The productivity of marine coastal ecosystems is vital for all of us. If photosynthesizing organisms, such as microscopic algae that live on coastal bottoms, produce biomass effectively, they provide good-quality and adequate nutrition for invertebrates. Invertebrates are then a food source to fish that we eat.
The extinction of species and the consequent decreasing biodiversity are severe problems all around the world and in all ecosystems. When talking about decreasing biodiversity, we usually think about large animal and plant species that can be seen with a naked eye. However, biodiversity also includes microscopic organisms that can affect the functioning of ecosystems as much as larger species.
"In this study we looked at marine benthic diatoms, which are microscopic algae that grow on shallow bottoms. We wanted to know how the diversity of these diatoms affects the coastal ecosystem and its productivity," says doctoral candidate Leena Virta from the University of Helsinki.
Sediment samples from the Baltic Sea
Shallow bottoms of coastal zones are covered with microphytobenthos, which is the green layer observable also with a naked eye. Microphytobenthos consists of different microscopic algae, such as diatoms, cyanobacteria and green algae. However, diatoms are usually the most productive group of organisms, especially in the cold waters of high latitudes. Productivity refers to the effectiveness of photosynthesizing organisms in converting energy to biomass.
Researchers from the University of Helsinki collected sediment samples from the Baltic Sea. The study site was located on the Finnish coast, in the Hanko archipelago.
"Using a microscope, we found 328 different diatom species in our samples. This shows that diatoms are a diverse group of organisms even in the Baltic Sea, where the low salinity generally leads to low species richness, compared to the oceans," says Leena Virta.
The results showed that the diversity of diatoms is very important for the functioning of the ecosystem, because it sets the lower boundary for ecosystem productivity. In other words, productivity varied considerably in ecosystems with low diversity of diatom communities, but was constantly high in ecosystems with highly diverse diatom communities. However, even more important than the diversity of species, was the diversity of traits, or in other words the characteristics of the community. Communities with, for example, both small and large species, both low- and high-growing species, and both attached and free-moving species were the most productive.
The effect of diatoms on fish stocks is still a question mark
The effect of the diversity of marine benthic diatoms on ecosystem functioning and productivity has not been studied before.
Researchers believe that the results of this study can be generalized, not only to the whole Baltic Sea, but to other marine areas as well. This is because the selection of traits is similar in all marine waters despite changing species. This study is a good start for learning about the role of marine benthic diatoms, but these results still cannot indicate, for example, the effect of diatoms on fish stocks.
This study was conducted as a part of the Bonus COCOA –project, funded by the EU and the Academy of Finland.
The diversity of benthic diatoms affects ecosystem productivity in heterogeneous coastal environments: Leena Virta, Johanna Gammal, Marie Järnström, Guillaume Bernard, Janne Soininen, Joanna Norkko, Alf Norkko. Ecology 2019. https://esajournals.onlinelibrary.wiley.com/doi/epdf/10.1002/ecy.2765