National Committee on Marine Sciences (NCMS)
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- Dissolved and particulate carbon export from a tropical mangrove‐dominated riverine systemRay, Raghab; Miyajima, Toshihiro; Watanabe, Atsushi; Yoshikai, Masaya; Ferrera, Charissa M.; Orizar, Iris; Nakamura, Takashi; San Diego‐McGlone, Maria Lourdes; Herrera, Eugene C.; Nadaoka, Kazuo (Wiley, 2021-09-24)Despite being a major component in the mangrove carbon (blue carbon) budget, “outwelling” flux (or export to the sea) has gained little attention relative to other biogeochemical fluxes and reservoir carbon stock estimations. This study aims to estimate lateral exchange fluxes of dissolved and particulate organic carbon (DOC, POC) and dissolved inorganic carbon (DIC) from the watershed through a microtidal mangrove-dominated estuary to the coastal sea in Panay Island, Philippines. Along the estuarine transect, consistent addition of DOC, DIC, and POC at higher salinities were attributed to mangrove organic matter input. Upstream groundwater input (carbonate weathering) and downstream mangrove organic matter decomposition (possibly sulfate reduction) were the main controls on DIC. DOC corresponded to relatively pure mangrove sources in creek water, while POC was a mixture of detrital and algal organic matter. The mangrove system acted as net exporter of carbon to the sea in both dry and wet seasons. From short-term observations, outwelling fluxes of mangrove-derived DOC, DIC, and POC contributed 27–53%, 8–31%, and 42%, respectively, to their estuarine outflow. Unlike other studies, such low percentage for DIC might result from other external nonmangrove input (e.g., watershed carbonate weathering). Overall estuarine carbon flux was dominated by DIC (90–95%) with only minor contribution from DOC. The approach utilized in this study to estimate lateral carbon flux specific to a small mangrove setting can be useful in delineating blue carbon budgets that avoid geographical and methodological biases.We are grateful to the Japan International Cooperation Agency (JICA) and Japan Science and Technology Agency (JST) through the Science and Technology Research Partnership for Sustainable Development Program (SATREPS) for financially supporting the Project “Comprehensive Assessment and Conservation of Blue Carbon Ecosystems and their Services in the Coral Triangle (BlueCARES).” We are indebted to Dr Gerd Gleixner and Steffen Ruehlow (MPI-Jena, Germany) for providing support in δ13DOC analyses, and Dr Naoko Morimoto for POM analyses. We sincerely thank Dr Kenji Ono for sharing fine root production data. We are thankful to Dr Ariel Blanco (Department of Geodetic Engineering, UP Diliman) for providing delineation of mangrove area and Dr. Enrico C. Paringit, program leader of Phil-LiDAR 1, for providing the LiDAR products for map preparation. We thank Jeffrey Munar, Jesus Abad, John Michael Aguilar, Dominic Bautista, Bryan C. Hernandez and Mr Tsuyoshi Kanda for their assistance during field surveys. We are grateful for the overall support given by the University of the Philippines, Diliman and Aklan State University to the project. Finally, we thank the Journal Editor, Associate Editor, and three reviewers for their valuable comments and corrections on the manuscript.
- Strong genetic structure and limited gene flow among populations of the tropical seagrass Thalassia hemprichii in the PhilippinesNakajima, Yuichi; Matsuki, Yu; Fortes, Miguel D.; Uy, Wilfredo H.; Campos, Wilfredo L.; Nadaoka, Kazuo; Lian, Chunlan (MDPI AG, 2023-02-05)Seagrasses are marine angiosperms, and seagrass beds maintain the species diversity of tropical and subtropical coastal ecosystems. For proper understanding, management and conservation of coastal ecosystems, it is essential to understand seagrass population dynamics. Population genetic studies can cover large geographic scales and contribute to a comprehensive understanding of reproductive dynamics and potential dispersal among locations. The clonal and genetic diversity and genetic connectivity of Thalassia hemprichii in the Philippines were estimated by a population genetics approach. The geographic scale of this study has a direct distance of approximately 1600 km. Although high clonal diversity was found in some sites (R = 0.07–1.00), both sexual and asexual reproduction generally maintains separate populations. Genetic diversity is not definitely correlated with latitude, and genetic differentiation is significant in all pairs of sites (FST = 0.026–0.744). Complex genetic structure was found in some regions, even at a fine geographic scale. The migration of fruits and seedlings was elucidated as an infrequent and stochastic event. These results suggest the necessity for the conservation of this species due to a deficiency in migrants from external regions.We thank members of CECAM project.
