[show abstract][hide abstract] ABSTRACT: Exchangeable organic carbon (OC) dynamics and CO2 fluxes in the Antarctic Peninsula region during austral summer are highly variable. By stations, the region is a weak source of CO2 to the atmosphere, however, continuous records of CO2 revealed this area as a weak sink. OC fluxes are also in both directions but generally towards the ocean and much higher than CO2 fluxes, sometimes by a factor of 10. Surface exchangeable dissolved organic carbon (EDOC) measurements had a 43±3 μmolCL−1 overall mean, while the gaseous organic carbon equilibrated in water as given by the Henry’s Law constant (H0) resulted in (GOC H0−1) concentrations of 46±3 μmolCL−1. EDOC represents around 66% of surface dissolved organic carbon (DOC) in Antarctic waters. There is a tendency towards low partial pressures of CO2 in waters with high Chlorophyll a (Chl a) content and high fCO2 in areas with high krill densities. However, such relationships were not found for EDOC. Depth profiles of EDOC were also quite variable and followed Chl a profiles, but only in some instances, while diel cycles of EDOC revealed two distinct peaks around midday and middle of the short austral dark period concurrent with solar radiation maxima and krill night migration patterns. However, there was no evident diel pattern for GOC H0−1. The pool of exchangeable OC reveals itself as an important compartment of the carbon budget in the Antarctic Peninsula and adds to previous studies highlighting its importance in the redistribution of carbon in marine environments.
[show abstract][hide abstract] ABSTRACT: Macrophytes growing in shallow coastal zones characterized by intense metabolic ac- tivity have the capacity to modify pH within their canopy and beyond.We observed diel pH ranges is in shallow (5–12m) seagrass (Posidonia oceanica) meadows from 0.06 pH units in September to 0.24 units in June. The carbonate system (pH, DIC, and aragonite saturation state (ΩAr)) and O2 within the meadows displayed strong diel variability driven by primary productivity, and changes in chemistry were related to structural pa- rameters of the meadow, in particular, the leaf surface area available for photosynthesis (LAI). LAI was positively correlated to mean and max pHNBS and maxΩAr. Oxygen production positively influenced the range and maximum pHNBS and the range of ΩAr. In June, vertical mixing (as Turbulent Kinetic Energy) influenced ΩAr, while in September there was no effect of hydrodynamics on the carbonate system within the canopy. ΩAr was positively correlated with the calcium carbonate load of the leaves, demonstrating a direct link between structural parameters, ΩAr and carbonate deposition. There was a direct relationship between ΩAr, influenced directly by meadow LAI, and
CaCO3 content of the leaves. Therefore, calcifying organisms, e.g. epiphytes with car- bonate skeletons, might benefit from the modification of the carbonate system by the meadow. The meadow might be capable of providing refugia for calcifiers by increasing pH and ΩAr through metabolic activity. There is, however, concern for the ability of seagrasses to provide this refugia function in the future. The predicted decline of seagrass meadows may alter the scope for alteration of pH within a seagrass meadow and in the water column above the meadow, particularly if shoot density and biomass decline, both strongly linked to LAI. Organisms associated with seagrass communities may therefore suffer from the loss of pH buffering capacity in degraded meadows.
[show abstract][hide abstract] ABSTRACT: The organic carbon fluxes mediated by planktonic communities in two cyclonic eddies (CEs) and two anticy-clonic eddies (AEs) at the Canary Eddy Corridor were stud-ied and compared with the dynamics in two far-field (FF) stations located outside the eddies. We observed favorable conditions and signs for upwelling at the center of CEs and for downwelling and mixing at the centers of AEs. CEs were characterized by a higher concentration of nutrients and the highest concentration of chlorophyll a (chl a), associated with the highest abundance of microphytoplankton and di-atoms. AEs displayed concentrations of chl a values and nu-trients similar to those at the FF stations, except for the high-est ammonium concentration occurring at AE and a very low concentration of phosphorus at FF stations. AEs were tran-sient systems characterized by an increasing abundance of pi-cophytoplankton and heterotrophic bacteria. While primary production was similar between the systems, the production of dissolved organic carbon (P DOC) was significantly higher in the AEs. Phytoplankton cell mortality was lowest in the CEs, and we found higher cell mortality rates at AE than at FF stations, despite similar chl a concentration. Environ-mental changes in the AEs have been significantly prejudi-cial to phytoplankton as indicated by higher phytoplankton cell mortality (60 % of diatoms cells were dead) and higher cell lysis rates. The adverse conditions for phytoplankton as-sociated with the early-stage anticyclonic systems, mainly triggered by active downwelling, resulted in higher cell mor-tality, forcing photosynthesized carbon to fuel the dissolved pool.
