bluuebunny/crossref_metadata_2025 huggingface dataset:
Contrasting photoacclimation costs in ecotypes of the marine eukaryotic picoplankter Ostreococcus
Authors: Six Christophe , Finkel Zoe V. , Rodriguez Francisco , Marie Dominique , Partensky FrÉdÉric , Campbell Douglas A.
Published: November 2010

Ostreococcus, the smallest known marine picoeukaryote, includes low‐ and high‐light ecotypes. To determine the basis for niche partitioning between Ostreococcus sp. RCC809, isolated from the bottom of the tropical Atlantic euphotic zone, and the lagoon strain Ostreococcus tauri, we studied their photophysiologies under growth irradiances from 15 µmol photons m−2 s−1 to 800 µmol photons m−2 s−1 with a common nutrient replete regime. With increasing growth irradiance, both strains down‐regulated cellular chlorophyll a and chlorophyll b (Chl a and Chl b) content, increased xanthophyll de‐epoxidation correlated with nonphotochemical excitation quenching, and accumulated lutein. Ribulose‐1,5‐bisphosphate carboxylase/oxygenase content remained fairly stable. Under low‐growth irradiances of 15‐80 µmol photons m−2 s−1, O. sp. RCC809 had equivalent or slightly higher growth rates, lower Chl a, a higher Chl b : Chl a ratio, and a larger photosystem II (PSII) antenna than O. tauri. O. tauri was more phenotypically plastic in response to growth irradiance, with a larger dynamic range in growth rate, Chl a, photosystem cell content, and cellular absorption cross‐section of PSII. Estimating the amino acid and nitrogen costs for photoacclimation showed that the deep‐sea oceanic O. sp. RCC809 relies largely on lower nitrogen cost changes in PSII antenna size to achieve a limited range of σ‐type light acclimation. O. sp. RCC809, however, suffers photoinhibition under higher light. This limited capacity for photoacclimation is compatible with the stable low‐light and nutrient conditions at the base of the euphotic layer of the tropical Atlantic Ocean. In the more variable, high‐nutrient, lagoon environment, O. tauri can afford to use a higher cost n‐type acclimation of photosystem contents to exploit a wider range of light.
Resource levels, allometric scaling of population abundance, and marine phytoplankton diversity
Authors: Cermeño Pedro , Marañín Emilio , Harbour Derek , Figueiras Francisco G. , Crespo Bibiana G. , Huete-Ortega María , Varela Manuel , Harris Roger P.
Published: November 2010

We analyzed the relationship between population abundance and cell size in phytoplankton assemblages from coastal, shelf, and open‐ocean environments. Our results show that across the entire size spectrum considered, population abundance increases over two orders of magnitude from subtropical to coastal regions. We find a highly significant linear relationship between nutrient concentration and the intercept of the log‐log relationship between population abundance and cell size. In contrast to overall patterns reported mainly for vascular plants and animals, marine phytoplankton diversity does not show any consistent trend along either latitudinal or productivity gradients. These results imply that large‐scale (biogeographic) variations in phytoplankton standing stocks are controlled by changes in population abundances rather than by systematic variations in species richness. These findings provide a mechanistic connection among nutrient availability, population dynamics, and phytoplankton diversity over macroecological scales.
Maximum phytoplankton concentrations in the sea
Authors: Jackson George A. , Kiørboe Thomas
Published: November 2010

A simplification of plankton dynamics using coagulation theory provides predictions of the maximum algal concentration sustainable in aquatic systems. These predictions have previously been tested successfully against results from iron fertilization experiments. We extend the test to data collected in the North Atlantic as part of the Bermuda Atlantic Time Series program as well as data collected off Southern California as part of the Southern California Bight Study program. The observed maximum particulate organic carbon and volumetric particle concentrations are consistent with the predictions. The results imply that physical processes control maximum particle concentrations in planktonic systems.
Production, oxygen respiration rates, and sinking velocity of copepod fecal pellets: Direct measurements of ballasting by opal and calcite
Authors: Ploug Helle , Iversen Morten Hvitfeldt , Koski Marja , Buitenhuis Erik Theodoor
Published: November 2010

Production, oxygen uptake, and sinking velocity of copepod fecal pellets egested by Temora longicornis were measured using a nanoflagellate (Rhodomonas sp.), a diatom (Thalassiosira weissflogii), or a coccolithophorid (Emiliania huxleyi) as food sources. Fecal pellet production varied between 0.8 pellets ind−1 h−1 and 3.8 pellets ind−1 h−1 and was significantly higher with T. weissflogii than with the other food sources. Average pellet size varied between 2.2 ×105 µm3 and 10.0 ×105 µm3. Using an oxygen microsensor, small‐scale oxygen fluxes and microbial respiration rates were measured directly with a spatial resolution of 2 mm at the interface of copepod fecal pellets and the surrounding water. Averaged volume‐specific respiration rates were 4.12 fmol O2 µm−3 d−1, 2.86 fmol O2 µm−3 d−1, and 0.73 fmol O2 µm−3 d−1 in pellets produced on Rhodomonas sp., T. weissflogii, and E. huxleyi, respectively. The average carbon‐specific respiration rate was 0.15 d−1 independent on diet (range: 0.08‐0.21 d−1). Because of ballasting of opal and calcite, sinking velocities were significantly higher for pellets produced on T. weissflogii (322 ± 169 m d−1) and E. huxleyi (200 ± 93 m d−1) than on Rhodomonas sp. (35 ± 29 m d−1). Preservation of carbon was estimated to be approximately 10‐fold higher in fecal pellets produced when T. longicornis was fed E. huxleyi or T. weissflogii rather than Rhodomonas sp. Our study directly demonstrates that ballast increases the sinking rate of freshly‐produced copepod fecal pellets but does not protect them from decomposition.
Light‐induced changes of plankton growth and stoichiometry: Experiments with natural phytoplankton communities
Authors: Striebel Maren , Spörl Gertrud , Stibor Herwig
Published: November 2010

