Phytoplankton In Surface Waters Research Articles

Tracking suspended particulate organic matter biochemistry from glacial meltwater runoff to coastal waters of an Antarctic fjord

Increased glacier melting runoff in Antarctica involves intensification of freshwater, nutrients, sediments and organic matter inputs from land to the sea, which is impacting coastal ecosystems. Basic environmental characteristics of water and biochemical composition of suspended particulate organic matter (POM) both in the proglacial melting runoff system (PROGLARS) of Collins Glacier and marine surface waters of Collins Bay was studied based on organic biopolymers and molecular level analysis of amino acids (AAs), to discern among sources and degradation state in the two environments. Hierarchical Clustering Analysis revealed that PROGLARS stations and marine stations form two distinct groups in terms of water physicochemical characteristics and suspended POM biochemical composition. These differences are the consequence of low restricted contribution of freshwater from Collins Glacier runoff into the coastal-marine environment. Our results evidenced low concentrations of terrestrial suspended POM in marine waters of Collins Bay mainly attributed to low meltwater inputs between the 1st and 7th of February 2018. In terms of macromolecular composition, the predominance of proteins, denote the labile nature of suspended POM in the two environments. Suspended POM in Collins Bay is labile, poorly degraded, representing a protein supplemented food resource, with high energetic value and easily assimilated by heterotrophic marine organism. AAs composition supported less degraded suspended POM derived from marine phytoplankton in surface waters of Collins Bay, whereas, great degradation of suspended POM in the proglacial runoff system of Collins Glacier. Changes in the biochemistry of suspended POM caused by glacial melting and retreat, may affect food features and availability, the productivity of ecosystems, and ultimately, the capacity of Antarctic fjords to act as carbon sinks and climate regulators. Considering low influence of Collins Glacier meltwater in coastal marine waters of Collins Bay, due to the relatively slow retreat of Collins Glacier and low development of its meltwater runoff system, the results of our work are relevant as baseline information for comparison with other Antarctic fjords. Further knowledge about meltwater runoff and suspended POM input dynamics in Antarctic coastal ecosystems, is critical, particularly in areas prone to undergo increased glacier melting in the following decades.

MAP-IO: an atmospheric and marine observatory program on board Marion Dufresne over the Southern Ocean

Abstract. This article is devoted to the presentation of the MAP-IO observation program. This program, launched in early 2021, has enabled the observation of nearly 700 d of measurements over the Indian and Southern Ocean with the equipment of 17 meteorological and oceanographic scientific instruments on board the ship Marion Dufresne. Several observational techniques have been developed to respond to the difficulties of observations on board the ship, in particular for passive remote sensing data, as well as for quasi-autonomous data acquisition and transfer. The first measurements made it possible to draw up unprecedented climatological data of the Southern Ocean regarding the size distribution and optical thickness of aerosols, the concentration of trace gases and greenhouse gases, UV, and integrated water vapor. High-resolution observations of phytoplankton in surface waters have also shown a great variability in latitude in terms of abundance and community structure (diversity). The operational success of this program and these unique scientific results together establish a proof of concept and underline the need to transform this program into a permanent observatory. The multi-year rotations over the Indian Ocean will enable us to assess the trends and seasonal variability of phytoplankton, greenhouse gases, ozone, and marine aerosols in a sensitive and poorly documented climatic region. Without being exhaustive, MAP-IO should make it possible to better understand and assess the biological carbon pump, to study the variability of gases and aerosols in a region that is remote in relation to the main anthropogenic sources, and to monitor the transport of stratospheric ozone by the Brewer–Dobson circulation. The meteorological MAP-IO data set is publicly available at https://www.aeris-data.fr/catalogue-map-io/ (last access: 26 August 2024) (atmospheric data) and at https://doi.org/10.17882/89505 (Thyssen et al., 2022a) (phytoplankton data).

