Indo-Pacific Coral Reefs

The Pacific and Indian Oceans combined cover just over half of the Earth's surface. Thus, Indo-Pacific coral reefs are widely distributed over a truly huge area. This vast region contains an abundance of all three major types of coral reefs (atolls, barrier reefs, and fringing reefs).

An Indo-Pacific atoll. © Fotolia

There are hundreds of atolls (see photo, left) in the Indo-Pacific, making them one of the most common type of open ocean reefs in the region. Likewise, barrier reefs are considerably more widespread in the Indo-Pacific than in the Caribbean region.

Fringing reefs are not nearly as prevalent in the Indo-Pacific region as they are in the wider Caribbean. They are however common in some areas, particularly in the high islands of French Polynesia, the Red Sea, and areas off east Africa.

Characteristics Of Indo-Pacific Coral Reefs

There are some major differences in certain coral reef characteristics between coral reefs of the Indo-Pacific region and those of the Greater Caribbean region.

Most healthy Indo-Pacific reef surfaces are composed nearly exclusively of hard coral colonies, unadorned by extensive growth of octocorals and large sponges as is so commonly the case with shallow Caribbean coral reefs.

Another major difference is the widespread presence of a prominent algal ridge on the seaward margin of Indo-Pacific reef crests. In comparison, algal ridges are relatively rare and poorly developed on Caribbean reefs.

Indo-Pacific reefs also often contain extensive reef flats composed of consolidated coralline sands situated immediately shoreward of the reef crest, a feature rarely seen in the Caribbean region.

Biodiversity of Indo-Pacific Reefs

Along with the greater balance in the relative numbers of major reef types, the incredible biodiversity housed on Indo-Pacific coral reefs is one of the biggest differences between reefs of this region and those of the Greater Caribbean.

The diversity of reef life that can be found on the most diverse Indo-Pacific coral reefs is truly staggering, with perhaps as many as 700 or so species of corals present, along with perhaps 3,000 kinds of coral reef fishes.

Indo-Pacific coral reefs are rich in coral species diversity. © Fotolia.com

However, all these species are not present throughout the entire region. Rather, most species are restricted (endemic) to particular (and sometimes quite small) portions of the region. For example, about 25% of all the inshore fishes found in Hawaii are endemic (found nowhere else).

Thus, although there is a common thread of like species throughout most of the region, many distinctive sub regions exist (such as the Red Sea). Because of its sheer size and remoteness, many Indo-Pacific reefs remain largely unexplored, and new species of fishes and other reef life are continually being discovered.

The center of biodiversity for the Indo-Pacific region as a whole is a rough triangle encompassing an area extending from the southern Philippines to eastern Indonesia and western New Guinea. The farther a reef is located from this center, the correspondingly fewer species of fishes, coral and other reef life will be found.

The South Pacific includes most of this area, except for reefs around the islands of Indonesia which are located within the Indian Ocean.

There are two likely reasons for the far higher biodiversity found on Indo-Pacific coral reefs and their Caribbean counterparts. First, the sheer size of the region occupied by Indo-Pacific coral reefs, as well as the length of coastline where corals can successfully grow is much greater than in the Caribbean, allowing more room and opportunities for species diversification.

Secondly, most Indo-Pacific coral reefs did not experience the severe temperature changes the Caribbean region suffered during the Pleistocene ice ages. This likely resulted in more species of coral, fishes, and other types of reef life surviving into the current post-glacial epoch.