Do coastal wetlands drive or buffer coastal acidification?

peer reviewe

Nutritional composition of suspended particulate matter in a tropical mangrove creek during a tidal cycle (Can Gio, Vietnam)

Mangrove forests are highly productive ecosystems and mangrove-derived organic matter has generally been assumed to play a basal role in sustaining coastal food webs. However, the mechanisms of mangrove-derived organic matter utilisation by consumers are not fully understood. In this study, we were interested in hourly changes in the nutritional quality of suspended particulate matter (SPM) entering and departing a mangrove creek during a tidal cycle. We determined the fatty acid composition and delta C-13 stable isotope signature of SPM during a 26 h tidal cycle in a creek of the Can Gio Mangrove Biosphere Reserve (Southern Vietnam). Regarding fatty acids, the nutritional quality of SPM was low during most of the tidal cycle. However, it greatly increased during the first part of the strongest flood tide, occurring during daytime. The pulse of highly nutritive organic matter brought to the ecosystem was mostly composed of algal cells growing in specific shallow zones of the mangrove, that use nutrients and CO2 exported during the preceding ebb tide and originating from the mineralisation of mangrove-derived organic matter, as evidenced by their delta C-13 signatures. This study confirms that mangrove-derived carbon plays a basal role in sustaining trophic webs of mangrove tidal creeks, but that its nutritive value is greatly enhanced when a first step of mineralisation is achieved and CO2 is photo-synthesised by algal cells

Trophic relationships and basal resources utilization in the Can Gio Mangrove Biosphere Reserve (Southern Vietnam)

Fatty acid biomarkers and dual stable isotopes (δ13C and δ15N) were used to identify the preferred food sources of consumers in a mangrove tidal creek and nearby unforested (mud bank) and forested areas located in the Can Gio Mangrove Biosphere Reserve (Southern Vietnam). We analysed 15 macro-invertebrates and 1 fish species representing primary consumers and their immediate predators in this area. Specific groups of fatty acids were used to trace the fate of various food sources (i.e., suspended particulate organic matter, mangrove litter and sedimentary organic matter). The δ13C and δ15N of consumers ranged from −26.9 to −18.8‰ and from 1.1 to 9.9‰, respectively. The trophic pathway based on mangrove litter, characteristic of mangrove ecosystems, is nutritionally sustaining various crab and snail species. In contrast, it appears that the most mobile species (fish and shrimps), living in the water column and possibly migrating with tides, are mostly feeding on suspended particulate organic matter, suggesting that this trophic pathway is of great importance for connectivity among tropical coastal ecosystems. Our study suggests that snails and crabs mainly act as mineralisers, processing high quantities of detrital material to meet their nutritional needs and thus releasing nutrients through the production of faeces, that are further mineralised by microorganisms, while locally grown phytoplankton reintegrates these compounds into its biomass and feeds migrating species. We highlight here a possible link between mangrove litter and coastal food webs

Longitudinal changes in activity patterns, physical capacities, energy expenditure, and body composition in severely obese adolescents during a multidisciplinary weight-reduction program

OBJECTIVE: To determine the longitudinal changes in body composition, physical capacities, and time and energy expenditure (EE) devoted to various activities in the course of a 9-month weight-reduction period. DESIGN: Longitudinal, clinical intervention including lifestyle education, moderate energy restriction, progressive training, and psychological follow-up. SUBJECTS: A total of 27 (13 boys and 14 girls) severely obese adolescents (mean BMI: 33.9 kg/m2; 41.5% fat mass (FM)), aged 12-16 y. MEASUREMENTS: Before the beginning and after the weight-reduction program, body composition was assessed by dual-energy X-ray absorptiometry (DXA), physical capacities by multistage treadmill test, and EE both by whole-body calorimetry and in free-living conditions using the heart rate-recording method. During 8 months of the weight-reduction period, type and duration of each activity were recorded using a daily controlled activity diary. RESULTS: One boy resigned after 5 months. Body weight (BW) and FM decreased (-19 and -42%, respectively, P<0.001) both in boys and in girls, but fat-free mass (FFM) decreased only in girls (-6%, P<0.001). VO2max (l/min) did not vary significantly, but strength and fitness were improved (P<0.001). Time and EE spent at sedentary activities decreased significantly (P<0.001) to the benefit of moderate (recreational) activities and total physical activities (P<0.001) at the institution during the weekdays, and at home during the weekends and holidays. CONCLUSION: The great BW and FM losses, preservation of FFM, and improvement of physical capacities of obese adolescents obtained under experimental conditions were associated with increases in leisure physical activities in free-living conditions at the expense of sleep and sedentary activitie

Mangrove Blue Carbon in the Face of Deforestation, Climate Change, and Restoration

10.1002/9781119312994.apr0752Annual Plant Reviews33427-45

Carbon biogeochemistry and CO2 emissions in a human impacted and mangrove dominated tropical estuary (Can Gio, Vietnam)

The quantitative contribution of tropical estuaries to the atmospheric CO2 budget has large uncertainties, both spatially and seasonally. We investigated the seasonal and spatial variations of carbon biogeochemistry downstream of Ho Chi Minh City (Southern Vietnam). We sampled four sites distributed from downstream of a highly urbanised watershed through mangroves to the South China Sea coast during the dry and wet seasons. Measured partial pressure of CO2 (pCO(2)) ranged from 660 to 3000 mu atm during the dry season, and from 740 to 5000 mu atm during the wet season. High organic load, dissolved oxygen saturation down to 17%, and pCO(2) up to 5000 mu atm at the freshwater endmember of the estuary reflected the intense human pressure on this ecosystem. We show that releases from mangrove soils affect the water column pCO(2) in this large tropical estuary (similar to 600 m wide and 10-20 m deep). This study is among the few to report direct measurements of both water pCO(2) and CO2 emissions in a Southeast Asian tropical estuary located in a highly urbanised watershed. It shows that the contribution of such estuaries may have been previously underestimated, with CO2 emissions ranging from 74 to 876 mmol m(-2) day(-1) at low current velocity (< 0.2 m s(-1)). Corresponding gas transfer velocities k(600), ranging from 1.7 to 11.0 m day(-1), were about 2 to 4 times of k(600) estimated using published literature equations