99 



Ansell, Alan D.,and K. F. Lander. 1967. 



Studies on the hard-shell clam, Venus meroenaria , in British waters. III. 

 Further observations on the seasonal biochemical cycle and on spawning. 

 J. Appl. Ecol. 4(2): 425-435. 



Clams were collected along the downstream bank of the outfall channel of a 

 power station in Southampton Water in the same area used in earlier studies. 

 From Jan 1963 to Oct 1964 percentage wet and dry flesh weight followed an 

 upward trend, with peaks in early June and Aug in 196 3 and a peak in May in 

 196 4. Trend in wet weight over nearly 2 yrs was from about 13% to about 

 17%. Trend in dry weight was from about 2.2% to about 3.6%. Spawning 

 potentiality peaked in early June, in Aug and in Oct in 1963, and in May in 

 1964. These trends were accompanied by a downward trend in water content 

 of flesh. Spawning invariably led to a rise in water content. Studies in 

 1961 and 1962 showed differences in cycle of condition changes between small 

 and large clams. No significant size difference was seen in 1963-64. The 

 autumn peak is more likely to produce a set of young clams. Total N content 

 reached a minimum between Nov and Feb and peaked in May or June. Total N 

 fell after spring spawning and rose to a second peak prior to autumn 

 spawning. In 1962 changes in carbohydrate and protein occurred together, 

 leading to the conclusion that this was related to development of gonad and 

 spawning, and that storage of reserve carbohydrate was not very important. 

 But in 1963 total carbohydrate rose rapidly in spring, but although N fell 

 at spawning, carbohydrate remained high until Nov. In 196 4 carbohydrate did 

 not rise appreciably until July. Ash content of flesh showed no significant 

 cycles. The population studied is not characteristic of the whole clam 

 population in Southampton water because cooling water of the plant keeps 

 water temp higher. In other areas, away from influence of warm water, wet 

 and dry flesh rise to a peak in July-Aug, then fall. There is apparently 

 no spring spawning. Increases in organic production associated with growth 

 accounted for 64% of total production in 1962, 51.9% in 1963, 69.6% in 1964. 

 Losses from spawning were 1 g in 1962 and 1.4 g in 1963. Thus, total 

 organic material released as spawn was 26.5% in 1962 and 25.9% in 1963. By 

 the end of summer there is a net gain in stored reserves, accounted for by 

 an increase in total carbohydrate content. In winter part of this reserve 

 is utilized. As carbohydrate is used up, water content rises, so the 

 change is not reflected in wet weight percentage. On a dry weight basis 

 gonad production is between 40 and 60% of total organic production each 

 year. About 16% of total production may be used in winter, when metabolic 

 rate may fall to 5% of summer rate. Where natural populations of clams are 

 sparse, only intermittent spawning occurs, probably because not enough sex 

 products are produced to stimulate all clams to spawn. Spring spawning in 

 the area of the power plant does not produce recruitment for the clam 

 population as a whole because temp outside the warmed area is too low. 

 Years when successful sets have occurred have been years of hot, dry summers. 

 Water temp may act directly by determining whether eggs and larvae can 

 survive and grow. Low rainfall reduces flushing and aids retention of 

 larvae until setting. The good setting years 1955 and 1959 were anomalous 

 in seasonal pattern of zooplankton production and possibly also in 

 phytoplankton abundance. Zooplankton production was low in fall, hence 

 grazing of phytoplankton was reduced. Reduction in competition may favor 

 survival of clam larvae. - J.L.M. 



100 



Ansell, Alan D., and F. A. Loosmore . 1963. 



Preliminary observations on the relationship between growth, spawning and 

 condition in experimental colonies of Venus meroenaria L. J. Cons. 28(1): 

 285-294. 



Despite the commercial importance of Venus (Meroenaria) meroenaria in the 

 U.S. few studies have been made of ecology and growth of adults. Major 

 works, abstracted elsewhere in this bibliography, are identified. Obser- 



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