Diel photosynthetic production of cellular organic matter in natural phytoplankton populations,measured with13C and gas chromatography/mass spectrometry

Diel photosynthetic production of water-extractable and residual carbohydrates in natural phytoplankton populations was investigated by analyzing monosaccharide components with combined gas chromatography/mass spectrometry (GC/MS) and¹³C tracer methods. The applicability of this technique for measuring the photosynthetic production of natural phytoplankton populations was examined. Phytoplankton was collected in August 1984 from Kinu-ura Bay, Japan, and incubated under natural light and dark conditions for 24 h. Cell density and concentration of chlorophylla increased about four- and three-fold, respectively, during the experimental period. Production of glucose, galactose, mannose, rhamnose, ribose, fucose, xylose and arabinose was measured in the water-extractable and residual carbohydrate fractions of the phytoplankton. Most of the monosaccharides in both fractions were produced the monosaccharides in both fractions were produced mainly during the daytime. Glucose was a major component in the water-extractable carbohydrate fraction produced by the phytoplankton, and decreased markedly at night. Thus, most of the glucose in the water-extractable carbohydrates seemed to be a constituent of the storage glucan of algal cells. Most monosaccharide components of the water-extractable carbohydrate fraction except glucose did not decrease significantly at night. Ribose of the water-extractable carbohydrate fraction was synthesized at a maximum rate in the morning, prior to the other monosaccharide constituents of this fraction. The major monosaccharide constituent in the residual carbohydrate fraction produced by the phytoplankton was glucose, which decreased significantly at night. Diel change in the production of monosaccharide constituents in residual carbohydrates indicated wide variability in the monosaccharide composition of cell-wall material in algae. The ratios of production of water-extractable and residual carbohydrates to POC production ranged from 8.8 to 28% and from 3.7 to 5.9%, respectively, throughout the daytime and nighttime.     

A detailed analysis of carbohydrates in marine particulate matter

Detailed profiles of organic carbon, organic nitrogen, carbohydrate and proteinous amino acid have been determined in particulate matter from various depths at a station in Sagami Nada off eastern Honshu, Japan. The profiles suggest that carbohydrate is decayed from particulate matter more rapidly than proteinous amino acid in the euphotic zone, while the latter is removed to a higher extent than the former in deep waters,which results in the increase of the C/N values of particulate matter in the depths. All of the particulate matter gave D-galactose, D-glucose, D-mannose, D-xylose and D-glucuronic acid upon acid hydrolysis. Vertical change of the monosaccharide composition of this particulate matter indicates that only D-glucose and its polymers are preferentially removed from it during its descent. Carbohydrates from the particulate matter of 20 m depth were fractionated into water-soluble and insoluble carbohydrates. Detailed analysis of these fractions indicates that 1,3-glucan and its related low molecular weight carbohydrates from the water-soluble fraction decay between 50 and 300 m depth, to leave waterinsoluble carbohydrates, immune to biological attack during the course of further sinking. On the basis of these facts, the effects of the biochemical nature of these carbohydrates on the vertical change of the particulate carbohydrate distribution are discussed.     

Carbohydrate metabolism in the marine diatom Skeletonema costatum

This is a study on the metabolism of the algal biochemical constituents of a marine diatom, Skeletonema costatum. The carbohydrates, protein, and lipid, of the diatom grown under light and dark conditions were analyzed. The composition of the organic compounds did not vary in the alga grown under continuous light conditions throughout the experiment, although a little accumulation of carbohydrate and lipid was observed in the stationary phase of the algal growth. When the diatom, at maximum growth stage, was transferred to darkness, 44.4% of the carbohydrate, 57.8% of the protein, and 27.0% of the lipid were used by respiration within a few days. Detailed analysis of the algal carbohydrate demonstrated that low molecular weight carbohydrates, consisting of glucose, and -1,3-glucan, were readily metabolized by algal respiration, leaving cell-wall carbohydrates consisting of mannan and pentosan which are immune to algal respiration. The respiratory utilization of carbohydrates is discussed in relation to the rapid decay of glucan from marine particulate matter during the course of its sinking to further depths in the ocean, as observed previously by the present author.     