- Genetic connectivity and diversity between tropical and subtropical populations of the tropical horned sea star Protoreaster nodosus in the northwest PacificNakajima, Yuichi; Yasuda, Nina; Matsuki, Yu; Arriesgado, Dan M.; Fortes, Miguel D.; Uy, Wilfredo H.; Campos, Wilfredo L.; Nadaoka, Kazuo; Lian, Chunlan (Springer, 2024-06-01)Seagrass beds are ecologically and economically important coastal ecosystems, and seagrass-associated organisms are a key part of their biodiversity. Marine organisms that reproduce through broadcast spawning are likely to have less genetic differentiation among populations than those that use other modes of reproduction, but this has not been well studied. Here, we investigated the genetic diversity, genetic differentiation, and migration patterns of the seagrass-associated sea star Protoreaster nodosus across 12 sites spanning approximately 2500 km from the Ryukyu Archipelago, Japan, to the Philippines. We genotyped 405 individuals by using seven microsatellite loci and analyzed allelic richness and expected heterozygosity as indices of genetic diversity. Of these two indices, only expected heterozygosity decreased slightly with increasing latitude. These results suggest that genetic diversity has not clearly decreased, even in the isolated Ryukyu Archipelago populations. Geographic distance was significantly correlated with genetic differentiation (pairwise FST: − 0.005 to 0.049). However, populations in the Ryukyu Archipelago and the Philippines showed relatively low genetic structuring and the pairwise genetic differentiation between these regions was often non-significant. Analysis of historical migration rates showed bidirectional north–south migration, which appears to be influenced by the Kuroshio Current and its countercurrents.We thank members of the project ‘Coastal Ecosystem Conservation and Adaptive Management under Local and Global Environmental Impacts in the Philippines’ (CECAM project: https://sites.google.com/view/cecam-project).
- Hydrodynamics rather than type of coastline shapes self‐recruitment in anemonefishesSato, Masaaki; Honda, Kentaro; Nakamura, Yohei; Bernardo, Lawrence Patrick C.; Bolisay, Klenthon O.; Yamamoto, Takahiro; Herrera, Eugene C.; Nakajima, Yuichi; Lian, Chunlan; Uy, Wilfredo H.; Fortes, Miguel D.; Nadaoka, Kazuo; Nakaoka, Masahiro (Wiley, 2023-07-25)Many marine species have a pelagic larval phase that undergo dispersal among habitats. Studies on marine larval dispersal have revealed a large variation in the spatial scale of dispersal and self-recruitment. However, few studies have investigated the influence of types of coastline (e.g., bay vs. open coast) on marine larval dispersal. Bays or lagoons generally enhance the retention of larvae, while larvae are more likely to be flushed by strong currents in open coasts. To examine associations between larval dispersal, coastline type, and hydrodynamics, we compared fin-scale dispersal patterns, self-recruitment, and local retention (LR) of two anemonefishes (Amphiprion frenatus and Amphiprion perideraion) between a semi-enclosed bay and an open coast in the Philippines combining genetic parentage analysis and biophysical dispersal modeling. Contrary to our expectations, parentage analysis revealed lower estimates of self-recruitment in the semi-closed bay (0%) than in the open coast (14–15%). The result was consistent with dispersal simulations predicting lower LR and self-recruitment in the semi-closed bay (0.4% and 19%) compared to the open coast (2.9% and 38%). Dispersal modeling also showed that cross-shore currents toward offshore were much stronger around the semi-closed bay and were negatively correlated with LR and self-recruitment. These results suggest that stronger cross-shore currents around the semi-closed bay transport anemonefish larvae to the offshore and mainly contributed to the lower self-recruitment. Our results highlight importance of hydrodynamics on larval dispersal and difficulty in predicting self-recruitment from coastline type alone.