Both low and high rates of light supply can restrict herbivore growth rates by limiting either the quantity (photosynthetically fixed carbon) or the nutritional quality (nutrient content per fixed carbon) of the herbivores– food. The “light‐nutrient hypothesis,” therefore, predicts that, if phosphorus (P) supply is sufficiently low, production of herbivorous zooplankton should be unimodally related to light intensity. We manipulated the light regime of six different algal communities in a field experiment and investigated the effect of these manipulations on Daphnia growth. The algal communities came from six lakes having different total phosphorus concentrations, ranging from oligotrophic to eutrophic. Seston carbon (C) and seston carbon‐to‐phosphorus ratios in communities from oligotrophic and mesotrophic lakes increased with higher light availability. Across all lakes, the strength of these responses was related to algal diversity. More diverse algal communities showed a stronger increase than less diverse communities in both their carbon biomass and their C: P ratio with increasing light. Furthermore, in oligotrophic and mesotrophic treatments, Daphnia growth was highest at intermediate light intensities. In contrast, seston parameters and Daphnia growth were only weakly related to light supply in communities from eutrophic lakes.
Effects of nitrate and phosphate on grazer‐induced toxin production in Alexandrium minutum
Authors: Selander Erik , Cervin Gunnar , Pavia Henrik
Published: November 2010

Two strains of Alexandrium minutum were exposed to waterborne cues from copepod grazers in factorial combinations of nitrate and phosphate concentrations to evaluate the importance of grazer‐induced paralytic shellfish toxin (PST) production under different nutrient regimes. In nitrate‐rich treatments, the presence of waterborne cues from grazers resulted in significantly increased cell‐specific PST content. In low nitrate treatments, however, waterborne cues from grazers did not result in any detectable increase in cell‐specific PST content. The grazer‐induced increase in cell‐specific PST content in nitrate‐rich treatments was comparable in size to the effects of nitrate in the absence of grazers. Effects of phosphate limitation were less consistent, resulting in increased PST content in nitrate‐rich treatments in one of the A. minutum strains, but had no significant effect in the other. The ability of dinoflagellates to sense and respond to the presence of grazers by increased PST production may be one of the most important factors affecting cell‐specific PST content under nitrogen replete conditions.
Rates of carbonate dissolution in permeable sediments estimated from pore‐water profiles: The role of sea grasses
Authors: Burdige David J. , Zimmerman Richard C. , Hu Xinping
Published: November 2010

In this study we estimate sediment carbonate dissolution rates for sandy sea grass sediments on the Bahamas Bank using an inverse pore‐water advection/diffusion/reaction model constrained by field observations. This model accounts for sea grass O2 input to these sediments, and also parameterizes pore‐water advection through these permeable sediments as a nonlocal exchange process. The resulting rates of carbonate dissolution are positively correlated with sea grass density, and are comparable with previous rate estimates for Florida Bay sediments. In contrast, the advective uptake of O2 by these sediments decreased with increasing sea grass density. This suggests that the competing interplay between bottom‐water flow, near‐seabed pressure gradients, and the presence of a sea grass canopy is important in controlling this type of sediment oxygen uptake. When the carbonate dissolution rates estimated here are examined in the context of carbonate budgets for shallow‐water carbonate platforms systems, they suggest that carbonate dissolution may be a significant loss term in these budgets. Sea grass‐mediated carbonate dissolution may also exert a negative feedback on rising atmospheric CO2, although the magnitude of this effect remains to be quantified.
Dissolved oxygen transfer to sediments by sweep and eject motions in aquatic environments
Authors: O'Connor Ben L. , Hondzo Miki
Published: November 2010

Dissolved oxygen (DO) concentrations were quantified near the sediment‐water interface to evaluate DO transfer to sediments in a laboratory recirculating flume and open channel under varying fluid‐flow conditions. DO concentration fluctuations were observed within the diffusive sublayer, as defined by the time‐averaged DO concentration gradient near the sediment‐water interface. Evaluation of the DO concentration fluctuations along with detailed fluid‐flow characterizations were used to quantify quasi‐periodic sweep and eject motions (bursting events) near the sediments. Bursting events dominated the Reynolds shear stresses responsible for momentum and mass fluctuations near the sediment bed. Two independent methods for detecting bursting events using DO concentration and velocity data produced consistent results. The average time between bursting events was scaled with wall variables and was incorporated into a similarity model to describe the dimensionless mass transfer coefficient (Sherwood number, Sh) in terms of the Reynolds number, Re, and Schmidt number, Sc, which described transport in the flow. The scaling of bursting events was employed with the similarity model to quantify DO transfer to sediments and results showed a high degree of agreement with experimental data.
Hydrodynamic forces and surface topography: Centimeter‐scale spatial variation in wave forces
Authors: O'Donnell Michael J. , Denny Mark W.
Published: November 2010