Estimates of the Isotope Effect for Nitrate Assimilation in the Indian Sector of the Southern Ocean

AbstractThe Southern Ocean is a high‐nutrient, low‐chlorophyll (HNLC) region characterized by incomplete nitrate (NO3−) consumption by phytoplankton in surface waters. During this incomplete consumption, phytoplankton preferentially assimilate the 14N‐ versus the 15N‐bearing form of NO3−, quantified as the NO3− assimilation isotope effect (15ε). Previous summertime estimates of the 15ε from HNLC regions range from 4 to 11‰. While culture work has shown that the 15ε varies among phytoplankton species, as well as with light and iron stress, we lack a systematic understanding of how and why the 15ε varies in the field. Here we estimate the 15ε from water‐column profile and surface‐water samples collected in the Indian sector of the Southern Ocean—the first leg of the Antarctic Circumnavigation Expedition (December 2016–January 2017) and the Crossroads transect (April 2016). Consistent with prior work in the mid‐to‐late summer Southern Ocean, we estimate a higher 15ε (8.9 ± 0.6‰) for the northern Subantarctic Zone and a lower 15ε (5.4 ± 0.9‰) at and south of the Subantarctic Front. We interpret our data in the context of coincident measurements of phytoplankton community composition and estimates of iron and light stress. Similar to prior work, we find a significant, negative relationship between the 15ε and the average mixed‐layer photosynthetically active radiation flux of 30–100 μmol m−2 s−1, while above 100 μmol m−2 s−1, 15ε increases again. In addition, while we observe no robust relationship of the 15ε to iron availability or phytoplankton community, mixed‐layer nitrification over the Kerguelen Plateau appears to strongly influence its magnitude.

Hydrocarbon-Degrading Bacteria Found Tightly Associated with the 50–70 μm Cell-Size Population of Eukaryotic Phytoplankton in Surface Waters of a Northeast Atlantic Region

The surface of marine eukaryotic phytoplankton can harbour communities of hydrocarbon-degrading bacteria; however, this algal–bacterial association has, hitherto, been only examined with non-axenic laboratory cultures of micro-algae. In this study, we isolated an operationally-defined community of phytoplankton, of cell size 50–70 μm, from a natural community in sea surface waters of a subarctic region in the northeast Atlantic. Using MiSeq 16S rRNA sequencing, we identified several recognized (Alcanivorax, Marinobacter, Oleispira, Porticoccus, Thalassospira) and putative hydrocarbon degraders (Colwelliaceae, Vibrionaceae) tightly associated with the phytoplankton population. We combined fluorescence in situ hybridisation with flow-cytometry (FISH-Flow) to examine the association of Marinobacter with this natural eukaryotic phytoplankton population. About 1.5% of the phytoplankton population contained tightly associated Marinobacter. The remaining Marinobacter population were loosely associated with either eukaryotic phytoplankton cells or non-chlorophyll particulate material. This work is the first to show the presence of obligate, generalist and putative hydrocarbonoclastic bacteria associated with natural populations of eukaryotic phytoplankton directly from sea surface water samples. It also highlights the suitability of FISH-Flow for future studies to examine the spatial and temporal structure and dynamics of these and other algal–bacterial associations in natural seawater samples.

Observations of surface water phytoplankton community in the Indian Ocean: A transect from tropics to polar latitudes

Phytoplankton, the primary producers in all aquatic systems, plays an important role in key biogeochemical processes that are linked to higher trophic levels and climate variability. The present study deals with the phytoplankton community structure in the Indian Ocean, particularly in the higher latitudes with respect to environmental variables to understand the region specific dominant community and its governing environmental settings. The study areas were selected along the latitudinal transect between 3oN and 53oS (northern Indian Ocean to Indian Ocean sector of Southern Ocean). The surface water phytoplankton community based on microscopy coupled with diagnostic pigment indices showed marked variation in community structure from tropical to polar latitudes of the Indian Ocean. The Prokaryotic diagnostic pigment (ProkDP) dominated in the Equatorial and South Equatorial regions, the Flagellate diagnostic pigment (FlagDP) in the North Equatorial region (NER), Southern Tropical Indian Ocean and Sub-tropical Front (STF) region whereas, the Diatom diagnostic pigment (DiatDP) dominated only at the Polar Front (PF) region. The influence of a suite of environmental variables - temperature, nutrients, salinity and mixed layer depth (MLD), on the dominant phytoplankton groups at the STF and PF was observed. This understanding of community dominance from this poorly explored area with respect to influencing factors is very vital baseline information to design the perturbation experiments in future work to understand the phytoplankton process studies of each region.

