Sea ice, planc­ton and rela­ted issues …

The polar sea ice has its widest dis­tri­bu­ti­on during the late win­ter. The return of the sun­light in spring brings the algal bloom under the ice floes. As a result, zoo­plank­ton comes from deeper water lay­ers to the ice to feed on the algae. The­se small ani­mals are again prey for lar­ger orga­nisms such as fish and seals and thus, direct­ly or indi­rect­ly, for the who­le rest of the food chain up to polar bears. The basics of this sys­tem are com­mon know­ledge, but sci­en­tists are still working on many important details.

Mari­ne bio­lo­gists from the uni­ver­si­ty in Lon­gye­ar­by­en (UNIS) have found out that the litt­le crustaceae (in this case Cala­nus gla­cia­lis) are per­fect­ly adapt­ed to the sea­so­nal deve­lo­p­ment of sea ice in spring. The adult fema­les eat as much as they can in the twi­light under the clo­sed sea ice cover, until they are able to repro­du­ce. Two months later, their off­spring is lar­ge enough to pro­fit from a second algal bloom when the sea ice breaks up. The­se young, fat crustaceae are ide­al food for polar cod, seals, sea­birds such as guil­l­emots and wha­les.

In case the sea ice is get­ting thin­ner and thin­ner due to cli­ma­te chan­ge, the break­up will be ear­lier and the second algal bloom accor­din­gly ear­lier. As a result, the young phy­to­plank­ton might not yet be old enough to feed suf­fi­ci­ent­ly, which might lead to signi­fi­cant wea­k­e­ning of this important link in the arc­tic food chain, pos­si­bly lea­ding to major dis­tur­ban­ces of the arc­tic eco­sys­tem as we know it.

The colou­ra­ti­on of the ice is due to algae. In the midd­le a bea­ched repre­sen­ta­ti­ve of the arc­tic mari­ne fau­na that depends on the algal bloom for food.

Source: Sval­bard Sci­ence Forum

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