We measured the variability in hydrodynamic forces among locations separated by only centimeters along three horizontal transects on a steep rocky shore. Our results extend previous work showing that wave forces have the characteristics of 1/f‐noise, in which variability in wave forces decreases exponentially with decreasing scales of measurement. Furthermore, our results suggest that protection from hydrodynamic forces is not a certain consequence of a rugose substratum, suggesting that investigators should directly test (rather than assume) small‐scale topographic protection from hydrodynamic forces.
Doughnut in the desert: Late‐winter production pulse in southern Lake Michigan
Authors: Kerfoot W. Charles , Budd Judith W. , Green Sarah A. , Cotner James B. , Biddanda Bopaiah A. , Schwab David J. , Vanderploeg Henry A.
Published: November 2010

Contrary to expectations of fairly uniform and unstratified waters, sea‐viewing wide field‐of‐view sensor (SeaWiFS) and moderate‐resolution imaging spectroradiometer (MODIS) imagery revealed a spatially complex chlorophyll a pattern, termed the “doughnut,” in southern Lake Michigan during March to April. Phosphorus‐rich coastal waters and sediments are entrained along gyre convergence zones and moved into deeper waters, stimulating a ring of production. Cross‐lake surveys (April 2001 and April 2006) with two separate profiling instruments (vertical Seabird CTD casts, horizontal Acrobat tows) uncovered columnar patterns for Chl a, temperature, and other variables (colored dissolved organic matter, transmissivity) consistent with a spatially complex, rotating gyre structure. Optical plankton counter transects, plankton net tows, and sonar documented that the spatial heterogeneity extends to higher levels of food webs (zooplankton). The horizontal and vertical patterns suggest a previously unrecognized coupling between late‐winter storm‐induced gyre formation, coastal water plus sediment capture, and deep‐water productivity. The pulse may explain how certain zooplankton species characteristic of the Great Lakes can successfully overwinter through what was previously perceived as a very unproductive and resource‐stressful period. The magnitude of the winter pulse may be linked to climate change, as higher temperatures and more frequent winter storms suppress coastal ice formation and encourage movement of nutrient‐enriched waters and sediments into deeper waters.
Relating phytoplankton photophysiological properties to community structure on large scales
Authors: xUitz Julia Uitz , Huot Yannick , Bruyant Flavienne , Babin Marcel , Claustre HervÉ
Published: November 2010

We analyzed a large dataset of simultaneous measurements of phytoplankton pigments, spectral specific absorption coefficient for phytoplankton [a*(λ)], and photosynthesis versus irradiance (P versus E) curve parameters to examine the possible relationships between phytoplankton community structure and photophysiological properties at large spatial scales. Data were collected in various regions, mostly covering the trophic gradient encountered in the world’s open ocean. The community composition is described in terms of biomass of three phytoplankton classes, determined using specific biomarker pigments. We present a general empirical model that describes the dependence of algal photophysiology on both the community composition and the relative irradiance within the water column (essentially reflecting photoacclimation). The application of the model to the in situ dataset enables the identification of vertical profiles of photophysiological properties for each phytoplankton class. The class‐specific a*(λ) obtained are consistent with results from the literature and with previous models developed for small and large cells, both in terms of the absolute values and the vertical patterns. Similarly, for the class‐specific P versus E curve parameters, the magnitude and vertical distribution obtained with this method are coherent with previous observations. Large cells (mainly diatoms) may be more efficient in carbon storage than smaller cells, whereas their yield of light absorption is lower. We anticipate that such photophysiological parameterizations can improve primary production models by providing estimates of primary production that are specific to different phytoplankton classes on large scale.
Combined effects of leaf litter inputs and a flood on nutrient retention in a Mediterranean mountain stream during fall
Authors: Argerich Alba , Martí Eugènia , Sabater Francesc , Ribot Miquel , von Schiller Daniel , Riera Joan L.
Published: November 2010

This study examined the effect of increasing in‐channel leaf standing stocks on hydrologic transient storage and nutrient retention in a Mediterranean mountain stream. A flood at the end of the leaf fall period provided the opportunity to examine the effect of abrupt removal of much of the leaf material. Twenty‐one chloride additions were performed from October to December 2004. In 13 of these, we also added ammonium and phosphate to estimate nutrient uptake lengths and uptake velocities to assess nutrient retention. The one‐dimensional transport with inflow and storage (OTIS) model was used to estimate transient water storage parameters. Although discharge remained constant during leaf fall, water residence time increased because of in‐channel litter accumulation, as did nutrient uptake velocity. Flooding reduced leaf benthic standing stocks by 65% and dramatically altered hydraulic and nutrient retention properties of the channel. After recession, the stream rapidly recovered in terms of nutrient retention, especially for phosphate. Abrupt changes in discharge under flood conditions largely determined the variability in stream nutrient retention. However, leaf litter inputs played an important role in nutrient dynamics during constant flow. Because both the flood regime and the timing of leaf fall are being regionally altered by climate change, our results have implications for stream nutrient dynamics under climate change scenarios.
Radon‐222 budget in Catalina Harbor, California: 1. Water mixing rates
Authors: Colbert S. L. , Hammond D. E. , Berelson W. M.
Published: November 2010

