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As the world's leading producer of farmed aquatic food products, China faces great uncertainty concerning the further sustainable development of its aquaculture industry due to high and increasing pressure from environmental and resource constraints. To realize truly sustainable development, it is imperative to establish an evaluation system that integrates social, economic, environmental and resource criteria, and optimizes aquaculture systems through a holistic approach. Here, we used analytical hierarchy processes combined with expert judgment and objective data to assess the sustainability of 10 major aquaculture production systems (APSs) in China. Based on the evaluation results, we propose the ecological intensification of aquaculture systems (ELIAS), rationally integrating anthropogenic inputs with aquaculture ecosystem services, to improve the sustainability of APSs. The holistic evaluation system and ELIAS are fundamental and critical for the future development of aquaculture in China and globally.

Chilean salmon farms release inorganic nutrients excreted by the fish into the surrounding water in Patagonian fjords. The objective of this experiment from the Comau Fjord (42.2° S) in southern Chile was to study how increased input of ammonium (NH4) and phosphate (PO4) from salmon farms might affect the community structure of bacteria in surface waters where fish farms are located. We used microcosms (35 l) with NH4-N and PO4-P added to the natural seawater in a gradient of nutrient-loading rates, with the same N:P ratio as in salmon aquaculture effluents. Additionally, we measured bacterial community structure at different depths in the Comau Fjord to assess the natural variation to compare with our experiment. We used denaturing gradient gel electrophoresis (DGGE) to create 16S rDNA fingerprints of the bacterial communities and monitored biological and environmental variables (chlorophyll a, inorganic nutrients, pH, microbial abundance). The nutrient-loading rate had a significant impact on the bacterial community structure, and the community dissimilarity between low and high nutrient additions was up to 78%. Of the measured environmental variables, phytoplankton abundance and increased pH from photosynthesis had a significant effect. We observed no significant changes in bacterial diversity, which remained at the same level as in the unmanipulated community. Thus, the bacterial community of the fjord was not resistant, but resilient within the time frame and nutrient gradient of our experiment. © The authors 2017. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are unrestricted. Authors and original publication must be credited.

Aquaculture has the potential to become a major food supplier in a world with an increasing human population, and increased consumption of fish will likely have positive health implications. For marine aquaculture, the production of high quality juveniles is a bottleneck. Survival until the juvenile stage is typically as low as 10–15% for many species, which indicates suboptimal rearing conditions. Substantial evidence indicates that the poor performance and viability of larvae is largely due to detrimental larvae-microbiota interactions. This emphasises the need for microbial management strategies in the cultivation of marine fish larvae. Disinfection and probiotics are the most studied microbial management methods so far. However, most studies on these methods overlooked the role of mutualistic relationships between microbes and hosts, and have not proposed or examined methods steering toward such relationships. Based on ecological theory and a number of experiments, we find support for the hypothesis that current practise in aquaculture generally selects for r-strategic, opportunistic microbes, which results in detrimental host–microbiota interactions. Thus, the challenge is to develop technology and methods for microbial management at the ecosystem level that creates a K-selected microbial community, and by this mean select against r-strategic opportunists. Here we summarise experiments done during 25 years and with marine larvae of five different species showing that: (1) K-selection strategies result in different water microbiota with less opportunists, (2) this influences the microbiota of the fish larvae, and (3) the larvae cultivated in water inhabited by a K-selected microbiota perform better. Improved performance of larvae includes improved appetite, earlier onset of and faster growth, increased survival, and increased robustness to stress. K-selection as a method for management of the microbial community is a robust approach that allows steering of host–microbiota interactions in larviculture toward mutualism. It could also be applicable for young stages of other domesticated animals. Our review illustrates that a change from a “beat-them” to a “join-them” strategy for microbial management in larval rearing can lead to a more sustainable aquaculture industry. Copyright © 2018 Vadstein, Attramadal, Bakke and Olsen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY)

Combining a minimum food web model with Arctic microbial community dynamics, we have suggested that top-down control by copepods can affect the food web down to bacterial consumption of organic carbon. Pursuing this hypothesis further, we used the minimum model to design and analyse a mesocosm experiment, studying the effect of high (+Z) and low (-Z) copepod density on resource allocation, along an organic-C addition gradient. In the Arctic, both effects are plausible due to changes in advection patterns (affecting copepods) and meltwater inputs (affecting carbon). The model predicts a trophic cascade from copepods via ciliates to flagellates, which was confirmed experimentally. Auto- and heterotrophic flagellates affect bacterial growth rate and abundance via competition for mineral nutrients and predation, respectively. In +Z, the model predicts low bacterial abundance and activity, and little response to glucose; as opposed to clear glucose consumption effects in –Z. We observed a more resilient bacterial response to high copepods and demonstrate this was due to changes in bacterial community equitability. Species able to use glucose to improve their competitive and/or defensive properties, became predominant. The observed shift from a SAR11-to a Psychromonodaceae – dominated community suggests the latter was pivotal in this modification of ecosystem function. We argue that this group used glucose to improve its defensive or its competitive abilities (or both). Adding such flexibility in bacterial traits to the model, we show how it creates the observed resilience to top-down manipulations observed in our experiment. © The Author(s) 2018. This article is licensed under a Creative Commons Attribution 4.0 International License.

The availability of high-quality juveniles is a bottleneck in the farming of many marine fish species. Detrimental larvae-microbe interactions are a main reason for poor viability and quality in larval rearing. In this review, we explore the microbial community of fish larvae from an ecological and eco-physiological perspective, with the aim to develop the knowledge basis for microbial management. The larvae are exposed to a huge number of microbes from external and internal sources in intensive aquaculture, but their relative importance depend on the rearing technology used (especially flow-through vs. recirculating systems) and the retention time of the water in the fish tanks. Generally, focus has been on microbes entering the system, but microbes from growth within the system is normally a substantial part of the microbes encountered by larvae. Culture independent methods have revealed an unexpected high richness of bacterial species associated with larvae, with 100–250 operational taxonomic units associated with one individual. The microbiota of larvae changes rapidly until metamorphosis, most likely due to changes in the selection pressure in the digestive tract caused by changes in host-microbe and microbe-microbe interactions. Even though the microbiota of larvae is distinctly different from the microbiota of the water and the live food, the microbiota of the water strongly affects the microbiota of the larvae. We are in the early phase of understanding larvae-microbe interactions in vivo, but some studies with other animals than fish emphasize that we so far have underestimated the complexity of these interactions. We present examples demonstrating the diversity of these interactions. A large variety of microbial management methods exist, focusing on non-selective reduction of microbes, selective enhancement of microbes, and on improvement of the resistance of larvae against microbes. However, relatively few methods have been studied extensively. We believe that there is a lot to gain by increasing the diversity of approaches for microbial management. As many microbial management methods are perturbations of the microbial community, we argue that ecological theory is needed to foresee and test for longer term consequences in microbe-microbe and microbe-larvae interactions. We finally make some recommendations for future research and development. Copyright © 2018 Vadstein, Attramadal, Bakke, Forberg, Olsen, Verdegem, Giatsis, Skjermo, Aasen, Gatesoupe, Dierckens, Sorgeloos and Bossier. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY).

