Scavenging abyssal benthic amphipods trapped under oligotrophic central North Pacific Gyre waters

Two traps baited with fish were placed on the bottom (5720 m) of the central North Pacific Gyre. A total of 1793 lyssianassid amphipods were collected no ovigerous females and no identifiable males were caught. Five amphipod species were represented [1 undescribed species of Orchomene; 2 undescribed species of Paralicella; Eurythenes gryllus (Lichtenstein); and Cyclocaris sp.], 2 by single specimens. Amphipod samples give no evidence of size-classes. Evidence for scavenging as the amphipods' primary mode of existence is discussed. Forty-four copepods, of a single harpacticoid genus (Tisbella), were also collected.     

Inorganic nitrogen metabolism in marine bacteria: Nitrate uptake and reduction in a marine pseudomonad

Growth experiments in batch cultures indicated that the uptake of nitrate by the marine pseudomonad PL1 was inhibited in the presence of ammonia provided that the ammonia concentration was higher than 1 mM. At ammonia concentrations of less than about 1 mM, however, both nitrate and ammonia were utilised simultaneously. The saturation constants for nitrate and ammonia uptake were both 2.6x10^-4 M, and similar to the Michaelis constants of nitrate reductase for nitrate (2.9x10^-4 M) and glutamine synthetase for ammonia (2x10^-4 M). Nitrate reductase activity linked to NADH was detected in chemostat-grown cultures with nitrate as nitrogen source, and in cultures containing limiting concentrations of nitrate and ammonia, ammonia or glutamate. Enzyme synthesis appeared to be repressed in cultures containing an excess of ammonia or glutamate. Chemostat cultures utilised ammonia or glutamate in preference to nitrate, while there was no marked preference between ammonia and glutamate.     

Predicting fish behaviour in response to abyssal food falls

Estimates of fish abundance based on arrival rates and numbers present at baited cameras allow multiple, replicate assessments where data are not available by other means. Unfortunately such estimates are strongly affected by the assumed behaviour of the fish species concerned. Three of the possible foraging strategies of deep-sea fish were modelled and the likely patterns of fish arrival calculated for the same fish density, swimming and current velocities and odour plume properties. Cross-current foraging resulted in the highest numbers of fish at bait, with arrival rates that fitted well to field data. The sit-and-wait strategy produced lower arrival rates with passive drifting animals arriving slowest. Each model produces a distinctive pattern of animal arrivals that may be diagnostic of each foraging strategy. The advantages, disadvantages and likely metabolic and sensory demands of each strategy are discussed. Published online: 17 September 2002     

Microbial populations in surface films and subsurface waters: Amino acid metabolism and growth

Sea surface microlayer (film) and subsurface microbial populations (biomass and activities) were studied in the Damariscotta (Maine) estuary in May and September, 1987. Dissolved free and combined amino acids (DFAA, DCAA), bacterial numbers, microbial ATP, bacterial and microbial DNA synthesis (via³H-thymidine and³H-adenine), and amino acid (³H-glutamic acid) metabolism were measured. DFAA and DCAA were typically enriched in the surface microlayers relative to surface waters, although utilization of glutamic acid was usually more rapid in subsurface waters, as was incorporation of thymidine. Bacteria represented 12 to 40% of the microbial biomass as determined by ATP, except during microalgal blooms in the microlayer. Bacteria were generally not enriched in the surface films, although ATP usually was enriched. Rain input appeared to deplete population densities but stimulated population activities. Two stations which contained similar microbial populations (as estimated by bacterial counts, chlorophylla and ATP) showed very different microbial activities, apparently due to the effects of a substantial rainstorm on one of the stations. The bacterially-dominated processes utilizing thymidine and glutamic acid were enhanced approx five-fold after the rain. Autotrophic carbon production increased approx two-fold, while total microbal community DNA synthesis (as estimated by adenine incorporation into DNA) increased nearly tenfold. The observations of this study indicate that surface microlayers in the temperate waters off the coast of Maine contain highly active heterotrophic and autotrophic populations. The microbial community responds rapidly to changes in nutrient and dissolved organic matter concentrations resulting from both seasonal and temporal effects, including rain and runoff.     

