Marine biodiversity includes coastal and marine plant and animal species, their genetic variety, the habitats and ecosystems they form part of, and the ecological processes that support all of these.

The Earth is home to an estimated 10 million species. The largest of these are divided by biologists into 3 main kingdoms: fungi, plants and animals. The animal kingdom is divided into a further 33 distinct groups (or phyla).

Humans belong to the phylum called chordates, which includes all mammals, fishes, reptiles and birds. Other common phyla of the animal kingdom include the arthropods (insects and crustacea: crabs, shrimps and lobsters) and molluscs (snails, squid, octopus, cockles and mussels).

There are 11 phyla existing in terrestrial environments and 28 phyla living in the sea, of which 15 are exclusively marine. Examples of exclusively marine phyla include the echinoderms (starfish and their relatives), ctenophores (comb jellies), hemichordates (acorn worms) and the echiurans (trumpet worms).

Far greater diversity than land
The marine environment therefore includes a far greater diversity of animal groups than the terrestrial environment, which is not surprising since living organisms first appeared in the seas several hundred millions years before life on land evolved. Whether in the sea or on land, most plant and animal species are grouped into assemblages or communities characteristic of recognisable habitats.

Forming a marine ecosystem
The eastern African coast, for example, includes mangrove, seagrass and coral reef habitats. Each of these requires specific environmental conditions for its development. In the case of the mangrove habitat, shelter from wave action and soft mud or sand are the basic conditions that allow the community to flourish.

The combination of habitats forms the marine ecosystem. This ecosystem, the various habitats, communities and species they comprise, constitute the marine biodiversity of the eastern African region.