Why Size Matters – How the Loss of the Ocean’s Megafauna is Affecting Our Ecosystems
Heracles, better known by his Roman name Hercules, is one of the most famous characters of Greek mythology. An illegitimate child of the Greek God Zeus, Heracles was the source of jealousy for Zeus’s legitimate wife Hera, hence his mother’s naming him Heracles, which translates to “Hera’s glory”. Hera remained unmoved and in the red mist of anger, tricked Heracles into killing his wife and children, a crime for which his punishment became known as the 12 labours of Heracles.
Heracles’ 12 labours, were in essence, ridding the Greek universe of some of its most fearsome creatures such as lions, hydras, boars and bulls. I will save sharing more details because I can easily get lost in the delightful absurdity of Greek mythology. However, in modern terms, these would be creatures, or animals that we would call megafauna.
Megafauna are the planet’s largest animals. The term generally refers to vertebrates: herbivores weighing over 1,000 kilograms (2,200 pounds) and carnivores weighing over 100 kilograms (220 pounds). The largest terrestrial herbivore on the planet today is the African elephant; an average adult weighing around 5,500 kg (12,000 pounds). The largest terrestrial carnivore is the polar bear; an average adult weighing around 500 kg (1,100 pounds).The largest animal alive, is a marine mammal, the Antarctic blue whale with adults weighing up to 181,500 kilograms (over 400,000 pounds) and reaching 30 meters (98 feet) in length1.
Even after his 12 labours were finished, Heracles was still tasked with removing these beasts from the Earth. My theory is that he just hasn’t gotten to the likes of Blue whales, sharks, orcas, elephants, giraffes and rhinoceroses just yet. He did do an efficient job with the dinosaurs however (what asteroid?). Indeed, the majority of megafauna that once traversed the terra firma now reside below it or in books and memories. The various theories as to their demise exist but I know who I blame, looking at you “Hera’s glory”.
On a serious note, the loss of megafauna does have some trickle-down effects on the ecosystems they are or once were a part of. I use the term trickle down intentionally as one of the main consequences of loss of megafauna is the loss of mega manure.
Phosphorus, normally one of the limiting nutrients in any ecosystem, was once spread, to great effect, by megafauna, through one of the most abundant media, faeces or “poop”. Through this medium, mammoths, mastodons and giant sloths were once extremely effective at fertilizing the soil. Their demise has been accompanied by an 8 percent drop in natural fertilization by poop since the last ice age2.
The ocean is no different as ‘megapoop’ levels have also shown a decrease. Whales, one of the major sources of nutrients, feed deep in the ocean, but defecate their nutrient-rich waste in shallower water. Since megafauna usually have much larger ranges, their nutrients are spread between ecosystems over a wider range of the sea floor. They tend to perform long migrations, linking ecosystems that would otherwise never be connected. The phosphorus from megafauna serves as an important fertilizer for phytoplankton- tiny marine plants that form the base of the marine food web and absorb large amounts of carbon dioxide. Phytoplankton are also an important source of carbon capture, estimated to sequester 37 billion tonnes of carbon dioxide each year3.
Apart from plankton, megafauna themselves are carbon sinks as their bodies transport large amounts of organic material to the seafloor upon their demise. They also function as indicators of a healthy ecosystem. Unsurprisingly, all is not well in the marine megafauna megaverse.
Marine megafauna such as seabirds, marine turtles, marine mammals, sharks and rays are all in danger and not just from Heracles but from very real, non-mythical mega problems in the form of anthropogenic activities.
Gill nets (and drift nets in particular) have emerged as a primary concern for marine biodiversity because they results in a high degree of mortality of megafauna globally. Whales, dolphins and porpoises, known collectively as cetaceans, are especially vulnerable to incidental capture (bycatch), vessel collision, and pollution-related threats. For the Indian Ocean, estimates of annual catch in tuna gill net fisheries include 100,000 cetaceans, 97,000 tonnes of elasmobranchs (sharks, rays, skates and sawfish) and 29,500 sea turtles 4.
These numbers are concerning, especially when considering the behavioural and life-history traits of megafauna. They have long life spans and take a long time to breed, which makes even small increases in mortality more significant as their populations are vulnerable to decline.
Scientific studies have shown that loss of megafaunal populations causes direct and indirect effects on other species and ecosystem functions5. In many instances, megafaunal extinction will cause disproportionate ecological disruption relative to the loss of other smaller animals. Most megafauna are top predators, helping to keep ecosystems in balance by controlling populations of smaller predators and herbivores. Another of the many reasons why loss of megafauna is of urgent concern.
Megafauna need immediate attention, not unlike many other species. This is not a competition as indeed the environment and planet writ large is in need of our attention. This is nothing ground – breaking as the conservation drum has been beating loudly for decades, a drum beat that is only becoming louder and faster.
While large creatures can appear fearsome and warrant stories of great mythological adventures, they are irreplaceable to a healthy ecosystem and a functioning planet. Our battle today is not to rid the world of these fantastic beasts, but to protect them from the scourge of climate change and the indiscriminate practices that place their lives at risk. Heracles was tasked with twelve labours as a punishment for his crimes in a time when gigantic beasts were a danger to mankind. Now our roles have been reversed as mankind poses a much bigger threat to the invaluable guardians of the ecosystems, our precious megafauna. Protecting megafauna will not only affect these species in particular, but will have an umbrella effect on the ecosystems they depend on as well as those below them on the food chain.
To quote physician and anthropologist Paul Farmer, “The idea that some lives matter less is the root of all that’s wrong with the world.” From microbes to megafauna, the preservation of all of earth’s life, all creatures great and small, is imperative to a healthy planet.
For more information please see the links below
1. https://greentumble.com/what-is-megafauna
2. https://www.pnas.org/doi/abs/10.1073/pnas.1502549112
3. https://www.ox.ac.uk/news/2022-03-03-large-mammals-can-help-climate-change-mitigation-and-adaptation
4. https://www.sciencedirect.com/science/article/abs/pii/S0278434318304448
5. https://academic.oup.com/bioscience/article/67/3/197/2900177
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Author: Mr. Attish Kanhai, Research Officer;
Photograph: Marine Myths Measured – Marine Megafauna;
Image Credit and Courtesy: National Geographic.