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Interannual variability in the reproductive cycle of Ruditapes philippinarum influenced by environmental and parasitic factors on the west-coast of Korea

Wed, 01 Jan 2025 00:00:00 GMT

Title: Interannual variability in the reproductive cycle of Ruditapes philippinarum influenced by environmental and parasitic factors on the west-coast of Korea Authors: Thatchaneshkanth, S.; Jeong-Hwa, K.; Kwang-Sik, C.; Hyun-Sung, Y. Abstract: Extensive studies have shown that geographic variation, primarily driven by environmental factors, affects the reproductive cycle duration, gametogenesis, and spawning periods of the Manila clam, Ruditapes philippinarum. From February 2008 to December 2010, we monitored the annual reproductive cycle of Manila clams on a tidal flat in Garorim Bay, located on Korea’s west coast. In adult males, spermatogenesis began between December and February, reaching a peak (90 %) by March and April. Partial spawning in males occurred from May to July, coinciding with seawater temperatures rising from 11.2 to 20.0 ◦C. In females, oogenesis commenced between January and February, while spawning began in June, reaching a peak activity level of 36 %.A brief 3-month spawning period was recorded in 2009, while in other years, spawning extended for 4–5 months. The condition index (CI) of the clams ranged from 78 to 139, and fluctuations in CI during the spawning season indicated multiple spawning peaks in males, while females exhibited a single peak. The intensity of the protozoan parasite Perkinsus olseni infection ranged from 0 to 1.4x105 cells per gram of gill tissue, reflecting a low infection level compared to clams from other tidal flats on the west coast. Overall, variations in reproductive stages and CI at the study site appeared to be primarily influenced by seasonal fluctuations in water temperature and food availability, with negligible impact from parasite infection.

Global warming impacts on marine diversity and key indicator species in East Asia

Wed, 01 Jan 2025 00:00:00 GMT

Title: Global warming impacts on marine diversity and key indicator species in East Asia Authors: Thatchaneshkanth, S.; Sukgeun, J.; Xiaoxia, S.; Tatsuya, K.; Vallejo, B.; Tatyana, O.; Jinho, C.; Hye-Won, M.; Donggu, J.; Christophe, V.; Hongjun, L.; Shingo, U.; Hyun-Sung, Y.; Hee-Yoon, K.; Ronald, G.N.; Ning, L.; Kwang-Sik, C. Abstract: Marine ecosystems in the northwest Pacific are known for their high biodiversity, with many marine species, from tiny plankton to huge macroalgae. Marine biodiversity is affected by irreversible global warming, mainly the increase of greenhouse gas emissions from anthropogenic activities. For the past several decades, marine ecosystems in East Asia have been changing due to the increase in sea surface temperature (SST), which has changed some important environmental factors, including rainfall patterns, extreme weather, and ocean circulation. Such modifications in the environmental parameters have altered the physiology, phenology, and distribution pattern of marine organisms. The SST increase has also altered population and community structure, and the functioning of the ecosystem. Certain subtropical and tropical fauna and flora are now extending their range of distribution from the warm southern area to the temperate regions, disrupting or modifying the biotic interactions in the temperate ecosystem. Collaborative conservation projects and responsible policies are crucial to safeguard the environmental value of East Asia’s marine ecosystems for future generations and mitigate the negative effects of global warming on marine biodiversity. Conservation and management of East Asia’s marine environments hold significant implications for global biodiversity and ecological balance, making them a pivotal focus in addressing climate change challenges in marine ecosystems.

