Combined effect of salinity and temperature on Spirorbis spirorbis L. and Circeus spirillum L. larvae from the White Sea

The combined effect of salinity and temperature on Spirorbis spirorbis L. and Circeus spirillum L. larvae from the White Sea was studied in the laboratory experiments. In the White Sea, S. spirorbis is distributed through the depth of 1-20 m and is affected by all varieties of fluctuations in salinity and temperature. C. spirillum lives in more wide range of depths 1-55 m and is more stenohaline. S. spirorbis larvae are sufficiently more resistant to the low salinity (10‰) than C. spirillum larvae. Both species are stenothermic. Highest survivorship of S. spirorbis larvae was marked under 5 °C in all experimental salinities. Under temperature treatments of 10-15 °C, the larval survivorship was sufficiently restricted in all salinities. Highest survivorship of C. spirillum larvae was also marked under 5 °C but in more narrow salinity range.The number of larvae undergoing metamorphosis in both species was very low, only about 10% of the total number. Highest number of successful attachments in both species was marked in high salinities (25-30‰) and does not exceed 25% of survivors. Experimental data suggests that salinity and temperature affect directly general survivorship of the larvae and secondary-attachment and metamorphosis processes.