Sea Creatures make
a healthy ocean planet, air included
by Debbie MacKenzie, July 2006
Ocean animals serve their own ends, which includes actively boosting the growth of their plankton-based food supply, which entails pulling carbon dioxide out of the atmosphere. Thus the importance of fish in the grand scheme of engineering the biosphere.
- Fish-eating predators:
how their loss causes an ‘immune deficiency’ or ‘AIDS’-like
effect in the ocean
Fish-eating predators: how their loss causes an ‘immune deficiency’ or ‘AIDS’-like effect in the ocean
Fish eating other fish: this drama has played in the world ocean for 400 million years. The paradox of the natural predator is that it actively builds the general life force in the ocean by killing and eating live prey. Fish, whales, seabirds, and even marine plankton-feeders, history tells us that all enjoyed greatest prosperity when fish-eating predators ran rampant throughout the world ocean. But that is only circumstantial evidence of a beneficial impact of predators. A theoretical argument is needed too.
Fish predators are vanishing and ocean health is failing, and this seems to be cause and effect. Large ocean fish are becoming a global rarity. Smaller ocean fish are declining too, as are many whales, seabirds, turtles and marine invertebrates. Increasing growth in the ocean today is seen virtually only in microbes, including bacteria.
Bacterial growth poses a threat to animal life. Although animals have always coexisted with bacteria, and they have a degree of dependence on bacteria, microbes are a serious threat that animals actively work to suppress. As with the saying about fire, from the perspective of animals, the bacterial element “makes a good slave, but a bad master.”
Several defensive strategies are used by animals against bacteria, and common themes repeat on many scales, from single organisms to large interdependent webs.
In our bodies we have defensive cells called phagocytes (‘eating cells’) that move about killing and eating bacteria and any body cells that harbour viruses. In an internal ‘war’ of sorts, phagocytes also kill and eat body cells that are old, injured, dead or dying. In other words, many body cells constantly being “eaten alive” by other body cells is part of a normal, natural anti-bacterial strategy that is used by complex organisms. This sanitation scheme removes small body parts before they can become food, and provide a foothold, for microbes. This strategy used by the human immune system is mirrored in other animals, and in animal ecosystems.
Bacteria pose a greater threat to animals in water than they do on land, because bacteria can remove all the oxygen from the water, killing the animals. When weather patterns cause bacteria-dominated water to shift, fish can be engulfed, smothered and killed en masse. Similar events do not occur in air.
If the web of sea animal life is considered as a single organism, predatory animals work as cells in an anti-bacterial immune system, quickly eating tissues that might otherwise be consumed by bacteria instead, and thereby protecting the health of all animals in the system. Marine animals evolved anti-bacterial methods similar to ours. Underwater, a Darwinian battle rages between the ancient bacterial regime and the newer animal constituency. In this fight, animals function as a cooperative unit against their common ‘large predator,’ which is bacteria.
Marine animals of all sizes suppress the growth of bacteria. The smallest eat bacteria directly, while the entire array of animal life competes for every food source that could be used by bacteria instead, including food dissolved in the water and food sunken to bottom. Regardless of which marine animal species live or die, or how long any individual animal survives, it is the maintenance of a sufficient density and bulk of active animal players that determines if the ‘animal organism’ can hold the ‘bacteria organism’ at bay.
Therefore, large-scale bulk removal of animals from the ocean lowers the natural immunity of the ocean animal web against bacterial overgrowth: if animal strength declines, bacterial strength rises. Today’s ocean problems resemble human AIDS (acquired immune deficiency syndrome) because bacterial infection results from predators, or ‘phagocytes,’ having been disabled. ‘Infection’ is spreading in the ocean today in the form of expanding microbe-dominated dead zones.
