Environmental DNA could measure coral reef biodiversity more accurately

NEW DELHI : Environmental DNA, or eDNA, extracted from a litre of surface seawater, provides for a more effective and accurate means to measure coral reef biodiversity, according to a new research.

eDNA refers to the DNA that living creatures release into the environment, through skin, waste products, and mucus.

The research from Okinawa Institute of Science and Technology (OIST), Japan, paved the way for large-scale comprehensive surveys of coral reefs to take place, rather than relying on scientific scuba diving or snorkeling for obtaining direct observations.

Scientific divers have confirmed the method to work through observations made in the same area of ocean.

The method is described in the journal Proceedings of the Royal Society B: Biological Sciences.

Owing to global warming and other bleaching-causing factors, survival of many coral reefs have been threatened.

''Beautiful coral reefs in subtropical and tropical seas account for only 0.2 per cent of the entire ocean,'' said co-author Nori Satoh, Principal Investigator of OIST's Marine Genomics Unit.

''However, they are the most biodiverse areas of the oceans, home to about 30 per cent of all marine life,'' said Satoh.

The first step towards the conservation and protection of coral reefs involves understanding the make-up of a coral and how it changes over time. By analysing the eDNA extracted from seawater, without having to enter water, a clear picture of the organisms inhabiting that part of the ocean can be formed.

Previous methods involved scientific scuba diving and snorkeling to record the species and the changes over time, which were time consuming, expensive, and labour intensive.

The researchers tested the effectiveness and accuracy of these new tools by conducting a large-scale survey of the ocean surrounding Okinawa using both the eDNA method and scientific divers. Over a four-month period, from early September to late December 2021, 62 sites from around the main Okinawa Island were surveyed and two to four dominant coral genera at each reef were recorded.

''We found that the eDNA analysis matched that of the direct scientific observations with more than 91 per cent accuracy,'' said OIST Research Scientist, Koki Nishitsuji, first author of the paper.

''In fact, 41 out of the 62 sites were identical. The eDNA method indicated the presence of five dominant coral genera at all 62 sites surveyed. What's more the results of the environmental DNA method suggest the presence of corals never before recorded along the coast of Okinawa,'' said Nishitsuji.

The eDNA method requires complex sequencing information, and due to this, only 45 of the estimated 236 genera can currently be detected. With more information, the effectiveness of the eDNA method will increase, the study said.