LARVAL TRANSPORT BY OCEAN CURRENTS 459 



much. We also know about rearings in aquariums for which the 

 rate of development was more rapid than in nature. So, taken as 

 a whole and roughly, it seems that the figures obtained from 

 laboratory experiments may give a fairly correct picture of the 

 average rate of development. 



Furthermore, it must be kept in mind, that figures from such 

 laboratory experiments, for the present calculations, have been 

 accepted only if the larvae were reared to their very oldest stage 

 or through metamorphosis in a healthy state; for our purpose, what 

 is most important to know is how slowly the larvae may develop 

 without losing their ability to settle and metamorphose in a 

 healthy state. So, what we must look for in the literature is the 

 longest duration of the pelagic life of each individual species, which 

 results in a successful settling and metamorphosis. If, for example, 

 it is indicated for a larval species, that it may metamorphose 

 within a space from 3 to 6 weeks after hatching, this will in the 

 author's calculations be regarded as a 6-week pelagic life, since at 

 least some of the larvae may be transported by the currents for 

 that space of time. 



We shall soon have to note other sources of error, but let us 

 first look at Fig. 1, based on figures for 195 species of larvae. The 

 data for this were brought together from about 300 different 

 papers, but it does not seem reasonable to give all these references 

 in a review paper such as this. All data for the diagram are, 

 however, available in the author's files and he will gladly forward 

 them to those who are especially interested. To the left are the 

 systematic group and the number of species examined. The number 

 of weeks from hatching to metamorphosis is given at the top and 

 the black blocks show the percentage of all species examined within 

 each group, which metamorphoses within each of the weeks 

 indicated above. At the bottom the hatched block (in double scale) 

 gives the total for all larvae. From this we may conclude, first, 

 that about 70 per cent of all pelagic larval species examined thus 

 far will on an average metamorphose and settle after less than 5 

 weeks of pelagic life, while about 80 per cent of all larvae will 

 settle after less than 6 weeks of pelagic life and 86 per cent after 

 less than 8 weeks of pelagic life. Or, to put it in another way, only 



