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Physiological response of blue mussel Mytilus edulis L. to the distant threat of sea star Asterias rubens L.

The elaboration of effective measures in protection of cultivated mussels Mytilus edulis L, from predators, main of which are sea stars Asterias rubens L., is very important for industrial aquaculture of mussels of the White Sea. In some natural settlements these predators are capable to destroy up to 80% of mussels. Reaching the artificial substrata, adult stars can destroy completely mussels grown there. The mussels cultivation biotechnology developed by proceeding from the specific conditions of the White Sea, such as an annual strong dilution of superficial layers of salty water, allows effectively to contend with this danger. Nevertheless, large number of sea stars attracted by falling mussels accumulate on the ground under artificial substrata in immediate proximity from the settlement of clams. It has been observed that in some cases when artificial substrata were in immediate proximity to a congestion of sea stars on the bottom, the growth rate of cultivated mussels slowed down considerably. The evidence obtained formed the basis for realization of special research on distant influence of predator on the prey. The main purpose was to define the character of influence and find out the mechanisms determining it. We examined the influence of excreted metabolites of sea stars on the changes in respiration rate and production of byssus threads of mussels exposed to the distant presence of sea stars. The measures developed on the basis of this research will be taken into consideration for optimization of aquaculture of mussels in the White Sea. Material and methods Specimens of the mussels Mytilus edulis L. with shell size 20-25mm were removed from the artificial substrates used as collectors for aquaculture at the White Sea. Sea stars Asterias rubens L. of the middle sizes were gathered from a depth of 0.5-l m from the bottom surface in the same area. Laboratory experiments were carried out at the White Sea Biological Station of the Zoological Institute, RAS. Animals were kept in isothermal cameras at stable ambient temperature 11 °C and salinity 24 ‰. Byssus threads. The intensity of byssus formation in young blue mussels