bluuebunny/crossref_metadata_2025 huggingface dataset:
Algal responses to dissolved organic carbon loss and pH decline during whole‐lakeacidification: Evidence from paleolimnology
Authors: Leavitt P. R. , Findlay D. L. , Hall R. I. , Smol J. P.
Published: May 2010

Fossil pigment analyses and 19 year‐long historical records were used to quantify whole‐lake algal response to changes in optical and chemical properties following experimental acidification of Lake 302 with H2SO4 (south basin, 302S; 1981—1989) or HNO3 (north basin, 302N; 1982–1986) and HCl (1987–1989). Undisturbed sediments were collected by freeze‐coring, sectioned in approximately annual intervals, and analyzed for fossil carotenoids, chlorophylls, and derivatives by high performance liquid chromatography. Concentrations of fucoxanthin (diatoms, chrysophytes, some dinoflagellates) were correlated with algal standing crop (r2 = 0.67, P < 0.05; 1978–1989) and increased 6‐fold following acidification of Lake 302S with H2SO4 from pH 6.6 to 5.0, consistent with observed reductions in dissolved organic carbon (DOC) from 7 to 4.5 mg liter−1, improved water clarity, and increased biomass of deep‐water chrysophytes. However, fucoxanthin concentrations declined to baseline values in sediments from 1988 to 1990, concomitant with severe acidification to pH 4.5, continued DOC loss (<1.5 mg liter−1) and an estimated 8‐fold increase in the penetration of UVb radiation (UVR‐b). Increased penetration of ultraviolet radiation (UVR) was recorded also by increased relative abundance of pigments characteristic of UVR‐transparent environments. In contrast, pigments from green algae (Chl b, pheophytin b, lutein‐zeaxanthin) doubled during acidification with H2SO4, while those from cryptophytes (alloxanthin) were unaffected and diatoxanthin from diatoms declined. Patterns of ubiquitous β‐carotene, Chl a, and pheophytin a suggested that total algal biomass increased ∼200–400% by the mid‐1980s, but declined to near‐baseline under severe acidification. Variance partitioning using redundancy analysis captured 80–83% of variation in fossil chlorophylls and carotenoids and suggested that the direct effects of pH were greater (~50% of total variance) than those of irradiance (~12%), but that ∼20% of variance was attributable to factor interactions. Fossil concentrations of pigments from green algae and diatoms increased ~100% following acidification of Lake 302N to pH 6.1, but there were few signals of deep‐water blooms, possibly because DOC remained 3.5–5.0 mg liter−1. Such complex interactions between pH, DOC, and light may help explain the high variability of algal biomass response to lake acidification.
Multiple stresses from a single agent: Diverse responses to the experimental acidification of Little Rock Lake, Wisconsin
Authors: Frost Thomas M. , Montz Pamela K. , Kratz Timothy K. , Badillo Tracy , Brezonik Patrick L. , Gonzalez Maria J. , Rada Ronald G. , Watras Carl J. , Webster Katherine E. , Wiener James G. , Williamson Craig E. , Morris Donald P.
Published: May 2010

A single stress, acidification with sulfuric acid, was applied to Little Rock Lake in a whole‐ecosystem manipulation. We documented a wide range of responses to the acidification, including increases in the concentrations of various chemicals, shifts in microbial processes and a major increase in water clarity to UV‐B radiation. Each of these changes could in itself be considered as a separate ecosystem stress that is distinct from the intended manipulation. Acidification in Little Rock Lake was accompanied by a number of substantial changes in the occurrence of organisms. A series of detailed investigations indicates that the mechanisms underlying these organismal changes are varied but cannot usually be tied to the direct effects of acidification. Overall, our results demonstrate how multiple stresses can arise from a single agent operating on an ecosystem and suggest that singly operating stresses may actually be quite rare.
Nutrient cycling at the landscape scale: The role of diel foraging migrations by geese at the Bosque del Apache National Wildlife Refuge, New Mexico
Authors: Kitchell James F. , Schindler Daniel E. , Herwig Brian R. , Post David M. , Olson Mark H. , Oldham Michael
Published: May 2010

Wildlife refuges are sites of dense aggregations of wintering waterfowl. Refuge managers are concerned about local water‐quality effects and the amount of birdborne nutrient load that might cause eutrophication in roosting ponds and(or) be exported to downstream systems. We initiated this research effort to test the hypothesis that daily feeding migrations by geese represented a significant source of nutrients to wetland systems at the Bosque del Apache National Wildlife Refuge in the middle Rio Grande River valley of New Mexico. We documented the role of geese in translocating nutrients through a combination of time budget and mass balance models for birds, bioassays of phytoplankton growth, and stable isotope methods that trace the source of nitrogen to food webs. Geese increased the nutrient loading rates in some wetland ponds by up to 40% for total nitrogen and 75% for total phosphorus. Bioassays revealed that nitrogen was consistently limiting to primary production by algae in the ponds. Chlorophyll levels increased in proportion to bird densities. Fish and crayfish from the ponds intensively used by birds had very low stable nitrogen signatures relative to those from the Rio Grande River. This result derived from the low 15N in alfalfa and corn, which were the primary forage for birds, and accumulated through food webs in proportion to bird use of individual ponds as roosting areas. In general, the wetland ponds functioned efficiently in retaining the birdborne, allochthonous nutrient load and only modest amounts of the total nitrogen or phosphorus were exported downstream.
Variability in responses to nutrients and trace elements, and transmission of stressor effects through an estuarine food web
Authors: McDowell Judith E. , Lancaster Bruce A. , Leavitt Dale F. , Rantamaki Pirjo
Published: May 2010

