The heterotrophic phase of plankton succession in the Japan Sea

The vertical structure, composition and productivity of a plankton community was studied in the Japan Sea in June, 1972 during a period of thermocline formation; the parameters measured were: phytoplankton production and biomass; number, biomass, and production of planktonic bacteria; biomass of phagotrophic flagellates, ciliates and remaining microzooplankton. The concentration of micro- and mesozooplankton attained a basic maximum in a layer near the upper part of the thermocline. The biomass and calculated production of the heterotrophic part of the community exceeded considerably the amount of primary production. The heterotrophic phase of the seasonal succession of a plankton community in a temperate sea is described, when heterotrophic metabolism and production predominate. Heterotrophs at this stage use mostly energy from organic matter accumulated during the previous spring phytoplankton bloom.     

Interactions between nutritional status and long-term responses to ultraviolet-B radiation stress in a marine diatom

Influences of nutritional status on the photoinhibitory effects of ultraviolet-B radiation (UVBR: 290 to 320 nm) on the specific growth rates (_obs) and biomass of Phaeodactylum tricornutum were determined using nutrient-replete batch cultures and nutrient-limited continuous cultures. P. tricornutum cultures were exposed to UVBR doses representative of current mid-latitude and ozone-depletion intensities. Specific growth rates and biomass were inhibited from 2 to 16% by UVBR during nutrient-replete growth. However, no effect of UVBR on _obs or biomass was detectable when nutrient limitation exceeded the potential for limitation by UVBR. Thus, a competitive interaction appears to occur between macronutrient stress and UVBR stress, such that _obs and biomass will be determined by the most limiting factor. Our results suggest that measurable decreases in phytoplankton _obs and biomass from UVBR are most likely in nutrient-rich areas of the ocean, while these parameters may not be appropriate for measuring UVBR stress in regions of nutrient limitation.     

Seston composition of the bottom waters of Great Lameshur Bay,St. John,US Virgin Islands

Seston composition [particulate organic carbon (POC), particulate nitrogen (PN), phyto- and microzooplankton numbers and biomass] was investigated in the bottom waters of Great Lameshur Bay, St. John, Virgin Islands (USA), in October, 1970 during Tektite II Mission 17–50. Mean values of 67.4 g POC · I^-1 and 7.2 g PN · I^-1 were determined. A mean phytoplankton carbon content of 42.2 g · I^-1 and zooplankton carbon content of 5.5 g · I^-1 were calculated from counts. The phytoplankton consisted mainly of dinoflagellates 71.2% phytoplankton carbon. Copepods were the dominant zooplankters (61.8% zooplankton carbon), followed by larvaceans (30.9% zooplankton carbon). Organic carbon content of counted zooplankton faecal pellets ranged between 0.4 and 1.6 g · I^-1, and amounted probably to about 15% of the total zooplankton carbon value. Plankton and detritus components as possible food for coral-reef animals are discussed. The ratio carbon: nitrogen of suspended particles is compared to that of sedimented matter.     

Age-structure dependence of the “specific production” in zooplankton populations

This account represents the results of investigations on the production of some zooplankton populations. For comparing different populations the index specific production (the production rate of the unit of the biomass) is used. The correlation between specific production and age-structure for some populations is described. On the basis of the growth theory of Von Bertalanffy (1938) a theoretical model which helps to explain the relation between specific production and age-structure of the population is proposed.     

Le système assimilation-régénération des sels nutritifs dans les eaux superficielles de l'océan Austral

