Beached seagrass debris quantified
A University study has estimated that 42,000 cubic metres of seagrass debris, composed mostly of Posidonia oceanica (Neptune grass, or alka in Maltese), weighing some 1,150 metric tons, equivalent to 112.8 metric tons per kilometre, is deposited on...
A University study has estimated that 42,000 cubic metres of seagrass debris, composed mostly of Posidonia oceanica (Neptune grass, or alka in Maltese), weighing some 1,150 metric tons, equivalent to 112.8 metric tons per kilometre, is deposited on Maltese shores at any one time.
A biotechnology company was recently reported to be planning to open two plants in Malta to process this significant quantity of biomass into fuel.
Large quantities of this seagrass biomass are deposited annually along most Mediterranean shores where there are seagrass meadows growing offshore, to form accumulations called ‘banquettes’.
The study by staff from the University’s Department of Biology, which formed part of postgraduate research projects by Stephen Saliba and Alan Deidun, were conducted under the supervision of Patrick Schembri, and was presented at the annual congress of the Società Italiana di Biologia Marina, held in Olbia, Italy, last month.
The study assumed that the seagrass is deposited on low-lying coastlines bordering shallow water meadows of the live seagrass. Low-lying shores where there are no offshore seagrass meadows such as the Grand Harbour area, were therefore excluded from the calculations.
The mean height and width of banquettes was established through field surveys on a number of shores, and the mean mass of one cubic metre of dry seagrass was measured in the laboratory based on samples collected from these shores.
In addition to the quantification of beached material, the study also characterised the seagrass of three beaches that are ‘groomed’, that is, where seagrass is regularly removed, and three ‘ungroomed’ beaches where it is left to accumulate naturally.
One interesting result was that the seagrass accumulations on the ungroomed beaches were characterised by shorter leaf lengths of the component seagrass fragments, suggesting that there is a higher degree of seagrass breakdown on these beaches which, in turn, might translate into more detritus and nutrients being released from it to the surrounding beach ecosystem. This suggests that decomposing wrack accumulations on local shores may play a significant ecological role.