Program

The inner Gulf of Thailand is a semi enclosed sea covering an area of about 10,000 km². This Gulf is characterized by complex and highly productive coastal ecosystems. However this rich legacy is influenced by large volume of freshwater passing through riverine runoff. Importance and role of terrestrial organic matter (including anthropogenic wastes) input to the gulf ecosystems have not been clearly defined. In order to distinguish sources of organic materials that contribute within the gulf, stable carbon and nitrogen isotopic ratios have been implemented to define the spatial and temporal variability of organic matter in this semi enclosed sea. The aim of this study is to understand interactions between terrestrial and coastal ecosystems, and to extend the available information on 13C and 15N of the inner Gulf of Thailand for further understanding the source and subsequent movement of organic matter in the gulf ecosystems.

Jakarta Bay is among the most eutrophic bay in the world which is classed as hyper-eutrophic and eutrophic levels. This study is done aimed to examine the amount of riverine nutrient loads and its effects in the adjacent bay waters, especially to the eutrophication syndrome : algae biomass bloom and its associated effects.

Dissolved inorganic nutrients measurements of DIN, phosphorus and silicate, phytoplankton species composition and its abundance and chlorophyll-a have been conducted at 17 rivers in the city of Jakarta and 15 stations in the bay over from 2007, 2013 and 2016. Measurements were conducted covering spatial and temporal variability of the area.

Loads of nitrogen was accounted to 21,895 ton N/year, phosphorus was 3,405 ton P/year and silicate was 10,433 ton Si/year. Dissolved oxygen levels were in low values, showing 30% in the value between 3 - 6 mg/L and 70% were below 3 mg/L. The nutrient pattern corresponds to the distribution of phytoplankton biomass with highest Chl-a concentrations (31.4 µg Chl-a/L) in the river mouths. In the near coastal waters chlorophyll-a levels decreased by a factor of 2 (15.8 µg Chl-a/L), followed by a 4 folds decrease towards the center of the bay (7.8 µg Chl-a/L) and a decline down to very low concentrations of about 2.2 µg Chl-a/L in the transient waters to the Java Sea. According to its relatively stable but high level of nutrient pollution, Jakarta Bay can be classified into three trophic categories with a hyper-eutrophic zone in the near-shore area, eutrophic conditions in the middle and mesotrophic waters at the outer part of the bay. Algae blooms and hypoxia are a regular phenomenon in the hypertrophic coastal area, sometimes accompanied by mass mortality of fish.

Submarine Groundwater Discharge (SGD) has been shown to be an important pathway between land and sea for the transport of terrestrial materials. SGD results in various biogeochemical changes in the coastal environments, such as coastal primary production, eutrophication, and benthic production. Therefore, it is important to investigate the ecological significance of SGD. In the present study we investigated two subjects 1) whether the δ¹³ C of ambient water reflect the proportion of fresh water flow rate in SGD, 2) whether the δ¹³ C recorded in the shell of the sessile bivalve reflect that of the ambient water. The SGD rate and the proportion of fresh water flow rate in SGD were measured by the seepage meter at Kamaiso beach along the Mt. Chokai volcanic coast in June and September 2016. The rock-oyster was also sampled at Kamaiso Beach and adjacent 3 areas (Mega, Takinoura, Torisaki). There was a positive significant relationship between salinity and the δ¹³ C of ambient water (p<0.01). The δ¹³ C of the shell was high at high SGD flow rate sites and the positive significant correlation was found between the δ¹³ C of the shell and that of ambient water. In order to estimate the proportion of fresh water flow rate in SGD from the δ¹³ C of the rock-oyster shell, we used the two end member mixing model including DIC concentration of both sea water and fresh underground water. The estimated average fresh water flow rate in SGD ranged from 4 % (Torisaki) to 35% (Mega). These values are higher than those estimated from the δ¹³ C of ambient water (1.3% Torisaki and 18.1% Mega). The difference of these results are seems to be the difference of local SGD environment around rock-oyster.

