Reproduction and morphological variability of Cyprideis torosa under different water temperatures and salinities in laboratory cultures

Natural habitats consist of a large variety and variability of environmental factors. Reproduction in laboratory cultures is thus a highly effective way to pinpoint and quantify the impact of a specific environmental factor on a species which is hardly possible in natural environments.

The most common ostracod species in European marginal marine environments is Cyprideis torosa (Jones, 1850). It is a morphologically variable species but laboratory reproduction experiments of C. torosa are scarce and thus reducing an undisputed use of its morphological variability as a paleo-environmental proxy.

Although it is usually intended to use ostracod valves as paleo-thermometer, the nature of the impact of temperature on ostracods and on their morphology remains questionable. We aim to test whether temperature plays a significant role influencing the morphological characteristics of C. torosa in different salinities. In addition, laboratory cultures are a great opportunity to better understand the life cycle of ostracods, their reproduction times and juvenile numbers.

We collected samples from Marano Lagoon (Italy) at salinity levels of 7.2, 17.2 and 29.6 psu. For our experimental setup, we transferred boiled (= sterile) sediment (<150µm) from each of the newly established cultures in five crystallizing dishes, added lagoon water from each sampling location, and added 8 male and 12 female adult specimens of C. torosa. We placed one dish per salinity level in incubators at fixed 15, 20, 30 or 35°C and one outdoors. After finding at least 10 hatched juveniles, adult specimens were removed and remaining juveniles were raised to adulthood. Subsequently, we continued to check the abundance of juveniles and remove newly grown adults from the culture in monthly sievings. The morphological characteristics of the original and new adults were mutually compared.

The first results of our cultivation experiment suggest a rather stable reproduction rate at constant temperatures and salinities. The reproductive activity of C. torosa is highest in the lower saline cultures at 20 and 30°C and decreases with higher salinities as well as extreme low and high temperatures. First morphometric results indicate a phenotypic salinity-temperature modification of its size, ornamentation and shape.