Showing papers in "Limnology and Oceanography in 1985"

Diffusive boundary layers and the oxygen uptake of sediments and detritus1

Abstract: The thickness of diffusive boundary layers and their role for the oxygen uptake of sediments and detritus were studied by the use of microelectrodes. Gradients of oxygen were always detectable within the boundary layer, which varied in thickness from 0.2 mm to > 1 mm. The thickness depended on the flow velocity of the water and on the roughness of the solid surface. Oxygen diffused through the boundary layer with a mean diffusion time of 1.2-9 min. The diffusive boundary layer constituted a transfer resistance for oxygen flux across the solid-water interface which limited the oxygen flux at high uptake rates. Sediments or detritus exposed to aerated water could therefore be almost anoxic at the surface, provided that they had sufficiently high rates of oxygen uptake. This can explain the occurrence of microaerophilic or anaerobic bacteria on exposed sediments where fully oxic conditions would intuitively have been expected.

Anaerobic methane oxidation rates at the sulfate‐methane transition in marine sediments from Kattegat and Skagerrak (Denmark)

Abstract: Concomitant radiotracer measurements were made of in situ rates of sulfate reduction and anaerobic methane oxidation in 2-3-m-long sediment cores. Methane accumulated to high concentrations (> 1 mM CH/sub 4/) only below the sulfate zone, at 1 m or deeper in the sediment. Sulfate reduction showed a broad maximum below the sediment surface and a smaller, narrow maximum at the sulfate-methane transition. Methane oxidation was low (0.002-0.1 nmol CH/sub 4/ cm/sup -3/ d/sup -1/) throughout the sulfate zone and showed a sharp maximum at the sulfate-methane transition, coinciding with the sulfate reduction maximum. Total anaerobic methane oxidation at two stations was 0.83 and 1.16 mmol CH/sub 4/ m/sup -2/ d/sup -1/, of which 96% was confined to the sulfate-methane transition. All the methane that was calculated to diffuse up into the sulfate-methane transition was oxidized in this zone. The methane oxidation was equivalent to 10% of the electron donor requirement for the total measured sulfate reduction. A third station showed high sulfate concentrations at all depths sampled and the total methane oxidation was only 0.013 mmol m/sup -2/ d/sup -1/. From direct measurements of rates, concentration gradients, and diffusion coefficients, simple calculations were made of sulfate and methane fluxes andmore » of methane production rates.« less

Comparison between steady state and non-steady state competition: experiments with natural phytoplankton

Abstract: Chemostat competition experiments with natural phytoplankton communities are compared to experiments in which either one (phosphorus) or two (phosphorus and silicon) key nutrients were added discontinuously at l-week intervals. In all types of experiments wide ranges of Si:P ratios were tested. Deviation from steady state was found not only to increase the number of coexisting species, but also to shift the regions of dominance of species and of higher taxa along the gradient of Si:P ratios. Pulsed nutrient addition was mainly to the advantage of green algae and to the disadvantage of diatoms.

Growth‐irradiance relationships in phytoplankton1

Abstract: The steady state growth rates of three species of marine phytoplankton, Thalassiosira weisflogii, Isochrysis galbana, and Prorocentrum micans, were followed in turbidostat culture. At each growth irradiance, photosynthesis and respiration were measured by following changes in oxygen. Together with measurements of optical absorption cross sections, cellular chlorophyll, carbon and nitrogen, and excretion rates as well as knowledge of the quantum flux, the quantum requirement for growth and photosynthesis were calculated. Our results suggest that variations in growth rate caused by changes in irradiance may be related to changes in respiration rates relative to growth as well as changes in optical absorption cross sections for a given species. Interspecific differences in growth rate at a given irradiance are not related to changes in respiration however, but are primarily attributable to differences in optical absorption cross sections normalized to chlorophyll and differences in chlorophyll:carbon ratios.

