The Microalgae Community Structure Of Arctic Coastal Lagoons

The Arctic is rapidly changing, demonstrated through declines in sea ice extent and thickness, species range shifts, and permafrost melt, driven by Arctic surface air warming four times faster than the global average. Arctic lagoons, extremely productive habitats located at the land-sea interface, make up nearly half of Alaskan Arctic shorelines and are hotspots for coastal primary production. Microalgae in these systems form the base of a dynamic and complex food chain, and dictate carbon budgets, net ecosystem metabolism, and trophic transfer within these lagoons. The Beaufort Lagoon Ecosystems Long-Term Ecological Research program (BLE-LTER) collects dynamic long-term data on these understudied ecosystems at a series of lagoons along Alaska’s Beaufort Sea coast to address several knowledge gaps. This study leverages BLE-LTER data and sampling schemes to examine the microalgae community composition of ice-associated, pelagic, and benthic microalgae within these lagoons. We used high performance liquid chromatography (HPLC) derived pigment data, verified against 18S rRNA gene amplicon sequencing, to determine microalgae community structure. Clustering methods were used to determine natural grouping in the community composition of samples. Samples (n = 174) were collected from lagoons (n = 5) and rivers (n = 6) along the Beaufort Sea coast of Alaska, during the Ice Cover (~April), Break Up (~June), and Open Water (~August) periods of 2023, and Ice Cover in 2024, from all microalgae habitats. Ice-associated samples were not collected in Open Water, or at all stations during Break Up, due to lack of sea ice. We found that ice-associated and benthic microalgae communities remained stable in their community composition over space and time, and both methods agreed that these communities were dominated by diatoms. In contrast, phytoplankton communities varied both spatially and temporally through the identification of six unique clusters. The data showed that seasonality (temporal variations) and freshwater influence (spatial variation) were the primary distinction between clusters, but that Ice Cover and Open Water also had intraseasonal variations (spatial variation) in community structure that were likely due to differences in nutrient limitation and freshwater influence. The two methods agreed on general overarching trends in the data, although HPLC analyses greatly underestimated the contribution of dinoflagellates and chrysophytes, which were shown to be prevalent in all clusters through 18S analyses. This study demonstrates that Arctic lagoonal microalgae distinctly vary their community structure with the seasons, and that Arctic freshening under climate change may further shift community structure within the lagoons with continued climate change. Further, our work supports that for the best determination of microalgae communities, multiple methods (i.e., HPLC, 18S, microscopy) should be used, especially within understudied environments.