Lateral carbon export of macroalgae and seagrass from diverse habitats contributes particulate organic carbon in the deep sea of the Northern South China Sea.

Our study explored the lateral export of macroalgae and seagrass to the deep sea of the Northern South China Sea (NSCS). Particulate organic carbon (POC) collected from a depth of 500 m off southwestern Taiwan (station T) and Dongsha Atoll (station K) underwent environmental DNA (eDNA) and stable isotope assays. Metabarcoding using 18S V9 rDNA revealed lateral export of macrophyte detritus in NSCS. At station K, seagrass detritus predominated, while at station T, macroalgae-derived detritus was dominant. The consistency in the stable carbon isotope signature between POC and macrophytes indicates that stable carbon is an ideal bio-indicator for tracking macrophyte detritus destination and transformation after it has been laterally exported. Based on robust scientific methods, these findings provide valuable insights into the lateral export of macrophyte detritus to the deep sea in POC, influenced by habitat species, and shaped by distinct oceanographic physics around NSCS.

Assessing CO2 sources and sinks in and around Taiwan: Implication for achieving regional carbon neutrality by 2050.

Taiwan has pledged to achieve net-zero carbon emissions by 2050, but the current extent of carbon sinks in Taiwan remains unclear. Therefore, this study aims to first review the existing nature-based carbon sinks on land and in the oceans around Taiwan. Subsequently, we suggest potential strategies to reduce CO2 emissions and propose carbon dioxide removal methods (CDRs). The natural carbon sinks by forests, sediments, and oceans in and around Taiwan are approximately 21.5, 42.1, and 96.8 Mt-CO2 y-1, respectively, which is significantly less than Taiwan's CO2 emissions (280 Mt-CO2 y-1). Taiwan must consider decarbonization strategies like using electric vehicles, renewable energy, and hydrogen energy by formulating enabling policies. Besides more precisely assessing both terrestrial and marine carbon sinks, Taiwan should develop novel CDRs such as bioenergy with carbon capture and storage, afforestation, reforestation, biochar, seaweed cultivation, and ocean alkalinity enhancement, to reach carbon neutrality by 2050.

Ocean acidification increases inorganic carbon over organic carbon in shrimp's exoskeleton.

Ocean acidification (OA) may either increase or have a neutral effect on the calcification in shrimp's exoskeleton. However, investigations on changes in the carbon composition of shrimp's exoskeletons under OA are lacking. We exposed juvenile Pacific white shrimps to target pHs of 8.0, 7.9, and 7.6 for 100 days to evaluate changes in carapace thickness, total carbon (TC), particulate organic carbon (POC), particulate inorganic carbon (PIC), calcium, and magnesium concentrations in their exoskeletons. The PIC: POC ratio of shrimp in pH 7.6 treatment was significantly higher by 175 % as compared to pH 8.0 treatment. Thickness and Ca% in pH 7.6 treatment were significantly higher as compared to pH 8.0 treatment (90 % and 65 %, respectively). This is the first direct evidence of an increased PIC: POC ratio in shrimp exoskeletons under OA. In the future, such changes in carbon composition may affect the shrimp population, ecosystem functions, and regional carbon cycle.

Carbon capture by macroalgae Sarcodia suae using aquaculture wastewater and solar energy for cooling in subtropical regions.

Rapid growth in the aquaculture industry and corresponding increases in nutrient and organic carbon levels in coastal regions can lead to eutrophication and increased greenhouse gas emissions. Macroalgae are the organisms primarily responsible for the capture of CO2 and removal of nutrients from coastal waters. In the current study, we developed a novel wastewater treatment system in which the red macroalga, Sarcordia suae, is used to capture CO2 under thermostatic conditions in subtropical regions. In 2020 (without temperature control), the carbon capture rate (CCR) of Sarcordia suae varied considerably with the season: winter/spring (2.1-3.9 g-C m-2 d-1) and summer (0.09 g-C m-2 d-1). In 2021, solar powered cooling reduced summer seawater temperatures from 31 to 33 °C to 23-25 °C with a corresponding increase in the mean CCR: winter/spring (2-7 g-C m-2 d-1) and summer (1.33 g-C m-2 d-1). The proposed aquaculture wastewater system proved highly efficient in removing nitrogen (20.7 mg-N g-1 DW d-1, DW = dry weight) and phosphorus (4.4 mg-P g-1 DW d-1). Furthermore, the high density of Sarcodia (1.10 ± 0.03 g cm-3) would permit the harvesting and subsequent dumping of Sarcodia in deep off-shore waters. This study demonstrated a low-cost land-based seaweed cultivation system for capturing CO2 and excess nutrients from aquaculture wastewater year-round under temperature controlled environments in subtropical regions.

The effects of low pH on the taste and amino acid composition of tiger shrimp.

Recent research has revealed that shrimp sensory quality may be affected by ocean acidification but we do not exactly know why. Here we conducted controlled pH exposure experiments on adult tiger shrimp, which were kept in 1000-L tanks continuously supplied with coastal seawater. We compared survival rate, carapace properties and flesh sensory properties and amino acid composition of shrimp exposed to pH 7.5 and pH 8.0 treatments for 28 days. Shrimp reared at pH 7.5 had a lower amino acid content (17.6% w/w) than those reared at pH 8.0 (19.5% w/w). Interestingly, the amino acids responsible for the umami taste, i.e. glutamate and aspartic acid, were present at significantly lower levels in the pH 7.5 than the pH 8.0 shrimp, and the pH 7.5 shrimp were also rated as less desirable in a blind quality test by 40 volunteer assessors. These results indicate that tiger shrimp may become less palatable in the future due to a lower production of some amino acids. Finally, tiger shrimp also had a lower survival rate over 28 days at pH 7.5 than at pH 8.0 (73% vs. 81%) suggesting that ocean acidification may affect both the quality and quantity of future shrimp resources.

Elevated carbon flux in deep waters of the South China Sea.

We measured particulate organic carbon (POC) fluxes from the euphotic zone into the twilight zone and deep waters (>1000 m) that occurred between the shelf and the basin in the South China Sea (SCS) and at the SouthEast Asia Time Series Station (SEATS) using floating sediment trap arrays. Additionally, selected sinking particles were imaged by scanning electron microscope (SEM) to reveal particle morphology and composition. Results showed large variations in POC fluxes with elevated values (32-104 mg-C m-2 d-1) below the euphotic zone and a trend towards lower values in the deep SCS. Vertical POC fluxes measured in deep waters between the shelf and the SCS basin were much higher than those estimated by Martin's attenuation equation. These elevated POC fluxes in deep waters were attributed to lateral particle transport as opposed to enhanced settling out of the euphotic zone. SEM images of sinking particles at 150 m show abundant marine biogenic detritus, while those in deep waters contained a higher proportion of lithogenic material. A great deal of the spatial variability in POC fluxes across the twilight zone and deep waters of the SCS cannot be represented by current biogeochemical models.