Reviews and syntheses: Insights into deep-sea food webs and global environmental gradients revealed by stable isotope (<i>δ</i><sup>15</sup>N, <i>δ</i><sup>13</sup>C) and fatty acid trophic biomarkers

Abstract. Biochemical markers developed initially for food-web studies of terrestrial and shallow-water environments have only recently been applied to deep-sea ecosystems (i.e., in the early 2000s). For the first time since their implementation, this review took a close look at the existing literature in the field of deep-sea trophic ecology to synthesize current knowledge. Furthermore, it provided an opportunity for a preliminary analysis of global geographic (i.e., latitudinal, along a depth gradient) trends in the isotopic (δ15N, δ13C) and fatty acid composition of deep-sea macro- and megafauna from heterotrophic systems. Results revealed significant relationships along the latitudinal and bathymetric gradients. Deep-sea animals sampled at temperate and polar latitudes displayed lower isotopic ratios and greater proportions of essential ω3 long-chain polyunsaturated fatty acids (LC-PUFAs) than did tropical counterparts. Furthermore, δ15N and δ13C ratios as well as proportions of arachidonic acid increased with increasing depth. Since similar latitudinal trends in the isotopic and fatty acid composition were found in surface water phytoplankton and particulate organic matter, these results highlight the link across latitudes between surface primary production and deep-water communities. Because global climate change may affect quantity and quality (e.g., levels of essential ω3 PUFAs) of surface primary productivity, and by extension those of its downward flux, the dietary intake of deep-sea organisms may likely be altered. In addition, because essential ω3 PUFAs play a major role in the response to temperature variations, climate change may interfere with the ability of deep-sea species to cope with potential temperature shifts. Importantly, methodological disparities were highlighted that prevented in-depth analyses, indicating that further studies should be conducted using standardized methods in order to generate more reliable global predictions.

The shelf-to-basin iron shuttle in the Black Sea revisited

Continental shelf sediments are a major source of iron (Fe) for phytoplankton in surface waters. In this study, we investigate the mechanisms that control release of Fe from shelf sediments and its lateral transport (“shuttling”) in oxic and hypoxic waters on the northwestern Black Sea shelf. We find that at two coastal stations near the outflow of the Danube river high input of organic matter drives strong reductive dissolution of Fe(oxyhydr)oxides (henceforth termed Fe oxides) in surface sediments, supporting high rates of Fe release to oxygenated bottom waters (∼0.36 mmol m−2 d−1). We suggest that bioirrigation plays a key role in the release of Fe from these sediments. At four stations further offshore organic matter deposition is lower resulting in limited mobilization of Fe2+ in the sediment and low benthic fluxes of Fe (<0.07 mmol m−2 d−1). Lateral transport of Fe from the coastal zone towards the deep basin mostly takes place in colloidal and/or particulate form (>0.2 μm) in the lower part of the water column, likely through repeated deposition and resuspension of Fe oxides from surface sediments. Using synchrotron-based X-ray spectroscopy and sequential chemical extractions, we demonstrate that the suspended matter and surface sediments are enriched in easily reducible Fe oxides (mostly ferrihydrite) and Fe associated with clay. The mobilization of Fe in the coastal zone and subsequent lateral transport of these Fe-bearing particles results in higher ratios of Fe/Al in surface sediments at outer shelf stations (ca. 1.2 to 2 wt.% wt.%−1) than at coastal stations (ca. 0.5 to 0.9 wt.% wt.%−1). However, below the sediment surface layer Fe/Al ratios are similar at all stations indicating limited burial of the laterally transported Fe. Our results highlight the critical role of organic matter input, associated biological activity and riverine Fe input as drivers of Fe shuttling on continental shelves. We also show that in shelf areas where sediments receive low inputs of organic matter, physical transport controls the ultimate fate of the shuttled Fe.This article is part of a special issue entitled: “Cycles of trace elements and isotopes in the ocean - GEOTRACES and beyond” - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.

