Use of Environmental DNA Metabarcoding to Trace Deep-Sea Cephalopod Distribution and Biodiversity in the Eastern Tropical Atlantic

The analysis of environmental DNA (eDNA) is an increasingly used method in biological studies for determining species diversity and distribution without the necessity of capture of organisms. Technological and logistical challenges associated with direct physical sampling in the deep sea combined with the unexplored nature of this largest ecosystem render eDNA analysis an attractive tool for biodiversity and distribution analysis.

Cephalopods are abundant marine molluscs, which link plankton with top predators in oceanic foodwebs. Their single reproductive cycle followed by mass mortality events may result in localized pulses of carbon to the seafloor and therefore contributing to the regional carbon pump. To understand the role of cephalopods in the biological carbon pump, information on their local presence is needed. This study focuses on eDNA analysis of cephalopods by a) developing a workflow for analyzing cephalopod eDNA from seawater, b) producing a reference database of Atlantic cephalopods and c) establishing a biodiversity and distribution baseline for deep-sea cephalopods in the eastern tropical Atlantic.

We used a multigene approach (nuclear 18S rRNA and mitochondrial 16S rRNA) using universal cephalopod primers that were developed specifically for amplifying degraded DNA filtered from seawater samples. Next-generation sequencing was applied to assess the spatial and vertical distribution of cephalopods from 154 samples taken at 5 stations at depths from 50 to 2500 m off the Cape Verde islands. The eDNA results were compared with existing databases (GenBank) and our reference library of 62 species with DNA barcoded voucher specimens. The eDNA data will also be compared to regional net catches and pelagic video transects.