Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 466:69-79 (2012) - DOI: https://doi.org/10.3354/meps09928 Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism E. Gacia1,*, N. Marbà2, J. Cebrián3,4, R. Vaquer-Sunyer2, N. Garcias-Bonet2, C. M. Duarte2,5 1Biogeodynamics and Biodiversity Group, Centre d'Estudis Avançats de Blanes, Consejo Superior de Investigaciones Cientificas (CEAB-CSIC), Blanes 17300, Spain 2Department of Global Change Research, Mediterranean Institute for Advanced Studies (IMEDEA; UIB-CSIC), Miquel Marqués 21, Esporles 07190, Spain 3Dauphin Island Sea Lab, 101 Bienville Blvd, Dauphin Island, Alabama 36528, USA 4Department of Marine Sciences, University of South Alabama, Mobile, Alabama 36688, USA 5The UWA Oceans Institute, The University of Western Australia, 35 Stirling Highway, Crawley 6009, Western Australia, Australia *Email: gacia@ceab.csic.es ABSTRACT: Meadows of the endemic seagrass Posidonia oceanica are threatened in the Mediterranean due to a general deterioration of the light environment that becomes critical when light irradiance is insufficient to meet the carbon requirements of the system. Here, we conduct a 3 wk, in situ shading experiment (8 levels plus controls) to determine the threshold of irradiance for balanced metabolism in a shallow P. oceanica meadow and further assess the recovery of the system 1 wk later. Reduced light irradiance decreased the net community production of the meadow, which may turn negative (i.e. respiration exceeded gross community primary production) under 338 µE m−2 s−1. Shading throughout the experiment did not appear to cause sustained physiological damage to the system since values of net community production after the cessation of shading were similar to pre-experimental, ambient levels. Sediment acid volatile sulfide pools ranged between 0.002 and 0.058 mol m−2 across shading treatments, and the highest pools were observed in the most shaded sediments. At high light impairment, meristematic cell divisions were low, and carbohydrate content in young rhizomes decreased throughout the experiment. Eight days after the cessation of shading, reduced rhizome carbohydrate stores and elevated sediment sulfide levels still persisted in the previously intensively shaded areas. The present study provides evidence of resistance and resilience of the seagrass Posidonia oceanica to light impairment for short (3 wk) periods of time. Although the compensation irradiance of the system varied by ~2-fold, it provides a quantitative estimate of the irradiance threshold at which seagrass meadows may shift from being coastal carbon sinks to CO2 sources. KEY WORDS: Seagrass · Ecosystem · Production · Respiration · Compensation Irradiance · Mediterranean Full text in pdf format Supplementary material PreviousNextCite this article as: Gacia E, Marbà N, Cebrián J, Vaquer-Sunyer R, Garcias-Bonet N, Duarte CM (2012) Thresholds of irradiance for seagrass Posidonia oceanica meadow metabolism. Mar Ecol Prog Ser 466:69-79. https://doi.org/10.3354/meps09928 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 466. Online publication date: October 15, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.