A Functional Approach to the Assessment of the Nutritional Value of Particulate Organic Matter

Organic matter lability can be determined with different approaches, based on the quantitative and qualitative estimate of its nutritional value. the C/N ratio and the particulate organic matter (as the sum of protein, carbohydrate and lipid bulks) vs total suspended matter (POM/TSM) deal with a quantitative assessment of the organic matter bulk, while other indices such as proteins/carbohydrates ratio (PRT/CHO) may give also qualitative information. Gordon (1970) proposed a functional approach, based on organic carbon decrease after enzymatic digestion. Coupling Gordon's approach with the evaluation of the main biochemical components (proteins, carbohydrates and lipids) contained in the particulate organic matter, a simple method to assess lability and nutritional value of organic substrates is proposed.

Water samples were collected at the surface and close to the bottom in a shallow coastal station (10 m depth) in the Marconi Gulf (Ligurian Sea, NW Mediterranean). the difference between “total labile” and “hydrolyzed labile” organic matter (respectively before and after enzymatic digestion) suggests a relevant presence of resuspended refractory materials vs about 60% of labile hydrolyzed organic matter, thus confirming the importance of a more qualitative approach to organic matter studies.     

Vertical fluxes and ecological significance of organic materials during the phytoplankton bloom during austral summer in Breid Bay,Antarctica

A mooring system consisting of an in situ fluorometer at a depth of 50 m and a time-series sediment trap at a depth of 110 m was deployed at the sediment trap site (70°11.536'S; 24°18.679'E; water depth: 300 m) in Breid Bay, Antarctica in austral summer from 28 December 1985 to 13 February 1986. Sinking particles, consisting of diatoms (mainly Thalassiosira antarctica), were analyzed for organic materials, stable carbon and nitrogen isotopes. Vertical fluxes of organic carbon and nitrogen were determined to be within the ranges of 12.3 to 116 mg C m^-2 d^-1 and 1.79 to 15.4 mg N m^-2 d^-1, respectively, with maxima in the middle of January 1986, after which time the organic carbon and nitrogen fluxes tended to decrease with a steep gradient. High values of ¹³C were found in the organic matter of the sinking particles collected before the middle of January, indicating that the organic matter was derived from the diatoms in the logarithmic phase of their growth. Increased abundance of glucose was found in the water-extractable carbohydrate, which was one of the sinking particles collected in the middle of January. This fact clearly indicated that the diatoms were no longer in the growth phase but rather in the stationary phase, because reserved glucan as well as various cellular organic materials were reportedly accumulated within the algal cells in the stationary phase. Fifteen species of protein amino acids with trace amounts of -alanine, -aminobutyric acid and ornithine were found in the sinking particles upon acid hydrolysis, but the amino acid composition of these samples had not been affected much by biological agents. The essential amino acid index was calculated for the sinking particles collected in the course of the sediment trap experiment. The indices obtained indicated that the sinking particles collected in Breid Bay were more ecologically significant than the sinking and suspended particles from deep waters.     

Changes in the Biochemical Composition of Tetraselmis Suecia and Isochrysis Galbana During Growth and Decay

The variations of the biochemical composition of Tetraselmis suecica and Isochrysis galbana during growth and decay were determined. the content of chlorophyll a (Chl-a) of the cultures, as expected, slowly degraded into phaeopigments during decay, confirming that chlorophyll measurements do not always provide an accurate estimate of phytoplanktonic biomass and, consequently, may fail if used to measure the food availability of particulate matter for consumers. Measurements of total amounts of proteins, carbohydrates and lipids, related to the nutritional value of particles in terms of caloric content, are shown to provide information on the readily available food for consumers, particularly during the blooms. the protein/carbohydrate, C/N and POC/Chl-a ratios were used to evaluate the differences between these two species during the growth and the decomposition processes. A comparison between experimental and field conditions was undertaken to implement our understanding of the growth and degradation processes of particulate organic matter of phytoplanktonic origin in the sea and its role on natural systems, during and after phytoplankton blooms.     

