11 research outputs found
Resource use efficiency is affected by phytoplankton community changes and geochemical shifts over time in a coastal upwelling area (NE Atlantic).
abstractTime series records are crucial to understand the dynamical processes that occur within phytoplankton communities. This is even more important in the context of the current global change that is already forcing alterations of unprecedented nature and might have unknown consequences for multiple ecosystem processes. Here we present time series analyses of the biogeochemical trends that occurred in the shelf of the Galician coast (station 2 off A Coruña, NE Atlantic) since late 1980s. Upwelling strength and sea temperature in the area have not changed substantially during the last decades. However, while nitrate fertilization from upwelled waters has remained relatively stable, phosphate concentration has increased leading to a negative trend in the N:P ratio. Those trends have impacted the phytoplankton resource use efficiency jointly with the evenness of the community. Phytoplankton used resources more efficiently at higher values of upwelling strength and at lower values of nutrient concentration and evenness. Phytoplankton communities that were more even had higher dinoflagellate diversity contrasting to dominance of diatoms that used resources more efficiently. Moreover, variability in resource use efficiency increased with evenness.IEO (RADIALES-11
Bottom-up control of common octopus Octopus vulgaris in the Galician upwelling system, northeast Atlantic Ocean
This paper investigates the possible underlying causes of the wide interannual fluctuations
in catch of the common octopus Octopus vulgaris Cuvier, 1797 in one of the main small-scale
fisheries off the coast of Galicia (northwest Spain). Galicia is at the northern boundary of the
Iberian–Canary current upwelling system in the northeast Atlantic Ocean, where local winds induce
seasonal upwelling, largely driving the annual cycles of primary and secondary production. We
hypothesize that such dynamics are also fundamental for the survival of the planktonic stages of
octopus and set the year class strength. We address this hypothesis by investigating the influence of
upwelling on time-series of octopus fishery data. Wind stress structure during the spring–summer
(prior to the hatching peak) and autumn–winter (during the planktonic stage) was found to affect the
early life phase of this species, and explains up to 85% of the total variance of the year-to-year
variability of the adult catch. Despite this bottom-up modulation via environmental conditions, our
results also provide evidence for a between-cohort density-dependent interaction, probably caused
by cannibalism and competition for habitat.Postprin
Advection, diffusion and patch development in the rias Baixas
6 pages, 3 figures, 2 tablesThis work was supported by the EC MAST-CT90-0017 on the Control of the Phytoplankton DominanceN
Production and degradation of fluorescent dissolved organic matter in surface waters of the eastern north Atlantic ocean
The distribution and fate of coloured dissolved organic matter (CDOM) in the epipelagic Eastern North Atlantic was investigated during a cruise in the summer 2009 by combining field observations and culture experiments. Dissolved organic carbon (DOC) and nitrogen (DON), the absorption spectra of CDOM and the fluorescence intensity of proteins (Ex/Em 280/320 nm; F(280/320)) and marine humic-like substances (F(320/410)) were measured in the upper 200 m. DOC and DON showed higher concentrations in the top 20 m than below, and DOC increased southwards, while DON decreased. F(280/320) and F(320/410) showed maxima near the deep chlorophyll maximum (at about 50 m), suggesting that these fluorophores were linked to phytoplankton production and the metabolism of the associated microbial community. The coloured and fluorescent fractions of DOM showed low levels south of the Azores Front, at about 35 °N, likely due to the accumulated photobleaching of the waters transported eastwards by the Azores current into the study area (at 20°W). Twelve culture experiments were also conducted with surface water (5 m) to assess the impact of microbial degradation processes on the bulk, coloured and fluorescent fractions of DOM. After 72 h of incubation in the darkness, 14±9% (average±SD) of the initial DON was consumed at an average rate of 0.24±0.14 µmol l-1 d–1 and the protein-like fluorescence decayed by 29±9% at a net rate of 0.06±0.03 QSU d–1. These rates were significantly lower south of the Azores front, suggesting that DOM in this region was of a more recalcitrant nature. Conversely, the marine humic-like fluorescence increased at a net rate of 0.013±0.003 QSU d–1. The close linear relationship of DON uptake with F(280/320) consumption (R2= 0.91, p <0.0001, n=12) and F(320/410) production (R2= 0.52, p <0.008, n=12) that we found during these incubation experiments suggest that the protein-like fluorescence can be used as a proxy for the dynamics of the labile DON pool and that marine humic-like materials can be produced as a by-product of microbial DOM degradation
Dissolved organic carbon leaching from plastics stimulates microbial activity in the ocean
Approximately 5.25 trillion plastic pieces are floating at the sea surface. The impact of plastic pollution on the lowest trophic levels of the food web, however, remains unknown. Here we show that plastics release dissolved organic carbon (DOC) into the ambient seawater stimulating the activity of heterotrophic microbes. Our estimates indicate that globally up to 23,600 metric tons of DOC are leaching from marine plastics annually. About 60% of it is available to microbial utilization in less than 5 days. If exposed to solar radiation, however, this DOC becomes less labile. Thus, plastic pollution of marine surface waters likely alters the composition and activity of the base of the marine food webs. It is predicted that plastic waste entering the ocean will increase by a factor of ten within the next decade, resulting in an increase in plastic-derived DOC that might have unaccounted consequences for marine microbes and for the ocean system
Linkages between bacterioplankton community composition, heterotrophic carbon cycling and environmental conditions in a highly dynamic coastal ecosystem
12 páginas, 4 figuras, 1 tablasWe used mesocosm experiments to study the bacterioplankton
community in a highly dynamic coastal
ecosystem during four contrasting periods of the
seasonal cycle: winter mixing, spring phytoplankton
bloom, summer stratification and autumn upwelling.
A correlation approach was used in order to measure
the degree of coupling between the dynamics of
major bacterial groups, heterotrophic carbon cycling
and environmental factors. We used catalysed
reporter deposition-fluorescence in situ hybridization
to follow changes in the relative abundance of
the most abundant groups of bacteria (Alphaproteobacteria,
Gammaproteobacteria and Bacteroidetes).
Bacterial carbon flux-related variables included bacterial
standing stock, bacterial production and microbial
respiration. The environmental factors included
both, biotic variables such as chlorophyll-a concentration,
primary production, phytoplankton extracellular
release, and abiotic variables such as the
concentration of dissolved inorganic and organic
nutrients. Rapid shifts in the dominant bacterial
groups occurred associated to environmental
changes and bacterial bulk functions. An alternation
between Alphaproteobacteria and Bacteroidetes was
observed associated to different phytoplankton growth phases. The dominance of the group
Bacteroidetes was related to high bacterial biomass
and production. We found a significant, nonspurious,
linkage between the relative abundances
of major bacterial groups and bacterial carbon
cycling. Our results suggest that bacteria belonging
to these major groups could actually share a function
in planktonic ecosystemsThis research was supported by the MEC contract
IMPRESION (VEM2003-20021). E.T. was funded by a European
Community Marie Curie Reintegration Fellowship
(MERG-CT-2004-511937) and a Juan de la Cierva-MEC
contractPeer reviewe