How animals fought with bacteria to gain power and control in the ocean
Animals enjoy a competitive love-hate relationship with microbes. The conditions that allowed the first marine animals to survive resulted from the work of bacteria, because bacterial decomposition of food releases plant-fertilizing chemicals into the water and stimulates new plant growth. This process is called nutrient cycling. Bacteria-controlled nutrient cycling supports animal life because plant growth provides food and oxygen, but on the other hand, the tendency of bacteria to suffocate animals by draining all the oxygen from the water has led to a tense coexistence.
Tiny sea animals in the surface water also decompose food and release plant fertilizers, speeding the rate of nutrient cycling and increasing the growth of the plants. The rate of plant growth in the ocean determines how much energy is captured from the sun and locked into food, and it also determines how much carbon dioxide is removed from the atmosphere in the process.
In the earliest eras, while sea animals remained tiny plankton creatures, they shared the inability of bacteria to move around much on their own. Nutrient cycling was done as quickly as possible at the surface, but eventually food sank into deeper water, and it could then only be recycled again into more new plant growth after ocean currents lifted it back to the surface.
Neither bacteria nor animals could control the movements of currents, and only bacteria could live without oxygen in the depths. So initially, sunken food was used exclusively by bacteria. The overall rate of nutrient cycling and plant growth in the sea, including the boost given by tiny animals at the surface, therefore ultimately depended on the whims of the weather in causing currents to lift fertilizer-rich bottom water back to the surface. With no weather-driven water movement to complete the cycle, plant growth would eventually fizzle out as reusable materials sank and stayed below the sunlit zone. It is in this sense that, as science tells us, “physics limits biology” in the ocean.
About 600 million years ago, during the Cambrian era, animals began living on the sea bottom. As life expanded, oxygen accumulated on the planet, in air and sea both, and oxygen-containing water now spread to the shallower sea bottom. Slow-moving creatures like sea urchins and starfish appeared there and competed with bacteria for food that fell from above, eating food formerly claimed by bacteria and bacteria themselves.
Urchins and starfish are typical bottom invertebrates, and they divert a major fraction of the food they eat into billions of rich, tiny eggs. When released into the water, these eggs float to the surface, delivering a fertilizing boost to the conglomerate of tiny plants and animals living there. The living eggs release plant fertilizer, some are eaten, some hatch into tiny animals that participate in nutrient cycling, and only a miniscule fraction survive to ultimately live as adults on bottom. The net effect of spawn release by bottom animals is an increase in plant growth at the surface. In doing this, animals achieved two important advantages: they achieved a measure of freedom from the limits “physics” had placed on their food and oxygen supply, and, by changing their environment to speed food production for themselves, they began to control a positive feedback loop that could self-accelerate indefinitely.
The basic advancement plan that marine animals used to overcome their initial oppression by bacteria was to steal as much food as possible away from bacteria, to hoard it to themselves, and to accelerate the food and oxygen supply by controlled fertilizer release. Animals achieved these ends by living longer, by some of them growing to large sizes and becoming increasingly mobile, by feeding off one another’s wastes, and by releasing plant-fertilizing materials at the surface to strategic advantage.
More plant growth, less bacteria, these were keys to the recipe for overall animal success. Active vertical movement by animals was another one, and this eventually included much more than floating eggs.
As example, consider the sperm whale: a massive, 50-ton animal dives several kilometres to the mid-ocean depths to eat giant deep-sea squid. The whale rises to breathe, also releasing digested squid in a plume of floating feces at the surface. Birds, fish and other animals snatch bits of whale feces, as it still contains food value for them. Billions of tiny invertebrate animals emerge from the whale feces in the form of worm eggs. These were incubated in the warm belly, as even healthy whales host masses of worms. Plant fertilizing materials also seep directly from the feces into the water. The result is that plant growth speeds up at the ocean surface through various spin-off routes after the whale ‘leaves its calling card’. The sperm whale will behave in this manner repeatedly, perhaps for a century.
Without the sperm whale, the giant squid might eventually die and be decomposed at the bottom instead. Plant fertilizing materials thereby released into deep-sea bottom water will not be returned to the surface by water movement for a long time, perhaps not for a thousand years.
