Light and temperature demands of marine benthic microalgae and seaweeds in polar regions

Abstract

Polar algae have a striking ability to photosynthesize and grow under very low light and temperatures. In seaweeds, minimum light demands for photosynthetic saturation and compensation can be as low as 10 and 2 μmol photons m-2 s-1, respectively. For benthic microalgae, these values can be even lower because of the limited irradiance reaching deep sea floors. The extreme shade adaptation of these organisms sets their distributional limits at depths close to 40 m and enables them to tolerate long periods of extended darkness. In addition to their capability for efficient photosynthesis at extremely low light levels, polar algae possess metabolic adaptations to persist at low temperatures, which permit them to complete their life cycles at year-round temperatures close to 0°C. Seaweeds with the lowest temperature demands are the species endemic to the Antarctic while Arctic algae are comparatively less cold-adapted. These adaptive characteristics allow benthic marine algae to make high contributions to high latitude coastal primary productivity and energy fluxes, exceeding or equaling the production of primary producers in more temperate systems. The studies summarized here give important insights into the major physiological adaptations allowing marine benthic microalgae and seaweeds to colonize these extreme habitats.

Primary producers and production in Hornsund and Kongsfjorden – comparison of two fjord systems

“…-Seaweeds can reach high primary productivity in some areas, which can be comparable to or even higher than that of phytoplankton (Gómez et al 2009). Arctic macroalgal primary productivity reaches up to 20 g C m -2 ·y -1 (estimated for the brown algal species Laminaria solidungula).…”

“…Arctic macroalgal primary productivity reaches up to 20 g C m -2 ·y -1 (estimated for the brown algal species Laminaria solidungula). However, depending on the species, it may be only 1-2 g C m -2 ·y -1 (for Saccharina latissima, Gómez et al 2009). Benthic micro-and macroalgae in Arctic coastal areas may potentially provide 28% and 13% of the net primary production, respectively (Gómez et al 2009).…”

“…For the purposes of this paper, we assume, following Gómez et al (2009), that the macroalgal primary production in Hornsund and Kongsfjorden may range from 2.0 to 20 g C m -2 ·y -1 and that the production rate depends on the surface of the seabed in the euphotic zone.…”

Stress tolerance of Antarctic macroalgae in the early life stages

“…However, some comparative studies at 0°C indicate that microscopic gametophytes and embryonic sporophytes of the endemic brown alga Desmarestia menziesii show higher photosynthesis than adult sporophytes [13]. Overall, upper temperatures for development of early phases appear to be lower than those for macro thalli, showing a remarkable capacity to tolerate temperatures well above those measured in situ [1]. For example, some spores and gametophytes of Antarctic Desmarestiales grow in conditions reaching 15°C with upper survival temperatures as high as 18°C [14].…”

“…Macroalgae thrive by virtue of their highly efficient metabolic adaptations to photosynthesize and grow at low temperature and almost permanent low light conditions. However, during maturation and development of early phases, e.g., spores, gametes and embryonic thalli, Antarctic macroalgae can be vulnerable, especially to episodic enhanced solar radiation during late winter-spring, following break-up of the ice cover (reviewed by [1]). Although studies have reported on the effects of UV radiation, temperature and their interactive effects on Antarctic macroalgae, they have mostly focused on the adult stages (e.g., [2,3]), while studies on early life stages are scarce.…”