Variability of biochemical composition and size distributions of seston in the euphotic zone of the Bay of Biscay: implications for microplankton trophic structure

Particle-size distributions and several biochemical components of seston were studied from October 1986 to December 1987 in surface waters of the Bay of Biscay. Variance partitioning of hydrographic and seston parameters indicates that, although seasonal variability related to the thermal cycle was important, most of the differences in seston concentration were caused by spatial components of variance. Changes in the vertical structure of the water column appeared to be the principal source of variability. Phytoplankton blooms in spring and fall and the effects of the coastal upwelling and the thermocline during summer were traced using seston concentration and biochemical composition. The different seston measurements were scaled according to their correlations with total concentration and particle size. Photosynthetic pigment biomass was related to both large and small partieles. However, concentrations of particulate proteins, lipids and carbohydrates were more related to small particles. Although not specifically analysed, low concentrations of inorganic particles and detritus can be expected in the study area, thus most of the particulate organic matter was associated with small, non-pigmented organisms, particularly in surface waters during the period of thermal stratification. The variability in concentrations of total seston and particulate organic matter was mainly due to variations in particulate proteins, lipids and carbohydrates; pigment concentrations were of secondary importance. Expressed as the ratio chlorophyll a: particulate protein-nitrogen, phytoplankton constituted an important fraction of the microplankton biomass only during spring blooms, when it averaged 75% of the particulate protein-nitrogen. In constrast, <30% of protein-nitrogen was related to chlorophyll a during the summer. These results suggest that an oligotrophic structure based on the microbial-loop prevails in microplankton assemblages of surface waters for most of the year.     

Relationships between dissolved and particulate carbohydrate temporal patterns and mucilaginous aggregates formation: evidences from time series analysis and biochemical composition of aggregates

A 3-year monitoring of dissolved and particulate carbohydrate concentrations in four transects located in the Adriatic and Tyrrhenian Seas was performed in order to get information on the role played by carbohydrates in the mucilage formation in these areas. The application of time series analysis pointed out that the concentration of dissolved carbohydrates does not vary significantly in coincidence of the mucilage appearance showing an almost constant state with respect to time. In contrast, wider temporal variations of carbohydrate amounts, either increase or decrease, were observed when mucilages were lacking or reduced. This almost constant state of carbohydrate amounts observed in presence of mucilages that we define 'steady state' could be associated to an alteration of the complex chemical equilibrium between synthesis and degradation (either hydrolysis or oxidation) reactions of the organic polymers which are typical of the humification processes in the marine environment. The results of this study suggest that the monitoring of carbohydrates can represent an useful tool for the comprehension of the most relevant phenomena of mucilage appearance in the Northern Adriatic Sea.     

Lipid and fatty acids in naturally occurring particulate matter during spring and summer in a high arctic fjord (Kongsfjorden, Svalbard)

The total lipids and fatty acid composition of natural particulate matter and nutritional quality for zooplankton grazers was studied on a seasonal basis in the Arctic fjord Kongsfjorden (Svalbard) during the spring, summer of 2007 and during the early summer of 2006. Both years were abnormally warm, and the study attempted to evaluate the potential impact of the intrusion of North Atlantic waters. Samples were collected in surface layers and at deep chlorophyll maximum (DCM when present). Both years, chlorophyll concentrations were low (<2 μg L^?1) even during bloom periods. Species determination indicated Phaeocystis spp. as main constituent of the May bloom while ciliates and flagellates dominated the rest of the survey period. Total lipids showed similar changes at both depths with maximum values in mid-summer of 2007, while it showed reverse patterns between surface and DCM in 2006. Total fatty acid composition was dominated by saturates and monoenoic acids at both depths with significant percentages of pentaenoic acids and 22:6n-3 (DHA) recorded at all times. The 2007 fatty acid dynamics identified four main successions in term of particulate assemblage related mainly to the succession of living cells versus detrital material and to a lesser extent to phytoplankton community changes (diatoms versus non-diatoms). Redundancy analysis confirmed that live phytoplankton is one of the main drivers in the fatty acid changes. Temperature and density of the surface water are also influential in relation to water mass dynamics. Concentrations of fatty acids available to consumers showed n-3 PUFA ranging from 2 to 15 μg L^?1 and n-6 PUFA ranging from 0.3 to 2 μg L^?1. Concentration of EPA (20:5) and DHA are potentially limiting, suggesting a negative impact of Phaeocystis pouchetti-type phytoplankton linked to advection of Atlantic waters in relation to global warming of Arctic waters.     