Biosynthesis of dimethylsulfide and dimethylpropiothetin by Hymenomonas carterae in relation to sulfur source and salinity variations

Abstract: The marine coccolithophorid phytoplankton species Hymenomonas carterae (class Prymnesiophyceae) produces both dimethylpropiothetin (DMPT) and dimethylsulfide (DMS) in axenic cultures. The rate of DMS production is closely regulated by the cell; it remains independent of environmental sulfate concentration down to levels of 2.5% of the seawater value. Below this sulfate level, DMS production decreases with decreasing sulfate concentration, but significant amounts of DMS are released even under conditions of sulfate-limited growth. Hymenomonas carterae can grow on sulfite, thiosulfate, and cysteine as sulfur sources, but not on methionine. The rate of DMS output is similar for the different sulfur sources. Both the intracellular concentration of DMPT and the rate of output of DMS by H. carterae increase with increasing salinity of the medium. This increase is observed when either salt or sucrose is used to control the osmolarity of the growth medium. Variations in DMPT levels and DMS output were observed within hours after transferring cells to a medium of different osmotic pressure. The intracellular DMPT concentration is of the order of 0.3 mole per liter and contributes significantly to the osmotic pressure in the cell. These results suggest that DMPT plays an important role in osmoregulation by H. carterae.

234Th:238U disequilibria within the California Current1

Abstract: Profiles of dissolved and particulate /sup 234/Th were determined at several stations within the California Current. Modeling of the disequilibria between the /sup 234/Th and /sup 238/U within the surface waters provides for estimates of the residence time of dissolved thorium with respect to particle scavenging, the particle residence time, and the particulate /sup 234/Th flux exiting the surface layer. The model-derived, first-order scavenging rate constant for dissolved thorium is observed to be proportional to the rate of primary production. Particle residence times seem to be governed by the rate of zooplankton grazing and the types of zooplankton present. Model-derived particulate /sup 234/Th fluxes are in good agreement with direct measurements by sediment traps.

Chlorophyll budgets: Zooplankton grazing and phytoplankton growth in a temperate fjord and the Central Pacific Gyres1

Abstract: The processes controlling the daily production and fate of phytoplankton pigments were evaluated in a moderately productive fjord (Dabob Bay, Washington) and the oligotrophic open ocean (North and South Central Pacific Gyres). The processes included phytoplankton growth, macrozooplankton grazing, microzooplankton grazing, the downward vertical flux of pheopigments, photodegradation, dark degradation, cell sinking, cell senescence, and physical mixing. A model was constructed describing the dynamic budget of chlorophyll and pheopigments within the euphotic zone. The model provides estimates of phytoplankton growth, macrozooplankton grazing, and microzooplankton grazing based on field measurements of the vertical distribution of pigments, the vertical flux of pigments out of the euphotic zone, and the flux of solar radiation through the water column. The pigment-specific rates (d−1) provided by the model are derived in situ without manipulation of either the phytoplankton or zooplankton, and the experiments are largely container-free. Growth rates, averaged over the whole euphotic zone, varied seasonally in Dabob Bay (0.05–0.9 d−1) and ca. 67% of the total daily grazing rate was due to macrozooplankton herbivores. Phytoplankton growth rates, averaged over the whole euphotic zone, were ca. 0.2 d−1 in the oceanic gyres, regardless of season or location, and ca. 95% of daily grazing was due to microzooplankton herbivores. The model suggests that grazing and growth are in balance.

The distribution and abundance of phototrophic ultraplankton in the North Atlantic1,2

Abstract: We compared the vertical distribution and abundances of procaryotic chroococcoid cyanobacteria (Synechococcus) and eucaryotic phototrophic ultraplankton at 50 stations in the North Atlantic. At 34 of these stations, cells were also separated by filter-size fractionation, permitting comparison of the distribution of size classes with the distribution of pigment types. Both eucaryotic ultraplankton and cyanobacteria have subsurface numerical maxima. In vertically stable water, cyanobacterial abundance peaks at about the 1% light level and that of the eucaryotic ultraplankton at about the 0.5% light level. Cyanobacterial abundance decreases with northerly increasing latitude, and this decrease correlates with decreasing temperature. The eucaryotic assemblage is numerically dominated by the ultraplankton. The numbers of the ultraplankton generally range one order of magnitude less than the cyanobacteria, but they may equal or exceed cyanobacteria at depth and in northerly latitudes.

Molybdenum in the Northeast Pacific Ocean1

Abstract: The concentration of dissolved molybdenum has been determined in several profiles from the Northeast Pacific Ocean. The salinity-normalized concentration is essentially constant in all open-ocean samples (107 nM, 1σ = 2.5 nM). The dissolved distribution is not significantly affected by biological cycling.

