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SPECIALTY GRAND CHALLENGE article Front. Mar. Sci., 02 December 2014Sec. Global Change and the Future Ocean https://doi.org/10.3389/fmars.2014.00063

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 207:1-11 (2000) - doi:10.3354/meps207001 Nutrient accumulation at different supply rates in experimental Mediterranean planktonic communities Montserrat Vidal*, Carlos M. Duarte Instituto Mediterráneo de Estudios Avanzados (IMEDEA), CSIC - Universitat de les Illes Balears, Miquel Marqués 21, 07190 Esporles (Mallorca, Islas Baleares), Spain *Present address: Laboratoire d¹Océanographie Biologique- UMR 7621, Laboratoire Arago, BP 44, 66651 Banyuls-sur-Mer Cedex, France. E-mail: mvidal@arago.obs-banyuls.fr ABSTRACT: A mesocosm experiment was conducted between June 18 and July 8, 1997, in the Bay of Blanes (NE Spain) to test for the effect of nutrient inputs on Mediterranean plankton communities. The experiment involved a gradient of daily nutrient additions to mesocosms (14 m high, 4.2 m2 cross-sectional area and 33 m3 effective volume), which were scaled to the nutrient loading of the Bay of Blanes in summer (0.64 µM N d-1, referred to as the Œbusiness as usual¹ control). This paper deals with the accumulation of nutrients in different size components (0.2-2, 2-20 and 20-200 µm) of the community and the efficiency with which these size components retain the added nutrients. Summer Mediterranean plankton responded significantly to nutrient additions by increasing their biomass, up to more than 100-fold that initially present in the enclosed water, and by changing the community structure, from an initial dominance of picoplankton to increased dominance of the 2-20 µm size component of the community (which contributes to more than 90% of the accumulated N and P) as the nutrient load increased. Though the initial community was able to accumulate nutrients exceeding the already high summer loading of the Bay of Blanes and thus acted as strong nitrogen (N) and phosphorus (P) sink, it was unable to trap the nutrients above a certain threshold: 4-fold (for N) and 8-fold (for P) the Œbusiness as usual¹ load. Conspicuous biomass increases were most noticeable after the nutrient inputs were increased 16-fold that value. Nevertheless, the biomass response was relatively low and involved a low efficiency (8%) in the trapping of added nutrients. As efficiencies were transiently higher (of 50% or even greater, between consecutive sampling days) we suggest factors other than a low assimilation by osmotrophs as responsible for the resilience of the plankton community for the trapping of nutrients in biomass in response to nutrient additions. The tendency of a lower biomass response to nutrient additions in the warm oligotrophic Mediterranean waters than in more eutrophic waters, if confirmed, should have profound consequences concerning the management of the coastline and the delineation of critical nutrient loadings. KEY WORDS: Nutrient accumulation · Coastal plankton · Size structure · Eutrophication · Mesocosm · NW Mediterranean Sea Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 207. Online publication date: November 22, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Меры по сохранению морской флоры и фауны приносят свои плоды: они уже позволили остановить сокращение численности некоторых видов и восстановить нарушен- ные морские экосистемы. Однако для восстановления здоровья океана в больших масштабах нужно активнее бороться с загрязнением, чрезмерным выловом рыбы и последствиями изменения климата.

