1,738 publications from this institution
Abstract. The potential effects of UV on community metabolism (NCP, GPP and R) were assessed along the Southeast Pacific off the Chilean coast during the Humbold-2009 cruise (54.80° S–23.85° S) on board R/V Hespérides from 5 to 15 March 2009. Estimates of community metabolism were performed at eight stations, including three stations on Patagonian fjords and five stations on the Humboldt Current System. The effect of UVB radiation on net community production (NCP) was evaluated at the stations in the Humboldt Current system by comparing metabolic rates derived using quartz bottles, largely transparent to UVB, and borosilicate glass, which is opaque to UVB and part of UVA, incubated under the ambient solar radiation. Autotrophic planktonic communities with variable NCP prevailed along the area, with the highest NCP rates (7.1–11.1 mmol O2 m−3 d−1) observed in the Patagonian fjords and the northernmost station. All five experiments showed significantly different NCP rates between communities incubated under the full ambient radiation and those incubated under reduced UVB. One of the experiments showed elevated NCP when the community was exposed to the full solar radiation, while four experiments showed a significantly lower NCP in the presence of UVB. These results suggest that the intense UVB radiation in this area, partly inhibits NCP in the Southwest Pacific off Chile.
Abstract. The Mediterranean Sea is warming faster than the global ocean, with important consequences for organisms and biogeochemical cycles. Warming is a major stressor for key marine benthic macrophytes. However, the effect of warming on marine N2 fixation remains unknown, despite the fact that the high productivity of macrophytes in oligotrophic waters is partially sustained by the input of new nitrogen (N) into the system by N2 fixation. Here, we assess the impact of warming on the N2 fixation rates of three key marine macrophytes: Posidonia oceanica, Cymodocea nodosa, and Caulerpa prolifera. We experimentally measured N2 fixation rates in vegetated and bare sediments at temperatures encompassing current summer mean (25 and 27 ∘C), projected summer mean (29 and 31 ∘C), and projected summer maximum (33 ∘C) seawater surface temperatures (SSTs) by the end of the century under a scenario of moderate greenhouse gas emissions. We found that N2 fixation rates in vegetated sediments were 2.8-fold higher than in bare sediments at current summer mean SST, with no differences among macrophytes. Currently, the contribution of N2 fixation to macrophyte productivity could account for up to 7 %, 13.8 %, and 1.8 % of N requirements for P. oceanica, C. nodosa, and C. prolifera, respectively. We show the temperature dependence of sediment N2 fixation rates. However, the thermal response differed for vegetated sediments, in which rates showed an optimum at 31 ∘C followed by a sharp decrease at 33 ∘C, and bare sediments, in which rates increased along the range of the experimental temperatures. The activation energy and Q10 were lower in vegetated than bare sediments, indicating the lower thermal sensitivity of vegetated sediments. The projected warming is expected to increase the contribution of N2 fixation to Mediterranean macrophyte productivity. Therefore, the thermal dependence of N2 fixation might have important consequences for primary production in coastal ecosystems in the context of warming.
Abstract The net plankton community metabolism of oceanic surface waters is particularly important as it more directly affects the partial pressure of CO 2 in surface waters and thus the air‐sea fluxes of CO 2 . Plankton communities in surface waters are exposed to high irradiance that includes significant ultraviolet blue (UVB, 280–315 nm) radiation. UVB radiation affects both photosynthetic and respiration rates, increase plankton mortality rates, and other metabolic and chemical processes. Here we test the sensitivity of net community production (NCP) to UVB of planktonic communities in surface waters across contrasting regions of the ocean. We observed here that UVB radiation affects net plankton community production at the ocean surface, imposing a shift in NCP by, on average, 50% relative to the values measured when excluding partly UVB. Our results show that under full solar radiation, the metabolic balance shows the prevalence of net heterotrophic community production. The demonstration of an important effect of UVB radiation on NCP in surface waters presented here is of particular relevance in relation to the increased UVB radiation derived from the erosion of the stratospheric ozone layer. Our results encourage design future research to further our understanding of UVB effects on the metabolic balance of plankton communities.