Grazing, respiration, excretion, and growth rates of tintinnids1

Abstract: Clearance, ingestion, and growth rates of two coastal tintinnid ciliates were measured in batch culture as a function of temperature and phytoplankton concentration. Oxygen consumption and ammonium excretion rates were determined at food concentrations which supported maximum growth rates at each temperature. Clearance, ingestion, respiration, excretion, and growth rates of both species increased with temperature. Clearing rates declined with increasing phytoplankton abundance. Ingestion and growth rates increased asymptotically with phytoplankton abundance and declined at high food concentrations. Gross growth efficiency was highest at phytoplankton concentrations which supported maximum growth rates. Over a range of temperatures, respiration and excretion were linearly related and exhibited significant linear relationships with ingestion and curvilinear relationships with growth. 0 : N ratios were 4-7, assuming an RQ of 1 .O. The metabolic data were combined with previous measurements of in situ production by tintinnids to estimate their potential carbon requirements and NH,+ regeneration in Narragansett Bay, Rhode Island. Tintinnids ingested a carbon equivalent of 16-26% of the total annual net primary production and 32-52% of < IO-urn nanonlankton oroduction. Nitrogen excretion was sufficient to support 1 l18% of net primary production.

Species‐specific rates of growth and grazing loss among freshwater algae1

Abstract: Recent investigations into the population dynamics of phytoplankton communities have emphasized the variabilities of loss rates rather than growth rates in governing the changes that occur. Many freshwater phytoplankton, however, grow at rates that are measurably less than their maximum physiological capability because of nutrient limitation. At any moment the nutrient most limiting in situ division rates varies from species to species within an assemblage and the extents of limitation change with time. Rates of mortality inflicted by herbivorous zooplankton are likewise species-specific, but the size of algal particles is a good predictor of whether the particle will be grazed at all. We manipulated grazer abundances and nutrient concentrations in enclosures to examine the effects on algal net growth rates. Grazed species were usually unicellular organisms. Some colonial species showed increased growth rates in the presence of grazers; in all cases these species were limited by N or P in situ. The variability of algal growth rates was much greater than that of measured loss rates due to grazing. Alternate loss rates, primarily sinking, seem to exhibit variability similar to growth rates in comparisons among all species in the assemblage.

A remote-sensing reflectance model of a red-tide dinoflagellate off west Florida1

Abstract: A mathematical model that simulates the spectral curves of remote-sensing reflectance of blooms of the red-tide dinoflagellate Ptychodiscus brevis is developed. The model is compared to measurements obtained from a low-flying helicopter for P. brevis populations with chlorophyll-like pigment concentrations from 7 to 77 mg m-3 found in the case 2 waters along the west Florida shelf in October 1983. The model simulates the effects of backscattering from water, phytoplankton, and detritus, and the effects of absorption due to water, phytoplankton, detritus, and yellow dissolved matter (“Gelbstoff”) for case 1 and case 2 waters. It can be easily modified to simulate the spectral reflectance of phytoplankton from other pigment color groups. Matching the model spectral curves to measured remote-sensing reflectance curves provides accurate estimates of chlorophyll a plus pheophytin a and also estimates of Gelbstoff and detritus concentrations. Comparison of remote-sensing reflectance data to model reflectance data allows calculation of the quantum efficiency of fluorescence for a given phytoplankton population, which provides a remote measurement of a factor that has been found to increase with the nutrient stress of the population. Most algorithms used extensively in the remote sensing of chlorophyll a plus the associated pheophytin a pigments (henceforth referred to as chlorophyll a) are typically of the spectral ratio type, which are considered valid only for case 1 waters (those for which phytoplankton and their derivative products play a dominant role). Such algorithms are not analytic in nature, and the ratioing process tends to camouflage or merge several distinct effects (see Gordon and Morel 1983). Our approach here is to provide an analytic model describing how various seawater constituents affect remote-sensing reflectance measurements. By matching the model values to the measured values of remotesensing reflectance, we provide estimates of Chl

Migrating haemulid fishes as a source of nutrients and organic matter on coral reefs1

