clam shells were found on oyster ground in Menai Straits at Caernarvon. 

 They probably came in shipments of American oyster. There was no evidence 

 of successful breeding. In the 1950s and 1960s several quahog colonies were 

 discovered in the vicinity of Southampton Water. In France introductions 

 were attempted in the Arcachon Basin in 1861 and 1863. By 1864 the first 

 lot had grown about 2 cm. Apparently the colonies did not spawn. About 

 1910 a successful introduction was made in the Seudre Basin. These clams 

 spawned prolif ically , and a commercial fishery was in operation in the 

 1950s. This is a mariculture operation, in which clams are handled much as 

 oysters are in France, holding them in claires in which gills and mantles 

 become green from feeding on Navioula ostrearia. In Brittany importation of 

 American clams began about 1936, where they were laid down mostly in the 

 River Belon. After the war this operation was resumed in 1954. Clams were 

 held only a short time in local waters, then sold, but a few remained. From 

 prewar plantings large clams, up to 14 cm long and up to 500 g, were found 

 in claires in the Gulf of Morbihan and River Penerf in the 1950s. Old clams 

 also were found in places where none had been introduced, from which it was 

 assumed that some successful breedings had occurred. A recently dead valve 

 was found in Zeeland, Neth. in 1933 and a live specimen in Ostend Harbor in 

 1937. It was not certain whether these were imported from France or that 

 this was evidence of a natural extension of range. Life history of hard 

 clam is described from American literature. From ages of clams taken in 

 European waters it was calculated that they could have been spawned in a 

 summer when water temp was distinctly above average. In England temp was 

 considered to be adequate for spawning, at least on the south coast. The 

 colony discovered in 1956 at Lee-on-the-Solent was 7 1/2 yrs old, which 

 meant that they were spawned in the notoriously hot summer of 1949. In 1955 

 the weekly max sea water temp in Southampton Water was higher than 2 0°C from 

 mid-July to mid-Sept and a successful spawning took place in that year. 

 Assuming that min temp for spawning of quahog is 20-21°C, conditions for 

 spawning in Southampton Water are reached in most years. Type of substrate 

 is important for survival and growth of quahog, and unsuitable bottom may 

 explain failure of some introductions. Aside from unsuccessful introductions 

 already mentioned the following attempts or fortuitous plantings were made: 

 1) estuary of the Humber River - accidental introductions with American 

 oyster - no evidence of breeding - water temp too low; 2) Hilbre Island - 

 clams laid down for storage - no permanent colony survived. - J.L.M. 



825 



Heusser, C. J. 1949. 



History of an estuarine bog at Secaucus , New Jersey. Bull. Torrey Botan. 

 Club 76(6) : 385-406. 



R 2fi 



Hibbert, C. J. 1976. 



Production studies of a bivalve population on an intertidal mudflat, with 

 particular reference to the energy budget of Meroenaria meroenaria (Linne 1 ) . 

 Ph.D. Thesis, University of Southampton (England), 225 p. 



The community was dominated by M. meroenaria and Cerastoderma edule. Total 

 biomass, 27 to 129 g/m^ ash-free dry weight, was high compared to previous 

 studies of intertidal and sublittoral sites. Predators remove an estimated 

 10.7 tonnes ash-free dry weight/m^/yr . Total production of 3 species, 

 M. meroenaria, C. edule, and Venerupis aurea (34 to 87 g/m^/yr) was 

 significantly higher than comparable studies. The scavenger-decomposer food 

 chain receives 18.2 tonnes/yr. Growth of M. meroenaria was studied and 

 compared with other hard clam populations, and temperature effects and 

 factors limiting growth were discussed, but details are not contained in the 

 summary. Seasonal cycle in ash-free dry weight for an individual of constant 



229 



