High degrees in endemism usually denotes the relative isolation of a region for a prolonged period of time.  The degree of endemism is roughly proportional to the to the degree and duration of the isolation.

Isolating mechanisms act differently on different groups.  Something that blocks the spread of one group may have little or no effect on another.

Marine zoogeography is aimed at understanding the geographical history of marine animals.

Surface water temperature is extremely important in determining the distribution of epipelagic and shelf fauna.  Remember, organisms live near their upper limits of tolerance for temperature.  This explains why warm tropical waters are relatively free of organisms that occur in colder waters to the north and south.  Colder waters are populated by animals moving from warmer waters.  Once adapted to the colder water they cannot move back into warmer waters again because of greater physiological risk and because their niches are rapidly filled by other animals.

FAUNA OF TROPICAL AND SUBTROPICAL REGIONS

Conditions in the tropics are very stable.  Competition is intense and most niches are occupied.  Organisms may be highly specialized for their specific niche.  There is little chance for ecological succession, and diversity is extremely high with each species having a relatively low biomass.  The tropics displays the highest degree of endemism. Subtropical waters contain more eurythermal tropical fauna and a far smaller number of temperate fauna. Subtropical waters do contain some endemic fauna but fewer than the tropics.

The position of the continents and the vast deepwater stretch, the East Pacific Barrier separates tropical shallow marine fauna into three major regions:

 (1) Indo-West Pacific
 (2) Tropical Atlantic
 (3) Tropical East Pacific

THE INDO-WEST PACIFIC

This region is centered around the Malay Archipelago off Southeast Asia. It extends west to the eastern coast of tropical Africa, east to Hawaii and the Taumotu Archipelago, south to the northern coast of Australia, and north to the Korea Strait and Japan. This region is one the the riches in the world with respect to marine fauna. The Malay Archipelago (faunal center) includes extensive areas less than 200M in depth. Central Pacific islands have animals derived from this rich faunal center, but species decrease in numbers with distance from the faunal center. The Hawaiian islands are on the north-eastern boundary of this region and lack many of the groups characteristic of the faunal center.

THE TROPICAL ATLANTIC

The West Indies is the world's second largest archipelago and occupies a faunistic region in the Atlantic similar to the Malay Archipelago in the Pacific.  The West Indies have a rich and varied fauna although not quite as rich as the Malay region.  Some of the worlds most extensive mangrove swamps have developed in the Florida Keys.

In contrast, the tropical eastern Atlantic fauna is rather poor.  It seems odd, but there appears to be a closer relationship between West Indian and Indo-West Pacific fauna than Eastern Atlantic and West Indian fauna which are in the same ocean.  Fossil evidence also shows that in the geologic past, a closer relationship existed between the West Indies and the Indo-West Pacific than currently exists.  This phenomenon is explained by continental drift.  The continents have not always had the same relationship to each other as they do today.  Geologists believe that during the Mesozoic Era, there were two great land masses, a northern one (Laurasia) consisting of what is now North America, Greenland, and Northern Eurasia, and a southern land mass (Gondwanaland) consisting of South America, Africa, India, Australia, and Antarctica.  They were separated by the warm Tethys Sea which circumscribed the globe between them.  This open communication presumably existed for some time after continental drift began tearing the land masses apart.
It  is believed that during the Cretaceous and Tertiaty periods, the Atlantic coastal waters of Africa and Europe contained a rich tropical fauna, continuous at first with the Indo-Pacific.  This fauna has now largely disappeared from this region and to a considerable degree from the entire Atlantic.  The presence of the West Indies fauna can be regarded as a relic of the more ancient tropical Atlantic fauna.

TROPICAL EAST PACIFIC

The Isthmus of Panama forms a barrier between the tropical Atlantic coast and the tropical American Pacific coast.  The east Pacific coast fauna shows a closer relationship to the West Indian fauna than the Indo-West Pacific fauna.  The relationship is most evident at the generic level indicating that the present barrier has been there long enough for considerable speciation to have occurred, but not so long that if has excluded present day genera.

NORTHERN REGIONS

When the Northern hemisphere is considered as a whole it becomes apparent that the major faunistic break is between the warm subtropical-tropical regions and the cool to cold temperate-boreal-arctic regions.

The northern European boreal region is centered in the North Sea and extends Northward off the coast of Norway.  This area is dominated by the relatively warm North Atlantic Current.  This current is cooled somewhat by eddies from the Greenland Current.  On the American side, the New England Coast is influenced by the warm waters of the Gulf Stream and colder inshore waters derived in part from the Labrador Current.  The New England coast is essentially boreal.  Many species are shared with both sides of the boreal North Atlantic.  These waters support some of the world's most productive fisheries.

