46 Routes from the Sea 



Islands 



Islands surrounded by ocean are more or less isolated environ- 

 mental units which usually have a fauna and flora limited to com- 

 paratively few species (Stefani, 1929; Gulick, 1932) . Such an area 

 as an island oifers is soon invaded by animals which have recently 

 come from the ocean, especially crustaceans such as the crabs be- 

 longing to the genera Ocypode and Geograpsus; terrestrial hermit 

 crabs (Coenobita, Birgus) ; isopods; and amphipods. The food of 

 such animals is chiefly vegetation and organic refuse (Andrews, 

 1900; Borradaile, 1903; Pearse, 1929, 1931). Gulick (1932) has 

 emphasized the fact that isolated islands are not populated by land 

 plants, snails, and vertebrates by spreading migrations from the 

 ocean, though he admits that such animals as the gobies that live in 

 Hawaiian streams have come from the neighboring littoral waters. 

 "Really radical new departures seem to require a longer time allow- 

 ance than these geologically not very permanent islands can fur- 

 nish." Gulick believes that insular animals such as he discusses are 

 disseminated by wind storms and flight, and to a less extent by 

 transportation on flotsam. The seeds of some island plants remain 

 viable after being immersed in sea water for from thirty to ninety 

 days (Borza dC Bujorean, 1927) . 



The islands Verlaten and Krakatoa, which lie between Java and 

 Sumatra, were covered by volcanic ashes in 1883, and most or all 

 of the life on them was thus destroyed. Dammerman (1926, 1928) 

 has studied the repopulation of these islands. He observed that the 

 first animals to appear were largely vegetarians and scavengers. A 

 large percentage of these were animals that were able to fly or 

 balloon. Within a few years land crustaceans, land moUusks, earth- 

 worms, lizards, and snakes were present. It is possible that life was 

 not completely destroyed on these islands (Scharif, 1926; Backer, 

 1930) , but Dammerman states that the islands were covered with 



