The Davis Strait - DCE - Nationalt Center for Miljø og Energi

The coastal zone of the assessment area normally has open water year round
but may be impacted by drift ice. This ice as well as the marked seasonal
changes in light regime and low water temperatures call for efficient adaptative
strategies. The ability to support a photosynthetic performance comparable
to that of macroalgae in temperate regions might be explained by low
light compensation points and relatively low respiration rates during periods
of poor light conditions, and indicates an adaptation to constant low
temperatures and long periods of low light intensities (Borum et al. 2002).
Furthermore, a fast response in photosynthetic performance to changing
light conditions is considered to be part of a physiological protection strategy
in a highly variable environment as in, e.g., the littoral zone, as well as to
ensure optimal harvest of light when available (Krause-Jensen et al. 2007,
Becker et al. 2009). No studies elucidating the macroalgal production or photosynthetic
strategies have been conducted in the assessment area, though.
The sea ice also exerts a high physical impact factor on the macroalgal vegetation
because of ice scouring. The mechanical scouring of floating ice floes
prevents especially perennial fucoid species establishing in the littoral zone,
which is the zone mostly influenced by the ice dynamics. Even though the
assessment area is an open water region (Mosbech et al. 1996b) pack ice from
Baffin Bay and East Greenland may impact exposed coast lines, which then
may be subject to the phenomenon of opportunistic green algae development.
Perennial species from the littoral zone do tolerate temperatures at or close
to freezing, and might survive at an ice foot, when this phenomenon occasionally
occurs in the assessment area, and the ice foot melts without disrupting
the vegetation. It was shown for Fucus distichus from Spitsbergen
that the species was able to halt the photosynthetic activities at subzero temperatures
and resume almost completely when unfrozen (Becker et al. 2009).
Water of low salinity or fresh water may influence the macroalgal vegetation
especially in the intertidal zone when exposed to rain and snow during low
tide and when sea water mixes with fresh and melt water during seasons
with high water run off from land. Low tolerance to hyposaline conditions
may result in bleaching (strong loss of pigments) or increased mortality,
which suggests that hyposalinity may impact on the photosynthetic apparatus,
as shown for kelp species at Spitsbergen (Karsten 2007).
Substratum characteristics are also important for the distribution and abundance
of macroalgal vegetation, and only hard and stable substratum can
serve as a base for a rich community of marine, benthic macroalgae. However,
commonly some macroalgal species are attached to shells, small stones or
occur loose-lying in localities with a soft, muddy bottom. Naturally occurring
loose-lying macroalgae tend to be depauperate, probably due to poor
light and nutrient conditions. When not attached to stable substratum the
algal material drifts and clusters result in self-shading and nutrient deficiency
within the algal cluster. Furthermore, soft bottom localities, often located
in the inner parts of fjords, are created and influenced by resuspended particles
in melt water. The light conditions are impacted due to significantly reduced
water transparency as well as sedimentation of resuspended particles
on the macroalgal tissue results in shading. Along the coasts of the calm
fjords around Nuuk in the assessment area loose-lying macroalgae of brown
and green algae was observed by Christensen (1981).
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