Abstract: Juvenile french and white grunts (Haemulon jlavolineatum and Haemulon plumierl) rest over coral colonies during the day and feed only at night in surrounding seagrass beds. We examined the amount of nitrogen, phosphorus, particulate organic carbon, and calories which these fishes deposited over the coral colonies that were their resting sites. Weight-specific rates of nitrogen excretion by grunts decreased with increasing fish size. Rates of phosphorus excretion were not related to fish size. Excretory products were rich in nitrogen (molar N:P = 48), primarily ammonium, whereas fecal material was richer in phosphorus (N:P = 8). Feces leached over half of their phosphorus content within the first day. Half of the daily excretion and defecation occurred during the first 4 h after grunts returned to the reef, in which time they doubled the amount of NH.,+ available to corals under calm conditions. Seasonal patterns of nutrient and particulate organic carbon (caloric) input to coral colonies varied with grunt biomass on the colony. The maximum input to colonies of Porites jiircata from grunts occurred during August, which coincided with the time of highest coral growth rate. Grunts deposited an average of 164 and 251 mg m-2 d-’ of particulate organic carbon (feces) on the P. furcata and Acropora palmata colonies over which they rested, an energy supplement to the colonies of 0.8 and 1.2 kcal m-2 d-l. Rates of nutrient and organic matter input from grunts are comparable to or greater than rates observed in other naturally or artificially enriched ecosystems.

Polarographic analysis of sulfur species in marine porewaters1

Abstract: We describe a scheme to determine the major sulfur species found in marine porewaters With polarographic techniques, it is possible to measure thiosulfate, sulfite, bisulfide, and polysulfide ions at a mercury electrode Polysulfide ions, SX2--, can be considered to be composed of one sulfur in the 2- oxidation state, S(2-), and the remaining (x - 1) sulfurs in the zero-valent oxidation state, S(0) The number of sulfur atoms in each is measurable Tetrathionate and other polythionates can be measured as well but have not been detected in porewaters studied to date Salt marsh and subtidal porewater profiles contain significant concentrations of thiosulfate, bisulfide, and polysulfide The ratio of S(2-) to S(0) is higher in subtidal porewaters than in salt marsh porewaters and indicates the importance of zero-valent sulfur to the biogeochemical processes prevalent in the salt marsh ecosystem The S(0) concentrations in porewaters from salt marsh sediments are greater than those predicted from equilibrium calculations

A conceptual framework for predicting the occurrence of sediment focusing and sediment redistribution in small lakes

Abstract: Four processes are important in causing either sediment focusing or overestimation of sediment accumulation rates by traps, or both. A simple model to predict the occurrence of these events was constructed from published data for monomictic and polymictic lakes which contained sufficient detail to identify the major redistribution process. Boundaries between the regions where different mechanisms dominate were calculated from the expected mode of operation of the processes. The model was tested using sediment trap and accumulation rate vs. water depth data from the literature. Other published work is in general agreement with the predictions of the model.

Phototrophic sulfur bacteria in two Spanish lakes: Vertical distribution and limiting factors1

Abstract: The anaerobic zones of Lakes Cis6 and Vilar (Banyoles karstic area, NE Spain) had mass developments of purple sulfur bacteria during summer 1982. In Lake Vilar, Chromatium spp. was dominant (up to 92% of the microbial biovolume). In Lake Ciso, the predominant microorganisms were Chromatium spp. (up to 7 1%) and another purple sulfur bacterium forming aggregates (20%). The bacterial layer could be divided according to the physiological state of the cells into a top part of maximal specific activity, a peak of maximal abundance, and a bottom part of inactive cells. The bacteria in the peak were predominantly limited by light; sulfide, phosphate, and acetate were not limiting in the middle of the day. The light limitation started at the depth having the maximal concentration of cells; the top of the layer appeared to be sulfide-limited. Specific contents of photopigments, elemental sulfur, and reserve polymers decreased from the top to the bottom of the bacterial layer. These phenomena point to the crucial role of light in the development of layers of phototrophic bacteria in stratified lakes.

