Marine Micro- and Macroalgae in the Polar Night

Abstract

The chapter illucidates aspects of the ecology of micro-and macroalgae with a focus on the dark sesason. It comprises of six parts and starts with an introduction (4.1) about Arctic marine micro-and macroalgae. Section 4.2 reviews the key abiotic environmental variables related to micro-and macroalgae growth and survival. The description of the different groups of microalgae are shown in section 4.3, comprising phytoplankton, microphytobenthos and seaice algae. Section 4.4 describes the three classes of macroalgae (phaeo-, rhodo-and chlorophytes) with information about biological variables, seasonal processes and habitats. Section 4.5 describes the ecophysiology of microalgae and macroalgae in the Polar Night. The last section 4.6 gives conclusive remarks of what we know and don't know with suggestions for future research. Microalgae have unique adaptions including life cycles and ecophysiology that allows them to rapidly grow once light comes back in spring, while some macroalgae can utilize the Polar Night for growth. For microalgae, resting stages and mixotrophy appear to be adaptive traits to survive the winter season. In contrast, some macroalgal species may act as "season anticipators" and utilize the winter darkness or initial spring period as major growth seasons. We still lack basic knowledge about the overall biodiversity, ecology and physiology of microalgae and both annual and perennial species of macroalgae during the winter months.

Under-Ice Phytoplankton Blooms: Shedding Light on the “Invisible” Part of Arctic Primary Production

“…The initiation of an UIB requires a viable seed population of algal cells present in the euphotic zone of the water column under the ice. There are three potential seeding sources for UIBs: (a) algal cells in the water column, (b) vegetative cells or resting stages at the sediment surface, and (c) algal cells or resting stages entrapped in sea ice that are released during melt onset at the underside of the ice (Johnsen et al, 2020). Very little is known about the relative importance of these three different seeding strategies, but it likely varies strongly depending on mixing depth, bottom topography, and sea-ice conditions.…”

“…This leads to extended periods where ambient irradiances are not sufficient for in situ primary production in ice-free surface waters (Kvernvik et al, 2018), and even less so underneath sea-ice cover (see also the previous section "Physiological Phytoplankton Assemblage Responses to Varying Light Regimes"). Phytoplankton have adapted through various strategies to cope with these conditions, ranging from mixotrophy/heterotrophy, resting stage formation, and utilization of internal lipid stores to survival of vegetative cells with lowered metabolic activity (Johnsen et al, 2020). Phytoplankton communities during wintertime are characterized by very low cell concentrations and a predominance of small, flagellated cells, as well as heterotrophic dinoflagellates (Lovejoy et al, 2007;Błachowiak-Samołyk et al, 2015;Brown et al, 2015;Vader et al, 2015).…”

Seasonal Variability in the Zooplankton Community Structure in a Sub-Arctic Fjord as Revealed by Morphological and Molecular Approaches

“…This synchronization allows the acquisition and accumulation of energy and an efficient energy transfer to higher trophic levels. The dark winter season is particularly poorly studied for activity of phyto-and zooplankton, although recent research demonstrated that this season is by no means a period of inactivity, and several trophic levels remain active and complete important parts of the life cycles in the dark season (Berge et al, 2020;Johnsen et al, 2020).…”

The Polar Night Shift: Annual Dynamics and Drivers of Microbial Community Structure in the Arctic Ocean

“…In this regard, the polar night is of key interest, when physical mixing [24][25][26] and microbial recycling of detrital and inorganic matter 27,28 replenishes nutrients to fuel the subsequent phytoplankton bloom. Arctic phototrophic taxa are thought to persist in dormancy 29 , responding rapidly when light and stratification return 30 .…”