Extreme extremophiles: more novel forms in the very deep sea (Introduction)

by David Turell @, Sunday, May 02, 2021, 23:13 (11 days ago) @ David Turell

Giant single-celled types:


"The seafloor comes into view, and there they are. A garden made of giant cells.

These single-celled organisms, called xenophyophores, can grow as large as basketballs. Xenophyophores growing on the sediment can resemble carnations, roses, or lattices, and like corals in shallow water, their bodies create unique habitat in the deep sea. Though surveys are difficult to conduct at the depths where they live and much of the abyssal plains have not been explored, we do know that xenophyophore meadows may cover large areas and that they inhabit the Atlantic and Pacific oceans. Xenophyophores “represent a little known element of marine biodiversity,” said Lisa Levin, a marine ecologist at Scripps Institution of Oceanography.


"Each massive cell forms a house made from the sediment around it; some extend long searching filaments, like hairs, to find and grab the best particles for construction, and eschew those that are too large or small. Despite being only a single cell, each will assemble these materials into elaborate masonry.

"With their houses in order, many xenophyophores feed on the marine snow that sinks from the world above, digesting these old remains in their viscous interior before exuding waste that resembles animal feces, though a single cell isn’t supposed to merit that term. When scientists led by ecologist Andrew Gooday of the University of Southampton used CT-scanning to peer into xenophyophore shells and visualize bodies within, they found that each cell spreads within its casing like the branches of a tree, reaching into every corner but with room to spare.

"With the elaborate structure of these shells, and the waste they produce, each cell creates a miniature world. In the late 1980s, when Levin first studied xenophyophores as a hobby and few other scientists paid much attention to them at all, she found that more than 15 major animal groups, including sponges, mollusks, crustaceans, and polychaete worms, inhabit these single-cell castles, with some cells hosting more than 100 individual animals. Some are nourished by their host’s waste. "They function like apartment houses for animals," said Levin. In 2019, she and fellow Scripps biologist Greg Rouse discovered a whole new group of animals that may rely on xenophyophores: fish.


"In fact, xenophyophores are so important to deep sea biodiversity that they’re among the organisms designated by the United Nations as indicators of Vulnerable Marine Ecosystems where communities are particularly sensitive to disturbance. When those indicators were evaluated according to their uniqueness and function and fragility, xenophyophores ranked beside deep-sea corals. “Most are very fragile and turn into a pile of sediments if not handled carefully,” Levin said They are especially vulnerable to disruption.


"One study of xenophyophores in the Atlantic found them to be quick-growing, increasing in volume severalfold over a period of eight months, but it may not be reasonable to extrapolate from those species to xenophyophores in the Clarion-Clipperton. Just as plants like bamboo and oak grow at different rates, the same may be true for these giant cells. Scientists also know very little about xenophyophore reproduction, their ability to disperse, or how long it may take them to repopulate a mined area. That, of course, only applies to xenophyophores who don't live on the nodules themselves, which will take tens of millions of years to form anew.


"...we do know that xenophyophores live in a world unlike any other humanity has encountered. These are cells as large as human fists, that create habitat for other species that compare to corals in their importance to their ecosystems. “I want people to learn to care about the deep sea, and how wonderful and weird it is, and phenomenally unusual,” said Levin. Xenophyophores, she said, are iconic. "

Comment: Weird and wonderful. Obviously part of a sea-floor ecosystem that is vital.

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