Nitrogen uptake by phytoplankton in surface waters of the Indian sector of Southern Ocean during austral summer

This study reports the nitrogen uptake rate (using 15N tracer) of phytoplankton in surface waters of different frontal zones in the Indian sector of the Southern Ocean (SO) during austral summer of 2013. The investigated area encompasses four major frontal systems, i.e., the subtropical front (STF), subantarctic front (SAF), polar front-1 (PF1) and polar front-2 (PF2). Southward decrease of surface water temperature was observed, whereas surface salinity did not show any significant trend. Nutrient (NO3– and SiO44–) concentrations increased southward from STF to PF; while ammonium (NH4+), nitrite (NO2–) and phosphate (PO43–) remained comparatively stable. Analysis of nutrient ratios indicated potential N-limited conditions at the STF and SAF but no such scenario was observed for PF. In terms of phytoplankton biomass, PF1 was found to be the most productive followed by SAF, whereas PF2 was the least productive region. Nitrate uptake rate increased with increasing latitude, as no systematic spatial variation was discerned for NH4+ and urea (CO(NH2)2). Linear relationship between nitrate and total N-uptake reveals that the studied area is capable of exporting up to 60% of the total production to the deep ocean if the environmental settings are favorable. Like N-uptake rates the f-ratio also increased towards PF region indicating comparatively higher new production in the PF than in the subtropics. The moderately high average f-ratio (0.53) indicates potentially near equal contributions by new production and regenerated production to the total productivity in the study area. Elevation in N-uptake rates with declining temperature suggests that the SO with its vast quantity of cool water could play an important role in drawing down the atmospheric CO2 through the “solubility pump”.

Light absorption by phytoplankton in the southern Baltic and Pomeranian lakes: mathematical expressions for remote sensing applications

Summary The absorption properties of phytoplankton in surface waters of the Baltic Sea and coastal lakes are examined in the context of their relationships with the concentration of the main photosynthetic pigment, chlorophyll a. The analysis covers 425 sets of spectra of light absorption coefficients aph(λ) and chlorophyll a concentrations Chla measured in 2006–2009 in various waters of the Baltic Sea (open and coastal waters, the Gulf of Gdansk and the Pomeranian Bay, river mouths and the Szczecin Lagoon), as well as in three lakes in Pomerania, Poland (Obleskie, Łebsko and Chotkowskie). In these waters the specific (i.e. normalized with respect to Chla) light absorption coefficient of phytoplankton aph*(λ) varies over wide ranges, which differ according to wavelength. For example, aph*(440) takes values from 0.014 to 0.124 mg−1 m2, but aph*(675) from 0.008 to 0.067 mg−1 m2, whereby Chla ranges from 0.8 to 120 mg m−3. From this analysis a mathematical description has been produced of the specific light absorption coefficient of phytoplankton aph*(λ), based on which the dynamics of its variability in these waters and the absorption spectra in the 400–700 nm interval can be reconstructed with a low level of uncertainty (arithmetic statistical error: 4.09–10.21%, systematic error: 29.63–51.37%). The relationships derived here are applicable in local remote sensing algorithms used for monitoring the Baltic Sea and coastal lakes and can substantially improve the accuracy of the remotely determined optical and biogeochemical characteristics of these waters.

Unveiling the Si cycle using isotopes in an iron-fertilized zone of the Southern Ocean: from mixed-layer supply to export