ARCTIC OCEAN

The Arctic Ocean is at least partially covered by ice at all times. Arctic conditions extend southward along the Atlantic coast of Greenland and and northern Canada because of the cold Greenland and Canadian currents, and along the Asian coast of the Pacific because of the cold Oyashio current.

The fauna includes a large number of endemic species most of which are circumpolar.  The term high arctic species is used for those restricted to the coldest waters and low arctic species for those living in somewhat warmer water. Those which live throughout the arctic are called pan-arctic species. The arctic contains fewer species of animals than the lower latitudes but the species that do occur may be in very large numbers.  There is also a tendency for organisms in colder water to be larger in size.  Although their growth rate may be slower, they generally mature later, live longer, and thus attain a larger size.

NORTH PACIFIC

The continents form a barrier around the North Pacific from lower California to Japan.  The shallowness of the Bering Straits is also an effective barrier to organisms.

The Sea of Okhotsk is arctic to subarctic because of the cold Oyashio current.  The warm Japan Current flows northward and turns eastward as the North Pacific Current bringing warm waters to American shores.

Along the American coast conditions are similar to the boreal of Europe.  Upwelling of deeper water along the California coast keep shelf waters cooler than they might otherwise be and the N. Pacific Current moderates water temperatures of the Pacific Northwest.  The N. Pacific current turns north as the Alaska Current and south as the California Current.  The California Current turns westward off lower California becoming the North Equatorial Current.

Roughly 1/2 the species along the N. American coast are endemic.  The N. Pacific exceed all other areas in number and diversity of sea stars.  The cooler temperatures of the northern parts of the N. Pacific Coast presents a barrier to some species so that faunal differences occur between Southern and Northern California.

SOUTHERN PACIFIC

Whereas the shelf regions of the Northern Hemisphere are almost continuous around their northern parts, those of the Southern Hemisphere are more limited in extent.

The oceans of the Southern hemisphere are continuous with the Southern Ocean which encircles the globe of north Antarctica.  The circumpolar eastward-flowing current, the West Wind Drift, carries surface waters around the world giving rise to northward-flowing cold currents along the western shores of South America and Africa.
(Humbolt of Peru Current along the S. America and the Benguela Current along Africa).

along the west coast of S. America, the Peru Current plus extensive upwellings combine to keep surface temperatures low and  make the waters very productive.

Southern South America and the oceanic islands of this region have a cold-water, anti-boreal biota distinct from the more temperate regions of the north.

SOUTH ATLANTIC

The western shores of Africa are bathed by the cold north-flowing Benguela Current and cooled further by upwelling, a situation similar to the western shores of S. America. Water temperatures here are 14-15°C in the south, increasing northward and becoming subtropical beyond Cape Frio (current turns west as S. Equatorial Current).

faunal zonation around the southern tip of Africa is complicated by the meeting of warm southwest-flowing currents from the Indian Ocean (Agulhas & Natal Currents).

SOUTHERN OR ANTARCTIC OCEAN

The southern ocean is more than just a running together of the Pacific, Atlantic and Indian Oceans.  It has an identity of its own.  It is difficult, however, to define its northern boundaries.  Biologically. The Antarctic Convergence is the sharpest line of demarcation between the typically antarctic surface waters and those of the other oceans.  The strongest flow in of the West Wind Drift coincides with the Antarctic Convergence.

Fossils discovered in Antarctica clearly demonstrates that this continent has not always been covered with ice.  Fossil trees with well-defined rings indicate rapid growth in a temperate climate.

ANTARCTIC OCEAN FAUNA

Large-scale upwelling make the surface waters of the Antarctic extremely rich in nutrients. This along with the short growing season combines to produce dramatic outbursts of plankton growth dominated by diatom blooms. One species of zooplankton, Euphausia superba, commonly called krill, is the major link between phytoplankton and larger marine life in the Antarctic. The richness of the ocean enables it to support an abundant benthic population. Sponges, for example, are better developed here than anywhere else in the world. The shoreline is barren, however because the ice prevents the attachment of rocky intertidal organisms. This barrenness may extend 10 or more meters below the surface of the ice. Below this level there is a rich benthos. There is a high degree of endemism in the fauna of the Antarctic Ocean. About 73% of the 256 species of echinoderms are endemic to the region.

Assessing the distribution of beep sea benthos is difficult because of sampling difficulties. The deep ocean basins are somewhat isolated from each other by thermal barriers along the rises between them. It was once thought that deep sea benthos was relatively uniform, but it is now clear that the abyssal fauna of the Atlantic, Pacific, and Indian Oceans are distinct, especially at the species level. Because of the lack of food, deep sea benthos are relatively sparse when compared to shelf fauna. The deeper and further one goes from land, the fewer the eurybathic species. Abyssal bottoms have a relatively high degree on endemic forms.