NATURAL WORLD FACTS
Deep Sea Gigantism Explained
There is a pattern in the deep sea of organisms growing far larger than many creatures from the shallows. The reasons behind it remain a mystery, but the phenomenon has been given a name.
Deep Sea Gigantism - the tendency of deep sea creatures to grow far larger than their shallow water relatives. There are a number of theories that try to explain this phenomenon. Read on for more.
Larger Animals are More Efficient
Kleiber's Rule states that 'animals that are larger will tend to be more efficient.' This can be demonstrated by comparing a whale to a small fish. The whale, with a mass hundreds of times larger than that of the fish, will have a greater metabolism. The smaller surface area to volume ratio gives the whale the advantage of conserving greater energy, with less energy lost to the surroundings through heat. In the deep, food is scarce, with most of the nutrients falling as marine snow - a trickle of organic debris from shallower waters. Thus, food is scarce, so there is an incentive to conserve this energy and to grow larger.
Furthermore, larger animals have the ability to ingest larger prey. They will be more likely to survive environmental extremities or attacks from predators, and are able to cover larger distances in search of food or a mate. Reproductive success is also therefore aided by an organism being larger.
Abyssal Gigantism
To understand this phenomenon, we first must understand why larger organisms are more efficient, and thus why deep sea creatures like the giant isopod tend to grow to these sizes.
Sea Animals Grow Larger in Cold Climates
Bergman's rule states that 'sea animals tend to increase in body size with a decrease in temperature.' This certainly matches observations in colder regions like the arctic deep, where some of the largest ocean creatures like Greenland sharks, and giant sea spiders are found. The low temperatures lead to their cells growing larger. By slowing their metabolic rate, the cold also means creatures in such climates have longer lifespans.
Slowed metabolisms cause polar creatures to live in 'relative slow motion', and the rich supply of oxygen found in cold water allows them to grow to gigantic sizes.
Sea Spiders
Pycnogonida
These arthropods are commonly found scuttling along much of the ocean floor. They are abundant, with 1,300 known species, and are usually rather small at 0.04 inches (1mm). But in the depths of the Antarctic, they can be 3 feet long (1m). this is because the cold water carries more oxygen, so more of it diffuses into the sea spider's body, allowing it to grow larger.
deep sea isolation
In 2006, biologist Craig R McClain investigated the gradient from the shallows to the deep sea. His findings seemed to mirror the framework of terrestrial islands, where these isolated areas of land develop indigenous biodiversity. More specifically, he found that the deep sea seemed to mirror the 'Island Rule', an idea that small-bodied life on islands grows much larger in its isolation than life on major land-masses, due to limited resources, predation and competition.
According to McClain, 'the deep sea is functionally similar to an island'. The deep also has limited resources, few predators, and is isolated from the shallows. It follows that the diversification of life in the deep mirrors that on islands - the isolated communities develop larger body sizes in response to the conditions stated above.
RELATED topics
Life at Cold Seeps
Cold seeps are areas of the ocean floor where hydrogen sulphide, methane, and other hydrocarbon-rich seepage occurs. Through a number of process, the chemicals support a biome of highly specialised creatures that live around these cold seeps.
The Open Ocean
The open ocean is an entirely different world to the benthic zone of the sea floor. The endless blue stretches away in all directions, while the black abyss hangs gaping below. Currents are stronger here. There is no shelter to be found, and food is hard to come by.
The Deep Sea Floor
Deep sea life must choose whether to live on the bottom at the benthic zone, or to brave the expansive open ocean of the pelagic midwater zone. These two groups of organisms could not be more different, but which is a more effective way of life?
Cold-Water Reefs
Deep Sea Coral Reefs represent areas of astounding biodiversity. Lush cold water coral and sponge gardens thrive in the icy waters. An expanse of colourful coral structures blooming out of the sea floor, providing important habitats for deep-dwelling life.
Deep Sea Food Web
The exact nature of the deep sea food web is still not fully understood, but advancements in technology and research in recent years have granted us a greater understanding of how these separate settlements of life are interconnected as one. Let’s take a closer look at the food web of the deep sea.
Plastic in the Ocean
The main threats seen in our oceans are species loss, habitat degradation, and changes in ecosystem function. Human activities causing a rise in extinction rates has lead to a decrease in biodiversity, particularly in coral reefs, 88% of which are threatened by excessive CO2 emissions.
