Six hours later, as the tide has ebbed and a much greater expanse of the shore is exposed, a mix of sand, mud or rock may stretch away from the beach for 500m or more.

This intertidal zone is accessible on foot, and a short stroll will reveal myriad forms of shells, crabs, seagrasses, seaweeds (algae), starfishes and other creatures. In rock pools small fish, shrimps, coral colonies, sponges and seasquirts can be seen, while at the back of sheltered bays and inlets, where wave action is reduced, mangrove stands and forests are found.

For a fuller understanding of the marine biodiversity of these warm, tropical waters however, it is necessary to take a mask and snorkel and drift or swim in the shallow waters over the coral reefs and seagrasses where a spectacle of biodiversity can be seen.

High rates of endemism
About 15% of the marine plant and animal species occurring in the region are pan-tropical, that is they can be found in all warm seas. Between 60-70% are found only across the Indo-Pacific, a vast area of similar tropical conditions that stretches from eastern Africa to the eastern Pacific Ocean islands of Hawaii and Polynesia. About 10-15% of the eastern African marine life is found nowhere else on earth.

And they come in all sizes
All of the larger animals and plants of the ecoregion can be seen with the naked eye, but there is also an abundance of minute life forms. These microscopic creatures include much of the plankton, bacteria and fungi.

Though vital to all other life, these tiny creatures are much less well known, but could well number tens of thousands of species, and thus the larger creatures represent only a small percentage of the total marine biodiversity of the region. As research continues we will learn more.

Still more to be known, discovered
Even for the larger animals there is still insufficient information on species distributions and abundance. For example, the well-known, deep water, ancient fish, the coelacanth, first discovered in 1938 by fishermen off South Africa, was thought to be endemic to the SW Indian Ocean until the discovery in 1998 of a close relative of this fish off Sulawesi (Indonesia), 10,000 km from its previously known population

Variety of habitats
On the seashores, and in the shallow coastal waters, the habitats that contain the bulk of the larger plants and animals are easy to identify. These are the sand beaches and dunes, mangrove forests, river deltas, seagrass beds, rocky shores, mud flats, coastal lagoons, coral reefs and open waters.

Each habitat has its characteristic compliment of species, though many species require more than one habitat. Fish and shrimps for example will move from one habitat to another for food, breeding or for refuge.