368 SECTIONAL TRANSACTIONS.— D. 



6. Discussion on Tlie Fauna of the Sea-Bottom. 



(a) Opener: Dr. 0. G. Joh. Petersen. 



I confine myself to discussing methods of investigation. From 1883 1 

 carried out investigations on the Bottom-Fauna of Danish waters by means 

 of the dredge, and charted the occurrence of each single specimen. No good 

 general survey of the animals existed at that time ; different groups of animals 

 were treated by different specialists who published in different papers. Later 

 I introduced the bottom sampler for the purpose of investigating the problem 

 as to why the plaice grows faster in some parts of the Limfjord than in 

 others. The conception of the ' fauna of the level bottom ' and that of the 

 ' epifauna ' was introduced, as also that of ' animal communities ' based upon 

 characteristic animals. The theory of probability must be applied to this 

 line of investigation, the degree of exactitude depending upon the number of 

 stations worked. Seasonal and annual variations. Bearing upon the fisheries 

 (plaice). Knowledge of Metabolism of the Sea, based upon quantitative investiga- 

 tions of the bottom fauna and flora. Dredge rather capricious, mixing com- 

 munities together and confusing level-bottom fauna and epifauna. 



(fc)Mr. r. M. Davis. 



During the last year work has been carried out in the North Sea with 

 the Petersen Bottom Sampler with a view to finding out the distribution of the 

 non-predatory benthos forming the food of fish. The work has been mostly 

 concentrated on the central area of the Dogger, where 391 stations have been 

 worked, while 145 others have been worked in other areas. The following 

 are the commonest animals found : Sjni^iila subtntncata (maximum 3.280 per 

 square metre), Mactra stultorum (maximum 55), Telllna fahula (maximum 40), 

 Natica aldcri (maximum 40), Nephthys cccca (maximum 25), Echinocardium 

 cordatum (maximum 3). Many other animals — e.g. Vcnua gaUina, Psammobia 

 ferroensw, Sijndoi'inya pri.^matica, Ophelia limacina, Goniada maculata, and 

 other forms — are widely, though not intensively, distributed, not usually 

 occurring more than 5 per square metre. This appears to coincide approximately 

 with Petersen's Danish ' Venus ' and ' Deep Venus ' communities, but the 

 predominant species are Spisula .subtnincata (intensively distributed) and 

 Nephthy^^ ctcca (extensively distributed). It has been found that Spisula 

 subtruncaf.a and the more intensively distributed animals lie in patches. In 

 a recent voyage a patch of Spisula was intensively sampled, and was found 

 to extend over an area of approximately 38 square miles, with an average 

 intensity of 795 half-grown individuals per square metre (maximum 2,520, 

 minimum 0). 



(c) Mr, J. O. BOHLEY. 



A discussion of the distribution of the sea-bottom fauna in the North Sea 

 on the basis of samples obtained by the dredge. 



{d) Prof. R. D. Laurie, Miss E. Horsman, and Mr. E. E. 

 Watkin. — The Fauna of Cardigan Bay, off Aberystwyth. 



Mechanical analyses of samples of the bed of a trawling ground off Aberyst- 

 wyth give the following as a typical result : coarse sand 4.5 per cent., fine sand 

 30 per cent., silt 19 per cent., fine silt 20 per cent., clay 11 per cent., soluble 

 matter, etc., 14 per cent. A typical collection of organisms obtained by the 

 Petersen Bottom Samjjler in -^^ sq. metre is: Amnhiuru filiformis (21). 

 Tunitetia cuinmunis (7), Synapta inficcrens (1), S. digitata (1), Pectinaria 

 ■aiiricoma (2), Nephthys cccca (2), Sthenclais limicola (2), Evarne impar (1), 

 Phascolosoma procerum (1), Montaciita bidentata (1), Syndosmya alba (1), 

 'Corbula gibba (1), and other forms less frequently, among them Echinocardium 

 •cordatum. *This Amphiura-Turritella 'community' does not correspond to 

 lany of Petersen's. Among the immature fish trawled on this ground, plaice and 

 skate do not appear to be serious competitors with one another for food ; the 

 former having a marked preference for the brittle-star. Amphiura filiformis, 

 whereas the hitter avoid it but specially select the Amphipods, Ampdisca typica 



