The life cycle, population dynamics, growth and secondary production of Bithynia graeca (Westerlund, 1879) (Gastropoda) in Lake Kerkini, Northern Greece
N. Eleutheriadis et M. Lazaridou-dimitriadou, The life cycle, population dynamics, growth and secondary production of Bithynia graeca (Westerlund, 1879) (Gastropoda) in Lake Kerkini, Northern Greece, J MOLLUS ST, 67, 2001, pp. 319-328
The life cycle, population dynamics, growth and secondary production of the
freshwater prosobranch snail Bithynia graeca (Westerlund 1879) were studie
d in the artificial Lake Kerkini (Serres, Northern Greece) where water volu
me and depth fluctuate dramatically. B. graeca faces deterministic and stoc
hastic aspects of this environment. Growth and reproduction were studied fo
r two populations, one being covered by the water almost throughout the yea
r and the other not. B. graeca is a semelparous annual freshwater snail who
se life expectancy decreased with increasing age. Maturity was attained 4 m
onths earlier for the first population. Reproduction took place in spring.
The majority of adults died after egg-laying. Growth rate was rapid during
spring, and activity ceased during winter. B. graeca is a prosobranch snail
whose short turnover time (77.9 and 84.3 days) was similar to that seen in
freshwater pulmonate snails. Productivity was assessed in two ways, by a s
ize frequency method and by using cumulative biomass. Observed values, for
the two methods respectively, were for mean biomass 18.53 and 22.8 g dry bo
dy weight/m(2), for annual production (P) 86.81 and 88.38 g dry body weight
/m(2) or 9.56 gC/m(2) year respectively, and for annual turnover ratio (P/(
B) over bar) 4.68 and 3.87/year. Net reproductive rate R-o was 2.99 and per
capita rate of increase (r(c)) was 0.091.