16:15 〜 16:30
[BPT02-09] Growth Rate Variations in the Three Japanese Precious Corals Species
キーワード：Precious corals, Corallium japonicum, Pleurocorallium elatius, Pleurocorallium konojoi, growth rate
Precious corals, valued for their rarity and beauty, play a vital role in traditional arts and fishing industries while serving as crucial components of deep-sea ecosystems. Their slow growth and extended lifespans make them invaluable for paleoenvironmental studies, aiding in comprehending their history and identifying conditions essential for survival. This research focuses on the growth rate variabilities within one of the high-yielding fishing fields in Japan, off the Ashizuri Cape, aiming to improve understanding, contribute to environmental reconstruction, assess climate change impacts, and inform conservation and fisheries management.
This study investigated the diametric growth rate for 21 thin sections (17 Corallium japonicum, 3 Pleurocorallium elatius, and 3 P. konojoi) from the fishing field. The thin sections were made after resin embedding, polished to around ~100 µm thickness, and observed by a high-resolution digital microscope (VHX-2000, Keyence). In order to enhance the annual ring visibility and verify ambiguous lines, we used imaging software, Affinity Photo 2.
The analysis of 21 sections unveiled wider growth rate variations, challenging previous narrow range assumptions. The slowest growth rate was observed in C. japonicum, with an average of 0.19 ± 0.04 mm per year, spanning a range of 0.15 ± 0.1 to 0.30 ± 0.08. In comparison, P. elatius and P. konojoi displayed relatively similar growth rates, with averages of 0.21 ± 0.03 mm per year and ranges of 0.18 ± 0.02 to 0.24 ± 0.2 and 0.17 ± 0.1 to 0.24 ± 0.03, respectively. These results indicate that all examined samples of the three species grow more slowly than previously reported. An analysis of the correlation between growth rates and estimated ages across these species revealed a consistently inverse relationship, suggesting that growth rates decrease as age increases. Additionally, the study also showed growth rate variations throughout the lifespan, with a faster rate in the early stage but a slower rate in the latter stage. In addition, cyclic changes in thickness were also observed in CaCO3-rich layers, suggesting the existence of an irregular growth period. The wider range and the cyclic change in growth rates can be attributed to environmental and/or physiological factors. These factors can be investigated in more detail in the future through comparison with environmental data and trace element analysis of skeletons.
This study investigated the diametric growth rate for 21 thin sections (17 Corallium japonicum, 3 Pleurocorallium elatius, and 3 P. konojoi) from the fishing field. The thin sections were made after resin embedding, polished to around ~100 µm thickness, and observed by a high-resolution digital microscope (VHX-2000, Keyence). In order to enhance the annual ring visibility and verify ambiguous lines, we used imaging software, Affinity Photo 2.
The analysis of 21 sections unveiled wider growth rate variations, challenging previous narrow range assumptions. The slowest growth rate was observed in C. japonicum, with an average of 0.19 ± 0.04 mm per year, spanning a range of 0.15 ± 0.1 to 0.30 ± 0.08. In comparison, P. elatius and P. konojoi displayed relatively similar growth rates, with averages of 0.21 ± 0.03 mm per year and ranges of 0.18 ± 0.02 to 0.24 ± 0.2 and 0.17 ± 0.1 to 0.24 ± 0.03, respectively. These results indicate that all examined samples of the three species grow more slowly than previously reported. An analysis of the correlation between growth rates and estimated ages across these species revealed a consistently inverse relationship, suggesting that growth rates decrease as age increases. Additionally, the study also showed growth rate variations throughout the lifespan, with a faster rate in the early stage but a slower rate in the latter stage. In addition, cyclic changes in thickness were also observed in CaCO3-rich layers, suggesting the existence of an irregular growth period. The wider range and the cyclic change in growth rates can be attributed to environmental and/or physiological factors. These factors can be investigated in more detail in the future through comparison with environmental data and trace element analysis of skeletons.