Fatty acid composition, element concentration and isotope ratios of sea ice algae sampled in Rijpfjorden, Svalbard

The accelerating decrease of Arctic sea ice substantially changes the growth conditions for primary producers, particularly with respect to light. This affects the biochemical composition of sea ice algae, which are an essential high-quality food source for herbivores early in the season. Their high nutritional value is related to their content of polyunsaturated fatty acids (PUFAs), which play an important role for successful maturation, egg production, hatching and nauplii development in grazers. We followed the fatty acid composition of an assemblage of sea ice algae in a high Arctic fjord during spring from the early bloom stage to post bloom. Light conditions proved to be decisive in determining the nutritional quality of sea ice algae, and irradiance was negatively correlated with the relative amount of PUFAs. Algal PUFA content decreased on average by 40 % from April to June, while algal biomass (measured as particulate carbon, C) did not differ. This decrease was even more pronounced when algae were exposed to higher irradiances due to reduced snow cover. The ratio of chlorophyll a (chl a) to C, as well as the level of photoprotective pigments, confirmed a physiological adaptation to higher light levels in algae of poorer nutritional quality. We conclude that high irradiances are detrimental to sea ice algal food quality, and that the biochemical composition of sea ice algae is strongly dependent on growth conditions.北极海冰 (Arctic sea ice) 的加速消融显著改变了初级生产者 (primary producers) 的生长条件，其中光照条件的变化尤为突出。这一变化会影响海冰藻类 (sea ice algae) 的生化组成，而海冰藻类是季节早期草食动物 (herbivores) 赖以生存的优质食物来源。海冰藻类的高营养价值与其多不饱和脂肪酸 (polyunsaturated fatty acids, PUFAs) 的含量密切相关，这类脂肪酸对于牧食者 (grazers) 的顺利成熟、产卵、孵化以及无节幼体 (nauplii) 发育均具有重要作用。本研究于春季对北极高纬度峡湾 (fjord) 中的海冰藻类群落从早期水华 (bloom) 阶段到水华后期的脂肪酸组成进行了追踪监测。研究结果表明，光照条件是决定海冰藻类营养品质的关键因素，且辐照度 (irradiance) 与PUFAs的相对含量呈负相关关系。4月至6月间，藻类的PUFA含量平均下降了40%，而藻类生物量 (以颗粒碳 (particulate carbon)，C计) 则无显著变化。当积雪减少导致藻类暴露于更高辐照度环境中时，PUFA含量的下降幅度更为显著。叶绿素a (chlorophyll a, chl a) 与碳的比值，以及光保护色素 (photoprotective pigments) 的水平，均证实了营养品质较低的藻类会通过生理适应以应对更高的光照水平。本研究最终得出结论：高辐照度会损害海冰藻类的食物品质，且海冰藻类的生化组成强烈依赖于其生长环境条件。