Marine bivalve molluscs such as the blue mussel (Mytilus edulis) and the soft shell clam (Mya arenaria) have been used as sentinel organisms of contaminant bioavailability and the biological consequences of contaminant exposure. Biological responses that may contribute to the impairment of reproductive and developmental processes include responses that can be categorized as interfering with bioenergetic processes such as feeding and nutrient allocation; biosynthetic processes, such as the synthesis of energy stores; and morphogenic processes, such as those involved in structural development. Case studies within New Bedford and Boston Harbors (Massachusetts) are used to examine the relationship between contaminant uptake and effects on the reproductive cycle and bioenergetics of mussels and soft shell clams. The results observed illustrate that disruption in bioenergetics in bivalve molluscs exposed to chemical contaminants can result in loss of reproductive output and increased susceptibility to disease. Differences in the extent of reproductive impairment may be linked specifically to energetic strategies of individual species.
How environmental stress affects the impacts of parasites
Authors: Lafferty Kevin D. , Kuris Armand M.
Published: May 2010

Parasites occur in nearly every population. They often interact in complex ways with other stressors. In some cases, the interaction may lead to a disproportionately negative effect on the host population. In other cases, the stressor may ameliorate the effects of parasitism. Here we illustrate intersections of four types of environmental stressors with infectious diseases. First, pollutants may increase parasitism by increasing host susceptibility or by increasing the abundance of intermediate hosts and vectors. Pollutants can also decrease parasitism if infected hosts suffer differentially high mortality, parasites are more susceptible to pollution than their hosts, or if pollutants negatively affect intermediate hosts or vectors. These effects vary depending on the particular parasite and pollutant that interact. Second, habitat alterations such as impounding water or development can affect both intermediate host and vector populations such that the abundance of their attendant parasites is either increased or reduced. Third, fisheries can impact populations already stressed by disease. However, they may act to lower the density of a host population below the threshold for sustained transmission to such an extent that the parasite population can no longer persist. Fourth, introduced species may introduce new diseases to susceptible native populations or they may gain an advantage if they invade without the parasites from their native range. The complexity and ubiquity of these interactions are good arguments for considering parasitism when evaluating stressors of aquatic systems.
Multiple stressors on coral reefs: A long ‐term perspective
Authors: Hughes T. P. , Connell J. H.
Published: May 2010

Coral reefs are subject to a high frequency of recurrent biological and physical disturbances. The temporal and spatial scales of these are often large and difficult to study, so that most of our knowledge of disturbances on coral reefs comes from investigations conducted at one or a few sites, over short periods of time. We argue that studying single events in isolation can be misleading and that a longer term approach is necessary for understanding the responses of coral reef assemblages to multiple stressors. We present first a brief review of the impacts of physical disturbance (e.g., cyclones, hurricanes) on the community dynamics of coral reefs, with special attention to the effects of recurrent events. We then examine two unusually detailed, long ‐term data sets from Heron Island, Australia, and Jamaica which demonstrate some of the complexities of multiple stressors (broadly defined as natural or man‐made disturbances).
Non‐indigenous species as stressors in estuarine and marine communities: Assessing invasion impacts and interactions
Authors: Ruiz Gregory M. , Fofonoff Paul> , Hines Anson H. , Grosholz Edwin D.
Published: May 2010

Invasions by non‐indigenous species (NIS) are recognized as important stressors of many communities throughout the world. Here, we evaluated available data on the role of NIS in marine and estuarine communities and their interactions with other anthropogenic stressors, using an intensive analysis of the Chesapeake Bay region as a case study. First, we reviewed the reported ecological impacts of 196 species that occur in tidal waters of the bay, including species that are known invaders as well as some that are cryptogenic (i.e., of uncertain origin). Second, we compared the impacts reported in and out of the bay region for the same 54 species of plants and fish from this group that regularly occur in the regionÂ's tidal waters. Third, we assessed the evidence for interaction in the distribution or performance of these 54 plant and fish species within the bay and other stressors. Of the 196 known and possible NIS, 39 (20%) were thought to have some significant impact on a resident population, community, habitat, or process within the bay region. However, quantitative data on impacts were found for only 12 of the 39, representing 31% of this group and 6% of all 196 species surveyed. The patterns of reported impacts in the bay for plants and fish were nearly identical: 29% were reported to have significant impacts, but quantitative impact data existed for only 7% (4/54) of these species. In contrast, 74% of the same species were reported to have significant impacts outside of the bay, and some quantitative impact data were found for 44% (24 /54) of them. Although it appears that 20% of the plant and fish species in our analysis may have significant impacts in the bay region based upon impacts measured elsewhere, we suggest that studies outside the region cannot reliably predict such impacts. We surmise that quantitative impact measures for individual bays or estuaries generally exist for <5% of the NIS present, and many of these measures are not particularly informative. Despite the increasing knowledge of marine invasions at many sites, it is evident that we understand little about the full extent and variety of the impacts they create singly and cumulatively. Given the multiple anthropogenic stressors that overlap with NIS in estuaries, we predict NIS‐stressor interactions play an important role in the pattern and impact of invasions.
Temporal changes of microbial assemblages in the ice and snow cover of a high mountain lake
Authors: Felip Marisol , Camarero Lluís , Catalan Jordi
Published: May 2010

