The influence of temperature and salinity on the duration of embryonic development, fecundity and growth of the amphipod Echinogammarus marinus Leach (Gammaridae)

The effects of salinity and temperature on the duration of embryonic development, fecundity and growth of the amphipod Echinogammarus marinus Leach from the Mondego estuary (Portugal) were studied in laboratory experiments. Combinations of three temperatures (10, 15 and 20 degreesC) and four salinities (10, 15, 20 and 25 parts per thousand) were used. The duration of embryonic development was 33 +/- 0.7 d (mean +/- S.E.) at 10 degreesC, 32 +/- 0.5 d at 15 degreesC, and 17 +/- 0.3 d at 20 degreesC. Analysis of variance demonstrated that the duration of E. marinus embryonic development, reared under different combinations of salinity and temperature, was significantly affected only by temperature (P < 0.001). A positive correlation between the number of newborn juveniles and the size of E. marinus females (as head length) was observed. The number of juveniles released per female was higher at 10 degreesC and lower at 20 degreesC. Analysis of variance showed that only temperature significantly affected the number of juveniles released per female (P < 0.001). Experimental data were used to calibrate the von Bertalanffy growth model. Results showed that growth was continuous throughout life under all laboratory conditions. Intrinsic growth rates were higher at 20 degreesC and lower at 10 degreesC. Analysis of covariance applied over the initial 90 d after hatching showed significant differences between growth rates of E. marinus under different salinity and temperature conditions. Extrapolation of laboratory data to the field scenario suggests that E. marinus in the Mondego estuary have a multivoltine life cycle. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.