Spring bloom dynamics in Kongsfjorden, Svalbard: nutrients, phytoplankton, protozoans and primary production

Interaction between phytoplankton and heterotrophic bacteria in Arctic fjords during the glacial melting season as revealed by eDNA metabarcoding

The hydrographic variability in the fjords of Svalbard significantly influences water mass properties, causing distinct patterns of microbial diversity and community composition between surface and subsurface layers. However, surveys on the phytoplankton-associated bacterial communities, pivotal to ecosystem functioning in Arctic fjords, are limited. This study investigated the interactions between phytoplankton and heterotrophic bacterial communities in Svalbard fjord waters through comprehensive eDNA metabarcoding with 16S and 18S rRNA genes. The 16S rRNA sequencing results revealed a homogenous community composition including a few dominant heterotrophic bacteria across fjord waters, whereas 18S rRNA results suggested a spatially diverse eukaryotic plankton distribution. The relative abundances of heterotrophic bacteria showed a depth-wise distribution. By contrast, the dominant phytoplankton populations exhibited variable distributions in surface waters. In the network model, the linkage of phytoplankton (Prasinophytae and Dinophyceae) to heterotrophic bacteria, particularly Actinobacteria, suggested the direct or indirect influence of bacterial contributions on the fate of phytoplankton-derived organic matter. Our prediction of the metabolic pathways for bacterial activity related to phytoplankton-derived organic matter suggested competitive advantages and symbiotic relationships between phytoplankton and heterotrophic bacteria. Our findings provide valuable insights into the response of phytoplankton-bacterial interactions to environmental changes in Arctic fjords.

Taxonomic and functional stability overrules seasonality in polar benthic microbiomes

Coastal shelf sediments are hot spots of organic matter mineralization. They receive up to 50% of primary production, which, in higher latitudes, is strongly seasonal. Polar and temperate benthic bacterial communities, however, show a stable composition based on comparative 16S rRNA gene sequencing despite different microbial activity levels. Here, we aimed to resolve this contradiction by identifying seasonal changes at the functional level, in particular with respect to algal polysaccharide degradation genes, by combining metagenomics, metatranscriptomics, and glycan analysis in sandy surface sediments from Isfjorden, Svalbard. Gene expressions of diverse carbohydrate-active enzymes changed between winter and spring. For example, β-1,3-glucosidases (e.g. GH30, GH17, GH16) degrading laminarin, an energy storage molecule of algae, were elevated in spring, while enzymes related to α-glucan degradation were expressed in both seasons with maxima in winter (e.g. GH63, GH13_18, and GH15). Also, the expression of GH23 involved in peptidoglycan degradation was prevalent, which is in line with recycling of bacterial biomass. Sugar extractions from bulk sediments were low in concentrations during winter but higher in spring samples, with glucose constituting the largest fraction of measured monosaccharides (84% ± 14%). In porewater, glycan concentrations were ~18-fold higher than in overlying seawater (1107 ± 484 vs. 62 ± 101 μg C l-1) and were depleted in glucose. Our data indicate that microbial communities in sandy sediments digest and transform labile parts of photosynthesis-derived particulate organic matter and likely release more stable, glucose-depleted residual glycans of unknown structures, quantities, and residence times into the ocean, thus modulating the glycan composition of marine coastal waters.

Impacts of Atlantic water intrusion on interannual variability of the phytoplankton community structure in the summer season of Kongsfjorden, Svalbard under rapid Arctic change