Low primary-productivity levels in high-nutrient environments of the Southern Ocean are not yet well understood. An accurate knowledge of nutrient assimilation by phytoplankton, at the base of the pelagic food-web, therefore appears to be essential. A study of the mesoscale hydrological structure and chemical observations in the upper layers of the Indian sector of the Antarctic Ocean (Cruise MD-25 FIBEX of M.S. Marion Dufresne, January–February 1981) permitted us to develop a method for estimating nutrient consumption by phytoplankton. After strong vertical mixing in winter, the homogeneous Antarctic Surface Water (ASW) is, in summer, divided into two parts by a well-formed pycnocline. In the upper layer, corresponding approximately to the photic zone, we observed nutrient depletion resulting from photosynthetic activity, while the underlaying thermal minimum layer displayed unaltered winter characteristics, including nutrient concentrations typical of winter surface-water conditions. Taking into account the nutrient depletion in summer, we calculated the assimilation ratios for Antarctic phytoplankton as follows: ([NO ₃ ^- lower]-[NO ₃ ^- upper]):([PO ₄ upper])=N:P=11.2±2.4 and N:Si=0.27±0.05. These ratios are lower than the classical Redfield ratios (N:P=16 and N:Si=1), but are in good agreement with the elementary composition of phytoplankton samples collected during the same cruise. Moreover, they agree with previously published data on stoechiometric determinations of particulate matter in surface-water samples. Besides, in the transition layer between the lower layer and Warm Deep Water (WDW), the calculated mineralization ratios were slightly higher than the assimilation ratios: N:P=14.6 and N:Si=0.37. From these ratios, it would appear that, in these surface layers of the Southern Ocean (down to 250 m), assimilation-regeneration mechanisms operate in such a way that phosphate and silicate contents decrease much more than nitrate content during the northward drift of the surface waters. The determination of assimilation ratios taking into account the nutrient depletion of the upper layer allowed us to evaluate the carbon net-production which integrates time-space variations in the photic layer over the whole early summer period. We estimated a production rate (0.4 g C m^-2 d^-1) of the same order of magnitude as the mean value obtained by the ¹⁴C method (0.2 g C m^-2 d^-1). The theoretic silicium consumption by phytoplankton along a meridian transect, calculated using an estimated assimilation ratio of C:Si=1,85, indicates that the marked south-north decrease in silicate concentration in the Antarctic Surface Water would mainly result from biological activity. The silicate concentrations thus calculated were in good agreement with concentrations measured along a previous transect across the Southern Ocean.

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Le système assimilation-régénération des sels nutritifs dans les eaux superficielles de l'océan Austral

     

Primary production in Dumbell Bay in the Arctic Ocean

Photosynthesis, chlorophyll, inorganic nutrients, and related factors were measured throughout a productive season in a small coastal inlet of the Arctic Ocean. Significant production was confined to 5 m for a very limited time period beacause of both light and nutrient limitations. Maximum chlorophyll was 8.2 mg Chl a m^-3 and maximum gross and net photosynthesis rates were 830 and 550 mg C m^-2 d^-1. Annual gross and net photosynthesis is estimated at about 12 and 9 g C m^-2 respectively. The effect of light stimulation on assimilation is described, sources of coastal zone nutrient enrichment are considered, and discrepancies between gross and net photosynthesis are discussed with reference to the growth characteristics of the phytoplankton population.Bigelow Laboratory for Ocean Sciences. Contribution No. 76008     

Relationship between phytoplankton cell size and the rate of orthophosphate uptake: in situ observations of an estuarine population

Orthophosphate uptake by a natural estuarine phytoplankton population was estimated using two methods: (1) ³²P uptake experiments in which filters of different pore sizes were used to separate plankton size-fractions; (2) ³³P autoradiography of phytoplankton cells. Results of the first method showed that plankton cells larger than 5 m were responsible for 2% of the total orthophosphate uptake rate. 98% of the total uptake rate occurred in plankton composed mostly of bacteria, which passed the 5 m screen and were retained by the 0.45 m pore-size filter. There was no orthophosphate absorption by particulates in a biologically inhibited control containing iodoacetic acid. Orthophosphate uptake rates of individual phytoplankton species were obtained using ³³P autoradiography. The sum of these individual rates was very close to the estimated rate of uptake by particulates larger than 5 m in the ³²P labelling experiment. Generally, smaller cells were found to have a faster uptake rate per m³ biomass than larger cells. Although the nannoplankton constituted only about 21% of the total algal biomass, the rate of phosphate uptake by the nannoplankton was 75% of the total phytoplankton uptake rate. Results of the plankton autoradiography showed that the phosphate uptake rate per unit biomass is a power function of the surface: volume ratio of a cell; the relationship is expressed by the equation Y=2x10^-11 X ^1.7, where Y is gP m^-3 h^-1 and X is the surface: volume ratio. These results lend support to the hypothesis that smaller cells have a competitive advantage by having faster nutrient uptake rates.     