The effects of light and short-term temperature elevation on the 48-h egg hatching success (HS) of cold-stored (2 °C) Acartia tonsa Dana (Copepoda: Calanoida) eggs were examined in the present study. The eggs can be stored for up to 7.5 months and maintain their high hatching rate under optimal conditions. Intensively produced eggs from the copepod A. tonsa may be hatched and used as an inoculum for producing copepod nauplii as live feed for fish larvae. The HS for eggs that were directly exposed to LED light declined rapidly after 1 month of storage (from 91 to 25 %), and these eggs did not hatch at all after 3 months of storage. The highest HS found was for eggs stored in complete darkness. The HS for eggs stored in normoxic (≥7 mg DO L−1) and anoxic (≤0.03 mg DO L−1) seawater was not affected by short-term temperature transitions from 2 °C up to 9 or 17 °C for a period of 12 or 24 h, when hatched 1 week post-exposure. The global mean HS for eggs stored in normoxic seawater was 85.9 % and significantly lower compared to eggs stored under anoxic conditions after 3 weeks of storage (91.8 %) (P = 0.001; SNK).

We combined data from an outdoor mesocosm experiment with carbon budget modelling and an ecological network analysis to assess the effects of continuous nutrient additions on the structural and functional dynamics of a marine planktonic ecosystem. The food web receiving no nutrient additions was fuelled by detritus, as zooplankton consumed 7.2 times more detritus than they consumed algae. Nutrient supply instantly promoted herbivory so that it was comparable to detritivory at the highest nutrient addition rate. Nutrient-induced food web restructuring reduced carbon cycling and decreased the average number of compartments a unit flow of carbon crosses before dissipation. Also, the efficiency of copepod production, the link to higher trophic levels harvestable by man, was lowered up to 35 times by nutrient addition, but showed signs of recovery after 9 to 11 days. The dependency of the food web on exogenous input was not changed by the nutrient additions.

The feeding selectivity of Calanus finmarchicus was studied by carrying out three incubation experiments; two experiments with natural seawater sampled during spring bloom (Exp. 1) and post-bloom conditions (Exp. 2) and a third experiment with cultured dinoflagellates and ciliates (Exp. 3). In the first two experiments a gradient in ciliate concentration was created to investigate the potential for prey density dependent selective feeding of C. finmarchicus. Results of microplankton counts indicated C. finmarchicus to be omnivorous. Diatoms contributed chiefly to the diet during spring bloom conditions. Despite the high microphytoplankton biomass during the spring bloom (Exp. 1), ciliates were selected positively by C. finmarchicus when the ciliate biomass exceeded 6.5 μg C L− 1. A selection in favor of large conic ciliates such as Laboea sp. and Strombidium conicum was indicated by positive selectivity indices. Ciliates were throughout positively selected by C. finmarchicus during Exp. 2, and selectivity indices indicated a negative selection of diatoms. The results from Exp. 3 showed that C. finmarchicus has the ability to switch from dinoflagellates to ciliates as sole food source, even if the dinoflagellate was offered in surplus. This suggests that other factors, such as nutrition may be of significance for the feeding selectivity of C. finmarchicus.

Variability of biofouling communities on fish cage nets : A 1-year field study at a Norwegian salmon farm

For most marine aquaculture species, one of the main bottlenecks is the stable production of high quality juveniles. The high and unpredictable mortality in the first weeks after hatching of marine fish larvae remains a challenging problem that needs to be solved. The severity of the problem differs between species, but cannot be considered adequately solved for any species. Both scientific evidence and experience in hatcheries for a variety of fish, shrimp and shellfish species are accumulating as support for the hypothesis that detrimental fish-microbe interactions are the cause of these problems. Host-microbe interactions in reared fish are still poorly understood, except for a few pathogens, and empirical data of the quality required to test this hypothesis, are lacking. This article provides an overview on the current knowledge of the microbial environment of fish larvae, including methodological aspects to characterize the microbial community (both using culture-dependent and culture-independent methods). Further, the current knowledge of the immunology of fish larvae is reviewed, including recent advances in the understanding of toll-like receptors, inflammatory cytokines, mast cells and piscidins, and the ontogeny of the adaptive immune system. Finally, we provide an overview of the state of the art with respect to steering of microbial communities associated with fish larvae - both steering of community composition and of its activity (e.g. by quorum sensing interference).

The vertebrate gut is host to large communities of bacteria, and one of the beneficial contributions of this commensal gut microbiota is the increased nutritional gain from feed components that the host cannot degrade on its own. Fish larvae of similar age and under the same rearing conditions often diverge with regards to growth. The underlying reasons for this could be differences in genetic background, feeding behavior or digestive capacity. Both feeding behavior and digestion can be influenced by differences in the microbiota. To investigate possible correlations between the size of fish larvae and their gut microbiota, we analyzed the microbiota small and large genetically homogenous killifish and genetically heterogeneous cod larvae by Bray-Curtis Similarity measures of 16S DNA DGGE patterns. A significant difference in richness (p = 0.037) was observed in the gut microbiota of small and large killifish, but the overall gut microbiota was not found to be significantly different (p = 0.13), indicating strong genetic host selection on microbiota composition at the time of sampling. The microbiota of small and large cod larvae was significantly different with regards to evenness and diversity (p = 0.0001), and a strong correlation between microbiota and growth was observed. This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

Calanus finmarchicus is the dominant zooplankton species in the North Atlantic. This zooplankton is also of interest for commercial harvesting due to its high abundance and biochemical contents. In the present study, copepodite stage V of C. finmarchicus was sampled at different depths from January to June in 2009, 2010 and 2011 in the Trondheimsfjord (63°29'N 10°18'E). The fatty acid composition was analyzed in individual copepods and in the seston. It was found that the fatty acid profile of copepods was related to the fatty acid profile of potential food sources. This study indicates that the onset of vertical migration of stage V, which was observed in May, has a strong link to the production of phytoplankton and lipid accumulation in C. finmarchicus. The content of 14:0 and 16:0 fatty acids in the specimens did not increase from February to May in surface waters. This suggests that these fatty acids in the diet were used as precursors for the biosynthesis of 20:1n-9 and 22:1n-11 fatty acids and fatty alcohols. A potential harvesting season of C. finmarchicus could be when the species is abundant in surface waters; the content of n-3 fatty acids will vary throughout this season. The peak abundance of C. finmarchicus in the spring varied substantially between the years studied.