Scavenging abyssal amphipods from the North-East Atlantic ocean

A baited trap set on the bottom (4855 m) in the eastern North Atlantic Ocean caught over 600 specimens belonging to 7 species of lysianassid amphipods. Photographic evidence showed a slow build up of numbers and demonstrated fluctuations apparently related to current and pressure changes and to the presence of fish. Length-frequency distributions for the more abundant species reveal size classes related to growth stages. Paralicella caperesca produces a single brood of about 90 eggs. Maturity in this species may be attained in 7 to 11 moults, the precise number possibly being determined by food availability. Orchomene gerulicorbis requires about 11 moults to reach maturity, and females are double-brooded. Mortality within the trap is discussed. A comparison of species of Paralicella and Orchomene based on morphological, developmental, reproductive and ecological characters indicates that the former genus are specialized necrophages whereas the latter are opportunist generalists. The abundance and mobility of necrophagous amphipods indicate that they play a very significant role in the trophic web.     

Nitrate metabolism in sediments from seagrass (Zostera capricorni) beds of Moreton Bay,Australia

The fate of nitrate in sediments from seagrass (Zostera capricorni Aschers.) beds of Moreton Bay on the subtropical eastern coast of Queensland, Australia, was investigated. Added nitrate was metabolised at rates of 0.4 to 3.4 g N cm^-3 d^-1 when sediments were incubated under anaerobic conditions with a large excess of nitrate. The potential rate of nitrate utilization was as rapid in sediments from subtidal bare areas as from adjacent seagrass beds. Ammonium was produced rapidly from¹⁵N-nitrate by microbial action in all the subtidal sediments examined. After 12 h of incubation, 13 to 28% of the¹⁵N initially added as labelled nitrate was detected as labelled ammonium in the sediments. Denitrification, although not measured directly, appeared to be a relatively minor fate of nitrate. Benthic microbes took up large amounts of¹⁵N but only after a delay of 6 h; this pattern could have been due to induction and synthesis of the enzymes necessary for nitrate uptake, and the assimilation of labelled ammonium. Under field conditions, assimilation by seagrasses and denitrification by bacteria were probably not significant sinks for nitrate in comparison with uptake by benthic microbes and dissimilatory reduction to ammonium.     

Long-term change in benthopelagic fish abundance in the abyssal northeast Pacific Ocean

Food web structure, particularly the relative importance of bottom-up and top-down control of animal abundances, is poorly known for the Earth's largest habitats: the abyssal plains. A unique 15-yr time series of climate, productivity, particulate flux, and abundance of primary consumers (primarily echinoderms) and secondary consumers (fish) was examined to elucidate the response of trophic levels to temporal variation in one another. Towed camera sled deployments in the abyssal northeast Pacific (4100 m water depth) showed that annual mean numbers of the dominant fish genus (Coryphaenoides spp.) more than doubled over the period 1989-2004. Coryphaenoides spp. abundance was significantly correlated with total abundance of mobile epibenthic megafauna (echinoderms), with changes in fish abundance lagging behind changes in the echinoderms. Direct correlations between surface climate and fish abundances, and particulate organic carbon (POC) flux and fish abundances, were insignificant, which may be related to the varied response of the potential prey taxa to climate and POC flux. This study provides a rare opportunity to study the long-term dynamics of an unexploited marine fish population and suggests a dominant role for bottom-up control in this system.     

Temporal persistence of biological patch structure in an abyssal benthic community

An analysis of living and dead components of a population of deep-sea agglutinated Foraminifera reveals that both segments of the fauna are dispersed nonrandomly on a scale of centimeters. Significant positive correlations between the distribution of living and dead individuals in several species imply that small-scale patch structure in this environment may persist for more than one generation. Mechanisms maintaining such structure may include habitat selection and reproductive patterns and suggest that dispersion pattern is the result of an active interaction between amimals and a heterogeneous physical and biotic environment.     

Zooplankton biomass and indices of grazing and metabolism during a late winter bloom in subtropical waters

