Timing of blooms, algal food quality and Calanus glacialis reproduction and growth in a changing Arctic

Abstract

The Arctic bloom consists of two distinct categories of primary producers, ice algae growing within and on the underside of the sea ice, and phytoplankton growing in open waters. Long chain omega-3 fatty acids, a subgroup of polyunsaturated fatty acids (PUFAs) produced exclusively by these algae, are essential to all marine organisms for successful reproduction, growth, and development. During an extensive field study in the Arctic shelf seas, we followed the seasonal biomass development of ice algae and phytoplankton and their food quality in terms of their relative PUFA content. The first PUFA-peak occurred in late April during solid ice cover at the onset of the ice algal bloom, and the second PUFA-peak occurred in early July just after the ice break-up at the onset of the phytoplankton bloom. The reproduction and growth of the key Arctic grazer Calanus glacialis perfectly coincided with these two bloom events. Females of C. glacialis utilized the high-quality ice algal bloom to fuel early maturation and reproduction, whereas the resulting offspring had access to ample high-quality food during the phytoplankton bloom 2 months later. Reduction in sea ice thickness and coverage area will alter the current primary production regime due to earlier ice break-up and onset of the phytoplankton bloom. A potential mismatch between the two primary production peaks of high-quality food and the reproductive cycle of key Arctic grazers may have negative consequences for the entire lipid-driven Arctic marine ecosystem.

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…This is mostly because ice algae are attached to the ice and therefore not subject to vertical motion in the water column affecting average light exposure of phytoplankton in a mixed layer. Ice algae also provide a critical early season and high-quality food source for the growth and reproduction of pelagic herbivores [Søreide et al, 2010;Flores et al, 2012].…”

Advection in polar and sub-polar environments: Impacts on high latitude marine ecosystems

“…Conversely, expanded areas of open water may delay the phytoplankton bloom due to wind-induced mixing delaying the formation of the seasonal pycnocline, as is apparently the case in the eastern Bering Sea (Baier and Napp, 2003;Bluhm and Gradinger, 2008;Hunt et al, 2011). Changes in timing of bloom events may have repercussions for herbivorous zooplankton and ice fauna species as the probability for a ''mismatch" increases if the sequential timing is altered for primary production blooms relative to life history events of herbivores that rely on energetic input from the blooms (e.g., for reproduction and recruitment; Baier and Napp, 2003;Søreide et al, 2010;Varpe, 2012;Daase et al, 2013). In the southeastern Bering Sea, a mis-match between the timing of blooms related to sea-ice retreat and the needs of hebivores appears to have severe negative impacts on the recruitment and subsequent abundance of large copepods and euphausiids (Baier and Napp, 2003;Hunt et al, 2011;in press;Renner et al, 2016).…”

“…Species diversity has already declined, at least regionally (Melnikov et al, 2002), but differences in sampling efforts also need to be taken into consideration when determining change. Allochthonous macrofaunal species, as well as ice algae and meiofauna, are expected to be less affected since they rely on sea ice for only part of their life cycles and can re-colonize seasonal ice (Søreide et al, 2010;Hop et al, 2011). Changes in the location of sea ice will impact the fate of ice-dwelling organisms when the ice melts and will also affect the vertical flux of particulate organic matter to the benthos.…”

“…The main effect of changes in ice cover and timing of ice melt may be on the timing and fate of ice algae and phytoplankton blooms (Søreide et al, 2010;Leu et al, 2011). Early ice retreat and thinner ice will lead to an increase of irradiance in the water column and under the ice, which may shift the onset of ice algal and phytoplankton production to earlier in the season (Arrigo and van Dijken, 2011;Frey et al, 2011;Ji et al, 2013).…”

“…For example, in the Arctic, early retreat of sea ice may affect the productivity of Calanus glacialis, since their reproduction and/or the growth of the new generation depends on energy provided by ice algae, (e.g., ice-associated diatoms, such as Nitzschia frigida), as well as on the timing of ice algae and pelagic blooms relative to each other (Runge and Ingram, 1991;Søreide et al, 2010). Likewise, in the Southern Ocean, loss of sea ice would affect the productivity of both Antarctic krill and copepods (Atkinson et al, 2004).…”