Humans Have Broken One of The Natural Power Laws Governing Earth's Oceans

Similar to planetary and molecular systems, mathematical laws are also possible that can accurately describe and permit for predictions in chaotically-dynamic ecosystems - if we zoom in enough.
Humans are having such a negative impact on the planet's life, that even natural universalities are being thrown into chaos.

Ryan Heneghan, a marine ecologist at the Queensland University of Technology said that humans have had a greater impact on the ocean than simply capturing fish.

"It seems we have broken the size spectrum, one of the largest power laws distributions known in the natural world."

The power law can be used in biology to describe many things, including patterns of neural activity and foraging trips of different species. It is when two quantities, regardless of their starting points, change in proportion to one another.

The two quantities in the above example are the body size and abundance of a specific type of power law. It was first described by Raymond W. Sheldon in 1972. The smaller they are, the fewer individuals in a given species size group.

Krill is 12 orders of magnitudes smaller than tuna and 12 orders of magnitudes larger than tuna. Hypothetically, all of the tuna flesh (tuna biomass) in the world is approximately the same (to within the same orders of magnitude at most) as all of the krill biomass.

Scientists had not tested this natural scaling pattern in the aquatic environment since 1972 when it was first proposed. This pattern was true for all species, from marine plankton to freshwater fish. The biomass of smaller species was approximately equal to that of the larger species.

Ian Hatton, Max Planck Institute ecologist and his colleagues looked at whether this law also captures what is happening globally.

Hatton says that comparing organisms that span bacteria and whales can be difficult because of their vast scale differences.

"The ratio between their masses and that of a human being is equal to that of the entire Earth." From more than 200,000 global water samples, we estimated organisms at the low end of the scale. However, larger marine life required entirely different methods.

The team used historical data to confirm that the Sheldon spectrum was consistent with this relationship for pre-industrial oceanic conditions (pre-1850). Over 12 types of sea life (including bacteria, algae and fish) there was roughly equal biomass in all sizes of organisms.

Eric Galbraith, McGill University geoscientist, says that it was a surprise to find that each class of order of magnitude contains around 1 gigaton biomass worldwide.

(Ian Hatton et al, Science Advances, 2021)

Hatton and his team explored possible explanations, including the limitations imposed by predator-prey interactions and metabolism. Many of these factors can also be correlated with organism size. These factors are speculation.

Galbraith said, "The fact that marine wildlife is equally distributed across different sizes is amazing." We don't know why this should be so - why can't there be more small than large items? Or an ideal size in the middle? The results show how little we know about the ecosystem in that way.

Two exceptions to this rule were found at the extremes of both the size scales. Bacteria was much more plentiful than predicted by the law, while whales were far less. It is still a mystery why.

These findings were then compared to data and samples from the present. The power law was still generally applicable, but there was a marked disruption in its pattern with larger organisms.

The team stated that "Human impact appears to have significantly reduced the upper one-third" of the spectrum in their paper. "Humans are not only replacing the ocean's top predators, but have fundamentally altered the flow and energy of the ecosystem through the cumulative effect of the last two centuries."

(Ian Hatton et al, Science Advances, 2021)

The team discovered that fishes make up less than 3% of human food intake annually, but we have reduced marine mammal biomass by 60% since the 1800s. Even worse is the situation for Earth's largest living creatures - historic hunting has resulted in a 90% reduction of whales.

Galbraith points out that this really highlights the inefficiency and wastefulness of industrial fishing. The current strategies we use are wasting a lot more biomass and the energy that it contains than they actually consume. We have not replaced the importance of biomass, even though it is now the largest vertebrate species in terms of biomass.

The ocean's largest species groups have lost around 2.7 gigatonnes of their biomass, while humans account for around 0.4 gigatonnes. The team stated that further research is required to understand the impact of this huge loss in biomass on the oceans.

Galbraith states, "The good news here is that we can reverse this imbalance by decreasing the number of fishing vessels around the globe." "Reducing overfishing can also make fisheries more sustainable and profitable - it's possible to win-win if we get our act together."

Their research was published by Science Advances.