It has recently been shown that a rich community of microorganisms inhabits the slush layers of the winter cover of high mountain lakes. In this study, temporal changes in species assemblages and environmental conditions in the ice and snow cover of Lake Redó in the Pyrenees (Spain) are presented. The winter cover was a highly dynamic environment, in which major changes occurred in physical structure and chemical characteristics. The biomass and species composition of the microbial groups present (autotrophic and heterotrophic flagellates, ciliates, and bacteria) reflected these physicochemical alterations. After an initial phase, during which the ice sheet formed and the first snows accumulated with little or no development of slush layers, there were two stages of microbial assemblages, which coincided with the two main phases in the physical change of the cover: the growth period (from January to mid‐April) and the ablation period (from mid‐April to ice‐out in June). Initially, microbial biomass originated from inputs of phytoplankton‐rich (5.9 μg chlorophyll a liter−1 ) surface lake water that flooded the cover as a result of the hydrostatic adjustment induced by the progressive accumulation of snow on top of the ice sheet. This was followed by a differential growth of mixotrophic or heterotrophic flagellated species, such as Ochromonas sp., Cryptomonas spp., Monosiga ovata and Oikomonas termo, which peaked at different times. Species depended primarily on bacterivory for their growth, since during this period, light did not reach the slush layers. By April, the transition from cover growth to ablation was marked by a reduction in biomass and in the number of species. During the ablation period, the rate of change of the cover was greater, and microbial assemblages were characterized by the vertical segregation and by the appearance of new species, some of which were typically nonplanktonic. During that time, the cover was highly influenced by the large amount of water from the melting of the snowpack within the catchment. This water likely provided chemicals and organisms, while increased light availability allowed for the growth of algae (Pteromonas sp. and other volvocales) and of the associated food web in the upper slush. In deeper layers, however, a bacteria‐based food web provided prey for large ciliates (Urosoma sp., Dileptus sp., and Lacrymaria sp.), probably carried from littoral or watershed soils.
Chemical tracing of salinity sources in Lake Kinneret (Sea of Galilee), Israel
Authors: Kolodny Yehoshua , Katz Amitai , Starinsky Abraham , Moise Tamar , Simon Ehud
Published: May 2010

Lake Kinneret is a freshwater lake in northern Israel that receives a major part of its salt input from unmonitored springs that discharge through the lake's bottom. We attempt to characterize the nature of these springs by estimating their chemical composition. While the springs around Lake Kinneret are subject to wide spatial and temporal variations in their ionic concentrations, specific sodium (Na), potassium, magnesium (Mg), strontium, bromine, and lithium to chlorine (Cl) ion ratios are almost constant within individual springs and spring groups. The radium : Cl ratio and the δ18O‐Cl relationship confirm the notion that the spring waters result from recent mixing between saline brines and freshwater.

Available compositional data from past years along with new analyses of the lake and its known springs allow identification of the salinity source that causes the observed deficit in the lake's salt budget (e.g., 91–93% chloride). The relative contributions from these saline springs are different for different ions; this contribution is highest for bromide (95%), decreases to 84% for Na, and is less than 50% for Mg.

Two independent approaches have been used for balancing the salts in the lake, and they are as follows: (1) an annual mass balance between salt removal and supply of the different ions, assuming a steady‐state lake; and (2) simulation of the lake's evolution from 1964 (the beginning of salt removal from the lake via the Salinity Diversion Channel) until the present. Both methods predict very similar ionic ratios for the (yet unknown) average saline spring(s), testifying to the reliability of both approaches. The ionic ratios so obtained closely resemble Fuliya (± Tabgha)‐type waters, excluding the Tiberias and eastern shore springs as significant salt sources. This inferred composition of the average unmonitored springs depends strongly on present‐day diversion of saline springs (this diversion thus prevents their flow into the lake). The different ionic ratios that identify the various spring groups reflect the respective compositions of the brine pockets that feed them. Our simulation also shows that the layered structure of Lake Kinneret enhanced the evolution rate of the lake after the implementation of the salt diversion program in 1964.
Patterns of groundwater discharge into Florida Bay
Authors: Corbett D. Reide , Chanton Jeffrey , Burnett William , Dillon Kevin , Rutkowski Christine , Fourqurean James W.
Published: May 2010

