The role of ciliates,heterotrophic dinoflagellates and copepods in structuring spring plankton communities at Helgoland Roads,North Sea

Mesocosm experiments coupled with dilution grazing experiments were carried out during the phytoplankton spring bloom 2009. The interactions between phytoplankton, microzooplankton and copepods were investigated using natural plankton communities obtained from Helgoland Roads (54°11.3′N; 7°54.0′E), North Sea. In the absence of mesozooplankton grazers, the microzooplankton rapidly responded to different prey availabilities; this was most pronounced for ciliates such as strombidiids and strobilids. The occurrence of ciliates was strongly dependent on specific prey and abrupt losses in their relative importance with the disappearance of their prey were observed. Thecate and athecate dinoflagellates had a broader food spectrum and slower reaction times compared with ciliates. In general, high microzooplankton potential grazing impacts with an average consumption of 120% of the phytoplankton production (P _p ) were measured. Thus, the decline in phytoplankton biomass could be mainly attributed to an intense grazing by microzooplankton. Copepods were less important phytoplankton grazers consuming on average only 47% of P _p . Microzooplankton in turn contributed a substantial part to the copepods’ diets especially with decreasing quality of phytoplankton food due to nutrient limitation over the course of the bloom. Copepod grazing rates exceeded microzooplankton growth, suggesting their strong top-down control potential on microzooplankton in the field. Selective grazing by microzooplankton was an important factor for stabilising a bloom of less-preferred diatom species in our mesocosms with specific species (Thalassiosira spp., Rhizosolenia spp. and Chaetoceros spp.) dominating the bloom. This study demonstrates the importance of microzooplankton grazers for structuring and controlling phytoplankton spring blooms in temperate waters and the important role of copepods as top-down regulators of microzooplankton.     

A new source of dimethylsulfide (DMS) for the arctic atmosphere: ice diatoms

We report the first evidence that pennate diatoms growing within the bottom layer of first-year ice in the Arctic produce significant amounts of particulate dimethylsulfoniopropionate (DMSP_p) and dissolved DMSP+DMS. In 1992 in Resolute Passage, a tributary of Barrow Strait, DMSP_p concentrations within the bottom layer of ice reached 1055 mg S m^-3 at the end of the vernal bloom, a value one order of magnitude higher than the maximum value reported in antarctic ice. Bottom-ice concentrations in DMSP_p and DMSP_d+DMS were significantly correlated with the abundance of the dominant pennate diatom Nitzschia frigida. Intracellular concentration in DMSP of ice algae was very low (0.001 pg cell^-1) at the end of April when algae were light-limited and reached 1.17 pg cell^-1 in mid-May following an increase in light and algal growth. We calculate that the rapid release of the dissolved DMSP+DMS from the ice into surface waters following the ice break-up will generate a sea-to-air DMS flux of 0.7 mg S m^-2 d^-1, a pulse ten times higher than the mean arctic summer flux. We estimate that this 1-d pulse represents up to 5% of the annual DMS emission in the Arctic.     

DMSP-lyase activity in five marine phytoplankton species: its potential importance in DMS production

Activity of DMSP-lyase, which cleaves dissolved DMSP (henceforth DMSP_d-lyase), was examined in five axenically cultured phytoplankton species, including both DMSP-producing and non-DMSP-producing species. High DMSP_d-lyase activity was found in two DMSP producers, Heterocapsa triquetra strain NIES-7 and Scrippsiella trochoidea strain NIES-369 (Dinophyceae). The DMS production rates at 100 nM DMSP_d were 0.5 fmol cell⁻¹ min⁻¹ for H. triquetra and 0.3 fmol cell⁻¹ min⁻¹ for S. trochoidea. In a non-DMSP producer, Heterosigma akashiwo strain NIES-6 (Raphidophyceae), the DMSP_d-lyase activity was not found. Two DMSP-producing Prymnesiophyceae species, Isochrysis galbana strain CCMP-1323 and Gephyrocapsa oceanica strain NIES-353, did not show any obvious activity either, in contrary to other authors' findings on Phaeocystis sp., another DMSP-producing Prymnesiophyceae species. The comparison of the DMSP_d-lyase activity of the two Dinophyceae species with bacterial DMSP consumption and DMS production activity in Tokyo Bay showed that the DMSP_d-lyase activity of H. triquetra and S. trochoidea could be an important mechanism for DMS production during their blooms. Received: 9 April 1999 / Accepted: 10 December 1999     

