Oceans of life could soon be dead
View(s):By Ranil P. Nanayakkara
The earth came into existence about 5,000 million years ago. The vast expanse of time that elapsed since then can be divided into five major periods, the Pre-Cambrian, the Palaeozoic, the Mesozoic, the Tertiary and the Quarternary. Life is said to have originated in the primordial salt concentrated oceans in the Pre-Cambrian period when the combination of physical and chemical conditions then prevalent gave rise to living organisms.
From the single-celled organisms there evolved a wealth of invertebrates on the one hand and plants on the other. The earliest vertebrates evolved probably from a larval echinoderm during the Ordovician period, after 150 million years of dominance by the invertebrates. One of the most significant and important steps in evolution occurred in the Devonian period, when there was a migration of animals and plants onto land from the sea.
Sea water is a dilute solution of many salts derived from the earth’s crust and from the decomposition of animal and plant matter. By far the most important of these salts is common salt (sodium chloride), making up about 77.8% of total salts in the sea and amounting to about 35 parts per thousand of water.
Though an artificial solution of sea water can easily be prepared in the laboratory, it will not support life. Certain essential ingredients would be found lacking which occur in small amounts in true natural sea water. These essential compounds known as the nutrient salts, are an absolute requisite for the life and growth of animals and plants. The main nutrient salts result from the excretions and decay after death of the very creatures which themselves make use of them.
Each spring in the temperate seas, a proliferation of plant and animal life takes place, not only in shallow inshore waters but also far out in mid-ocean. In the upper 200ft below the surface of the sea, to which depth the sunlight penetrates, life proliferates, both vertebrate and invertebrate. Sunlight is essential for the growth of the plants in the sea just as on land. As summer progresses and the cold approaches, plants and animals die off having completed their cycle of life, their decaying remains sink, leaving nutrient salts at the lower levels.
The colour of the seas, from the blue-black of the mid-ocean to the grey-green of the coastal waters, comes from the pigment of the drifting organism “phytoplankton”. This plant “plankton” is as basic to the life of the sea, as grass and other plants are to life on land.
Man’s exploitation of the ocean may have dire consequences
Oceanic phytoplanktons are microscopic plants whose life cycle lasts just a few days, yet they are crucial to all marine life. Phytoplanktons are at the bottom of the food chain, their organisms sustaining marine life forms ranging from the microscopic to gigantic whales.
Like all green plants, phytoplankton contains chlorophyll and other pigments which absorb sunlight. This provides the energy for photosynthesis, during which carbon dioxide is removed from seawater and oxygen released as a by-product. Some carbon dioxide is removed by land vegetation during photosynthesis. Much more, is absorbed by the oceans, some recent estimates suggest a staggering 2.5 billion tons.
Phytoplankton absorbs carbon from seawater. This is replaced by carbon dioxide from the atmosphere. When the phytoplankton dies, some of them fall to the bottom of the ocean, taking carbon with them. Thus carbon is deposited on the sea bed and never returned to the atmosphere, unlike the carbon removed by land plants, which eventually re-cycles back into the atmosphere. It is now believed that 99% of the planet’s carbon is stored in sediments on the ocean floor.
Life in the sea, including plankton, is more abundant in cold than in warm waters because sea water contains more dissolved oxygen at lower temperatures. It is more abundant inshore than in the open sea because inshore waters are richer in dissolved salts. In warm waters the pace of life (metabolic rate) is higher than in cold waters, so the tropics are the home of a bewildering variety of different forms while their actual numbers are small. In cold waters there are fewer species but they have bigger populations.
Whenever biodiversity is discussed, the sea is neglected, yet it is the richest part of the biosphere. Of the 1.5 million species named by science, to date 80% are terrestrial. But this figure is misleading. It will also be an indication of our lack of knowledge of the life forms of the marine environment. It could merely reflect the disproportionate concentration on land by scientists. An example would be that only a trickle of new bird and mammal species is reported each year, but in 1983 a whole new phylum was reported from the oceans.
The biodiversity of the world’s coastal zone rivals that of the tropics. It covers an area one and a half times the size of Africa and its volume is the same as that occupied by the whole of the terrestrial biosphere. Its coral reefs are as species-rich as some rainforests, it contains the most productive ecosystem in the world, and within its ecosystem are a greater variety of life forms with more levels in the food chain.
Even though the oceans cover such a greater area than land in the world, very little is understood of the ocean. The seas that surround us governs the climate on land by ways of the current and atmospheric conditions, yet man’s wanton and irresponsible exploitation of the oceans resources go unabated. The over harvesting of species of fish in an unsustainable rate is highlighted by various reports stressing on the dwindling catches of fish.
The pumping of toxic effluents, the dumping of garbage, etc, by man on the marine ecosystem, destroys the very organisms that support life in the oceans.
Through ignorance and greed, man keeps on taking Mother Nature and the Earth for granted, little knowing that we are sitting on a time bomb that will one day explode with wide ranging consequences for all. This is the only home we have, not only for us but every living organism from the microscopic to the goliaths and all have every right to live in this world. Man’s selfishness alone is destroying this unique planet in the universe. One must think and take into consideration that though many planets are known to have frozen ice or seas that have vanished, that they might have been very similar to Earth eons ago. Did man inhabit those planets in times gone by? Is it man’s doing that these planets are what they are today……….barren and lifeless….
We are about to experience the next mass extinction in recorded history.
- The writer is a biologist
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