Natural chemical tracers of groundwater discharge (222Rn and CH4) were surveyed to evaluate possible patterns of groundwater interactions with surface water in Florida Bay. Radon and methane concentrations in water samples collected from wells, solution holes, canals, and Florida Bay showed a significant correlation, despite the fact that these two trace gases have independent sources. Groundwater flux was also measured directly via seepage meters in several Florida Bay locations. Natural abundance of nitrogen isotopes measured on attached algae and seagrass showed the greatest 15N enrichment near the Keys. Collectively, our results suggested greater groundwater flow along the bay side of the Florida Keys. Nutrient flux estimates, based on interstitial nutrient concentrations and groundwater flux measurements, suggested that groundwater in the eastern part of Florida Bay may provide as much nitrogen (110 ± 60 mmol N m−2 yr−1) and phosphate (0.21 ± 0.11 mmol PO43− m−2 yr−1) as surface freshwater sources from the Everglades (i.e., Taylor Slough and C‐111). However, the inputs are clearly not uniform, and areas near solution holes or tidal springs may have a substantially greater nutrient flux into surface waters then these estimates.
Sediment accumulation and Pb burdens in submerged macrophyte beds
Authors: Benoy Glenn A. , Kalff Jacob
Published: May 2010

This study quantifies the role of lake morphometry and submerged macrophyte beds on the accumulation of sediments in the littoral zone. Stable Pb, a historical marker of lacustrine sediments in southern Quebec, was used to date the sediments (∼110 yr) and to calculate three long‐term sediment accumulation rates (SARs) in Lake Memphremagog (located in Quebec and Vermont). The anthropogenic Pb burden in the littoral zone of Lake Memphremagog was found to be two to eight times greater (per m2) than the Pb burdens in the profundal zone of surrounding eastern township lakes. Pb concentrations were nearly fourfold higher than background Pb concentrations (115 and 31 μg g−1, respectively), providing a reliable marker for littoral sediment core analysis. Lake morphometry is related to the three accumulation rates measured by providing distinct threshold limits (i.e., littoral slope, >10% exposure, >10 km2) where sediments are unable to accumulate. Macrophyte beds are shown to disproportionately accumulate sediments at rates 2 to 20 times greater (per m2) than in the profundal zone. Linear regression models show that both the total SAR (mean, 1.7 mm yr−1) and organic SAR (mean, 83.1 g m−2 yr−1) are best predicted by the biomass density of the macrophytes, closely followed by plant mean biomass. Bulk SAR, principally representing the larger, inorganic fraction of sediments, is least predictable. Biomass density, but not mean biomass, was related to the accumulation rate of stable Pb (mean, 37.7 mg m−2 yr−1), supporting empirical models that show growth form to be an important determinant of both sediment and plant tissue elemental concen‐trations. The variety of macrophyte communities sampled across Lake Memphremagog demonstrates that the conclusions drawn are not restricted to monospecific stands but to assemblages as a whole.
Diversity in planktonic communities: An experimental test of the intermediate disturbance hypothesis
Authors: Flöder Sabine , Sommer Ulrich
Published: May 2010

According to Connell's intermediate disturbance hypothesis (IDH), diversity within a community is maximal at intermediate frequencies and intensities of disturbances. In order to test the IDH, disturbances of different frequencies and intensities were imposed on natural plankton communities in controlled field experiments. These disturbances consisted of an artificial deepening of the mixed layer, leading to the dilution of epilimnetic populations and to a higher level of nutrients. Intervals between disturbances ranged from 2 to 12 d. Different intensities of disturbance were caused by differences in the experimental mixing depth (150 and 225% of the original epilimnion depth). Investigation focused on the effect that disturbances had on the diversity of natural phytoplankton communities. Additionally, we were interested in determining the effect of grazing by zooplankton. The results of the field experiments show for the first time the applicability of the IDH to phytoplankton within complete planktonic communities. Diversity showed a clear maximum at the intermediate disturbance interval of 6 d. Similarly, species number peaked at intermediate interval length (6–10 d).
Interactive effects of flow speed and particle concentration on growth rates of an active suspension feeder
Authors: Genovese Salvatore J. , Witman Jon D.
Published: May 2010

Suspension‐feeding organisms dominate subtidal habitats in the Gulf of Maine (GOM) at depths of 25–40 m. Parasmittina jeffreysi is an encrusting cheilostome bryozoan found in this zone throughout the GOM. Regional variation between coastal and offshore locations in both flow speed and particle concentration makes the GOM an ideal location to study the effect of these factors on the growth of P. jeffreysi. Particle flux measurements at two offshore and two coastal sites indicated that flow speeds were >3‐fold greater offshore than at coastal sites. Chlorophyll a concentrations and particulate quantity and quality were greater at offshore sites, but sedimentation rates were greater in the coastal region. The growth rate of P. jeffreysi was measured at each of the sites using unob‐structed colonies free from spatial competition and colonies that remained within their natural community.

Both unobstructed colonies and those in quadrats within the natural community displayed no regional difference in growth rates, despite higher particle flux in the offshore region. The interactive effects of flow speed and particle concentration are acting upon growth rates in opposite directions, resulting in the net effect of no regional differences in growth. Growth of unobstructed colonies at one of the coastal sites (Halfway Rock) was less than that at any of the other three sites and may have resulted from the combination of high sedimentation and extremely low flow at this site.

