These Stunning Miniature Sea Creatures Keep the Oceans in Balance

These Stunning Miniature Sea Creatures Keep the Oceans in Balance
A live foraminifera, a single-celled protist that is probably the world's tiniest geochemist. (Photo: Laura Haynes, Vassar College)
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Never underestimate the power of one cell. That’s how many cells foraminifera — little sea creatures with striking shells — have. But boy can they do a lot with it. They’re the world’s tiniest geochemists, tinkering with the ocean.

These tiny creatures are found everywhere from coasts to the open ocean. But they do more than play the role of geochemists; they can also help us understand our ocean’s past so we can anticipate its future. It’s a fascinating paradox that single-celled protists can help us learn about the oceans, which are infinitely bigger than they are. Plus, they look rad.

Let’s take a tour of foraminifera — dubbed “forams” for short (and definitely easier to pronounce) — around the world, with guidance from experts. Earther talked to Adriane Lam, a postdoctoral fellow in the department of geological sciences and environmental studies at Binghamton University SUNY, and Bärbel Hönisch, a professor at Columbia University’s department of earth and environmental sciences and its Lamont-Doherty Earth Observatory, and asked them to introduce us to forams and tell us the most interesting things about them.

The Two Types of Forams

Various scanning electron images of fossil benthic foraminifera. (Image: Images courtesy of Brian Huber, Laurel Collins, and Pearson et al. (2018)) Various scanning electron images of fossil benthic foraminifera. (Image: Images courtesy of Brian Huber, Laurel Collins, and Pearson et al. (2018))

There are two types of forams: planktic and benthic. Planktic forams — which are all typically very small and fit on the head of a pin — live in open marine environments and float (these fellas don’t swim) in the upper part of the water column. Some planktic species live near the surface of the water, Lam said. Others have little friends in the form of photosynthesising algae.

Benthic forams live on or within surfaces, sediments, and at the bottom of the ocean, as well as in freshwater, brackish water, and marine environments. They come in a variety of sizes, ranging from the size of a grain of sand to the size of a tennis ball. Hönisch said that to identify them, scientists study their shape, which help them classify each species. The little creatures have a quick life cycle, ranging from a few days to a few years. Experts still aren’t sure how many foram species there are living today, Lam said, with estimates running between 4,000 and 10,000.

Although many forams are very small, they don’t let that affect their appetite. Lam said forams use sticky appendages that extend from their shells called pseudopodia to trap and eat animals such as brine shrimp. Planktic forams eat animals that are up to 10 times bigger than the diameter of their shell, she said.

“It’s essentially the equivalent of if I were to throw a turkey at you and expect you to eat that turkey every other day.” Hönisch said. “ I mean they’re really voracious eaters. In some ways, they’re really kind of creepy creatures because what they do is they just stick all their filaments into their prey and they suck it out.”

Their Shells!

Various scanning electron images of fossil planktic foraminifera. (Image: Images courtesy of Megan Fung, Brian Huber, and Lam and Leckie (2020).) Various scanning electron images of fossil planktic foraminifera. (Image: Images courtesy of Megan Fung, Brian Huber, and Lam and Leckie (2020).)

One of the most interesting characteristics about forams is their tests, or shells. Planktic forams grow their own shells using calcium carbonate, the material used to make the same shells you can find on the beach. Since planktic forams are so tiny, you need a microscope to see their shells. Benthic forams, on the other hand, make their shells out of calcium carbonate and other materials, Lam explained, such as organic material, pieces of sediment particles, and sometimes even small planktic forams, all of which are glued together with organic cements.

Inside, the shells are a series of hollow chambers. Forams continue adding more chambers throughout their lifetimes. From the outside, some of them also have spines that protrude from their shells. Their shells can also have pores or small holes.

The shells honestly look like little sculptures. It’s amazing to think that these unicellular organisms are able to create something so beautiful and complex, and that they’ve been doing it for millions of years.

Forams Also Help Scientists Learn More About Our Oceans

Forams are more than a just pretty face, though. They can tell scientists about the ocean. When forams grow their shells, they incorporate the chemistry of the water into them, which allows researchers to reconstruct the specific water conditions under which they lived. To do this, scientists analyse the shells of dead forams, which sink to the bottom of the ocean. Sediments there contain layers and layers of forams accumulated over eons, allowing researchers to create a timeline.

