Indo-West-Pacific Region

Indo-West-Pacific Region 

the most extensive zoogeographic region of the world’s oceans. The region encompasses benthal fauna of the continental shelf and island shores of the tropical zone of the Indian Ocean and the western region of the Pacific Ocean. It is one of the regions of the Tropical kingdom. The Indo-West-Pacific Region extends from the eastern coast of Africa and the Red Sea in the west to the outlying islands of Micronesia, Melanesia, Polynesia, and Indonesia in the east; its northern limit is the coasts of Korea, southern Japan, and the Hawaiian Islands; in the south it extends as far as the southern tip of Africa, Shark Bay on the western coast of Australia, and Sidney on its eastern coast.

The present habitat, as in the past, is particularly favorable for the development of life. High water temperature (27°–28°C; in outlying regions not lower than 24°C) is almost constant throughout the year. Twelve-hour alterations of night and day do not vary. During the year there are only two seasons: a dry winter and a rainy summer, associated with changes in the direction of monsoons. A great diversity of ecological niches has resulted from a very jagged coastline (an abundance of coves, bays, straits, islands, and archipelagoes). All this has contributed to the development in the Indo-West-Pacific region of unusually rich and diverse fauna, with which no other marine fauna can compare in terms of wealth of species and abundance of endemic families and genera.

The invertebrates of the region are primarily Zoantharia (which form coral reefs), boring sponges, piddocks, worms embedded in layers of coral reef (polychaetes, Sipunculidae), barnacles, and whimsically shaped crabs, paper-thin (of the genus Percnon) or with powerful pincers that cover the openings of entrances to the reef hollows and channels where they live. Most common of the vertebrates are coral parrotfish, which crack open coral to feed on animals living in the reef. Mangrove vegetation is found most abundantly here. Among this vegetation live oysters (Ostrea glomerata) attached to tree branches, various crabs (Pachygrapsus and others), mudskippers (Periophthal-midae), and certain marine dwellers that have entered onto dry land and adapted to land life.

Very mild changes in climate since ancient times and preservation of a tropical climate even during the ice age have resulted in the maintenance of ancient forms. Here many “living fossils” have been preserved—representatives of otherwise long since extinct groups that flourished during the Mesozoic and even the Paleozoic. Such “living fossils” include members of the order Xiphosura, represented by three species (of two genera), tetra-branch Cephalopoda of the Nautilus family, several species of pearly nautilus Octopoda (Argonauta), Braciopoda of the family Linguliidae (several species of the genus Lingula, known from the Ordovician), extremely primitive varieties of mollusks (of the genera Pleurotomaria and Neotrigonia), barnacles (Mitella mitella), and Acrania. Among Echinodermata are species of genera that flourished during the Jurassic and are now for the most part extinct. Vertebrates include the famous latimeria. Many marine invertebrates mainly native to the Indo-West-Pacific Region have become terrestrial; only during breeding periods do they return to the sea to spread eggs and larvae (for example, the decapod robber, or coconut, crab).

E. F. GUR’IANOVA