The Impact of Low Temperatures on the Hatching Success of Eurytemora pacifica (Copepoda, Calanoida) Resting Eggs

This study investigated the tolerance of resting eggs of Eurytemora pacifica to storage under low temperatures, which is of particular interest in light of the recent use of nauplii as living food in aquaculture, other than conditions experienced also in the wild during winter cold events in the Northern Hemisphere. Sediment samples collected in August 2020 were used to store the resting eggs at two different freezing temperatures (−5 and −20 °C) for five different durations (1, 3, 6, 9, and 12 months). The mean hatching success rates of the resting eggs after one month of storage were 85.3 ± 1.5% (−5 °C) and 85.0 ± 3.6% (−20 °C), with no significant difference between freezing temperatures. However, significant differences emerged over time, with the mean hatching success rate remaining at 85.0 ± 3.6% at −5 °C after three months, while it dropped sharply to 1.7 ± 2.1% at −20 °C. For the non-freezing conditions, the hatching success at 10 °C increased gradually over the one-month incubation period, ultimately reaching 71.0%. These findings demonstrate the remarkable cold tolerance of E. pacifica but also indicate a limit to this tolerance at longer durations. These results underscore the importance of considering the adoption of storage freezing for resting eggs to be used for aquaculture and also suggest the possibility of the species better surviving the extreme weather events in comparison with other species.