A long-term copper exposure on freshwater ecosystem using lotic mesocosms: individual and population responses of three-spined sticklebacks (Gasterosteus aculeatus).

Three-spined stickleback (Gasterosteus aculeatus) was used as the highest trophic level predator in an outdoor mesocosm study assessing the effect of environmentally realistic copper concentration (0, 5, 25 and 75 microgL(-1)) over 18 months of continuous exposure. Condition factor, organosomatic indices (HIS, GSI and SSI) as well as copper bioaccumulation in the liver were measured at 15 days, 2, 4, 6, 10, 14 and 18 months after the beginning of the contamination. Population monitoring was realised after 6 and 18 months of contamination, allowing two reproduction periods to be measured. Results showed that condition factor was affected at medium and high copper concentrations and HSI was sporadically affected in all copper exposure, depending on the sex of the fish. GSI did not show any significant differences and SSI was lowered in the medium and high copper levels. Bioaccumulation was significantly different in males and females and fluctuated with season. A negative correlation was observed between copper bioaccumulation in the liver and fish size and a positive correlation with nominal copper concentration in the water was found. There was a negative correlation between condition factor, organosomatic indices and bioaccumulation in the liver. Population monitoring showed a significantly higher fish mean length after 6 months and a higher abundance after 18 months of exposure at the highest copper level. We conclude that indirect effects such as food and habitat availability or lower predation pressure on eggs and juveniles might have led to higher stickleback population abundances at the highest copper level. This highlights the need to study all the trophic levels when monitoring ecosystem health. Considering the population and the individual responses after 18 months of copper exposure, the NOEC for three-spined sticklebacks was 25 microgL(-1) (or 20 microgL(-1) if we consider the average effective concentration), with a LOEC of 75 microgL(-1) (or 57 microgL(-1), AEC).