Data from 7 mesocosms with a gradient in daily nutrient loading rate (LN) and inverse modelling were used to estimate all C, N and P flows in an idealised food web. The gradient in LN created autotrophic production (AP) of 7 to 314 μg C l−1 d−1 (mean values over 18 d). The production of dissolved organic C (DOC) decreased from 240 to 40% of AP, and was dominated by heterotrophs (80 to 58%), with heterotrophic bacteria (BAC) producing 48 ± 8% (means ± SD) by excretion or lysis. The consumption of DOC by BAC was 133 to 86% of AP, and DOC accumulated when experimental LN ≥ natural LN. C of BAC origin constituted 5.5 to 0.2% of the C consumed by copepods. The production of dissolved N and P was mainly by heterotrophs (92 ± 2% of DN, 92 ± 4% DP), but autotrophs produced 26 ± 7% of dissolved organic N (DON) and 21 ± 8% of dissolved organic P (DOP). For the production of inorganic N and P (DIN and DIP, respectively), BAC predators produced >50% of DIN and >70% of DIP at low or moderate LN (averages 37 ± 16% of DIN and 66 ± 14% of DIP). The contribution by BAC was low for DIN (12 ± 6%) and zero for DIP. For the re-mineralisation of N and P, the significance of BAC was as N and P rich food particles. DOP accumulated more than DOC, despite the high demand for P. Turnover time of dissolved organic matter (DOM) decreased from around 80 to 12 d with increasing LN. These data provide new insights into the role of various functional groups of organisms for the cycling of DOM, and to the differences in C, N and P cycling.

Marine fish larvae are sensitive to infections by opportunistic bacteria. Procedures like disinfection and pulse feeding may destabilise the microbial community and promote r-selection and proliferation of opportunists in intensive rearing tanks. Recirculation aquaculture systems (RAS) have been hypothesised to stabilise and mature the microbial community, creating a more beneficial environment for the larvae during the live feed period. Two marine RAS with Atlantic cod larvae (Gadus morhua L.) with either moderate ozonation (RAS O3) or high intensity UV-irradiation (RAS UV) were compared with a flow-through system (FTS). The two RAS developed a different and more stable composition of the microbial community than the FTS. The RAS O3 had a more mature and stable microbial community than the RAS UV. The density and the activity of bacteria were higher in the rearing tanks than in the in-flowing water in the RAS UV system, whereas for the RAS O3 system densities and activity of bacteria were similar, indicating low disinfection efficiency with moderate ozonation. Atlantic cod larvae reared in the RAS O3 showed the best survival and growth, whereas the RAS UV larvae performed equally well or better than their siblings in the FTS. This was in spite of the fact that the physicochemical water quality of the two RAS was inferior to that of the FTS. The agar-based method used to quantify opportunists may be too general to capture important differences in the microbial community of the rearing water. For the future, molecular methods could be used to identify which functional groups or species of bacteria are contributing to the observed RAS effect. Our results support the hypothesis of RAS as a microbial control strategy during first feeding of larvae. However, a RAS for marine larvae should probably not include strong disinfection because it leads to a reduction in bacterial numbers, which is likely to result in a destabilization of the microbial community.

Marine hatcheries represent high value, low waste systems for larvae that are sensitive to general infections by opportunistic bacteria. In intensive cultivation several procedures destabilise the microbial community of the rearing water and favour growth of potentially harmful microbes. Recirculation aquaculture systems (RASs) have properties that may contribute to microbial stabilisation, including long water retention time and a large surface area of biofilters for bacterial growth. Moreover, the microbial community in RAS biofilters has the possibility to stabilise at a similar carrying capacity as the larvae tanks, which could potentially limit the chances of proliferation of opportunistic microbes in the rearing water. The development of the microbial community in a RAS with moderate ozonation (to 350 mV) was compared to that of a conventional flow-through system (FTS) for the same group of Atlantic cod, Gadus morhua. The feed and intake water were the same for the two groups. The RAS developed and maintained a more diverse and stable microbial community composition compared to the FTS. Water treatment regime explained most of the variation in microbial composition during the live feed period, and in addition it accounted for ten times higher variation in the composition of bacteria in the FTS than in the RAS. Less variability in bacterial composition was found between replicate fish tanks of the RAS than between tanks of the FTS. The RAS had a more even microbial community structure with higher species diversity and periodically a lower fraction of opportunists. The fish in the RAS performed better than their siblings in the FTS, despite being exposed to an apparent inferior physiochemical water quality.

The objective of the present study was to examine how N and P availability interact with C metabolism in marine heterotrophic plankton and whether or not heterotrophic groups are likely to be subjected to essential nutrient limitations in natural coastal waters. The nutrients stud- ied were mineral P and N; the latter is a proxy for essential amino acids. We present a general the- oretical framework and criteria for evaluating essential nutrient limitations in heterotrophs. Data were derived from a comprehensive mesocosm experiment, where food-web flows were esti- mated using inverse modelling. Bacteria of the mesocosm communities were severely P-deficient throughout. The heterotrophic nanoplankton was most likely limited by another essential nutrient or by food C availability. Ciliates were most likely P-limited, whereas copepods might experience P limitation, but were more likely limited by another essential nutrient or food C in the present experiments. The N contents of the food were close to the theoretical requirements for copepods and ciliates. All planktonic groups released dissolved inorganic nitrogen (DIN), and all except bacteria released dissolved inorganic phosphorus (DIP). Our results suggested that P limitation might be readily experienced by bacteria, ciliates and perhaps also by copepods, but not by het- erotrophic nanoplankton in natural North East Atlantic coastal waters. A predator must balance its energy metabolism and growth under the variable availabilities of essential nutrients, and we pro- pose that C growth efficiency is a dynamic variable mainly dependent on the availability of the most limiting nutrient. We support the view that C availability alone cannot be used as a proxy for the food limitation of bacterial and zooplankton growth. Specific essential nutrients should be regarded as potential limiting factors, as for phytoplankton. The variable nutritional requirements of heterotrophic predators will then represent a major driver of heterotrophic species diversity, allowing a broad diversity of heterotrophic species in plankton communities.

