Coral Reefs [antikvár]

Coral reefs are very special places. They are the oldest richest natural communities on our planet. In diem, thatmost wondrous and mysterious of all natural phenomena, life, has found its fullest expression. Nowhere else can one find so many diverse creatures living so closely together in such abundance. Complementing and enhancing this exQ-aordinary intensity of life is its exquisite beauty of form, colour, and motion. This is truly nature's richest realm, a fairytale world beyond imagining were it not real. On a coral reef one can find, all together at the same place and time, living representatives of all the major levels of over a billion years of life's evolution on our planet. The entire spectrum of being is present from blue-green algae and bacteria through all of the numerous types of invertebrate animals to fishes, reptiles, birds, and even mammals with brains larger and more complex than our own (whales and dolphins). These are vasdy ancient comraunities. Primitive coral reefs existed nearly half a billion years ago, a time predating any evidence of life on land. Though these early r^efs were quite different from modem reefs some of the same types of creatures which inhabited them still survive on today's reefs. Many of the genera of present day reef animals are found as fossils dating back to the Eocene epoch some 50 million years ago and some date back to the Cretaceous period or age of dinosaurs about 100 million years ago. Even today's living reefs often have surprisingly lengthy histories. Ceno-al Pacific atolls have reef strata dating back to the Eocene and the northem portion of the Great Barrier Reef began growing in the Miocene epoch about 25 million years ago. The persistence of these communities through vast spans of time with only gradual change underlies their richness. It has afforded a stable environment in which the products of evolution could survive, accumulate and fine ojne themselves into die richest, most complex natural systems existing. A dive on a coral reef is hke a tiip in a time machine to the world before we humans even existed. If we could somehow go back in time for 10 million years we would find many of the same reefs we have today and their inhabitants would be little different from those we know. Evolution on reefs is a much more gradual process than in less stable environments where adaptation and extinction is mandated more frequendy by significant changes in the ecosystem. In the American tropics we find a unique natural experiment which graphically demonstrates the rate of evolution of coral reef creatures. About 5 million years ago the Central American isthmus arose from the sea, dividing the coral reef area of that region. Since then the separate evolution of populations on either side has produced several hundred geminate or twin species pairs of various reef creatures. After5 million years the difference amounts to a few scale rows, or fin rays, or spines more or less and slight differences in colouration. Meanwhile our own ancestors evolved through four or more distinct and subsequendy extinct species from ape to modem man. Coral reefs have not only been significantiy exempt from natural extinctions but, dius far, human induced ones as well. Despite the popular mythology of primitive man living in harmony with nature, all over the world the appearance of mankind in the geological record coincides with, or is shordy followed by, a wave of extinctions in the native fauna. There is, however, no known instance of human induced extinction of any reef fish or invertebrate. The worldwide total for extinctions of all reef organisms of any type since the advent of mankind stands at one, the Caribbean monk seal. Today's reef fauna still exists in all its primordial richness. Inaccessibility, large populations scattered over vast geographic areas and the capacity of individuals to produce thousands to millions of offspring have all contributed to the continued survival of reef creatijres despite the impacts of man and nature. This, however, does not complete the explanation of the reef community's resilience and tenacity. Part of the explanation lies in the very richness and complexity itself. The extraordinary diversity of the reef fauna is not simply an effect of stability but is also a cause of it. In reality this is less paradoxical than it might seem. Stability contributes to diversity and vice versa. It begins with the physical environment of reefs. Vast reaches of equatorial ocean buffer reefs from environmental extremes. There are no droughts or floods or exffemes of temperature here. Even the ice ages only reduced their geographic