• There are good maps available due to ongoing hydrographic surveys and advances in satellite remote sensing, aerial photography and airborne sensor technology.
• The species of the major groups, especially corals and fish, have been thoroughly determined, although there are still major gaps for many minor groups, affecting our capacity to document and protect biodiversity.
• Surveys have shown the many different types of sea-floor and reef communities needing to be represented in biodiversity conservation.

• The basis for distinguishing human impact from natural change has been developed through surveys and monitoring of corals, fishes and seagrasses over a wide area. Such studies show that recovery periods for naturally disturbed habitats can range from years to many decades.
• The discovery in the mid-1980s of mass spawning and wide dispersal of coral and fish eggs and larvae led to recognition of coral reefs as a network of interconnected and interdependent patches.

• Habitats separated by tens to hundreds of kilometres are now considered as 'sources' (of eggs and larvae) and 'sinks' (of juveniles ready to settle down and grow to maturity) for each other, and these ideas have become a major consideration in planning for use and protection of habitats.
• It is now possible to reconstruct the distance and direction of movement of eggs and larvae each breeding season over the last several decades. These reconstructions rely on decade-long data from current meters, correlated with sea levels routinely measured in ports.
• Long-term monitoring has shown that in 'good years' about 10-100 times more small juvenile fishes reach coral reefs than in 'bad years'.

Figure 1g The scale of an individual coral colony, showing annual growth bands which can be used to age the coral and which contain a record of the environment in which it grew. For living ancient corals, this record extends backwards several hundred years before the present.

Photo: Terry Done.

• The basis for managing fisheries was given a boost when scientists learned to age fish by reading growth rings in their ear bones.
• Banding patterns in centuries old corals, reminiscent of tree rings (see Figure 1g), have been shown to be libraries of information about past environmental conditions, including temperature and river runoff.
• No convincing signal of widespread environmental degradation has been detected in coral bands. However, it has been shown that the growth of today's corals is within the bounds of variation of the past several centuries.