Abstract. A massive diatom bloom forms annually in the surface waters of the naturally iron-fertilized Kerguelen Plateau (Southern Ocean). In this study, silicon isotopic signatures (δ30Si) of silicic acid (DSi) and suspended biogenic silica (BSi) were investigated through the whole water column with unprecedented spatial resolution, during the KEOPS-2 experiment (spring 2011). We used δ30Si measurements to track the sources of silicon that fuelled the bloom, and investigated the seasonal evolution of the Si biogeochemical cycle in the iron-fertilized area. We compared the results from stations with various degrees of iron enrichment and bloom conditions to an HNLC reference station. Dissolved and particulate δ30Si signatures were highly variable in the upper 500 m, reflecting the effect of intense silicon utilization in spring, while they were quite homogeneous in deeper waters. The Si isotopic and mass balance identified a unique Winter Water (WW) Si source for the iron-fertilized area that originated from southeast of the Kerguelen Plateau and spread northward. When the WW reached a retroflection of the Polar Front (PF), the δ30Si composition of the silicic acid pool became progressively heavier. This would result from sequential diapycnal and isopycnal mixings between the initial WW and ML water masses, highlighting the strong circulation of surface waters that defined this zone. When comparing the results from the two KEOPS expeditions, the relationship between DSi depletion, BSi production, and their isotopic composition appears decoupled in the iron-fertilized area. This seasonal decoupling could help to explain the low apparent fractionation factor observed in the ML at the end of summer. Taking into account these considerations, we refined the seasonal net BSi production in the ML of the iron-fertilized area to 3.0 ± 0.3 mol Si m−2 yr−1, which was exclusively sustained by surface water phytoplankton populations. These insights confirm that the isotopic composition of dissolved and particulate silicon is a promising tool to improve our understanding of the Si biogeochemical cycle since the isotopic and mass balance allows resolution of processes in the Si cycle (i.e. uptake, dissolution, mixing).

A sclerochronological archive for Antarctic coastal waters based on the marine bivalve Yoldia eightsi (Jay, 1839) from the South Orkney Islands

The scarcity of long instrumental series from the Southern Ocean limits our understanding of key climate and environmental feedbacks within the Antarctic system. We present an assessment for the Antarctic mollusc bivalve Yoldia eightsi as an Antarctic coastal climatological archive, based on annually-resolved growth pattern of 20 live-collected specimens in 1988 from Factory Cove, Signy Island (South Orkney Islands). Two detrending methods were applied to the growth increment series: negative exponential detrending and regional curve standardization (RCS) detrending. The RCS-chronology showed consistent synchronous growth in the population for a 20 year period (1968-1988; expressed population signal ⩾ 0.85), a negative correlation between the RCS-chronology and the fast-ice duration record (r= -0.41, N= 24, P⩽ 0.05) and winter duration (r= -0.52, N=24, P⩽ 0.01) and positive correlations with mean winter sea surface temperature (SST; r= 0.57, N= 24, P⩽ 0.01), mean summer SST (r= 0.46, N= 24, P⩽ 0.05) and mean annual SST (r= 0.48, N= 24, P⩽ 0.05). The chronology appears to record the environmental conditions generated during the Weddell Polynya event (1973 -1976) as detectable abrupt changes in the annual growth patterns. Over eight years (1973-1980) a negative relationship between shell growth and suspended chlorophyll (i.e. a proxy for surface productivity) is apparent which is likely influenced by the seasonal deposition of organic phytodetritus on the seabed following surface water phytoplankton blooms. Our results form a basis for establishing Y. eightsi as an environmental archive for coastal Antarctic waters.

Phytoplankton–bacterial interactions mediate micronutrient colimitation at the coastal Antarctic sea ice edge

Southern Ocean primary productivity plays a key role in global ocean biogeochemistry and climate. At the Southern Ocean sea ice edge in coastal McMurdo Sound, we observed simultaneous cobalamin and iron limitation of surface water phytoplankton communities in late Austral summer. Cobalamin is produced only by bacteria and archaea, suggesting phytoplankton-bacterial interactions must play a role in this limitation. To characterize these interactions and investigate the molecular basis of multiple nutrient limitation, we examined transitions in global gene expression over short time scales, induced by shifts in micronutrient availability. Diatoms, the dominant primary producers, exhibited transcriptional patterns indicative of co-occurring iron and cobalamin deprivation. The major contributor to cobalamin biosynthesis gene expression was a gammaproteobacterial population, Oceanospirillaceae ASP10-02a. This group also contributed significantly to metagenomic cobalamin biosynthesis gene abundance throughout Southern Ocean surface waters. Oceanospirillaceae ASP10-02a displayed elevated expression of organic matter acquisition and cell surface attachment-related genes, consistent with a mutualistic relationship in which they are dependent on phytoplankton growth to fuel cobalamin production. Separate bacterial groups, including Methylophaga, appeared to rely on phytoplankton for carbon and energy sources, but displayed gene expression patterns consistent with iron and cobalamin deprivation. This suggests they also compete with phytoplankton and are important cobalamin consumers. Expression patterns of siderophore- related genes offer evidence for bacterial influences on iron availability as well. The nature and degree of this episodic colimitation appear to be mediated by a series of phytoplankton-bacterial interactions in both positive and negative feedback loops.

