Figure 5.14: The ice alga Melo-
sira arctica on the underside of
Arctic multi-year sea ice.
Photo: Haakon Hop, Norwegian Po-
lar Institute
Ice algae – the primary producers Ice fauna – the secondary producers
Ice algae are the primary producers in ice-associated food The smallest animals (less than 1 millimetre) associated
webs, and consist primarily of diatoms, but also include with Arctic sea ice include nematode and turbellarian
other types of algae originating from the pelagic (open- worms, crustaceans and other tiny invertebrates such as
water) system
46,47
. Large strands of the ice diatom Melosira rotifers
47
. These organisms feed on algae and microbes
53
.
arctica (Figure 5.14) are found in Arctic multi-year ice
48
. The macrofauna (animals large enough to be seen with
The algae attach to ice-crystal structures on the underside the naked eye) in drifting sea ice consist mainly of several
of Arctic ice
49
, whereas in Antarctica, an important fea- species of ice amphipods (Figure 5.15b), but also include
ture of the sea ice is the infiltration communities of algae, polychaete worms and a species of copepod crustacean
54,55
.
associated with the nutrient-rich snow–ice interface
50
. The abundance and biomass of the macrofauna varies
with the type of ice as well as the under-ice topography
54
.
Ice algal production may constitute up to 20 to 25 per Land-fast ice may also house amphipods as well as mysids
cent of the total primary production in Arctic waters
46,51
(another small crustacean)
56
that feed on a mix of ice algae,
and 10 to 28 per cent of primary production in Antarctic ice-associated fauna, zooplankton and detritus. Polar cod
ice-covered waters
1
. In the Arctic, the production of ice are often associated with sea ice, where they feed on ice-
algae starts in February and March, about two months amphipods as well as the floating zooplankton
57,58
.
earlier than the phytoplankton (free-floating algae)
bloom. During the seasonal ice melt, ice algae contribute In the Antarctic copepods are the dominant crustaceans
substantially to the vertical movement of organic matter found in the small spaces within the sea ice, but am-
in the water column and provide food for the inverte- phipods and krill (the shrimp-like crustaceans that are
brates and fishes living in the depths of the ocean
52
. Ar- so important to Antarctic food webs) are also associated
eas with extensive ice and algal biomass thus represent with ice
59
. Adult krill are mainly herbivorous, feeding on
“hot spots” with high biomass. These areas can have diatoms, although they have a flexible feeding behaviour
rich shrimp grounds and abundant clam populations, and are capable of capturing other types of food from
providing food for marine mammals – for example the different habitats. Adult krill are generally in open water,
walrus, who feed extensively on clams. but can also be found underneath the ice cover. How-
CHAPTER 5 ICE IN THE SEA 81
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