Eutrophication and the rate of denitrification and N20 production in coastal marine sediments

Abstract: Large (13 m/sup 3/, 5 m deep) microcosms with coupled pelagic and benthic components were used to measure the effect of nutrient loading and eutrophication in coastal marine ecosystems on the rates of benthic denitrification (N/sub 2/) and N/sub 2/O production. After 3 months or daily nutrient addition, average denitrification rates ranged from about 300 ..mu..mol N m/sup -2/ h/sup -1/ in the sediments of the control microcosm to 880 in the most enriched microcosm, which received 65 times the nutrient input of the control. Increases in the production of N/sub 2/O were more dramatic and increased by a factor of about 100, from 0.56 ..mu..mol N m/sup -2/ h/sup -1/ in the control to 51 in the most enriched microcosm. Although there was a clear increase in the denitrification rate in the more eutrophic systems, the amount of fixed nitrogen removed was a constant or progressively smaller fraction of the nitrogen input. Even in the most enriched microcosm, at least 16% of the N input was removed by denitrification.

Bacterivory by microheterotrophic flagellates in seawater samples

Abstract: Etude de la consommation bacterienne journaliere des zooflagelles dans un echantillon d'eau de mer. Un nombre de bacteries superieur a environ 10 E ml −1 soutient la croissance des flagelles

Shifts in phytoplankton size structure and community composition during grazing by contrasting zooplankton assemblages

Abstract: Contrasting zooplankton assemblages consistently produced different compositional shifts in a phytoplankton community. Two experiments in 120-liter enclosures were used to assess the responses of the algae to two different-sized zooplankton communities. Grazing by a mixture of small copepods, Bosmina longirostris, and rotifers led to increased growth of phytoplankters with greatest axial linear dimensions < 25 pm and ratios of surface area to volume ~2.6, such as Chlamydomonas and Chlorococcales. Larger phytoplankton taxa such as Asterionellafirmosa, Closteriopsis Iongissimus, and Synedra sp. declined in the presence of small zooplankters. In contrast, a mixture of large zooplankters dominated by Daphnia pulex and Diaptomus oregonensis caused declines in phytoplankters with greatest axial linear dimensions ~60 pm and ratios of surface area to volume ~2.75, while larger algae such as Aphanocapsa and Dinobryon increased. Discriminant analyses showed that volume and surface area were the most effective characters for determining the response of algae to grazers. Zooplankton community structure was important in determining the responses of algal assemblages to-grazing.

Symbiotic photosynthesis in a planktonic foraminiferan, Globigerinoides sacculifer (Brady), studied with microelectrodes1

Abstract: The chemical environment and the symbiotic photosynthesis of the spinose foraminiferan, Globigerinoides sacculifer, from the Gulf of Aqaba, northern Red Sea, were studied with O2 and pH microelectrodes at a resolution of 50-l 00 pm. In the dark, the foraminiferan respiration lowered the 0, concentration at the shell surface to 50% of air saturation, while pH was lowered from the ambient value of 8.23 to 8.15. In the light, the 0, increased to 2.5 times air saturation while pH reached 8.62. These steep chemical gradients were established over a diffusive boundary layer between the spines, which partly separated the animal from the bulk seawater. The 0, pool around the shell was very dynamic, with residence times down to 5 s in the light. Photosynthetic rates were mapped around and within the animal. The compensation light intensity of the symbionthost system was 26-30 PEinst m-2 s-l, while the light saturation intensity, Ik, was 160-170 PEinst m-2 s-l. The action spectrum of symbiont photosynthesis showed peaks at 450 and 670 nm due to chlorophyll a as well as a broad peridinin peak at 500-550 nm. Total respiration of one symbionthost system was 3.0 nmol0, h-l and was not significantly different between dark and light. Gross photosynthesis at light saturation was 18.1 nmol O2 h-l per foraminiferan. The high net photosynthesis showed that the zooxanthellae could theoretically provide all organic carbon required for growth and respiration of the host. Model calculations indicated, however, that the foraminifera were diffusion-limited in the uptake of dissolved nitrogen and phosphorus. The capture of prey was therefore a necessary source of these nutrients, while symbiotic photosynthesis could cover the energy requirements and allow efficient internal recycling of nutrients.