A comparison between unobstructed colonies and those in natural quadrats suggested that growth was limited by spatial competition in the natural community. A significant site interaction effect indicates that this response did not occur at all four sites and was absent at Halfway Rock because of poor growth of unobstructed colonies. Any differences in growth due strictly to differential food acquisition (e.g., unobstructed colonies) appear to be dampened by competitive interactions in the natural community.
Blooms of the picoplanktonic cyanobacterium Synechococcus in Florida Bay, a subtropical inner‐shelf lagoon
Authors: Phlips Edward J. , Badylak Susan , Lynch Tammy C.
Published: May 2010

Seventeen sites in Florida Bay were sampled on a monthly basis for 51 months to describe the spatial and temporal patterns of phytoplankton blooms. The study focused on the picoplanktonic cyanobacterium Synechococcus. The greatest frequency and intensity of blooms was observed in the north‐central region of Florida Bay, where cellular biovolumes of this species regularly exceeded 10 × 106μm3 ml−1 and chlorophyll a concentrations were frequently >20 mg m−3. Synechococcus blooms were often restricted to this region of the bay, in part because of the network of shallow mudbanks and islands that restrict water exchange with other regions and outlying waters of the Atlantic Ocean and Gulf of Mexico. The most severe blooms occurred in the summer and fall (May–December). High concentrations of Synechococcus also appeared during the fall in the south‐central region of the bay. The appearance of blooms in this region coincided with the onset of seasonal cold fronts, whose strong northerly and northwesterly winds appear to drive bloom‐laden water from the north‐central region into adjacent parts of the bay. A number of physical and chemical factors appear to contribute to the remarkably high phytoplankton biovolumes observed in the north‐central region of Florida Bay. Physical factors include the shallowness and hydrological isolation of the region. The dominance of Synechococcus in the center of the bay may be attributable to several of the unique physicochemical characteristics of this species, including its small size, cyanobacterial metabolism, euryhaline character, buoyancy, and tolerance to high light intensity.
Effects of water velocity on algal carbon isotope ratios: Implications for river food web studies
Authors: Finlay Jacques C. , Power Mary E. , Cabana Gilbert
Published: May 2010

We used variation in algal d13C between river habitats to study the spatial scale of energy flow through river food webs. We found a strong negative relationship between herbivore d13C (which reflects algal d13C) and water velocity in three productive Northern California rivers but not in unproductive streams. The contrast among habitats suggests that water velocity affects algal d13C most strongly when CO2 availability is low relative to photosynthetic rates. Our results help explain the wide variation in published river biota d13C and show that past studies using carbon isotope analyses may have significantly underestimated the importance of algal‐derived carbon to river food webs. While flow‐related variation in d13C complicates this common application of carbon isotope analysis, we show that it provides a natural tracer of the flux of algal production derived from different habitats within rivers to higher trophic levels. Measurements of consumer d13C showed that most invertebrate and vertebrate consumers relied on local production, except for filter‐feeding insects and steelhead trout, which relied on production derived from multiple sources. Stable carbon isotopes may thus be used to spatially delineate the habitats that support river food webs, providing previously unavailable information for understanding and managing river ecosystems.
Long‐term dynamics of algal and invertebrate communities in a small, fluctuating tropical soda lake
Authors: Verschuren Dirk , Cocquyt Christine , Tibby John , Roberts C. Neil , Leavitt Peter R.
Published: May 2010

Lake Sonachi, Kenya, is a small alkaline‐saline crater lake that over the past 175 years has experienced considerable fluctuations in lake depth (Zmax = 3–18 m) and an alternation of meromictic and holomictic episodes lasting from a few years to several decades. Paleolimnological methods were used to reconstruct the long‐term dynamics of algal and invertebrate communities in Lake Sonachi in relation to the historical evolution of their physical and chemical environment. Multivariate statistical analysis revealed only weak correlation between the stratigraphic distributions of fossil algal pigments, diatoms, and chironomid larvae in 210Pb‐dated sediment cores and the documented or reconstructed variation in lake depth, mixing regime, and surface‐water conductivity. The eventful biological history of Lake Sonachi exemplifies the complexity of long‐term community dynamics in tropical African soda lakes and reveals how phytoplankton community structure can exert direct control on benthic and planktonic invertebrate communities. The modest phytoplankton abundance and photosynthetic activity of Lake Sonachi when compared with other tropical African soda lakes represent recent lake conditions, resulting from a dramatic decline of filamentous cyanobacteria (e.g., Spirulina platensis) between the 1930s and 1970s and incomplete replacement by the small coccoid cyanobacteria (e.g., Synechococcus bacillaris), which are dominant today. This reduction in algal biomass favored benthic and planktonic invertebrates by reducing the prevalence of complete water‐column anoxia associated with intense nighttime respiration of cyanobacterial blooms. Anoxia‐intolerant halobiont chironomids expanded during an episode of low lake level (Zmax < 4 m), holomixis, and high conductivity (>9,000 µS cm−1) in the late 1940s and 1950s, whereas they had failed to do so under similar conditions in the late 19th century when algal abundance was high. Planktonic cladocerans developed high population densities only during two short meromictic phases in the 1970s when conductivity was modest (3,000–6,000 µS cm−1) and algal abundance was low. The decline of filamentous cyanobacteria also increased water‐column transparency but apparently did not increase benthic diatom abundance.
Depth selection behavior, fish kairomones, and the life histories of Daphnia hyalina × galeata hybrid clones
Authors: De Meester Luc , Weider Lawrence J.
Published: May 2010

