Rate and efficiency of organic carbon assimilation by aquacultured juvenile sandfish Holothuria scabra

Diet assimilation rate is crucial to the growth and survival of Holothuria scabra juveniles during culture. To understand the assimilation rate and efficiency we assess organic carbon assimilation, which is closely related to the growth and source of variations in diet. We conducted a two-factor experiment, i.e., juvenile origin (cultured and wild H. scabra juveniles), and diet treatment (one control with no additional diet, and three additional diets, i.e., rice bran, dried cow manure, and seagrass Enhalus acoroides extract). We monitored the amounts of each diet that the juveniles consumed and the fecal pellets they egested. The diet, sediment, body walls, and organic carbon content of the fecal pellets were measured using an elemental analyzer combined with an isotope ratio mass spectrometer. Exponential growth was seen in the juveniles fed with rice bran, which had a fecal pellet egestion of 0.12–0.21 gC/d. Stable isotope analysis showed that the contribution of the diet proportion to the growth of the sandfish did not exceed 30%. The range of the assimilation rate was 35.3–62.4 gC/d. The average assimilation efficiency of organic carbon was 43.6 ± 27.7% (max 57.9%). Considering the assimilation rate and efficiency, we suggest a feeding interval of once every two days or twice per week at a rate of 3–5% of the total H. scabra biomass for a juvenile culture system

Stable Carbon Isotope Signature of Particulate Organic Matter in the Southwestern Sumatran Waters of the Eastern Indian Ocean

The Southwestern Sumatran Waters of the Eastern Indian Ocean are known to be affected by the South Java Current and the South Equatorial Counter Current. Many studies have been carried out in relation to upwelling and the Indonesian Through Flow. However, there has been no systematic study into the properties of the particulate organic matter in the Southwestern Sumatran Waters. Therefore, the organic matter in these waters in terms of its origin is unknown. As part of the Widya Nusantara Expedition 2015 research cruise, this study aimed to examine the stable isotope ?13C signature of particulate organic matter (POM), especially with regards to the origins of the organic matter. The stable isotope ?13C is complemented by other variables such as chlorophyll-a, particulate organic carbon (POC), and nutrients (phosphate, silicate, ammonium and nitrate). The POC tends to be depth-dependent. The values of ?13C are ?23.56, ?24.30 and ?24.06‰ for 5, 100 and 300 m depths, respectively. We found that POM tended to be isotopically lighter with increasing POC and chl-a, especially in the surface water, potentially due to the preferential lighter carbon isotope for metabolism by the primary producer. The origin of POM in the Southwestern Sumatran waters is marine end-member in the surface (up to 100 m depth) and mixed compositions at the surface of twilight zone (100–300 m depth). The next layer, i.e. twilight zone (more than 300 m depth), is terrigenous end-member. The surface POM of SSW, as shown in 5 m depth, is not freshly produced and tends to be either autochthonous or allochthonous

SEDIMENT CARBON STOCK OF WEST KALIMANTAN MANGROVE FORESTS

We investigate variation in sediment carbon stock at Mempawah and Bakau Besar in West Kalimantan by analyzing organic carbon content from sediment samples taken within 20 cm depth. Our results show that organic carbon stock of sediments in Bakau Besar is generally higher than in Mempawah that may be due to riverine input of organic carbon into the mangrove forests. The riverine input of organic carbon is influenced tides, in which we find that organic carbon loads are higher during high tide compared to low tide. In particular, we find high organic carbon contents at a station in Mempawah (Station 3; 6.46 ± 0.23 tons C/ha) and another station in Bakau Besar (Station 2; 14.93 ± 1.43 tons C/ha). These two stations have mangrove density of 13,519 individuals/ha and 9,928 individuals/ha, respectively. We conclude that high organic carbon is influenced by riverine input as well as a high density of mangrove and the dominant type of mangrove vegetation at the sites

ORGANIC MATTER AND NUTRIENT PROFILE OF THE TWO-CURRENT-REGULATED-ZONE IN THE SOUTHWESTERN SUMATRAN WATERS (SSW)

The Indian Ocean is influenced by monsoon systems which alter the ocean’s physical and chemical properties. Specifically, the southwestern Sumatran waters in the eastern Indian Ocean are considered a dual current regulated zone i.e. affected by South Equatorial Counter Current (SECC) and South Java Current (SJC). This area is considered as having an important role in the transfer of organic matter or the biological pump. However, the information about this area is minimal, especially in terms of organic matter and nutrient profile. This study will update the recent information about the area, including the profile of particulate organic matter (POM), macro-nutrients, total suspended solids (TSS), macromolecule-degradingbacteria, and soft bottom macrobenthic organisms sampled from 26 stations in both the SECC-regulated zone and the SJC-regulated zone. The physical profile is typical of tropical watersand both zones have a distinct profile of organic matter and nutrients. The particulate organic carbon (POC), particulate organic nitrogen (PON), and TSS of the SECC-regulated zone can be considered higher than those of the SJC-regulated zone. This region is categorized as mesotrophic waters, especially from the surface up to 100 m. The production of nutrients and organic matter in the water column in this area contribute significantly to the abundance of heterotrophic bacteria and benthic organisms

Establishing an Ocean Acidification Monitoring System for the Tropical Waters of Indonesia Facing Regional Climate Variability

The emission of greenhouse gases, including high CO_2 and other materials, initiates global warming and climate change. Atmospheric CO_2 that affects the carbonate system of seawater causes ocean acidification (OA). OA affects marine organisms directly, as well as humans economically and ecologically. Considering the high impact of OA and following the United Nations’ Sustainable Development Goals, systematic research and monitoring of OA is necessary in Indonesia, whose seas play an important role in this emerging phenomenon. This review discusses the urgency of OA monitoring systems and suggests carbonate system monitoring, as well as carbon biogeochemistry. OA significantly affects marine production and alters ecosystem services, and it is likely to have an impact on habitats shifting from calcified to non-calcified and reducing benthic complexity. Its effect on calcifying organisms can also be found, i.e., coral calcification and/or dissolution of CaCO_3 of calcifying organisms. Acidity (pH), as well as the carbonate system variables of seawater, fluctuate, especially with variations in space and time. Coastal ecosystems that are directly affected by terrestrial input will have carbonate system variables that fluctuate more. The annual rate of decreasing seawater pH, especially over an open and large spatial scale, may indicate OA. Therefore, a monitoring system must be implemented to obtain systematic and comprehensive information on OA. Here, we also introduce a biogeochemical monitoring initiative for OA in Lombok with the established protocols. Improvement of many aspects, including analysis instruments, analysis methods, sample treatment, and sampling frequency will provide new insight into further research and monitoring of OA.See discussions, stats, and author profiles for this publication at:"References" URI.本論文の統計や著者について、「関連URI」から見ることができます