Fish – evolutionary milestones and the nature of the beasts
To further emphasize the importance of natural fish predators in promoting ocean health, consider their history.
The First Fish – 400 Million years ago
Fish arrived in a burst of evolution 400 million years ago. Not only small fish, but many sizes and shapes of fish appeared virtually simultaneously, including 20-foot long sharks. Fish ate other fish from the start, in a relationship that is likely essential for the very survival of fish. No evidence suggests, for instance, that small fish enjoyed a heyday before bigger fish evolved to prey upon them.
Predatory fish affect their prey in a consistent pattern, with the odds of being eaten by a predator highest for the young, weak or infirm. Consider the pattern of interaction with natural predators through the lifespan of a typical fish, which can be viewed as a three-act play. The same script has always been used; over time only the names of the players have changed.
Act I – Juvenile - baby fish are born
Fish release millions of floating eggs into the water, many hatching into larvae that survive only briefly as plankton. Predators eat the vast majority of newborn fish, either as eggs, larvae or small juvenile fish, in effect pruning numbers down to a realistic size (i.e. a number of fish that matches the food available to support them.)
Barring predation on their young, ocean fish seem to have the potential for rapid self-destruction.
“A fishery biologist once calculated how many cod there would be in the world if all the eggs spawned by all female cod in one spawning season were to hatch and survive to adulthood: the number was astronomical. He concluded that the oceans of the world, from shore to shore and from bottom to surface, would be one mass of wriggling cod, with no room for anything else.” (Albert Jensen, in “The Cod,” 1972)
Clearly, death would overtake cod before they could literally fill the sea, death by starvation and suffocation. Should such a scenario develop, it seems the species itself might be eliminated, along with others nearby. Therefore, the most obvious direct impact of natural predators on the early life stages of fish is to ensure their ultimate survival, by killing most of them.
Act II – Mature – fish in their prime
Mature fish reach what biologists call a ‘size refuge.’ Safe from earlier predatory threats, they have grown too fast to be caught and too big to be swallowed. Most ocean predators can only eat food they can swallow whole. Mature fish often grow big enough to become fish-predators themselves. Healthy adult fish can avoid many natural predators, so the death-risk is relatively low during this phase. But fish health wanes with time, partly because fish, unlike mammals, continue to grow larger after they reach maturity.
Hardships mount for fish at greater sizes: greater difficulty in feeding, plus a tendency to divert ever more energy into spawn. This energetic squeeze eventually weakens mature fish. The timing of this change is determined in large measure by how supportive the environment is to the continued growth of the particular fish, and the food supply is crucial.
After reaching the safety of the ‘size refuge,’ therefore, fish continue growing until they slide into a ‘size trap,’ the size advantage working as a double-edged sword.
Act III – Spent – old fish caught in the size trap
Like old body cells, mature fish eventually become worn out, or spent. When older fish slow down they are killed by predators, who, acting like phagocytes, target and eat individual fish programmed for death. Spawning or environmental stress, such as extremes of temperature, are common triggers that push weaker fish over the edge and into the mouths of predators.
For smaller species, mature fish can be swallowed whole by predators. But for larger fish, no other animal can swallow them whole. This is where sharks come in: because sharks can tear apart and eat animals of their own size or larger, they are the most efficient large animal recyclers in the sea.
The First Air-breathing fish eaters – 225 million years ago
Almost 200 million years after fish first appeared in the sea, a mass extinction episode (the ‘end-Permian event’) eliminated most of them, along with much other sea life. The ocean became severely oxygen-drained (or ‘anoxic’) at this time, effectively reverting to its earlier condition. The original transformation of the ocean from an anoxic bacterial dead zone to an oxygen-rich, animal supporting environment was a long and gradual process, and one that was aided by the animals’ use of antiseptic, oxygen-conserving methods to modify their environment.