Anthropogenic emissions of reactive nitrogen (N) due to fossil fuel combustion and modern agriculture practices have dramatically increased in global scale. In the Japanese watershed along the Sea of Japan, large amounts of reactive N emitted from northeastern Asia have deposited onto forest ecosystems, and thus N concentrations in rivers and groundwater have been increasing year to year. Remotely modified N concentrations of terrestrial waters in local watersheds would alter coastal ecosystems. However, influence of N export from the watershed along the Sea of Japan on coastal ecosystem is still unclear. In this study, we assessed effects of chronically increasing nitrogen loading from the watershed on the semi-enclosed embayment (Obama Bay) within central Wakasa Bay using the sediment cores. We have taken four sediment cores, and then were sectioned into 1 cm intervals for the working subsamples. We measured the activity of 210Pb and 137Cs of the subsamples to determine sedimentation rate and age. Simultaneously, we measured biogeochemical variables of TOC, TN, TP, BSi, d13C, d15N of the subsamples. Mean sedimentation rates within the bay have been rapidly increasing from 0.19±0.10 g cm^-2 yr^-1 in 1960-1980 to 0.55±0.04 g cm^-2 yr^-1 in 2000-2015. Corresponding to long-term increase of N concentrations in the rivers, water content and TN of the sediment cores mainly derived from marine autochthonous organic matter have increased year to year. BSi fluxes also increased from 0.5±0.3 mg cm^-2 yr^-1 in 1960-1980 to 1.8±0.3 mg cm^-2 yr^-1 in 2000-2015. These results suggested that an increase of nitrogen loading from the watershed would promote primary production rates of autochthonous particulate organic materials. In addition to N-limited condition in the past, a drastic decrease of seagrass and seaweed might induced a regime shift of Obama Bay ecosystem approximately in 2000.

Estuarine and shallow coastal systems (ESCS) are recognized as not only significant organic carbon reservoirs but also emitters of CO2 to the atmosphere through air-water CO2 gas exchange, thus posing a dilemma on ESCS's role in climate change mitigation measures. However, some studies have shown that coastal waters takes up atmospheric CO2 (Catm), although the magnitude and determinants remain unclear. We argue that the phenomenon of net uptake of Catm by ESCS is not unusual under a given set of terrestrial inputs and geophysical settings. We assessed the key properties of systems that show the net Catm uptake and propose that ESCS are worthy of investigation as a contributor to climate change mitigation.

Deep-sea environment remains the biggest but least known ecosystem in the planet Earth. The recent discovery of rich methane gas-hydrate resources in seep environments of the South and East China Sea provide a potential energy resolution to the neighborhood countries. However, exploring such resources presents not only a great engineering challenge but also possible anthropogenic perturbation which may result in ecological instability and threaten the deep-sea biological diversity. The study is aimed to investigate biological compositions and trophic relationships of benthic megafauna at the seep and surrounding ecosystems of deep oceans in the South China Sea for further environmental impact assessment. Based on the samples collected during 2013 to 16, we had recognized more than 190 taxa from over 2100 pieces of large benthic animal specimens. The stable isotopic measures (δ13C, δ15N) were taken from tissues of represented samples to elucidate the trophic relationships among major functional groups and eventually result in a novel food web model including seep and nearby bathypelagic fauna. We then apply this model with scenario removal of direct methane-utilizer, the deep mussels, to assess the potential impact on the system and biodiversity. Our simulations suggested the overall system energy, biomass, cycling but not stability indices were affected considerably when >50% of mussel biomass was depleted. Although our preliminary results indicated the isolation nature of deep-water seep ecosystem, the local impact of methane gas-hydrate exploration remains to be carefully assessed and monitored.

Oligotrophication is one of the serious problems in the Seto Inland Sea, Japan, due to rapid reduction measures of nutrient from the land. The effects are reported not only on discoloration of cultured Nori but also cultured bivalves. Although the oyster farming in Hiroshima Bay is a top production in Japan, it has been decreasing to 2/3 as low as that of the peak production in 1980s. Water transparency is usually 2 times high in the oyster culture raft compared to those surrounding area, which indicates high filtering activities by oysters, and implies that feed phytoplankton abundance may not be sufficient for oysters in the rafts. We applied fertilizer containing a proper elemental ratio to enhance oyster growth through enhancing phytoplankton growth. Individual oyster weight at which 600 g packed fertilizer was added per 20 individuals was 20% higher than those of control site without fertilizer. Three-dimensional numerical simulation in diffusion of eluted nutrients showed almost no influence to the surrounding area. We also propose an appropriate amount of fertilizer to be applied to enhance the oyster growth in harmonizing with environmental conditions at the presentation.