From planktic forams, which live at the sea surface where gases exchange between the atmosphere and surface seawater, scientists can learn about water temperature, precipitation, evaporation, and even the extent of ice sheets. Meanwhile, benthic forams, which live deeper in the water column on or within the seafloor sediments, tell scientists about how much carbon was stored in the ocean, how high the nutrient concentrations were in deep water, and what the water temperature was like.

Researchers don’t only use forams to study what happened in the oceans over the last hundreds or thousands of years; they also use them to analyse what they were like millions of years ago. That ancient history allow researchers to understand what’s happening to our climate today.

History Repeats Itself — and Sometimes So Does Climate

Specimens of Cylorbiculina compressa, Peneroplis pertusus and Heterostegina depressa. (Image: R. G. Muller and courtesy of Pamela Muller)

Hönisch, who uses forams to reconstruct climate change, gave us the Paleo-Eocene Thermal Maximum as an example. It’s an event that happened about 56 million years ago when a lot of carbon dioxide was pumped into the atmosphere, causing the planet to get really warm. Hönisch reconstructed how acidic the ocean was during the PETM using foram shells, and found that the acidification then is similar to what scientists are expecting to happen by the end of this century.

But there was one big difference: During the PETM, this increase of carbon dioxide in the atmosphere happened over the course of a few thousand years. Today, humans are putting all this carbon dioxide in the atmosphere over the course of a couple hundred years.

“That tells us that what we’re doing today is really significant, and we can learn from that,” Hönisch said. “What is happening today will actually have severe consequences for the ocean.”

Forams Are More Than Just Ocean Chemists

According to Laura Haynes, an assistant professor of earth science at Vassar College, this is a photo of a fossil planktic (surface-ocean) foraminifera from a cemented limestone, meaning that it has been hardened into rock. (Image: Laura Haynes, Vassar College)

Forams don’t just record the climate. They can also take care of it (and thank God, since humans need all the help we can get).

Their shells are the key. Hönisch said there are hundreds of meters of sediments on the seafloor, and most of them are made up of forams’ fossil calcium carbonate shells. When you bring a lot of acidic seawater down to the bottom of the ocean, Hönisch said, you can neutralise the acidity of that water by dissolving these calcium carbonate shells.

“Having them in the ocean actually allows us to buffer climate change,” Hönisch said, adding, “So, they’re really helping us, they’re helping the planet reduce the climate swings that we’re seeing.”

That’s not all they do, though (which kind of makes me feel like an underachiever). Lam explained that scientists use benthic forams as biomonitors of pollution. Several species of benthic forams live in shallow marine and brackish water environments close to the coast, which are areas significantly affected by terrestrial runoff. Lam said that a lot of this runoff contains pollution from industrial and municipal sources. To get a picture of the degree and severity of pollution in a region, scientists analyse the abundance of certain benthic species, their shell characteristics, and what species are present as well as what species are not.

“For example, there are some benthic species that absolutely love sewage, and will increase in numbers when there is plenty of it (sewage to them is food, except when there is too much pollution, such as heavy metals, in the sewage),” Lam said.

Heavy metal pollution actually causes adverse effects in benthic forams, Lam said. Scientists have found that their shells become small, exhibit stunted growth, and can become abnormally shaped.

But How Do Scientists Study Them?

Lucky yet? These critters are tiny! (Photo: Bärbel Hönisch)

As far as how researchers study these little fellas and their shells — which, let us remember, are on the seafloor — Hönisch told us about the two things she does. For paleoclimate reconstruction, she relies on sediment cores drilled from the bottom of the ocean, which contain forams that died long ago.

She also works with live forams, which she collects from the surface ocean by scuba diving in places like California, Catalina Island, or Puerto Rico, and takes to the lab to grow under controlled conditions. There, Hönisch and her team can change a variety of variables, such as the temperature, seawater chemistry, food, and light. At the end of the forams’ lifecycle, Hönisch and her team collect the empty shells and analyse them. This allows them to make a direct connection between the chemistry of the forams’ shells and the chemistry and physical conditions under which they lived. Hönisch said that she and other researchers can then apply these relationships to reconstruct ancient environments from the fossil shells they find in sediment cores.