Scope for growth of Mytilus?galloprovincialis (Lmk., 1819) in oligotrophic coastal waters (Southern Tyrrhenian Sea, Italy)

The ‘scope for growth’ (SFG) tool was used to study the growth performance of cultivated populations of Mytilus galloprovincialis (Lmk., 1819) in an oligotrophic area of the Southern Mediterranean Sea. The study was carried out between 1993 and 1996 by using data from four seasonal oceanographic cruises and from growth experiments. Water samples were collected and analysed for total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PON), particulate lipids, proteins and carbohydrates and chloropigments. The sum of the carbon equivalents of carbohydrates, proteins and lipids is indicated as the total biopolymeric particulate organic carbon (BPC) and was converted into a unit of energy in order to calculate the SFG of a theoretical mussel of 5 cm length. In order to test the performance of mussel growth at two depths (5 and 15 m water depth), mussel body size [as ash free dry weight (AFDW)] and the actual concentrations of BPC were used to calculate the monthly SFG using the physiological energetic relationships suggested in the current literature. Data from the field cruises led us to characterise the study site as ultra-oligotrophic (annual average of chloropigment concentration approximately 0.5 μg L⁻¹). SFG calculations allowed us to identify a site where mussels grown successively were found to reach a commercial size in approximately 12 months. The good agreement obtained between energetic response and subsequent production response suggests that the available energy from particulate food could be fully available for organic production for maintaining “proportionate” growth trajectories, even in a ultra-oligotrophic system.     

Scope for growth of <Emphasis Type="Italic">Mytilus galloprovincialis</Emphasis> (Lmk., 1819) in oligotrophic coastal waters (Southern Tyrrhenian Sea,Italy)

The ‘scope for growth’ (SFG) tool was used to study the growth performance of cultivated populations of Mytilus galloprovincialis (Lmk., 1819) in an oligotrophic area of the Southern Mediterranean Sea. The study was carried out between 1993 and 1996 by using data from four seasonal oceanographic cruises and from growth experiments. Water samples were collected and analysed for total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PON), particulate lipids, proteins and carbohydrates and chloropigments. The sum of the carbon equivalents of carbohydrates, proteins and lipids is indicated as the total biopolymeric particulate organic carbon (BPC) and was converted into a unit of energy in order to calculate the SFG of a theoretical mussel of 5 cm length. In order to test the performance of mussel growth at two depths (5 and 15 m water depth), mussel body size [as ash free dry weight (AFDW)] and the actual concentrations of BPC were used to calculate the monthly SFG using the physiological energetic relationships suggested in the current literature. Data from the field cruises led us to characterise the study site as ultra-oligotrophic (annual average of chloropigment concentration approximately 0.5 μg L⁻¹). SFG calculations allowed us to identify a site where mussels grown successively were found to reach a commercial size in approximately 12 months. The good agreement obtained between energetic response and subsequent production response suggests that the available energy from particulate food could be fully available for organic production for maintaining “proportionate” growth trajectories, even in a ultra-oligotrophic system.     