Effects of Perkinsus olseni parasitism and environmental conditions on the gonad maturation and reproductive effort of female Manila clam (Ruditapes philippinarum) on the west and south coasts of Korea

Wed, 01 Jan 2025 00:00:00 GMT

Title: Effects of Perkinsus olseni parasitism and environmental conditions on the gonad maturation and reproductive effort of female Manila clam (Ruditapes philippinarum) on the west and south coasts of Korea Authors: Thatchaneshkanth, S.; Hyun-Ki, H.; Kyung-Il, P.; Young-Ghan, C.; Kwang-Sik, C. Abstract: In the intertidal zone, the reproductive dynamics of bivalves are influenced by both biotic and abiotic factors, including spatial and temporal fluctuations in sea surface temperature (SST), food availability, and diseases. Notably, disease proliferation is markedly enhanced under conditions favorable to pathogen entities, such as elevated SST and low food availability. This study examined the associative impacts of Perkinsus olseni parasites on the reproduction of the Manila clam Ruditapes philippinarum, across a latitudinal range covering four sampling sites along the west and south coasts of Korea, ranging approximately 400 km. In late June, we collected adult female clams to assess their condition index, reproductive output, and the prevalence of P. olseni infection. Histology indicated that 94 % of clams from SJ tidal flat, the cooler northwest coast were in the ripe stage. In contrast, clams from WD and GS, the warmer regions of the southwest and south exhibited more progressed stages of gonadal maturation, including the spent and resting phases. Notably, clams at the ripe stage in WD and GS demonstrated significantly lower gonad somatic index (GSI, P < 0.05) than their counterparts in the northwest. Moreover, the intensity of P. olseni infection was substantially higher (P < 0.05) in WD in the south compared to SJ in the northwest. The histopathological index (HPI) revealed minimal tissue damage and lower HPI scores at SJ, in stark contrast to the progressively severe tissue damage and elevated HPI scores observed moving southward along the latitudinal gradient. It was postulated that the combined effects of higher SST, low food availability, and high levels of P. olseni infection are key factors contributing to the reduced GSI and condition index (CI) in ripe clams in WD on the warm southern coast. Additionally, the lower CI observed in clams from WD potentially heightens their vulnerability to diseases by weakening their immune defenses during critical reproductive phases, such as spawning and post-spawning.

Spatio‐Temporal Variation in Perkinsus olseni Infection Intensity in Manila Clam Ruditapes philippinarum in Anmyeondo and Cheonsu Bay Tidal Flats on the West Coast of Korea

Mon, 01 Jan 2024 00:00:00 GMT

Title: Spatio‐Temporal Variation in Perkinsus olseni Infection Intensity in Manila Clam Ruditapes philippinarum in Anmyeondo and Cheonsu Bay Tidal Flats on the West Coast of Korea Authors: Thatchaneshkanth, S.; Young‐Ghan, C.; Hye‐Mi, L.; Jeong‐Hwa, K.; Jong‐Seop, S.; Mun‐Gyeong, K.; Gwang‐Il Jang, J.; · Kwang‐Sik, C. Abstract: The alveolate protist Perkinsus olseni infections impose considerable stresses on the host Manila clam Ruditapes philippinarum, often reducing their tissue weight due to the drain on energy resources. However, the relationship between condition factors and P. olseni infection exhibits inconsistency in different scenarios, as it is influenced by various factors such as environmental conditions, food availability, and reproductive conditions. To gain deeper insights, we surveyed Manila clams occurring on tidal flats in Anmyeondo Island, Cheonsu Bay to assess P. olseni intensity and its effects on the fitness of Manila clams. The Ray’s fluid thioglycollate medium assay revealed that P. olseni infection in clams from inner Cheonsu Bay had considerably greater P. olseni intensities in May and September 2021 than those from outer Cheonsu Bay and reference sites (P < 0.05). Despite the high level of P. olseni infection, condition index (CI), a ratio of the flesh weight to the shell weight, in clams from inner Cheonsu Bay was also significantly higher than in clams from outer Cheonsu Bay and reference sites (P < 0.05). A noteworthy finding of this study was the positive association between P. olseni infection intensity and CI in clams, which suggests that despite the high parasite load, clams were able to maintain a higher CI, possibly due to the abundance of nutrients and organic matter present in the inner bay. The P. olseni infection intensities measured in September were significantly higher at most of the sampling sites in the inner and outer bay, which could be associated with the poor health condition of clams during a post-spawning period. These results highlight the complexity of bivalves’ ecological relationships in Cheonsu Bay and offer new insights into their adaptability accompanied by other factors to parasite stressors.