The study of life: from microscopic diatoms to gigantic whales

Although geophysics and geology are the primary focus of our PS134 expedition, its biological component is perhaps smaller, but not less impactful. Today, I will therefore put in the spotlights the work conducted by my fellow biologists on board, which study a wide range of organisms, from microscopic diatoms, mysterious jellyfish, and zooplankton to gigantic whales.

But first, let’s rewind 125 years back and have a look at the biology covered during the Belgica expedition. A Titaness task that was left to only one man: the Romanian naturalist Emil Racovitza. Enlisted at the age 29 because of its obvious expertise on polar fauna and flora. Or so you would think. For all students out there wondering if their thesis topic was the right career choice, worry no more. Because you will never know where a college degree in law, followed by a career switch to natural sciences, resulting in publications on French marine worms (i.e., Annelids and Polychaetes), the behavior of crabs, and the reproduction of octopuses will lead you (I am not making this up). In the case of Racovitza, this brought him beyond the Antarctic circle on board of the Belgica, where his collections of botanical and zoological material would be the basis of numerous scientific reports published between 1900 and in 1949. Racovitza himself wrote two books, one on cetacean (i.e., whales and dolphins), and another unpublished one on pinnipeds (i.e., seals and sea lions). But as any researcher that ever took part in an expedition are (painfully) aware of, the work does not start at the beginning of the expedition. Scientific expeditions require an immense preparation work, long before its departure. For instance, in the case of my small jellyfish team, this required the packing of over 20 freight boxes and numerous plankton nets, six long months prior to our departure, Polarstern being luckily already equipped with lab spaces. The preparation work of Racovitza started already in August 1896, one year before the departure of the Belgica voyage.  During this time, he oversaw the lay outs of the labs, planned the necessary research freight (including various camera and photography equipment), and the indispensable library. During the expedition, his work strongly focused on the behavior of marine mammals and sea birds. But if you think that a great Belgian Antarctic expedition would have led to the description and the naming of some fancy new seal or penguin species, then you don’t know my country. Nicknamed the country of surrealism, it is only appropriate that we ended up with Belgica antarctica, aflightless midge fly.

Emil Racovitza, naturalist on board of the Belgica. His valuable botanical and zoological data collected during the expedition would lead to countless of scientific reports published between 1900 and 1949. Picture credit: De Gerlache Family Collection

But let’s go back to 2023. With Antarctica in summer holding some of the main feeding grounds of countless whales, it is no surprise that here on board of the Polarstern, similar as to the Belgica expedition, there is a strong focus on marine mammals. The “whale team” is composed of three marine biologists (Nadya Ramirez Martinez, Johannes Baltzer, and Klaus Lucke), one veterinarian (Luca Schick), and two drone pilots (Chris Stevenson, and John Newton). Their goal is to study how the distribution, behavior and relative abundance of different marine mammal species changes in the vicinity of the ship due to sound propagation in the area. For this, they are using a combination of ship observations, aerial observations with helicopters and drones (weather dependent), and hydroacoustics (sounds recorded underwater from hydrophones attached to a mooring). The four most frequently spotted marine mammals during our expedition so far comprised Antarctic minke, humpback, and killer whales, and many seals, mostly crab-eater seals. As marine mammals are considered “umbrella” species (i.e., a wide-ranging species whose requirements include those of many other species), the study of these animals can then help as a proxy, to understand the state of the oceans.

A crab-eater seal spotted during our expedition, one of the most common seal species in the area. Their name is however misleading, as they feed primarily on fish. Picture credits: Pascal Daub.

As a marine biologist studying jellyfish, I am here to convince you that marine mammals are not the only charismatic critters swimming around these waters. Despite the importance of gelatinous zooplankton (generally known as “jellyfish”) in marine pelagic systems, these animals stayed largely understudied in the Bellingshausen Sea. Thus, the goal of my “jellyfish team” is to study the distribution, diversity, ecology, trophic role, and genetic connectivity of Antarctic jellyfish. To do so, we collect various specimens using plankton nets and water samples for environmental DNA analyses (i.e., traces of DNA organisms leave in their environment). But you will learn more on our jellyfish work, in a future special dedicated vlog. Besides the collection of jellyfish, we also catch quite diverse zooplankton species. And since we were talking about whales before, I wanted to share a magnificent picture of a krill or “whale food” caught within our Bongo plankton nets.

Antarctic krill, or “whale food”, caught with our plankton nets. Picture credits: Joan J. Soto-Àngel

From zooplankton, we can even go smaller, down to the microscopic diatoms, studied on board by Zelna Weich. These single cell algae are characterized by beautiful glass shells (made of silicate), making fine and intricate patterns. In Antarctica, their life cycle is often tightly linked with the sea ice, in which some species grow. Eventually the diatoms will die and sink to the bottom of the ocean, forming layers of diatoms, from which we can estimate the past abundances of different species. Studying these layers will then provide local information on past sea ice growth and retreat, at up to a decadal resolution, well prior to the use of satellites to survey ice coverage. This is of particular importance to be able to predict the future of the Antarctic ice cover, which unlike the Arctic, has been acting in a very erratic manner under recent climate events, alternating between more dramatic ice buildup and losses. These diatom layers can also indicate past algae blooms, which are typically linked to an increase of sea productivity, which has benefitted all the way up the food chain, from grazing zooplankton, to predating jellyfish and to krill eating whales. As you can see, all marine life in the Antarctic is connected. At least through their stomachs.

Example of an Antarctic Sea ice associated diatom, Thalassiosira antarctica (left), and a cosmopolitan Southern Ocean Sea ice avoiding species, Fragiliariposis kerguensis (right). Pictures credit: Zelna Weich.

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