Atlantification, known as impacts of high-latitude Atlantic water inflows on the Arctic Ocean has strengthened owing to climate change, corresponding to the rapid ice retreat in the Arctic. The relationship between phytoplankton and environmental changes in the Arctic on the interannual scale is unclear because of the lack of long-time series data. In this study, we discuss the ecological response to Atlantic water intrusion in the Kongsfjorden,Svalbard. We measured chlorophyll a and photosynthesis pigments for the water column samples from a fixed section along the Kongsfjorden to study the response of phytoplankton biomass and communities to Atlantic water intrusion in the summer season from 2007 to 2018. The results showed that dinoflagellates, prasinophytes, cryptophytes, and chlorophytes consistently accounted for over 50% of the total biomass, with the distinct annual variation of chlorophyll a. Bioavailable nitrogen was the main limiting factor on phytoplankton growth in the study area, as inferred by its concentration and nutrients ratios. The relationship between phytoplankton and water mass analysis suggested that the intrusion of Atlantic water in Kongsfjorden may cause interannual variability of the phytoplankton biomass and community structure by influencing the nutrient supply and water stratification in the fjord region. Our study provides insights into the ongoing impact of Atlantification on the phytoplankton community in the Arctic fjord.

Selection processes of Arctic seasonal glacier snowpack bacterial communities

BACKGROUND

Arctic snowpack microbial communities are continually subject to dynamic chemical and microbial input from the atmosphere. As such, the factors that contribute to structuring their microbial communities are complex and have yet to be completely resolved. These snowpack communities can be used to evaluate whether they fit niche-based or neutral assembly theories.

METHODS

We sampled snow from 22 glacier sites on 7 glaciers across Svalbard in April during the maximum snow accumulation period and prior to the melt period to evaluate the factors that drive snowpack metataxonomy. These snowpacks were seasonal, accumulating in early winter on bare ice and firn and completely melting out in autumn. Using a Bayesian fitting strategy to evaluate Hubbell's Unified Neutral Theory of Biodiversity at multiple sites, we tested for neutrality and defined immigration rates at different taxonomic levels. Bacterial abundance and diversity were measured and the amount of potential ice-nucleating bacteria was calculated. The chemical composition (anions, cations, organic acids) and particulate impurity load (elemental and organic carbon) of the winter and spring snowpack were also characterized. We used these data in addition to geographical information to assess possible niche-based effects on snow microbial communities using multivariate and variable partitioning analysis.

RESULTS

While certain taxonomic signals were found to fit the neutral assembly model, clear evidence of niche-based selection was observed at most sites. Inorganic chemistry was not linked directly to diversity, but helped to identify predominant colonization sources and predict microbial abundance, which was tightly linked to sea spray. Organic acids were the most significant predictors of microbial diversity. At low organic acid concentrations, the snow microbial structure represented the seeding community closely, and evolved away from it at higher organic acid concentrations, with concomitant increases in bacterial numbers.

CONCLUSIONS

These results indicate that environmental selection plays a significant role in structuring snow microbial communities and that future studies should focus on activity and growth. Video Abstract.

The Interplay of Mycosporine-like Amino Acids between Phytoplankton Groups and Northern Krill (Thysanoessa sp.) in a High-Latitude Fjord (Kongsfjorden, Svalbard)

We investigated pigment and mycosporine-like amino acid (MAA) concentrations of phytoplankton and Northern krill (Thysanoessa sp.) in sub-Arctic Kongsfjorden. Chlorophyll a (Chl-a) concentrations in the surface and middle-layer water were 0.44 μg L⁻¹ (±0.17 μg L⁻¹) and 0.63 μg L⁻¹ (±0.25 μg L⁻¹), respectively. Alloxanthin (Allo, a marker of cryptophytes) was observed at all stations, and its mean values for surface and middle-layer water were 0.09 μg L⁻¹ (±0.05 μg L⁻¹) and 0.05 (±0.02 μg L⁻¹), respectively. The mean MAA-to-Chl-a ratios at the surface (3.31 ± 2.58 μg (μg Chl-a)⁻¹) were significantly higher than those in the middle-layer water (0.88 ± 0.49 μg (μg Chl-a)⁻¹), suggesting that these compounds play an important role in reducing UV photodamage. In gut pigment levels of Northern krill, the most abundant accessory pigment was Allo (2.79 ± 0.33 μg g⁻¹ dry weight; d.w.), as was the accumulation of Chl-a (8.29 ± 1.13 μg g⁻¹ d.w.). The average concentration of MAAs was 1.87 mg g⁻¹ d.w. (±0.88 mg g⁻¹ d.w.) in krill eyes, which was higher than that in all other body parts (0.99 ± 0.41 mg g⁻¹ d.w.), except for the gut. Thysanoessa sp. was found to contain five identified MAAs (shinorine, palythine, porphyra-334, mycosporine-glycine, and M-332) in the krill eye, whereas shinorine and porphyra-334 were only observed in the krill body, not the eyes and gut. These findings suggest that Northern krill accumulate MAAs of various compositions through the diet (mainly cryptophytes) and translocate them among their body parts as an adaptation for photoprotection and physiological demands.

