ISSN : 1225-3480
The blotched nerite Nerita albicilla (Linnaeus, 1758) is widely distributed in intertidal areas of the Indo-Pacific. Interestingly, it is known that they inhabit in the southernmost region of Jeju Island, Korean Peninsula. Recently, it has been proposed that N. albicilla can be divided into two different species based on COI sequences. Herein, we describe the new species, N. originalis Hong, Park & Hwang, sp. nov., in Korea and Thailand. In addition to, we conduct the morphometric analysis between the two nerite species based on nine morphological characteristics of shells. The results show that there are no significant morphological differences of the shells between the two species. However, under SEM, we find a different morphological characteristic (lateral teeth on radula). Nerita albicilla has an inflection point close to a V-shape at the base in the lateral tooth, whereas N. originalis Hong, Park & Hwang, sp. nov. has a gentle inflection point. Through further study, we need to examine much more samples and more morphological characteristics to seek for significant morphological differences between the two species.
This study was conducted to investigate the impacts of shell-boring polychaete worms and biofouling organisms on the overwintering oysters (Magallana gigas) cultivated in the southern coast of Korea during May 2023. The mean biomass of biofoulers in Jaran Bay was 25.7 g wet/oyster which is 34.5% of mean oyster biomass. The proportion of biofoulers per oyster increased to 40.2 g wet corresponding to 47.8% of oyster biomass in Jinhae Bay. The main biofouler was different between two oyster farms; colonial ascidians were major biofouler in Jaran Bay while ghost sea squirts were dominated in Jinhae Bay. The individual number of shell-boring worms per oyster was in the range of 0 to 7. There were no significant correlations between the fresh weight or condition index and the shell-boring worms or biomass of biofoulers in this study during this period. We discussed the possibility of increasing impacts from biofouling and shell-boring before oysters are completely harvested until September of this year.
Ark shell, Scapharca subcrenata were collected at different harvest period to induce sexual maturation. The gonad index varied according to when the first entry, ranging from 1.15 in January to 1.34 in February and 1.84 in April. It was observed that the gonadal index increased as the season progressed, with higher values recorded in later months. When water temperature stimulation was used to induce sexual maturity, the time to maturity was 123 days in January, 89 days in February and 53 days in April. The accumulated water temperature was 944°C in January, 812°C in February and 780°C in April, giving a total difference in accumulated water temperature between January and April of △T = 164°C. Analysis of the gonadal tissues at the end of the experiment showed that the female/male ratio and the frequency of immature individuals varied according to the collection season. In January the female-to-male ratio was 63.3%, in February 40.0% and in April 36.7%. Similarly, the proportion of immature individuals was 3.3% in January, 16.7% in February and 20.0% in April. A total of 600 ark shells were used for artificial seed production on June 8th. The fertilization rate was approximately 89%, and the hatching rate was 90%. In total, 3.04 billion fertilized eggs were collected, resulting in 1.1 billion hatching. The initial D-shape larvae measured 80.4 ± 3.9 μm in length and 60.6 ± 2.8 μm in width.