Is it possible to recover genetic information from plankton samples preserved in formalin for seven years? The answer is yes. This is demonstrated by a new study resulting from a collaboration between the University of Trieste (UniTS) and the National Institute of Oceanography and Applied Research (OGS), recently published in the Journal of Plankton Research.

The study analysed samples of mesozooplankton collected in the Gulf of Trieste in 2017 and preserved in formalin for approximately seven years.

What is mesozooplankton? It refers to the community of small animal organisms that live in seawater and, although often invisible to the naked eye, play a fundamental role in marine ecosystems. It includes, for example, small crustaceans, larvae, and other organisms that form an essential component of the marine food web.

These organisms are normally identified under a microscope. This study instead applied DNA metabarcoding, extracting and sequencing genetic material from zooplankton samples collected and fixed in formalin. In practice, rather than searching for and identifying organisms one by one, the method analyses the “genetic code” present in the sample to reconstruct which species or groups of organisms are present.

Formalin damages DNA, making these analyses particularly challenging. Despite this obstacle, the researchers were able to recover a significant amount of biological information. Comparison with microscopic identification showed that the molecular method can identify a substantial proportion of the organisms present.

Historical collections as biodiversity archives

The most important finding of the study concerns future prospects. Research institutes and museums around the world hold vast historical collections of plankton, collected over decades and often preserved in formalin.

These samples could therefore represent not only archives of biodiversity observable under a microscope, but also genetic archives of marine life from the past.

Analysing them could make it possible to reconstruct how marine communities have changed over time, by comparing present-day biodiversity with that of decades ago. It could also help retrospectively identify the presence of non-native species, including during the early stages of their appearance in a given area.

The study was supported by the Interconnected Nord-Est Innovation Ecosystem (iNEST) and the National Biodiversity Future Center (NBFC)**, both funded by the European Union – NextGenerationEU under the National Recovery and Resilience Plan (PNRR)**.