Animals control the health of the sea: it’s why tuna are much better off in the sea

I’ve been asked, is the ocean more important than land? This really depends on your context (as I discussed in this previous blog “Is the Ocean or Land more Important?“). Overall though, animals control the health of the sea and we can’t live without the land and ocean operating together. And when it comes to fish like tuna, we find the ocean can’t exist without them, at least not in a way that supports human or other animal life. This means that the key to restoring tuna populations is not to catch fewer but to restore all the other wildlife in the ocean.

Is the ocean different to land?

On first appearances, it would seem marine vertebrates function(Of an ecosystem). A subset of ecosystem processes and structures, where the ecosystem does something that provides an ecosystem service of value to people. More more significantly in the ocean than their terrestrial counterparts do, on land. This has led many scientists working on land or ocean, to think the two systems are different. I don’t believe this.

I think this common opinion arises from an observation bias, based on two things:

First, compared to land, oceans still have intact megafaunaThe largest animals that represent the top of the trophic pyramid. These are the final building blocks in ecosystem structures for maximum entropy production. Megafauna can be measured at any spatial scale. The largest animal that ever lived on Earth is the Blue Whale. In a grassland, spiders could be considered megafauna The term is generally reserved for animals larger More like whales and dolphins.

At least up until very recently, humans weren’t exploiting the sea. Most land-based megafauna went extinct in the Pleistocene, 30,000 or more years ago. On land, we’re not seeing anything near to intact ecosystemsHow ecosystems function An ecosystem is a community of lifeforms that interact in such an optimal way that how ecosystems function best, is when all components (including humans and other animals) can persist and live alongside each other for the longest time possible. Ecosystems are fuelled by the energy created by plants (primary producers) that convert the Sun's heat energy More. It’s like comparing apples and oranges … or more accurately, comparing an apple on a tree, to a spent apple core on the ground.  

Second, marine animals are more visible than land animals.

On land “we can’t see the animals for the trees”. We underestimate the importance of land animals in ecosystem processes because they are concealed by vegetation and many wild animal populations have already declined massively.

In the ocean, plants are substituted for invisible micro-fauna like marine algae and cyanobacteriaAn early form of life that still exist today and are super-abundant in our oceans. They are similar to bacteria and are not algae but are capable of photosynthesis. More. Incredibly, bacteria make up 78% of the world’s total carbon-based biomassThe weight of living organisms. Biomass can be measured in relation to the amount of carbon, the dry weight (with all moisture removed) or living weight. In general it can be used to describe the volume of energy that is contained inside systems, as the size of animals relates to their metabolism and therefore, how much energy they contain and More [1] and are the most abundant organisms in the ocean. Yet we can see through them, so fish and other marine animals appear more visible and significant to us.

Animals control the health of the sea

There is an advantage to understanding how the ocean works. It literally gives us a clearer insight into how animals control the health of the sea. Wildlife is essential to the integrity of any ecosystems, land or sea. In the ocean, we are observing something closer to how it should be working and without too much of our own observation bias.

The ocean is deep and has many different layers. However, things are significant for humans, only as a result of the great oxygenation event, which happened about two billion years ago. This was when cyanobacteria evolved a silica-based sunscreen, protecting their fragile DNA from the Sun’s ultraviolet radiation. This set into motion the oxygenation of our atmosphere and the whole course of evolution that led to land plants, land animals and ultimately, us.

If we want to protect our future, we have to be thinking about rebuilding populations of fish, seabirds, marine mammals and so on. Because, from a human survival perspective, the domain we live in, is the one shared with animals most like us, the ones that are also oxygen-breathing and connect us to the nutrientA substance that contains the raw materials for life. At a chemical level, these are contained inside compounds that are absorbed into the body and essential energy-containing molecules are extracted, so that energy can be transformed into other chemical processes that use the energy for living. More and climate cycles that provide mutual food security.

The magnitude of animal impact on the sea

Just in the last few years, there has been a flurry of studies that describe the magnitude of effect this animal impactWhat is Animal Impact? Without wildlife, Earth would not be habitable for humans, because it's animals that stabilise ecosystems. It’s a fundamental law of nature that animals (and humans) exist because we are the most likely lifeforms to minimise environmental chaos. Animal impact, therefore, is a measure of how much all wildlife is collectively responsible for creating a habitable Earth. The More on Earth’s biodiversityWhat is the definition of biodiversity? When we ask, what is the definition of biodiversity? It depends on what we want to do with it. The term is widely and commonly misused, leading to significant misinterpretation of the importance of how animals function on Earth and why they matter a great deal, to human survival. Here I will try to More. One published recently in the Journal of Limnology and Oceanography [2] quantifies the animal impact of marine fish, finding that they are responsible for 16% of the carbon cycle. Marine vertebrates as a whole, are responsible for up to a third of all physical ocean mixing [3].