We describe mixing on the basis of the radon distribution in Catalina Harbor, a small embayment on the southwest side of Catalina Island, California. During June 1998, there was a 2–3‐m‐thick warm surface layer in the inner harbor, underlain by cooler water. A radon budget for this system was constructed with the objective of evaluating boundary fluxes and developing a box model to describe mixing and transport into and within the harbor waters. Benthic inputs were evaluated with in situ benthic flux chambers. Loss via decay and gas evasion was characterized by surveys of radon concentration in the water column. Closure of the budget required another large radon source, which was assumed to be tidal pumping of seawater through beach sands. The budget indicates that inputs were primarily attributable to benthic input (55%) and tidal pumping (38%). Losses were due to evasion to the atmosphere (29%), radioactive decay (35%), and mixing to the open ocean (36%). The average upwelling velocity into surface water was 0.73 m d−1. Horizontal mixing was parameterized as an eddy diffusion, calculated to be 0.54 ± 0.19 m2 s−1, which was consistent with mixing predictions on the basis of scaling arguments.
Islands under islands: The phylogeography and evolution of Halocaridina rubra Holthuis, 1963 (Crustacean: Decapoda: Atyidae) in the Hawaiian archipelago
Authors: Craft Jonathan D. , Russ Atlantis D. , Yamamoto Mike N. , Iwai Thomas Y. , Hau Skippy , Kahiapo John , Chong Charlie T. , Ziegler-Chong Sharon , Muir Cam , Fujita Yoshihisa , Polhemus Dan A. , Kinzie Robert A. , Santos Scott R.
Published: November 2010

The genetic structure and evolutionary history of an endemic anchialine species, the shrimp Halocaridina rubra Holthuis, 1963 (Crustacean: Decapoda: Atyidae), was investigated across its range in the Hawaiian archipelago using mitochondrial (e.g., cytochrome oxidase subunit I and large subunit ribosomal) gene sequences. A survey of 573 individuals collected from 34 sites on the islands of Hawai’i, Maui, and Oahu revealed 13 distinct genetic groups belonging to eight divergent lineages. In general, a Halocaridina genetic group or lineage was restricted to a particular region of a single Hawaiian Island, with no individuals being exchanged between them. This pattern stems from a combination of intrinsic organismal properties such as large egg size, abbreviated development, restricted larval habitat and larval feeding mode, and extrinsic obstacles to gene flow in the form of a marine barrier and geologic features that compartmentalize the islands' aquifers. The phylogeographic structuring on and between islands suggests that evolutionary diversification in Halocaridina is driven by population fragmentation, isolation, and subsequent diversification in the aquifers of the Hawaiian Islands. Calibration of cytochrome oxidase subunit I sequence divergence between sister Halocaridina lineages to the geologic age of Kilauea volcano on Hawai'i implies that diversification in the genus is proceeding at a short‐term rate of 20% per million years. The examined mitochondrial genes were generally inadequate for inferring phylogenetic relationships between the Halocaridina lineages.
Nutrient biogeochemistry in a Gulf of Mexico subterranean estuary and groundwater‐derived fluxes to the coastal ocean
Authors: Santos Isaac R. Santos , Burnett William C. , Chanton Jeffrey , Mwashote Benjamin , Suryaputra I G. N. A. , Dittmar Thorsten
Published: November 2010

We hypothesize that biogeochemical processes in a subterranean estuary in the northeastern Gulf of Mexico significantly alter nutrient concentrations that are discharged into the ocean via submarine groundwater discharge (SGD). This subterranean estuary is a site of steep gradients over small spatial scales, so selecting the appropriate groundwater endmember for flux calculations is difficult. Two‐endmember mixing models typically applied to investigate biogeochemical processes in surface estuaries are not useful in this case because of aquifer heterogeneity and complex solid‐fluid interactions. Groundwater residence times, redox potential, source strength, and aquifer matrix appear to be the most important drivers for dissolved organic carbon (DOC) and nutrient concentrations in this pristine coastal plain aquifer. The distribution of dissolved species was consistent with a sequence of reactions in a narrow (~2 m) surface layer in which nitrate is initially exhausted (likely because of denitrification), organic nitrogen is remineralized releasing ammonium, and some DOC remains. On the basis of a 222Rn‐derived non‐steady state box model, total (terrestrial + marine) SGD rates were estimated to oscillate around 11 cm d−1. The SGD is composed almost entirely of recirculated seawater (accounting for ~95% of total SGD fluxes). Conservative estimates of groundwater‐derived nitrogen inputs into the coastal ocean were 8.2± 1.2 mmol m−2 d−1, consisting of ammonium (58%), organic nitrogen (28%), and nitrate (14%). We suggest that these mainly represent recycled rather than new nutrient additions. When extrapolated to the Florida Gulf coast, the nitrogen and DOC fluxes were comparable to the main regional rivers, supporting the proposition that SGD plays a major role in coastal biogeochemistry.
Specificity and stability in high latitude eastern Pacific coral‐algal symbioses
Authors: LaJeunesse T. C. , Bonilla H. Reyes , Warner M. E. , Wills M. , Schmidt G. W. , Fitt W. K.
Published: November 2010