We studied life‐history characteristics of 22 genetically distinct Daphnia hyalina 3 galeata clonal lineages isolated from samples taken at different depths in the Schöhsee Lake (Germany) in the presence and absence of fish kairomones. Substantial genetic variability was observed for all traits investigated. The presence of fish kairomones had a significant effect on all traits except relative length of the tail spine and age at maturity. All genotypes (clones) had a significantly smaller size at maturity and produced smaller offspring in the presence of fish kairomones, an observation that is consistent with the hypothesis of an adaptive response. Overall, reproductive output was less for fish‐induced animals, but the effect was relatively small for the size of the first clutch and for the intrinsic rate of increase compared to the differences observed for size of the second and subsequent clutches. Adult body size was related to habitat selection behavior. Clones established from animals that were caught in the epilimnion during the day and early in the evening (termed “risk‐tolerant” [RT] depth selection behavior) were found to be smaller, both in the absence and presence of fish kairomones, than clones isolated from the hypolimnion (termed “risk‐averse” [RA] depth selection behavior). This relationship suggests a coadaptation between size‐related life‐history traits and habitat selection (depth selection) in zooplankton. There were no significant differences in the shifts in life‐history characteristics between clones exhibiting RT and RA depth selection behavior in response to the presence of fish kairomones.
Short‐term responses of coral reef microphytobenthic communities to inorganic nutrient loading
Authors: Dizon Romeo M. , Yap Helen T.
Published: May 2010

The responses of coral reef flat microphytobenthos to short‐term exposure to elevated levels of inorganic nitrogen (N) and phosphorus (P) were investigated in 1994 and 1995. Sand samples collected from the reef flat were maintained over 7 d in triplicate cultures with N‐enriched (100 µM NO3), P‐enriched (10 µM PO4), and ambient seawater. A fourth experiment used a treatment of combined N and P enrichment. The sediment samples were assessed for chlorophyll a (Chl a) content and photosynthesis‐irradiance (P‐I) responses. P‐I curves, constructed from area‐and Chl a‐specific metabolic rates, showed consistently higher maximal rates in the nutrient enriched samples. Sediments exposed to enhanced levels of N exhibited the highest Chl a content while both N‐ and P‐enriched samples showed increased photosynthetic yield. Very little depletion of nutrients in the water column was detected over time in the batch cultures except in the N:P‐enriched treatments where nutrient values dropped to near‐ambient levels. Results from these experiments point to N and P colimitation in tropical carbonate sediments.
Density‐induced water circulations in atoll coral reefs: A numerical study
Authors: Leclerc A.‐M. , Jean‐Baptiste P. , Texier D. , Broc D.
Published: May 2010

Groundwater flow in an idealized atoll platform is simulated with CASTEM 2000, a computer code developed at the CEA (Commissariat À lÂEnergie Atomique). Darcy's law and a coupled solute transport equation (diffusion‐dispersion‐convection) is solved by the mixed‐hybrid finite element method. Inward and upward circulations of oceanic water are shown to occur. These steady state circulations result from temperature and, to a lesser extent, salinity gradients. Inclusion of a karstified dolomitic horizon, observed at the base of the carbonate structure of certain atolls, is necessary to account for the negative vertical temperature gradient indicated by field data. The position of the platform in relation to the oceanic temperature and salinity distributions exerts a significant control on the interstitial hydraulic regime. The effect of a secondary karstic layer closer to sea surface is also modeled. In this case, calculations show that the near‐surface carbonate edifice is deprived of a significant portion of the flow. Finally, an upper limit on the possible flow rate through the platform is calculated. This upper estimate is shown to be independent of the possible uncertainties on the hydraulic conductivity of the system. Corresponding upper limits on the nutrient fluxes of PO43− and NO3− are evaluated. A comparison with current import and export data for the surface ecosystem indicates that in every case, nutrient fluxes hardly reach a few percent of the exports. Therefore, the deep oceanic nutrient pool brought to the surface by thermally driven interstitial circulation is only a minor nutrient source for the reef ecosystem.
Molecular weight distribution of proteinaceous material in Long Island Sound sediments
Authors: Pantoja Silvio , Lee Cindy
Published: May 2010

Proteinaceous material usually accounts for much of the total nitrogen and organic carbon in marine sediments. Thus, decomposition of protein is frequently investigated as a measure of labile organic matter turnover. The fraction of protein that escapes remineralization to CO2 undergoes transformations that may reflect pathways of preservation in sedimentary environments. We analyzed the molecular weight distribution of sedimentary proteinaceous material extracted with NaOH and evaluated the results in terms of diagenetic changes experienced by this pool. Total protein concentrations were determined in Long Island Sound sediments as total hydrolyzed amino acids (THAA), the sum of concentrations of individual amino acids measured after acid hydrolysis. Although the total fraction of THAA extracted by NaOH decreases slightly downcore, from 55% to 40%, the molecular size of that THAA increases. Proteinaceous material >100 kD increases in relative importance with depth and age of sediment, reaching 70% of the total THAA pool at 3 m depth, or roughly 1,000 yr of sediment accumulation. The fraction of THAA between 10 and 100 kD decreased from 25% to 5% of the total over this depth. The relative abundance of the peptide‐size fraction (<3 kD) remained essentially unchanged. The processes of bacterial production, selective adsorption, geo‐polymerization, and selective preservation were explored to explain these changes.
Dimension effects of enclosures on ecological processes in pelagic systems
Authors: Mine Berg Gry , Glibert Patricia M. , Chen Chung‐Chi
Published: May 2010