Suspended particulate organic matter in a Mediterranean submarine cave

Submarine caves display a paucity of benthic density and biomass that may be related to low trophic resources. Analysis of organic carbon, organic nitrogen, carbohydrate, protein and lipid content of suspended particulate matter was made during the period July 1985–July 1987 in a Mediterranean cave (Marseille, France) in order to determine any differences in the particulate organic matter composition along an horizontal transect. Particulate organic matter content clearly declined from the entrance of the cave to the dark inner area. This impoverishment could not be explained by a simple decrease in a few organic compounds, but appeared to be related to the combination of a decrease in both the amount and the composition of the suspended particles. Three progressive levels of impoverishment were identified towards the dark inner area of the cave: (i) decreasing amounts of seston; (ii) decreasing organic content of particles; (iii) increasing proportions of the geopolymeric (i.e., humic) components in the remaining organic matter, indicating increased degradation. The cave appeared to be sharply divided into two distinct sections — a twilight outer section whose waters contained slightly lower amounts of particulate organic matter than the open sea, and a dark inner section, 8 to 10 m higher, separated from the outer section by a steep rise and with waters of low organic matter content. The water in the twilight section appeared to be in thermal equilibrium with the open sea, and that in the dark inner section displayed thermal stratification. These differences indicated the presence of two distinct water bodies with contrasting average residence times, estimated as 1 d in the outer twilight section and 8 d in the dark inner section. The joint action of sedimentation and degradation resulted in an abrupt depletion of particulate organic matter in the dark inner section accompanied by a decrease in the benthic fauna. The decline in benthic heterotroph populations is probably related to the abrupt transition to oligotrophic conditions.     

Decomposition of faecal matter and somatic tissue of Mytilus galloprovincialis: changes in organic matter composition and microbial succession

Variations in the biochemical composition of pseudo-faeces and faeces egested by Mytilus galloprovincialis (Lamarck) and in detritus derived from the somatic tissue of mussels during the decomposition process were investigated by means of two intensive experiments. During the degradation process, the biochemical composition of pseudo-faeces and faeces showed a clear increase in protein content related to the microbial colonization. Changes also occurred in the biochemical composition of particulate organic matter (POM) in the surrounding water due to faecal matter decomposition, heterotrophic utilization and conversion of particulate carbohydrates and proteins to the dissolved pool. The study of production and heterotrophic utilization of the POM derived from the somatic tissue of M. galloprovincialis collected in the Gulf of Tigullio, Italy in 1990 indicates that this kind of material is rapidly decomposable and largely available for benthic consumers. Bacteria utilized selectively the different compounds, and proteins proved to be the most suitable substrate for bacterial growth. The input of organic detritus into the experimental system resulted in an enhancement of bacterial activity and consequently of the RNA/DNA ratio. Bacterial DNA accounted on average for 17% of particulate DNA. During decomposition processes, nutrient release was about ten times higher than the value calculated from individual excretion rates, indicating that mussel beds may be important sites for nutrient regeneration. Carbon conversion efficiency for bacteria growing on faecal matter was, on average, 17.2%. The potential importance of faecal output and bacterial production as a carbon resource for benthic communities near mussel culture areas is discussed.     

Hydrodynamic and chemical conditions during onset of a red-tide assemblage in an estuarine upwelling ecosystem

The hydrodynamics and nitrogen/silicon biogeochemistry accompanying the development of a red-tide assemblage were examined in the Ría de Vigo (northwest Spain), a coastal embayment affected by upwelling, during an in situ diel experiment in September 1991. Despite a low N:Si molar ratio (0.5) of nutrients entering the surface layer, which was favourable for diatom growth, the diatom population began to decline. Limited N-nutrient input, arising from moderate coastal upwelling in a stratified water column, restricted net community production (NCP = 630 mg C m⁻² d⁻¹). In addition, light-limitation of gross primary production (GPP = 1525 mg C m⁻² d⁻¹) was observed. The relatively high f-ratio (= NCP:GPP) recorded (0.41, characteristic of intense upwelling conditions) would have been as low as 0.15 had not GPP been limited by light intensity. Temporal separation of carbohydrate synthesis during the photoperiod from protein synthesis in the dark could be inferred from the time-course of the C:N ratio of particulate organic matter. Severe light-limitation would lead to diatom collapse were the diatoms not able to meet all their energy requirements during the hours of darkness. Under the hydrodynamic, nutrient and light conditions of the experiment, an assemblage of red-tide-forming species began to develop, aided by their ability to migrate vertically and to synthesize carbohydrates during the light in surface waters and protein during the dark at the 4 m-deep pycnocline. Thermal stratification, reduced turbulence, intense nutrient mineralization, and the limited nitrogen input through moderate upwelling were all favourable to the onset of a red-tide assemblage. Received: 15 February 1997 / Accepted: 26 September 1997     

