Phytoplankton Successions in the Canadian Arctic 627 



hydrograpliical character of waters deri\^ed from different bio- 

 geographical regions, such as Polar and Atlantic, as well as fresli 

 water. Similar diversity was found in phytoplankton at Point Bar- 

 row, Alaska, with 90 diatoms, 78 dinoflagellates, and 22 flagellates, 

 compared to Isachsen, with 48 diatoms, 38 dinoflagellates and 

 20 flagellates. These localities, 990 miles apart, show different 

 ecological conditions. Point Barrow plankton originates in dif- 

 ferent areas, such as tlie Pacific, Bering Sea and Arctic Ocean, 

 while tlie Isachsen plankton is essentially polar autoclithonous. 



The general course of seasonal successions in the Canadian 

 arctic is similar to that in Denmark Strait, according to Braarud 

 (3), in the East Greenland Current, according to Steeman Niel- 

 sen (10), and East Greenland waters (6), although the taxonomic 

 composition of the standing crops differs according to locality. 



Certain pennate diatoms are exclusively arctic endemic, and 

 their range seems to parallel the distribution of ice, which in- 

 creases the capacity for attachment. Ice creates ecological niches 

 for surface blooms, microflora of meltwater ponds on the ice 

 surface, and for films of diatoms on the under surface. Arctic 

 neritism is characterized l)y the abundance of neritic, freshwater 

 and brackish forms permitted by the existence of the ice. The 

 pennate diatoms, adapted to reduced light under the ice, initiate 

 their growth probably as late as late May at Isachsen, April at 

 Igloolik, possibly in March in James Bay and southern Hudson 

 Bay, and in the winter in tlie Gulf of St. Lawi'ence. Arctic 

 endemic diatoms are known in the Gulf of Maine (1, 8), and are 

 common in the Gulf of St. Lawrence according to Gran (7). A 

 brown-green film of diatoms taken from ice in the Gulf of St. 

 Lawrence in April, 1957, consisted mostly of arctic endemic 

 forms, in which Pennatae dominated in biomass. These vanish 

 from the plankton when tlie ice melts in spring. This earlv-spring, 

 ice-loving succession has its southern range limited by the dura- 

 tion of ice. 



Freshwater green flagellates, Euglena, Chlamyclomonas, 

 Polyhlepharis, ChloreUa, and the chrysomonads, AlaUomonas and 

 Ochromonas, constitute an autotrophic, acclimatized arctic suc- 

 cession, abundant in Ijrackish and high salinity waters. Although 

 Peridineae are rare, fair numbers of them live in the arctic. Some 

 holophytic Gymnodinioideae become abundant at the end of 