Small‐scale variability patterns of DMS and phytoplankton in surface waters of the tropical and subtropical Atlantic, Indian, and Pacific Oceans

AbstractHigh‐resolution surface measurements of dimethylsulfide (DMS), chlorophyll a fluorescence, and the efficiency of photosystem II were conducted together with temperature and salinity along five eastward sections in the tropical and subtropical Atlantic, Indian, and Pacific Oceans. Analysis of variability length scales revealed that much of the variability in DMS concentrations occurs at scales between 15 and 50 km, that is, at the lower edge of mesoscale dynamics, decreasing with latitude and productivity. DMS variability was found to be more commonly related to that of phytoplankton‐related variables than to that of physical variables. Unlike phytoplankton physiological data, DMS did not show any universal diel pattern when using the normalized solar zenith angle as a proxy for solar time across latitudes and seasons. The study should help better design sampling and computing schemes aimed at mapping surface DMS and phytoplankton distributions, taking into account latitude and productivity.

An overview of dissolved Fe and Mn distributions during the 2010–2011 U.S. GEOTRACES north Atlantic cruises: GEOTRACES GA03

High-resolution dissolved Fe (dFe) and dissolved Mn (dMn) distributions were obtained using a trace metal clean rosette during the GEOTRACES GA03 zonal transect cruises (USGT10 and USGT11) across the North Atlantic Ocean. This manuscript provides a general overview of the dFe, as well as dMn and dissolved Al (dAl) distributions that reveal several Fe inputs at varying depths across the study region. Elevated dFe concentrations correlate with elevated dAl concentrations in the surface waters of the subtropical gyre, indicating a significant atmospheric source of Fe, in contrast there is no apparent significant dust source for Mn. In the subsurface waters, dFe maxima are a result of the remineralization process, as revealed by their correspondence with dissolved oxygen minima. Within the oxygen minimum, the ratio of dFe to apparent oxygen utilization (AOU) is lower than would be expected from the measured Fe content of surface water phytoplankton, suggesting that a significant amount of dFe that is remineralized at depth (~63–90%) is subsequently scavenged from the water column. The rate of remineralization, which is based on the slope of dFe:AOU plot, is similar across a wide area of the North Atlantic. In addition to the remineralization process, sedimentary inputs are apparent from elevated dMn signals in the eastern basin, particularly near the African coast. In the western basin, sedimentary input is also occurring along the advective flow path of the Upper Labrador Sea Water (ULSW), as ULSW transits along the North American continental shelf region. The largest dFe anomaly (~68nM), which also corresponds to a dMn anomaly (up to ~33nM) is seen in the neutrally buoyant hydrothermal plume sampled over the Mid-Atlantic Ridge, and that signal is visible for ~500km to the west of the ridge.

Cyanobacterial bloom detection based on coherence between ferrybox observations

Cyanobacterial bloom detection from flow-through optical sensors on ships-of-opportunity (‘ferryboxes’) is challenging in periods of strong stratification and due to varying cell physiology and phytoplankton community composition. Wavelet coherence analysis between ferrybox parameters (chlorophyll-a fluorescence, phycocyanin fluorescence, turbidity) was used to delineate blooms in a dataset of ten ferrybox transects, recorded during the 2005 cyanobacterial bloom season in the Baltic Sea. Independent wind speed and sea-surface temperature data were used to classify areas of cyanobacterial dominance as mixed, stratified, or surfacing bloom. These classified subsets of ferrybox observations were compared against remotely sensed chlorophyll-a concentrations, which resulted in a scheme for the interpretation of surface water phytoplankton biomass from multi-source observations.Ferrybox optical signals were significantly coherent from the onset until the end of the cyanobacterial bloom period under both stratified and mixed conditions. This suggests that the coherence analysis is sensitive to high-level community composition. Strongly stratified and suspected surfacing bloom was associated with unrealistically high remotely sensed chlorophyll-a estimates, indicating the need to flag stratified bloom areas when interpreting remote sensing imagery. The ferrybox fluorescence and turbidity signals at the 5-m sampling depth were, paradoxically, low under these conditions, suggesting that direct comparison between remote sensing and flow-through observations is not useful for stratified blooms. Correlations between ferrybox measurements and remotely sensed observations improved consistently when stratified or surfacing cyanobacterial bloom was excluded from the regression.It is discussed how coherence analysis of ferrybox observations can aid the interpretation of remotely sensed data in situations where meteorological observations suggest incomplete vertical mixing.