Phosphorus limitation of lotic periphyton growth rates: An intersite comparison using continuous-flow troughs (Thompson River system, British Columbia)1

Abstract: Periphyton growth rates and relative degrees of phosphorus deficiency were compared with onsite, continuous-flow troughs in three parts of the Thompson River system. Soluble reactive phosphorus (SRP) in the lower Thompson, North Thompson, and South Thompson Rivers averaged 3.4, 1.1, and 0.7 pg liter-‘. Several physiological and chemical composition parameters ranked the degree of P deficiency in the rivers in the same sequence as did SRP. Among these were alkaline phosphatase activity, V,,, for 32P043- uptake, and cellular N:organic P, Chl a:ATP, C:ATP, and C:organic P. Specific growth rates (EL) estimated by biomass accrual and by 14C0, uptake usually, but not always, indicated higher p with greater availability of P. However, relative specific growth rates (p:p,,.J consistently reflected the influence of P limitation. As assessed from N:organic P and by application of the Droop and Goldman-Carpenter equations, p:prnax was 0.8-0.9 at the lower Thompson, 0.3-0.6 at the North Thompson, and 0.0-0.3 at the South Thompson sites. Hence, periphyton growth rates in the lower Thompson River were near the maximum set by temperature and light at ambient SRP of only 3-4 pg liter-l. Evidence of P-limited growth rates in the South Thompson and North Thompson Rivers was found at temperatures approaching 0°C.

The fauna associated with drift algae captured with a plankton-mesh purse seine net1

Abstract: A plankton-mesh purse seine used to encircle drift algae in open coastal waters was compared with seines in open water and conventional ichthyoplankton hauls. Densities of small fish and invertebrates were higher in association with drift algae than in open water. Most fish that occurred with drift algae were well pigmented. The fauna of drift algae differed from that of attached algae. Large numbers of epiphytic animals vacated attached algae which were experimentally detached from the substratum. The fauna on drift algae, therefore, is largely the result of colonization from open water. Fish and invertebrates were quickly attracted to clumps of experimental algae that were left to drift. This suggested that drifting algae may quickly influence the distribution of animals in open water. Appreciable quantities of drift algae may influence the survivorship and recruitment processes of species which associate with algae during the planktonic phase of their life cycles. Drift algae are an important source of the material drifting in the surface layers of coastal and oceanic waters. The fish and invertebrates associated with drift algae have been studied in estuaries (Gore et al. 198 1; Kulczycki et al. 198 I), surf beaches (Lenanton et al. 1982), open coastal systems (Mitchell and Hunter 1970), and oceanic waters (Dooley 1972); there is often a positive correlation between the biomass of drift algae and the abundance of these animals in an area. An association between small animals and drift algae in open water is of potential interest to marine biologists; it may also provide plankton workers with an additional set of sampling problems if planktonic organisms that are widely dispersed in surface waters concentrate around drift material. Moreover it is unlikely that such a fauna could be adequately sampled by conventional plankton tows. We here assess the significance of this association by sampling drift material and by estimating the amount of it present in different areas. Our primary interest is the investigation of abundances and developmental patterns of the early life-history stages of teleost fish

Micromethod for lipids in aquatic invertebrates1

Abstract: Microtechniques with disposable, calibrated, capillary pipets were developed to measure amounts and classes of lipids in individual Lake Michigan benthic invertebrates. After lipids from an animal were partitioned into 100 µl of extraction solvent and purified, measured portions were weighed with an electrobalance. Lipids in some samples were also characterized by thin layer chromatography with flame ionization detection (TLC-FID). The extraction method was calibrated gravimetrically with cod liver oil and evaluated with a dry, ground fish sample. Lipid content was proportional (r = 0.99) to fish tissue dry weight over the range of 0.3–13 mg. TLC-FID measurements correlated well (r = 0.98) with gravimetric analysis for portions of extracts of individual amphipods (Pontoporeia hoyi) and oligochaetes (Stylodrilus heringianus). TLC-FID analysis indicated that <5% of the measured gravimetric weights was due to the inclusion of nonlipid material in the extracts.

Flux comparisons between sediments and sediment traps in the eastern tropical Pacific: Implications for atmospheric C02 variations during the Pleistocene1

Abstract: Regeneration rates of labile elements and biogenic components were measured at two sites in the Guatemala Basin by comparing fluxes of material caught in sediment traps to fluxes of that preserved in the sediments. From 95 to 99% of the N, P, organic C, CaCO3, opal, and Br reaching the sea floor are regenerated at the two sites. For elements bound largely in refractory phases (e.g. Al, Sc, Ti, and Fe), the particle-associated flux to the bottom is within 20% of the accumulation rate in the sediment. The two MANOP sites, about 800 km apart, have similar fluxes of organically associated N, P, and C, reflecting similar and relatively high primary productivity. There is a marked contrast in the opal/carbonate fluxes which leads to differences in CO2 cycling at the two locations. At least 95% of the total particulate organic carbon and >97% of the total particulate phosphate are regenerated at <1,500-m depth in the oceans. In contrast, much of the CaCO3 is destroyed at the sea floor. By a simple three-box ocean model we show that the recycling and storage depths of organic C, CaCO3, and P can be important factors in the control of the CO2 content of the atmosphere. We suggest that Pleistocene CO2 variations were due in part to global increases in upwelling during glacial periods with synchronous increases in total oceanic productivity and differences in diatom vs. carbonate productivity.

