Amphipod survival at different salinities and temperature: a contribution to studies of climate change

Coastal lagoons of Southeastern Brazil are highly unstable environments mainly due to abrupt salinity changes. The species Quadrivisio lutzi is the unique amphipod inhabiting the water column of unstable coastal closed lagoons at the north of Rio de Janeiro State. This study determined temperature and salinity range of tolerance and identified osmoregulatory strategies for survival. Bioassays were performed with gradual and non-gradual increases of salinity within the range of 0-60 mg/l. The median lethal salinity concentration in 48 h was evaluated. Haemolymph and water osmolality at different salinities were determined. Temperature tolerance in 48 h was evaluated with gradual increments/decreases of temperature in the range of 3-39°C. Results showed two osmoregulatory strategies in the amphipod Q. lutzi : hyper-regulation in freshwater and brackish water (0.5-11 ppt); and passive isosmotic condition at higher salinity (>11-21 ppt). The LC 50 for the species was 23.8 ppt with salinity range of tolerance of 0.5-21 ppt for 48 h. The amphipod tolerated in 48 h a temperature range of 8-32°C. Tolerance to temperature increased to 35°C when the amphipod is in passive isosmotic condition. The amphipod Q. lutzi is an euryhaline and eurythermic species. The range of environmental tolerance of the amphipod Q. lutzi allows it to overcome salinity changes determined by sea sand-bar opening; and to tolerate seasonal temperature variations characteristic of tropical regions. The euryhaline and eurythermal capacity of the species suggest that it may survive to climate changes.