Abstract
Mussels from two sites within the Baltic mussel (Mytilus edulis × M. trossulus) hybrid zone were used in a comparative study on the effects of salinity-changing rates on filtration activity. The acute effect of varying salinity-changing rates was found to be similar in M. edulis from the brackish Great Belt and in M. trossulus from the low saline Central Baltic Sea, and the relationships could be described by linear regression lines through 0.0 indicating that the acute effect of deteriorating conditions at decreasing salinities is the opposite as for improving conditions when the salinity is subsequently increased. Further, both M. edulis and M. trossulus acclimatized to 20 psu reacted to an acute salinity change to 6.5 psu by immediately closing their valves whereupon the filtration rate gradually increased during the following days, but only M. trossulus had completely acclimatized to 6.5 psu within 5 days which may be explained by different genotypes of M. edulis and M. trossulus which probably reflected an evolutionary adaptation of the latter to survive in the stable low-salinity Baltic Sea.
Highlights
Permanent low salinity as well as frequency, amplitude and rate of salinity changes may influence feeding, growth, early development and survival of mussels and other filter-feeding bivalves [1]-[13].The euryhaline blue mussel (Mytilus edulis L.) is able to live in both stable low salinity water areas and in estuaries with extreme salinity fluctuations
The results from 7 similar experiments with varying salinity-changing rates are shown in Figure 2 along with two other experiments performed with 20 mm shell length M. edulis from Great Belt and M. trossulus from the Central Baltic Sea, respectively
Therein) who found that the filtration-changing rate (ΔF) of 29 mm Mytilus edulis from Great Belt was strongly influenced by the salinity-changing rate (ΔS): “the faster the salinity was either reduced or increased, the more the change was pronounced in the filtration rate”
Summary
Permanent low salinity as well as frequency, amplitude and rate of salinity changes may influence feeding, growth, early development and survival of mussels and other filter-feeding bivalves [1]-[13].The euryhaline blue mussel (Mytilus edulis L.) is able to live in both stable low salinity water areas and in estuaries with extreme salinity fluctuations. When mussels from 6.5 psu in the Central Baltic Sea (Äskö, 70 km south of Stockholm) were initially acclimatized to 20 psu and subsequently re-exposed to 6.5 psu this initially caused a drastic reduction in the filtration rate, but the previous high filtration rate, comparable to that of Great Belt mussels, was regained after 1 - 2 days at 6.5 psu (see Figure 3 in Riisgård et al [16]) This difference in ability to fully acclimatize the filtration rate may be explained by different genotypes of the experimental mussels collected at the two sites within the Baltic Mytilus hybrid zone that is characterized by multilocus clines between M. edulis and M. trossulus [17]-[23]
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