Nutrient fluxes from an Arctic seabird colony to the adjacent coastal marine ecosystem

Seabirds are important vectors for nutrient transfer across ecosystem boundaries. In this seasonal study, we evaluate the impact of an Arctic colony (Alkhornet, Svalbard) of Black-legged Kittiwakes (Rissa tridactyla) and Brünnich’s Guillemots (Uria lomvia) on stream nutrient concentrations and fluxes, as well as utilization by coastal biota. Water samples from seabird-impacted and control streams were collected regularly throughout the melt season (June–September) for nutrient and organic carbon analysis. Stable carbon and nitrogen isotope analysis (δ13C and δ15N) was used to assess whether seabird-derived nitrogen (N) could be traced into filamentous stream algae and marine algae as well as consumers (amphipods). Concentrations of nitrate (NO3−) and nitrite (NO2−) peaked in July at 9200 µg N L−1 in seabird-impacted streams, 70 times higher than for control streams. Mean concentrations of phosphate (PO43−) in seabird-impacted streams were 21.9 µg P L−1, tenfold higher than in controls. Areal fluxes from seabird-impacted study catchments of NO3− + NO2− and PO43− had estimated ranges of 400–2100 kg N km−2 and 15–70 kg P km−2, respectively. Higher δ15N was found in all biota collected from seabird-impacted sites, indicating utilization of seabird-derived nitrogen. Acrosiphonia sp. from seabird-impacted sites had higher δ15N values (20–23‰ vs. 3–6‰) and lower C:N ratios (10.9 vs. 14.3) than specimens collected from control sites, indicating reliance on seabird-derived nitrogen sources and potentially higher N-availability at seabird-impacted nearshore sites. Our study demonstrates how marine nutrients brought onshore by seabirds also can return to the ocean and be utilized by nearshore primary producers and consumers.

Coastal Mesozooplankton Assemblages during Spring Bloom in the Eastern Barents Sea

Simple Summary

Arctic coastal waters have been strongly influenced by climatic fluctuations during the past decades. Recent studies reported clear warming processes in the Barents Sea and adjacent waters. Plankton assemblages are good indicators of environmental changes, and their composition and production affect all components of pelagic ecosystems. Most of data on the zooplankton in Arctic seas were obtained during summer seasons, and little is known about zooplankton communities in other seasons. Spring is one of the crucial periods in the Arctic marine environment, as primary production may reach the annual maximum. To investigate a spring pattern of Arctic mesozooplankton, we performed a study in the eastern Barents Sea. This research is the first report on the spring coastal zooplankton near the Novaya Zemlya Archipelago. We revealed high diversity and abundance of zooplankton taxa. Environmental variability had a significant impact on the mesozooplankton assemblages, with geographical location and phytoplankton density being the most important. Our data may be useful for future investigations dealing with Arctic plankton communities during the era of global climatic changes.

