This ancient "shelled" creature is the building block of the pyramids and the cornerstone of the marine food chain

When it comes to "plankton", the first thing that comes to mind is often the invertebrates in freshwater and the ocean that are too small to be seen with the naked eye, but are numerous; they are weak and tiny, and are as ubiquitous in water as dust in the air, and are an indispensable cornerstone of the food chain. However, there is a type of plankton that uses hard shells to protect itself, and can be called the "shell stacking" master in the microscopic world, and they are foraminifera.

Scientific drawing of foraminifera by biologist Ernst Haeckel | Wikimedia Commons

Single-celled organisms with shells

Foraminifera, meaning "covered with small holes", currently has 5 known classes and more than 50,000 species (including 6700-10,000 living species and at least 40,000 fossil species). Most foraminifera are small, with a shell diameter of no more than one millimeter. However, the Xenophyophorea, which lives in the deep sea at 500-10,600 meters, has a body diameter of up to 20 centimeters, which can be said to be the "giant" in the foraminifera family.

The biggest feature of Foraminifera is their hard shell made of agglomerated calcium carbonate. Unlike the calcium carbonate shells of familiar snails, clams, and other mollusks, the shells of Foraminifera, as single-celled organisms, are located in the protoplasm inside the cell membrane and are covered with many small holes, hence the name "foraminifera". The shells of many foraminifera have complex multi-layer structures and many small chambers. The shape and structure of the shells are also the main criteria for taxonomists to distinguish different groups of foraminifera. In addition to calcium carbonate, which is the main component, the shells of some foraminifera also contain other substances such as protein, calcite, and aragonite. There is even a type of foraminifera whose shells contain silicon to reinforce the shell and make it tougher.

Scientific drawing of foraminifera by biologist Ernst Haeckel | Wikimedia Commons

The various organelles in the foraminifera cells are mostly wrapped in this hard shell. Through these small holes, the foraminifera can extend filamentous pseudopods to exchange substances inside and outside the cell. Pseudopods can help foraminifera move in the water or on the sediments at the bottom of the water, and can also adhere to and capture diatoms and bacteria as food. Interestingly, many foraminifera have symbiotic organisms such as green algae, red algae, diatoms and dinoflagellates in their bodies, which can provide energy for foraminifera through photosynthesis; some other foraminifera will retain their chloroplasts for their own use after endocytosis and digestion of unicellular algae.

Ancient creatures that built the pyramids

Foraminifera are not only diverse in species, but also widely distributed. Most foraminifera live in the ocean, from the sunny surface of the sea to the deep sea thousands of meters deep. In addition to the planktonic species, there are also many benthic species; some members are distributed in fresh water, and some foraminifera have even entered the land and live in the moist soil on the surface of tropical rain forests.

Mesozoic Foraminifera fossils | Lyndsey R. Fox et al. / Journal of Micropalaeontology (2018)

At the same time, the history of foraminifera is also very old. The earliest foraminifera appeared in the Cambrian period about 542 million years ago. Their number in the world is so huge that it is estimated that foraminifera produce up to 43 million tons of calcium carbonate each year. A large number of fossil layers formed by the shells of dead foraminifera can be found in marine sediments all over the world. The ancient Egyptians dug and used the limestone formed by foraminifera fossils to build the world-famous pyramids. Paleontologists named the longest period of the Mesozoic Era, the Cretaceous, after the strata rich in foraminifera fossils.

Scientific drawing showing various tiny biological remains in limestone | Wikimedia Commons

Foraminifera fossils are also important indicator species for studying ancient climate and ancient ecology. The statistics of the number and types of foraminifera fossils found in deep-sea drilling cores provide a rare window for humans to understand the ancient ocean tens of millions of years ago.

Cornerstone of SeaWorld

Foraminifera, with a wide variety of species and large numbers, are crucial to the stability of the marine ecosystem. On the one hand, they can fix the carbon dioxide dissolved in seawater and seal it in the form of calcium carbonate in their small hard shells. As foraminifera die, their shells seal a large amount of carbon in the deep sea, mitigating their impact on global warming as a greenhouse gas. On the other hand, some species of foraminifera can also use symbiotic algae or chloroplasts obtained by stealing to perform photosynthesis, fulfilling the mission of producers in the ocean.

For many fish, including some economically important edible fish species, foraminifera are essential prey organisms for their fry. However, if the atmospheric carbon dioxide continues to rise, the concentration of dissolved carbon dioxide in seawater will be too high, making the seawater an increasingly concentrated carbonic acid solution, which is fatal to the calcium carbonate shells of foraminifera: their hard shells will be dissolved and they will not be able to survive in such a marine environment.

Living foraminifera | Haruka Takagi et al. / Biogeosciences (2019)

As an important cornerstone species in the marine food chain, the extinction and disappearance of foraminifera will affect everything above the food chain pyramid, from swimming fish, flying seabirds, leaping dolphins and huge whales, to humans who rely on the rich resources given by the ocean for survival and development. As an important carbon-fixing and reef-building species, once foraminifera are reduced in large numbers or even extinct, the challenges brought by climate change will become more severe and the situation will be even worse.

The tiny foraminifera not only serve as a mirror for us humans to understand the Earth's past climate and ancient ecology, but are also an important indicator for monitoring modern environmental changes on Earth. Their rise and fall and survival in the future are closely related to the future of each and every one of us.

Star-shaped remains in the sand, the shells of foraminifera | Geomr / Wikimedia Commons

Letter to Calendar Lady

2021 is coming to an end. Have you experienced any natural moments that impressed you this year?

After Calendar Girl asked this question to her colleagues, she received a lot of photos and videos.

@Jian Er woke up from a nap one day and witnessed a murder on his hat - a praying mantis was happily chewing an aphid fly;

When @麦麦 was walking in the park, I suddenly realized that the common white clover is actually very beautiful:

@黑jio妹妹 took a photo of a "sun dog" when she was slacking off one day. This is an optical phenomenon formed by the refraction of sunlight by ice crystals in the sky. At that time, there was a "small sun" on each side of the sun.

What is your #2021NaturalMoment#?

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