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The Precambrian ocean productivity model - why it does not work today

by Debbie MacKenzie

Below is a typical illustration of the "Life Cycle of the Sea," or ocean productivity model currently accepted by scientists (image reproduced from the book, "Wondrous World of Fishes," National Geographic Society, 1965). Animals that evolved during and since the Cambrian era are included in the model, but there is no indication that these animals play any role in delivering fertilizing chemicals to the sea surface. (continued below)

Six steps are described in the accepted model of the ocean life cycle:

1. Plant growth at the surface captures energy from the sun and builds basic food.
2. Tiny animals eat the tiny plants.
3. Fish eat the small animals.
4. Larger fish eat the smaller fish.
5. Food debris from plants and animals sinks to bottom, "there to nourish bottom dwellers and to decay."
6. "Chemicals from decomposition well up to the sunlight zone and replenish the life cycle."

Note that this model predicts no change in surface fertility if bottom feeding animals cease to exist, if all sunken food is just decayed by bacteria directly. That is because the model considers current-driven upwelling to be the only plant fertilizer-lifting vehicle in the picture; it misses the contribution of animals and/or their eggs that move up to the surface water of their own accord and there go on to fertilize new plant growth, without having undergone bacterial decomposition.

Similarly, all the fish and whales could theoretically be removed from the sea and this model would not predict any resulting change in surface plant fertility: the debris from the tiny plants and tiny animals could sink to bottom, decay, and eventually be swept back to the surface by ocean currents, completing the cycle. That describes how the cycle of life was completed in the Precambrian sea.

Rather than adding to the overall energy of this picture, fish, whales and bottom feeders are depicted here essentially as parasites, feeding off food produced by plants but giving nothing important back to the system that grew the plants. These animals are shown as passively dependent on the weather for the continuance of their food supply, and incapable of doing anything to sustain or kick-start plant growth themselves. But, as described elsewhere*, this is far from the truth.

Unfortunately, the Precambrian ocean productivity model has formed the foundation of the "science of sustainable fisheries" for about a century. This thinking led to the assumption that fish and whales could be removed wholesale from the ocean, and, while fishing might affect those populations if overdone (the 'overfishing' idea), fishing itself - regardless of what fraction of the original animal life was ultimately removed from the sea - had no potential to adversely affect the fundamental vitality or fertility of the sea itself. However, this appears to be wrong.

The accepted model has led oceanographers to focus on looking at signs of continued bacterial activity and ocean current action as indicators of stable ocean fertility. But this might give a false reassurance if the lost legions of sea animals actually worked as supplemental ocean fertilizing agents, catalysts to greater plant growth. Scientists today are mystified by indications that ocean plant growth driven by bacterial decay and ocean currents continues fairly steadily while fish - very few fish compared to numbers supported in years past - are stunted and starving for lack of food.

Today's scientific acceptance of the Precambrian ocean productivity model also allows for the assumption - still made by scientists studying the global carbon cycle and the increasing accumulation of carbon dioxide in the atmosphere - that the ocean today maintains the same carbon balance as it did in pre-Industrial times, and that the massive removal of sea animals accomplished by humans since that time has had no effect on marine plant growth and natural carbon dioxide removal from the air.

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