Abstract Seagrasses play an important role in climate change mitigation and adaptation, acting as natural CO 2 sinks and buffering the impacts of rising sea level. However, global estimates of organic carbon (C org ) stocks, accumulation rates and seafloor elevation rates in seagrasses are limited to a few regions, thus potentially biasing global estimates. Here we assessed the extent of soil C org stocks and accumulation rates in seagrass meadows ( Thalassia hemprichii , Enhalus acoroides , Halophila stipulacea , Thalassodendrum ciliatum and Halodule uninervis ) from Saudi Arabia. We estimated that seagrasses store 3.4 ± 0.3 kg C org m −2 in 1 m-thick soil deposits, accumulated at 6.8 ± 1.7 g C org m −2 yr −1 over the last 500 to 2,000 years. The extreme conditions in the Red Sea, such as nutrient limitation reducing seagrass growth rates and high temperature increasing soil respiration rates, may explain their relative low C org storage compared to temperate meadows. Differences in soil C org storage among habitats (i.e. location and species composition) are mainly related to the contribution of seagrass detritus to the soil C org pool, fluxes of C org from adjacent mangrove and tidal marsh ecosystems into seagrass meadows, and the amount of fine sediment particles. Seagrasses sequester annually around 0.8% of CO 2 emissions from fossil-fuels by Saudi Arabia, while buffering the impacts of sea level rise. This study contributes data from understudied regions to a growing dataset on seagrass carbon stocks and sequestration rates and further evidences that even small seagrass species store C org in coastal areas.
Comunicacion presentada en la Final CSA MarineBiotech Conference, celebrada los dias 11 y 12 de marzo de 2013 en Bruselas (Belgica).
Abstract Seagrass meadows rank among the most significant organic carbon (C org ) sinks on earth. We examined the variability in seagrass soil C org stocks and composition across Australia and identified the main drivers of variability, applying a spatially hierarchical approach that incorporates bioregions and geomorphic settings. Top 30 cm soil C org stocks were similar across bioregions and geomorphic settings (min‐max: 20–26 Mg C org ha −1 ), but meadows formed by large species (i.e., Amphibolis spp. and Posidonia spp.) showed higher stocks (24–29 Mg C org ha −1 ) than those formed by smaller species (e.g., Halodule, Halophila, Ruppia, Zostera, Cymodocea, and Syringodium ; 12–21 Mg C org ha −1 ). In temperate coastal meadows dominated by large species, soil C org stocks mainly derived from seagrass C org (72 ± 2%), while allochthonous C org dominated soil C org stocks in meadows formed by small species in temperate and tropical estuarine meadows (64 ± 5%). In temperate coastal meadows, soil C org stocks were enhanced by low hydrodynamic exposure associated with high mud and seagrass C org contents. In temperate estuarine meadows, soil C org stocks were enhanced by high contributions of seagrass C org , low to moderate solar radiation, and low human pressure. In tropical estuarine meadows formed by small species, large soil C org stocks were mainly associated with low hydrodynamic energy, low rainfall, and high solar radiation. These results showcase that bioregion and geomorphic setting are not necessarily good predictors of soil C org stocks and that site‐specific estimates based on local environmental factors are needed for Blue Carbon projects and greenhouse gases accounting purposes.
Abstract. CO2-driven compromises to marine life were examined along the Chilean sector of the Humboldt Current System, a particularly vulnerable hypoxic and upwelling area, applying the Respiration index (RI = log10 pO20.7) declining by half between 42° S and 28° S. The intermediate waters hardly reached those stations closer to the equator so that the increased pCO2 lowered pH and the saturation of aragonite. A significant fraction of the water column along the Chilean sector of the Humboldt Current System suffers from CO2–driven compromises to biota, including waters corrosive to calcifying organisms, stress to aerobic organisms or both. The habitat free of CO2-driven stresses was restricted to the upper mixed layer and to small water parcels at about 1000 m depth. pCO2 acts as a hinge connecting respiratory and calcification challenges expected to increase in the future, resulting in a spread of the challenges to aerobic organisms.
Thls study demonstrates that patch development in a Mediterranean con~munity of Cymodocea nodosa (Ucria) Ascherson, growing over highly mobile sandy sediments, proceeds by colonization by seedlings (0.047 m-' yr-'), and subsequent patch development by the surviving seedlings (< 10 %).Increased patch cover is obtalned by fast growlng rhizomes (average elongat~on = 1.6 m yr-'), and coalescence of neighbour patches.Honzontal patch growth varied substantially among patches due to enhanced patch elongat~on with Increasing patch slze, whereas growth vanance withln patches was attributable to interannual d~fferences consistent among d~fferent patches.Comparisons of the measured patch spread rates with those for other seagrasses specles show substantial variability (> 2 orders of m a g n ~t u d e ) in horizontal growth rates that ~m p l ~e s broad d~fferences in the potent~al for recovery among seagrass species