[show abstract][hide abstract] ABSTRACT: The relationship between the percent extracel-lular carbon release (PER) and the specific lysis rates of phytoplankton was examined across a range of communi-ties spanning from highly oligotrophic ones in the subtrop-ical Atlantic Ocean to productive ones in the N. African upwelling and the Southern Ocean. Communities in olig-otrophic waters supported high phytoplankton cell lysis rates and low particulate primary production rates but high dis-solved primary production and PER. The percent extracel-lular carbon released increased with increasing lysis rates to reach an asymptote at about 80 % PER with specific lysis rates > 1.5 d −1 , observed in the most oligotrophic conditions tested. These results confirm that high phytoplankton mortal-ity in the oligotrophic ocean leads to high PER, accounting for the large fraction of the photosynthetic carbon channelled through bacteria characteristic of oligotrophic marine com-munities.
[show abstract][hide abstract] ABSTRACT: Most eukaryotic phytoplankton require vitamin B12 to grow. However, the cycling of this organic growth factor has received substantially less attention than other bioactive substances such as trace metals in the marine environment. This is especially true in the Mediterranean Sea, where direct measurements of dissolved vitamins have never been reported. We report here the first direct measurements of dissolved vitamin B12 across longitudinal gradients in Mediterranean waters. The range of vitamin B12 concentrations measured over the whole transect was 0.5-6.2 pM, which is slightly higher than the range (undetectable-4 pM) of ambient concentrations measured in other open ocean basins in the Pacific and Atlantic oceans. The concentrations measured in the western basin were significantly higher (p < 0.05) than those of the eastern basin. They were positively correlated with chlorophyll concentrations in the most western part of the basin, and did not show any significant correlation with any other biological variables in other regions of the sampling transect.
[show abstract][hide abstract] ABSTRACT: Climate warming is especially severe in the Arc-tic, where the average temperature is increasing 0.4 • C per decade, two to three times higher than the global average rate. Furthermore, the Arctic has lost more than half of its summer ice extent since 1980 and predictions suggest that the Arctic will be ice free in the summer as early as 2050, which could increase the rate of warming. Predictions based on the metabolic theory of ecology assume that temperature increase will enhance metabolic rates and thus both the rate of primary production and respiration will increase. How-ever, these predictions do not consider the specific metabolic balance of the communities. We tested, experimentally, the response of Arctic plankton communities to seawater tem-perature spanning from 1 • C to 10 • C. Two types of com-munities were tested, open-ocean Arctic communities from water collected in the Barents Sea and Atlantic influenced fjord communities from water collected in the Svalbard fjord system. Metabolic rates did indeed increase as suggested by metabolic theory, however these results suggest an ex-perimental temperature threshold of 5 • C, beyond which the metabolism of plankton communities shifts from autotrophic to heterotrophic. This threshold is also validated by field measurements across a range of temperatures which sug-gested a temperature 5.4 • C beyond which Arctic plankton communities switch to heterotrophy. Barents Sea communi-ties showed a much clearer threshold response to temperature manipulations than fjord communities.
[show abstract][hide abstract] ABSTRACT: We assessed the relationship between zooplank-ton metabolism (respiration and inorganic N and P excre-tion) and "in situ" temperature through a grid of stations representing a range of natural temperature variation dur-ing the ATOS-Arctic cruise (July 2007). The objective was to explore not only the direct effects of temperature on zoo-plankton carbon respiratory losses (hereafter C R) and NH 4 -N and PO 4 -P excretion rates (hereafter N E and P E , respec-tively), but also to investigate whether these metabolic path-ways responded similarly to temperature, and so how tem-perature could affect the stoichiometry of the metabolic prod-ucts. Metabolic rates, normalised to per unit of zooplankton carbon biomass, increased with increasing temperature fol-lowing the Arrhenius equation. However, the activation en-ergy differed for the various metabolic processes considered. Respiration, C R , was the metabolic activity least affected by temperature, followed by N E and P E , and as a consequence the values of the C R : N E , C R : P E and N E : P E atomic quo-tients were inversely related to temperature. The effects of temperature on the stoichiometry of the excreted N and P products would contribute to modifying the nutrient pool available for phytoplankton and induce qualitative and quan-titative shifts in the size, community structure and chemical composition of primary producers that could possibly trans-late to the whole Arctic marine food web.
