20 president's address. 



Channel. Dr. Marie Lebour, who recently examined the store of 

 plankton gatherings at the Plymouth Laboratory, finds that as a matter 

 of fact this form did appear in abundance in the collections of October 

 1909, within a month of the time when according to our records it 

 reached Port Erin. "Whether or not this is an Indo-Pacific species 

 brought accidentally by a ship from the Far East, or whether it is 

 possibly a new mutation which appeared suddenly in our seas, there 

 is no doubt that it was not present in our Irish Sea plankton gatherings 

 previous to 1909, but has been abundant since that year, and has 

 completely adopted the habits of its English relations — appearing with 

 B. mobiliensis in late autumn, persisting during the winter, reaching a 

 maximum in spring, and dying out before summer. 



The Nauplius and Cypris stages of Balanus in the plankton fonn 

 an interesting study. The adult barnacles are present in enormous 

 abundance on the rocks round the coast, and they reproduce in winter, 

 at the beginning of the year. The newly emitted young are sometimes 

 so abundant as to make the water in the shore pools and in the sea 

 close to shore appear muddy. The Nauplii first appeared at Port Erin, 

 in 1907, in the bay gatherings on February 22 (in 1908 on Feb- 

 ruary 13), and increased with ups and downs to their maximum on 

 April 15, and then decreased until their disappearance on April 26. 

 None were taken at any other time of the year. The Cypris stage 

 follows on after the Nauplius. It was first taken in the bay on 

 April 6, rose to its maximum on the same day with the Nauplii, and 

 was last caught on May 24. Throughout, the Cypris curve keeps 

 below that of the Nauplius, the maxima being 1740 and 10,500 respec- 

 tively. Probably the difference between the two curves represents the 

 death-rate of Balanus during the Nauplius stage. That conclusion I 

 think we are justified in drawing, but I would not venture to use the 

 result of any haul, or the average of a number of hauls, to multiply by 

 the number of square yards in a zone round our coast in order to 

 obtain an estimate of the number of young barnacles, or of the old 

 barnacles that produced them — the irregularities are too great. 



To my mind it seems clear that there must be three factors making 

 for irregularity in the distribution of a plankton organism: — 



1. The sequence of stages in its life-history — such as the Nauplius 

 and Cypris stages of Balanus. 



2. The results of interaction with other organisms— as when a 

 swarm of Calanus is pursued and devoured by a shoal of herring. 



3. Abnormalities in time or abundance due to the physical environ- 

 ment — as in favourable or unfavourable seasons. 



And these factors must be at work in the open ocean as well as in 

 coastal waters. 



