Limnology and Oceanography
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The short‐term fate of fresh algal carbon in continental slope sediments Emplacement of a tracer mixture containing 13 C‐labeled green algae on the sea floor of the continental slope offshore of Cape Hatteras, North Carolina, elicited a rapid response over 1.5 d from the dense benthic community. Certain deposit‐feeding annelids (e.g. Scalibregma inflatum and Aricidea quadrilobata ) became heavily labeled with 13 C as a result of ingestion of the algae. “C‐labeled organic matter was transported to a depth of at least 4–5 cm into the seabed during the 1.5‐d period, presumably as a consequence of a feeding‐associated activity. Nonlocal transport produced subsurface peaks in organic 13 C at 2–3 cm. Dissolved inorganic 13 C, produced by the oxidation of the labeled algae, penetrated to 10‐cm depth. The transport of highly reactive organic matter from the sediment surface at initial velocities ≥3 cm d‒1 is expected to be an important control of subsurface benthic processes in slope environments characterized by abundant macrofaunal populations. Anaerobic processes, which are enhanced on the Cape Hatteras slope relative to adjacent areas, may be promoted by the rapid injection of reactive material into subsurface sediments. The transport, in turn, is a consequence of the dense infaunal populations that are supported by the rapid deposition of organic carbon in this region.
Limnology and Oceanography - Tập 41 Số 6 - Trang 1208-1219 - 1996
Bacterial exopolymer utilization by a harpacticoid copepod: A methodology and results Exopolymer mucus secretions of bacteria and diatoms are potential foods for benthic animals. These secretions are coincidently ingested by animals during consumption of microbial cells and sediments. The utilization of microbial secretions was investigated with exopolymer derived from a marine bacterium (Pseudomonas sp.) from seagrass beds and a harpacticoid copepod Laophonte sp. from the same habitat. A new technique was developed to examine ingestion, absorption, and absorption efficiencies of these bacterial secretions by consumers. Exopolymer mucus (from the bacterium in stationary phase) was labeled with 14 C, collected, purified, and bound onto bacterium‐sized beads. The exopolymer slime coating mimicked the coatings associated with many marine bacteria. Results from feeding experiments where the coated beads were mixed with sediment demonstrated that the mucus‐exopolymer secretions of bacteria were ingested and utilized by Laophonte sp. Absorption efficiencies, determined directly, were > 80% in the presence of other food resources, indicating that the exopolymer is potentially a highly labile C resource for this animal.
Limnology and Oceanography - Tập 35 Số 5 - Trang 1039-1049 - 1990
An investigation ofhydrogen peroxide chemistry in surface waters of Vineyard Sound with H218O2 and 18O2 18 O‐labeled H2 O2 and O2 have been used to determine absolute rates and pathways of peroxide formation and decay processes in surface waters of a coastal marine site. Reactions were followed by incubating seawater samples with 1 8 2 or H2 18 O2 and following the chemical transformation of the isotope label.Decomposition of H2 18 O2 was dominated by biological processes and led to the formation of 18 O2 and H2 18 O; the product distribution indicates that 65–80% of the decay was due to catalase with 20–35% due to peroxidase activity. Photochemical oxidation of H2 18 O2 to 18 O2 was also observed. Particle‐dependent, light‐independent peroxide production was also observed in freshly collected samples, with rates ranging from 0.8 to 2.4 nM h−1 . These rates are low relative to photochemical production rates in surface waters, but may be important under conditions of low light intensity. Experiments with a metabolic inhibitor suggest that at least some of this production was biologically mediated. However, there was no evidence for light‐dependent biological production.
Limnology and Oceanography - Tập 35 Số 6 - Trang 1221-1229 - 1990
Hydrogen peroxide production by a marine phytoplankter1 Hymenomonas carterae , a calcified marine phytoplankter, produces hydrogen peroxide extracellularly. Hydrogen peroxide production by a washed cell suspension occurs in the dark and is inhibited by cell‐impermeable protein modification reagents. A cell‐surface redox enzyme is thus likely responsible for production of H2 O2 . The physiological function of this potentially toxic compound is unknown. If the production rate of 1–2 × 10−14 mol cell−1 h−1 measured in cultures of H. carterae could be generalized, marine phytoplankton would be an important source of the hydrogen peroxide found in the marine environment.
Limnology and Oceanography - Tập 32 Số 6 - Trang 1365-1369 - 1987
Critical depth and critical turbulence: Two different mechanisms for the development of phytoplankton blooms A turbulent diffusion model shows that there are two different mechanisms for the development of phytoplankton blooms. One of these mechanisms works in well‐mixed environments and corresponds to the classical critical depth theory. The other mechanism is based on the rate of turbulent mixing. If turbulent mixing is less than a critical turbulence, phytoplankton growth rates exceed the vertical mixing rates, and a bloom develops irrespective of the depth of the upper water layer. These results demonstrate that phytoplankton blooms can develop in the absence of vertical water‐column stratification.
Limnology and Oceanography - Tập 44 Số 7 - Trang 1781-1787 - 1999
Transitions between <i>Auhcoseira</i> and <i>Anabaena</i> dominance in a turbid river weir pool The transitions between the diatoms Aulacoseira spp. (Melosira ) and the cyanobacteria Anabaena spp. as dominant phytoplankton species in a turbid‐river weir pool are shown to depend directly on the establishment or destruction of persistent thermal stratification. A transition from high to low flow through the pool resulted in the establishment of persistent thermal stratification, causing Aulacoseira to sink out of the euphotic zone at a speed of 0.95 m d−1 . Concurrently, the slightly buoyant Anabaena grew within the euphotic zone with a specific growth rate of 0.37 d−1 , climaxing after approximately 14 d at a population of 20,000–30,000 cells ml−1 , at which point its biomass may have been limited by the availability of phosphorus. The stratification thus caused the phytoplankton population to separate into two distinct layers, with Anabaena occupying the illuminated surface layer and Aulacoseira found only in the lower layer below the euphotic depth. Under stratified conditions, the ratio of the surface layer depth to euphotic depth, z sl :z eu , was approximately 1, whereas for a mixed water column that ratio was >3. Access to light appeared to be the main factor determining the dominant phytoplankton species.
