Text By Shatakshi Gawade
Photo: Public Domain/Flickr.
You and I, we are made of stardust! Carbon, the building block of all lifeforms on the planet, is formed from the debris of supernovae, and is found in the sun and other stars; carbon is also at the heart of the climate crisis. As the world (or at least the conscientious fragment) races to capture different forms of carbon, to minimise further saturation of the carbon-choked atmosphere, it’s just another day at the office for photosynthetic bacteria. Just like plants, these absorb and utilise carbon dioxide dissolved into the ocean from the atmosphere and release oxygen as a byproduct. They ‘scrub’ carbon from the atmosphere and add it to the food web, making the ocean a massive carbon sink. The miniscule photosynthetic bacterium is part of this mega carbon cycle that ensures carbon does not accumulate in the atmosphere.
The mesopelagic zone, which is also known by the more romantic-sounding name of ‘The Twilight Zone’, extends from 200 m. to 1,000 m. Despite the depth, however, some sunlight can still be detected here. The abundant mesopelagic fish that reside here, make up 95 per cent of all oceanic fish, weighing in at an astounding, estimated, 10 billion metric tonnes. These quirky little fish include lanternfish and blobfish, which live in the Arabian Sea, Mediterranean Sea and the north Atlantic. Their presence is much lower in the south Atlantic and polar seas.
Every night, in the safety of the dark, this colossal mass of fish migrate vertically to the surface where they eat photosynthetic bacteria, phytoplankton, and tiny plants, gathering up all the biomass – and thus carbon – near the surface. They then rush back to their depths to avoid daytime predators, transporting the carbon deeper within the ocean. This might well prove to be the largest daily migration of any lifeform on the planet! When these fish defecate or die and decompose, the carbon enters the deep ocean. This phenomenon is known as the ‘biological pump’. Excretions from fish amount to 16 per cent of all the carbon – about 1.5 billion metric tonnes every year – that sinks into the ocean’s top layers. All these processes, driven by mesopelagic fish are responsible for slowing global warming. Some studies estimate that without them, atmospheric CO2 levels would probably be 50 per cent greater.
Photo: Public Domain/Rawpixel.
Disturbingly, mesopelagic fish are being looked upon as an ‘unexploited resource’, to feed farm animals and for human consumption. Disturbances to this population of fish could risk the smooth functioning of the marine carbon biological pump. The oceans in which these key marine organisms live are outside national jurisdictions. This endangers their survival in the absence of any binding treaties. Recently, COP15 vowed to protect 30 per cent of the oceans (and 30 per cent of land) by 2030 – we must work with the youth of the world to pressure their elders to fulfill the promises they so publicly make, yet routinely and irresponsibly renege on.
COVID-19 demonstrated that a weakened immune system increases the chances of the viral infection turning fatal. The exact same logic applies to weakened ecosystems, and threatened species of the orders crocodilia (gharial, crocodile and alligators) and testudines (tortoises and turtles).
For an ecosystem to function, different animals and plants play specialized roles. This characteristic is known as functional diversity – the range of things an organism can do in an ecosystem or a community. Researchers found that for species of crocodilia and testudines that are already suffering at the hands of anthropogenic pressures such as pollution and habitat degradation, the loss of functional diversity is higher than it would have been in un-pressured circumstances. When compared with any other threat, the loss of habitat could double the loss of functional diversity. The study also found that if all ‘Critically Endangered’ species were to go extinct, 13 per cent of “unique life strategies would be lost” (a life strategy is how a creature uses its energy and available resources between growth, reproduction and survival). Further, if a species has unique life strategies (such as parental care among gharial by fathers), pollution, disease and local consumption would take a greater toll of them. They also found that species that have higher reproductive outputs, such as clutch sizes, were more susceptible to pollution.
Photo: Public Domain.
The higher threat to survival among crocodiles, tortoises and turtles is a danger to other species and the ecosystem, since these reptiles often influence the health of ecosystems by keeping prey populations in check, and by digging burrows which other animals use. In short, there is an urgent need to conserve and protect crocodilian and testudine species, for the wellbeing of entire ecosystems. The researchers also suggest incorporating functional diversity into conservation strategies so that local stakeholders can take customised actions.
By 1995, non-native species had decimated the population of Antiguan racers Alsophis antiguae, endemic to the twin-island country of Antigua and Barbuda, to an alarming level of a mere 50 individuals remaining on just one islet. Mongoose, which were introduced to control rats, feasted on these snakes and their prey (lizards). Once the alien species was cleared, the snake population bounced back, and there are now 1,100 Antiguan racers at four sites!
Photo: Public Domain/Rawpixel.
In the context of rewilding, that moment of deep diving into the Earth isn’t surprising any more! Elephants are keystone species and ecosystem engineers, shaping and maintaining habitats as they serenely pass through the forest or savannah. Their passage creates pathways for other animals and offers more space for new vegetation to flourish. In savannah grasslands, elephants, for instance, knock down trees, thus maintaining the grassland ecosystem. Even an elephant footprint can become a microhabitat – when the depression in the ground fills with water, it becomes a home for tadpoles and other organisms! Elephants also disperse seeds and actively cycle nutrients. As elephant populations continue to decline, it is vital to tackle threats to this species from global trade, and habitat loss. Researchers in Denmark even proposed that Asian elephants should be introduced near Copenhagen to bring back the benefits associated with megaherbivores! In Australia, some researchers suggested bringing elephants and rhinos to help control wildfires, as was observed in the Serengeti after the successful population restoration of the wildebeest. (This would be hopelessly ill advised!)
As crucial as elephants are, a study found that some smaller animals such as gazelles and impalas prefer elephant- (and giraffe-) free habitats. The complexity of such unintended consequences of restoring and reintroducing species must be kept in mind, since existing species may also be threatened with endangerment.
