454 ANNVAL REPORT SMITHSONIAN INSTITUTION, 19 63 



By this mechanism the coral provides for long-range exploratory 

 colonization by the first produced larvae which have a long free life, 

 and for more assured colonization of the immediate environment by 

 the later produced forms which are ready for sessile life almost im- 

 mediately. The observable contagious distribution of corals in the 

 Antarctic argues that the latter distributional means prevails; corals 

 occur in local high density populations because of their short larval life. 

 The current pattern of the Southern Ocean is well calculated to 

 develop a widely distributed shallow- water fauna about the Antarctic 

 Continent. The West Wind Drift should effectively carry the shallow 

 water marine fauna of South America to the Subantarctic Islands 

 along the route of the sea mounts and high ridges, as should the fauna 

 of the southern portion of New Zealand be distributed through its 

 Subantarctic Islands. The range of these faunas is now being studied. 

 One feature that has emerged is that the West Wind Drift, while being 

 effective as a transportation agent, is also acting as a barrier to the 

 distribution of animals from the subantarctic regions to the Antarctic. 

 For example, the Scotia Arc should provide an excellent series of 

 steppingstones for the shallow fauna of the South American coast to 

 reach the Antarctic. Instead, we find that the region between Cape 

 Horn and Shag Rock (fig. 2) is apparently a barrier — that the Ant- 

 arctic fauna extends to Shag Rock, while the South American fauna 

 has not been notably successful in crossing Drake Passage. The 

 strong winds and current which are a means for such short-flighted 

 birds as the Rail to make the jump from Tierra del Fuego to South 

 Georgia are an effective barrier to a number of marine organisms. 

 Near shore the East Wind Drift should be the distributing mechanism 

 about the Antarctic, and the circumpolar aspect of the fauna attests 

 to its effectiveness. However, we are basing our claims upon the sup- 

 position that surface currents are effective to the depth of the conti- 

 nental shelves. It may be that bottom currents acting in different 

 directions are the actual distiibuting mechanisms, for the larvae of 

 the corals do not rise far above the bottom if they are advanced in 

 development upon liberation. A fascinating, but as yet incompletely 

 tested hypothesis dealing with this aspect suggests that the direction 

 of movement of the Antarctic Bottom water should influence the dis- 

 tribution of species. One shred of evidence for this was collected 

 when at approximately 2,000 meters on the Argentine Continental 

 Slope a trawl containing a few species of "Argentine" corals also con- 

 tained individuals of a species characteristic of shallow waters on the 

 Antarctic Shelf. Could this be an instance of the animal following the 

 temperature gradient and possibly migrating across the Drake Pas- 

 sage? Many more finds of a similar nature will be required to give a 

 definite answer. The distribution of corals at depths greater than 

 those of the Continental Shelves is difficult to generalize about, for as 



