by simon
Why are the oceans important? The importance of wildlife.

The importance of the oceans, their wildlife and ecosystems

The land and oceans are part of one system: Earth. So when we ask, why are the oceans important? We’re asking about our own future. Life began in the ocean billions of years before the first plants or animals colonised land. Oceans regulate the state of our atmosphere because they are 99 per cent of the volume of living space for animals and wildlife is the mechanism that drives stability.

Climate change has always been the symptom of biodiversity loss … that’s to say, the breakdown of the complex connectivity between lifeforms that allows Earth to flex in response to changing conditions. Ocean wildlife has, for the large part, acted as a buffer against the most catastrophic effects and since about fifty million years ago, has kept our climate quite stable.

Industrial fishing only happened recently in our planet’s history and this reduction in the abundance of wildlife represents our greatest challenge for survival.

Below you will find a range of articles designed to inspire an understanding of the magnitude of animal impact on our oceans.

What’s more important, the ocean or the land?

The importance we bestow on the land is anthropocentric because we live there. It’s naturally important to us that we protect it. Nonetheless, if life in the ocean dies, we suffer irreversible changes to land-based ecosystems and climate.

In this article, we take a look at many of the ways that land and oceans are linked together.

The answer to the question, ‘why are the oceans important’, is that we live on the land but the oceans regulate Earth’s temperature. The oceans are equally vital to the land we live on.

Latest posts about why the oceans are important

Wildlife Conservation Artwork.Hammerhead Shark over coral reef, Drawing by Simon Mustoe
How do you reduce shark attacks?
Hammerhead sharks have suffered some of the worse declines of any shark. They represent something quite unique. Traditionally, millions would have paraded between the shallows, like pictured here in the Banda Sea, to the deepest oxygen-less depths of the global oceans. We know virtually nothing about what they used to do but their role in the transportation, amplification and concentration of nutrients would have been staggering, not to mention the physical mixing effect the pods would have had on the surface layers. Today we are only observing a fragment of the power these animals had over ecosystems they helped enrich over millions of years and we have no idea what a future without them will be like for humans.

Ecology is a complex science and so often, our simplest assumptions about how things work, don’t hold up in practice. Take sharks for example. How do you reduce shark attacks? We imagine more sharks means more attacks but in order to have fewer shark attacks, we probably need more sharks. We know other large marine predators like billfish (marlin, sailfish) are commonest near our coasts during El Niño. This is when warm water from the Eastern Tropical Pacific dominates the ocean’s top layer and a strengthened East Australian current pushes nutrient-rich warm-water deeper. The depth of this mixing layer determines how productively animals can feed. It takes more energy to reach deeper food.

How do you reduce shark attacks?
Warmer surface water pushes the nutrient-filled mixed layer deeper, meaning sharks and their prey, swim closer to the coast, where upwellings physically push the nutrients to the surface. Predators do well and prey are concentrated in hotspots.
How do you reduce shark attacks?
Cooler surface water means the nutrient-filled mixed layer is shallow. With a lot of food about, animals spread out across the ocean but it means density of prey is lower, which means a bumper time for prey but harder for predators to make a living.

How do mobile marine animals find food?

During these times, mobile animals like sharks and billfish, swim up against coastlines or islands, where the mixing layer is lifted closer to the surface, after it collides with the land (above, left). El Niño and La Niña are two opposites of a climate cycle that swings back and forth like a pendulum.

In La Niña, the surface is less warm, so the mixing layer is shallower (above, right). This doesn’t directly help the predators either. In these conditions, there is more surface nutrient, so preferred food becomes thinly spread-out across the ocean, also making it a struggle to find enough to eat. Predators travel longer distances offshore in search of ‘hotspots’ and can’t gather together and breed.

This creates a contradictory situation.

Seabirds for example, have bumper breeding years during El Niño, when overall, there is least available (deeper) surface nutrient. This is because extremely high-energy prey, such as filter-feeding anchovy are also forced nearer to islands where the mixing layer is shallow and where the birds breed. It becomes a lot easier for seabirds to raise chicks, when there is an abundance of prey in adjacent waters. Sharks benefit the same way, as they are feeding in the same food chain.

Predators and prey cycle together

Already you can see how an assumption about quantity of food versus quantity of animals can be the opposite of what we might expect. It’s not as simple as saying, more food equals more animals or more predators equals fewer prey.

Marine predators benefit from periods when there is less surface productivity … but only as long as there are plentiful periods in between. This boom-bust cycle, where animals expand and then contract geographically, is necessary to allow recovery of fish populations. Fluctuations in the numbers of predator and prey can then track each other closely over the long-term (see the example, below). The patterns are predictable.

Predprey-graph.png
Canadian Lynx and Snowshoe Hare populations over 90 years, from MacLulich, (1937) [1] showing how predator and prey populations follow the same pattern.

Now imagine the peaks and troughs in these cycles as the amount of energy the system is absorbing. That’s it’s biodiversity value and when the peaks are highest, there are more fish, more stable ecosystems and a robust and predictable ocean and atmospheric climate.

Removal of predators destabilises ecosystems

When we kill sharks through overfishing, bycatch, or in nets and drumlines, in an effort to reduce shark attacks, we make the situation worse, not better. Our efforts are counter-effective as we suppress the productivity of the ecosystem and the natural cyclical patterns break down.