Dimethylsulfide and the algaPhaeocystis pouchetii in antarctic coastal waters

The concentrations of dimethylsulfide (DMS), dimethylsulfoniopropionate (DMSP) and dimethylsulfoxide (DMSO) were measured in water collected from the Southern Ocean 10 km offshore from Davis Station, Antarctica, during the period May 1987 to January 1988, inclusive. During winter and spring, when the sea-ice was up to 1.9 m thick, DMS, DMSP and DMSO concentrations were low (0.2 to 1.5 nM), as were phytoplankton numbers. The maximum concentration of the sulfur compounds generally occurred in the top 10 m of the water column. DMS levels rose dramatically from early December onwards, reaching a peak of 290 nM at a depth of 15 m in January. This concentration is higher than reported elsewhere in the ocean. These high concentrations occurred at the same time as a bloom of the algaPhaeocystis pouchetii. A significant correlation occurred between DMS concentration and cell numbers of the alga. The ratio of DMS concentration to the number of cells of the alga was considerably higher than reported for blooms of this species elsewhere in the ocean. Up to 10% of the total global flux of DMS to the atmosphere may emanate from antarctic seas.     

Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters

Phytoplankton growth and microzooplankton grazing were measured in two productive coastal regions of the North Pacific: northern Puget Sound and the coastal Gulf of Alaska. Rates of phytoplankton growth (range: 0.09–2.69 day⁻¹) and microzooplankton grazing (range: 0.00–2.10 day⁻¹) varied seasonally, with lowest values in late fall and winter, and highest values in spring and summer. Chlorophyll concentrations also varied widely (0.19–13.65 μg l⁻¹). Large (>8 μm) phytoplankton cells consistently dominated phytoplankton communities under bloom conditions, contributing on average 65% of total chlorophyll biomass when chlorophyll exceeded 2 μg l⁻¹. Microzooplankton grazing was an important loss process affecting phytoplankton, with grazing rates equivalent to nearly two-thirds (64%) of growth rates on average. Both small and large phytoplankton cells were consumed, with the ratio of grazing to growth (g:μ) for the two size classes averaging 0.80 and 0.42, respectively. Perhaps surprisingly, the coupling between microzooplankton grazing and phytoplankton growth was tighter during phytoplankton blooms than during low biomass periods, with g:μ averaging 0.78 during blooms and 0.49 at other times. This tight coupling may be a result of the high potential growth and ingestion rates of protist grazers, some of which feed on bloom-forming diatoms and other large phytoplankton. Large ciliates and Gyrodinium-like dinoflagellates contributed substantially to microzooplankton biomass at diatom bloom stations in the Gulf of Alaska, and microzooplankton biomass overall was strongly correlated with >8 μm chlorophyll concentrations. Because grazing tended to be proportionally greater when phytoplankton biomass was high, the absolute amount of chlorophyll consumed by microzooplankton was often substantial. In nearly two-thirds of the experiments (14/23), more chlorophyll was ingested by microzooplankton than was available for all other biological and physical loss processes combined. Microzooplankton were important intermediaries in the transfer of primary production to higher trophic levels in these coastal marine food webs. Received: 12 November 1999 / Accepted: 4 October 2000     

Anti-grazing activity and seasonal variation of dimethylsulfoniopropionate-associated compounds in the invasive alga <Emphasis Type="Italic">Codium fragile</Emphasis> ssp. <Emphasis Type="Italic">tomentosoides</Emphasis>

