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Murray-Darling Freshwater Research CentreMDFRC item.

Murray-Darling Freshwater Research CentreMDFRC item.The late summer phytoplankton of Lake Rotongaio contained an almost pure population of Anabaena minutissima var. attenuata, a gas vacuolate species producing thin solitary filaments. The population was uniformly distributed through the top meter of the water column and then declined with depth to near zero at 6 m. The majority of the Anabaena filaments were buoyant with flotation velocities of c. 0.1 m/d. When samples of lakewater were artificially held at the surface the proportion of buoyant filaments dropped to 88.9% after 9 h of daylight, and to 44.9% at the end of the second day. Turgor pressure varied from 0.33 to 0.43 MPa and could therefore be neglected as a cause of buoyancy loss. Most of the cellular ballast could be accounted for by protein (P) and carbohydrate (C), and increases or decreases in carbohydrate ballast appeared to be the main cause of buoyancy change. A transect along the east-west axis of the lake showed an increase in C/P with distance down-wind at 0 m, and a decrease with distance upwind at 3 m. Hydrodynamic measurements on this date indicated the existence of a wind-driven circulation cell with upwelling at the western (upwind) end of the lake. A computer simulation of this population in Lake Rotongaio indicated that under completely stable conditions the Anabaena would form a maximum at 0.88 m with oscillation of +/-0.01 m over the day/night cycle. In the real lake this depth lies within the mixed layer and stratification would therefore never occur. The time scale of vertical mixing in the Lake Rotongaio was extremely short relative to that required for buoyancy control, and was considered to select in favor of positively buoyant but slowly moving filaments with an ability to exploit a low average irradiance.

Unicellular nitrogen fixing cyanobacteria (UCYN) are abundant members of phytoplankton communities in a wide range of marine environments, including those with rapidly changing nitrogen (N) concentrations. We hypothesized that differences in N availability (N2 vs. combined N) would cause UCYN to shift strategies of intracellular N and C allocation. We used transmission electron microscopy and nanoscale secondary ion massspectrometry imaging to track assimilation and intracellular allocation of13C-labeled CO2 and 15N-labeled N2 or NO3 at different periods across a diel cycle in Cyanothece sp. ATCC 51142. We present new ideas on interpreting these imaging data, including the influences of pre-incubation cellular C and N contents and turnover rates of inclusion bodies. Within cultures growing diazotrophically, distinct subpopulations were detected that fixed N2 at night or in the morning. Additional significant within-population heterogeneity was likely caused by differences in the relative amounts of N assimilated into cyanophycin from sources externaland internal to the cells. Whether growing on N2 or NO 3, cells prioritized cyanophycin synthesis when N assimilation rates were highest. N assimilation in cells growing on NO3 switched from cyanophycin synthesis to protein synthesis, suggesting that once a cyanophycin quota is met, it is bypassed in favor of protein synthesis. Growth on NO3 also revealed that at night, there is a very low level of CO2 assimilation into polysaccharides simultaneous with their catabolism for protein synthesis. This studyrevealed multiple, detailed mechanisms underlying C and N management in Cyanothece that facilitate its success in dynamic aquatic environments.

The cryptophyte Rhodomonas sp. is a potential feed source for aquaculture live feed and resource for phycoerythrin (PE) production. This research investigates the influence of light, both quality and quantity, on the biomass productivity, composition and growth rate of Rhodomonas sp. The incident light intensity used in the experiments was 50 μmolphotons m−2 s−1, irrespective of the colour of the light, and cultivation took place in lab-scale flat-panel photobioreactors in turbidostat mode. The highest productivity in volumetric biomass (0.20 gdry weight L−1 day−1), measured under continuous illumination, was observed under green light conditions. Blue and red light illumination resulted in lower productivities, 0.11 gdry weight L−1 day−1 and 0.02 g L−1 day−1 respectively. The differences in production are ascribed to increased absorption of green and blue wavelength by phycoerythrin, chlorophyll and carotenoids, causing higher photosynthetically usable radiation (PUR) from equal photosynthetically absorbed irradiance (PAR). Moreover, phycoerythrin concentration (281.16 mg gDW−1) was stimulated under red light illumination. Because photosystem II (PSII) absorbs poorly red light, the algae had to induce more pigments in order to negate the lower absorption per unit pigment of the incident available photons. The results of this study indicate that green light can be used in the initial growth of Rhodomonas sp. to produce more biomass and, at a later stage, red light could be implemented to stimulate the synthesis of PE. Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated a significant difference between the cells under different light quality, with higher contents of proteins for samples of Rhodomonas sp. cultivated under green light conditions. In comparison, higher carbohydrate contents were observed for cells that were grown under red and blue light.

