When hearing about reefs you might probably start dreaming about warm weather, snorkeling fun in warm waters, colorful fish schools, the dark blue open sea, greenish-blue clear lagoons, and white palm beaches at lonely islands. This shows already how accurately reefs reflect distinct ecological needs. Most of our reefs grow in latitudes between about 30 degrees north and south, in seas with waters up to 30 (and never below 20) centigrade warm. Reef building corals grow in shallow, clear, often strongly wave-agitated waters. In most cases, waters contain very little nutrients and floating matter, causing very clear waters with colors from blue to bluegreen, depending on depth (SCI-NOTE).

Many reef organisms, particularly the stone corals possess calcareous skeletons and in the course of thousands of years build themselves up to the sea level. Waves and many boring organisms grind many skeletons to sand size. Storms may heap up this sand to romantic coral sand cays which will subsequently be vegetated, for instance, by palms.

Fig. 2: Small coral sand cays are typical for reef settings. These piles of calcareous sands are mostly created by storms. (Image: small 6kb; large 24 kb)

The success of reef organisms in this, at first glance, hostile environment (which is characterized by scarcity of nutrients, high wave energy, frequent tropical storms) is only possible due to many adaptations and interdependant relationships of organisms among each other. This makes reefs one of the most complex ecosystems on our planet. Reefs may be described as a "superorganism" which functions only by the interplay of his individual parts. This "superorganism reef" is perfectly adapted to its environment. But this is why it also may be easily affected by diseases and even die whenever the environment changes. This allows to use reefs as monitors for the state of health of our seas and our entire globe.

Abb. 3: Environmental factors must be in perfect equilibrium to allow reef growth. If one factor changes (for example, sea level rises, hence water depth increases), the change of another factor (for example, waters become less turbid) may counteract the effect. Reefs may keep on growing, although the composition of reef fauna might change). (Image: 13kb)

Reefs of Ancient times often were completely different to modern reefs. This is partially due to regional and global environmental conditions different to those of our modern world. It is also partially caused by the lack of many modern reef organisms which had not yet evolved but were preceded by other organisms, often with contrasting ecological demands. Such different reefs were nevertheless perfectly adapted to their environments and hence may be used as monitors for paleo-environmental conditions which were partly quite different from today's.

The Jurassic Period, particularly the Epoch of the Late Jurassic (that was about 160 to 135 Million years ago), was such a time where many different reef types existed. Some show similarities with modern ones, whereas the majority of reefs was quite in contrast to their modern counterparts. As a matter of fact, global climate and environments were quite different from the modern world, which we will discuss later on in this article.

A view at the Jurassic reefs, their builders, and their ecological settings also emphasizes the importance of modern reefs as indicators of the state-of-health of our globe and pinpoints how some changes in the composition of reefs may just represent the forerunners of catastrophic, regional or global, environmental change. Many of our modern reefs do show strong deterioration which possibly could be the forerunner of an approaching catastrophe. But proceed with the article and picture this to yourself.....