In this study, we present evidence that the invasive alga Codium fragile ssp. tomentosoides is chemically defended against grazing by a wound-activated chemical defense involving dimethylsulfoniopropionate (DMSP) and the products of its cleavage, dimethylsulfide (DMS), and acrylic acid (AA). DMSP in C. fragile ssp. tomentosoides was present throughout the year, but concentrations varied seasonally and were highest in the winter. Intra-thallus variation was neither large, nor consistent over time. High DMSP concentrations were uncommon among northwestern Atlantic macrophytes. Of 26 other species tested, only two, Ulva lactuca and Polysiphonia harveyi contained concentrations comparable to, or higher than, those of C. fragile ssp. tomentosoides. DMS and AA, both individually and together, deterred grazing by the green sea urchin Strongylocentrotus droebachiensis at “natural” concentrations. These results suggest that DMS and AA contribute to the avoidance of C. fragile ssp. tomentosoides by S. droebachiensis. As a result, the production of DMSP and its subsequent cleavage, upon injury, may reduce herbivory on C. fragile ssp. tomentosoides and contribute to its success.     

Zooplankton grazing on the coccolithophore Emiliania huxleyi and its role in inorganic carbon flux

Grazing and faecal pellet production by the copepods Calanus helgolandicus and Pseudocalanus elongatus, feeding on the coccolithophore Emiliania huxleyi, were measured under defined laboratory conditions, together with the chemical characteristics and sinking rates of the faecal pellets produced. Ingestion rates of both copepods were equivalent at comparable cell concentrations, the relationship between ingestion rate (I, cells copepod^-1 h^-1) and food concentration (C, cells ml^-1), being I=0.558C for both species. P. elongatus produced a larger number of smaller faecal pellets than C. helgolandicus, but egested a larger volume of material per individual. Only between 27 and 50% of the ingested coccolith calcite was egested in the faecal pellets, and it is possible that acid digestion in the copepod gut is responsible for these considerable losses. Average sinking rates of faecal pellets containing E. huxleyi coccoliths, produced by both species, were >100 m d^-1. The implications of the quantitative laboratory estimates for the vertical flux of inorganic carbon are considered using recently studied shelf-break and oceanic E. huxleyi blooms in the N. E. Atlantic as examples.     

Short-term effects of sucralose on Calanus finmarchicus and Calanus glacialis in Disko Bay,Greenland

The potential effects of sucralose on the Arctic copepods Calanus finmarchicus and Calanus glacialis were studied in Disko Bay, Greenland. Sucralose is a non-calorie sweetener and chlorine derivate of sucrose containing three chlorine atoms. Scandinavian screening studies of sucralose in 2007, revealed sucralose in all effluent samples. To investigate whether sucralose is harmful to the Arctic aquatic ecosystems, possible short-term effects were investigated on egg production, hatching rate, food intake and mortality of two species of Arctic copepods. The copepods were exposed to six different concentrations (0–50,000 ng · L^?1) of sucralose, which spans the range of concentrations found in the screening studies. Exposure led to no mortality among the copepods. Food intake by C. glacialis increased with increasing concentrations of sucralose. In C. finmarchicus, food intake did not differ with increasing concentrations. No effect of sucralose was observed on egg production of C. finmarchicus. Despite increased food intake with increasing concentrations of sucralose, C. glacialis did not increase its egg production. The results show that both species responded weakly to sucralose, but with C. glacialis being possibly slightly more sensitive to sucralose than C. finmarchicus.     

Growth and grazing loss rates in single-celledPhaeocystis sp. (Prymnesiophyceae)

Growth and grazing loss rates of naturalPhaeocystis sp. single cells were measured using a seawater dilution technique. Measurements were performed during an intensePhaeocystis sp. bloom in the North Sea between 19 April and 5 May 1988. Experimental results yielded rapid carbon turnover rates. Population growth rates varied from 0.033 to 0.098 h^–1, grazing loss rates from 0.037 to 0.174 h^–1. From measured growth rates, average doubling rages of 1.3 doublings d^–1 were calculated. The growth rates would have resulted in maximum carbon production rates of 146 mg C m^–3 d^–1. Grazing rates increased in the course of the bloom and exceeded growth rates at the end. Grazing loss was caused primarily by microzooplankton feeding. Ciliates and heterotrophic dinoflagellates were identified as the major potential consumers of single cells ofPhaeocystis sp. at the beginning of the bloom. The grazing impact of larger microzooplankton species appeared to increase during the progressing bloom.     