Fractionated phytoplankton primary production,exudate release and bacterial production in a Baltic eutrophication gradient

The distribution of phytoplankton primary production into four size fractions (>10 m, 10-3 m, 3-0.2 m and <0.2 m), the utilization of algal exudates by bacteria and the bacterial production were studied in a eutrophication gradient in the northern Baltic proper. The polluted area exhibits substantially increased nutrient, especially nitrogen, levels while only minor differences occur in salinity and temperature regimes. Total primary production was 160 g C · m^-2 · yr^-1 at the control station and about 275 g C · m^-2 · yr^-1 at the eutrophicated stations. The estimated total exudate release was 16% of the totally fixed ¹⁴CO₂ in the control area and 12% in the eutrophicated area (including the estimated bacterial uptake of exudates). The difference in¹⁴CO₂ uptake rates between incubation of previously filtered water (<3, <2, <1 m) and unfiltered water was used to estimate bacterial uptake of phytoplankton exudates which were found to contribute about half of the estimated bacterial carbon requirement in both areas. Bacterial production was estimated by the frequency of dividing cells (FDC) method as being 38 g C · m^-2 · yr^-1 at the control station and 50 g C · m^-2 · yr^-1 at the eutrophicated stations. To estimate the mean in situ bacterial cell volume a correlation between FDC and cell volume was used. The increased annual primary production in the eutrophicated area was due mainly to higher production during spring and autumn, largely by phytoplankton cells (mainly diatoms) retained by a 10 m filter. Primary production duringsummer was similarin the two areas, as was the distribution on different size fractions. This could possibly explain the similar bacterial production in the trophic layers at all stations since the bulk of bacterial production occurs during summer. It was demonstrated that selective filtration does not quantitatively separate photoautotrophs and bacteria. A substantial fraction of the primary production occurs in the size fraction <3 m. The primary production encountered in the 3-0.2 m fraction was due to abundant picoplankton (0.5 to 8 · 10⁷ ind · l^-1), easily passing a 3 m filter. The picoplankton was estimated to constitute up to 25% of the total phytoplankton biomass in the control area and up to 10% in the eutrophicated area.     

A comparative study of photoadaptation in four diatoms isolated as endosymbionts from larger foraminifera

Four endosymbiotic diatoms were isolated from 2 species of larger foraminifera collected in the Red Sea and Hawaii. The photoadaptive responses of the cultured diatoms were measured at 312, 19 and 7 W cm^-2. Two of the diatoms (Fragilaria shiloi and Nitzschia laevis), both isolated from Amphistegina lessonii, grew fastest at 312 W cm^-2. The other two diatoms (N. valdestriata and N. panduriformis) which were isolated from Heterostegina depressa, grew best at 19 W cm^-2. Of the four diatoms, F. shiloi grew best at high light levels. Also in F. shiloi, chlorophyll c content per cell was directly proportional to light intensity; in contrast chlorophyll a and carotenoids increased to maxima at 19 W cm^-2. The chlorophyll a and c and carotenoid content of N. valdestriata were also maximal at 19 W cm^-2. Photosynthetic rates, measured by respirometry, suggested that the diatoms were photoinhibited at higher light intensities and did well at moderately low light intensities (175W cm^-2). The photocompensation points of all 4 diatoms were about 2% of the light available in the spring at 1-m depth at Elat on the Red Sea. At Elat the photocompensation point would lie between 40 and 50 m if the algae were free in nature. The amount of attenuation of light by the shells of the host has not yet been measured. Presumably photocompensation of the algae within hosts is reached at depths less than 40 m.     

Benthic response to sedimentation events during autumn to spring at a shallow water station in the Western Kiel Bight

Seasonal variations in bacterial populations (total number, biomass, biomass-spectrum, number of dividing cells) as well as in concentrations and decomposition rates of particulate organic material were followed in a sandy mud sediment of the Western Kiel Bight (Baltic Sea; FRG). The strong seasonal variations observed could be traced back to the effect of certain ecological situations and events in the sediment from which the input of the phytoplankton blooms in autumn and spring, respectively, the accumulation of organic material during winter, and the spring development of the benthic fauna turned out to be the most important. Bacterial carbon net production following the breakdown of the phytoplankton blooms ranged between 9 g (autumn) and 16 g (spring) per g of dry weight sediment per day. The consequences of shifts in the size composition of the bacterial populations as well as the importance of the measurement of enzymatic decomposition rates of particulate organic material in sediments are demonstrated and discussed in relation to the events mentioned above.Publication No. 420 of the Joint Research Program at Kiel University (Sonderforschungsbereich 95 der Deutschen Forschungsgemeinschaft)     

