Biochemical Indicators of Atlantification and Diapause Strategy in Arctic Copepods Point to a Decrease in Copepod-mediated Carbon Sequestration

Arctic ecosystems are critically endangered by rising temperatures and changing hydrography, especially the intrusion of increasingly warm water from the Atlantic Ocean known as Atlantification. In addition to housing fragile biodiversity, Arctic copepods and their lipids play a crucial role in cycling carbon by transporting carbon into the deep ocean through their diapausing behaviors. Here, we explored the lipidomes of the Arctic copepod Calanus glacialis, collected from three fjords around Svalbard during November 2022 when C. glacialis are known to be in diapause. These three field sites provide a natural laboratory experiment, as they are influenced by different water masses with varying degrees of Atlantic water, and experience vast differences in sea ice coverage over the year. These environmental differences were clearly reflected in the lipidomic analysis, with stations influenced most by Atlantic Warm Water having the lowest total lipid concentrations and the lowest accumulation of storage lipids necessary for entering diapause. Membrane lipids were a significant proportion of the Svalbard copepod lipidomes, with the highest ratios observed at the Atlantified site. The high membrane lipid and high triacylglycerol concentrations were interpreted as signs of active feeding. This was further corroborated by fatty acid composition analysis, which revealed dietary biomarkers of carnivory at Atlantified sites. The copepods from the site most insulated from Atlantic influence had more than double the amount of storage lipids per individual and fatty acids associated with diatom biomass, indicating assimilation in the spring. Ultimately, the decrease in lipid content observed in association with Atlantification around Svalbard will impact diapause patterns, as Calanus species need 20-30% more WE to successfully complete diapause. In turn, this will impact the magnitude of carbon sequestration through the seasonal lipid pump, not to mention having radiating effects through the Arctic food web where Calanus glacialis plays an important role. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/738257v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@fc9321org.highwire.dtl.DTLVardef@1f6336org.highwire.dtl.DTLVardef@aaa3a1org.highwire.dtl.DTLVardef@dcd2a8_HPS_FORMAT_FIGEXP M_FIG C_FIG