Calanipeda aquaedulcis and Arctodiaptomus salinus are exceptionally euryhaline osmoconformers: evidence from mortality, oxygen consumption, and mass density patterns

Abstract

Mortality, respiration rate, and body mass density of the estuarine copepods Calanipeda aquaedulcis and Arctodiaptomus salinus and their eggs were studied over a wide range of salinities. Empirical hydrodynamic modeling was applied to calculate body mass density using the sinking speed of the copepods. According to the index of median lethal salinity (LS 50 ), the salinity tolerance ranges of C. aquaedulcis and A. salinus reared at 18 psu were 0.1 to 50 and 0.1 to 35 psu, respectively. No significant effect of salinity on the specific oxygen consumption rate was found in the range from 0.1 to 40 psu in both species, while mean body mass density increased iso-osmotically with water salinity from (mean ± SD) 1.053 ± 0.007 to 1.077 ± 0.005 g cm −3 in C. aquaedulcis and from 1.039 ± 0.004 to 1.062 ± 0.007 g cm −3 in A. salinus. However, body density contrast and sinking speed were stable in both species, allowing them to avoid buoyancy problems with changing salinity. The mean mass density of resting eggs in A. salinus gradually increased isoosmotically following gradual changes in salinity. In contrast to resting eggs, the mass density of subitaneous eggs was not altered by changes in the surrounding salinity, suggesting a hysteresis response in these eggs.

Osmoregulation, bioenergetics and oxidative stress in coastal marine invertebrates: raising the questions for future research

“…Freitas et al, 2015;Shumway and Davenport, 1977), crustaceans (e.g. McAllen et al, 1998;Svetlichny et al, 2012) and echinoderms (e.g. Castellano et al, 2016a,b).…”

“…Some authors have suggested that the increased energetic cost may be linked to increased activity (McAllen and Taylor, 2001) as the animal attempts to escape from unfavorable conditions (Gross, 1957). In other osmoconforming copepods, environmental salinity does not influence oxygen consumption rates (Svetlichny et al, 2012). However, most sources indicate that osmoconformers have low energetic requirements when exposed to decreased salinity.…”

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“…In Sevastopol Bay minimum O. davisae number ranged between 1 (Almeda et al, 2011), where CDW = 0.0021 L 2.14 for nauplii, L is body length and CDW = 0.0318 L pr 1.61 for copepodites and females. (Svetlichny et al, 2012a), where ρb is equal to 1.05 g cm -3 (Svetlichny and Hubareva 2014), L, lpr and dpr are given in mm. and 400 ind m -3 when the water temperature was around 6-8ºC, and in Fukuyama Harbor it was recorded up to 5 x 10 3 ind m -3 when the surface temperature was around 10-13ºC.…”

Copepods in Hypersaline Waters Worldwide: Diversity, Environmental, Social, and Economic Roles

“…Aquatic organisms with various salt tolerances adapt to their environments through osmoregulation and osmoconformation. Many copepods are osmoconformers (Bayly and Boxshall, 2009;Svetlichny et al, 2012).…”