During eight years weekly seawater samples were collected from the coast of Hokkaido in northern Japan to investigate how many species is possible to identify from a single location based on their DNA. The main organisms of interest were microscopic algae and small animals (zooplankton) as they form the two first links in the marine food chain and without them, no other bigger organisms, such as fish, seals, or whales, could exist in the ocean. During the eight years, we identified more than 2500 species. This is a significant finding as it is the first known report of so many species detected from a single location, writes Sirje Sildver, TalTech, Assistant Professor, Head of Laboratory - Laboratory of Marine Ecology: Department of Marine Systems. A research paper on this topic was recently published in Environmental DNA.
Environmental DNA marks the DNA found in skin cells or fur shed by the organism, which is used to identify the organism that left those. For example, animals can be identified based on DNA found in soil, feces, and hairs/fur. A similar approach is used by criminalists to identify suspects when the DNA found from the crime scene is compared with potential suspects and/or with databases containing DNA sequences from convicted criminals. Environmental DNA provides an opportunity to investigate animals without disturbing them as well as animals that are timid and are not easily spotted or just pass by the area. In the ocean, the environmental DNA approach is important for investigating organisms not visible by the naked eye such as microscopic algae and zooplankton as well as larger organisms such as sharks.
Usually, microscopic algae and zooplankton are identified and investigated by observing them under a microscope, however, the DNA-based approach allows us to identify even the organisms for which it is not possible by microscopy. For larger organisms, DNA left behind in the environment is usually used for analysis, but in the case of microscopic organisms, all microscopic organisms in the sample are investigated. It is important to know, which species are present in the marine environment as some of them can produce toxins that are dangerous to the other organisms in the ocean as well as to humans or the presence of alien species that could outcompete native species.
In this study, the focus was on microscopic organisms as the area of interest, Sea of Okhotsk, is important as a nursery for juvenile salmon and for aquaculture. The microscopic algae and zooplankton are directly and indirectly an important food source for the juvenile salmon. Thus, the results of this study provide an overview of the food that is available. From the same water used for environmental DNA analysis, various environmental parameters such as salinity and temperature were measured, and nutrient concentrations were analyzed. This was done to evaluate, which conditions are favouring or hindering the life of various species and whether their preferences are the same between different years or not. This knowledge allows us to evaluate how are those species influenced by the changes in the environment and what kind of effect would it have on other organisms in the ocean as well as on humans through for example the amount of fish that can be caught or grown in certain conditions.
Similar studies are also ongoing in the Baltic Sea in the framework of the Estonian Research Council`s personal research grant (PSG735), which also supports the investigation on how to get even more data based on eDNA. .