Limnology and Oceanography - Tập 43 Số 8 - Trang 1902-1915 - 1998
Primary Production in Flowing Waters1 Respiration, photosynthetic production, and diffusion interact to produce the daily curve of oxygen change in a segment of flowing water. Conversely, the observed curves of oxygen in streams can be used to calculate the component rates of production, respiration, and diffusion. New production values obtained with these analyses of oxygen curves from various sources, as well as a few previously existing estimates of primary production, indicate a generally higher rate of production in flowing waters than in other types of aquatic environments. The ratio of total primary production to total community respiration is used to classify communities quantitatively according to their predominantly heterotrophic or autotrophic characteristics. Longitudinal succession within a stream tends to modify the ratio towards unity from higher values for autotrophic and from lower values for heterotrophic communities. The behavior of this ratio is described for the annual cycle in a stream, for the sequence of pollution recovery, and for diverse types of communities.
Limnology and Oceanography - Tập 1 Số 2 - Trang 102-117 - 1956
Enhancement of new production in the northeast subarctic Pacific Ocean during negative North Pacific index events We examined interannual variability in the 1965–1990 winter‐summer differences in surface nitrate (ΔNO3 ) in the northeast subarctic Pacific Ocean (Station P, 50°N, 145°W). Increases in ΔNO3 , of 30–70% above the mean value occurred during four events (1969, 1971‐1972, 1979, 1983). The ΔNO3 time series was highly correlated (r = 0.86) with the spring‐summer nitrate utilization rate from 1970 to 1980. The ΔNO3 time series was negatively correlated with the North Pacific index (NPI) (r = ‐0.72) and positively correlated with solar radiation in the spring (r = 0.48) and summer (r = 0.46). A simple ecosystem model forced with observed incident solar radiation and mixed‐layer depth during the spring‐summer period predicted increases in export production that were 50% of the observed increase for 1970–1972 and 1977–1979. Comparison between the ΔNO3 and sedimenting particulate organic nitrogen (PON) showed that the high ΔNO3 event of 1983 was associated with a dramatic increase in PON fluxes. A simple ecosystem model underpredicts observed interannual variations in export production, and this result combined with the observed PON fluxes suggests that a combination of increased phytoplankton production and increased f ratio produced the observed increase in ΔNO3 . The increase in f ‐ratio implies a change in the community structure of the phytoplankton during the elevated ΔNO3 events that appears connected to changes in the NPI.
Limnology and Oceanography - Tập 43 Số 7 - Trang 1418-1426 - 1998
UPTAKE OF AMINO ACIDS BY MARINE INVERTEBRATES1 The capacity for removal of amino acids from solution by marine animals was studied by following the concentration of an acid added to the ambient sea water. Thirty‐five genera representing 11 phyla were examined. The representatives of 10 of the phyla removed significant quantities of glycine from solution during an observation period of from 16 to 24 hr. This capacity for uptake of glycine was not limited to filter‐feeding animals. Observations using representatives of 3 phyla and various amino acids indicated that uptake could occur whether the acid concerned behaved as a cation or an anion at the pH of sea water. Comparison of the amino acid concentrations at the incurrent and excurrent siphons of the clam, Spisula , indicated that removal of glycine took place in the mantle cavity of this animal. Differences as great as 14% were observed. Disappearance of glycine at ambient concentrations as low as 1.5 mg/L could be demonstrated.
Limnology and Oceanography - Tập 6 Số 2 - Trang 175-181 - 1961
Essential fatty acids in the planktonic food web and their ecological role for higher trophic levels We measured concentrations of essential fatty acids (EFAs) in four size categories of planktonic organisms— seston (10–64 µm), microzooplankton (100–200 µm), mesozooplankton (200–500 µm), and macrozooplankton (≫500 230m)—and in rainbow trout (Oncorhynchus mykiss ) in coastal lakes. Size‐dependent patterns in concentrations of specific fatty acids (FAs) are important for ecosystem function, because planktivorous fish and some invertebrates are size‐selective predators. We demonstrate that the retention of individual FAs differs among the four size categories of planktonic organisms in our study systems. Changes in individual EFA concentrations within the planktonic food web were similar in all coastal lakes sampled, which indicates the generality of our findings. Although concentrations of arachidonic acid, eicosapentaenoic acid (EPA), and linoleic acid increased steadily with plankton size, the concentration of a ‐linolenic acid decreased slightly in larger size fractions of zooplankton. Concentrations of another EFA, docosahexaenoic acid (DHA), declined sharply from mesozooplankton to the cladoceran‐dominated macrozooplankton size class. Our results indicate that the retention of EFAs, as a function of plankton size, is related, in part, to the taxonomic composition of planktonic food webs. We suggest that, in general, zooplankton exhibit an EPA‐retentive metabolism with increasing body size, whereas different taxonomic groups within the planktonic food web retain DHA differently. Finally, we conclude that EPA is highly retained in zooplankton, whereas in rainbow trout DHA is highly retained.
Limnology and Oceanography - Tập 49 Số 5 - Trang 1784-1793 - 2004
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