The Gulf of California (Sea of Cortez) acts as a refuge for zooxanthellate coral communities at high northern latitudes in the eastern Pacific. The diversity of dinoflagellate endosymbionts living with cnidarians (9 genera, 16 species) was examined using denaturing gradient gel electrophoresis (PCR‐DGGE) fingerprint analysis of the rDNA Internal Transcribed Spacers (ITS) 1 and 2. Although geographically isolated from the rest of the Pacific, coral‐algal associations in the Gulf of California were similar in cladal composition (dominated by clade C Symbiodinium). However, levels of host‐symbiont specificity appeared to be greater than in the western Pacific, where host diversity is considerably higher and environmental conditions are relatively stable. As a result, the cnidarian community lacked a host‐generalist symbiont. Most colonies of the ecologically dominant genus Pocillopora contained uniform populations of either Symbiodinium D1 (in ~70% of colonies) or C1b‐c (~30%). The proportions of D versus C colonies (i.e., D and C holobionts) remained stable between the years 2004 and 2006. The specificity, stability, and prevalence of Symbiodinium D1 found among individuals of Pocillopora spp. in a region minimally impacted by coral bleaching indicate that these symbiotic combinations, exhibiting specific variability, appear to be products of long‐term ecological and evolutionary processes.
Spatial variability of climate and land‐use effects on lakes of the northern Great Plains
Authors: Pham Samantha V. , Leavitt Peter R. , McGowan Suzanne , Peres-Neto Pedro
Published: November 2010

Evaluation of the effects of climate change and human activities on lakes requires improved understanding of how stressors interact and the degree to which individual sentinel lakes represent broad spatial patterns of ecosystem response to disturbance. We surveyed modern water chemistry (major ions, conductivity, salinity, lake volume) and sediments (algal pigments, stable isotopes) in 21 lakes that surround Humboldt Lake, Saskatchewan, site of a 2,000‐yr climate reconstruction, to quantify spatial synchrony (S, the mean among‐lake correlation coefficient) of prairie lake response to climate variability, land use, and their interactions. Whole‐lake mass balances of total dissolved substances constructed at each site revealed that evaporation of water controlled seasonal changes in salt content only in years with dry summers (2003), leading to widespread spatial coherence of ecosystems (S = 0.78). In contrast, variations in hydrologic inputs (precipitation, groundwater) and solute fluxes regulated salt balances of lakes during years with wet summers (2004, 2005) and substantially reduced lake synchrony (S = 0.13‐0.58). Furthermore, >25% of sites exhibited increased nitrogen influx (as d15N) and cyanobacterial production (as fossil pigments) between ca. 1920 and 2003, with particularly strong effects of land use recorded for northeastern sites, where evaporative forcing was greatest. Finally, principal component and canonical ordinations with redundancy analysis both explained ~50% of the variance in lake sensitivity to climate and land use and revealed that the effects of climate and land use interacted strongly, but that the unique effects of each factor remained identifiable in modern lake surveys.
A framework for developing ecosystem‐specific nutrient criteria: Integrating biological thresholds with predictive modeling
Authors: Soranno Patricia A. , Cheruvelil Kendra Spence , Stevenson R. Jan , Rollins Scott L. , Holden Sarah W. , Heaton Sylvia , Torng Eric
Published: November 2010

We present a novel ecosystem‐specific framework for developing nutrient criteria from biological thresholds and predictive modeling (BTPM) and an application of this framework to lakes in Michigan, U.S. The four main components for the BTPM framework are: (1) to predict each ecosystem's ‘expected nutrient concentration’ in the absence of human effects using a predictive model, (2) to identify important biological thresholds along a nutrient gradient (i.e., biological [BIO] benchmarks), (3) to determine each ecosystem's current nutrient concentration, and (4) to use the above information to derive a nutrient criterion for each ecosystem using the BTPM algorithm. The BTPM framework is extremely flexible in that it can be applied to any aquatic ecosystem type or nutrient and the four components can be implemented in a variety of ways. Our BTPM framework has two additional features: it recognizes that prior to human disturbance, ecosystems varied in their natural nutrient concentrations, and it incorporates risk into the decision‐making process. In the simplest scheme, a nutrient criterion is set at a BIO benchmark greater than the expected nutrient concentration. However, to protect ecosystems more conservatively, a criterion is set at current lake nutrient concentrations if current is less than the BIO benchmark. In our application of the BTPM framework, we developed total phosphorus (TP) criteria for a diverse set of 374 lakes in MI. The expected lake TP concentrations in the absence of human effects ranged from 3 µg L−1 to 24 µg L−1, suggesting that a single criterion approach would not be appropriate.We found two predominant benchmarks in the biological data along the TP gradient, one for zooplankton metrics at 8 µg L−1, and one for phytoplankton metrics at 18 µg L−1. We present the sequence of analyses and decisions that could be used to apply this approach in a management context using Michigan lakes as an example.
Trophic relationships of exotic anadromous salmonids in the southern Patagonian Shelf as inferred from stable isotopes
Authors: Ciancio Javier E. , Pascual Miguel A. , Botto Florencia , Frere Esteban , Iribarne Oscar
Published: November 2010

