Increased irradiance reduces food quality of sea ice algae

Abstract

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.

Assessing the importance of terrestrial organic carbon in the CHUKCHI and Beaufort seas

“…The C:N ratios reported for this area can all be broadly classified as marine, and are similar to previously reported values (Feder et al, 1994). C:N ratios above 12 have been reported for sea ice algae Leu et al, 2010), and also for water column POM in the Northeast Water polynya (Bauerfeind et al, 1997); the C:N ratios we report are lower than this. Consequently, we suggest that sites with higher C:N ratios could reflect contributions from low-quality, N-poor algal matter rather than high C:N terrestrial debris.…”

A (too) bright future? Arctic diatoms under radiation stress

“…This was manifested in significant differences between the algal cells exposed at 8 m compared to 0.5-m depth, together with a lack of significant differences between UVR and PAR treatments at the same depth. The physiologically important polyunsaturated fatty acids were reduced in all species compared to their start conditions, and in two of three species, we found higher values at 8 m than at 0.5 m. This is in line with previous studies about the detrimental effect of high-PAR irradiances on algal PUFAs (Leu et al 2006b, c;2010). Leu et al (2006c) found rapid changes in the biochemical composition of another Arctic diatom culture Thalassiosira antarctica var.…”

Temperature- and light-dependent growth and metabolism of the invasive red algaeGracilaria vermiculophylla– a comparison with two native macroalgae

“…Low temperatures and ice cover (i.e. low light) have been proposed to limit the distribution of G. vermiculophylla in the Baltic Sea (Nyberg et al, 2009) but in the present experiment, we found positive growth rates at conditions that are relatively similar to those found under ice (1 µmol photons m -2 s -1 and 5°C: Leu et al, 2010;Smethie et al, 2011). Our results are consistent with the findings of Yokoya et al (1999, see Table 5), who also found positive growth rates at a temperature of 5°C in culture experiments.…”