Recent years, nutrient concentration in Hiroshima Bay is quite low causing the low primary production of the bay. The growth of oysters intensively cultured in the bay is suspected to be suppressed by the low concentration of feed phytoplankton. To understand the structure of prey-predator interactions between phytoplankton and filter feeders, field observations carried out to collect filter feeder animals from June to August 2016 at 3 oyster raft stations and 7 shoreline stations in the northern Hiroshima Bay (nHB). Temporal variation of temperature, salinity, and underwater fluorescence were also monitored at 5 stations in the nHB using underwater fluorescent-turbid meters. We conducted a numerical simulation to evaluate why the settlement of oyster larvae is often unsuccessful and how much the cultured oysters are suppressed by other competing filter feeders. To calculate phosphorus cycles in prey-predator interactions in the nHB, 14 compartments were set in the model according to the observation results; large-sized phytoplankton, small-sized phytoplankton, zooplankton, oysters, oyster larvae, mussels, mussels at shoreline, barnacles, barnacles at shoreline, polychaeta, clam worms, in addition to DIP, DOP, and detrital phosphorus. Although the total chlorophyll a concentration was not so low with the average of 11 g/l (2.6-35.9 g/l in the range), small-sized chlorophyll a component which is supposed to be a good feed for oyster larvae was very low with the value of almost zero during the study period. It is considered to be the most crucial cause as an obstacle to prevent the development and settlement of oyster larvae. Zooplankton were the most influential filter feeders to the phytoplankton biomass in the nHB. Adult oysters occupying 94% in weight at cultured rafts can be a potential filter feeder to oyster larvae. Jellyfish, whose abundance changes year by year, might have a negative effect on the survival of oyster larvae by decreasing zooplankton biomass through their feeding.

Harmonizing coastal fishery with water-quality improvement has become an essential factor for the sustainable use of coastal ecosystem services. Here, we present the scope of our study based on an interdisciplinary approach including ecological actions, socio-economical actions and psychological actions. We chose to focus on the interaction between oyster aquaculture and seagrass vegetation as a typical ecological action using the Coastal Ecosystem Complex (CEC) concept. Coastal organisms have adapted their traits to the environment over a long period of time, so that restoration of the CEC represents reconstruction of the original process of coastal production. Subtidal seagrass vegetation with intertidal oyster reefs is the original CEC in Japan, so that it would be expected to enhance coastal production by improving the production efficiency without adding nutrients. In addition, the seagrass meadows has been used as an oyster aquaculture area for a long time, which is known as a typical indigenous and local knowledge in some regions of Japanese oyster culture. A simple field experiment with carbon and nitrogen stable isotope analysis revealed that oyster spats cultivated on a tidal flat adjacent to seagrass beds had higher nitrogen concentrations and higher δ13C ratios than spats cultivated in an offshore area using only pelagic production. This result suggests that utilization of the CEC, which enables oysters to use both pelagic and various benthic production, has potential to provide higher quality of food provisioning service for humans.

Rationale: Eutrophication has been reduced in coastal waters of Japan as a result of mitigation efforts over the past thirty years. Reduction in nutrient load to the coastal environment, however, is believed to have reduced the productivity of many fishery resources, and there is a possibility that putting aquaculture effluent into practical use enhances the coastal fishery and unfed aquaculture production. To acquire basic information, environmental surveys were conducted to investigate the behaviour of nutrients around finfish aquaculture cages. Methods: Seawater samples were collected at 19 points in Gokasho Bay, Mie prefecture, and at 47 points around red seabream aquaculture cages in Hasamaura, a semi-closed cove inside Gokasho Bay, from November 2016 to January 2017. Analyzed parameters were as follows: dissolved inorganic nitrogen (DIN, NH₄⁺, NO₂^-, NO₃^-), PO₄^3- and SiO₂. A CTD was also used to obtain temperature, salinity, dissolved oxygen (DO), chlorophyll a and depth data. Results and Discussion: While DIN-N and DO levels were comparable to those from the 1980s where aquaculture was more prosperous, PO₄-P level was an order of magnitude lower perhaps due to diminished aquaculture production and improved feeding management. In a case of diatom bloom observed in November, availability of SiO₂, but not N or P, seemed to be the limiting factor for diatom growth. Chlorophyll a level was higher and NO₃-N lower around red seabream cages than in the surrounding water. This might have been caused by enhancement of primary production triggered by NH₄-N supply from the aquaculture effluent, rapidly depleting not only NH₄-N but NO₃-N in the area. The elevation of chlorophyll a indicates the possibility of productive co-culture of finfish and bivalves in the vicinity of the fish cages.