A system for automatic control of the growth and density of rotifer cultures is presented and tested. The system computes feeding rates based on a setpoint for rotifer density, and provides a fast growth period followed by rapid stabilization of the rotifer density. At the same time, overfeeding is prevented, thereby reducing the risk of culture crashes. Feeding rates are automatically computed based on measurements of the culture’s density and egg rate, and internal setpoints for growth rate and egg rate. The controller is tested and tuned against a mathematical model of a rotifer culture before being applied to four experimental cultures. The experimental results show densities in all tanks increasing from 60 to 90 ml−1 to the setpoint densities of 500 and 1000 ml−1 in 5–7 days, after insignificant growth on the first day. Gross growth rates slowed down considerably towards the end of the experiment, as the controller reduced feed rations in order to stabilize densities. The cultures were stabilizing at higher densities compared to their setpoints, while there was no such bias in the observed egg rates. This indicates that a part of the controller algorithm needs further tuning. The approach to the setpoint densities was fast, and within the experimental period there were no indications of oscillations beyond those caused by daily dilution.

The objective of the present study was to study the dynamics of protozoan and metazoan zooplankton food webs in coastal NE Atlantic waters exposed to variable nutrient input. Data were derived from a mesocosm experiment (7 units, 40 m 3 , 12 m deep) receiving variable nutrient input. The food web included 3 autotrophic groups based on size, and 4 functional heterotrophic groups mainly based on trophic position. Inverse modelling was used to construct networks of carbon flows for the planktonic food web. Heterotrophic nanoplankton, microplankton and mesoplankton (HNP, CIL and COP, respectively) were found to be equally important contributors to grazing and carbon release during undisturbed summer situations. The release of dissolved organic carbon by zooplank- ton was comparable to that of phytoplankton. Autotrophic food was generally more important for zoo- plankton than heterotrophic (mean 75%). Assimilation and growth efficiencies (AE and GE, respec- tively) of zooplankton groups in undisturbed situations were in the range of 33 to 69% and 10 to 41%, respectively. Values were inversely related to gross primary production (GPP). Sedimentation rates of carbon were low. High nutrient input rates increased food availability and most CIL and COP carbon flows. HNP did not respond, and neither did its food, that is, bacteria and picoautotrophs. The response in biomass was generally lower than that for the flows. Values of AE and GE of the zoo- plankton during high nutrient input and food availability varied between 11 and 29% and 5.7 and 19%, respectively, and throughout were lower than at low nutrient input. The sedimentation rate of particulate carbon increased strongly, resulting in an enhanced organic input rate in deep water.

Measurements of in situ phytoplankton growth and grazing by zooplankton normally involve different techniques. We show that a single dilution experiment based on dialysis bags can be used to do these estimates in situ. Dialysis bags allow an estimate of the in situ phytoplankton gross growth rate whereas the dilution gradient allows a simultaneous estimate of microzooplankton grazing. The comparison of the phytoplankton net growth rate outside dialysis bags and the estimated apparent growth rate of phytoplankton in undiluted samples within dialysis bags allows estimating additional loss processes such as mesozooplankton grazing. The method is especially useful in mesocosms experiments.

An individual-based dynamic energy budget model is used in a Lagrangian simulation to compute population dynamics for the rotifer strain Brachionus plicatilis. This model structure allows description of transient as well as stationary conditions, making the model useful for a variety of applications. It also has the advantage of allowing the use of dynamic energy budged (DEB) theory in describing rotifer energetics. The model is developed with aquaculture-related applications in mind, including planning, monitoring and control of rotifer production systems and first feeding of marine fish larvae. Simulations show acceptable agreement with measured data on the population level, with regard to steady-state egg ratio, yields of daily diluted cultures, and maximum net growth rate. Further refinement of the model can enable its application for processes such as essential nutrient enrichment of rotifers for first feeding of larval fish.

In a mesocosm experiment providing a gradient of semi-continuous addition of mineral nutrient, production rates and mortality of phytoplankton were estimated. Heterotrophic bacterial biomass and production rates and their responses to the mineral nutrients additions were also estimated. The purpose of the experiment was to establish responses of the major biological factors as a function of nutrient amendments. Initial primary production was � 0.47 m gCL � 1 day � 1 . In the most fertilized mesocosm, phytoplankton biomass increased at a specific rate of 0.4 day � 1 during the first week of the experiment, and on day 9 primary production reached a peak at 1027 m gCL � 1 day � 1 . The responses in the other fertilized mesocosms were intermediate, and in an unfertilized control the variables measured stayed almost constant throughout the experiment. The termination of the blooms in the fertilized mesocosms was a consequence of nitrogen limitation, and nitrogen limitation subsequently induced storage of intracellular organic material in the phytoplankton. In the mesocosm receiving the highest daily dose of nutrients, strong post-bloom nutrient limitation resulted in high phytoplankton mortality, and release of organic material from the algae supported the gradient’s highest heterotrophic bacterial production.

A recent meta-analysis indicates that trophic cascades (indirect effects of predators on plants via herbivores) are weak in marine plankton in striking contrast to freshwater plankton (Shurin et al. 2002, Ecol. Lett., 5, 785–791). Here we show that in a marine plankton community consisting of jellyfish, calanoid copepods and algae, jellyfish predation consistently reduced copepods but produced two distinct, opposite responses of algal biomass. Calanoid copepods act as a switch between alternative trophic cascades along food chains of different length and with counteracting effects on algal biomass. Copepods reduced large algae but simultaneously promoted small algae by feeding on ciliates. The net effect of jellyfish on total algal biomass was positive when large algae were initially abundant in the phytoplankton, negative when small algae were dominant, but zero when experiments were analysed in combination. In contrast to marine systems, major pathways of energy flow in Daphnia-dominated freshwater systems are of similar chain length. Thus, differences in the length of alternative, parallel food chains may explain the apparent discrepancy in trophic cascade strength between freshwater and marine planktonic systems.

Appendicularians, an important group of marine gelatinous zooplankton, are highly efficient filter feeders of small phyto- and bacterioplankton. It is not known which factors regulate their abundance and biomass in the field. In a mesocosm experiment, we manipulated nutrient load- ing and initial densities of calanoid copepods (almost exclusively the genera Temora sp., Centro- pages and Pseudocalanus) and followed plankton dynamics over 2 wk. Peak appendicularian densi- ties were inversely related to initial copepod densities. We observed more than 100-fold variation in Oikopleura dioica density among treatments, even though our experimental variables were kept within ecologically relevant magnitudes. The differences between copepod-reduced and copepod- enhanced treatments were much larger at high and moderate nutrient loadings than in treatments without nutrient enrichment. Thus, appendicularians are under strong pressure from calanoid cope- pods. Calanoid copepods appear to structure the plankton community via direct negative effects on large algae, ciliates and appendicularians and indirect positive effects on small algae resulting from the release of these from predation by ciliates and appendicularians.