Ammonium regeneration by microzooplankton in the Oslofjord

Concentrations of dissolved inorganic nitrogen compounds above the pycnocline in the Oslofjord are very low in the summer, with turnover times of the inorganic N pools of no more than a few hours. To investigate the possibility that continued phytoplankton growth in the summer depends on ammonium excretion by microzooplankton, rates of NH ₄ ⁺ regeneration and assimilation were measured by a ¹⁵N isotope dilution method. Daytime regeneration rates at 0–2 m depth were 0–28% of the calculated assimilation rates at ambient NH ₄ ⁺ concentrations. Regeneration was faster during a dinoflagellate bloom in August than in mixed diatom-dinoflagellate blooms in June and September. Most of the NH ₄ ⁺ appeared to be produced by juvenile copepods, rotifers, tintinnids, and heterotrophic dinoflagellates in the size fraction 45–200 m.     

Copepod grazing during a declining spring phytoplankton bloom in the Northern North Sea

Grazing rates of larger (Calanus finmarchicus) and smaller (Acartia clausii Pseudocalanus elongatus etc.) copepods on naturally occurring phytoplankton populations were measured during a declining spring phytoplankton bloom. During the initial period, dominated by Chaetoceros spp. diatoms, constant ingestion rates were observed in Calanus finmarchicus at suspended particulate concentrations above 300 g carbon l^-1. Average daily intake during this time amounted to 35 to 40% of body carbon and reached a maximum of 50%. The feeding response of the smaller copepods was not so well defined, although a maximum daily intake of 56% body carbon was recorded. In both groups, feeding thresholds were at particulate concentrations around 50 g C l^-1. The feeding response of C. finmarchicus was correlated with both a change in their own population and in the food cell type. Linear regressions describing the concentration-dependent feeding response were: ingestion rate (IR)=1.16 total particulate volume (TPV)-36.15 during the initial part of the period compared with IR=0.41 TPV-12.18 for the latter period. C. finmarchicus filtered out slightly larger (x 1.2 diameter) particles than the small copepods and, in both groups, some filtering adjustment was made to accomodate to modal changes in the phytoplankton population from 20–30 m to 10 m diameter cells. Particle production during feeding was frequently evident in the smallest size ranges of particles and the ratio of particle production to ingestion rate was greater at low feeding rates.     

Regulation of body dimethylsulfoniopropionate (DMSP) content by the copepod Temora longicornis: a test of four mechanisms

Copepods contain dimethylsulfoniopropionate (DMSP) in their tissues in addition to the DMSP in their gut contents and therefore constitute an additional pool of DMSP in the ocean. In the estuarine copepod Temora longicornis Müller, this dynamic pool of DMSP is reduced when external salinity decreases. In the present study the mechanism(s) used by T. longicornis to adjust its DMSP content were examined. Four possible mechanisms were tested in experiments conducted between July 1997 and May 1999: (1) DMSP cleavage, (2) demethylation, (3) conversion to methionine, and (4) release from the body. Tissue extracts of T. longicornis did not exhibit the ability to cleave or demethylate DMSP. In incubation experiments, when external salinity decreased, T. longicornis individuals reduced their DMSP content without increasing their methionine content. The total amount of DMSP in the incubation vials was conserved regardless of salinity. The copepods retained most of the DMSP in their tissues in 30‰ water, but when salinity was reduced to 20‰, the copepods released 41 to 55% of their body DMSP to the surrounding medium; 89 to 91% of the total DMSP was recovered. This suggests that estuarine copepods represent a reservoir of DMSP, which is released as dissolved DMSP upon salinity decline. Therefore, while osmoregulation by these copepods may have little impact on the chemical properties of DMSP, it will affect the partitioning of DMSP between particulate and dissolved phases in the water column. Received: 20 August 1999 / Accepted: 28 March 2000     