[show abstract][hide abstract] ABSTRACT: Seagrasses are key components of coastal marine ecosystems and many monitoring programmes worldwide assess seagrass health and apply seagrasses as indicators of environmental status. This study aims at identifying the diversity and characteristics of seagrass indicators in use within and across European ecoregions in order to provide an overview of seagrass monitoring effort in Europe. We identified 49 seagrass indicators used in 42 monitoring programmes and including a total of 51 metrics. The seagrass metrics represented 6 broad categories covering different seagrass organizational levels and spatial scales. The large diversity is particularly striking considering that the pan-European Water Framework Directive sets common demands for the presence and abundance of seagrasses and related disturbance-sensitive species. The diversity of indicators reduces the possibility to provide pan-European overviews of the status of seagrass ecosystems. The diversity can be partially justified by differences in species, differences in habitat conditions and associated communities but also seems to be determined by tradition. Within each European region, we strongly encourage the evaluation of seagrass indicator–pressure responses and quantification of the uncertainty of classification associated to the indicator in order to identify the most effective seagrass indicators for assessing ecological quality of coastal and transitional water bodies.
[show abstract][hide abstract] ABSTRACT: We assessed the relationship between zooplankton metabolism (respiration
and inorganic N and P excretion) and "in situ" temperature through a
grid of stations representing a range of natural temperature variation
during the ATOS-Arctic cruise (July 2007). The objective was to explore
not only the direct effects of temperature on O2 consumption
and NH4-N and PO4-P excretion, but also to
investigate the possible relationships between temperature and the
stoichiometry of the metabolic products. Zooplankton metabolic rates
increased according to the rising temperature conditions, following the
Arrhenius equation. However, the activation energy differed for the
various metabolic processes considered. Respiration was the metabolic
activity less affected by temperature, followed by NH4-N and
PO4-P excretion, and as a consequence the values of the C :
N, C : P and N : P quotients of the metabolic products were inversely
related to temperature. The effects of temperature on the stoichiometry
of the excretion products would contribute to modify the nutrient pool
available for phytoplankton and induce qualitative and quantitative
shifts in the characteristics of primary producers that could possibly
translate into the whole Arctic marine food web.
[show abstract][hide abstract] ABSTRACT: The study of the structural and functional properties of key components of polar marine ecosystems has received increased
attention in order to better understand the ecological consequences of future sea temperature rise and seasonal ice retraction.
Owing to this purpose, during the ATOS-Arctic cruise, held in July 2007 in the framework of the 2007–2008 International Polar
Year, we studied the respiratory carbon demand of mesozooplankton as well as their contribution to the regeneration of inorganic
nitrogen and phosphorus (NH4-N and PO4-P) via excretion. The studied area comprised several stations along a latitudinal gradient in the East Greenland current, plus a
network of stations NW of the Svalbard islands. The specific respiratory carbon losses and phosphorus (PO4-P) excretion rates were similar or slightly higher than some reports for Arctic mesozooplankton, but the nitrogen (NH4-N) excretion rates were higher by a factor of 3 when compared with previous data sets. The mesozooplankton respiratory losses
were equivalent to 23% of primary production, and at turn zooplankton contributed by excretion to more than 50% of the N and
P required by phytoplankton. Although C:N, C:P and N:P metabolic atomic quotients almost coincided with the average Redfield’s
stoichiometric ratios, the low C:N values when compared to previous reports suggested a predominance of protein-related metabolic
substrates. The potential consequences of changes observed in the C:N, N:P and C:P metabolic ratios of mesozooplankton for
Arctic marine ecosystems are discussed.
[show abstract][hide abstract] ABSTRACT: Morphology, elemental content and isotopic composition of leaves of the seagrasses Posidonia oceanica and Cymodocea nodosa were highly variable across the Illes Balears, a Spanish archipelago in the western Mediterranean, and varied seasonally
at one site in the study area. The data presented in this paper generally expand the reported ranges of nitrogen, phosphorus,
iron and arsenic content and δ13C and δ15N for these species. Nitrogen and phosphorus content of P. oceanica leaves also showed significant seasonal variability; on an annual basis, P. oceanica leaves averaged 1.55% N and 0.14% P at this monitoring site. Both N and P were more concentrated in the leaves in winter
than in summer, with winter maxima of 1.76% N and 0.17% P and summer minima of 1.34% N and 0.11% P. There was no significant
annual pattern observed in the δ13C of P. oceanica leaves, but there was a repeated 0.6‰ seasonal fluctuation in δ15N. Mean annual δ15N was 4.0‰; δ15N was lowest in May and it increased through the summer and autumn to a maximum in November. Over the geographic range of
our study area, there were interspecific differences in the carbon, nitrogen and phosphorus content of the two species. Posidonia oceanica N:P ratios were distributed around the critical value of 30:1 while the ratios for C. nodosa were lower than this value, suggesting P. oceanica we collected was not consistently limited by N or P while C. nodosa tended toward nitrogen limitation. Nutrient content was significantly correlated to morphological indicators of plant vigor.