Copepods and ciliates are 2 functionally different types of herbivores that dominate marine ecosystems. Ciliates have a higher reproductive capacity than copepods, but copepods can graze on ciliates. Hence we have an omnivorous system in which the inferior grazer can graze on its competitor. We conducted a 3 2 factorial mesocosm experiment with natural plankton communities to explore how the copepod -ciliate interaction affects algal development on the timescale relevant for algal blooms. We used nutrient load and copepod biomass as the experimental variables. Ciliate bio- mass was positively correlated to nutrient addition and negatively correlated to copepod biomass, with copepod biomass as the predominant factor at the highest densities tested. Both increasing copepod biomass and nutrient addition resulted in increased algal biomass, with the strongest effect on nanoalgae. The mechanism involved was carnivory by copepods and a resulting trophic cascade through ciliates to algae. We conclude that even a moderately high biomass of copepods may pro- mote algal blooms when the initial size distribution of the algal community is appropriate (i.e. domi- nance of algae eaten primarily by ciliates).

In the natural food web, zooplankton constitutes a major part of the diet for marine fish larvae and it is generally believed that copepods can meet the nutritional requirements of fish larvae. In this study, different copepod species were analysed for total lipid content, fatty acid and protein content and used in first feeding experiments with halibut larvae (Hippoglossus hippoglossus L.) together with enriched nauplii and juvenile stages of Artemia franciscana. Special attention was paid to the DHA content in both the live food organisms and the fish larvae. Copepodid and adult stages of the marine copepods Temora longicornis and Eurytemora sp. had a total lipid content varying between 7% and 14% of dry weight (DW). Copepodid stages I, II and III of Calanus finmarchicus had a lipid content varying between 10% and 19% of DW, increasing to 22–25% in copepodid stages IV, V and the adult stages. The predominant fatty acids of all copepods were docosahexaenoic acid (DHA; 22:6n−3), eicosapentaenoic acid (EPA; 20:5n−3) and the saturated fatty acid 16:0. In T. longicornis and Eurytemora sp. DHA constituted 26–42%, EPA 15–24% and 16:0 8–12% of total fatty acids. In C. finmarchicus, the DHA content ranged between 21% and 32.5%, whereas the content of EPA and 16:0 was 15–21% and 9–15% of total fatty acids, respectively. The sum of n−3 HUFA was highest in T. longicornis and Eurytemora sp. (55–62% of total fatty acids) and lowest in C. finmarchicus (38–47%). The loss rate (% day−1) of the total lipid and fatty acid content during starving conditions was 18 and 24% day−1 in T. longicornis, and 12 and 16% day−1 in Eurytemora sp., respectively. In both copepods, the relative content of DHA (% of total fatty acids) increased with time during starvation, reaching 43% in T. longicornis and 49% in Eurytemora sp. The quantitative content of DHA decreased steadily although at a lower rate than that of other fatty acids. The protein content of various copepods varied between 52.4% and 57.6% of dry weight (DW), and was significantly higher than in A. franciscana (41% in newly hatched nauplii and 34% after 24-h enrichment). There was a close relationship between the percent DHA content in 28–36-day-old halibut larvae and the live food organisms they were fed on. High percent DHA content in the live food organism resulted in a high percent DHA content in the fish larvae and vice versa. The relatively high DHA content in the larvae was significantly reduced after 8 days when given enriched A. franciscana. For the rest of the feeding period, the DHA content decreased steadily when fed on A. franciscana, whereas it remained at the initial high level in larvae-fed copepods.

Cage fish farms release the inorganic nutrients ammonium (NH4) and phosphate (PO4) into the surrounding water. The objectives of this experiment from the Comau fjord (42.2° S) in southern Chile was to study how increased input of NH4 and PO4 to pelagic waters affects the biomass of defined functional groups of the microbial food web and the community composition of the micro-autotrophs. We used microcosms with NH4 and PO4 added in a gradient of concentrations, with the same N:P ratio as in aquaculture effluent. In addition, silicic acid was added in a 1:1 ratio with nitrogen to mimic the rich supply of silicon from both deep water and river water entering this fjord. A positive biomass response to nutrient loading rate was observed in the microautotroph, micro-heterotroph, and meso-heterotroph functional groups dominated by microphytoplankton, ciliates, and copepods, respectively. Silicon concentration was reduced to a low level, but the Si supply ratio maintained a dominance of diatoms. Biomass increase was accompanied by a succession in the diatom-dominated community towards large and elongated, possibly grazer-resistant species and some small elongated species adapted to silicon-limited conditions. Grazers had a role in the succession by removing successful non-elongated competitors. Silicon, which is not released by fish farms, played a crucial role in the phytoplankton response. With reduced freshwater input in Patagonia as predicted due to climate change, the supply of silicon to the productive zone below the brackish layer might be reduced, which could shift the phytoplankton community more in favor of dinoflagellates or other non-silicified species. © 2014 The Authors. Published by Inter Research. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