Trophic interactions and life strategies of epi- to bathypelagic calanoid copepods in the tropical Atlantic Ocean

Copepods play central roles in pelagic food webs linking primary production to higher trophic levels. Biomarkers (lipids, stable isotopes) provide modern approaches to study dietary preferences and trophic interactions. A cluster analysis based on the fatty acid (FA) and fatty alcohol compositions of calanoid copepods (copepodids C4/C5 and adult stages) from the southeastern tropical Atlantic identified five distinct groups according to lipid composition and storage strategy, coinciding with differences in vertical distribution from the surface to 1800 m depth. Most epipelagic species were characterized by low lipid levels ( 10% of dry mass, DM), low quantities of wax esters (WE) and low dN ratios indicating low trophic positions. In contrast, surface-dwelling Rhincalanus cornutus had higher lipid levels (.29% DM) and stored WE (.90% of total lipid), whereas vertically migrating Pleuromamma species did not store WE. Most mesopelagic copepods belonged to another cluster, defined by high lipid level (max. 47% DM), high amounts of the FA 18:1(n-9) and high dN ratios .9‰ indicating carnivorous feeding at a higher trophic level. Diapausing Calanoides carinatus (copepodids C5), collected at great depth, formed a separate cluster with low dN ratios and high amounts of herbivory markers. The latter were apparently accumulated during active feeding on phytoplankton in surface waters and transferred to the deep sea during ontogenetic vertical migrations. In conclusion, these tropical calanoid copepod species from the surface to the deep sea have adopted diverse feeding strategies and occupy a wide range of ecological niches, affecting energy flux and carbon cycling in the tropical Atlantic.

锦州湾浮游植物群落结构特征及其对环境变化的响应

Phytoplankton plays a vital role in marine ecosystem functioning. It generates roughly 50% of the global primary production,affects the climate process and biogeochemical cycles and sets the upper limits to fishery yield. In addition,due to its fast population responses to water quality and environment stressors,phytoplankton is usually employed as an indicator for assessing eutrophication caused by excess nutrient input and ecosystem health. Jinzhou Bay( 120°55'—121°14'E,40°42'—40°52'N) is a small and shallow semi-enclosed bay in north China with a area of 151. 5 km2 and an averaged depth of3. 5 m. It has a long history of heavy pollution featured by water column eutrophication and heavy metals contamination.Two cruises were carried out during August 2011 and May 2012 respectively to study the spatial distribution and assemblage structure of phytoplankton as well as their ecological responses to the environment changes. Surface water phytoplankton samples were collected at 26 stations and the relevant environmental parameters,i. e. water temperature,salinity,pH,DO,SPM,and nutrient( nitrate,phosphate,silicate) concentrations were measured or sampled simultaneously. The phytoplankton assemblages in Jinzhou Bay were mainly composed by diatom and dinoflagellates groups,and most of them were temperate coastal types. A total of 62 species belong to 4 phylum and 41 genera were identified in the summer andspring cruises. Diatoms were dominant both in species number and cell abundance,with a relatively higher proportion of benthic species. The phytoplankton community structures were significantly different between the two sampling periods. In August 2011,the average cell abundance was 41. 44×103cell /L and the first two dominant species were Thalassiosira spp.and Cerarium furca. In May 2012,the average cell abundance was 13. 80 ×103cell /L and the first two dominant species were Cylindrotheca closterium and Skeletonema costatum. The species diversity was relatively higher in spring( mean 2. 46)than in summer( mean 1. 98). Multivariate ordination techniques were employed to explore the relationships between phytoplankton species and environmental parameters by CANOCO 4. 5. Detrended correspondence analysis( DCA) for the species data showed the maximum gradient length was lower than 3,therefore linear model was applied. Furthermore,the results of redundancy analysis( RDA) indicated that nitrate concentrations and water temperature was the most important influencing factor in summer and spring respectively. Compared with the historic data,the dominant phytoplankton species significantly changed during the last 30 years. Smaller-sized phytoplankton and the species typically found in the eutrophicated environment tended to dominant in Jinzhou Bay. In contrast,the Chaetoceros sp. and Coscinodiscus sp. which were common and important in coastal areas,were both low in species number and cell abundance. This variation trend suggested that the culture eutrophication together with other contaminants might produce certain impacts to the species composition of phytoplankton community in Jinzhou Bay. Systematic and long-term monitoring and study is needed to reveal the ecological responses of phytoplankton assemblage to environment changes and to identify the species capable of indicating the water column eutrophication and heavy metal pollution status of Jinzhou Bay.

