MICROPLANKTON 



241 



Table 17. Secotid survey (spring). Estimated total diatoms and numbers in the main diatom groups 



siosira showed specific differences, and there was a very marked increase in the typically oceanic 

 Planktoniella sol (absent inshore) from station WS 1099 seawards. 



Some of the dominant coastal chaetocerids persisted (in reduced numbers) to the outer end of the 

 line, but again more typically offshore forms such as C. convolutum and C. lorenzianum showed marked 

 increase in relative importance from station WS 1099 seawards. Similar specific differences were 

 shown within the two other groups also: Inshore Rhizosolenia setigera and Leptocylindrus danicus were 

 the most important solenoids, while offshore Rhizosolenia styliformis and Dactyliosolen mediterraneus 

 were the most abundant of all the diatoms at this time. Fragilaria karsteni and Asterionella japonica 

 were among the dominant ' Pennatae ' inshore. The former was not seen more than 30 sea-miles from 

 land, and though Asterionella was found farther out it was present only in relatively small numbers 

 there. The cosmopolitan Nitzschia seriata was observed in both localities, but offshore it appeared 

 that N. delicatissima was the most numerous species of the group at this season. 



