Comparison of carbon stores by two morphologically different seagrasses
The Royal Society of Western Australia
Faculty of Health, Engineering and Science
School of Natural Sciences / Centre for Marine Ecosystems Research
The recent emphasis on global change has intensified research in the carbon sequestration potential of seagrass ecosystems (Nellemann et al. 2009). Most estimates on seagrass carbon storage are, however, derived from studies of a few species and habitats. Lavery et al. (2013) showed an 18-fold difference in carbon stores among Australian seagrasses highlighting the importance of inter-habitat variability in carbon stocks. One implication from this is that the factor of seagrass species may play a key role in the variation in carbon stores beneath those studied meadows. Different seagrass species have inherently dissimilar traits, well summarised by the seagrass functional-form model in Carruthers et al. (2007). This functional-form model differentiates seagrasses based on morphological plasticity, rhizome persistence and occurrences in varying depositional environments, among other traits. A further extension of this model is suggested such that the seagrass species may shift from low to high transitions of standing crop biomass between extreme ends of the model. Of interest, the two seagrass genera Halophila and Posidonia are placed at opposite ends of the functional-form model. Halophila has a small biomass with less persistent rhizomes while Posidonia has the opposite traits. We hypothesise that meadows of smaller, ephemeral seagrasses with low standing crop will have less accumulated carbon compared to the larger and more persisting forms with higher productivity and biomass. Estuarine seagrass habitats dominated by Halophila ovalis and Posidonia australis were studied to compare the total carbon stocks and origin of the preserved carbon.