Abstract

Mesozooplankton play an important role in Arctic shelf ecosystems as a trophic link and a key food source for many larval fish species. The distribution of mesozooplankton in the eastern Barents Sea was studied along a 500 nautical mile-long transect in May 2016 during the spring bloom. Mesozooplankton were sampled using a Juday net hauled from the surface to the bottom at 12 stations. We found good correspondence between the distribution of water masses and mesozooplankton assemblages. Mesozooplankton abundance (mean 73·10³ individuals m⁻²) in Novaya Zemlya coastal water was dominated by Copepoda ova and nauplii, Thyssanoessa spp. nauplii and Oithona similis. Parasagitta elegans and Calanus finmarchicus comprised most of the total mesozooplankton biomass (mean 0.9 g dry mass m⁻²) in that water mass. A second assemblage (mean abundance 171·10³ individuals m⁻²) was associated with the colder Barents Sea water, with Oithona similis, Copepoda nauplii, Fritillaria borealis and Cirripedia nauplii being the most numerous. In that water mass, C. finmarchicus, Metridia longa, Cirripedia nauplii and Calanus glacialis contributed most to the total biomass (mean 3 g dry mass m⁻²). The dominance of young stages of Copepoda and a high proportion of meroplankton were typical of spring mesozooplankton assemblages. The spatial distribution of mesozooplankton abundance and biomass was strongly correlated with latitude, longitude and chlorophyll a concentration, which together explained 10% of the total variance in mesozooplankton density. The present investigation is a baseline study for the assessment of the spring mesozooplankton assemblage in the eastern Barents Sea, and for an evaluation of the possible impact of future environmental changes on the Arctic shelf marine ecosystem.

The interplay between plankton and particles in the Isfjorden waters influenced by marine- and land-terminating glaciers

Climate-induced glacial retreat in the Arctic results in an increased supply of meltwater with suspended terrigenous material into the marine environment. Despite increasing research efforts, effects of glacial retreat on functioning of plankton are not well documented and understood. Thus, we studied a hydro-optical seawater regime along with particle/plankton concentrations and composition structure in a high Arctic fjord (Isfjorden, West Spitsbergen) during mid-summer in 2019. This comprehensive study of the upper 50 m water layer presented a sharp distinction between 'muddy' waters influenced by glacial and river runoff and 'clear' open fjordic waters in the form of a notable difference in chlorophyll a concentrations, extent of euphotic zone depth, turbidity, inorganic/organic particle concentrations, and water colour. In this study, we present that the effects of glacial retreat on Arctic pelagial depend not only on different types of glaciers (marine- and land-terminating), but presumably, also on fjord topography and exposure to oceanic water inflow. The contrasting glacial, hydrological, and topographical conditions had different effects on the share of zooplankton and marine snow. Despite adaptation of the planktonic communities in the Arctic to high sediment loads and resultant light limitations, our study shows that continuing retreat of tidewater glaciers will have negative effect on planktonic communities especially in enclosed shallow fjord branches. Moreover, seawater darkening due to high turbidity could negatively affect tactile predators, such as gelatinous zooplankton. Additional division of plankton into functional groups typically used in the biogeochemical models demonstrated that diatoms, flagellates and mesozooplankton are influenced by suspended matter, whereas microzooplankton are highly adaptive to increased sediment loads. Since we investigated the largest Svalbard fjord system and incorporated multiple components of the pelagic realm, the current study delivers important recommendations for including marine snow and gelatinous zooplankton in ecosystem models applied in polar regions.

Bacterial communities in temperate and polar coastal sands are seasonally stable

Coastal sands are biocatalytic filters for dissolved and particulate organic matter of marine and terrestrial origin, thus, acting as centers of organic matter transformation. At high temporal resolution, we accessed the variability of benthic bacterial communities over two annual cycles at Helgoland (North Sea), and compared it with seasonality of communities in Isfjorden (Svalbard, 78°N) sediments, where primary production does not occur during winter. Benthic community structure remained stable in both, temperate and polar sediments on the level of cell counts and 16S rRNA-based taxonomy. Actinobacteriota of uncultured Actinomarinales and Microtrichales were a major group, with 8 ± 1% of total reads (Helgoland) and 31 ± 6% (Svalbard). Their high activity (frequency of dividing cells 28%) and in situ cell numbers of >10% of total microbes in Svalbard sediments, suggest Actinomarinales and Microtrichales as key heterotrophs for carbon mineralization. Even though Helgoland and Svalbard sampling sites showed no phytodetritus-driven changes of the benthic bacterial community structure, they harbored significantly different communities (p < 0.0001, r = 0.963). The temporal stability of benthic bacterial communities is in stark contrast to the dynamic succession typical of coastal waters, suggesting that pelagic and benthic bacterial communities respond to phytoplankton productivity very differently.