<strong class="journal-contentHeaderColor">Abstract.</strong> The carbon burial in vegetated sediments, ignored in past assessments of carbon burial in the ocean, was evaluated using a bottom-up approach derived from upscaling a compilation of published individual estimates of carbon burial in vegetated habitats (seagrass meadows, salt marshes and mangrove forests) to the global level and a top-down approach derived from considerations of global sediment balance and a compilation of the organic carbon content of vegeatated sediments. Up-scaling of individual burial estimates values yielded a total carbon burial in vegetated habitats of 111 Tmol&nbsp;C&nbsp;y^-1. The total burial in unvegetated sediments was estimated to be 126 Tg&nbsp;C&nbsp;y^-1, resulting in a bottom-up estimate of total burial in the ocean of about 244 Tg&nbsp;C&nbsp;y^-1, two-fold higher than estimates of oceanic carbon burial that presently enter global carbon budgets. The organic carbon concentrations in vegetated marine sediments exceeds by 2 to 10-fold those in shelf/deltaic sediments. Top-down recalculation of ocean sediment budgets to account for these, previously neglected, organic-rich sediments, yields a top-down carbon burial estimate of 216 Tg&nbsp;C&nbsp;y^-1, with vegetated coastal habitats contributing about 50%. Even though vegetated carbon burial contributes about half of the total carbon burial in the ocean, burial represents a small fraction of the net production of these ecosystems, estimated at about 3388 Tg&nbsp;C&nbsp;y^-1, suggesting that bulk of the benthic net ecosystem production must support excess respiration in other compartments, such as unvegetated sediments and the coastal pelagic compartment. The total excess organic carbon available to be exported to the ocean is estimated at between 1126 to 3534 Tg&nbsp;C&nbsp;y^-1, the bulk of which must be respired in the open ocean. Widespread loss of vegetated coastal habitats must have reduced carbon burial in the ocean by about 30 Tg&nbsp;C&nbsp;y^-1, identifying the destruction of these ecosystems as an important loss of CO₂ sink capacity in the biosphere.

Hurricanes are large-scale disturbances with the potential to exert extensive damage in coastal ecosystems. On August 29, 2005 Hurricane Katrina catastrophically impacted a large area of the Gulf of Mexico spreading from coastal Alabama to Louisiana. For five months before hurricane landfall we were assessing the structure and functioning of a mixed seagrass bed located in an area greatly affected by the hurricane. The storm provided an opportunity to assess the effect of a large-scale disturbance on the structure and functioning of that seagrass bed. A comparison of surveys before and after the hurricane showed no decreases in seagrass density, associated fauna, or the microalgal abundance in the water column and sediment. We found no major impact on gross primary productivity, respiration, or net productivity of the water column or the sediment, suggesting that the hurricane had little impact on the metabolism of the seagrass bed studied. Overall, natural temporal changes recorded before the storm were larger than any post-hurricane changes. These findings indicate that this seagrass meadow was naturally highly dynamic and very resistant to Hurricane Katrina.

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 224:291-298 (2001) - doi:10.3354/meps224291 Growth and sediment space occupation by seagrass Cymodocea nodosa roots Núria Marbà*, Carlos M. Duarte Grup d¹Oceanografia Interdisciplinar, Institut Mediterrani d¹Estudis Avançats (CSIC-UiB), Miquel Marquès 21, 07190 Esporles (Illes Balears), Spain *E-mail: ieanmb@clust.uib.es ABSTRACT: The development, growth, and space occupation by the canopy and rhizosphere of a temperate Mediterranean seagrass meadow of Cymodocea nodosa, and the possible effects of meadow seasonal development on sediment redox conditions, were examined during the 1998 growth season. The meadow supported maximum biomass of leaves and rhizomes during July, and maximum root biomass in August. The meadow maintained 123.6 g dry wt m-2 of leaves and 94.4 g dry wt m-2 of rhizomes (July data), and 121.2 g dry wt m-2 of roots (August data) during peak biomass. On average, the root network contained 607 m of roots m-2, had 3.6 cm between neighbouring roots and comprised 1.7% of sediment volume. Half of the root biomass occupied the top 12.6 cm of sediment, although a few roots reached >35 cm sediment depth. The meadow developed 70, 62 and 50% of leaf, rhizome and root biomass during the growth season respectively, showing that the structure of the temperate seagrass rhizosphere is highly dynamic. C. nodosa produced leaves, rhizomes and roots at rates ranging between 1.17 and 3.98 g dry wt m-2 d-1, 0.01 and 0.75 g dry wt m-2 d-1, and 0.04 and 0.84 g dry wt m-2 d-1, respectively. C. nodosa meadow grew on sediments where redox conditions during the growth season varied from -74 to 396 mV, being between 21 and 112 mV more positive than adjacent unvegetated sediments from July to September. The magnitude of redox potential anomaly in seagrass rhizosphere tended to be coupled to the above and belowground meadow biomass, suggesting that C. nodosa metabolism alters sediment redox conditions. Structural change of seagrass meadows during the growth season, therefore, is expected to influence benthic biogeochemical processes. KEY WORDS: Cymodocea nodosa · Growth season · Canopy · Rhizosphere · Biomass · Production · Redox potential · Sediment Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 224. Online publication date: December 18, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.