The development of the so-called late winter bloom in subtropical water was studied in an oceanic area north of the Canary Islands from January to May 2000. Zooplankton was sampled at short-term intervals (1–4 days) during the bloom (January–March), and biomass, indices of grazing (gut fluorescence) and metabolism (electron transfer system activity, ETS) were measured in four different size fractions (100–200, 200–500, 500–1000 and >1000 µm). During the bloom, ETS activity and gut fluorescence increased before the development of zooplankton biomass. At the end of February, the presence of an impressive cloud of dust formed in the Sahara desert was related to an increase in chlorophyll and small zooplankton a week later. The increments in biomass were the consequence of consumption by zooplankton as inferred from the indices of grazing and metabolism. Estimated grazing from gut fluorescence and gut evacuation rates during the period of study accounted for 55% of the assessed total ingestion from respiration and normal values of assimilation, showing the importance of the non-pigmented food in the diet of zooplankton in these waters. In contrast, the sharp decreases in zooplankton biomass observed during the bloom appeared during the dark period of the moon, the days in which the diel vertical migrants reach the shallower layers, in agreement with previous works in the area. Thus, the development of the late winter bloom in this region is suggested to be driven by the interplay between resource and consumer controls.Communicated by S.A. Poulet, Roscoff     

Community change in the variable resource habitat of the abyssal northeast Pacific

Research capable of differentiating resource-related community-level change from random ecological drift in natural systems has been limited. Evidence for nonrandom, resource-driven change is presented here for an epibenthic megafauna community in the abyssal northeast Pacific Ocean from 1989 to 2004. The sinking particulate organic carbon food supply is linked not only to species-specific abundances, but also to species composition and equitability. Shifts in rank abundance distributions (RADs) and evenness, from more to less equitable, correlated to increased food supply during La Ni?a phases of the El Ni?o Southern Oscillation. The results suggest that each taxon exhibited a differential response to a sufficiently low dimension resource, which led to changes in community composition and equitability. Thus the shifts were not likely due to random ecological drift. Although the community can undergo population-level variations of one or more orders of magnitude, and the shape of the RADs was variable, the organization retained a significant consistency, providing evidence of limits for such changes. The growing evidence for limited resource-driven changes in RADs and evenness further emphasizes the potential importance of temporally variable disequilibria in understanding why communities have certain basic attributes.     

Abundance and size distribution dynamics of abyssal epibenthic megafauna in the northeast Pacific

The importance of interannual variation in deep-sea abundances is now becoming recognized. There is, however, relatively little known about what processes dominate the observed fluctuations. The abundance and size distribution of the megabenthos have been examined here using a towed camera system at a deep-sea station in the northeast Pacific (Station M) from 1989 to 2004. This 16-year study included 52 roughly seasonal transects averaging 1.2 km in length with over 35600 photographic frames analyzed. Mobile epibenthic megafauna at 4100 m depth have exhibited interannual scale changes in abundance from one to three orders of magnitude. Increases in abundance have now been significantly linked to decreases in mean body size, suggesting that accruals in abundance probably result from the recruitment of young individuals. Examinations of size-frequency histograms indicate several possible recruitment events. Shifts in size-frequency distributions were also used to make basic estimations of individual growth rates from 1 to 6 mm/month, depending on the taxon. Regional intensification in reproduction followed by recruitment within the study area could explain the majority of observed accruals in abundance. Although some adult migration is certainly probable in accounting for local variation in abundances, the slow movements of benthic life stages restrict regional migrations for most taxa. Negative competitive interactions and survivorship may explain the precipitous declines of some taxa. This and other studies have shown that abundances from protozoans to large benthic invertebrates and fishes all have undergone significant fluctuations in abundance at Station M over periods of weeks to years.     

Bacterial flora from echinoderm guts and associated sediment in the abyssal Vema Fault

Individuals of the asteroid Solaster sp. and the holothurian Pseudostichopus villosus (Theel) were collected from deep-sea bottom of the Vema fault in the mid-Atlantic ridge during the BIOVEMA cruise (November, 1977) of the R.V. Jean Charcot. Heterotrophic aerobic bacteria of the guts were isolated, identified and compared with bacterial isolates from surface sediment of the same area. Bacterial population structures displayed a predominance of Gram-negative rods in the echinoderm guts and a predominance of Gram-positive bacteria (particularly cocci) in the surface sediment. Investigation of the metabolic potentialities of the isolates suggested that the microflora of echinoderms, and in particular of the Asteroidea, have more specialized orientations in the catabolism of organic compounds. Single-linkage cluster analysis of all the isolates (130 strains) based on 139 phenotypic features revealed that out of 15 identified clusters, only one included both enteric and sediment isolates. The bacteria in this cluster were similar to the genus Micrococcus.     