On the basis of their thermal preferences, salmon introduced in South America can distribute over the whole Southern Patagonian Shelf Ecosystem (SPSE). Stable isotope (δ13C andδ15N) data show that the SPSE is dominated by zooplanktivorous species (15 of 37), and its community is distributed over six trophic levels (TL), with salmonids occupying levels 4.2 to 4.9. A dual isotope mixing model was used to estimate diet proportions of adult salmonids (validated with stomach content analyses) and showed that chinook salmon (TL 4.9) and brown trout (TL 4.7) feed largely on sprats (96% and 79% predicted by the model) and were clustered together with intermediate size fish and cephalopod predators (TL 4.6‐5), a diet similar to that in their native ranges (North Pacific and North Atlantic Oceans). Adult anadromous rainbow trout clustered together with zooplanktivorous species (TL 3.2‐4.4), and the model predicted a diet dominated by planktonic crustaceans (55%), very different from the diet dominated by fish and squids characteristic of adult steelhead in the North Pacific Ocean. Diet predictions based on stable isotopes for Chinook salmon were indistinguishable from direct assessments of stomach contents of fish captured by bottom trawlers and overlapped widely with the diet of Magellanic penguins. The lack of reports on captures of anadromous rainbow trout by bottom trawlers suggests that this species has a shallower distribution. Stable isotope data for rainbow trout are very similar to those of rockhopper penguins, which feed on planktonic crustaceans, fish larvae, and juveniles.
Linking juvenile habitat utilization to population dynamics of California halibut
Authors: Fodrie F. Joel , Levin Lisa A.
Published: November 2010

We investigated the nursery role of four coastal ecosystems for the California halibut (Paralichthys californicus) using the following metrics: (1) contribution in producing the fish that advance to older age classes, (2) connectivity of coastal systems resulting from migration of fish from juvenile to subadult habitats, and (3) effect of nursery habitat usage and availability on subadult population size, specifically evaluating the concentration hypothesis. Potential nurseries were grouped using a robust classification scheme that segregated exposed, bay, lagoon, and estuarine environments. Assignment of nursery origins for individual subadult fish via elemental fingerprinting indicated that exposed coasts, bays, lagoons, and estuaries contributed 31%, 65%, 1%, and 3% of advancing juvenile halibut during 2003, versus 49%, 33%, 16%, and 2% during 2004, respectively. These results were remarkably similar to “expected” nursery contributions derived from field surveys, suggesting that in this system juvenile distributions were a good indicator of unit‐area productivity of juvenile habitats and that densitydependent mechanisms during the juvenile phase did not regulate recruitment pulses. Elemental fingerprinting also demonstrated that individuals egressing from bays did not migrate far from their nursery origins (<10 km), resulting in reduced connectivity along the 110‐km study region over the timescale of approximately one generation. Consequently, we observed considerably higher subadult densities at sites near large bays, while populations distant from large bays appeared to be more influenced by nursery habitat limitation. Over large (~100 km) scales, the location and availability of nursery habitat alternatives had significant effects on the population dynamics of an important member of the ichthyofaunal community of southern California.
Nitrogen and phosphorus co‐limitation of bacterial productivity and growth in the oligotrophic subtropical North Atlantic
Authors: Mills M. M. , Moore C. M. , Langlois R. , Milne A. , Achterberg E. , Nachtigall K. , Lochte K. , Geider R. J. , J. La Roche
Published: November 2010

Bacterial productivity and biomass are thought to be limited by dissolved organic carbon (DOC) in much of the world's oceans. However, the mixed layer of oligotrophic oceans is often depleted in dissolved inorganic nitrogen and phosphate, raising the possibility that macronutrients may also limit heterotrophic bacterial growth. We used nutrient bioassay experiments to determine whether inorganic nutrients (N, P, Fe) and/or DOC could limit bacterial productivity and biomass in the central North Atlantic during the spring of 2004 (Mar‐Apr). We observed that both heterotrophic bacterial productivity and biomass were co‐limited by N and P in the oligotrophic North Atlantic, and additions of labile DOC (glucose) provided no stimulation unless N and P were also added. Flow cytometry results indicated that only a small subset of large cells high in nucleic acid content were responsible for the increased productivity in the combined NP amendments. In contrast, nutrient additions elicited no net change on the dominant component of the bacterial population, composed of small cells with relatively low nucleic acid content. In the combined NP treatments the relative increase in bacterial production was greater than that measured when phytoplankton productivity was relieved of nitrogen limitation. These results suggest that N and P co‐limitation in the bacterial community results in increased competition between the heterotrophic and autotrophic components of the surface communities in the Central North Atlantic Ocean, and potentially impacts the cycling of organic matter by the bacterioplankton.
Diel carbon monoxide cycling in the upper Sargasso Sea near Bermuda at the onset of spring and in midsummer
Authors: Zafiriou Oliver C. , Xie Huixiang , Nelson Norman B. , Najjar Raymond G. , Wang Wei
Published: November 2010