Detritus-Bacteria-Meiofauna interactions in a seagrass bed (Posidonia oceanica) of the NW Mediterranean

The biochemical composition of the sediment organic matter, and bacterial and meiofaunal dynamics, were monitored over an annual cycle in aPosidonia oceanica bed of the NW Mediterranean to test the response of the meiofauna assemblage to fluctuations in food availability. Primary production cycles of the seagrass and its epiphytes were responsible for relatively high (compared to other Mediterranean systems) standing stocks of organic carbon in sediments (from 1.98 to 6.16 mg Cg^–1 sediment dry weight). The biopolymeric fraction of the organic matter (measured as lipids, carbohydrates, and proteins) accounted for only a small fraction (18%) of the total sedimentary organic carbon. About 25% of the biopolymeric fraction was of microphytobenthic origin. Sedimentary organic carbon was mostly refractory (56 to 84%) and probably largely not utilizable for benthic consumers. The biopolymeric fraction of the organic matter was characterized by high carbohydrate concentrations (from 0.27 to 5.31 mg g^–1 sediment dry weight in the top 2 cm) and a very low protein content (from 0.07 to 0.80 mg g^–1 sediment dry weight), which may be a limiting factor for heterotrophic metabolism in seagrass sediments. RNA and DNA concentrations of the Sediments varied significantly during the year. High RNA and DNA values occurred during the microphytobenthic bloom and in correspondence with peaks of bacterial abundance. Bacteria accounted for a small fraction of the total organic carbon (0.65%) and of the biopolymeric organic carbon (4.64%), whilst microphytobenthos accounted for 3.79% of total organic carbon and for 25.08% of the biopolymeric carbon. Bacterial abundance (from 0.8 to 5.8 × 10⁸ g^–1 sediment dry weight) responded significantly to seasonal changes of organic matter content and composition and was significantly correlated with carbohydrate concentrations. Bacteria might be, in the seagrass system, an important N storage for higher trophic levels as il accounted for 25% of the easily soluble protein. pool and contributed significantly to the total DNA pool (on average 12%). Total meiofaunal density ranged from 236 to 1858 ind. 10 cm^–2 and was significantly related, with a time lag, to changes in bacterial standing stocks indicating that microbes might represent an important resource. Bacterial abundance and biomass were also significantly related to nematode abundance. These results indicate that bacteria may play a key role in the benthic trophic     

Effect of clay minerals on extractability of heavy metals and sewage sludge mineralization in soil

An incubation experiment lasting 111 d was carried out to study the effect of the addition of three clay minerals (Na-bentonite, Ca-bentonite, and zeolite) to soil derived from sewage sludge on water-extractable and exchangeable forms of four heavy metals (Zn, Cd, Cu, and Ni), as well as on soil organic matter mineralization, microbial biomass C and the release of inorganic N. The addition of clay minerals led to a significant decrease in water-extractable and exchangeable forms of heavy metals. The extent of decrease ranged from 14 to 75% for the water-extractable heavy metals and from 12 to 42% for the exchangeable form over the incubation time, as compared with untreated soil. The reduction in extractability of heavy metals was greater due to the addition of Na-bentonite and Ca-bentonite than that due to the addition of zeolite. Addition of clay minerals did not affect any of the following microbiological parameters in the soil: microbial biomass C, organic C (C_org) mineralization, and metabolic quotient (qCO₂), and release of inorganic N during the first 3 weeks of incubation. However, as the incubation period increased, these parameters were significantly increased by the addition of clay minerals, especially by the addition of Na-bentonite and Ca-bentonite. This result is explained by a strong reduction in extractability of heavy metals after the addition of Na-bentonite and Ca-bentonite.     

