The potential of sedimentary ancient DNA to reconstruct past ocean ecosystems

Sedimentary ancient DNA (sedaDNA) offers a novel approach to investigating past marine ecosystems—from the smallest bacteria to phytoplankton and their predators— over geological timescales. Knowledge about such paleo-food webs can provide broad-scale biological context to paleoceanographic and environmental reconstructions. However, the field of marine sedaDNA research is still in its infancy; community reconstructions are com-plicated by the minuscule amounts of ancient DNA preserved in the sediments. Consequently, the identification of most prokaryotes and eukaryotes in sedaDNA is difficult, and sedaDNA sampling, extraction, and analysis require optimized procedures and rigorous contami-nation control to ensure that the sedaDNA signal is authentic and not overridden by modern environmental DNA. This article describes some of the latest developments in marine sedaDNA research, including the use of metagenomics to study past marine food webs, and new experimental and computational techniques to maximize taxonomic resolution, partic-ularly that of eukaryotes. An example of bioinformatic techniques designed to increase taxonomic insight is presented, demonstrating the breadth of paleogenetic signals that could be extracted from marine sediments. With ongoing improvements in genetic reference databases, sedaDNA extraction techniques, species-specific enrichment approaches, and computational tools, marine sedaDNA will continue to improve our understanding of how marine ecosystems evolved in concert with changing environmental conditions.