Swimming pattern as an indicator of the roles of copepod sensory systems in the recognition of food

The roles of copepod sensory systems in the recognition of food were investigated using the Bugwatcher, a video-computer system designed to track and describe quantitatively the swimming patterns of aquatic organisms. The swimming behavior of the copepodPseudocalanus minutus in the presence of phytoplankton is characterized by a decrease in average swimming speed and an increase in pause behaviors compared to its swimming behavior in filtered seawater. Copepods exposed to chemosensory stimulation alone (filtered phytoplankton exudate) exhibited an increase in average swimming speed and an increase in the number of burst swimming behaviors. When exposed to a novel, non-food chemosensory stimulus (morpholine), no change in swimming behavior was observed unless the copepods had been conditioned to this odor in the presence of phytoplankton. Copepods exposed to mechanosensory stimulation alone (plastic spheres) exhibited a decrease in swimming speed and an increase in pause behaviors. When exposed to both forms of stimulation simultaneously (phytoplankton exudate and plastic spheres), a further decrease in swimming speed and increase in pause behaviors occurs, yielding a swimming pattern similar to that found in the presence of phytoplankton. This analysis of swimming pattern indicates that both chemoreception and mechanoreception contribute to the recognition of food inP. minutus.Contribution No. 406 of the US EPA Environmental Research Laboratory; Narragansett, Rhode Island 02882, USA     

Excretion of ammonia by zooplankton and its potential contribution to nitrogen requirements for primary production in the Catalan Sea (NW Mediterranean)

Excretion of ammonia by mesozooplankton (>200 m zooplankton) and its potential contribution to the nitrogen requirement for phytoplankton growth has been estimated for different hydrographical situations along a transect across the Catalan Sea (Northwestern Mediterranean). The nitrogen excreted as ammonia was estimated from mesozooplankton biomass and specific excretion rates. Nitrogen requirements of phytoplankton were estimated by means of carbon fixation rates and C:N ratios of <200 m particulate organic matter. Minimum C:N ratios and maximum primary production, zooplankton biomass, phytoplankton nitrogen requirements, and nitrogen excretion of zooplankton occurred near the Catalan density front. On average, the nitrogen regenerated by the mesozooplankton accounted for 43% of the nitrogen requirements of the phytoplankton. The specific excretion rates of ammonia and the percentage of phytoplanktonnitrogen requirements supplied by excreted nitrogen were higher at coastal stations. In some coastal and frontal stations, the ammonia excreted exceeded the phytoplanktonnitrogen demand. Bacteria competing for nutrient supply and the possible uncoupling between rate processes and standing stocks of phyto- and zooplankton could explain the apparent excess of regenerated ammonia.     

Isotopic characterization of atmospheric nitrogen inputs as sources of enhanced primary production in coastal Atlantic Ocean waters

Current estimates indicate that atmospheric nitrogen deposition is responsible for 26 to over 70% of new nitrogen (N) input to North Carolina estuaries and coastal waters. Concentrations of N in coastal rainfall events in a 2-yr period (August 1990 to 1992) ranged from 0.7 to 144 M for NO ₃ ^- and 0.5 to 164 M for NH ₄ ⁺ . The ¹⁵N values of the NO ₃ ^- and the NH ₄ ⁺ were determined in 15 rain events. NH₄ ⁺ values averaged-3.13 (range:-12.5 to+3.6), while NO ₃ ^- plus dissolved organic N fractions had an average ¹⁵N of+1.0 (range:-2.0 to+4.7). The uptake of this isotopically light N into particulate N, in parallel with primary productivity and biomass (as chlorophyll a) determinetions, was examined in microcosm and mesocosm bioassays. As phytoplankton productivity and biomass increased with added rainwater N, the ¹⁵N of particulate N decreased. To investigate the effects of significant atmospheric N loading with stable isotope tracers, we measured the ¹⁵N of the>1 m fraction from surrounding coastal waters. Owing to the episodic nature of atmospheric deposition and the great variation in N loading with each event, a simple assessment of the atmospheric contribution was not possible. During a period in which rainfall inputs were significant and frequent (August 1992), ¹⁵N values were several more negative than during periods of drought (Fall 1990). These experiments and observations emphasize the contribution of atmospheric nitrogen deposition to new production in coastal waters.     

