I. General Part. 



Notes on the external conditions under which the Caulerpas 

 live in Danish West India. 



Before mentioning in more detail the ecology and classification of the 

 Caulerpas, it seems to me advisable to give a short survey of the conditions of 

 life in the localities where we meet with these forms. 



It may at once be said that the much exposed shores which, not being 

 sheltered by off-lying rocky islands or coral-reefs, are open to the whole power of 

 the sea, can be left out of all consideration, as I have never met with Caulerpas at 

 these places. This agrees also with the observations of Svedelius in Ceylon, who 

 did not find Caulerpas growing in the most exposed localities. Out in the open 

 sea it is only in deeper water that we find the Caulerpas. 



To facilitate the survey 1 believe that we can distinguish three types of 

 localities which, however different they are mutually, are naturally united imper- 

 ceptibly to each other. To these can be given the following delimitations; the 

 somewhat exposed localities, the sheltered localities and the deeper 

 water. 



As to the more exposed localities where Caulerpas are to be found, these 

 commonly consist of stretches with shallow water behind the coral-reefs which 

 shelter them. The force of the sea is always broken by the reef which reaches 

 nearly to the surface, but nevertheless the waves commonly wash over the reef 

 and continue their motion, but weakly, towards the shore itself. Cin the open side, 

 where the sea breaks, we do not find anj' Caulerpa; these occur only at some 

 distance from the surf. Where on the other hand some shelter occurs, e. g. fore- 

 lying islands, we can also find a few Cau/erpa-species on the exposed side of the 

 reef and they can likewise grow along the shores of the more or less reef-broken 

 parts of the sea where a considerable surf can occur, at least in the larger bays 

 e. g. on the south coast of St. Croix, where the reef often lies at a considerable 

 distance from the shore. Thus, as the waves when they break on the reef partly 

 wash over it, the water is constantly renewed in the basin behind the reef and 

 an outrunning current is therefore always to be found at the places where the 

 reef is low. This renewing of the water has also importance from the fact that 

 the tide is wanting or in every case is of no practical significance in the Danish 



