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PACIFIC SCIENCE, Vol. XXII, October 1968 
U.S. Fish and Wildlife Service. No plants are 
known to occur in the western Aleutian Islands, 
probably due to the lack of protected bays. 
Plants are known from Kamchatka Peninsula 
and Bering Island on the Asian side of the 
Bering Sea (Hulten, 1926:75, 1960:69). 
In the Bering Sea Zostera forms extensive 
meadows in the numerous coastal lagoons of 
the Alaska Peninsula (Fig. 1 and Table 1). 
The meadows in Izembek Lagoon on the Penin- 
sula are the largest known single stand of the 
species (McRoy, 1966:103). Farther north, 
Zostera occurs in Nanvak and Chagvan bays 
and in many of the lagoons at the mouths of 
rivers on Nunivak Island (King, personal com- 
munication, 1963). No other Zostera beds have 
been found between King Salmon and St. 
Michael. 
Porsild (1932:90-94) recorded the northern 
distribution of Zostera from St. Michael to Port 
Clarence (Fig. 1 and Table 1). Kjellman 
(1883:53) first observed Zostera in Port Clar- 
ence, the accepted northern limit in Alaska. 
Recently, Zostera has been seen beyond Bering 
Strait in the lagoons (Lopp and Ikpek) of the 
north coast of the Seward Peninsula (Burns, 
personal communication, 1967). I have also 
extended surveys to portions of the coast be- 
tween Kotzebue and Barrow, but have not 
uncovered any other Zostera producing areas. 
Mechanisms of Dispersion 
The distribution of Zostera in Alaska and 
elsewhere in the Northern Hemisphere is the 
result of dispersion by several mechanisms. 
Oceanic currents appear to be the most effective 
means of long range dispersion, although there 
is some disagreement on this. Love (1963:195) 
observes that saltwater plants are adapted to 
dispersal in sea water and cites as an example 
the seeds of Zostera with their corky appendages 
and bouyant vegetative parts. Sculthorpe (1967: 
358), on the other hand, considers Love’s view 
of dispersal an "unfortunate generalization,” 
since the seeds of Zostera and other marine 
angiosperms either float for only a short time 
or sink immediately. The seeds of Zostera have 
a specific gravity of 1.17 (Arasaki, 1950:70- 
76), a value somewhat greater than the 1.025 
average of the ocean (Von Arx, 1962:118) 
and so would be expected to sink. In fact, how- 
ever, the seeds are released attached to a repro- 
ductive stem which has several leaves and is 
capable of floating for long distances. Mats of 
Zostera and other marine angiosperms have 
been seen at sea several hundred miles from 
the coast (Menzies, Zaneveld, and Pratt, 1967: 
112). There can be no doubt that dispersion 
on a large scale is accomplished through the 
seed -producing and perhaps vegetative plants 
that annually detach and drift with oceanic 
surface circulation. 
The several species of waterfowl that feed 
on Zostera are another vehicle for dispersion. 
Love and Sculthorpe concur. Arasaki (1950: 
70-76) demonstrated that ducks do not destroy 
the viability of all seeds they ingest. The coast 
of Alaska is a flyway for numerous species of 
waterfowl that annually transport seeds over at 
least short distances and probably farther. This 
is a mechanism for dispersion in a direction 
opposite to that of the coastal oceanic currents. 
In a local area Zostera extends its cover prin- 
cipally by vegetative growth from rhizomes, a 
process quantitatively more important than the 
growth of new seed plants. Again, Arasaki 
(1950:70-76) has shown that a single plant 
will cover 30 cm 2 the first year, 1 m 2 the second, 
and 2 m 2 the third. At this rate, it would not 
take long for a population to develop in a 
new area once a plant has been introduced. 
Bio geo graphical Considerations 
The global distribution of this species is 
discontinuous circumboreal. The other species 
of the seagrasses, with few exceptions, are trop- 
ical or subtropical and are considered to have 
originated in the Indian Ocean (Setchell, 1935: 
564— 572). The genus Zostera , however, has no 
tropical representatives and apparently arose in 
the western Pacific Ocean, dispersing into the 
Northern and Southern hemispheres at a time 
when the tropics were less tropical. This his- 
tory is supported by the present distribution of ; 
the 11 species of Zostera (Setchell, 1935:572) 
and the locations of fossils of Zostera ancestors 
in Japan (Koriba and Miki, 1930:165-204; 
Miki, 1932:774-778). 
If the origin of Zostera marina was the west- 
ern Pacific, then migration could have taken 
either of two routes. In the first case, dispersion 
could have moved in two directions from the 