The goal of the studies that are reported in this thesis was to develop adequate methods for the production of good quality fry of Atlantic halibut (Hippoglossus hippoglossus L.). In this connection, prey preferences of the Atlantic halibut larvae is important. When giving en the choice between rotifers and short term (ST) enriched nauplii, the Atlantic halibut larvae showed no preferences for any of these the first two days of the live feed period. From day 3 and onwards the larvae preferred ST nauplii. When the larvae had the opportunity to select between different size classes of A. franciscana, the preferred size was the newly hatched nauplii during the first 3 weeks. Around day 20 at 3-4 mg dry weight (DW), the larvae showed a pronounced shift in their preferred size of A. franciscana, and they started to select for individuals of 1.2-1.4 mm length or longer. The size corresponds to A. franciscana cultivated for 3 days.The larvae apparently digested the newly hatched nauplii better than the ST nauplii during the first weeks, this presumably because of the high lipid content of the latter. Also, the bigger size classes of A. franciscana seemed to be more effectively digested that the ST nauplii by larvae of less then 2.4mg DW. Bigger larvae showed almost equal and very efficient digestion of all size classes of A. franciscana. The larvae never selected positively for ST nauplii, and use of newly hatched nauplii for some time may be beneficial based on the selection and digestion patterns of the larvae. However, the newly hatched nauplii do not contain DHA (docosapentaenoic acid) and are therefore nutritionally inadequate for the larvae. This size class of Artemia may be beneficially used for a few days after onset of exogenous feeding provided that the nutritional status of the larvae at the onset of exogenous feeding is adequate and that the nutritional quality of the feed used later is satisfactory. The larvae selected positively for larger A. franciscana in a period before the reached the size when they normally start to accept formulated food. Prey of the size 1.2-1.4 mm (i.e. 3-day-old A. franciscana) seemed to be the optimal size for the larvae after about day 20 in the lived feed period. It was possible to produce 3-day-old A. franciscana with 18 mg DHA g-1 DW and a DHA/EPA ratio > 1.0 by using a diet containing more than 39% lipids and 10% DHA, respectively. A high DHA/EPA ratio (>1.0) is needed after the production because A. franciscana appears to transform DHA to EPA (eicosapentaenoic acid) relatively efficiently. Attempts were made to stabilise the content of DHA in A .franciscana in the larval tanks by incubating them with the DHA rich microalgea I. galbana. However, 6 mg C 1-1 or higher levels of this alga were negative for the DHA contents of ST A. franciscana which then decreased more rapidly during the first 24 h than at lower algal concentrations. This was most likely due to a replacement of lipids by algal cells in the gut of the nauplii. In the case of 3- and 4-day old A. franciscana, the effect of addition of I. galbana on the DHA level in the animals was small for the algal levels normally used in the larval tanks (1-2 mg C1-1). The microalgea Tetraselmis sp. was used to reduce bacterial level and change bacterial flora associated with the live feed. During a 4 h incubation of 2-day-old A. franciscana with this alga, the number of associated bacteria and Vibrio spp. were reduced significantly. This effect was even more pronounced after transfer to first feeding conditions. The composition of the microbial flora associated with the animals became more diverse, and less dominated by Vibrio alginolyticus, which was the dominating species associated with 2-day-old A. franciscana. The results also showed that the algae indirectly affected the larvae through changing the associated bacterial flora of the live feed. Larvae which received algal-treated 2-day-old A. franciscana had significantly lower numbers of Vibrios and bacteria with haemolytic activity compared to larvae fed non-treated- feed. In another first feeding experiment, 4-day-old A-franciscana had high numbers of associated bacteria, and especially of bacteria exhibiting haemolytic activity, even if the procedure for algal incubation was used. Differences in bacterial flora associated with the live feed may lead to differences in growth of larvae.Atlantic halibut juveniles with better quality was obtained with 20% perfect larvae when juvenile A. franciscana was used as feed compared to about 4% with the use of St nauplii. The 3-day-old A. franciscana seems to be the optimal size of the larvae from about day 20 after first feeding because this size has many useful properties. It is the most preferred size by larvae from this time in the live feed period, it is effectively digested by the larvae and it can be produced with a relatively high DHA content (

Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l−1) for 11 d at 26 to 28 °C, and 34 ppt salinity. Three groups of brine shrimp were used in the feeding experiments: metanauplius III and IV (Group 1), post-metanauplius II and III (Group 2) and post-metanauplius VIII (Group 3), corresponding to 4-, 7- and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages at different concentrations of 14C-labeled I. galbana ranging from 0.05 to 30 mg C l−1. The handling time of algae was determined for all three groups. The ingestion rate (I, ng C ind−1 h−1) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maximum level (I max) and remained constant at food concentrations ≥10 mg C l−1 (saturated food concentrations). The clearance rate (CR, μl ind−1 h−1) increased with increasing food concentration up to a maximum rate (CR max), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consistent with Holling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2 and 3) differed significantly from a Type 2 response (p

In a first feeding experiment, halibut larvae were offered either short term enriched (ST) 1-day old Artemia franciscana or A. franciscana of successively increasing size (ST, 2-, 3- and 4-day old juveniles), from day 0 to day 60. No differences, either in growth (approximately 6.5% daily weight increase, DWI) or in survival (ca. 25%) between the two treatments were observed, but both were satisfactory. However, feeding increasing sizes of A. franciscana increased the number of completely pigmented and metamorphosed larvae from 4 to 20%. Protein/lipid ratio in the feed seems to be important for pigmentation and metamorphosis, provided the levels of essential fatty acids (esp. DHA) are sufficient. Juvenile A. franciscana may therefore be a better live feed than ST A. franciscana for halibut larvae. The fact that a relatively high load of bacteria was introduced by 4-day old A. franciscana , may have had a negative influence on the growth of the larvae. Tests indicated that a great part of the bacteria exhibited hemolytic activity, and many of the bacteria were apparently Vibrios . Strict microbial control in the production of live feed is very likely just as important as control of the nutritional composition of the larval feed. This is a challenge for further work.

The effect of three different rotifer enrichments was examined on growth, survival, pigmentation and viability of first feeding turbot larvae. The diets differed in rotifer content of protein, lipid and ratio of protein/lipid. The diets were fed to turbot with or without algae ( Isochrysis galbana ) added to the larval tanks. The turbot larvae were fed rotifers for 10 days and thereafter the same Artemia diet was fed to all treatments for the rest of the experimental period. Growth and survival of fish larvae were higher in tanks containing algae than in tanks where no algae were added. Independent of algal addition, the highest growth rate and survival was obtained by feeding rotifers containing the highest protein content. Larvae reared in greenwater consumed higher numbers of rotifers during the stagnant period than larvae kept in clearwater conditions, while analysis of the larval gut contents showed lower rotifer numbers in the gut of larvae reared in greenwater conditions. This must imply longer residence time of the food in the larval gut, and presumably also higher digestion and assimilation efficiencies of larvae maintained without algae than in larvae maintained with algae. Calculation of protein and carbon conversion efficiency showed higher utilization in larvae maintained without algae (18–28% for protein, 12–19% for carbon) than in larvae maintained with algae (6–9% for protein, 4–7% for carbon). No significant differences in pigmentation rate and stress sensitivity were observed among the larvae of the various treatments.

Before transfer to larval incubators, water was membrane filtered to remove >95% of the bacteria and then transiently maintained in a biofilter that promoted recolonization of the water by non-opportunistic bacteria. The process is termed microbial maturation of the water. Hypothetically the bacterial flora in the matured water should protect the marine larvae from colonization and proliferation by opportunistic bacteria. Testing of the hypothesis demonstrated 76% higher survival of yolk sac larvae of Atlantic halibut (Hippoglossus hippoglossus) in matured than in membrane filtered water. Proliferation of opportunistic bacteria was observed in the rearing water after hatching of turbot eggs (Scophthalmus maximus), but to a less extent in the microbially matured water. In the early phase of first feeding of turbot larvae, the matured water induced qualitative differences in the gut microflora. Significantly higher initial growth rate of the turbot larvae in the matured water affected 51% higher average weight of 13 days old larvae than in membrane filtered water. Algal addition to the matured water enhanced the larval growth further. The experiments conducted supported the proposed hypothesis that microbial maturation selects for non-opportunistic bacteria, which protects the marine larvae from proliferation of detrimental opportunistic bacteria.

