survival and
feeding activity of oyster spat (ostrea edulis l) as a function of
temperature and salinity with implications for culture policies on the
swedish west coast.
E.M. Rödström, P.R. Johnsson-2000
Journal of Shellfish Research, 19(2): 799-808
Abstract:
This study evaluates the effects of temperature and
salinity on feeding activity and survival rate for spat of the European
oyster Ostrea edulis originating from the Swedish west coast. The main
objective was to investigate local adaptation to hydrographic conditions
with low temperatures and salinities with consequences for culture policies.
In laboratory experiments, mortality increased at lower temperatures except
at salinities below 18 ppt. Highest mortality was found in combination of
very low salinities and the high temperature treatment (10°C). Feeding
activity, measured as faecal production, was significantly lower in 5
compared to 10 °C. Feeding rate began to decline at 28 ppt and ceased at 16
ppt. The time to recover feeding activity depended upon the duration of
low-salinity exposure. Spat exposed to salinities below 16 ppt did not
regain their feeding activity when returned to full salinity, indicating
permanent damage. Increased exposure time also lead to higher mortality
after the return to full salinity. Comparison between rapid and gradual
change of salinity indicates a potential for acclimation. In a model forced
by field data on temperature and salinities, survival trajectories were
calculated for different water depths and for different seasons. The model
predictions were tested in a field experiment where the model could explain
winter and spring mortalities in terms of temperature and salinity. In the
summer, however, the model underestimates mortality, indicating the
importance of such other sources of mortality as fouling and predation. To
minimize mortality, this study suggests that culture policies should include
deployment below 6 m with initial transfer of spat to the sea at midsummer.
(Tjärnö Marine Biological Laboratory, Göteborg
University, SE-452 96 Strömstad, Sweden, e-mail: Eva.Marie.Rodstrom@tmbl.gu.se)