Inter-annual variations over a decade of primary production of the seagrass Posidonia oceanica

We acquired quasi-continuous measurements of community gross primary production (GPP) by mass balance of O-2 measured on a mooring, from August 2006 to October 2016 over a Posidonia oceanica meadow (10 m depth) in the Bay of Revellata (Corsica). Over the 2006-2016 period, annual GPP averaged 88 molO(2) m(-2) yr(-1) and ranged from 61 to 108 molO(2) m(-2) yr(-1). The 2 yr with the lowest annual GPP (2007 and 2015) were characterized by a low occurrence of fall-winter storms, probably leading to the accumulation of leaf litter in fall and early winter; we hypothesize this might have led to occultation of benthic macro-algae. Among the other years, the inter-annual variability of GPP was related to changes during the February-August period, as GPP was repeatable among years during the September-January period. For the February-August period, inter-annual variations of GPP were correlated to chlorophyll a (Chl a), solar radiation (SR) and water temperature. Computed phytoplankton GPP corresponded to a small fraction of community GPP, so the relation between GPP and Chl a probably reflected inter-annual variations of a common driver that we hypothesize to be nutrient inputs. The correlation of GPP with SR shows that light availability contributed to inter-annual variations of the development of P. oceanica. The positive relation between GPP and temperature was consistent with the fact that the observed temperatures in the Bay of Revellata were during the study period within the comfort range for the growth of P. oceanica, despite an increase of water temperature of 0.7 degrees C.