Exactly what do coral reefs and tropical forests have in common and why are they both in danger? At first glance they may seem totally different, but they share some striking similarities in location, structure, ecology and - unfortunately - vulnerability.

Where on Earth?
Both coral reefs and rainforests are sunlight harvesters, deriving their primary energy from solar radiation. They thrive in areas of maximum sunlight near the equator. Rainforests tend to exist within 10 degrees of the equator, where the average air temperatures are 25-35 degrees centigrade. Coral reefs have a wider distribution mostly between the latitudes 20 degrees north and south, and require sea temperatures between 20 and 28 degrees centigrade.

Rainforests are better able to cope with temperature changes because air temperature tends to fluctuate more and regularly reach extremes. As a result, many plants have adapted to cope with these extremes, such as by entering a dormant period to conserve energy.

The sea acts like a buffer and changes in temperature there are smaller. Having adapted to these more constant conditions, corals are less able to cope with temperature fluctuations. Below 20 degrees centigrade, coral growth more or less ceases. Above it, they eject their zooxanthellae and coral bleaching occurs. In tropical forests, trees can produce new leaves after the unfavourable season has passed, drawing on energy reserves which have been stored. Unfortunately, once corals have lost their algal partners they rarely recover.

Coral reefs are restricted to clean clear water and most prefer depths of less than 25m. Water depth and turbidity determine the amount of light reaching the photosynthetic algae within the corals. Consequently, coral reefs cover just 1 per cent of the sea area. This seems a small figure, but globally the oceans cover 71 per cent of the Earth’s surface. With rainforests, light does not restrict range in this way, and they colonise a much larger surface area covering 7 per cent of the land mass. Before humans started to destroy the forests, that figure was doubled.

Similarities in structure
The tropical rainforest is characterised by evergreen woody vegetation with a high and usually closed upper canopy 30-50m above the ground. Some larger trees protrude above the canopy and woody climbers, or lianas, climb up tree trunks towards the canopy.

Numerous seedlings and herbaceous plants cover the forest floor where the light levels can be extremely low. In the soil itself, bacteria, insects, fungi and other decomposers rapidly recycle nutrients from rotting vegetation. Orchids, ferns or bromeliads grow on the trunks of trees where light levels are higher. Plants which grow on the surface of others, away from the soil, are known as epiphytes and these produce a whole range of microhabitats, adding another layer to the forest structure. There can be around 3-5 distinct levels of vegetation giving the forest a diverse range of microhabitats.

On coral reefs a similar, though less extreme layering occurs. As in the forest, all species compete against each other for limited space to get the best sunlit areas. This similarity means that the corals branch and spread out forming a coral canopy. Below the canopy layers, different microhabitats occur much as in the forest. Crevices in corals offer homes for numerous species, dead corals provide surfaces for algae and sponges and other encrusting life form under the dead coral and rocks on the sea floor. Diverse communities exist here that have rarely been studied.

Given that competition for space and resources on both coral reefs and in tropical forests is fierce, an amazing variety of intimate symbiotic relationships has arisen in both habitats. These partnerships occur frequently and have allowed animals and plants to take advantage of different microhabitats. Classic examples of these symbioses are those that allow fixation of nutrients from the environment.

How to get ahead in nutrient deserts
Corals can obtain as much as 90 per cent of their energy from the photosynthetic algae or zooxanthellae which live within their tissues. This symbiotic partnership is essential because the oceans in which the coral reefs exist are, in effect, deserts. Without this relationship, in which enough sunlight energy is fixed to provide food and support life, nothing would be able to grow in these areas.

Tropical soils are similarly poor in nutrients. Warm climates and high rainfall leaches minerals from the soil, literally washing away anything of use to the plants. Like the coral reefs, the rainforests have developed an association which allows them to capture what little nutrients there are before thy are washed away. The rainforest trees do this with the help of fungi called mycorrhizae. These hair-like soil fungi incorporate themselves into the roots of plants, increasing the surface area of the root system and making them more efficient. The fungi sponge up nutrients from the soil and supply them to the rainforest trees and plants, and in return the fungi get energy back from the plants.

In both coral reefs and rainforests, when these vital partnerships are destroyed, the landscape soon reverts to a bleak, low-diversity system.

Biodiversity
In both rainforests and coral reefs, scientists have estimated that only around 10 per cent of the biodiversity has been measured so far. In other words, 90 per cent of the species within both these habitats have not been sufficiently studied to be identified.

Tropical forests contain over half of the world’s species, most or which are not found anywhere else. For example, tropical America has roughly 85,000 species of flowering plants whereas Europe just has 11,300 vascular plants. Coral reefs contain 25 per cent of all marine species with possibly as many as 75 per cent of the world’s fish species.

Although extinction is a natural process, scientists are predicting that the current rate of species loss may be 1-10 thousand times higher than pre-human levels. This represents rates of extinction nearing those of major extinction events of the past. Could we be heading the way of the dinosaurs? The huge losses are almost definitely due to the destruction of these two major habitats by man. Bearing in mind that it is estimated we only know 10 per cent of the possible species in coral reefs and rainforests, the situation could actually be worse than we realise.