Rapid bio‐oxidation of carbon monoxide (CO), a photoproduct of dissolved organic matter, results in diel cycles reflecting photochemical‐biogeochemical‐physical interactions. These cycles were characterized by time‐series studies of hydrography, meteorology, insolation, optics, and CO concentration ([CO]). Diel patterns of near‐surface [CO] generally varied little seasonally, despite different forcings. In summer 30% of CO was below the mixed layer (ML); ML depths and optics indicate that two‐layer photochemistry is common elsewhere. [CO] decayed at similar rates in both isolated layers. In spring CO extended to 150 m, reflecting nocturnal mixing. Cruise‐average profiles indicated a shallower ML defined by CO than that defined by density, illustrating short‐lived CO’s sensitivity to recent mixing. Below the ML, [CO] dropped exponentially with depth on scales controlled by photoproduction in summer but mixing in spring. Mass‐balance modeling of diurnal variations in CO column burden (CB) gave similar production rates in summer and spring (~50 µmol m−2 d−1 CO), but different biooxidation rates, 1.5 ± 0.2 d−1 (summer, 0‐50 m) and 0.52‐0.66 d−1 (spring, 0‐200 m). Outgassing averaged 4% of bio‐oxidation in summer and 14% in spring. Similar production and differing sinks resulted in different CBs: 39.3 µmol m−2 (summer) versus 94.9 µmol m−2 (spring). Insolation‐normalized CO productions were 1.8 times those in the oligotrophic equatorial Pacific. Improved, well‐blanked analyses found [CO] at 200 m always <0.1 nmol L−1 in summer, and usually in spring. Prior reports of [CO] systematically ≥0.2 nmol L−1 at depth in well‐stratified, oxic blue waters may be high because of method artifacts.
The influence of microorganisms on chlorophyll a degradation in the marine environment
Authors: Szymczak-Żyla Malgorzata , Kowalewska Grażyna , Louda J. William
Published: November 2010

This study investigated the action of natural microorganisms on the degradation (diagenesis) of chlorophyll a (Chl a). Unialgal cultures of the diatom Chaetocerus gracilis and the eustigmatophyte Nannochloropsis occulata were incubated with or without the addition of natural marine microorganisms in oxic (air) or anoxic (nitrogen sparge) conditions. Microorganisms were obtained from seawater recovered just above the sediment‐water interface of a coastal lagoon of southeastern Florida. Incubations were over periods of 2, 4, 8 and 24 weeks. Pigments were analysed by high‐performance liquid chromatography. The most rapid destruction of Chl a and its derivatives occurred in oxic conditions with added microorganisms. The next fastest rates of destruction were observed in oxic conditions without such additions. N. occulata and C. gracilis incubated under oxic conditions without added microorganisms were found to contain almost 50% or 25% of total chloropigments, respectively, as Chl a allomers after 24 weeks. Allomer formation is taken as a prelude to purpurin/chlorin formation and potential macrocyclic destruction. Pyropheophytin a and steryl chlorin (phorbide) esters were observed to form significantly under anoxic conditions, but only to a minor extent under oxic conditions, in cultures incubated with added microorganisms. The formation of the steryl chlorin esters was observed to occur in concert (R2 > 0.98) with the disappearance of pyropheophorbide a and pyropheophytin a. The direct intervention of microorganisms in the course of diagenetic processing of Chl a is concluded. Thus, cellular senescence, grazing‐induced cell disruption, physicochemical environment (O2 and so on), and microbial processing all need to be considered in order to fully address chlorophyll digenesis.
The production of volatile iodocarbons by biogenic marine aggregates
Authors: Hughes C. , Malin G. , Turley C. M. , Keely B. J. , Nightingale P. D.
Published: November 2010

We present the first reported measurements of volatile iodocarbon production by biogenic marine aggregates. Iodomethane (CH3I), iodoethane (C2H5I), 2‐iodopropane (CH3CHICH3), and 1‐iodopropane (CH3CH2CH2I) concentrations were determined in incubations of aggregates formed by concentrating the >53 µm fraction of the plankton during a field campaign in the Celtic Sea. All four iodocarbons increased significantly in concentration in the aggregate incubations relative to filtered seawater controls. Maximum production rates ranged from 0.01 pmol L−1 h−1 for CH3CHICH3 to 0.31 pmol L−1 h−1 for C2H5I. Accompanying pheopigment and bacterial heterotrophic production suggest that the processes taking place on the aggregates studied were a good representation of those known to occur on natural marine particles. We also report iodocarbon production rates observed in natural marine aggregates, including a diatom mucilage collected in the Celtic Sea and phytodetritus sampled from Kongsfjord in the Arctic. Detrital particles could be hotspots of iodocarbon production in the marine environment.
Availability of iron from iron‐storage proteins to marine phytoplankton
Authors: Castruita Madeli , Shaked Yeala , Elmegreen Lauren A. , Stiefel Edward I. , Morel François M. M.
Published: November 2010

We examined the bioavailability of iron‐storage proteins—including representatives of maxi‐ and miniferritins— to various species of marine phytoplankton. Both eukaryotic and prokaryotic species were able to grow rapidly with horse spleen ferritin (HoSF) or deoxyribonucleic acid (DNA)‐binding proteins from starved cells (Dps) from Trichodesmium erythraeum as the sole Fe source in the medium. In the presence of ethylenediaminetetra‐acetic acid (EDTA), cells grown with HoSF or Dps maintained exponential growth rates similar to those obtained at the same concentration of FeEDTA. Growth was also observed in the absence of EDTA, showing that a complexing agent is not necessary for Fe availability. The bioavailability of Fe in these storage proteins apparently results from a spontaneous release of Fe(III) to solution with an effective first‐order rate constant ~0.15 d−1. Genes coding for iron‐storage proteins are common in DNA samples from seawater. In iron‐deprived marine ecosystems, iron‐storage proteins may be important constituents of the recycled iron pool and modulate its availability to phytoplankton.
A photosynthetic strategy for coping in a high‐light, low‐nutrient environment
Authors: Mackey Katherine R. M. , Paytan Adina , Grossman Arthur R. , Bailey Shaun
Published: November 2010