Genomic insights into the molecular mechanisms of a Pseudomonas strain significant in its survival in Kongsfjorden, an Arctic fjord

Whole-genome sequence of Pseudomonas sp. Kongs-67 retrieved from Kongsfjorden, an Arctic fjord, has been investigated to understand the molecular machinery required for microbial association and survival in a polar fjord. The genome size of Kongs-67 was 4.5 Mb and was found to be closely related to the Antarctic P. pelagia strain CL-AP6. This genome encodes for chemotaxis response regulator proteins (CheABB1RR2VWYZ), chemoreceptors (methyl-accepting chemotaxis proteins), and flagellar system proteins (FliCDEFGOPMN, FlhABF, FlgBCDEFGHIJKL, and MotAB proteins) vital in cellular interactions in the dynamic fjord environment. A high proportion of genes were assigned to biofilm formation (pgaABCD operon) and signal transduction protein categories (EnvZ/OmpR, CpxA/CpxR, PhoR/PhoB, PhoQ) indicating that the biofilm formation in Kongs-67 could be tightly regulated in response to the availability of signalling-metabolites. The genome of Kongs-67 encoded for HemBCD, CbiA, CobABNSTOQCDP, and BtuBFR proteins involved in cobalamin biosynthesis and transport along with proteins for siderophore-mediated iron channelling (PchR, Fur protein, FpvA); crucial in a microbial association. The genomes of Arctic strain Kongs-67 and Antarctic strain CL-AP6 were similar which is indicative of retainment of the core genes in the polar Pseudomonas strains that could be vital in conferring evolutionary adaptation for its survival in a polar fjord. Thus, our study contributes to the knowledge on the genetics of a polar Pseudomonas member exhibiting biosynthetic potentials and suggest Pseudomonas sp. Kongs-67 as a suitable candidate for the investigation of functional aspects of molecular adaptations in the polar marine environment.

Survey of Bacterial Phylogenetic Diversity During the Glacier Melting Season in an Arctic Fjord

To understand bacterial biogeography in response to the hydrographic impact of climate change derived from the Arctic glacier melting, we surveyed bacterial diversity and community composition using bacterial 16S rRNA gene metabarcoding in the seawaters of Kongsfjorden, Svalbard, during summer 2016. In the present study, bacterial biogeography in the Kongsfjorden seawaters showed distinct habitat patterns according to water mass classification and habitat transition between Atlantic and fjord surface waters. Moreover, we estimated phylogenetic diversity of bacterial communities using the net relatedness, nearest taxon, and beta nearest taxon indices. We found the influence of freshwater input from glacier melting in shaping bacterial assemblage composition through the stochastic model. We further evaluated bacterial contributions to phytoplankton-derived dimethylsulfoniopropionate (DMSP) using a quantitative PCR (qPCR) measurement with demethylation (dmdA) and cleavage (dddP) genes of two fundamentally different processes. Our qPCR results imply that bacterial DMSP degradation follows the Atlantic inflow during summer in Kongsfjorden. These findings suggest that the Atlantic inflow and glacial melting influence bacterial community composition and assembly processes and thus affect the degradation of phytoplankton-derived organic matter in an Arctic fjord.