Community metabolism of adenylates by microheterotrophs from the Los Angeles Harbor and Southern California coastal waters

The natural concentration (S _n) of dissolved total adenylates TA(=AMP+ADP+ATP) in coastal seawater from a depth of 1 m at 5 stations (California, USA) sampled periodically for 1 yr had a mean value ±1 SD of 2.8±1.7 nmol TA1^-1. The specific uptake rates of TA by microheterotrophs at a station inside the Los Angeles Harbor and at a station 1.5 km offshore in the San Pedro Channel were studied by simple uptake and saturation-type kinetic analysis using ³H-AMP as a tracer. Within the harbor, the specific uptake rate (nmol TA 10⁹ cell^-1 h^-1) at S _n ranged 10-fold from 0.028 in December to 0.28 in August. K _t (half-saturation constant) values always exceeded theS _n concentrations in any given month, and were greater in the harbor than in the channel. Generally, over 80% of biological uptake of ³H-AMP was associated with organisms <1.0 m, a size class accounting for about 20% of the total particulate adenylate concentration in the 0.2 to 203 m size fraction. Assuming steady-state conditions for the dissolved adenylate pool, we propose a model in which losses from this pool are balanced by inputs to the pool through inefficient feeding, lysis and decomposition of particulate adenylates.     

Helium isotopic constraints on simulated ocean circulations: implications for abyssal theories

There is ongoing controversy as to the dynamical significance of geothermal heat flow in shaping the abyssal circulation. In this paper, we gauge the impact of geothermal heating and vertical mixing parameterizations in the general circulation model OPA. The experiments are evaluated by comparing simulated mantle ³He with observations collected during the GEOSECS and WOCE programs. This tracer is particularly adapted to the validation of our numerical simulations because its injection into the ocean interior is tightly linked to geothermal processes. In agreement with previous studies, the model circulation is found very sensitive to the parameterization of the vertical mixing. The meridional overturning circulation (MOC) is globally intensified when moving from a constant mixing to a version with enhanced mixing near the ocean bottom, with the most drastic variation observed for AABW (+ 50%). Adding the geothermal heat flux mainly affects AABW circulation in the model, enhancing it all the more as the meridional circulation is slow (low vertical mixing), but proportionally less so when it is more vigorous (enhanced vertical mixing). This can be understood from the requirement of the abyssal ocean to maintain heat balance. The evaluation with mantle ³He simulations reveals that the version with low vertical mixing, with its sluggish circulation, produces unrealistically high a ³He isotopic composition. However, with a vertical mixing that is enhanced at depth, the ³He distribution falls within an acceptable range of values in the deep ocean. Finally, adding the geothermal heating to this enhanced mixing case provides a substantial improvement of the simulation of AABW in all basins but the Indian Ocean. ³He isotopic composition is then in good agreement with the observations. Taken jointly with observational estimates of the MOC intensity, these independent isotopic constraints suggest that both geothermal heating and enhanced diapycnal mixing at depth are key ingredients in the realistic simulation of abyssal circulation.     

Nitrate reductase in Peru current phytoplankton

Nitrate reductase (NR) activity was assayed by measuring the NADH-dependent formation of nitrite in phytoplankton extracts. NR specific activity increased with the nitrate concentration of the water in upwelling areas of the Peru Current. The temperature optimum for NR for natural phytoplankton was 15° to 20°C. NR activity showed diel periodicity, with maximum activity about noon and minimum activity near midnight local time. Rate of nitrate reduction in the extracts averaged only about 15% of the rate of nitrate assimilation in the whole cells.     

Nitrate reductase activity in Zostera marina

Eelgrass (Zostera marina L.) has access to nutrient pools in both the water column and sediments. We investigated the potential for eelgrass to utilize nitrate nitrogen by measuring nitrate reductase (NR) activity with an in vivo tissue assay. Optimal incubation media contained 60 mM nitrate, 100 mM phosphate, and 0.5% 1-propanol at pH 7.0. Leaves had significantly higher NR activity than roots (350 vs 50 nmoles NO ₂ ^– produced g FW^–1 h^–1). The effects of growing depth (0.8 m MLW, 1.2 m, 3.0 m, 5.0 m) and location within the eelgrass meadow (patch edge vs middle) on NR activity were examined using plants collected from three locations in the Woods Hole area, Massachusetts, USA, in July 1987. Neither depth nor position within the meadow appear to affect NR activity. Nitrate enrichment experiments (200 M NO ₃ ^– for 6 d) were conducted in the laboratory to determine if NR activity could be induced. Certain plants from shallow depth (1.2 m) showed a significant response to enrichment, with NR activity increasing from >100 up to 950 nmoles NO ₂ ^– g FW^–1 h^–1 over 6 d. It appears that Z. marina growing in very shallow water (0.8 m) near a shoreline may be affected by ground water or surface run-off enrichments, since plants from this area exhibited rates up to 1 600 nmol NO ₂ ^– g FW^–1 h^–1. Water samples from this location consistently had slightly higher NO ₃ ^– concentrations (1.4 M) than all other collection sites (0.7 M). Thus, it is possible that chronic run-off or localized groundwater inputs can create sufficient NO ₃ ^– enrichment in the water column to induce nitrate reductase activity in Zostera leaves.     