A 3-dimensional hydrodynamic−ecological model system (SINMOD) was used to estimate the full-scale cultivation potential of the brown alga Saccharina latissima in integrated multi-trophic aquaculture (IMTA) with Atlantic salmon Salmo salar. A previously developed model for the frond size and composition (carbon and nitrogen content) of S. latissima sporophytes was adjusted to data from an outdoor mesocosm growth experiment and then coupled and run online with the 3-dimensional model system. Results from simulations were compared with data from an IMTA field experiment, providing partial validation of the hydrodynamic–ecological– kelp model system. The model system was applied to study the large-scale cultivation potential of S. latissima in IMTA with salmon and to quantify its seasonal bioremediation potential. The results suggest a possible yield of 75 t fresh weight S. latissima ha−1 in 4 mo (February to June) and about 170 t fresh weight ha−1 in 10 mo (August to June). The results further suggest that the net nitrogen consumption of a 1 ha S. latissima installation in the vicinity of a fish farm producing approximately 5000 t salmon in a production cycle is about 0.36 (0.15) t NH4 +-N, or a removal of 0.34% (0.41%) of the dissolved inorganic nitrogen effluent with a cultivation period from August (February) to June. Due to the differing seasonal growth patterns of fish and kelp, there was a mismatch between the maximum effluent of NH4 +-N from the fish farm and the maximum uptake rates in S. latissima. © The authors 2013. Open Access under Creative Commons by Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited.

The carbon (C), nitrogen (N) and phosphorus (P) compositions of salmon feed, fish and faeces were studied at a salmon farm in Badstuvika (63°31’N, 9°9’E) in central Norway. These data were used to estimate the release rates of wastes from 2 salmon cages and the qualities of particulate wastes as food resources for integrated multi-trophic aquaculture (IMTA). About 38% of feed C, 43% of feed N and 24% of feed P were retained as fish biomass. About 62% of feed C, 57% of feed N and 76% of feed P were lost into the environment. Around 40% of feed C was respired as CO2, and 39% of feed N and 24% of feed P were excreted as dissolved inorganic nitrogen and phosphorus, respectively. About 19% of feed C, 15% of feed N and 44% of feed P were released as particles. The chemical composition of feed was independent of time (p > 0.05). The faecal C content increased with increasing fish weight (r2 = 0.14, p < 0.05); however, other faecal chemical components showed no apparent relationships with fish weight (p > 0.05). Our results suggested that P digestibility of feed may be 30%, but more information is still needed to reach conclusions on this. The C content of faeces was 70% of that of feed and the N content of faeces was 50% of that of feed. The P content was far higher than that of feed. The lipid, docosahexaenoic acid and eicosapentaenoic acid contents of faeces were comparable to those of some phytoplankton species. The results suggested that both feed and faeces are adequate food for blue mussels and sea cucumbers co-cultured with salmon, and the nutrient content may meet their nutritional requirements. Copyright © 2013 Inter-Research. Open Access CC-BY

This study evaluated the use of egg ratio (eggs rotifer−1) and swimming speed (mm min−1) as prediction criteria for production and culture quality in mass cultures of the rotifer Brachionus plicatilis. Egg ratio was determined to be a suitable predictor of rotifer growth and production in the cultures. Low egg ratios (i.e., 0–0.17 eggs rotifer−1) indicate reduced rotifer population over time (i.e., negative net population growth rates). However, at this time egg ratio dynamics are not suitably understood to predict in advance a sudden population collapse.

The effects of fish elimination in the eutrophic Lake Haugatjern, Sør-Trøndelag County, Norway, were studied during 1979–84. Total elimination of the fish populations by rotenone in late 1980 resulted in a fourfold decrease in the algal biomass. The species composition changed from a dominance by the large-sized Anabaena flos-aquae and Staurastrum luetkemuelleri to smaller, fast-growing species and gelatinous green algae. The total zooplankton biomass remained at the same level in all years, but while the rotifers almost disappeared after the rotenone treatment, the daphnids increased their share of the biomass from 49–63% during 1979–80 to 74–90% during 1982–84. The mean individual size of the adult daphnids increased in the same period from 1.3 to 1.8 mm. A 30% drop in the total phosphorus concentration in the lake after the biomanipulation was explained by increased sedimentation of zooplankton and reduced phosphorus release from the epilimnetic sediments because of the lowered pH. The fish elimination also resulted in a lower yield of biomass per unit of phosphorus in the lake.

14 pages, 11 figures, 6 tables We quantify, compare, and generalize responses of experimental nutrient loadings (LN) on planktonic community structure and function in coastal waters. Data were derived from three mesocosm experiments undertaken in Baltic (BAL), Mediterranean (MED), and Norwegian (NOR) coastal waters. A planktonic model with seven functional compartments and 30–32 different carbon flows fit to all three experiments was used as a framework for flow-rate estimation and comparison. Flows were estimated on the basis of time series of measured biomass, some measured flows, and inverse modeling. Biomass and gross uptake rate of carbon of most groups increased linearly with increasing LN in the nutrient input range of 0–1 µmol N L-1 d-1 at all locations. The fate of the gross primary production (GPP) was similar in all systems. Autotrophic biomass varied by two orders of magnitude among locations, with the lowest biomass and response to nutrient addition in MED waters. The variation of GPP among sites was less than one order of magnitude. Mesozooplankton dominated by doliolids (Tunicata), but not those dominated by copepods, presumably exerted efficient control of the autotrophic biomass, thereby buffering responses of autotrophs to high nutrient input. Among the many factors that can modify the responses of autotrophs to nutrients, the time scale over which the enrichment is made and the precise mode of nutrient enrichment are important. We suggest a general concept that may contribute to a scientific basis for understanding and managing coastal eutrophication The work presented was undertaken jointly by the mesocosm partners of COMWEB, a project of the ELOISE Programme that was funded by the MAST Programme (MAST3-CT96-0052). The MED experiment received additional funding through a grant from the Spanish Commission for Science and Technology and the Research Council of Norway has contributed to the final scientific treatment of the NOR experiment

