Effect of temperature on embryonic development of the marine gastropod Charonia seguenzae (Aradas & Benoit, 1870).

The Mediterranean Triton Charonia seguenzae (Aradas & Benoit, 1870) is an endangered marine gastropod. Re-establishment of C. seguenzae populations in the depleted habitats requires knowledge of its biology and breeding in captivity. Temperature has been recorded to affect the development in marine gastropods. The present study aims to describe the encapsulated development and study the effect of three temperature regimes, that the embryos are exposed to in the wild (17, 20, 23οC), on it. At the stage of morula (7th Day After Deposition - DAD) 180 egg capsules were separated in three groups of 60 capsules. One group remained at 23 °C and the other two were acclimated at 20 and 17 °C. Two capsules were sampled randomly from each temperature setup (every day during the first 5 days, D1-D5, every other day from D7 to D17 and every other two days from D20 to eclosion), opened and the eggs, embryos or larvae were photographed under stereoscope. Stages of development and shape were assessed and dimensions were measured from microphotographs. All developmental stages were described in relation to temperature and time. At 23οC eclosion of free swimming veligers occurred 49 DAD, 17 days faster than the embryonic development at 20οC. Eclosion at 17 οC was not observed up until the 74th DAD when the last sampling was conducted. An increased amount of larval deformities was observed at 17οC reaching 94% during the last sampling (D74), while at eclosion only 4 and 3% of the hatching larvae were deformed at 20 and 23 οC respectively. In this study temperature appears as a key factor during the development of the marine gastropod Charonia seguenzae, affecting the survival and developmental rate. Although temperature affected the size of intermediate stages, the size of free swimming veligers at 20 and 23 οC did not differ.

Effect of temperature on the development of deformities during the embryonic stages of Charonia seguenzae (Aradas & Benoit, 1870).

The Mediterranean Triton Charonia seguenzae (Aradas and Benoit, 1870) is an endangered marine gastropod. Re-establishment of C. seguenzae populations in the depleted habitats requires knowledge of its biology and breeding in captivity. Deformities have a huge impact on offspring survival and quality. Temperature has been recorded to affect the development of deformities in marine gastropods. The present study aims to identify the stage of development at which deformities occur, under four temperature regimes (17, 23, 26 and 29 °C). At the stages of trochophore, veliger and free veliger larvae, three capsules that were acclimated at the examined temperatures at the stage of morula were collected, opened and 50 larvae per capsule sampled. Deformities were observed at every examined developmental stage under all tested temperatures. The lower rate of deformities at every stage occurred at 23 °C. The higher tested temperature (29 °C) was lethal and at the lower tested temperature (17 °C) almost every specimen was deformed (96.66%) at eclosion. The effect of acclimation at four developmental stages (morula, trochophore, shell formation and veliger) on the development of deformities at the free veligers of Charonia seguenzae, was studied under three temperature conditions (17, 26 and 29 °C). At eclosion, three capsules were collected, opened and 50 larvae per capsule were sampled. The acclimation at morula and trochophore larva stages led to the higher rates of deformities at eclosion. The size of the free veliger larvae was also affected by temperature with maximum size at eclosion observed at 23 °C. Charonia seguenzae's embryos tolerate elevated temperatures within environmental limits (26 °C) but near future global warming will probably pose a threat to their survival. The free veliger larvae survival at the environmental minimum is related to the time window of the acclimation, since Triton's embryos are more vulnerable to temperature alterations during the early developmental stages.