Abstract
The filtration rate and thermal effects on the rate were evaluated in various marine bivalves. 1) The filtration rates by a clam population (F, l · m-2 · h-1) estimated using the following equation were compared with Pseudocardium sachalinensis in Hamanaka Bay, Hokkaido and Ruditapes philippinarum in Banzu tidal flat, Tokyo Bay.
F=Σmn=1fn · RT · RS · Pn
where ; fn, filtration rate of a clam with Ln mm (mean shell length of divided size class) examined under the experimental conditions ; RT, correction coefficient for fn at field temperature T (°C) ; RS, correction coefficient for fn at field salinity S (psu), Pn ; clam density (no. · m-2) of 15 size classes in P. sachalinensis and 7 size classes in R. philippinarum ; m, number of size classes. Filtration rate and effects of body size, temperature and salinity on the filtration rate were examined using the clam collected from each study sites. Monthly changes of temperature, salinity and clam density were investigated in Hamanaka Bay, and were evaluated from analysis of available data in Tokyo Bay, 2) The individual filtration rate corrected for body size and temperature was compared between 4 bivalve species, P. sachalinensis, R. philippinarum, Mytilus galloprovincialis, and Perna viridis. 3) Thermal effects on the filtration rate were examined in 8 bivalve species, including Mactra chinensis, Meretrix lamarcki, M. lusoria, and Mytilus coruscus.
Following are major findings ;
1) The contribution of the 2 year-old population to the eatimated filtration rate was dominant in P. sachalinensis (65%) and R. philippinarum (58-78%). Following contributions were for the 3 (19%), 4 (8%), 1 (5%), and over 5 year-old (3%) in P. sachalinensis and over 3 (14-22%), and 1 year-old (8-20%) in R. philippinarum. In the case of P. sachalinensis, a irregular occurrence of dominant year class may be major factor affecting on the filtration.
2) The estimated filtration rates (l · indiv.-1 · h-1) of 30mm individual at 15°C were as follows : M. galloprovincialis (2.5), R. philippinarum (1.5), P. sachalinensis (1.3), and P. viridis (0.64).
3) The temperature considered to be optimum for filtration was 20°C for P. sachalinensis, M. lamarcki and M. lusoria, 25°C for M. chinensis, R. philippinarum and M. galloprovincialis, 27.5°C for M. coruscus, and 32.5°C for P. viridis.
