Environmental and Biological Determinants of Algal Lipids in Western Arctic and Subarctic Seas

Abstract

The Arctic is undergoing numerous environmental transformations. As a result of rising temperatures and additional freshwater inputs, ice cover is changing, with profound impacts on organisms at the base of food webs and consequently on the entire Arctic ecosystem. Indeed, phytoplankton not only provide energy as lipids, but also essential fatty acids (EFA) that animals cannot synthesize and must acquire in their diet. Omega-3 (ω3) and omega-6 (ω6) polyunsaturated fatty acids (PUFA) are essential for the healthy development and function of organisms. The high energy potential of monounsaturated fatty acids (MUFA) is of particular importance in cold waters, and various fatty acids including saturated fatty acids (SFA) are involved in organismal responses to environmental stressors. Yet relatively little is known of how variability or change in physicochemical seawater properties (e.g., temperature, light, salinity, pH and nutrients) may affect lipid synthesis in polar environments, either directly, by altering algal physiology, or indirectly, by promoting shifts in phytoplankton species composition. Here we investigated these two possibilities by sampling along a 3,000-km transect spanning 28 degrees of latitude across the subarctic and Arctic domains of Canada. The taxonomic composition of phytoplankton mainly drove the FA profiles measured in particulate organic matter (POM). Strong, positive correlations between 16:1ω7 and diatoms were observed while the proportion of PUFA and ω6 FA increased with flagellate abundance. Among specific FAs, eicosapentaenoic acid (EPA; 20:5ω3) was positively correlated with diatoms but the expected relationship between docosahexaenoic acid (DHA; 22:6ω3) and dinoflagellates was not observed. Decreasing pH had a negative effect on EPA and MUFA proportions, and DHA proportions tended to decrease with higher temperature. These two effects were primarily driven by differences in phytoplankton assemblage composition. Overall, the results of this geographically extensive study provide new information into the use of lipid markers and the ecological determinants of FA synthesis in the North. It also highlights the importance of long-lived subsurface chlorophyll maximum layers in supplying PUFA-rich POM to the food web and suggests that this situation may persist despite ongoing changes in the physical environment.

Phytoplankton and seston fatty acid dynamics in the northern Bering-Chukchi Sea region

“…Yet, the utility of FA biomarkers to partition phytoplankton taxa is known primarily from monoculture experiments (Cañavate, 2019;Dunstan et al, 1993;Jónasdóttir, 2019). Using FA biomarkers to distinguish phytoplankton taxa in field samples is more challenging (Reuss and Poulsen, 2002), variable, and less studied (Galloway and Budge, 2020;Marmillot et al, 2020). Nonetheless, field studies in other high latitude systems, such as the Beaufort Sea (Connelly et al, 2016;Marmillot et al, 2020), West Greenland Sea (Reuss andPoulsen, 2002), andBarents Sea (Falk-Petersen et al, 1998) have highlighted that changes in phytoplankton composition, including seasonal shifts from diatoms to flagellates, are visible in the seston FA pools.…”

Essential omega‐3 fatty acids are depleted in sea ice and pelagic algae of the Central Arctic Ocean

“…Moreover, the selected studies all present the FA profiles as mass percentage of TFAs and include the following 16 key FA: 14:0, 15:0, 16:0, 16:1( n ‐7), 16:2( n ‐4), 16:3( n ‐4), 16:4( n ‐1), 18:0, 18:1( n ‐9), 18:1( n ‐7), 18:2( n ‐6), 18:3( n ‐3), 18:4( n ‐3), EPA, 22:5( n ‐3) and DHA (Leu et al., 2020). However, some studies identify far more than those 16 FA peaks (i.e., 58 FA, Marmillot et al., 2020). To allow a cross‐study comparison of proportional FA, we re‐adjusted each dataset to the 16 key FA, which in most cases comprise >85% of the total mass of analysed FAs (Table 1).…”

Cellular Damage of Bacteria Attached to Senescent Phytoplankton Cells as a Result of the Transfer of Photochemically Produced Singlet Oxygen: A Review

“…Sympagic algal preservation can be monitored in sediments by using the concentration of intact and oxidized C 16:1ω7 (palmitoleic) acid. Given the dominance of diatom biomass (compared to bacteria) in the Arctic, palmitoleic acid is generally considered to be a robust marker of primary producers in this region [ 127 ]. In parallel to measuring the concentrations of intact and oxidized palmitoleic acid, we paid particular attention to the oxidation state of cis-vaccenic and C 16:1ω5 acids (bacterial fatty acids) [ 128 , 129 ].…”

“…This assumption is well-supported by the strong photooxidation state of bacteria observed in sinking particles that were also collected during the 2016 GreenEdge campaign [ 112 ]. Note that palmitoleic acid concentration (i.e., a marker of the preservation of sympagic algal material) [ 127 ] appeared to be highest at the stations containing strongly oxidized (and, thus, inactive) bacteria ( Figure 7 ). These observations clearly establish the link between the degree of oxidative alteration of bacteria and the efficiency of biodegradation processes.…”