- Sedimentary blue carbon dynamics based on chronosequential observations in a tropical restored mangrove forestRay, Raghab; Suwa, Rempei; Miyajima, Toshihiro; Munar, Jeffrey; Yoshikai, Masaya; San Diego-McGlone, Maria Lourdes; Nadaoka, Kazuo (Copernicus GmbH, 2023-03-03)Among the many ecosystem services provided by mangroves, the sequestration of large amounts of organic carbon (OC) in marine ecosystems (also known as “blue carbon”) has given these unique ecological environments enormous global attention. While there are many studies on the blue carbon potential of intact mangroves (i.e., naturally growing), there have been very few studies on restored mangroves (i.e., planted). This study aims to address this knowledge gap by examining the sediment development process during the early colonization (rehabilitation) of mangroves in an OC-poor estuary in Panay Island, Philippines. Based on source apportionment of multiple end-members in the sedimentary organic matter, the contribution of mangrove plant material was higher at the older sites compared to the younger sites or bare sediments where there is a higher contribution of riverine input. A clear increasing gradient according to mangrove development was observed for bulk OC (0.06–3.4 µ mol g−1, porewater OC (292–2150 µmol L−1, sedimentary OC stocks (3.13–77.4 Mg C ha−1), and OC loading per surface area (7–223 µmol m−2). The estimated carbon accumulation rates (6–33 mol m−2 yr−1) based on chronosequence are within the global ranges and show an increasing pattern with the age of mangroves. Hence, the sediments of relatively young mangrove forests appear to be a significant potential C sink, and short-term chronosequence-based observations can efficiently define the importance of mangrove restoration programs as a potential carbon sequestration pathway.We are grateful to the Japan International Cooperation Agency (JICA) and the Japan Science and Technology Agency (JST) through the Science and Technology Research Partnership for Sustainable Development (SATREPS) program for financially supporting the project Comprehensive Assessment and Conservation of Blue Carbon Ecosystems and their Services in the Coral Triangle (Blue CARES). We thank Jesus Abad, John Michael Aguilar, Dominic Bautista, Bryan C. Hernandez, and Tsuyoshi Kanda for their assistance during field surveys. We are grateful for the overall support given to the project by the University of the Philippines, Diliman, and Aklan State University. We are thankful to our Blue CARES colleague Charissa Ferrera for the support in language edits. Finally, authors sincerely thank AE (Jack Middelburg) and the reviewers for their constructive comments that have greatly improved the revised version of the manuscript.
- Phosphorus as a driver of nitrogen limitation and sustained eutrophic conditions in Bolinao and Anda, Philippines, a mariculture-impacted tropical coastal areaFerrera, Charissa M.; Watanabe, Atsushi; Miyajima, Toshihiro; San Diego-McGlone, Maria Lourdes; Morimoto, Naoko; Umezawa, Yu; Herrera, Eugene; Tsuchiya, Takumi; Yoshikai, Masaya; Nadaoka, Kazuo (Elsevier, 2016)The dynamics of nitrogen (N) and phosphorus (P) was studied in mariculture areas around Bolinao and Anda, Philippines to examine its possible link to recurring algal blooms, hypoxia and fish kills. They occur despite regulation on number of fish farm structures in Bolinao to improve water quality after 2002, following a massive fish kill in the area. Based on spatiotemporal surveys, coastal waters remained eutrophic a decade after imposing regulation, primarily due to decomposition of uneaten and undigested feeds, and fish excretions. Relative to Redfield ratio (16), these materials are enriched in P, resulting in low N/P ratios (~ 6.6) of regenerated nutrients. Dissolved inorganic P (DIP) in the water reached 4 μM during the dry season, likely exacerbated by increase in fish farm structures in Anda. DIP enrichment created an N-limited condition that is highly susceptible to sporadic algal blooms whenever N is supplied from freshwater during the wet season.
- 17-year change in species composition of mixed seagrass beds around Santiago Island, Bolinao, the northwestern PhilippinesTanaka, Yoshiyuki; Go, Gay Amabelle; Watanabe, Atsushi; Miyajima, Toshihiro; Nakaoka, Masahiro; Uy, Wilfredo H.; Nadaoka, Kazuo; Watanabe, Shuichi; Fortes, Miguel D. (Elsevier, 2014)Effects of fish culture can alter the adjacent ecosystems. This study compared seagrass species compositions in 2012 with those in 1995, when fish culture was less intensive compared to 2012 in the region. Observations were conducted at the same four sites around Santiago Island, Bolinao: (1) Silaqui Island, (2) Binaballian Loob, (3) Pislatan and (4) Santa Barbara, and by using the same methods as those of Bach et al. (1998). These sites were originally selected along a siltation gradient, ranging from Site 1, the most pristine, to Site 4, a heavily silted site. By 2012, fish culture had expanded around Sites 2, 3 and 4, where chlorophyll a (Chl a) was greater in 2012 than in 1995 by one order of magnitude. Enhalus acoroides and Cymodocea serrulata, which were recorded in 1995, were no longer present at Site 4, where both siltation and nutrient load are heavy.