Relationship of egg production of Calanus pacificus to seasonal changes in phytoplankton availability in Puget Sound, Washington

Abstract: Two methods of estimating daily, in situ egg production rate for Calanus pacificus, a planktonic marine copepod that releases its eggs directly into the sea, were developed. The model for both methods separates egg production rate into daily frequency of spawning (% day-‘) and clutch size (eggs female-l). One method involves direct observations of spawning frequency and clutch size in a random sample of females held in controlled conditions for a 12-24-h period immediately after capture. The second method involves a visual assessment of the ovaries of live or preserved females and uses the observation that egg laying in Calanus occurs at night to predict daily rates of spawning. The methods were used to examine the relationship between egg production rate and phytoplankton availability in two areas of Puget Sound with different seasonal patterns of phytoplankton abundance and size composition. Egg production rate was hyperbolically related to phytoplankton concentration. The results show the potential for factors influencing phytoplankton standing stock to influence the timing and magnitude of recruitment into Calanus populations. The life history of copepods in the genus Calanus appears to be well suited for effective utilization of the seasonal phytoplankton production in temperate oceans. Late preadult stages spend the winter in diapause, thus enduring the scarcity of food resources. In most species the overwintering stages molt into adults in late winter or early spring and are ready to take advantage of the vernal increase in algae. The spring increase of Calanus and its correlation with the spring bloom of phytoplankton are well documented (Heinrich 1962; Williams and Lindley 1980).

Nitrogen uptake by size-fractionated phytoplankton populations in Antarctic surface waters1

Abstract: Nitrogen uptake experiments in surface waters off the coast between Cape Ann and Mawson indicate that reduced nitrogen (ammonium and urea) supplied an average of 58% of phytoplankton requirements. Size-fractionation studies provided evidence for nitrogen resource partitioning between the algae of different size classes at three of the five stations. On average, regenerated production amounted to 62% for the nanoplankton and 75% for the picoplankton.

Chaoborus‐induced shifts in the morphology of Daphnia ambigua1

Abstract: A simple filtration procedure allows the isolation of a factor from Chaoborus spp. which induces morphological change in Daphnia ambigua Scourfield. Neonate morphology is unaffected by exposure to the compound, but adults develop both a large helmet and pronounced spinescence along the carapace margin. The term chemomorphosis is proposed to describe cases in which morphological variation is induced by an exogenous chemical agent. Daphnia ambigua Scourfield is a common inhabitant of lakes and ponds throughout the United States and eastern Canada and south into Central and South America (Brooks 1957; Clark et al. 1980; Matsumura-Tundisi 19 84). Populations of this species typically show marked seasonal shifts in morphology (Brooks 1946). The anterior margin of the head may either be rounded or possess a spikelike helmet, and the extent of spinulation on the carapace margin is conspicuously variable. Brooks ( 19 5 7) noted that individuals with large helmets tended to possess prominent spines on their carapace, suggesting that variation in both characters might be controlled by the same factor. Experimental studies have shown that water temperature plays an important role in determining helmet size in neonates of

Effects of sampling technique on measurements of porewater constituents in salt marsh sediments1

Abstract: We examined the effect of three methods of porewater extraction on the measured concentrations of seven porewater constituents in vegetated salt marsh sediments. Porewater extraction by standard core sectioning followed by squeezing or centrifuging was compared with two less destructive methods of water collection. The core sectioning technique significantly increased the concentration of total dissolved organic carbon and dimethylsulfide presumably due to root damage by cutting. Sampling technique did not appear to influence interstitial salinity or concentrations of dissolved inorganic carbon, dissolved ammonium, soluble sulfides, and dissolved sulfate as long as proper precautions were taken to prevent the loss of reduced compounds.