Salinity tolerance of Calanus euxinus in the Black and Marmara Seas

Abstract

We investigated how stenohalinic Black Sea Calanus euxinus, when migrating to the north-eastern Marmara Sea, can adapt to the pronounced salinity gradient there. During field observations (2005 to 2008) females of Calanus euxinus with significantly smaller body length (compared with those inhabiting the brackish Black Sea at 17 to 18 psu) were found in the deep, high-saline (~38.5 psu) layers of the Marmara Sea. Similar diameters of eggs laid by small-and large-sized females and similar respiration rates in nauplii hatched from these eggs indicated the Black Sea origin of the C. euxinus population found in the Marmara Sea. To understand the morphological and physiological changes in C. euxinus during acclimation to high salinity, we studied the effect of salinity on behaviour, food consumption, growth patterns, hatching success and respiration rate of C. euxinus individuals collected in the Black and Marmara Seas. It was shown that the range of salinity tolerance for adult C. euxinus (17 to 30 psu) from the Black Sea was extended gradually to 40 psu after 1 d of acclimation to the high salinity of the Marmara Sea. Long-term parental salinity acclimation facilitates survival of eggs descending through the salinity gradient of the Marmara Sea, from brackish upper layers to deep, high-saline strata, or eggs laid in deep layers. While weight-specific respiration rates at the same temperature did not differ for C. euxinus juveniles from the Black and Marmara Seas, they were ~2 times higher in preadults and adults from the Marmara Sea than from the Black Sea. This may be the reason for the decrease in length and weight increments of these stages probably leading to the small-sized individuals of the seasonal C. euxinus population inhabiting the Marmara Sea.

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

“…At the end of the exposure, a water sample from the experimental or control syringes was transferred to a flow chamber with a variable volume (up to 0.3 ml) created from a truncated all-glass syringe and joined to a luminescent dissolved oxygen sensor (Hach LDO™). Details concerning the oxygen concentration and respiration rate measurements are described in Svetlichny & Hubareva (2005) and Svetlichny et al (2010).…”

Vulnerability of copepod eggs in salinity and temperature gradients of the Marmara and Black Seas

“…On the contrary, the eggs of non-acclimatized to high salinity C. euxinus from the Black Sea could not reconstruct their form, or the nauplii developed inside these eggs were unable to rupture the outer membrane under high osmotic pressure. However, low salinity tolerance of eggs of the Black Sea females that were not acclimatized to high salinity does not contradict with the conclusion about the Black Sea origin of C. euxinus population in the Marmara Sea (Isinibilir et al 2009) because after parental acclimation to high salinity during 5 d, the tolerance range in C. euxinus eggs increased (Svetlichny et al 2010). …”

“…Adult Calanus euxinus were collected during daytime using a Nansen net (opening diameter: After sampling, adult females of Calanus euxinus, Acartia clausi and A. tonsa were sorted using a widemouth pipette and incubated in 1.0 l aquaria (not more than 20 individuals for Calanus or 50 for Acartia, respectively) filled with 0.45 µm-filtered natural seawater (18-22 and 17-18 psu for the specimens from MP and BSS, respectively) with an excess of food (dinoflagellate Prorocentrum minimum for C. euxinus and diatom Thalassiosira weissflogii for A. clausi and A. tonsa). For the experiments with C. euxinus collected at MP, we selected only small-sized (prosome length: 1.9 to 2.2 mm) females (see Isinibilir et al 2009, Svetlichny et al 2010. For the experiments with C. euxinus collected from the upper layers in the Bosphorus area (near Istanbul), we selected large females (prosome length: 2.5 to 2.8 mm).…”

“…According to Svetlichny et al (2010), an euryhaline sub-population of Calanus euxinus inhabiting both upper brackish and deep, high-saline layers is formed in the north-western Marmara Sea from stenohaline specimens recruiting from the Black Sea. Due to acceleration of the development of this species at the high temperature and salinity of the Marmara Sea, small-sized pre-adults and adults without large lipid reserves, which are typical for the Black Sea C. euxinus, occur in this area (Isinibilir et al (2009).…”

“…However, in the Marmara Sea we found high numbers of C. euxinus females in brackish subsurface layers during daytime. The individuals of the Black Sea C. euxinus transferred into the Marmara Sea to avoid high-saline layers and aggregate in the upper layers (Svetlichny et al 2010). Therefore, the eggs laid by females from the Black Sea in brackish (18 to 20 psu) subsurface layers of the Marmara Sea should descend to salinity gradient strata or even to a deep, high-saline (38.5 psu) zone.…”