Hönisch said she and her students go blue-water diving, or scuba diving in places where they can’t see the bottom of the ocean, for forams. The group goes on a boat with a black bottom and mainly looks for forams under the bottom of the boat, because you can see them against the black background. Hönisch compared them to “little white fluff balls,” although that doesn’t mean they’re always easy to find, even against a black background. Some dives have resulted in success in 20 minutes, she said, while others have lasted for two hours.

Like Much of Our Planet, Forams Are Going to Be Affected by Climate Change

A picking tray. Researchers put their forams on picking trays and pick up individual specimens with a very fine wet brush. (Photo: Bärbel Hönisch)

Even these tiny creatures can’t escape the climate crisis. According to Lam, their fate is directly tied to how much carbon dioxide humans pump into the atmosphere. When carbon dioxide interacts with seawater, it creates free hydrogen ions in marine waters, making it more acidic. Over the past roughly 200 years, Earth’s oceans have become 30% more acidic, Lam said, which is affecting marine protists, such as forams, and other animals that make their homes out of calcium carbonate.

Lab experiments where researchers grow these creatures under different pH conditions have found that this type of environment has negatively impacted planktic forams’ ability to create calcium carbonate, repair their damaged spines, and consume oxygen, Lam said.

“Foraminifera make their tests out of calcium carbonate, which dissolves in the presence of acid,” Lam said, referring to the term for foram shells. “In short, these marine plankton are having to expend more energy to create their shells because acidifying ocean waters are making it harder and harder for them.”

Forams Are Pretty Weird — And Really Cool

Amphistegina gibbosa in situ (in life position). (Image: Image by D. E. Williams and courtesy of Pamela Muller)

Sure, they can chow down on the equivalent of a turkey, but if we’re being real, forams are pretty cool. They tell us more about our world than nearly anything else. Though almost everyone loves dinosaurs, Lam said their fossil record isn’t great because terrestrial animals don’t preserve as well as marine invertebrates, such as clams or gastropods. Yet, she said not even marine invertebrates can compare to forams because their fossil record is obscured by changes in sea level and erosion.

Forams’ fossil record is fantastic because the critters have a quick life cycle, occur in high numbers, and have hard outer shells. In addition, their fossil record in open marine environments isn’t as easily disturbed by changes in sea level.

“For these reasons, foraminifera arguably have the most complete fossil record,” Lam said. “We can take ships out into the middle of the ocean, drill down through the seafloor, and bring back sediment cores that are absolutely filled with fossil foraminifera tests! In some areas of the world ocean, the sediments are almost 100% foraminifera tests, which is really spectacular.”

The Mysteries That Remain

Ammonia sp. specimens stained with red dye in ethanol from the Texas Gulf Coast. (Image: Image courtesy of Pamela Buzas Stephens)

If you all made it this far, bless you, you were just as captivated by these little geochemists as I was! While you may feel like you have more knowledge about forams than you know what to do with, scientists still have many questions that they want to answer.

Hönisch said that one of the most mysterious things about planktic forams is that scientists can’t reproduce them in a lab. This stands out considering the large number of animals on the planet that we can reproduce in a lab, Hönisch said, but when it comes to something as simple as this unicellular organism, “we have no idea how to reproduce it.” Nonetheless, Hönisch said that this makes studying forams fun, because it means scientists like her have to go out and do field work.

For Lam, there are still several unanswered questions regarding forams’ fossil record. Scientists still don’t have exact dates for when a certain foram species went extinct and another species evolved, for instance. They are also still unsure about which species of forams evolved from another. When it comes to where certain species of forams lived, there are also mysteries, such as whether some species changed where in the water column they lived on million-year timescales, Lam said.

“These unanswered questions seem daunting to tackle, but honestly, it’s quite exciting to know that there is so much more to learn about foraminifera!” Lam said. “I can’t wait to see what new research is published in the coming decades, and what fun new things we learn about these amazing protists.”

We can’t wait, either. Long live forams.