Phaeocystis blooms and eutrophication of the continental coastal zones of the North Sea

It is suggested that novel nuisance algal blooms can result from major shifts in N/P or NH₄ ⁺/NO₃ ^- ratios. Inland hydraulic engineering caused a shift from P-limitation (before 1977) towards N-limitation (after 1977) in the Marsdiep area (Dutch coastal waters). Following this shift the colonial flagellate Phaeocystis sp. became more abundant and started to bloom during the nutrient-controlled period (later spring to autumn). Competition experiments showed that the N/P ratio can influence the species composition of marine phytoplankton. In addition, the natural distribution of some species like Rhodomonas sp. and Emiliania huxleyi may be affected by the frequency of nutrient pulses in the system. Phaeocystis was a poor competitor under P-limitation and a good competitor under N-limitation. Colony formation was absent under P- and NH₄ ⁺-limitation. Colonies were formed under NO₃ ^--limitation. These preliminary results suggest that colony-forming Phaeocystic blooms may be restricted (besides light-controlled environments) to those N-controlled environments where nitrate is consumed by Phaeocystis. The distribution of Phaeocystis along the European continental coast is evaluated on the basis of its ability to compete for nutrients and to form colonies when nitrate is the major N-source.     

Impacts of copepods on marine seston,and resulting effects on<Emphasis Type="Italic"> Calanus finmarchicus</Emphasis> RNA:DNA ratios in mesocosm experiments

We investigated the impact of copepods on the seston community in a mesocosm set-up, and assessed how the changes in food quantity, quality and size affected the condition of the grazers, by measuring the RNA:DNA ratios in different developmental stages of Calanus finmarchicus. Manipulated copepod densities did not affect the particulate carbon concentration in the mesocosms. On the other hand, chlorophyll a content increased with higher copepod densities, and increasing densities had a positive effect on seston food quality in the mesocosms, measured as C:N ratios and 3:6 fatty acid ratios. These food quality indicators were significantly correlated to the nutritional status of C. finmarchicus. In contrast to our expectations, these results suggest a lower copepod growth potential on higher quality food. However, in concordance with earlier studies, we found that when copepods were in high densities the large particles (>1000 µm³) decreased and that the smaller particles (<1000 µm³) increased in number. These patterns were closely linked to the condition of C. finmarchicus, which were of better condition (RNA:DNA ratios) with increasing biovolumes of large particles, and, conversely, lower RNA:DNA ratios with increasing biovolumes of smaller particles. Consequentially, the selective grazing by copepods stimulated increased biovolumes of smaller plankton, and this increase was responsible for the increased food quality, in terms of C:N and 3:6 ratios. Thus, we conclude that the decreasing growth potentials of C. finmarchicus were a result of a decrease of favourably sized food particles, induced by copepod grazing.Communicated by O. Kinne, Oldendorf/Luhe     

Dimethylsulfoniopropionate and dimethylsulfide in the marine flatworm Convoluta roscoffensis and its algal symbiont