Phytoplankton is a diverse group of photosynthesizing organisms which account for approximately fifty percent of the primary production on Earth. Increasing our knowledge on phytoplankton dynamics (and plankton in general) is therefore of major importance. In the present research, we aimed to reveal the spatiotemporal dynamics of the phyto- and zooplankton community in the Eastern English Channel, Southern Bight of the North Sea and the Thames estuary. To do so, we organized a JERICO-NEXT Lifewatch cruise in May 2017 on board of the RV Simon Stevin and sampled 44 stations, involving five research institutions from France (CNRS-LOG,), The Netherlands (RWS, NIOZ) and Belgium (UGENT, VLIZ). To quantify the biomass of the phytoplankton community we used a unique combination of three flow cytometers and two Fast Repetition Rate Fluorometerss that were coupled to the underway ferrybox system. These observations were complemented with Water Insight Spectrometer and water profile data (by means of a CTD) and samples for zooplankton, pigment and nutrient analysis. A dedicated data workshop was organized with all partners to conduct a joint analysis on both the biotic and abiotic data. A first exploration of the data, by means of regression-based models and multivariate statistics, suggested that mainly nutrient discharges from the rivers influence the plankton structure. Furthermore, water turbidity is controlling photosynthetic activity and horizontal and vertical variations of photosynthetic properties can be discriminated.

Executive SummaryThe importance of the phytoplankton production indicator is clearly stated in the MSFD‐Foodweb homepage1: “the phytoplankton production indicator can reflect several pressures (e. g. hydrological changes,contaminants, nutrient inputs or climate changes). Hence, this indicator is highly sensitive and can be usefulas an early warning indicator for direct pressure on food webs. In a trophic context, primary production isprobably the most accurate metric for phytoplankton. Indeed, it is an indicator of potential matter flowneeded by higher trophic levels to produce”.However, Primary Production (PP) is not part yet of the OSPAR’s Joint Assessment and MonitoringProgramme (JAMP)(OSPAR Agreement 2014‐03), the Agreement which describes the strategy, themes andproducts that OSPAR Contracting Parties are committed to deliver. There are several reasons for this, butmost likely the method for measuring PP (e.g. the 14C‐technique) has been time‐consuming, expensive,labour intensive and limited by health‐and‐safety regulations.In this technical background document, part of EcApRHA Deliverable WP3.2, we give a short overview ofcurrent and new methods for measuring primary production. This document supports FW2 (Production ofphytoplankton) as a candidate indicator and proposes options for a common approach to measuringprimary production for OSPAR Contracting Parties.Currently, most primary production measurements are based on variations of the 14C‐technique whichmeasures the uptake of 14CO2 by algal biomass. This document highlights the pros and cons of thistechnique as well as of techniques based on measurements of changes in the oxygen concentration in thewater (either by using bottles or by measuring changes in the ambient O2‐concentration in the water). Newhigh resolution techniques, described in this report, are very promising: the fourier based oxygen methodand Fast Repetition Rate Fluorometry (FRRF). The former needs more testing, but the latter can already beused and is currently applied within the framework of the EU‐H2020 project Jericho‐next and the DutchMONEOS and IN‐PLACE programs. Measurements by FRRF are automated; however, as this methodmeasures the production of electron, calibration against C‐uptake measurements is necessary.Optical methods to measure PP are also described in this document. Application of remote sensing isadvised as it provides synoptic information about PP in the different OSPAR waters. We describe twoapproaches to estimate PP from remote sensing based on chlorophyll concentration (Biomass), photicdepth (P) and daily incident irradiance (I) (BPI models). Parametrization of the BPI model is necessary andcan be done using any technique to measure PP.It is advised that a combination of FRRF and remote sensing should be used by the OSPAR member statesfor developing a uniform monitoring strategy of phytoplankton production across OSPAR waters.

Executive SummaryThe main goal within the EU Marine Strategy Framework Directive (MSFD) is to achieve an ecosystem“Good Environmental Status” (GES). To go from indicator to ecosystem assessment, the Food Webs groupof the EcApRHA project (applying an Ecosystem Approach to (sub) Regional Habitat Assessments) suggestedto use the NEAT tool (http://www.devotes‐project.eu/neat/). NEAT is a free software tool designed to run aholistic status assessment including multiple indicators. To demonstrate its feasibility, our focus is on theintegration of two of the food webs indicators being developed for use within the North‐East Atlanticthrough OSPAR to support MSFD implementation “primary production” and “mean trophic level”. It shouldbe noted that in principle more indicators could be added in future.To run an assessment using multiple indicators in NEAT, the critical information needed is the definition ofa reference value for each indicator, which indicates GES, suggestively through expert knowledge. It isworth noting that the reference values that are proposed in this report are calculated for the purposes ofdemonstrating the NEAT tool and do not represent any agreement of reference values by EuropeanMember States within OSPAR.The result of the NEAT assessment is a value that indicates the environmental status for each spatialassessment unit, which is a value integrating all indicators considered. Per our present knowledge, theNEAT tool is currently one of the best statistical tools available for integrating multiple indicators. Thebiggest challenge encountered was to define the requested reference value and surrounding boundariesfor each indicator, which involved integrating information from experts’ knowledge and literature. It isworth noting however, that within the current revised Commission Decision (2010/477/EU), the EuropeanCommission expects each member state to define the reference value for GES(https://ec.europa.eu/info/law/better‐regulation/initiatives/ares‐2016‐5301702_en).