Production,composition and sedimentation of salp fecal pellets in oceanic waters

Rates of fecal pellet production have been recorded from seven species of oceanic salps feeding on natural diets. Expressed as g C defecated per mg salp body C per hour, the values range between 3.7 and 27.7. Carbon: nitrogen ratios of the salp fecal pellets average 11.4; the organic matter of the pellets is mainly protein and carbohydrate. Sinking velocities of the pellets are very high, ranging from 320 to 2 238 m d^-1 for pellets from three species. However, the pellets sink slower than would be predicted from extrapolation of rates for crustacean pellets, probably due to the shape of the pellets and their density. The high rates of defecation, large size and rapid sedimentation of salp fecal pellets make them likely mechanisms for rapid transport of small particulate matter from surface waters to deep water and the benthos.     

Diel variations in the nutritional physiology of Calanus glacialis from Lat. 78°N in the summer

Calanus glacialis (Jaschnov) from Isfjord, western Spitzbergen, showed no tendency to pronounced diurnal vertical migration or cyclic variations in feeding activity. The samples, taken regularly over a 24-h period and at three different depths in the beginning of August, did however show considerable individual variations in feeding activity. These variations, reflected in the results of gut analyses, were not related to variations in the concentrations of particulate protein, carbohydrate or algal pigments in the water. Analyses of the activities of two digestive enzymes and the electron-transport system (ETS) indicated that those few individuals always present below the photic zone were there temporarily, and showed no signs of slowing down their metabolism. The results suggest that the population of C. glacialis, during the Arctic summer, feeds continuously in the upper water layer, but that intermittent, non-synchronous individual feeding rhythms are the rule.     

Seasonal Fluctuations in the Nutritional Value of Particulate Organic Matter in A Lagoon

Water samples were collected on a fortnightly basis in the lagoon of S. Gilla (Sardinia, Mediterranean Sea) in order to study seasonal nutritional fluctuations of particulate organic matter. the lagoon is characterized by high quantities of suspended matter throughout the year. Thermohaline conditions had no effect on particulate matter quantity and composition, but the quantity as well as quality of suspended particles was drastically affected by the wind, the major effecter of sediment resuspension. As a result of sediment resuspension, seston was always richer in inorganic fraction. However, throughout the year of investigation, most particulate organic carbon was quite appealing for filter feeding communities, although the best POM quality was available during phytoplankton blooming. the phytoplankton pool of suspended matter was just a small fraction of the bulk, accounting for only 13% on average of particulate organic carbon. in terms of energy available in the seston, the highest amount was stored in organic matter heterotrophic fraction, whilst the smallest was to be found in living phytoplankton.     

Distribution and retention of the copepodEurytemora affinis hirundoides in a turbid estuary

The spatial and temporal distribution of the copepodEurytemora affinis hirundoides (Nordquist, 1888) in the Gironde estuary, southwest France, was investigated in 1976, and between 1981 and 1983. The distribution pattern of the population bore a clear relationship to the patterns of water circulation and transport of particulate matter. Laboratory experiments suggested thatE. affinis hirundoides is incapable of autonomous displacement against the direction of general circulation and behaves as passive particles. A major problem faced by species living in estuaries is that of the maintenance of endemic populations. Some authors have suggested that behavioural responses may play an important role in minimising population losses. Our study indicated that hydrodynamic processes are sufficient to explain the distribution and retention ofE. affinis hirundoides, whose populations are retained in the estuary in the same manner as the suspended sediment. Since the outflow of particulate matter from the Gironde estuary to the sea is very sporadic, we hypothesize that most of the production ofE. affinis hirundoides remains within the estuary, and does not fertilize the continental shelf, at least not in the form of particulate organic matter.