The United Nations has declared 2021 to 2030 as the Decade of Ocean Science for Sustainable Development as an effort to reverse the declining health of the oceans. To be able for this campaign to be successful, it needs data on the present global ocean conditions. Thankfully, these data are readily available through the Tara Oceans Expedition.
With over 35,000 samples from all over the world, ranging from the surface level to 1,000 meters deep, the Tara Oceans Expedition is considered as a treasure trove for marine biologists and scientists. The expedition is an international and interdisciplinary enterprise of researchers and scientists aboard the schooner called Tara.
Through this treasure trove of data, two papers were published this month dealing with the analysis of the diversity of plankton -- microscopic organisms that are key to the overall well-being of the ocean.
DIVERSITY OF PLANKTON
One of the papers focused on the diversity of plankton in the ocean, while another focused on the gene expression of this species to see how they adapt to the changing environmental conditions. In a statement, Chris Bowler, a scientist from the National Center for Scientific Research at the Institut de Biologie de l'Ecole Normale Superieure in Paris and the co-senior author of the study explains, "Everything in the ocean is connected, which means it has the potential to move around, this makes it important to assemble everything on a global scale. Doing deep analysis also allows us to catch the rare organisms in the biosphere in addition to those that are more abundant."
Co-senior author Lucie Zinger also explains that the focus on plankton is important because it is a major contributor to marine ecosystems in terms of their biomass, abundance, and diversity. "All types of life have representatives in the plankton-bacteria, archaea, protists, animals, and plants, as well as viruses. But the large majority of this diversity is invisible to the naked eye."
The study, which was published in Cell, reports that a large majority of plankton groups follow a gradient of diversity along latitudes and that diversity decreases as soon as it gets nearer to the poles. Zinger also explains that the ocean temperature is mainly the one responsible for this pattern, and as the oceans grow warmer due to climate change, this will lead to the tropicalization (also known as the increase of plankton diversity) in colder places like the temperate and polar regions. However, the scientists behind this study are still not sure what the consequences of this phenomenon.
In studying all the RNA or the transcriptome, the scientists combined metagenomic and metatranscriptomic data which allowed them to analyze which of the genes are activated and were present in microbial communities across gradients of depth and latitude (unlike previous studies which focused solely on the genomes).
Senior author Shinichi Sunagawa of the Institute of Microbiology and Swiss Institute of Bioinformatics at ETH Zurich explains the importance of transcriptomes. In the statement issued by Cell, he said: "Looking at transcriptomes is important for determining not just which microbes are present, but what those microbes are actually doing with regard to activities like photosynthesis and nutrient uptake." He also explained that one of the goals of the study was to learn whether or not microbial communities are able to adjust to environmental and temperature change in relation to each other or with changes in the gene expression of these communities.
In this study, the scientists discovered that there are distinct ecological boundaries separating both surface water and deep water between polar and nonpolar regions in terms of taxonomic, genomic, and transcriptomic composition.
However, there is one limitation to the data that came from the Tara Oceans Expedition: the samples were collected in a span of less than four years. It somehow made observing measurable trends in today's oceans related to climate change a bit difficult. Scientists required long-term studies to observe factors like acidification, deoxygenation, and pollution. "We need science to develop evidence that can better inform policies to implement viable solutions, as well as operational and transformative actions that can better impact societies, from local to global scales," Sunagawa said. "The Tara expeditions have multiple values. They allow us to collect local natural, chemical, and physical in situ data at the ocean scale. These data can feed into both basic and applied research. Tara's outreach programs can also be a driver of the most needed change in perception that the ocean is both highly valuable and vulnerable."