Vulnerability
Tropical forests cover approximately 970 million hectares compared to just 60 million hectares of coral reefs. Scientists have estimated that 60 per cent of the world’s reefs have been damaged beyond recovery by human activity. For the rainforests it is a similar story with over 50 per cent having been removed by man. More worryingly, it is predicted that coral reefs could disappear all together in the next 20-30 years. The outlook for rainforests is slightly more promising. This could be due to an earlier awareness of the massive scale of rainforest destruction, which has led to worldwide changes in forestry practices aiming towards sustainable resources. However, if forest destruction does continue at the same pace there could be virtually none left in 50 years time. At the moment 10-20 times more reforestation by planting is needed just to keep pace with this destruction.

Coral reefs have been around for more than 400 million years, although these ancient forms are long gone. Modern forms of the corals have only evolved in the last 25 million years. Rainforests are more recent in that flowering plants only evolved around 135 million years ago. Some corals can live for thousands of years, building up huge colonies. Rainforest trees have a much faster turnover with many large species reaching maturity in about 30 years.

The fact that rainforest trees can reach maturity in 30 years is encouraging some governments to manage the land more carefully. Logging can continue in strips alternating with tracts of untouched rainforest left to preserve the environment and shield the land from erosion. Replanting the felled strips means that the habitat in this section can recover before the untouched strip is felled. It is only through similar sustainable land use methods that the forests will survive.

For corals, time is running out and there is very little that can be done to manage the situation. This is because the sea temperatures are rising as a result of global warming and the corals cannot survive for long in the ever warmer waters. Unfortunately the destruction of the rainforests has added to the warming of the planet at an unprecedented level.

Carbon dioxide levels
Photosynthesis is undoubtedly the most important chemical reaction on this planet and both tropical rainforests and coral reefs are dependent on it to gather energy from the sun. Plants fix carbon dioxide from the atmosphere to form sugars which provide energy for growth. The tropical rainforests are massive carbon sinks absorbing huge quantities of carbon dioxide. When these carbon sinks are removed, not only does atmospheric carbon dioxide remain uncaptured, but when the forests are burnt, frequently on a massive scale, even greater quantities of carbon dioxide are created.

This most common greenhouse gas is capable of warming our planets atmosphere when its concentration increases. By destroying half of the rainforests to date, man has unwittingly released a massive amount of carbon dioxide into the atmosphere which has probably gone a long way towards causing today’s global warming.

Slash and burn techniques are the main culprit for loss of forests, and global warming affects this as well. The rainforests are experiencing droughts in some years, so when these fires are lit, the forests burn out of control and huge areas are destroyed. Whilst natural fires do occur, it is thought that most of the huge forest fires of recent years have been deliberately started to clear land.

The oceans are also massive carbon sinks with phytoplankton absorbing carbon dioxide in the same way as trees. On the coral reefs, the algae within the corals do the same job, and the coral polyps also act as a carbon sink, absorbing it from the sea to form their calcium carbonate exoskeletons. Unfortunately the increased carbon dioxide levels are bad for the reefs as they increase the acidity of the water. Corals are unable to produce calcium carbonate as efficiently and growth slows.

When you combine this factor with the effects of carbon dioxide as a greenhouse gas, the coral reefs are in real trouble. Increasing temperatures from global warming are pushing the corals close to their thermal limits and bleaching events leading to coral deaath are getting more frequent.

For what we are about to lose...
Over 120 prescription drugs and 25 per cent of all pharmaceuticals originate from the rainforests as did around 80 per cent of all fruits and vegetables in our diet. One rainforest plant, the Madagascar periwinkle (now extinct in the wild), has produced a drug that increases the survival rate in children with leukaemia from 20 to 80 per cent.

The value of plants from the rainforest has long been known by native tribes. Today, scientists have actively started to search for other plants which might yield valuable drugs and since there are so many species yet to be described, the potential for new discoveries is staggering.

Coral reefs have been less exploited by man because they are less accessible. As a result the majority of species living there have never been fully utilised. With the advent of scuba diving, reefs are being thoroughly examined by scientists for the first time and the potential for producing new drugs is emerging. In the past decade, several promising cancer cures have been extracted from marine invertebrates and these are currently undergoing clinical trials.

Coral reefs support a hugely diverse range of life forms which have been evolving together for millions of years. This habitat has been around for far longer than the rainforests and fierce competition between reef dwellers trying to get the edge over one another has produced numerous forms of chemical warfare. The types of chemicals produced by marine life are totally different from those produced by land plants. Even microscopic bacteria could be sources of future antibiotics. Some scientists believe that the potential for producing new drugs from coral reefs could even surpass that of the rainforests. In both habitats, the huge number of species which have yet to be discovered or studied is a huge incentive for research.