Several characteristics inherent to experimental ecosystems were examined for their influence on ecological processes in five cylindrical indoor benthic‐pelagic enclosures of different size and shape. Ecosystem development diverged significantly among the mesocosm dimensions even though environmental parameters such as surface photosynthetically available radiation (400–700 nm), turbulence intensity, water exchange rate, and nutrient input were held constant across systems. Here we show that factors that lead to the development of different plankton assemblages can be related to mesocosm geometry. The ratio of light‐receiving surface area‐to‐water column volume (As:V) was shown to control both the rate of NO3− consumption and gross primary productivity. The attenuation of water column irradiance was positively correlated with the wall area‐to‐volume ratio (Aw:V). This was manifested in greater light attenuation in systems with a high Aw:V ratio. In addition, notably greater microalgal biomass developed on the walls in systems with a high Aw:V ratio. Finally, the total surface area‐to‐volume ratio (At:V) of the mesocosms influenced the rate of energy gain and dissipation and water column temperature. The differences in temperature among dimensions possibly affected biological parameters such as bacterial biomass. Although the influence of area‐to‐volume effects on biological components in artificial systems may be substantial, our analysis indicates that some of these effects may be predictable and that future experiments can be explicitly designed to minimize artifacts of enclosure.
In situ habitat selection by settling larvae of marine soft‐sediment invertebrates
Authors: Snelgrove Paul V. R. , Grassle Judith P. , Grassle J. Frederick , Petrecca Rosemarie F. , Ma Hongguang
Published: May 2010

To test whether larval selectivity at settlement contributes to distributional patterns of benthic infauna, we conducted three reciprocal sediment transplant experiments at 15‐m‐deep coarse‐sand and muddy‐sand sites (∼3 km apart) on the continental shelf near Tuckerton, New Jersey. During 3‐ to 5‐d deployments in 1994, larvae of the surfclam, Spisula solidissima, selected coarse sand over muddy sand, and capitellid polychaetes selected muddy sand over coarse sand, regardless of site. Thus, larvae of both taxa selected sediments typical of adult habitats, displaying selectivity consistent with previous flume experiments. Settlement intensity changed significantly over the ∼6‐week period during which experiments were conducted. Several other taxa exhibited selectivity consistent with field distributions, and several were nonselective. Significant site differences in settlement intensity were also observed on some dates for several taxa. Plankton pump samples taken at the sites during tray experiments suggested that significant differences in supply of surfclam larvae over the 3‐km scale contributed to between‐site differences in settlement. In the later experiments, surfclams in experimental trays were larger than would be expected for recent settlers, suggesting that postsettlement migration and selectivity occurred on small scales. These experiments demonstrate that differences in larval supply over scales of kilometers and time scales of weeks can affect settlement intensity but that habitat selection by settling larvae of some species of soft‐sediment invertebrates may set initial distribution patterns.
Volatile bromocarbons produced by Falkenbergia stages of Asparagopsis spp. (Rhodophyta)
Authors: Marshall Rhoda A. , Harper David B. , McRoberts W. Colin , Dring Matthew J.
Published: May 2010

Volatile halocarbons released by 12 Falkenbergia phase isolates of Asparagopsis taxiformis and Asparagopsis armata collected from widely scattered geographical locations were identified using a purge and trap technique and gas chro‐matography/mass spectrometry. Production of the compounds under normal and high irradiance was quantified where possible. Bromoform (CHBr3), dibromomethane (CH2Br2), 1,2‐di‐bromoethylene (C2H2Br2), dibromochloromethane (CHBr2Cl), and tribromoethylene (C2HBr3) were identified as algal products. C2H2Br2 and C2HBr3 have not previously been recorded as natural products. Considerable qualitative and quantitative differences existed between isolates in the halocarbons released. The rates of CHBr3 and C2H2Br2 production were negatively correlated. Increased irradiance invariably resulted in higher rates of release of halocarbons. Initial rates of production ranged between <8 and 866 ng g−1 fresh weight (FW) h−1 for CHBr3, <3 and 59 ng g−1 FW h−1 for CH2Br2, and <0.4 and 17 ng g−1 FW h−1 for C2H2Br2.
Fish or jellies—a question of visibility?
Authors: Eiane Ketil , Aksnes Dag L. , BagØien Espen , Kaartvedt Stein
Published: May 2010