Executive SummaryThe Marine Strategy Framework Directive (MSFD) aims to achieve Good Environmental Status (GES) withinEuropean Commission waters through an ecosystem‐based approach. The MSFD requires Member Statessharing a marine region or sub‐region to cooperate to ensure that the Directive’s objectives are achievedWorking towards an ecosystem perspective: Proposals for the integration of pelagic, benthic and food web indicatorsand to coordinate their actions through Regional Seas Conventions e.g. the OSPAR Commission for theNorth‐East Atlantic. As part of the ‘applying an Ecosystem Approach to (sub) Regional Habitat Assessments’(EcApRHA) project, integration of indicators under Descriptor 1 (biodiversity), 4 (food webs) and 6 (seafloorintegrity), relating to pelagic and benthic habitats and food webs have been forwarded to work towards anecosystem’s approach in assessing habitats regionally. The content of this report covers differentapproaches developed to integrate indicators forwarded within the project.Five methods are described, four of which were developed to integrate indicators developed under theEcApRHA project. The fifth, OSPAR’s cumulative effect approach has also been summarised as an additionalapproach to integrate indicators. For each method, management implications; the advantages anddisadvantages in relation to being able to work toward assessment of GES; and the confidence in theassessments, are highlighted. The time it would take for the approach to become fully operational, itsfeasibility and costs are also discussed.From the five methods described, three main approaches are discussed:I. A quantitative method to draw links between indicators to assess pressures that have effectson the different aspects of the marine ecosystem (Chapters 3‐4).II. Use of the Nested Environmental status Assessment Tool (NEAT) to integrate differentindicators to provide an overall assessment (Chapters 5 and 6).III. Use of an industry led risk assessment tool (Bow‐Ties) to assess cumulative effects (Chapter 7).The integration approaches outlined within this document demonstrate the developments made within theEcApRHA project to ensure the various indicators under the different descriptors are not only operational,but also integrated in a way which permits a more holistic assessment of the marine environment. Usingsuch a two‐tiered approach of individual indicator and integrated analysis, will enable an understanding ofwhy certain aspects of the marine environment may not be in good condition, and thereby recommendspecific management measures to ameliorate them. Although the approaches forwarded have been initiallytrialled in the North‐East Atlantic, they are able to be applied to other MSFD Regional seas areas. Eachmethod addresses different levels of integration (indicator, habitat or ecosystem) and requires furtherdevelopment and testing. They should be thus considered as complementary and gaps should beprogressed in parallel to ensure coherent progress towards an overall ecosystem approach. In addition,with some further comparative testing between the different methods outlined within this document,options to continue forwarding integrated assessment of OSPAR indicators could be proposed. Themethods outlined within this document are a first step in applying an ecosystem’s approach to assessingthe state of our seas.

We present a method to calibrate and validate observational models that interrelate remotely sensed energy fluxes to geophysical variables of land and water surfaces. Coincident sets of remote sensing observation of visible and microwave radiations and geophysical data are assembled and subdivided into calibration (Cal) and validation (Val) data sets. Each Cal/Val pair is used to derive the coefficients (from the Cal set) and the accuracy (from the Val set) of the observation model. Combining the results from all Cal/Val pairs provides probability distributions of the model coefficients and model errors. The method is generic and demonstrated using comprehensive matchup sets from two very different disciplines: soil moisture and water quality. The results demonstrate that the method provides robust model coefficients and quantitative measure of the model uncertainty. This approach can be adopted for the calibration/validation of satellite products of land and water surfaces, and the resulting uncertainty can be used as input to data assimilation schemes.

