Harmonizing perspectives: an integrative approach to monitoring metazoan diversity in a Mediterranean coastal area through morphology and organismal eDNA

The use of metabarcoding has greatly improved the assessment of marine metazoans. However, it is still uncertain whether metabarcoding analyses (eDNA) accurately captures the diversity in the field. This study aims to use an integrated approach merging α-taxonomy and organismal eDNA analysis of two genetic markers (COI and 18S), to observe for the first time the metazoan community inhabiting in a submarine Canyon and compare it with already well-known at a Long-Term Ecological Research. Our research has emphasized the importance of harmonizing perspectives involved in assessing the planktonic metazoan community. This includes developing a consistent sampling strategy, obtaining high-quality DNA, ad hoc bioinformatic pipelines, interpreting results accurately, and finally microscopy-based identification to confirm molecular inference. All of these steps are crucial for monitoring metazoan diversity and distribution patterns. We have observed over 200 metazoan taxa and identified 174 species using COI, 107 using V9, and 84 using morphology-based methods. Our coverage is comprehensive and includes both holo- and mero-zooplanktonic organisms, with a wide taxonomic range that even includes fish. This study has revealed a extraordinary biodiversity of these Mediterranean Sea sites, highlighting both known and previously unidentified species (new entries and non-indigenous) and providing a holistic view of the pelagic realm.