Phytoplankton dynamics in a subarctic fjord during the under-ice - open water transition

The spring blooms of phytoplankton play a key role in the functioning of marine ecosystems in the polar regions. A spring bloom in the Subarctic White Sea was observed in order to determine the effect of ice cover on the distribution, composition, and temporal changes of phytoplankton communities. The obtained results clearly show that in the White Sea, as in other freezing Arctic seas, ice melting and ice removal both play an essential role in the onset and development of spring phytoplankton blooms. This facilitates the release of ice algae and ice-pelagic algae into the water, as well as the rapid development of true planktonic taxa within the euphotic zone. One major peak of algal biomass is associated with ice removal while the other is recorded in the early summer. Comparison of our results with earlier data from 1960s to 1990s indicated strong year-to-year variation in terms of ice removal, the onset of the spring bloom, and the abundance and composition of the dominant phytoplankton taxa.

Summer and winter MgCO3 levels in the skeletons of Arctic bryozoans

In the Arctic, seasonal patterns in seawater biochemical conditions are shaped by physical, chemical, and biological processes related to the alternation of seasons, i.e. winter polar night and summer midnight sun. In summertime, CO₂ concentration is driven by photosynthetic activity of autotrophs which raises seawater pH and carbonate saturation state (Ω). In addition, restriction of photosynthetic activity to the euphotic zone and establishment of seasonal stratification often leads to depth gradients in pH and Ω. In winter, however, severely reduced primary production along with respiration processes lead to higher CO₂ concentrations which consequently decrease seawater pH and Ω. Many calcifying invertebrates incorporate other metals, in addition to calcium, into their skeletons, with potential consequences for stability of the mineral matrix and vulnerability to abrasion of predators. We tested whether changes in seawater chemistry due to light-driven activities of marine biota can influence the uptake of Mg into calcified skeletons of Arctic Bryozoa, a dominant faunal group in polar hard-bottom habitats. Our results indicate no clear differences between summer and winter levels of skeletal MgCO₃ in five bryozoan species despite differences in Ω between these two seasons. Furthermore, we could not detect any depth-related differences in MgCO₃ content in skeletons of selected bryozoans. These results may indicate that Arctic bryozoans are able to control MgCO₃ skeletal concentrations biologically. Yet recorded spatial variability in MgCO₃ content in skeletons from stations exhibiting different seawater parameters suggests that environmental factors can also, to some extent, shape the skeletal chemistry of Arctic bryozoans.

In Situ Rates of Carbon and Nitrogen Uptake by Phytoplankton and the Contribution of Picophytoplankton in Kongsfjorden, Svalbard

Rapid climate warming and the associated melting of glaciers in high-latitude open fjord systems can have a significant impact on biogeochemical cycles. In this study, the uptake rates of carbon and nitrogen (nitrate and ammonium) of total phytoplankton and picophytoplankton (<2 μm) were measured in Kongsfjorden in early May 2017 using the dual stable isotope technique. The daily uptake rates of total carbon and nitrogen ranged from 0.3 to 1.1 g C m−2 day−1, with a mean of 0.7 ± 0.3 g C m−2 day−1, and 0.13 to 0.17 g N m−2 day−1, with a mean of 0.16 ± 0.02 g N m−2 day−1. Microphytoplankton (20–200 μm) accounted for 68.1% of the total chlorophyll a (chl-a) concentration, while picophytoplankton (<2 μm) accounted for 19.6% of the total chl-a, with a high contribution to the carbon uptake rate (42.9%) due to its higher particulate organic carbon-to-chl-a ratio. The contributions of picophytoplankton to the total nitrogen uptake rates were 47.1 ± 10.6% for nitrate and 74.0 ± 16.7% for ammonium. Our results indicated that picophytoplankton preferred regenerated nitrogen, such as ammonium, for growth and pointed to the importance of the role played by picophytoplankton in the local carbon uptake rate during the early springtime in 2017. Although the phytoplankton community, in terms of biovolume, in all samples was dominated by diatoms and Phaeocystis sp., a higher proportion of nano- and picophytoplankton chl-a (mean ± SD = 71.3 ± 16.4%) was observed in the relatively cold and turbid surface water in the inner fjord. Phytoplankton production (carbon uptake) decreased towards the inner fjord, while nitrogen uptake increased. The contrast in carbon and nitrogen uptake is likely caused by the gradient in glacial meltwater which affects both the light regime and nutrient availability. Therefore, global warming-enhanced glacier melting might support lower primary production (carbon fixation) with higher degrees of regeneration processes in fjord systems.