Remember, these animals are selectively manipulating ecosystem processes over massive areas and through sheer mobility and abundance, doing things at a scale we cannot possibly comprehend or replace. The impact of animals like sharks is more awesome than anything science is currently able to describe–mostly because the sharks are gone, so there is nothing left to measure!

More shark attacks during La Niña definitely doesn’t mean there are more sharks. Fewer sharks should mean fewer attacks but that isn’t happening. The only other explanation, and the one that’s most likely from an ecosystem perspective, is that overall shark distribution has changed, forcing a higher proportion of remaining sharks into some coastal areas. There are also countless examples of where animals move closer to areas of human occupation, as these tend to be the last vestiges of habitat, for all animals, as we deplete other areas.

Proving exactly how this works would be virtually impossible but what we do know, is that the extinction of predators leads to a more chaotic system. We move from the rhythm of a steady stable-state ecosystem to one that doesn’t conform to expectations, where neither other animals, or human fisheries, can depend on where and when to find food.

Chaos and disorder is not good for sharks or people

It’s this move towards disorder that explains how removing top predators reduces ecosystem richness and predictability. We are looking in the wrong place for an explanation of what is happening to our planet. We need to learn to think in terms of order <-> chaos, rather than in terms of more <-> fewer animals.

The impact of animals like sharks is more awesome than anything science is currently able to describe–mostly because the sharks are gone, so there is nothing left to measure!

If you happen to live somewhere with an inherently higher-risk of shark attack, the risk may increase, when shark populations are destroyed elsewhere and overall ecosystem production has declined. You are observing an intermediate effect, where starving sharks move into coastal areas, desperate to find food, just like they would have during El Niño.

When you remove top predators from the ecosystem, it drives energy into lower levels of the food pyramid, to the advantage of animals like squid and jellyfish–this is not an alternative state, it’s a state of disorder that could take thousands of years to reset, once the predators are gone. This is already happening off West Africa and the Eastern Tropical Pacific and it’s collapsing whole fishing economies, threatening the livelihoods and food security of millions of people.

Sharks attacks is a sign of ecosystem stability collapse

This isn’t a situation confined to the poorest countries either. There are a litany of examples of fisheries collapse from the Grand Banks in Canada to the world’s entire stocks of the most commercially-valuable tuna. If you don’t think wealthy western societies depend on fish stocks, you’re very wrong. Even the final days of negotiating a Brexit deal for the UK in December 2019 were stalled by disagreements about fisheries allocation.

Squid and jellyfish not only compete against sharks, their smaller size and abundance, creates a lot more random waste and chaos – free surplus energy – that sharks would have stabilised. As we continue to deplete the ocean, we flatten the peaks and troughs in the natural predator-prey cycles (above) and this leads to animal populations redistributing, breaking the ocean-climate-linked cycles that would shield us from global warming and further warming the ocean.

Sharks, like any large animal, shield us against climate instability by regulating the excess energy in a system that is constantly bombarded by solar radiation.

The latest report in the journal Nature [2] finds that we have lost 71% of the world’s sharks and rays since the 1970s.

The decline of 18 different shark species from 1970 to 2018.

Why won’t killing all the sharks make things better?

Ultimately, if you kill all the sharks, you’ll have no shark attacks. That’s for sure. In the short term though, you’re going to increase shark attacks.

There can be no doubt that this catastrophic loss of top predators is already having a huge impact on our fisheries and food security. If you think the only good shark is a dead shark but you like eating seafood or going fishing, then you’re going to end up disappointed.

Sharks are essential for the stability of food chains. Without them, we tip the balance in favour of a system that competes with sharks–we push ecosystem energy down the food chain to levels below that which we humans can survive in. When you consider sharks eat many of the same fish that we like to eat, we’re cutting our nose off to spite our face … we’re removing the sharks that make it possible for us to have healthy fisheries.

Meanwhile, if you want to live somewhere with fewer shark attacks, you aren’t going to make things any better by killing them. At best, you’re going to increase the uncertainty of shark attack and at worst, you might increase the number of sharks in certain places.

As a society we need to start understanding the ecological significance of our actions and make decisions to rebuild wildlife populations before it’s too late.

The question we need to ask ourselves is, can we afford to live in a world without sharks? How do you reduce shark attacks? I think the answer is obvious. Rebuild a better environment for people and sharks.


Spotlight

Another new conservation frontier opens up as recreational fishermen call for shark culls due to ‘higher numbers’ of sharks. WA has suffered repeated marine heatwaves and collapse of ocean food chains are driving remaining sharks close to coasts. Killing more sharks isn’t the answer. Read more.


  1. MacLulich D A (1937) Fluctuations in the Number of the Varying Hare (Lepus americanus) (Univ. of Toronto Press, Toronto)
  2. Pacoureau, N., Rigby, C.L., Kyne, P.M. et al. Half a century of global decline in oceanic sharks and rays. Nature 589, 567–571 (2021). https://doi.org/10.1038/s41586-020-03173-9 https://www.nature.com/articles/s41586-020-03173-9

0 FacebookTwitterPinterestLinkedinRedditWhatsappEmail

This website uses cookies to improve your experience. We'll assume you're ok with this, but you can opt-out if you wish. Accept Read More