SALINITY-TEMPERATURE TOLERANCE AND OSMOREGULATION IN EURYTEMORA-AFFINIS (POPPE) (COPEPODA, CALANOIDA) IN RELATION TO ITS DISTRIBUTION IN THE ZOOPLANKTON OF THE UPPER REACHES OF THE FORTH ESTUARY

• Published in: Journal of Experimental Marine Biology and Ecology
• Main Authors: RODDIE, BD, BERRY, AJ, Leakey, Ray
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1984
• Subjects: Copepods; Rotifer
• Online Access: https://pure.uhi.ac.uk/en/publications/3279dbf5-a3b0-452c-bddd-9b8b287a376e; https://doi.org/10.1016/0022-0981(84)90219-3

Eurytemora affinis (Poppe) was the dominant copepod in summer and winter surveys of the littoral zooplankton of the upper Forth estuary, Scotland. Maximum numbers were observed in the 0–10%. segment, reaching 500000· m−3 in summer and consistently exceeding main channel abundances reported from other studies. In winter, E. affinis was less abundant, and shared dominance with the rotifer Synchaeta , which occasionally reached numbers of 311000·m−3. Tidal movements and seasonal changes in freshwater flow were both observed to effect longitudinal displacement of plankton populations. Laboratory tests of salinity-temperature tolerance in Eurytemora showed optimal conditions to be 3–10%. at low temperatures, broadly matching distribution patterns in the estuary. Salinity acclimation tests and haemolymph concentration measurements showed that copepods could adapt to changing conditions within 12 h (i.e. the duration of a tidal cycle). Acclimation extended tolerance limits in the direction of the acclimation treatment, with survival being enhanced by gradual rather than abrupt changes in salinity. Investigation of haemolymph Δ°C in a range of test salinities revealed a pattern of hyper/hypo-osmoregulation, with concentrations hyperosmotic to the external medium below 15%. and evidence of hypo-osmoregulation at salinities >20%. Minimum haemolymph concentrations were found to be equivalent to ≈6%. sea water (Δ°C = 0.4) when held in fresh water. No evidence of salinity-associated respiratory distress was found in respiration experiments. The oxygen consumption values determined (5–7.5 μl O2·mg dry wt−1·h−1) at optimal salinities and temperatures were similar to reported values for copepods of comparable size.