geologically young body of water, the Gulf of Aden has a uniquebiodiversity that contains many varieties offish,coral,seabirds, andinvertebrates. This rich ecological diversity has benefitted from the relative lack of pollution during the history of human habitation around the Gulf, but environmental groups fear that the lack of a coordinated effort to control pollution may jeopardize the Gulf'secosphere.^[31]

The Gulf of Aden is an area known for acts ofpiracy,^[32]|-

TheGulf of Oman is agulf that connects theArabian Sea with theStrait of Hormuz which then runs to thePersian Gulf.

TheMozambique Channel is a portion of theIndian Ocean between the island ofMadagascar and southeastAfrica, namelyMozambique. The channel is approximately 460 kilometers across at its narrowest point betweenAngoche, Mozambique, andTambohorano, Madagascar. It reaches a depth of 3,292 meters about 230 kilometers off the coast of Mozambique. A warm current flows in a southward direction in the channel, leading into theAgulhas Current off the east coast ofSouth Africa. It is 1600 kilometers long and its width varies from 400 to 950 kilometers.

ThePersian Gulf is an extension of theIndian Ocean located betweenIran and theArabian Peninsula. The natural environment of the Persian Gulf is very rich with good fishing grounds, extensivecoral reefs, and abundantpearl oysters, but its ecology has become increasingly under pressure from the heavy industrialisation and in particular the repeated majorpetroleum spillages associated with recent wars fought in the region.

TheRed Sea occupies a part of theGreat Rift Valley, and has a surface area of 438,000 km². It is 2250 km long and, at its widest point, 355 km wide. It has a maximum depth of 2211 m in the central median trench and an average depth of 490 m (1,608 feet ), but there are also extensive shallow shelves, noted for their marine life andcorals. The sea is the habitat of over 1,000invertebrate species and 200 soft and hard corals and isthe world's most northern tropical sea.

The Red Sea is a rich and diverseecosystem. More than1100 species of fish^[33] have been recorded in the Red Sea, and around 10% of these are found nowhere else.^[34] This also includes around 75 species ofdeepwater fish.^[33] The rich diversity is in part due to the 2,000 km (1,240 mi) ofcoral reef extending along itscoastline; thesefringing reefs are 5000–7000 years old and are largely formed of stonyacropora andporites corals. The reefs form platforms and sometimeslagoons along the coast and occasional other features such as cylinders (such as theblue hole atDahab). These coastal reefs are also visited bypelagic species of red sea fish, including some of the44 species of shark.

Approximately 40% of the Red Sea is quite shallow (under 100 m/330 ft), and about 25% is under 50 m (164 ft) deep. About 15% of the Red Sea is over 1,000 m (3,300 ft) depth that forms the deep axial trough. Shelf breaks are marked by coral reefsContinental slope has an irregular profile (series of steps down to ~500 m/1,640 ft)