Stable-isotope labeling of phospholipid-derived fatty acids (PLFAs) is a potentially powerful technique to study group-specific primary production of phytoplankton, as many algal groups possess a specific PLFA composition, and it is relatively simple to measure the isotopic composition of a large number of PLFAs. Experiments with cultured algae showed that differences exist in labeling among PLFAs and between PLFAs and particulate organic carbon (POC), most likely owing to differences in biosynthesis pathways causing some components of the cell with short pathways to be labeled faster. These differences were constant, however, during the first few hours of incubation, and correction factors were used to convert PLFA labeling to total carbon uptake. In algal cultures, growth rates based on 13C-PLFA labeling agreed well with those based on biomass increases in terms of PLFA concentrations and cell numbers. At two contrasting sites in the Scheldt estuary, PLFA synthesis rates were calculated using 2-h incubations. Group-specific primary production was estimated from PLFA synthesis rates and PLFA compositional spectra of samples and algal taxa using the matrix factorization program Chemtax. When accompanied with studies or information on system-relevant phytoplankton, this sensitive method will be applicable to a wide range of pelagic ecosystems and also to benthic systems such as algal mats.

The present invention relates to a method for size-fractionating particles, comprising subjecting a fluid containing the particles to shearing, thereby inducing particle size segregation, and dividing the fluid in at least one fraction enriched in particles with a relatively high size and at least one fraction enriched in particles with a relatively low size. The invention further relates to an apparatus for carrying out a method according to the invention.

Being extremely turbid environments characterised by short residence times and rapid changes in salinity, the upper reaches of estuaries comprise an extreme environment for phytoplankton to live and grow in. Nevertheless, in many estuaries including the Schelde estuary, these reaches often support dense phytoplankton populations. In the past, these phytoplankton blooms in the upper reaches of estuaries have often been found difficult to explain. In this presentation, we will describe the extent and composition of phytoplankton blooms in the upper Schelde estuary and aim to evaluate the environmental conditions that allow these blooms to occur. In addition, the importance of these blooms in the functioning of the Schelde ecosystem will be discussed.

The question is reviewed whether a balance exists between production and consumption of biological particles in temperate tidal estuaries and what the relationships are between the magnitude of production and consumption processes and system carbon metabolism. The production terms considered are primary production by phytoplankton, microphytobenthos, macroalgae and vascular plants and the chemoautotrophic production, mainly by nitrifying bacteria. The consumption terms are generalized by considering pelagic and benthic mineralization, but major consumer compartments, heterotrophic bacteria, zooplankton, meiobenthos, and macrobenthos are considered in detail. The proposition that estuaries are heterotrophic systems, and become more so when nutrient inputs are higher, is confirmed, and a general equation relating respiration to production is proposed as log R = 0.081 + 1.02 log P (R and P in gC m(-2) yr(-1)). This equation suggests that the amount of heterotrophy is a constant fraction of production. Annual pelagic primary production values lower than 160 gC m(-2) yr(-1) in nutrient- rich or heterotrophic systems are the result of light limitation. The overall recycling efficiency is constant, between 0.7 and 0.8, and is thus independent of system characteristics. Organic loading, rather than inorganic nitrogen loading, ultimately appears to control the primary production in estuarine systems. It is difficult to predict and compare phytoplankton primary production in different estuaries because it is not always clear whether gross or net primary production has been measured. Annual production in some estuaries is probably nitrogen-limited. When phytoplankton is light-limited, annual gross primary production can reasonably be predicted from biomass, incident irradiance and light availability in the water column (photic depth). It appears that interannual variations in annual production are mainly due to (the timing of) different climatological conditions, such as the amount of rainfall and sunshine. Phytoplankton biomass is lower in macrotidal estuaries than in microtidal estuaries. Despite the fact that phytoplankton primary production is controlled by nutrients or light, phytoplankton biomass seems to be determined by the biomass of suspension feeders. Primary production by nitrifying bacteria can be important in estuaries with a heavy organic load. The main suspension feeders in macrotidal estuaries belong to the macrobenthos. The feeding relations between macrobenthos and the production and sedimentation of organic matter in the water are therefore emphasized. For macrobenthic suspension feeders, it is argued that the system-wide biomass and secondary production are limited by the planktonic primary production of the system, whereas the local biomass is highly dependent on hydrodynamic conditions. Macrobenthic deposit feeders take a share of the sedimenting organic matter that depends on the quality and quantity of the organic carbon arriving at the sediment/water interface. Surface deposit feeders directly take up a considerable fraction of the freshly deposited organic matter. Deep deposit feeding is limited by adverse chemical conditions al high organic loading; microbiota take the largest share under these conditions. At low and intermediate loading levels, deep-deposit feeding animals are responsible for a relatively large share of the macrobenthos. [KEYWORDS: Copepod eurytemora-affinis; long-island sound; particulate organic-matter; mesohaline chesapeake bay; coastal marine-sediments; eelgrass zostera-marina; st-lawrence-estuary; mytilus-edulis-l; macrobenthic community structure; bacterial sulfate reduction]