It’s not just the magnitude of the impact of animals to control the health of the sea though, it’s where and when it happens, that matters most of all. Animals have been sampling the environment for literally millions of years. They are a ‘remote sensing’ resource bigger and more accurate than anything scientists can replicate. This is why they are our greatest asset when it comes to nature-based solutions.

Animals can pinpoint exactly where and when it’s most effective to apply their trade. Based on their sampling efforts, animals have learned to transfer(of nutrients) the thing that sets animals apart from plants, is that they can move. Some of the biggest migrations on Earth every day, are the movement of insects like caterpillars, from the stem of a plant to a leaf and back, before turning into butterflies and transferring the energy elsewhere. Large-scale migration of grazing animals and migratory songbirds moves More, amplifyAmplification (of nutrients and energy). Animals consume plants and other animals and in doing so, reintroduce important energy-containing nutrients back into the environment, at even higher concentrations and in patches. Amplification of energy is driven by migration and happens at every scale, from insects moving daily in and out of your vegetable patch, to African wildebeest herds and the seasonal More and concentrate nutrientsEnergy and nutrients are the same thing. Plants capture energy from the Sun and store it in chemicals, via the process of photosynthesis. The excess greenery and waste that plants create, contain chemicals that animals can eat, in order to build their own bodies and reproduce. When a chemical is used this way, we call it a nutrient. As we More in precisely the right places, to minimise ecosystem collapse.

This way, animals work to their own survival advantage, while maximising the success of other resource dependent animals, that are doing the same. This is the very definition of biodiversity. It’s what animals do, not what ecosystems are, that matters.

Our fisheries resources depend on the health of the sea

Some of our greatest resources depend on animals controlling the health of the sea. The Coral Triangle, for instance, provides direct food security for 250 million people. However, the health of these coastal and marine ecosystems are also essential for global climate and food. Yet, 96% of fishers working in small-scale fisheries, overwhelmingly in developing countries, are some of the least-supported by fisheries grants and among the poorest people on Earth [4]. All our futures are entwined with protecting the living, animal-dominated ecosystems that sustain our most powerful global life support systems.

It seems to me, that it’s more apparent in the oceans, than anywhere else, that restoring native animal populations is essential to our prosperity and that this means restoring entire food chains that support those species of greatest importance to us. For example, restoring global tuna populations is clearly essential for food and climate security but can’t be done, without a supporting cast of other wildlife, as ecosystem stability cannot be upheld by any species out of proportion with the rest of the food chainA single thread in a food web illustrating the chain of animals that eat each other. At the base of the food chain are small high-energy (fast metabolism) animals and at the other end large low metabolism animals. An example would be whales eating krill that eat plankton that eat algae. Or lions that eat gazelles that eat grass. More.

The good news is, the by-product of conservationWhy is animal conservation important? Animal conservation is important, because animals are the only mechanism to create biodiversity, which is the mechanism that creates a habitable planet for humans. Without animals, the energy from today’s plants (algae, trees, flowers etc) will eventually reach the atmosphere and ocean, much of it as carbon. The quantity of this plant-based waste is so More is the greater capacity to absorb carbon, more stable climate and more predictable and ecologically-sustainable fisheries, plus food security for millions of people. Not a bad result to be achieved from just rebuilding wildlife populations, is it?

Now what we need is recognition that restoring wild animal populations everywhere, and that this learning from the ocean, is directly transferrable to land-based ecosystems as well.

1. Bar-On, Y., R. Phillips, and R. Milo, The biomass distribution on Earth. Proceedings of the National Academy of Sciences, 2018. 115: p. 201711842.
2. Saba, G.K., Burd, A.B., Dunne, J.P., Hernández‐León, S., Martin, A.H., Rose, K.A., Salisbury, J., Steinberg, D.K., Trueman, C.N., Wilson, R.W. and Wilson, S.E. (2021), Toward a better understanding of fish‐based contribution to ocean carbon fluxIt's not the amount of energy in a system that makes it possible for us to feed ourselves, it's the energy flux (the rate at which energy flows). For example, you can have a full water tank in your house but it's hardly any use to you, unless it's able to flow out of taps. This simple logic, proves why More. Limnol Oceanogr. https://doi.org/10.1002/lno.11709
3. Dewar, W., et al., Does the marine biosphere mix the ocean? Journal of Marine Research, 2006. 64.
4. Development, I.I.f.E.a. Action for an ocean for all:  Rethinking the blue economy to be inclusive, sustainable, fair and for everyone   2019 [last accessed, 13 April 2020].