Transcription
Today's video is sponsored by Klima. The deep sea can be a barren realm. With increasing depth, we find an exponential decline in biomass, which has driven creatures of the deep to adapt in weird and wonderful ways. Generally, these organisms must rely on marine snow as a source of food—a trickle of fecal pellets and dead organic material that drifts downwards from the surface waters where photosynthetic primary productivity is possible. Below 200 meters, levels of ambient light from the sun are too low for photosynthesis to occur, and at around 1,000 meters, aside from the infrequent twinkling of bioluminescence, the ocean is drowned in pure darkness.
[Music]
Without photosynthesis, the supply of scraps are all that remain to nourish any life.
[Music]
However, on the deep sea floor, there are important regions where primary production is possible via a different mechanism called chemosynthesis. These are the chemosynthetic oases of the deep sea, which represent some of the only locations on Earth where the ultimate source of energy for life is not sunlight, but the Earth itself. In this series of films, we'll delve into their formation and ecology, as well as the threats they face and the importance of stewardship for these fascinating environments.
[Music]
[Music]
[Music]
The process of chemosynthesis is similar to photosynthesis; both can be defined as the creation of organic matter from the fixation of inorganic carbon using energy. But what differs is the source of that energy. In parts of the deep sea, primary production is fueled by chemical energy rather than energy from the sun. But this can only take place at certain sea floor environments where the required chemicals are released into the water. The two main examples of such environments are hydrothermal vents and cold seeps. The former were only discovered in 1977 when scientists were exploring an oceanic spreading ridge near the Galapagos Islands. What they discovered was a hidden world that revolutionized our understanding of how and where life on Earth can exist.
[Music]
Since then, hundreds more vent fields have been discovered, often at depths of two kilometers or more, along Earth's convergent plate boundaries and at sea floor spreading regions where the oceanic crust is moving apart. One major site of high vent abundance is the East Pacific Rise, where the fast spreading rates have created vent fields dotted along the ridge tens of kilometers apart. In contrast, the vent fields of the much slower spreading Mid-Atlantic Ridge may be hundreds of kilometers apart.
[Music]
They form here because the rifting of tectonic plates creates fissures in the crust and allows hot magma from deep within the Earth to rise closer to the seabed. Upper parts of the sea floor are very permeable; cold seawater enters and percolates down through the crust where it becomes superheated and takes up minerals from the surrounding rocks. This mineral-rich fluid then jets back into the ocean at extremely high velocities and temperatures exceeding 400 degrees Celsius. As the fluids mix with cold seawater, the dissolved minerals precipitate out in smoke-like billows and build towering chimney structures on the sea floor.
[Music]
There are a few varieties of hydrothermal vent, characterized by the specific mineral content of the vent fluid. Black smokers emit the hottest, darkest plumes, forming chimneys over 50 meters tall with high levels of sulfides that precipitate on contact with the cold ocean to form the black smoke. In contrast, white smokers contain barium, calcium, and silicon. Other vents may be characterized simply by shimmering streams of water.
[Music]
Although the throat of vent chimneys can reach around 400 degrees Celsius, there is a very sharp temperature gradient between the fluid and the surrounding seawater across a distance of around 10 centimeters. Temperatures can drop from over 300 degrees to just 2 degrees Celsius. Most vent animals live at far cooler temperatures, but prokaryotic microbes, including forms of both archaea and bacteria, are able to tolerate fluids as hot as 122 degrees Celsius. Here they carry out chemosynthesis via a number of different pathways that depend on the specific conditions of their microenvironment and the chemicals that are present. Typically, they use energy stored in the chemical bonds of hydrogen sulfide and methane to create glucose from water and dissolved carbon dioxide. The result of this chemosynthetic primary productivity is the presence of vast assemblages of animal life concentrated at these regions.
[Music]
The supply of nutrients forms the basis of a food web for a diverse community of specialized organisms.
[Music]
An oasis of life in the deep.
[Music]
To understand just how significant these communities are, you only have to compare the life of hydrothermal vents with non-chemosynthetic deep-sea environments.
[Music]
Out on the abyssal plain, life is present but scattered; animals must spread out in order to stand a chance of gaining enough nutrients from marine snow to sustain themselves. But at the vents, the chimneys are encased with dense colonies of rust-colored snails, swarms of deep-sea shrimp, or expansive aggregations of ghostly white crabs competing for space on the rocks. Remarkably, these varied and abundant species are all sharing a single resource; they all rely on the chemosynthetic microbes as a source of food. Meaning vents are sites of significant interspecific competition—that is, competition between members of different species. Often, interspecific competition can lead to the extinction of one or more of the species competing. The species that is less suitably adapted may lose out on the resources it requires and become out-competed.
[Music]
The idea that in a stable ecosystem no two species can have exactly the same niche and stably coexist is known as the competitive exclusion principle.