In Japan, the forest rate is quite high (ca. 70%) in developed countries and the fisheries production has been breaking down proved by low self-sufficiency rate (ca. 60%). Artificial reef is a gear to enhance fishery production by providing hiding space for juvenile fish and feed animals for fish. Three types of artificial timber reefs (ATRs): simple ATRs, ATRs with oyster shells (ATRsOS) and ATRs with leaves and branches (ATRsLB) were deployed at 2 sites (Kazahaya and Kidani) in Mitsu Bay, Hiroshima, Japan, and their performance was evaluated by field observations from 2015 to 2017. Attached organisms, benthos, and fish at the sites were compared with those at control sites with no ATRs and existing artificial concrete reef (ACRs) sites. The results in Kazahaya and Kidani showed a successional processes of producers followed by higher trophic level animals. Attached organisms were abundant at ATRsLB compared to ATRs and ATRsOS. The mean abundance and wet weight of benthos and fish at all the ATRs were higher compared to those at the control site but still below those at ACRs at the last observation. Among 18 fish species observed, 5 dominant species and some other fish appeared are those economically valuable species. It is concluded that ATRs stuffed with leaves and branches are effective to enhance fishery production by which may perform as shelters and provide feed. Using thinning timbers along with leaves and branches for artificial fish reefs is a good practice to link forests and seas in terms of integrated coastal zone management in Japan where high forest rate and low fishery production.

Milkfish (Chanos chanos) aquaculture production in the Philippines continues to grow to augment the supply of fish from the wild, with annual production of 384,425 MT in 2015. Grow-out culture is dependent on the feeding of formulated feeds thus, uneaten feeds aside from the fecal matter were observed to cause deterioration of the environment within the culture enclosure and surrounding areas. This study aims to verify and improve IMTA systems suitable for farm conditions in coastal areas in the Philippines to mitigate environmental impacts of milkfish mariculture. IMTA such as the co-culture of milkfish in pen enclosures alongside the high-valued organic extractive sandfish (Holothuria scabra) and nutrient absorbing seaweed (Kappaphycus alvarezii) were tested in the coastal waters of Barangay Pandaraonan,Nueva Valencia in Guimaras Province. Monthly measurement of growth and survival of the organisms were conducted. Water and sediment collections, as well as physical and environmental parameters using data loggers, were carried out to assess changes in the environment.
Results showed that after 112 days of culture, milkfish growth with ABW of 300-400g is comparable to those grown in the monoculture system. Seaweed proliferated but is season dependent. Sandfish grew but at low survival which might be due to localized effects such as sediment quality which affects settlement behavior and predation of other organisms. Environmental indicators such as nutrient concentration did not show significant deterioration perhaps due to IMTA practice. However, sediment quality deteriorated as observed in the change of color intensity and the increase in acid volatile sulfide (AVS-S) levels particularly in areas where feeding occurred. Thus, IMTA involving the co-culture of nutrient-absorbing high-value aquatic animals and plants has potential to mitigate pollution in milkfish mariculture areas in the Philippines.

Recently, abrupt and unsteady degradation or extinction of macroalgal beds (Moba), which is called Isoyake, has been spreading around Japanese coast. The loss of Moba is especially remarkable along the western Japanese coasts facing to the open seas (Pacific Ocean and East China Sea) and influenced environmentally by warm currents. So far, increase of coastal water temperatures in the past several decades and grazing activation of herbivorous animals accompanied with it are hypothesized to be the most significant factors.
Seto Inland Sea is a semi-enclosed sea area which is interposed to Pacific Ocean coastal areas by Bungo and Kii Channels. There has been no serious occurrence of Isoyake in the Seto Inland Sea area so far, in contrast to the remarkable loss of Moba reported in the Pacific coastal area. A gradient of water temperature, which is > 5℃ in winter, exists in the channels between the two sea areas and due to a ‘cooler’ condition in the Seto Inland Sea, Moba is considered to remain intactly. However, future temperature increase forecasted to occur due to global warming will also cause serious damages to Moba in the Seto Inland Sea.
We are conducting 1) field surveys to detect a ‘inflection’ point of Moba situation along spatiotemporal temperature variations in those sea areas, 2) experiments on influences of temperature increase on eco-physiological situation of key organisms of Moba, 3) a collation of local Moba changes in the past several decades and coastal temperature conditions reproduced by an original high resolution numerical model. From these results, better understanding of the mechanisms of the effects of temperature increase on Moba, and high resolution prediction of coastal temperature condition and local Moba situation in the future will be offered for the effective measures of coastal zone management under the influences of global warming.