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Behavioural and physiological impacts of low salinity on the sea urchin Echinus esculentus.

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Reduced seawater salinity as a result of freshwater input can exert a major influence on the ecophysiology of benthic marine invertebrates, such as echinoderms. While numerous experimental studies have explored the physiological and behavioural effects of short-term, acute exposure to low salinity in echinoids, surprisingly few have investigated the consequences of chronic exposure, or compared the two. In this study, the European sea urchin, Echinus esculentus, was exposed to low salinity over the short term (11‰, 16‰, 21‰, 26‰ and 31‰ for 24 h) and longer term (21, 26 and 31‰ for 25 days). Over the short term, oxygen consumption, activity coefficient and coelomic fluid osmolality were directly correlated with reduced salinity, with 100% survival at ≥21‰ and 0% at ≤16‰. Over the longer term at 21‰ (25 days), oxygen consumption was significantly higher, feeding was significantly reduced and activity coefficient values were significantly lower than at control salinity (31‰). At 26‰, all metrics were comparable to the control by the end of the experiment, suggesting acclimation. Furthermore, beneficial functional resistance (righting ability and metabolic capacity) to acute low salinity was observed at 26‰. Osmolality values were slightly hyperosmotic to the external seawater at all acclimation salinities, while coelomocyte composition and concentration were unaffected by chronic low salinity. Overall, E. esculentus demonstrate phenotypic plasticity that enables acclimation to reduced salinity around 26‰; however, 21‰ represents a lower acclimation threshold, potentially limiting its distribution in coastal areas prone to high freshwater input.


Peer reviewed: True

Acknowledgements: N.J.B. would like thank Simon Morley at BAS for his advice and feedback on an early draft of the manuscript, Andrew Mathewson and the aquarium team at SAMS for technical support, Lars Brunner at SAMS for his advice on sea urchin husbandry, and Tom Forster for helping to run the acclimation experiment.

Publication status: Published

Funder: University of Cambridge; doi:


Acclimation, Climate change, Coastal freshening, Echinoderm, Osmotic stress, Phenotypic plasticity, Animals, Salinity, Seawater, Osmolar Concentration, Acclimatization, Sea Urchins

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J Exp Biol

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The Company of Biologists
NERC (NE/S007164/1)