Dark survival in a warming world

Abstract

Most algae regularly experience periods of darkness ranging from a few hours to a few days. During this time, they are unable to photosynthesize, and so must consume stored energy products. However, some organisms such as polar algae and some microalgal cysts and spores are exposed to darkness for months to years, and these must use alternative strategies to survive. Some taxa, such as dinoflagellates, form cysts and become dormant. Others use physiological methods or adopt mixotrophy. The longest documented survival of more than a century was for dinoflagellates buried in sediments in a Norwegian fjord. Seasonal changes in daylight hours are naturally unaffected by climate change. This means that polar microalgae will in the future need to survive the same period of seasonal darkness but at higher temperatures, and this will require a greater drawdown of stored energy. Recent experimental work has shown that both Arctic and Antarctic phytoplankton are able to survive increases of up to 6°C in the dark.

Effects of prolonged darkness and temperature on the lipid metabolism in the benthic diatom Navicula perminuta from the Arctic Adventfjorden, Svalbard

“…The chemical energy of lipid reserves can subsequently be used during long dark periods (McMinn and Martin 2013). Experimental evidence, however, about the utilization of lipid storage products for long term dark survival in diatoms, is still rare.…”

“…The lipid degradation was temperature independent, whereas the protein and carbohydrate consumption increased with temperature, especially at the beginning of the dark period (Dehning and Tilzer 1989). Consequently, a higher metabolic rate caused by an increase of temperature, as predicted in global warming scenarios, can lead to a more rapid catabolism of stored energy products and hence possibly to shorter dark survival times (McMinn and Martin 2013). This could be followed by the utilization of other potential energy sources, such as the degradation of organelles like chloroplasts (Baldisserotto et al 2005;Karsten et al 2012) or the switch to a heterotrophic lifestyle, i.e.…”

“…In diatoms different mechanisms have been described for long-term dark survival (McMinn and Martin 2013). Those include the utilization of stored energy products (Palmisano and Sullivan 1982), the reduction of metabolic activity (Palmisano and Sullivan 1982), formation of resting stages (Durbin 1978;McQuoid and Hobson 1996), and/or a facultative heterotrophic lifestyle (Lewin and Lewin 1960;Hellebust and Lewin 1977;Tuchman et al 2006).…”

Photosynthetic activation of the dark-acclimated diatom <i>Thalassiosira weissflogii</i> upon light exposure

“…Antia 1976). Several mechanisms for the survival of phytoplankton under dark conditions have been proposed, including the formation of resting cells, heterotro-phic nutrition, and reduced respiratory activity (McMinn & Martin 2013). However, for some phytoplankton species, such as the ubiquitous diatoms Asterionella japonica and Thalassiosira weissflogii, the formation of resting cells and heterotrophy do not appear necessary for survival in prolonged darkness (Smayda 1958, McQuoid & Hobson 1996, although reduced respiratory activity may occur.…”

Summer and fall distribution of phytoplankton in relation to environmental variables in Labrador fjords, with special emphasis on Phaeocystis pouchetii

“…In most arctic and subarctic ecosystems, the annual growth season of phytoplankton cells can be described as follows: in winter and early spring, low incident irradiance and sea-ice cover prevent any photosynthetic activity, and the community is dominated by nano-sized (2−20 µm) heterotrophic protists (Sherr et al 2003, Terrado et al 2008, Iversen & Seuthe 2011. Under these unfavourable conditions, some diatoms and dinoflagellates produce resting spores or cysts (Różań ska et al 2008) or become dormant in darkness (Smayda & Mitchell-Innes 1974, McMinn & Martin 2013. From April to mid-May, phytoplankton growth starts when warming and subsequent ice-melt lead to stratification of the water column, with the surface mixed layer becoming shallower than the critical depth (i.e.…”