Large-scale metabarcoding analysis of epipelagic and mesopelagic copepods in the Pacific

Abstract

A clear insight into the large-scale community structure of planktonic copepods is critical to understanding the mechanisms controlling diversity and biogeography of marine taxa in terms of their high abundance, ubiquity, and sensitivity to environmental changes. Here, we applied a 28S metabarcoding approach to large-scale communities of epipelagic and mesopelagic copepods at 70 stations across the Pacific Ocean and three stations in the Arctic Ocean. Major patterns of community structure and diversity, influenced by water mass structures, agreed with results from previous morphology-based studies. However, a largescale metabarcoding approach could detect community changes even under stable environmental conditions, including changes in the north/south subtropical gyres and east/west areas within each subtropical gyre. There were strong effects of the epipelagic environment on mesopelagic communities, and community subdivisions were observed in the environmentally stable mesopelagic layer. In each sampling station, higher operational taxonomic unit (OTU) numbers and lower phylogenetic diversity were observed in the mesopelagic layer than in the epipelagic layer, indicating a recent rapid increase in species numbers in the mesopelagic layer. The phylogenetic analysis utilizing representative sequences of OTUs revealed trends of recent emergence of cold-water OTUs, which are mainly distributed at high latitudes with low water temperatures. Conversely, the high diversity of copepods at low latitudes was suggested to have been formed through long evolution under high water temperature conditions. The metabarcoding results suggest that evolutionary processes have strong impacts on current patterns of copepod diversity, and support the "out of the tropics" theory explaining latitudinal diversity gradients of copepods. Diversity patterns in both epipelagic and mesopelagic copepods was highly correlated to sea surface temperature; thus, predicted global warming may have a significant impact on copepod diversity in both layers.

Three‐dimensional distribution of mesoplankton assemblages in the Central Atlantic

“…We suggest that vertical ranges of diel mesoplankton migrations are mostly within the sampled depth ranges of our dataset and, therefore, do not visibly affect mesoplankton structure. Similar conclusions were made by Hirai et al (2020) in the tropical and subtropical Pacific where the epi-and mesopelagic zooplankton differed by taxonomical structure with no influence of diel vertical migrations.…”

“…In fact, the South and the North Atlantic gyral systems harbour sister (Sutton et al, 2017) or cryptic (Kulagin et al, 2021) species and the species-level approach, especially coupled with molecular analyses, might separate the two assemblages from each other. However, this is not guaranteed because even a speciessensitive metabarcoding analysis showed a taxonomical similarity between the northern and southern gyre areas in the Pacific meso-and bathypelagic (Hirai et al, 2020). In any case, no division between the Northern and Southern Atlantic gyres was found in the genus-level taxonomic composition, which suggests that the meso-and bathypelagic assemblages (as well as the epipelagic assemblages) are shaped by trophic rather than by geographic factors.…”

“…Analyses of the zooplankton assemblages on an ocean basin scale are rare (Hirai et al, 2020;Woodd-Walker, 2001;Woodd-Walker et al, 2002).…”

Toward a global reference database of COI barcodes for marine zooplankton

“…DNA metabarcoding analysis of the diversity of marine zooplankton has been carried out using a variety of marker gene regions, including COI (Hirai et al 2015;Yang et al 2017;Djurhuus et al 2018), nuclear 18S rRNA (Bucklin et al 2019;Blanco-Bercial 2020), and frequently multiple gene regions used in combination (Sommer et al 2017;Hirai et al 2020;Questel et al 2021). Classification of the resulting sequences for any gene requires a taxonomicallycomprehensive and globally-extensive reference database of sequences determined from morphologically identified specimens, ideally with complete collection metadata (georeferencing).…”

Combining Multiple Markers in Environmental DNA Metabarcoding to Assess Deep-Sea Benthic Biodiversity

“…Makers such as the mitochondrial 16S rRNA gene or COI have often been used to recover specific metazoan groups (Djurhuus et al, 2020;West et al, 2020). The 28S rRNA gene has also been used to assess community diversity for metazoans (Machida and Knowlton, 2012), zooplankton (Hirai et al, 2020), or algae (Bittner et al, 2013).…”