Photo: Public Domain/Biodiversity Heritage Library.
The Prosopis genus has species that are xerophytes – they can thrive in desert environments. But the baavlia tree (‘the mad one’, in the Marwari language) Prosopis juliflora was never meant to be in Rajasthan, or in the United Arab Emirates (UAE), where its consumption of groundwater has increased by a staggering 7,372 per cent between the years 1990 and 2019. As in the UAE, P. juliflora, a Mexican shrub, was introduced to ‘green’ the desert of western India. Since the colonial British introduced the plant in a bid to increase availability of firewood, the rampantly invasive, thorny plant had spread to over half a million hectares by the start of the 21st Century across India’s arid zones. It also proved to be a menace in Gujarat, where it eliminated Asia's largest grasslands. In Delhi, it occupied over 90 per cent of the Delhi ridge forest. While creating the Rao Jodha Desert Rock Park in Jodhpur, Pradip Krishen, the park’s architect and author of Trees of Delhi, had to use herbicides, compressor-driven tools, even dynamite, and finally the skills of local sandstone miners to eradicate the stubborn baavlia from the rocky land before he could rewild the park with native species.
On the other hand, there is a Prosopis species that made environmental history – the khejri tree Prosopis cineraria, which is a lifeline for the local community. In 1730 CE, 363 Bishnois led by Amrita Devi and her daughters were killed by the king’s men for refusing to let the trees be cut. Even today, this moderately sized, thorny evergreen tree plays a major role in the rural economy of Rajasthan, and is, not surprisingly, considered sacred. The slender pods of the tree are used to make local delicacies such as ker sangri, the leaves are used to feed cattle, and the wood is used for furniture. Some documentation reports that the wood was used to make flour during a famine in 1869. The tree also provides shelter, nourishment and hydration to wildlife. The hardy khejri tree, also known as the ‘tree of life’, is perfect for the desert climate, and essential to the ecosystem.
As the male Eurasian Bittern Botaurus stellaris, a thickset heron, steps cautiously through the reeds by the water in wetlands, he emits a deep, far-carrying boom, which sounds a lot like a computer glitch! The planet almost lost this bird in the late 19th Century, following hunting and draining of wetlands, causing the extinction of breeding bitterns in the wild in the U.K. Alarm bells were set off, and efforts made to restore wetlands by expanding reedbed networks and pools. The secretive bird’s population is gradually recovering in the U.K. thanks to concerted conservation and management projects.
Did you know that an oyster also has a tiny, beating heart? It does not, however, have either a head or a central nervous system, so if you are one of those that swallow it whole with a dash of lime, it may feel hurt that you’re eating it, but it may not feel the pain.
The oyster never lives alone, it prefers company. This two-shelled mollusc grows in large clusters on the sea bed. When the salinity and temperature are perfect, the male oyster releases millions of sperm into the ocean, which sets off other males in the vicinity. The females too play their part immaculately – they release bursts of eggs into the sperm-laden water. Incredibly, these floating sperms and eggs come together to form larvae, which begin their life by floating gently with the tide. In an act of community formation, the larvae eventually attach themselves to another oyster on the bed, sometimes miles from where its parents emitted it, to add to a vast structure known as an oyster reef.
Photo: Public Domain.
Oysters are of great importance to the ecosystem. They filter coastal waters. When the bivalves suck in water, they pull in nutrient-rich organic matter and release filtered water back into the ocean, thus preventing an excess of nutrients from triggering an algal bloom, which would have consumed oxygen and made the waters uninhabitable for marine life. An individual oyster can clean up to five litres of water per hour, removing organic and inorganic toxins and preventing a disruption of the ecosystem. Oyster reefs provide a habitat for skilletfish, toadfish, and blue crabs. Up on land, oyster reefs reduce natural and climate change-induced coastal erosion and flooding. Though oysters have been harvested for thousands of years as food and help maintain healthy fish populations, they had lost about 85 per cent of their historic extent globally by 2012. This was the result of development-related erosion, decline in water quality, wetland loss, and unsustainable harvesting. And so, predictably, oyster reef restoration has been taken up on a large scale to ensure that their ecosystem services can be sustained. One of the methods to restore oyster reefs involves laying out shells and rocks for them to grow on, in the hope that new oyster reefs establish themselves. So… the next time you pick up a shell from the beach, think twice!
Introducing and protecting predator species might seem like a death sentence for prey species. But nature wouldn’t kill the golden goose, so to speak – predators would obviously go extinct without prey.
But guess what? How a species of predator finds its prey can influence not just the prey population but also how much carbon is stored in the ecosystem!
Some spiders weave a web and wait for the prey to walk into it, while other spiders actively go hunting for food. Researchers found that when a sit-and-wait spider species was the dominant hunter, grasshoppers (the prey) chose carbon-rich grasses to give them energy for the increased number of encounters with their predators. Conversely, when an active spider such as a peacock spider or jumping spider was the dominant predator, there were fewer encounters between grasshoppers and the arachnids.
Photo: Public Domain/ArgonNational Laboratory.
This made the grasshoppers choose grasses with less carbon content, letting carbon-rich species thrive, inadvertently increasing the carbon storage capacity of the grassland. The researchers estimated that there is a difference of 41 per cent of soil carbon between the two scenarios.
Beavers are marvellous engineers – when they build log dams across streams, they enable the creation of wetlands as the water builds up. The dam not only creates a ‘beaver lodge’ for them to live in, but it also shapes habitats for both aquatic and terrestrial plants and animals such as salmon and mule deer. The retention of water also helps make the landscape more resilient to drought and fire. They also help enhance carbon sequestration in boreal and temperate forests, as organic matter sinks in the pools.
