PLANKTON OF THE GULF OF MAINE 



53 



TROPICAL VISITORS 



The term "tropical visitors" is used here for such animals as are native to the Gulf 

 Stream and are able to survive only in its warm surface waters outside the edge of 



Portland 





Fig. 31.— Locality records for certain of the more typical planktonic animals of tropical or warm-Atlantic origin. A, Salpae, 

 • Thysanoessa gregaria; X, tropical copepods; O. Portuguese man-o-war (Physalia); A Physophora hydrostatica; 

 0, gulf weed (Sargassum); — , many tropical species 



the continent. Others equally of tropical origin, but which find conditions more 

 favorable for growth (though not for reproduction) in the mixed water, are discussed 

 as belonging to the latter, for it is by that route that they enter the Gulf. 