 A distinct smell of dimethylsulfide (DMS) was noted at the edge of the intertidal mudflat of Marennes-Oléron Bay, at the French Atlantic coast, where dense populations of the marine flatworm Convoluta roscoffensis Graff (Platyhelminthes: Turbellaria) were present. DMS is the cleavage product of dimethylsulfoniopropionate (DMSP). DMSP was shown to be present in high amounts in sediment containing the flatworm as well as in axenic cultures of the symbiotic alga Tetraselmis sp. that was isolated from the flatworm. In untreated sediment samples containing C. roscoffensis the concentration of DMS was as high as ∼55 μmol l⁻¹ sediment, and in samples that were fixed with glutaraldehyde the concentration of DMS was even three orders of magnitude higher (∼66 mmol l⁻¹ sediment). This rapid cleavage of DMSP to DMS in fixed samples was unexpected. Pure DMSP was stable in glutaraldehyde, and it was therefore concluded that a DMSP-lyase was responsible for cleavage in the field samples. The isolated symbiotic alga, Tetraselmis sp., did not show DMSP-lyase activity, indicating that DMSP-lyase may have been present in the flatworm, although the role of bacteria could not be excluded. The Chl a-specific DMSP content of C. roscoffensis (∼200 mmol g⁻¹) was much higher than that of Tetraselmis sp. (∼30 mmol g⁻¹). Possibly, DMSP was not only present in the symbiotic alga, but was also incorporated in the body tissue of the flatworm. It remains unclear what the function of DMSP is in C. roscoffensis. In Tetraselmis sp., but not in C. roscoffensis, DMSP increased with increasing salinity. It was concluded that salinity probably does not play an important role in the dynamics of DMSP and DMS in sediment containing C. roscoffensis. Received: 21 January 2000 / Accepted: 29 August 2000     

Nodularin accumulation during cyanobacterial blooms and experimental depuration in zooplankton

Cyanobacterial blooms are a common phenomenon in the Baltic Sea, and the hepatotoxin nodularin has been frequently detected in certain Baltic Sea fishes and mussels. However, there is no knowledge about the naturally occurring concentrations of nodularin in Baltic Sea zooplankton. The aim of this study was to survey the concentrations of nodularin in natural zooplankton assemblages, and to study the depuration of nodularin in one common copepod species, Eurytemora affinis, experimentally. The nodularin concentrations in common zooplankton species were determined from field-collected samples from the northern Baltic Proper in 2001 and 2002, during cyanobacterial blooms, and the samples were analysed by ELISA immunoassay. Nodularin could be detected from the field-collected zooplankton, suggesting that during a natural bloom event toxins accumulate in their tissues. The concentrations were relatively low (0.07±0.01 μg g⁻¹ ww), ranging from below detection limit to 0.62 μg g⁻¹ ww. Some variation occurred in the concentrations between species and years; generally concentrations were higher in 2001 than in 2002. In the depuration experiment E. affinis copepods were fed with toxic Nodularia spumigena for 24 h, and their toxin contents were monitored for 24 h after transferring them to filtered seawater. A rapid decrease in nodularin concentrations occurred during the first 0.5–3 h after the exposure. However, after a 24-h depuration period in filtered seawater, nodularin could be still detected in E. affinis tissues, indicating that part of the accumulated nodularin, or its derivatives, could be transferred to planktivores.     

Microzooplankton herbivory on the Grand Bank (Newfoundland,Canada): A seasonal study

Grazing impact of microzooplankton on phytoplankton was investigated on the Grand Bank, Newfoundland, Canada, in April, July and October 1984, using a seawater dilution method. In April a large proportion of chlorophylla was in the microplankton size fraction (> 20µm) while in mid-summer and fall most was in the nanoplankton size fraction (< 20µm). Diatoms were the dominant phytoplankters in April, while undetermined flagellates and coccolithophores were abundant in other seasons. Major grazers were oligotrichous ciliates in all seasons. Instantaneous grazing rates on nanophytoplankton, as measured by changes in chlorophylla, varied from 0.12 to 0.43 d^–1 and those on microphytoplankton from 0.19 to 0.68 d^–1. Grazing rates did not change over 24 and 48 h intervals. This level of grazing corresponded to a daily loss of about 20 and 30% of standing stock of chlorophylla and about 50 and 70% loss of potential production in the two size fractions respectively. Taxon-specific grazing rates, calculated from microscopic enumeration, showed that small diatoms were grazed heavily, and their growth was controlled by grazing in late spring. In late summer and fall, undetermined flagellates and coccolithophores were also grazed at high rates but their growth rates were higher than the grazing rates, and therefore, were not controlled by microzooplankton. In general, microzooplankton grazed on whatever appropriate sized food was dominant in the experimental water. Their potential ability to control the growth of certain food species may be one of the causes determining the species composition of phytoplankton communities.     