Evaluation of Fertilization Effects of Deep Ocean Water on Surface Water Phytoplankton community by Mesocosm Experiments in Subtropical Ocean

Evaluation of Fertilization Effects of Deep Ocean Water on Surface Water Phytoplankton community by Mesocosm Experiments in Subtropical Ocean

Primary description of surface water phytoplankton pigment patterns in the Bay of Bengal

Spatial and temporal variations in surface water phytoplankton pigment distribution in the Bay of Bengal were studied during the spring intermonsoon (SpIM, February–April) and the commencement of the summer monsoon (CSM, May–June), using pigment and diagnostic indices. The Prokaryotic pigment index (Prok DP) was dominant at all the oceanic stations whereas the Flagellate pigment index (Flag DP) was dominant at the near coastal stations. However, during the commencement of summer monsoon, an oscillation in the dominance of Prok DP and Flag DP was observed in the central oceanic bay, whereas flagellates and diatoms were dominant at the near coastal stations. This change in pigment pattern is possibly related to the influence of rainfall. Comparison of pigment data with microscopic cell counts indicated a significant relationship between the diatom pigment index (Diat DP) and diatom abundance. However, the relationship between the dinoflagellate pigment index (Dino DP) and dinoflagellate abundance was not significant. Studies coupling pigment composition analysis with microscopic analysis of phytoplankton in natural conditions should thus be a prerequisite in establishing valid biogeochemical and ecosystem models.

Large-scale patterns in summer surface water phytoplankton (except picophytoplankton) in the Eastern Mediterranean

The phytoplankton community structure (except picophytoplankton) and its relationship with environmental parameters were assessed in the surface waters of the Eastern Mediterranean from inshore to offshore areas during the summer for three years. A total of 105 phytoplankton species in six different algal classes, Dinophyceae (54%), Bacillariophyceae (43%), Haptophyceae (5%), Dicthyochophyceae (1%), Euglenophyceae (1%) and Chrysophyceae (1%), were observed in the Eastern Mediterranean. There were three main phytoplankton groups: the aquaculture area (AQ) group, represented by 11 stations; the coastal water (CW) group, represented by 18 stations; and the open-water (OW) group, represented by 43 stations, showing features typical of the Mediterranean coastal and open-water sites and the predominance of dinoflagellate species over other groups in oligotrophic eastern Mediterranean open waters. The OW group had the highest species richness and dinoflagellates were the most important component of these assemblages and there were differences in the dominant groups from the inshore to the offshore waters. Diatom species richness increased while dinoflagellate species numbers decreased in inshore waters that are nutrient-rich due to anthropogenic activities. There were also significant spatial differences in water conditions, including nutrients and water transparency, which were respectively higher and lower between inshore and offshore areas in the Eastern Mediterranean mainly as the result of local anthropogenic factors. Multiple post hoc comparisons (Tukey’s HSD, p < 0.05) showed that the phytoplankton community in the AQ areas had significantly higher values than in the other groups due to the high abundance of coccolithophores, Dactilosolen and Proboshia. Hence, the AQ group presumably exhibited favourable growth conditions along the coastal area. Furthermore, the community structure of the CW group was more similar to OW ( p > 0.001, R = 0.25) as several coastal stations were not affected by human activities and exhibited a relatively open-water character due to their hydrological conditions.