Shallow seas and surface water, areas where plants grow, became oxygenated first, and this is where animal life first appeared. But the great mass of anoxic bottom water long remained a threat to animals, as it could rise up and kill them with a whim of the weather. The shifting boundary between the old order and the new, between the dead zone and the domain of animals, must have lasted for a long time, and this environmental reality doubtless helped shape the evolution of sea animals. Animals eventually made successful inroads into virtually the entire ocean, as they ultimately swam everywhere.
With the original success of animals, bacteria were not eliminated from the sea, but they did retreat to a relatively subdued position, although remaining a dangerous force ready to take advantage of any opening, any opportunity for re-advancement of the dead zone. Bacteria took this opportunity during the end-Permian mass animal extinction and the dead zone expanded. But following the extinction event, fish made a successful comeback and the dead zone was pushed back again.
Reptiles had evolved on land by this time, and they gave rise to ichthyosaurs, dolphin-sized sea animals that ate fish. With huge eyes, ichthyosaurs could hunt in deep, low-light regions, and, by virtue of their breathing air, they could also hunt in low-oxygen waters. By eating dead or dying suffocated fish, ichthyosaurs could help ‘put out the fire’ of a potentially spreading bacterial dead zone more effectively than other fish could. The Triassic tag team, big fish and ichthyosaurs together, seems to have been stronger and more capable than the earlier fish only predator group in ultimately gaining animal control over the early dead zone.
Air-breathing fish predators have lived in the ocean ever since the appearance of the ichthyosaurs, and ocean anoxia on the scale of the end-Permian extinction has never occurred again. Air-breathing predators seem to provide a form of insurance against bacterial uprisings in the sea.
The First Birds – 195 Million Years Ago
Large flying reptiles and toothed birds next joined the ranks of the fish eaters. These were the first fish predators that were linked to land, because their young were not born in the water (as young ichthyosaurs were).
At this time, plant and animal life was gaining momentum on land, and the resulting fertilizer-rich runoff may have posed a bacterial threat in estuaries. If a heavy dose of plant fertilizer stimulates excessive plant growth in a waterway, beyond what the resident web of animals can consume, the result can be rotting vegetation and anoxic dead zone formation. Additional air-breathing ocean predators hanging near shore during this evolutionary phase may have been beneficial in protecting marine animal life in estuaries from run-off triggered dead zones.
Fish, sharks and ichthyosaurs continued to thrive after the appearance of the birds. Rather than ‘competition,’ the birds might better be described as ‘reinforcements’ for the existing predator group. The diversification of fish predators, including strong air-breathing components, seems to have worked to enhance environmental conditions and continue to expand options for fish and other ocean animals. The positive feedback cycle of animal life still forged ahead.
First Whales, Modern Birds – 55 Million Years Ago
A second major mass-extinction event occurred 65 Million Years Ago. Many species including dinosaurs and all other sea reptiles (except some turtles) died out at this time, but the damage sustained by animal life overall was less severe than during the end-Permian event. Birds, fish and sharks survived the crisis. Soon (geologically speaking) whales evolved as the newest air-breathing fish predators (55 million years ago).
Modern birds and whales brought a new twist: they were warm-blooded. With faster metabolism, these fish predators ate more food and cycled nutrients more quickly than cold-blooded animals.
The second major extinction event, like the earlier one, was followed by a time when carbon dioxide levels were higher and oxygen levels were lower than previously, in both the atmosphere and in the sea. This change was eventually reversed, however, as it has been on other similar occasions in the history of life on earth. As animal life regained strength after the mass-extinction episode, and it again worked to accelerate plant growth, carbon dioxide was again drawn down from the air and oxygen levels rose in the sea.
Marine animals actively helped to lower the carbon dioxide content of the atmosphere and increase the oxygen content of the ocean, to the extent that they accelerated nutrient cycling and plant growth.