Microbial Eukaryotes in an Arctic Under-Ice Spring Bloom North of Svalbard

Microbial eukaryotes can play prominent roles in the Arctic marine ecosystem, but their diversity and variability is not well known in the ice-covered ecosystems. We determined the community composition of microbial eukaryotes in an Arctic under-ice spring bloom north of Svalbard using metabarcoding of DNA and RNA from the hypervariable V4 region of 18S nrDNA. At the two stations studied, the photosynthetic biomass was dominated by protists >3 μm and was concentrated in the upper 70–80 m, above the thermocline and halocline. Hierarchical cluster analyses as well as ordination analyses showed a distinct clustering of the microbial eukaryote communities according to a combination of water mass and local environmental characteristics. While samples collected in the surface mixed layer differed distinctly between the two sites, the deeper communities collected in Atlantic Water were fairly similar despite being geographically distant. The differentiation of the microbial eukaryote communities of the upper mixed water was probably driven by local development and advection, while the lack of such differentiation in the communities of Atlantic Water reflects the homogenizing effect of water currents on microbial communities.

Variation of phytoplankton assemblages of Kongsfjorden in early autumn 2012: a microscopic and pigment ratio-based assessment

Phytoplankton species distribution and composition were determined by using microscopy and pigment ratios in the Kongsfjorden during early autumn 2012. Variation in sea surface temperature (SST) was minimal and matched well with satellite-derived SST. Nutrients were generally limited. Surface phytoplankton abundance ranged from 0.21 × 10(3) to 10.28 × 10(3) cells L(-1). Phytoplankton abundance decreased with depth and did not show any significant correlation with chlorophyll a (chl a). Column-integrated phytoplankton cell counts (PCC) ranged from 94.3 × 10(6) cells m(-2) (Kf4) to 13.7 × 10(6) cells m(-2) (Kf5), while chl a was lowest at inner part of the fjord (6.3 mg m(-2)) and highest towards the mouth (24.83 mg m(-2)). Biomass from prymnesiophytes and raphidophytes dominated at surface and 10 m, respectively. The contribution of Bacillariophyceae to biomass was low. Generally, heterotrophic dinoflagellates were great in abundance (12.82 %) and ubiquitous in nature and were major contributors to biomass. Various chl pigments (chl b, chl c, phaeopigments (phaeo)) were measured to obtain pigment/chl a ratios to ascertain phytoplankton composition. Phaeo were observed only in inner fjord. Chl b:a ratios and microscopic observations indicated dominance of Chlorophyceae at greater depths than surface. Furthermore, microscopic observations confirmed dominance of chl c containing algae throughout the fjord. The study indicates that pigment ratios can be used as a tool for preliminary identification of major phytoplankton groups. However, under the presence of a large number of heterotrophic dinoflagellates such as Gymnodinium sp. and Gyrodinium sp., pigment signatures need to be supplemented by microscopic observations.

Bioremediation using Gracilaria chouae co-cultured with Sparus macrocephalus to manage the nitrogen and phosphorous balance in an IMTA system in Xiangshan Bay, China

A cage experiment using the red alga Gracilaria chouae co-cultured with the black seabream Sparus macrocephalus in Xiangshan Bay, China was conducted to measure the nutrient flux of the integrated multi-trophic aquaculture (IMTA) system. Results showed that trash fish were the main nutrient input contributor and adult fish were the main nutrient output contributor in the system. Contents of N and P in adult fish accounted for 54.45% and 59.48% of N and P in trash fish and fry, which suggests that 45.55% of N and 40.52% of P generated by fish farming were released into to the water. G. chouae proved to be an efficient bioremediation species in this IMTA system. To balance the excess nutrients generated by the system, 231.09 kg of seedlings should be cultured and 5315.07 kg of adult seaweed should be harvested.