Carbon fixation in marine phytoplankton: carboxylase activities and stable carbon-isotope ratios; physiological and paleoclimatological aspects

We measured the activity of three carboxylases: RuBP carboxylase, PEP carboxylase and PEP carboxykinase of marine phytoplankton species in culture and in natural communities. Activities of the three carboxylases were measured simultaneously with stable carbon-isotope ratios. The enzymatic activities have been used to estimate the importance of carboxylation and its impact on the ¹³C:¹²C ratio (expressed as ¹³C). The marine phytoplankton species in culture were Fragilariopsis kerguelensis, Nitzschia turgiduloides, Skeletonema costatum, Phaeodactylum tricornutum, Isochrysis galbana, Dunaliella marina, and Prorocentrum micans, and the field samples were collected from different depths off the coast of Portugal (August/September, 1981). Our results indicate that, as in terrestrial plants, the ¹³C value is a good indicator of the extent of carboxylation. RuBP carboxylase activity was always predominant, whereas the ¹³C value never reached values typical of the C₄ pathway. The carboxylases could be PEP carboxylase (in dinoflagellates) or PEP carboxykinase (in diatoms). carboxylation increased at the end of the exponential growth phase in a diatom culture and with increased biomass in natural samples. We interpret these increases as an adaptative response mechanism to poor environmental conditions, especially to low light intensity.     

Temporal variation and distribution of trace metals in freshwater and fish from Calabar River, S.E. Nigeria

An investigation on the abundance and distribution of trace metals (Fe, Cu, Zn, Mn, Cr, Cd and Pb) in water, and nine species of fish samples from Calabar river was carried out in 1992. The concentrations of iron (6000–7240gl^–1), zinc (4910–7230gl^–1), and cadmium (3–7gl^–1) showed moderate pollution while those of copper (420–630gl^–1), manganese (23–48gl^–1), chromium (<10–20gl^–1) and lead (<1–10gl^–1) in water were well below WHO permissible levels. Significant seasonal changes (0.001p0.25) were obtained for iron, copper, zinc, manganese and cadmium in water. Furthermore, iron, zinc and cadmium showed statistically significant spatial changes (0.005p0.10). Of the nine fish species studied, no statistically significant relationship between body weight and the concentrations of the metals was observed. The concentrations of the metals per mean total body weight apparently decreases in the order Fe>Zn>Cu>Mn>Pb>Cd=Cr and were within the limits that were safe for consumption.     

Dependence of consumers on macroalgal (Laminaria solidungula) carbon in an arctic kelp community: δ13C evidence

Stable carbon isotope measurements (¹³C) were used to assess the importance of kelp carbon (-13.6 to-16.5) versus phytoplankton carbon (-25.5 to-26.5) to resident fauna of an isolated kelp bed community on Alaska's north arctic coast from 1979 to 1983. The predominant kelp, Laminaria solidungula, showed some seasonal variation in ¹³C which was correlated with changes in the carbon content of the tissue. Animals that showed the greatest assimilation of kelp carbon (>=50%) included macroalgal herbivores (gastropods and chitons,-16.9 to-18.2), a nonselective suspension feeder (an ascidian,-19.0) and a predatory gastropod (-17.6). Animals that showed the least incorporation of kelp carbon into body tissues (<=7%) included selective suspension-feeders (hydroids, soft corals and bryozoans,-22.8 to-25.1). Sponges, and polychaete, gastropod and crustacean omnivores exhibited an intermediate dependence on kelp carbon (15 to 40%). Within some taxonomic groups, species exhibited a broad range in isotopic composition which was related to differences in feeding strategies. In the polychaete group alone, ¹³C values identified four major feeding habits: deposit-feeders (-18.0), omnivores (-20.4), predators (-22.2) and microalgal herbivores (-23.0). Distinct seasonal changes in the ¹³C values of several animals indicated an increased dependence on kelp carbon during the dark winter period when phytoplankton were absent. Up to 50% of the body carbon of mysid crustaceans, which are key prey species for birds, fishes and marine mammals, was composed of carbon derived from kelp detritus during the ice-covered period.     