An 18-day mesocosm study was performed in central Norway to assess the effect of enhanced nutrient input to the marine plankton community. This paper reports the responses of micro- and mesozooplankton to increased food supply due to elevated nutrient input. Seven mesocosms (M1–M7) were added variable doses of N, ranging from 0 to 2.19 μm N l−1 d−1. Phosphorus and silicate was added in Redfield ratios. The ciliate community responded rapidly to the treatment, and reached maximum biomass of 88 μg C l−1 within a week in the most fertilised mesocosm (M7). Tontonia sp. and a small Strombidium sp. dominated biomass and numbers, respectively. Ciliate biomass declined rapidly after the peak, returning to initial values by the end of the experiment (Day 18). Mesozooplankton biomass increased from the second week, due to recruitment of Acartia spp., Centropages spp. and Oithona sp. Numbers of Temora longicornis and Pseudocalanus sp. remained low. Highest biomass of mesozooplankton (116 μg C l−1) was recorded in M6 by Day 18. Egg production rates for Acartia spp. peaked in M3 at Day 11, while calculated mortality rates for juvenile copepods was highest in M1 and M7. Estimated community net growth rates were highest in the most fertilised mesocosms for both copepods and ciliates. It is concluded that enhanced nutrient input affected both biomass and the relative species composition of the zooplankton community.

The objective of COMWEB was to develop efficient analytical, numerical and experimental methods for assessing and predicting the effects of nutrient (N, P, Si) supply on the stability and persistence of pelagic food web structure and function in coastal waters. The experimental comparative work included a geographic gradient covering Baltic, Mediterranean, and NE Atlantic waters and a NE Atlantic gradient in state of eutrophication. COMWEB has been an experimental approach to coastal eutrophication, studying effects of enhanced nutrient supply on components and flows of the entire lower pelagic food web. Flow network representations of pelagic food webs has been a framework of data reduction and flows were established by sophisticated inverse modelling. Fundamental information on physiological properties of functional key species in the pelagic food web was used to constrain flow estimations. A main conclusion derived from the flow networks was that very little energy and materials were transferred from the microbial food web to the main food chain. The lower food web could therefore be described as two parallel food chains with relatively limited interaction between heterotrophic groups. Short-term effects of nutrient perturbations were examined in mesocosms along the geographic gradient. The response was comparable in all systems, with a stronger effect on the activity and biomass of autotrophic groups than those of heterotrophic ones. Mediterranean waters showed much lower autotrophic biomass response than Baltic and NE Atlantic waters, which responded almost equally. The response of primary production was, however, more comparable. High phytoplankton lysis rate explained this low accumulation of biomass in Mediterranean waters. The study of Atlantic coastal waters of different eutrophic states revealed that the ecological response was higher in the closed nutrient perturbed mesocosms than in open systems exposed for > 4 summer months (summer/autumn season). The Atlantic lagoon evolved gradually from the natural oligotrophic situation towards the more eutrophicated North Sea during fertilisation. The responses observed on seasonal and long-term scale (> 10 years) may therefore be equal. The differences between short-term (weeks) and intermediate-term (seasonal) responses is most likely a result of the different time scales of perturbation and observation and the variable exchange rates with surrounding waters (water dilution rate). The analysis of pelagic flow networks provided a framework of diagnostic criteria for state and quality assessment of coastal waters. The nutrient loading rates related better to estimates of biotic fluxes than to concentrations of biotic compartments and total nutrients. On the contrary, the concentration of biotic compartments, or the biomasses, related better to total nutrient concentrations. Primary production, mesozooplankton grazing and growth, fraction of primary production consumed by grazers, bacterial production relative to primary production, cycling indices, and path lengths were all well related to nutrient loading rate. Autotrophic biomass, ratio of autotrophic to heterotrophic biomass, and fraction of picocyanobacteria of total autotrophic biomass were all related to total nutrients. Some of these variables, which responded equally in all systems, have the potential of becoming unified response functions in a management model for European coastal waters. COMWEB has provided further insight into the mechanisms behind coastal eutrophication. A main achievement is the conceptual framework for unified response functions, important components of management models for nutrient emission to coastal waters. © 2001 Elsevier Science Ltd. All rights reserved., The project COMWEB was funded by the MAST Programme (MAST3-CT96-0052) and has been a member of the ELOISE Programme. The comprehensive base of results is due to the hard work of all the enthusiastic project participants.

The rotifer Brachionus plicatilis can grow in a wide range of salinities and temperatures, but rapid shifts in both salinity and temperature may result in immobilized, non-swimming rotifers. The goal of this study was to examine the effect of perturbations in temperature and salinity on the swimming pattern of the rotifer.

During blooms in Norwegian waters phytoplankton communities are phosphorus limited in fresh and brackish waters, and balanced or even nitrogen limited in high-salinity marine waters. This results from the high N/P ratio for available nutrients before onset of blooms in freshwater relative to seawater (N/P (atoms) >100 and 12–16, respectively). Algal N/P ratios at nutrient saturation vary between 8 and 27 among species, and average 16. A low ratio at nutrient saturation may imply P limitation even in high-salinity waters (e.g. Skeletonema costatum). In general, nutrient deficiency becomes more pronounced as the biomass increases. Addition of sewage shifts natural systems toward N limitation, which may therefore be a secondary effect of accelerated eutrophication. interspecific competition in nutrient-limited communities depends on the nutrient requirement of individual species and the mode of nutrient uptake. In our example the desmid Staurastrum luetkemuellerii outcompetes the cyanobacterium Microcystis aeruginosa in a chemostat when the nutrient supply is continuous; the opposite happens when nutrient supply is pulsed.

A detailed study of the life history of the rotifer Brachionus plicatilis was done at 20 °C, 20 ppt salinity, and 90 mg C 1−1 food concentration. Rotifers were grown individually in culture plate wells (150 µl culture volume) and fed Isochrysis galbana Tahiti, Tetraselmis sp., Nannochloris atomus, or a l : 1 mixture (weight) of two of the algae. Observations were made every 2–8 hr and rotifers were sized and transferred to new food daily. A total of 19 different parameters were compared. Rotifers fed Isochrysis averaged 21 offspring per female, a 6.7 day reproductive period, a lifespan of 10.5 days and a mean length of 234 µm. After Isochrysis, the foods giving the highest growth, survival, and reproduction in decreasing order were Isochrysis + Nannochloris, Nannochloris, Isochrysis + Tetraselmis, Tetraselmis + Nannochloris, and Tetraselmis. Although the small volume culture system used in this study seems appropriate for studying life history of B. plicatilis, the results cannot always be directly applied to larger cultures.