<Emphasis Type="Italic">Lyngbya majuscula</Emphasis> blooms and the diet of small subtropical benthivorous fishes

Increasing concerns about the ecological impacts of ongoing and possibly worsening blooms of the toxic, carcinogenic cyanobacteria Lyngbya majuscula in Moreton Bay, Australia, led us to assess differences in meiofaunal prey assemblages between bloom and non-bloom substrates and the potential dietary impacts of dense L. majuscula blooms on the omnivorous benthivore, the Eastern Long-finned Goby, Favonigobius lentiginosus and the obligate meiobenthivorous juveniles of Trumpeter Whiting, Sillago maculata. Marked differences in invertebrate communities were found between sandy and L. majuscula bloom foraging substrates, with copepods significantly more abundant (18.49% vs. 70.44% numerical abundance) and nematodes significantly less abundant (55.91% vs. 1.21% numerical abundance) within bloom material. Gut analyses showed that bentho-planktivorous fishes exposed to L. majuscula in captivity had consumed a significantly greater quantity of prey by both total number (P < 0.0019) and volume (P < 0.0006) than fish exposed to sand treatments. Thus, it is likely for such fishes that L. majuscula blooms increase rates of prey encounter and consumption, with consequent changes in trophic relationships through shifts in predator–prey interactions between small benthivorous fishes and their meiofaunal prey.     

Dimethylsulfide,algal pigments and light in an Antarctic Phaeocystis sp. bloom

Dimethylsulfide (DMS) concentrations in sea water were found to be high (0.19 to 390 nM) in an Antarctic bloom of Phaeocystis sp. during October and November 1990. DMS concentrations were positively correlated with algal pigments, particularly 19-hexanoyloxyfucoxanthin, a prymnesiophyte pigment. Concentrations of DMS varied diurnally, possibly due to effects of sunlight, although the exact mechanism is unknown. Since oceanic DMS production has been linked to the global albedo through the formation of cloud condensation nuclei, light-mediated changes in DMS concentrations may affect the global climate. The flux of DMS from this bloom into the atmosphere is calculated to be 67±55 mol m^-2 d^-1.     

Copepod nutritional condition and pelagic production during autumn in Kosterfjorden,western Sweden

The in situ grazing rate and nutritional condition of copepods were studied during October/November 1985, by analyzing gut fluorescence (feeding), body size and lipid composition (nutritional state), and electron transport system (ETS) activity (respiration rate) of copepods from surface-and deep-water in Kosterfjorden on the Swedish west coast. These parameters were related to the physical and biological environment, as defined by light, hydrography, autotrophic and bacterial production and seston in the water column. The results show a gradual build-up of the autumn phytoplankton bloom in the uppermost meters, with a peak in total autotrophic production in mid October of ca 550 mg C m^–2 d^–1, and a bacterial net production corresponding to 15% of this. Phytoplankton exudates made up, on average, 47% of the primary production and more than 50% of this was utilized by the bacteria. Copepods occurring in the surface-water exhibited grazing rates corresponding to between 11 and 18% of their body C d^–1 and potential growth rates of 0 to 9% d^–1. Copepod populations in the surface water were composed of individuals with higher average body-weight and lower lipid-proportion than those from the deep-water.Calanus finmarchicus in the deep-water showed characters indicating diapause condition, while this was not observed forAcartia clausi. Differences in lipid content and composition indicate thatC. finmarchicus, Pseudocalanus sp. andA. clausi represent three successive points on a scale of tolerance for fluctuations in the food environment. Adult femaleMetridia longa was the only one among seven species/stages of copepods in the deep-water ( 50 m depth) that contained phytoplankton pigments.Study performed through Tjärnö Marine Biological Laboratory, University of Göteborg, S-452 00 Strömstad, Sweden