Shell density of planktonic foraminifera and pteropod species Limacina helicina in the Barents Sea: Relation to ontogeny and water chemistry

Metabarcoding reveals high diversity of benthic foraminifera linked to water masses circulation at coastal Svalbard

Arctic marine biodiversity is undergoing rapid changes due to global warming and modifications of oceanic water masses circulation. These changes have been demonstrated in the case of mega- and macrofauna, but much less is known about their impact on the biodiversity of smaller size organisms, such as foraminifera that represent a main component of meiofauna in the Arctic. Several studies analyzed the distribution and diversity of Arctic foraminifera. However, all these studies are based exclusively on the morphological identification of specimens sorted from sediment samples. Here, we present the first assessment of Arctic foraminifera diversity based on metabarcoding of sediment DNA samples collected in fjords and open sea areas in the Svalbard Archipelago. We obtained a total of 5,968,786 reads that represented 1384 amplicon sequence variants (ASVs). More than half of the ASVs (51.7%) could not be assigned to any group in the reference database suggesting a high genetic novelty of Svalbard foraminifera. The sieved and unsieved samples resolved comparable communities, sharing 1023 ASVs, comprising over 97% of reads. Our analyses show that the foraminiferal assemblage differs between the localities, with communities distinctly separated between fjord and open sea stations. Each locality was characterized by a specific assemblage, with only a small overlap in the case of open sea areas. Our study demonstrates a clear pattern of the influence of water masses on the structure of foraminiferal communities. The stations situated on the western coast of Svalbard that are strongly influenced by warm and salty Atlantic water (AW) are characterized by much higher diversity than stations in the northern and eastern part, where the impact of AW is less pronounced. This high diversity and specificity of Svalbard foraminifera associated with water mass distribution indicate that the foraminiferal metabarcoding data can be very useful for inferring present and past environmental conditions in the Arctic.

Ecological Constraints of Plankton Bio-Indicators for Water Column Stratification and Productivity: A Case Study of the Holocene North Aegean Sedimentary Record

This study presents novel findings on the drivers of the calcitic planktonic foraminiferal and aragonitic pteropod Holocene assemblages of the North Aegean Trough (northeastern Mediterranean), an area recording the interaction between dynamic water masses as they exchange between the northern and southern Mediterranean sub-basins. Both of these groups of microorganisms are the major producers of calcium carbonate in the ocean, and are particularly sensitive to climate and oceanographic changes over the late Quaternary. Downcore micropaleontological data from the gravity core AEX-15, supplemented with multivariate statistical Q-mode cluster and principal component analyses (PCA) results, provide significant insights on the water column dynamics during the Holocene. Focusing on the last ~10 calibrated thousands of years before the present day (ka cal BP), our integrated study reveals that primary productivity is the dominant factor controlling the planktonic foraminifera distribution in the North Aegean Sea, whereas water column stratification, and particularly the intensity of the oxygen minimum zone, seems to be the major driver on the pteropod distribution. Besides productivity and thermal stratification, which show the highest explanatory power for planktonic foraminifera and pteropod communities, respectively, though they affect both groups to a different extent, upwelling seems to further affect both faunal groups. Overall, our findings are consistent with those derived by published late Quaternary eastern Mediterranean records, highlighting in parallel a useful additional dimension on planktonic foraminiferal and pteropod ecology, which is inextricably linked with the factors of primary productivity and vertical stratification of the warm Holocene water column.