Microalga Stylodinium – A mysterious stranger from the peat bogs

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Even allowing for the huge diversity of dinophytes – a group which has long been an object of LMU biologist Marc Gottschling’s research – we can fairly say that this stalked species is something special: The unicellular alga Stylodinium generally lives as an epiphyte on the surface of multicellular algae. To do this, it has evolved a peculiar mechanism for attaching to the carrier organism. It secretes a sort of glue for binding itself to the surface of the carrier. By means of a subsequent backward movement, it develops a small, rigid stalk — and so Stylodinium becomes a nonmotile, epiphytic alga. Despite this unusual mode of life, there is extremely scant scientific knowledge about these organisms. And yet we have them on our doorstep, in the bog lakes of Upper Bavaria and other regions of Germany. To highlight the need for research into such unusual algae, scientists at the Phycology Section of the German Society for Plant Sciences have selected Stylodinium as Alga of the Year 2022.

The diversity of dinophytes

Stylodinium belongs to the group of protists known as dinophytes (or dinoflagellates). Gottschling’s team has been researching these unicellular organisms and their particular characteristics for years in close cooperation with scientists from the Alfred Wegener Institute (AWI) in Bremerhaven. Indeed, it was out of this collaboration that the suggestion emerged to nominate Stylodinium for Alga of the Year 2022. “A characteristic feature of many dinophytes is their cell wall, which is made up of a specific pattern of cellulose plates,” says algae researcher Urban Tillmann from AWI Bremerhaven. However, the plate pattern of Stylodinium, which could be used to characterize it precisely, has not yet been reliably determined.

In their free-floating form, the cell of dinophytes is divided into an upper segment and an under segment. The two halves are separated down the middle by a belt-like groove, in which one of the two lash-shaped appendages called flagella lies. This transverse flagellum is for turning in the water, while a second flagellum provides forward propulsion.

In addition to the free-living form that can be found in plankton, many species of dinophytes develop nonmotile cells without flagella. These cells can differ substantially in shape from their motile counterparts. Frequently, the purpose of the nonmotile cells is to survive hostile environmental conditions, such as the winter months in central and northern Europe. Stylodinium also displays this dimorphism: Although the nonmotile stage without flagella appears to dominate, motile cells with flagella have also been observed, albeit rarely. The precise function of the nonmotile cells of Stylodinium is still unknown. But overwintering is presumably not their purpose, as they also form in summer.

Threat to peat bog habitats of Stylodinium

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The uniqueness of peat bogs as a habitat is reflected in the unusual nature of the communities that live there. Although the vast majority of dinophytes are motile organisms, there is an group of dinophytes, the Phytodiniales, in which the nonmotile stage of development dominates and which are most commonly found in peat bogs. Stylodinium is a member of the Phytodiniales, and its mode of living as an epiphytic alga attached by a stalk is unusual in the microcosmos. This unusual microbial ecology is comparable with that of multicellular epiphytes such as orchids and bromeliads, which use trees as their carrier organism in the rainforest. The idea that Stylodinium might live parasitically at times — in other words, that it feeds on its carrier alga — is conceivable but it is a subject which has not yet been researched.

The North German Plain was once one of the most peat bog-rich regions of the Earth, recall the researchers from Munich and Bremerhaven, and its conservation as an effective carbon reservoir plays a critical role in climate and species protection efforts. In particular, the drainage of recent centuries and decades has led to a sharp decline in these habitats, which were originally home to unique biodiversity. Consequently, the curious little epiphytic alga Stylodinium could certainly “function as an icon of the microcosmos for species extinction through habitat destruction,” says LMU researcher Gottschling.