Today – No Big Fish
Fish and their predators are subdued today. The living biomass of sharks and other large fish is estimated to have fallen below 10% of original levels. Some have been driven to extinction. Really big specimens of any fish species have become very rare, and there are fewer small fish. Numbers of whales and seabirds are far below former levels, while seals have made only a partial recent recovery after near eradication by humans.
This great loss of animal life has been accompanied by a lowering of food production in the ocean. This can be seen in the increasingly poor condition of fish as they grow to larger sizes. Mature fish become spent today much more quickly than they were in the past.
Consider cod in Atlantic Canada, a fish that once grew to be a formidable predator itself at 6 feet long, 200 pounds, and living 40 or 50 years. Today, virtually all cod die before age 7. This is occurring with no human cod fishery. The size trap for cod has been set much lower than before, now at less than two feet long. Cod that approach this size become weak and emaciated and are killed by natural predators. The surviving natural predators are mostly seals, that now try to eat bigger spent cod in addition to thinning the numbers of small cod as was their traditional role. Less effective than sharks in eating bigger fish, seals often manage only to bite out the bellies from spent cod.
Today’s picture is of an AIDS-like syndrome affecting the ‘ocean animal organism’ because bacteria-fighting phagocytes/predators have been massively lost. Bacterial counts are rising in seawater, and bacterial and parasitic health problems are increasingly affecting marine animals. Dead zones, anoxic pockets of seawater, are spreading in many places.
Another classic sign of AIDS is emaciation. Generalized emaciation of the ocean animal component is seen in widespread failure of fish to grow as well as they did previously. Starvation of seabirds and marine mammals is also increasing.
The most drastic change is the disappearance of big fish, the original mainstay of ocean fish predators in the sea. The lowered general food supply also affects plankton-feeders, as tiny animal plankton counts (zooplankton) have fallen and their predators, including plankton-feeding fish and ancient invertebrates such as barnacles, snails and corals, also decline.
Advice to Management: look at the big picture
Ocean animals cannot be ‘protected’ or ‘sustainably managed’ one species at a time, or one chunk of ocean at a time, because all are parts of an interdependent whole. And that whole has been badly damaged and is now stretched very thin due to massive removal of sea animal life by humans. Animals now risk suffering major losses to bacteria.
Healthy sea animal life has an atmospheric carbon-dioxide lowering impact, although science has not acknowledged this. That is because scientists currently use an ocean model that considers the fertilization of ocean plants to be controlled only by the process of bacterial decomposition and ocean currents, plus nutrient cycling by tiny animals at the surface. Unfortunately, this describes the fertility pattern of the Precambrian sea, but it does not describe the workings of the modern ocean, because the model excludes the fertility boosting effect of all animals that evolved since the Precambrian era. As a result, the currently accepted model fails to predict that the ocean carbon balance can be affected by removing sea animals The model needs fixing, and the implications of this are enormous.
Techno-fixes for elevated atmospheric carbon dioxide are now being proposed whereby humans add artificial fertilizers to the ocean surface to accelerate the carbon dioxide uptake by plants. Also suggested are human “carbon sequestration” projects that aim to sink condensed atmospheric carbon dioxide into the deep ocean, in hopes of holding it away from the atmosphere. However, the safest and most reliable means to these ends is for humans to allow marine animal life to regenerate and reassert itself in the ocean. This will become obvious once the model is fixed.
Each time the web of ocean animals has suffered a major set-back, carbon dioxide has accumulated in the atmosphere, but on each occasion the extra carbon has been removed as sea animals regained strength. There is evidence not only of this occurring in the distant past, but this process seems also to have happened briefly during the twentieth century.
It will be best if the atmospheric benefit of marine animal life is realized before modern, highly efficient nutrient cyclers like whales and seals disappear, because any potential sea animal recovery will be significantly delayed if nature must first evolve new large predators.
See also: The Precambrian ocean productivity model - why it does not work today
copyright Debbie MacKenzie,
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