National Committee on Marine Sciences (NCMS)
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- Multiple severe storms revealed by coral boulders at Pasuquin, northwestern Luzon, PhilippinesGong, Shou-Yeh; Liu, Sze-Chieh; Siringan, Fernando P.; Gallentes, Adonis; Lin, Han-Wei; Shen, Chuan-Chou (Elsevier, 2022-11-15)Over 30 meter-sized coral boulders are scattered 45–140 m away from the edge and above high tide on a Holocene reef flat at Pasuquin, northwestern Luzon, Philippines. The boulders are overturned or tilted as indicated by the framework fossil corals in them, but have the same lithology as those along the reef edge and thus were likely broken off from there. The dimensions of boulders larger than 3 m were calculated from 3D models constructed by photogrammetry. Their volumes range from 10 to 53 m3. Assuming 2.1 g/cm3 for wet density, weights of boulders would range from 21 to 110 metric tons. Boulders of such size and weight can't be moved by normal waves, and thus must have been dislodged by extreme wave events (EWEs). Small and well-preserved corals found on the surface of seven boulders were collected for 230Th dating to reconstruct the timing of displacement. The ages of corals are 1781.6 ± 1.9, 1903.4 ± 2.7, 1945.8 ± 1.2, 1956.9 ± 1.2, 1956.75 ± 0.99, 1978.1 ± 1.5 and 2002.78 ± 0.88 CE, respectively. These ages are considered to constrain the timing of boulder displacement from the reef edge. We propose that typhoon-induced EWEs were responsible for the displacement of these boulders at Pasuquin.
- Natural and anthropogenic climate variability sgnals in a 237-year-long coral record from the PhilippinesInoue, Mayuri; Fukushima, A.; Chihara, M.; Genda, A.; Ikehara, Minoru; Okai, T.; Kawahata, Hodaka; Siringan, F. P.; Suzuki, Atsushi (American Geophysical Union, 2023-11-29)Both proxy and model studies conducted to understand anthropogenic warming have revealed historical variations in sea-surface temperature (SST) since the industrial revolution. However, because of discrepancies between observations and models in the late nineteenth century, the timing and degree of anthropogenic warming remain unclear. In this study, we reconstructed a 237-year-long record of SST and salinity using a coral core collected from Bicol, southern Luzon, Philippines, which is located at the northern edge of the western Pacific warm pool. The SST record showed volcanic cooling after several volcanic eruptions, including the 1815 Tambora eruption, but the pattern of change differed. Decadal SST variations at Bicol are connected to Pacific Decadal Variability (PDV). Therefore, it is suggested that the PDV conditions at the time of the eruption may have influenced marine conditions, such as the degree and duration of cooling and/or salinity, after the eruptions. Although there were discrepancies in SST variations among the modeled, observed, and proxy SST data from the late nineteenth to early twentieth centuries, SST data from the late twentieth century showed globally coherent anthropogenic warming, especially after 1976. In particular, summer SST in the northwestern Pacific has become more sensitive to anthropogenic forcing since 1976.
- Survival and growth of coral recruits in varying group sizesLigson, Charlon A.; Cabaitan, Patrick C.; Harrison, Peter L. (Elsevier, 2022-11)Coral larvae usually settle as solitary individuals but sometimes also in aggregations, especially when settlement sites are limited. Fusion of coral individuals can consist of different group sizes with varying numbers of adjacent coral spat. However, little is known about the performance of coral individuals in different group sizes, especially during the early post-settlement phase, where high mortality usually occurs. Here, we investigated the performance of Acropora verweyi juveniles in varying group sizes of fused coral spat. Specifically, we examined the survival and growth rate of coral individuals, with four group size levels: solitary spat, 2, 3–5, 6–9, and 10–28-spat group size, over 21 weeks post-settlement. The highest survival was detected in the 6–9 spat group size followed by the 3–5 and 10–28 group sizes, with lower survival in the 2-spat group size and solitary spat. Overall, 7.4% of the 338 coral individuals reared in ex-situ hatchery conditions survived up to the last monitoring at 21 weeks. At 15 weeks post-settlement, the mean surface areas of solitary and 2-spat group sizes were five- to eight-fold smaller than in larger fused coral individuals. However, there were no significant differences between the percent growth changes among the coral group sizes. The present study suggests that fused coral spat of larger group sizes can immediately gain size, but not necessarily have higher growth rates within the first 15 weeks post-settlement. Results also revealed that fusions of at least six A. verweyi spat had higher survival than small fused individuals and solitary spat, at least in the first few months after settlement. The advantage of such fusions, especially in larger group sizes, may offer an enhanced survival for coral spat during the critical period of early post-settlement. This outcome provides potential advantages for coral restoration using sexual production of larvae.