Light is an important limiting factor for the visual foraging process in fishes, and the light regime may potentially affect the competition between visual and tactile predators. We investigated two equal‐sized fjords of quite different pelagic food web structure. Earlier studies have revealed that the jellyfish Periphylla periphylla dominates Lurefjorden, while fish predators dominate in the other fjord, Masfjorden. Furthermore, the mesozooplankton stock of Lurefjorden is larger in both total biomass and size of the individuals. Hence, earlier hypotheses linking the competitive advantage of tactile gelatinous plankton predators to smaller sized mesozooplankton communities are unable to explain the present phenomenon. To see if the difference in the pelagic biota of the two fjords could be associated with characteristics of the light regime, we measured the light absorbance in the basin water of the two fjords. We found that, due to a slightly stronger influence of coastal water in the basin water of Lurefjorden, the exponential light absorbance coefficient below 100 m is two to three times higher there than in other fjords. This results in a reduction in light flux of several orders of magnitude, effectively reducing the possibility of visual foraging. The tactile mode of predation in jellyfish, however, is not influenced, and we hypothesize that the visibility regime has a decisive role in structuring the pelagic food webs of the two fjords.
Mesozooplankton influences on the microbial food web: Direct and indirect trophic interactions in the oligotrophic open ocean
Authors: Calbet Albert , Landry Michael R.
Published: May 2010

The phytoplankton in warm oligotrophic regions of the open oceans is dominated by <2 μm cells too small for efficient direct consumption by mesozooplankton. However, these primary producers are hypothetically linked to higher trophic levels via the cascading impacts of mesozooplankton grazing on intermediate consumers. To assess the magnitudes of these indirect trophic linkages, grazing experiments, involving different concentration treatments of the mixed mesozooplankton community, were performed during cruises in the subtropical North Pacific at station ALOHA. Mesozooplankton fed on a diverse assemblage of microzooplankton and nanoheterotrophs <5 μm, and their predation indirectly enhanced net growth rates of phytoplankton and 2–5 μm heterotrophs. Increasing the concentration of mesozooplankton also enhanced growth rates of heterotrophic bacteria, but this was more likely the result of organic enrichment than trophic transfer. Scaled to their natural abundance, the indirect grazing impacts of mesozooplankton on lower trophic levels are small, accounting for <0.005 d‐1 of the growth rates of each prey category examined. Thus, the larger consumers appear to exert little net influence on the dynamics at the base of the food web. In contrast, size‐fraction manipulations of consumers between 2 and 20 μm (i.e., the nanozooplankton) elicited strong responses among bacterial populations indicative of tightly coupled predatory chain of at least two steps. Given the present results, detailed studies of the interactions among pico‐ and nanoplankton appear to be the most profitable avenue for improving our understanding of community structure and function in this region and for acquiring useful data for developing and validating ecosystem models of the open oceans.
Intercontinental allozyme differentiation among four holarctic Daphnia species
Authors: Černý Martin , Hebert Paul D. N.
Published: May 2010

The species overlap between European and North American cladoceran faunas has been questioned from the very beginning of faunistic studies on Nearctic zooplankton and still remains unsettled. However, more recently, genetic techniques seem to overcome the limits of morphology as the basis for taxonomy. We analyzed 8–11 allozyme loci to assess the genetic differentiation between intercontinental counterparts of four daphniids: Daphnia curvirostris, Daphnia obtusa, Daphnia pulex, and Daphnia pulicaria. Despite their morphological likeness, all equivalents showed a large amount of genetic divergence between continents due to complete allelic substitutions and major gene frequency shifts. From an evolutionary perspective, this study shows that as in other organisms, geographic isolation seems to be sufficient to minimize gene flow to levels at which the origin of new daphniid species can be considered. From a practical point of view, a revision of Holarctic daphniid taxonomy should be considered.
A tank system for studying benthic aquatic organisms at predictable levels of turbidity and sedimentation: Case study examining coral growth
Authors: Anthony Kenneth R. N.
Published: May 2010

A tank system is described for long‐term exposure of sessile organisms to well‐defined ranges of particle loads on a background of natural flowing seawater. Using low technology and a simple mathematical model, the concentration of suspended particulate matter (SPM) and the rate of sedimentation could be predicted and sustained with high precision. The system and operational procedures were tested in an 8‐week experiment investigating the effect of SPM concentrations on the growth rates of two species of symbiotic scleractinian coral (Goniastrea retiformis and Porites cylindrica). To also evaluate the effect of shading by SPM on coral growth, two light levels corre‐sponding to 3–4‐m depth at the low and high particle concentrations were included in the design. The growth rates of corals in control tanks were not significantly different from those of conspecifics in situ. However, the patterns of growth rates vs. SPM and shading treatments differed between species. The growth rates of G. retiformis generally increased as a function of SPM concentration (range = ∼1–16 mg L−1), whereas the growth rates of P. cylindrica were unaffected by particle load. The shading effects corresponding to 16 mg SPM L−1 at 3–4‐m depth resulted in significantly reduced growth rates in both species. I hypothesize that the different growth patterns displayed by the two species are the results of different abilities to utilize SPM as a food source or different susceptibilities to SPM as a mechanical stress factor. The high level of environmental control and the constancy of SPM treatment levels were reflected in the absence of tank effects on growth rates and provided sufficient statistical power to detect relatively small differences in growth rates between corals from different treatments.