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Long-Term Population Dynamics and Production of Pisidium (Bivalvia) in the Profundal of Lake Esrom, Denmark

1983; Wiley; Volume: 41; Issue: 1 Linguagem: Inglês

10.2307/3544352

1600-0706

Ismo J. Holopainen, Pétur M. Jónasson, Pétur M. Jónasson,

Soil and Water Nutrient Dynamics

During the 21 years (1953-1973, 1976-1977) of routine quantitative sampling reported in this paper, three species of Pisidium (P. casertanum, P. subtruncatum and P. henslowanum) have been present in the profundal of the eutrophic Lake Esrom, Denmark. From 1955 to 1962 P. casertanum was numerically dominant (peak density of 3273 ind m2 was attained in 1957), at other times P. subtruncatum dominated (peak 3025 ind m2 in 1955). Since 1957-1958 the densities of both species have been below 1000 ind ml. The peak density of P. henslowanum (370 ind m2) was attained in 1957. All the species laid their eggs in spring (April-May), but the young were not released until the following winter, the exact time depending on the temperature and oxygen conditions. Only some of the eggs laid developed into young, and the size of the brood was dependent on parental size. The young reached maturity at the age of 2 yr, and a maximum life-span of 4-5 yr is suggested. The regularly occurring oxygen deficiency in the hypolimnion in summer caused heavy mortality in the dominant species and halted growth of individuals. Both the standing crop and annual production were lower in the population of P. subtruncatum, which is a smaller species. The annual P/B-ratios were ca. 1 in both the dominant populations.