Physiological ecology of picoplankton in the North Sea

The distribution of cyanobacteria in the surface waters of the North Sea was measured during July 1987. Numbers of cyanobacteria ranged from 2.5x10⁶ to 1.7x10⁸ cells 1^-1. In the majority of stations, cyanobacterial numbers were highest in the near-surface water and a subsurface maximum was found at only one station. The distribution of ¹⁴C among the end-products of photosynthesis was determined for picoplankton (<1 m) and other phytoplankton >1 m throughout the North Sea. The majority of label was found in the protein fraction of both picoplankton and >1 m phytoplankton; incorporation into lipids and polysaccharides plus nucleic acids was much lower. We interpret the large incorporation into protein to be a consequence of nutrient limitation of these natural assemblages. Photosynthetic parameters of the two size fractions were also determined. Assimilation number (P _m ^B ) and initial slope were greater for the picoplankton fraction than for phytoplankton >1 m but there was no evidence of significant photoinhibition of either fraction at irradiances up to 1 000 E m^-2 s^-1.     

Size classes and major taxonomic groups of phytoplankton at two locations in the subarctic pacific ocean in May and August, 1984

In order to assess the relative importance of the pico- and nanoplankton fractions, the composition of entire phytoplankton communities at Weathership Station P (50°N; 145°W) and at 53°N; 145°W were studied in May and August, 1984, using epifluorescence, scanning electron, and inverted light microscopy. The biomass of major taxa within five size classes was estimated from cell volume and cell concentration. For both months, approximately twothirds of the total phytoplankton carbon were contributed by cells<5 m. In May, 16% of plant biomass was contributed by cells<2 m, and in August 39%. (In both months 90% of plant carbon<2 m was contributed by the bluegreen coccoid Synechococcus spp.) Cells 2 to 5 m contributed about 39% to total plant carbon; they were mostly flagellates in May and nonmotile coccoids in August. The remaining one-third of algal carbon was composed of dinoflagellates, cryptomonads, other flagellates and diatoms, all >5 m. Very little difference between taxa was observed with respect to vertical stratification. Small taxonomic changes were observed in the community between May and August, and within each month.Contribution No. 1694 of the School of Oceanography, University of Washington, Seattle, Washington 98195, USA     

The role of male vs male interactions in maintaining population dialect structure

Summary Nonmigratory populations of Whitecrowned Sparrows in coastal California exhibit dialects in territorial male songs that are stable in space and time. By field playback experiments, we tested a prediction from the hypothesis that male aggressive interactions prohibit mixing of song dialects. Playback of the home dialect Clear song to territorial males singing the Clear dialect resulted in less response than that given to playback of the neighboring Buzzy dialect. Response to both Buzzy and Clear dialect songs by target Clear males, however, was greater than that given to the Bodega dialect recorded 55 km away (Figs. 2 and 3). We conclude that these results are consistent with the hypothesis that male-male aggressive interactions play an important role in reducing dialect mixing.     

Night irradiance and synchronization of lunar release of planula larvae in the reef coral Pocillopora damicornis

Pocillopora damicornis (Linnaeus), which is known to release planula larvae on a monthly cycle, was grown in full daytime solar irradiance, but with four treatments of night irradiance: (1) natural night irradiance, (2) shifted-phase (total darkness during nights of full moon with artificial irradiance at lunar intensity on nights of new moon), (3) constant full moon (full lunar irradiance every night), and (4) constant new moon (total darkness every night). The reproductive cycle of the corals held in the shifted-phase treatment moved out of synchrony with the cycle of corals exposed to a natural lunar cycle of night irradiance. Two previously described types of P. damicornis were tested. The Type Y normally start releasing larvae at full moon, with peak production at third quarter. In the shifted-phase treatment they began releasing planulae at new moon (artificial full moon), with peak production at first quarter. The Type B corals, that normally start releasing planulae at new moon with peak production at first quarter, began to release planulae at full moon (artificial new moon), with peak production at third quarter. Populations of corals grown either in the constant full moon or constant new moon treatment quickly lost synchronization of monthly larva production, although production of planulae continued. Thus spawning is synchronized by night irradiance.Contribution No. 702 of the Hawaii Institute of Marine Biology