Fe content of P. oceanica leaves varied by a factor of 5×, with a minimum of 31.1μgg−1 and a maximum of 167.7μgg−1. Arsenic was present in much lower tissue concentrations than Fe, but the As concentrations were more variable; the maximum
concentration of 1.60μgg−1 was eight times as high as the minimum of 0.20μgg−1. There were interspecific differences in δ13C of the two species; C. nodosa was consistently more enriched (δ13C=−7.8±1.7‰) than P. oceanica (−13.2±1.2‰). The δ13C of both species decreased significantly with increasing water depth. Depth related and regional variability in the δ13C and δ15N of both species were marked, suggesting that caution needs to be exercised when applying stable isotopes in food web analyses.
[show abstract][hide abstract] ABSTRACT: Recolonization dynamics from disturbance on a Philippine mixed seagrass meadow, containing species spanning more than 10-fold
in rhizome elongation rates and reproductive effort, was examined by following the recovery of a 1,200 m2 gap over 2.5 yr. The objective was to assess the contribution of contrasting species to the recovery process and to evaluate
the importance of sexual versus vegetative colonization. Large, slow-growing species,Thalassia hemprichii andEnhalus acoroides, that produce large, broadly-dispersed seeds dominated sexual colonization with a total of 2,643 and 210 seedlings, respectively,
recruiting to the area. Despite very rapid turnover of sexual recruits, the high frequency of seedling establishment ensured
successful development of new patches in areas devoid of vegetation, leading to a scattered and evenly distributed presence
of vegetation inside the gap. The small seagrass speciesCymodocea rotundata andHalodule uninervis, characterized by fast rhizome elongation rates but low reproductive output and limited seed dispersal, were the major contributors
to the overall 450 m2 increase in vegetation cover through fast lateral extension (144±6 cm yr−1) from meadow edge and surviving patches, forming a compact vegetation cover in one edge of the denuded area. We conclude
that contrasting recruitment strategies in the mixed-species seagrass community examined have implications for colonization
potential at different spatial scales. Fast clonal growth is only an efficient mechanism for colonization of disturbances
within established meadows (small gaps), whereas the large species, which combined high reproductive output with high seed
dispersal capacity, may act to accelerate the colonization process in large gaps or distant from established meadows.
Estuaries and Coasts 04/2012; 27(5):770-780. · 2.56 Impact Factor
[show abstract][hide abstract] ABSTRACT: Because freshwater covers such a small fraction of the Earth’s surface area, inland freshwater ecosystems (particularly lakes,
rivers, and reservoirs) have rarely been considered as potentially important quantitative components of the carbon cycle at
either global or regional scales. By taking published estimates of gas exchange, sediment accumulation, and carbon transport
for a variety of aquatic systems, we have constructed a budget for the role of inland water ecosystems in the global carbon
cycle. Our analysis conservatively estimates that inland waters annually receive, from a combination of background and anthropogenically
altered sources, on the order of 1.9PgCy−1 from the terrestrial landscape, of which about 0.2 is buried in aquatic sediments, at least 0.8 (possibly much more) is returned
to the atmosphere as gas exchange while the remaining 0.9Pgy−1 is delivered to the oceans, roughly equally as inorganic and organic carbon. Thus, roughly twice as much C enters inland
aquatic systems from land as is exported from land to the sea. Over prolonged time net carbon fluxes in aquatic systems tend
to be greater per unit area than in much of the surrounding land. Although their area is small, these freshwater aquatic systems
can affect regional C balances. Further, the inclusion of inland, freshwater ecosystems provides useful insight about the
storage, oxidation and transport of terrestrial C, and may warrant a revision of how the modern net C sink on land is described.
[show abstract][hide abstract] ABSTRACT: Carbon dioxide and coupled CO2 and O2-driven
compromises to marine life were examined along the Chilean sector of the
Humboldt Current System, a particularly vulnerable hypoxic and upwelling
area, applying the Respiration index (RI = log10 pO2 pCO2 ) and the
pH-dependent aragonite saturation (Ω) to delineate the water
masses where aerobic and calcifying organisms are stressed. As expected,
there was a strong negative relationship between oxygen concentration
and pH or pCO2 in the studied area, with the subsurface
hypoxic Equatorial Subsurface Waters extending from 100 m to about 300 m
depth and supporting elevated pCO2 values. The lowest RI
values, associated to aerobic stress, were found at about 200 m depth
and decreased towards the Equator. Increased pCO2 in the
hypoxic water layer reduced the RI values by as much as 0.59 RI units,
with the thickness of the upper water layer that presents conditions
suitable for aerobic life (RI>0.7) declining by half between 42°
S and 28° S. The intermediate waters hardly reached those stations
closer to the equator so that the increased pCO2 lowered pH
and the saturation of aragonite. A significant fraction of the water
column along the Chilean sector of the Humboldt Current System suffers
from CO2-driven compromises to biota, including waters
corrosive to calcifying organisms, stress to aerobic organisms or both.