Paraben-chlorinated derivatives in river waters

This article reports the first identification of paraben-chlorinated derivatives in river water. Parabens are widely used as preservatives in pharmaceuticals and personal care products. Parabens can be easily chlorinated by chlorinated tap water. The resulting chlorinated derivatives might pose a higher potential risk to humans and ecosystems than the corresponding parent parabens. However, the occurrence of such derivatives in rivers remains unknown so far. We studied 23 parabens and their chlorinated derivatives from rivers receiving effluents from sewage treatment plants in Shizuoka city, in the central Pacific region of Japan. The compounds were extracted by solid-phase extraction with a styrene polymer sorbent, trimethylsilyl-derivatized, and then identified by gas chromatography–mass spectrometry. Six chlorinated parabens and their primary degradation products, two chlorinated hydroxybenzoic acids, were found for the first time in river water. Moreover, in river water, chlorinated derivatives preferentially partition into the suspended-solid phase.     

Nitrate reductase for nitrate analysis in water

Nitrate analysis in water is one of the most frequently applied methods in environmental chemistry. Current methods for nitrate are generally based on toxic substances. Here, we show that a viable alternative method is to use the enzyme nitrate reductase. The key to applying this Green Chemistry solution for nitrate analysis is plentiful, inexpensive, analytical grade enzyme. We demonstrate that recombinant Arabidopsis nitrate reductase, expressed in the methylotrophic yeast Pichia pastoris, is a highly effective catalyst for nitrate analysis at 37°C. Recombinant production of enzyme ensures consistent quality and provides means to meet the needs of environmental chemistry.     

降低蔬菜硝酸盐含量的农业措施

过量的硝酸盐在人体内积累,会对人体产生毒害作用。目前各大城市普查的结果表明．蔬菜中硝酸盐含量超标2～8倍。控制蔬菜硝酸盐的积累,是一个迫切问题。本文提出了降低蔬菜硝酸盐含量的若干农业措施。     

Nitrate production and availability in residential soils

The rapid increase in residential land area in the United States has raised concern about water pollution associated with nitrogen fertilizers. Nitrate (NO3-) is the form of reactive N that is most susceptible to leaching and runoff; thus, a more thorough understanding of nitrification and NO3(-) availability is needed if we are to accurately predict the consequences of residential expansion for water quality. In particular, there have been few assessments of how the land use history, housing density, and age of residential soils influence NO3(-) pools and fluxes, especially at depth. In this study, we used 1 m deep soil cores to evaluate potential net nitrification and mineralization, microbial respiration and biomass, and soil NO3(-) and NH4+ pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types. These were compared to eight forested reference sites with similar soils. Our results suggest that a change to residential land use has increased pools and production of reactive N, which has clear implications for water quality in the region. However, the results contradict the common assumption that NO3(-) production and availability is dramatically higher in residential soils than in forests in general. While net nitrification (128.6 +/- 15.5 mg m(-2) d(-1) vs. 4.7 +/- 2.3 mg m(-2) d(-1); mean +/- SE) and exchangeable NO3(-) (3.8 +/- 0.5 g/m2 vs. 0.7 +/- 0.3 g/m2) were significantly higher in residential soils than in forest soils in this study, these measures of NO3(-) production and availability were still notably low, comparable to deciduous forest stands in other studies. A second unexpected result was that current homeowner management practices were not predictive of NO3(-) availability or production. This may reflect the transient availability of inorganic N after fertilizer application. Higher housing density and a history of agricultural land use were predictors of greater NO3(-) availability in residential soils. If these factors are good predictors across a wider range of sites, they may be useful indicators of NO3(-) availability and leaching and runoff potential at the landscape scale.