262 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



HYDEOGRAPJIIC CONDITIONS OFF PORT ERIN 

 IN APRIL TO JUNE (Drawn up by W. J. Dakin). 



This is an account of the hydrographical observations 

 made in conjunction with the plankton work carried on 

 by Professor Herdman in April, and of those made in 

 May and June whilst taking plankton samples myself. 

 The former, which are in greater detail, were carried out 

 on the steam yacht " Ladybird," the latter on a small 

 sailing boat. I have dealt chiefly with the temperature 

 and salinity of the water, but some oxygen determinations 

 were also made during April. In order to discuss 

 differences in catches of nets at different times and 

 places, it is necessary to know the prevailing conditions 

 of environment affecting the plankton, at those places. 

 The observations are confined practically to two stations 

 (I and III). They have, however, been very numerous 

 and probably such an intensive study at stations isolated 

 from the larger land masses is of rare occurrence. 



Much of the Grerman quantitative plankton research 

 has been carried out on the Baltic Sea, where the 

 kydrographic conditions are most varied and interesting, 

 but may, I think, lead to rather one-sided views. It is 

 quite obvious, for example, that if the surface salinity is 

 only 18 °/oc anc * that of the bottom water is 26 %o 

 it will make a marked difference in the plankton. It 

 seems natural under such circumstances to correlate 

 changes in plankton with changes in the hydrographical 

 conditions. 



These great changes, however, may completely mask 

 other smaller variations which exist in places where the 

 salinities and temperatures are approximately alike. It 

 is under these latter conditions thai plankton problems 

 must be attacked in the Irish Sea, which is, as far as 