The habitat free of CO2-driven stresses was restricted to the
upper mixed layer and to small water parcels at about 1000 m depth.
Overall pCO2 acts as a hinge connecting respiratory and
calcification challenges expected to increase in the future, resulting
in a spread of the challenges to aerobic organisms.
[show abstract][hide abstract] ABSTRACT: Estimates of dissolved organic carbon (DOC) release by marine macrophyte
communities (seagrass meadows and macroalgal beds) were obtained
experimentally using in situ benthic chambers. The effect of light
availability on DOC release by macrophyte communities was examined in
two communities both by comparing net DOC release under light and dark,
and by examining the response of net DOC release to longer-term (days)
experimental shading of the communities. All most 85% of the seagrass
communities and almost all of macroalgal communities examined acted as
net sources of DOC. There was a weak tendency for higher DOC fluxes
under light than under dark conditions in seagrass meadow. There is no
relationship between net DOC fluxes and gross primary production (GPP)
and net community production (NCP), however, this relationship is
positive between net DOC fluxes and community respiration. Net DOC
fluxes were not affected by shading of a T. testudinum community in
Florida for 5 days, however, shading of a mixed seagrass meadow in the
Philippines led to a significant reduction on the net DOC release when
shading was maintained for 6 days compared to only 2 days of shading.
Based on published and unpublished results we also estimate the global
net DOC production by marine macrophytes. The estimated global net DOC
flux, and hence export, from marine macrophyte is about 0.197 ±
0.015 Pg C yr-1 or 0.212 ± 0.016 Pg C yr-1
depending if net DOC flux by seagrass meadows was estimated by taking
into account the low or high global seagrass area, respectively.
[show abstract][hide abstract] ABSTRACT: Summary: A great diversity of organisms modify the physical structure of estuarine and coastal environments. These physical ecosystem engineers – particularly, dune and marsh plants, mangroves, seagrasses, kelps, reef-forming corals and bivalves, burrowing crustaceans and infauna – often have substantive functional impacts over large areas and across distinct geographic regions. Here we use a general framework for physical ecosystem engineering to illustrate how these organisms can exert control on sedimentary processes, coastal protection and habitat availability to other organisms. We then discuss the management implications of coastal and estuarine engineering, ending with a brief prospectus on research and management challenges.
[show abstract][hide abstract] ABSTRACT: The carbon fluxes mediated by planktonic communities in two cyclonic
eddies (CEs) and two anticyclonic eddies (AEs) at the Canary Eddy
Corridor were studied and compared with the dynamics in two far-field
(FF) stations located outside the eddies. We observed favorable
conditions and signs for upwelling at the center of CEs and for
downwelling and mixing at the centers of AEs. CEs were characterized by
higher nutrients concentration and highest chlorophyll a concentration,
associated with highest microphytoplankton and diatoms abundance. AEs
displayed similar chlorophyll a values and nutrients concentration
(except highest ammonium concentration) to those of the FF stations and
were characterized by increasing abundance of picophytoplankton and
heterotrophic bacteria. While primary production was similar between the
systems, the production of dissolved organic carbon (PDOC)
was significantly higher at AEs. Phytoplankton cell mortality was lowest
in CEs and we found higher cell mortality in AE than FF, despite similar
chl a concentration. Environmental changes at the AEs presented
significant prejudicial effects on the phytoplankton health as indicated
by higher phytoplankton mortality (e.g. 60% of dead diatoms cells) and
higher cell lysis rates observed at AEs than at two other systems. The
adverse conditions associated to the early-stage anticyclonic systems,
mainly triggered by active downwelling, resulted in higher consequent
PDOC production, corresponding to forcing of the carbon flux
to the dissolved pool and a weakness of the carbon pump.
[show abstract][hide abstract] 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 Hesp ́ rides
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 Hum-
boldt 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. Au-
totrophic planktonic communities with variable NCP pre-
vailed 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 incu-
bated under the full ambient radiation and those incubated
under reduced UVB. One of the experiments showed ele-
vated NCP when the community was exposed to the full so-
lar 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.