Practice question

Stenohaline animals tolerate only a narrow range of salinity. A change outside that range disrupts osmotic and ionic balance: cells may gain or lose water, while concentrations of sodium, chloride, and other ions depart from physiological limits. Because their gills, kidneys, integument, and ion-transport mechanisms have limited capacity to compensate, stenohaline species are especially affected when salinity fluctuates. Many strictly freshwater or marine organisms fit this category, whereas euryhaline species such as salmon and numerous estuarine animals can remodel osmoregulatory processes across a broad range. Euryphagic describes a broad diet and is unrelated to salt tolerance. Stenoecious refers more generally to a narrow ecological niche, which could involve salinity but is less specific. “Affected in narrow salinity ranges” is awkwardly phrased: a stenohaline species is adapted to a narrow acceptable range and is affected when conditions move beyond it. Tolerance can vary by life stage and acclimatization history, and even euryhaline animals may be harmed by abrupt transfer because physiological adjustment requires time. Salinity is therefore both an environmental filter and a major determinant of aquatic distribution.