Phytoplankton in high‐light, low‐nutrient ocean environments are challenged with maintaining high photosynthetic efficiency and simultaneously preventing photodamage that results from low levels of electron acceptors downstream of photosystem II (PSII). Here, we identify a process in open ocean picophytoplankton that preserves PSII activity by diverting electrons from the photosystem I (PSI) complex‐mediated carbon assimilation to oxygen via a propyl gallate‐sensitive oxidase associated with the photosynthetic electron transport chain. This process stabilizes diel photochemical efficiency of PSII, despite midday photoinhibition, by maintaining oxidized PSII reaction centers. Although measurements of the maximum photochemical efficiency of PSII, Fv : Fm show midday photoinhibition, midday CO2 fixation is not depressed. Moreover, CO2 fixation saturates at low irradiances even though PSII electron flow is not saturated at irradiances of 1,985 mmol photons m−2 s−1. This disparity between PSII fluorescence and CO2 fixation is consistent with the activity of an oxidase that serves as a terminal electron acceptor, maintaining oxidized PSII reaction centers even when CO2 fixation has saturated and the total number of functional reaction centers decreases because of photoinhibition (reflected in lower midday Fv : Fm values). This phenomenon is less apparent in coastal phytoplankton populations, suggesting that it is a strategy particularly distinctive of phytoplankton in the oligotrophic ocean. Spatial variability in features of photosynthetic electron flow could explain biogeographical differences in productivity throughout the ocean and should be represented in models that use empirical photosynthesis and chlorophyll fluorescence measurements from a limited number of ocean sites to estimate the productivity of the entire ocean.
Dynamics of dissolved carbohydrates in the Chesapeake Bay: Insights from enzyme activities, concentrations, and microbial metabolism
Authors: Steen Andrew D. , Hamdan Leila J. , Arnosti Carol
Published: November 2010

The interactions between heterotrophic microbes and high‐molecular‐weight (HMW) dissolved organic carbon in estuaries are complex and poorly understood. This study examined the coupling between hydrolysis of HMW carbohydrates (polysaccharides) and uptake of monosaccharides by bacterioplankton along a salinity gradient in the Chesapeake Bay water column and nearby coastal waters in order to evaluate the potential importance of polysaccharides as a carbon source for the estuarine microbial loop. We measured the rates of enzymatic hydrolysis of six polysaccharides (arabinogalactan, chondroitin sulfate, fucoidin, laminarin, pullulan, and xylan) as well as total carbohydrate and monosaccharide concentrations, bacterioplankton abundance, and monosaccharide assimilation rates. Enzymatic hydrolysis rates were sufficiently rapid to produce on a daily basis 40‐62% of the monosaccharides present in Chesapeake Bay surface waters but a lower percentage (23%) of monosaccharides present in surface water on the continental shelf. Rates of both monosaccharide assimilation and polysaccharide hydrolysis were markedly lower on the continental shelf than in the Chesapeake Bay. These measurements suggest that at the time of sampling, polysaccharides in the Chesapeake Bay were rapidly recycled, while rates of cycling were considerably slower on the nearby continental shelf. In contrast to the apparently rapid turnover of bulk polysaccharides, hydrolysis of two polysaccharides, pullulan and chondroitin sulfate, was essentially undetectable, implying that those substrates would be unavailable to the microbial communities sampled on a timescale of 10 d.
Absorption spectral slopes and slope ratios as indicators of molecular weight, source, and photobleaching of chromophoric dissolved organic matter
Authors: Helms John R. , Stubbins Aron , Ritchie Jason D. , Minor Elizabeth C. , Kieber David J. , Mopper Kenneth
Published: November 2010

A new approach for parameterizing dissolved organic matter (DOM) ultraviolet‐visible absorption spectra is presented. Two distinct spectral slope regions (275‐295 nm and 350‐400 nm) within log‐transformed absorption spectra were used to compare DOM from contrasting water types, ranging from wetlands (Great Dismal Swamp and Suwannee River) to photobleached oceanic water (Atlantic Ocean). On the basis of DOM size‐fractionation studies (ultrafiltration and gel filtration chromatography), the slope of the 275‐295‐nm region and the ratio of these slopes (SR; 275‐295‐nm slope : 350‐400‐nm slope) were related to DOM molecular weight (MW) and to photochemically induced shifts in MW. Dark aerobic microbial alteration of chromophoric DOM (CDOM) resulted in spectral slope changes opposite of those caused by photochemistry. Along an axial transect in the Delaware Estuary, large variations in SR were measured, probably due to mixing, photodegradation, and microbial alteration of CDOM as terrestrially derived DOM transited through the estuary. Further, SR varied by over a factor of 13 between DOM‐rich wetland waters and Sargasso Sea surface waters. Currently, there is no consensus on a wavelength range for log‐transformed absorption spectra. We propose that the 275‐295‐nm slope be routinely reported in future DOM studies, as it can be measured with high precision, it facilitates comparison among dissimilar water types including CDOM‐rich wetland and CDOM‐poor marine waters, and it appears to be a good proxy for DOM MW.