[Music]
But when this doesn't lead to extinction, interspecific competition can instead cause specialization of the different animals. A phenomenon called resource partitioning occurs where species with overlapping fundamental niches evolve different adaptations. It allows the species to co-exist because there is less direct competition between them. This is what occurred at hydrothermal vents to make them so stable. The competing crabs, worms, and shrimps may all be in pursuit of the same resources, but they have developed very different ways of acquiring them.
[Music]
Squat lobsters and limpets graze the microbial mats that surround many of the chimneys. We also find suspension feeders like deep-sea mussels feeding on free-living microbes that are suspended in the water. Yeti crabs farm the bacteria in filamentous, hair-like colonies on their bodies, reducing the pressure on the crabs to compete for space with other species like shrimps.
[Music]
The crabs are able to move around and take the bacteria with them, with the microbes acting as epibionts, inhabiting their surface.
[Music]
Giant tube worms are sessile, meaning they are fixed in one place and cannot move; their competitive advantage arises from their ability to form an endosymbiotic relationship with the microbes. They store them within their tubes, effectively holding them captive and benefiting from the nutrients they produce. The worms take up hydrogen sulfide and other chemicals from the vent fluids in order to feed the bacteria; in return, the bacteria provide the carbon that the tube worms require in order to live. It is also thought that the bacteria benefit by being sheltered within the tube worms and are therefore protected from predatory grazers like limpets and crabs. Another denizen of deep-sea vents, the Pompeii worm, farms bacterial colonies in a similar fashion to yeti crabs, but its higher thermal tolerance allows it to inhabit locations on the vent structures that are far hotter than those that the crabs can endure. Here they dwell within U-shaped tubes which can reach temperatures up to 80 degrees Celsius.
[Music]
Thus, much like we see with creatures of the rocky intertidal zone, there is zonation here between different animal species, which occurs due to the presence of a temperature gradient and varying abundances of different microbe varieties.
[Music]
In a way, the worms and crabs have become geographically isolated from one another within the same vent system. All the creatures we've discussed so far can be classed as primary consumers, but organisms from higher trophic levels are also present. The octopus, for example, is one of the top predators of deep-sea vents, along with white zoarcid fish, which feed on the tube worms and shrimps. Some deep-sea skates, which tend to dwell along the continental slope, visit hydrothermal vents to feed but also to lay their eggs. They do so in order to use the volcanic heat to accelerate egg development and reduce the usually years-long incubation time. The zonation of life advanced leads to a higher abundance of filter feeders and predators in the periphery, further from the chimneys. Animals like stalked barnacles and predatory anemones are less tolerant of the chemical-rich, low-oxygen conditions found closer to the fluids, but they can still make a living here. Beyond the periphery, we find non-vent deep-sea fauna existing on the abyssal plain near the vent systems at higher abundances than they're typically found. This is because, even hundreds of meters away from the vent itself, animals can still make use of some of the exported organic matter.
[Music]
In all, over 590 animal species have been identified living at hydrothermal vents, and a surprising majority of these organisms are unique to this environment, having become specialized in such a way that means they rely entirely on the chemosynthetic conditions of the vents.
[Music]
The discovery of deep-sea hydrothermal vents was groundbreaking for another reason: their unique conditions. The abundant nutrients of these chemical gardens led to scientists speculating whether these vents could be where life on Earth originated. Although unproven, there is substantial evidence to suggest this may be the case. Firstly, some of the thermophilic, or heat-loving, vent microbes are among the most primitive organisms known on Earth. Evidence is also given by the fact that many of the chemical building blocks of life are found at the vents, suggesting that the precursors of life harnessed carbon dioxide and hydrogen available in those primitive conditions to create complex organic molecules such as amino acids and nucleotides. In conclusion, hydrothermal vents support unique ecosystems and their communities of both highly specialized as well as simple organisms in the deep ocean. The islands of abundance they create in the otherwise barren depths are sites of outstanding scientific interest, providing a new insight into what is truly necessary for life to survive.
[Music]
But they are not the only major chemosynthetic oases in the deep sea. In part two, we'll explore the life of cold seeps, or cold vents. These are regions where cold, hydrocarbon-rich water escapes from the ocean floor, hosting their own distinct assemblages of life and forming peculiar landscapes at the bottom of the ocean.
[Music]
Today's video is sponsored by Klima. Around the world, April is Earth Month, a time of celebrating and increasing awareness about the environment. Suitably, today's sponsor, Klima, is a tool that lets you calculate your individual carbon footprint by taking into account the flights you take every year, what type of diet you have, how many car miles you use, and so on. Then, via an affordable monthly subscription, you can help fund climate projects that capture or reduce the same emissions elsewhere, such as planting trees, solar power plants, and clean cook stoves to neutralize your footprint. It also provides tips on how to further reduce your footprint, and in honor of Earth Month, you'll get 10 extra trees planted in your name. Just click the link and enter my code, NaturalWorld10, to claim your trees and take immediate climate action. Let's make our planet a greener place together.
[Music]
You