SEA-FISHERIES LABORATORY. 278 



the end of autumn the phytoplankton may suddenly 

 increase so as to constitute a second maximum in the 

 year, the first being in spring ; but that this possible 

 maximum may be so modified in time and in amount 

 by temperature and wind as to be unrecognisable. In 

 1906 it was very much more marked at Port Erin (see 

 XXth Ann. Report, p. 53) than in 1907, and extended 

 from September 20th to the end of the month. 



The phytoplankton minimum for the bay occurs in 

 August, no Diatoms being taken from August 9tli to 

 August 23rd (see curve), though nettings were taken on 

 all days, except three, included between these dates. 



As an example of a sudden change in the plankton 

 we may compare the surface hauls taken in the bay on 

 October 1st and 14th (see Form 122). The total quantities 

 of the two gatherings were 1*5 and 11*5 respectively ; on 

 the 1st, Diatoms were relatively abundant (over 91,000) ; 

 by the 14th they had disappeared. But Sagitta and 

 various larvae, and especially Copepoda, had greatly 

 increased in number by the latter date. The adult 

 Copepoda in all numbered only 1,045 on the 1st, while 

 they reached 27,790 by the 14th ; younger forms and 

 Nauplii had also become much more abundant. By 

 November, however, the Diatoms were back in quantity, 

 as is shown by the third column (November 8th), and 

 Copepoda have beguu to decrease again. 



Bay Copepoda throughout the Year. 



Copepoda are fairly abundant in Port Erin Bay from 

 April to November inclusive, but there are considerable 

 ups and downs, the number per haul varying often on 

 successive days within very wide limits. 



The curve (fig. 11) shows a gradual increase from the 

 latter part of March through April, then (with depressions 



