The global area and distribution of shallow water ecosystems (SWEs), and their projected responses to climate change, are fundamental for evaluating future changes in their ecosystem functions, including biodiversity and climate change mitigation and adaptation. Whereas previous studies have focused on a few SWEs, we modelled the global distribution of all major SWEs (seagrass meadows, macroalgal beds, tidal marshes, mangroves, and coral habitats) from current conditions (1986−2005) to 2100 under the RCP2.6 and RCP8.5 emission scenarios. Our projections show that global coral habitat shrank by as much as 75% by 2100 with warmer ocean temperatures, but macroalgal beds, tidal marshes, and mangroves remained about the same because photosynthetic active radiation (PAR) depth did not vary greatly (macroalgal beds) and the shrinkage caused by sea-level rise was offset by other areas of expansion (tidal marshes and mangroves). Seagrass meadows were projected to increase by up to 11 % by 2100 because of the increased PAR depth. If the landward shift of tidal marshes and mangroves relative to sea-level rise was restricted by assuming coastal development and land use, the SWEs shrank by 91.9% (tidal marshes) and 74.3% (mangroves) by 2100. Countermeasures may be necessary for coastal defense in the future; these include considering the best mix of SWEs and coastal hard infrastructure because the significant shrinkage in coral habitat could decrease wave energy. However, if appropriate coastal management is achieved, the other four SWEs, which relatively have high CO2 absorption rates, can help mitigate the climate change influences.

Aquatic models used for both freshwater and marine systems frequently need to account for submerged aquatic vegetation (SAV) due to its influence on flow and water quality. Despite its importance, simplified parameterizations are generally adopted that simplify feedbacks between flow, canopy properties (e.g., considering the deflected vegetation height) and the bulk friction coefficient. This study reports the development of a fine-scale non-hydrostatic model that demonstrates the two-way effects of SAV motion interaction with the flow. An object-oriented approach is used to capture the multiphase phenomena, whereby a leaf-scale SAV model based on a discrete element method is combined with a flow-dynamics model able to resolve stresses from currents and waves. The model is verified through application to a laboratory-scale seagrass bed. A force balance analysis revealed that leaf elasticity and buoyancy are the most significant components influencing the horizontal and vertical momentum equations, respectively. The sensitivity of canopy-scale bulk friction coefficients to water depth, current speeds and vegetation density of seagrass was explored. Deeper water was also shown to lead to larger deflection of vegetation height. The model approach can contribute to improved assessment of processes influencing, water quality, sediment stabilization, carbon sequestration, and SAV restoration, thereby supporting understanding of how waterways and coasts will respond to changes brought about by development and a changing climate.

We evaluated the contribution of biological effects (photosynthesis, respiration, and decomposition) to the carbonate parameters and air-water CO2 fluxes in Tokyo Bay, Ise Bay and Osaka Bay in Japan. The carbonate parameters were measured mainly by cargo ships travelling between Japan and other countries. We used the measurement data from three inner bays and surrounding outer bays in Japan along with reference data from previous studies for complementary analysis. We found that 1) the inner bays in this study were strong annual atmospheric CO2 sinks, 2) the annual biological effect on the air-water CO2 fluxes was about 5-25% of the measured CO2 fluxes and it affected the seasonal variation of the CO2 flux, and 3) the biological effect was largest in Tokyo Bay, and almost the same in Ise and Osaka Bays. The intensity of the biological effect corresponded mainly with nutrient concentrations, which seemed to be controlled by the wastewater treatment in urbanized areas around the bays. The CO2 flux was also affected by the seawater residence time, salinity, and stratification. Our results suggest that labile carbon/nutrient ratio of wastewater should be a major consideration for evaluating the biological effect on the carbon cycle in urbanized inner bays, which will continue to expand globally.

1. Dietary specialization is common in animals and has important implications for individual fitness, inter- and intraspecific competition, and the adaptive potential of a species. Differences in diet composition have been well-studied in shorebirds and their allies (Charadriiformes) and can be influenced by an individual’s morphology, social status, and acquired skills. In particular, sexual size dimorphism is thought to facilitate resource partitioning in some shorebird species. 2. We assessed the role of age- and sex-related dietary specialization in facilitating resource partitioning between seasons and among demographic groups in the sexually dimorphic western sandpiper (Calidris mauri). Using stable isotope mixing models, we quantified the contribution of biofilm, microphytobenthos, and benthic invertebrates to the diets of western sandpipers during mid-winter (January/February) and at the onset of the breeding migration (April). 3. Diet composition differed between seasons, among demographic groups, and among demographic groups within each season. In winter, prey consumption was similar among demographic groups, but, in spring, diet composition differed among demographic groups with bill length and body mass explaining 31% of the total variation in diet composition. Epifaunal invertebrates made up a greater proportion of the diet in males which had lesser mass and shorter bills than females. Consumption of Polychaeta increased with increasing bill length and was greatest in adult females. In contrast, consumption of microphytobenthos, thought to supply nutrition for migrating sandpipers, increased with decreasing bill length and was greatest in juvenile males. 4. Our results provide evidence that age- and sex-related dietary specialization in western sandpipers facilitate seasonal resource partitioning that would reduce competition during spring at the onset of the breeding migration. 5. Understanding resource partitioning throughout the annual cycle and among different demographic groups is critical because dietary specialization has important implications for the ecology, evolution, and conservation of a species.