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We investigated the phytoplankton species composition and abundance in two seasons in Mwanza Gulf, Lake Victoria (Tanzania). Phytoplankton was sampled and chlorophyll a content was measured in the dry and wet seasons of 2010–2011 at three stations, from the southern land-inward end of the Gulf towards the open lake. Cyanobacteria, mostly small colonial and filamentous species (e.g., Aphanocapsa spp., Planktolyngbya spp., Merismopedia spp.) dominated at each station (76–95 %), followed by Chlorophyta (5–21 %), whereas the contribution of Bacillariophyceae was small (0–6 %). Phytoplankton densities were generally higher in the rainy season and strongly increased going land-inward from the open lake. Low abundance of N-fixing phytoplankton species suggests that N-fixation was low. The chlorophyll a content in the mouth of the Gulf was low (mean values 4–6 µg/L) compared to values reported previously. Also, chlorophyll a values (means 11–14 µg/L) at land-inward stations of Mwanza Gulf were much lower than those in the northern gulfs (Napoleon Gulf, Murchison Bay and Nyanza Gulf). Between 2002 and 2009 the phytoplankton composition of Mwanza Gulf changed from a community mostly dominated by Bacillariophyceae into a community dominated by Cyanobacteria. In the open water of Lake Victoria, Bacillariophyceae and Cyanobacteria were both abundant. Cyanobacteria dominated both in the three northern gulfs and Mwanza Gulf, but all four showed substantial differences in species and genus compositions. Phytoplankton composition and abundance in Mwanza Gulf differs in many respects from the open water of Lake Victoria and its three northern gulfs.

Traits underlie organismal responses to their environment and are essential to predict community responses to environmental conditions under global change. Species differ in life-history traits, morphometrics, diet type, reproductive characteristics and habitat utilization. Trait associations are widely analysed using phylogenetic comparative methods (PCM) to account for correlations among related species. Similarly, traits are measured for some but not all species, and missing continuous traits (e.g. growth rate) can be imputed using ‘phylogenetic trait imputation’ (PTI), based on evolutionary relatedness and trait covariance. However, PTI has not been available for categorical traits, and estimating covariance among traits without ecological constraints risks inferring implausible evolutionary mechanisms. Here, we extend previous PCM and PTI methods by (1) specifying covariance among traits as a structural equation model (SEM), and (2) incorporating associations among both continuous and categorical traits. Fitting a SEM replaces the covariance among traits with a set of linear path coefficients specifying potential evolutionary mechanisms. Estimated parameters then represent regression slopes (i.e. the average change in trait Y given an exogenous change in trait X) that can be used to calculate both direct effects (X impacts Y) and indirect effects (X impacts Z and Z impacts Y). We demonstrate phylogenetic structural-equation mixed-trait imputation using 33 variables representing life history, reproductive, morphological, and behavioural traits for all >32,000 described fishes worldwide. SEM coefficients suggest that one degree Celsius increase in habitat is associated with an average 3.5% increase in natural mortality (including a 1.4% indirect impact that acts via temperature effects on the growth coefficient), and an average 3.0% decrease in fecundity (via indirect impacts on maximum age and length). Cross-validation indicates that the model explains 54%–89% of variance for withheld measurements of continuous traits and has an area under the receiver-operator-characteristics curve of 0.86–0.99 for categorical traits. We use imputed traits to classify all fishes into life-history types, and confirm a phylogenetic signal in three dominant life-history strategies in fishes. PTI using phylogenetic SEMs ensures that estimated parameters are interpretable as regression slopes, such that the inferred evolutionary relationships can be compared with long-term evolutionary and rearing experiments.

Feed-food competition is the allocation of resources that can be used to feed humans to animal feed instead, a current but unsustainable practise not well documented for aquaculture. Here, we analysed feed-food competition in aquaculture using two measures; natural trophic levels (TLs) and species-specific human-edible protein conversion ratios (HePCRs). The HePCR equals the ratio of human edible protein in feed (input) to the human edible protein in animal produce (output). To provide prospects on aquaculture's potential to convert human inedible by-products into edible biomass, data on aquaculture production were collected and categorized based on natural TLs. HePCRs were computed for four aquaculture species produced in intensive aquaculture systems: Atlantic salmon, common carp, Nile tilapia and whiteleg shrimp. Under current feed use, we estimated that the carp, tilapia and shrimp considered were net contributors of protein by requiring ~0.6 kg of human edible protein to produce 1 kg of protein in the fillet/meat. Considering soya bean meal and fishmeal as food-competing ingredients increased the HePCR to ~2 and turned all of the case-study species into net consumers of protein. To prevent this increase, the use of high-quality food-competing ingredients such as fishmeal, or soya bean products should be minimized in aquaculture feed. In the future, the role of aquaculture in circular food systems will most likely consist of a balanced mix of species at different TLs and from different aquaculture systems, depending on the by-products available.

Thiamine deficiency from the consumption of invasive, high-thiaminase prey fishes is considered to be a major barrier for lake trout restoration in the Great Lakes. In fishes, an understudied aspect of thiamine deficiency is its effect on cardiac function. I examined the effects of dietary thiaminase on cardiac function and morphology in lake trout, specifically as they relate to thermal tolerance. Two hatchery strains of lake trout (Seneca and Slate) were raised on a control or thiaminase diet for nine months. The thiaminase diet was associated with significant ventricle enlargement, impaired cardiac function, and reduced thermal tolerance; these effects were more pronounced in Slate strain fish. Similar cardiac morphological changes were observed in wild-caught lake trout from the Sudbury Basin. These results suggest that dietary thiaminase impairs cardiac function and alters cardiac morphology in fishes, and that such changes may become increasingly important as water temperatures increase through climate change.

Intertidal mudflat systems are shaped by geological processes and an interplay of hydrodynamics, sediment availability and ecological processes. All around the world these systems are affected by relative sea level rise (RSLR), changing climate and by human activities such as sediment nourishments, dredging, hydrological engineering and bottom trawling. These kinds of perturbations cause changes in morphology and sediment composition which may cause shifts in the composition, spatial distribution and productivity of benthic communities. We analyzed the spatial and temporal variability of the sediment grain size of almost 1200 km2 intertidal flats in the Dutch Wadden Sea in the period 2009-2019. The large scale coverage was achieved by yearly grid sampling at more than 4000 stations. Spatial paneldata models were used to analyse changes in median grain size and mud content between years and to estimate the effects of resuspension due to wind and the accumulation of silt during summer. We show that between years the sediments of the intertidal flats changed synchronously throughout the study area and that the flats became coarser during the period 2011-2015 and muddier again between 2015 and 2019. The system wide changes and the absence of clear local deviations leads to the hypothesis that a large scale factor like RSLR, variability in the composition of suspended sediment in the North Sea, changing microphytobenthic productivity, or sediment nourishments in the coastal zone were causally involved in the coarsening of intertidal flats. Our data and analysis provides a base for further scientific enquiry but longer time series on higher temporal resolution of both sediment data and the physical and ecological environment are required. Models simulating the environment may provide further insight into possible development of sediment composition of the intertidal flats of the Wadden Sea.

Selenium (Se) is an important micronutrient that has been used in aquafeeds for the normal growth, welfare and health of aquatic animals. Through nanotechnology, Se can be converted into nanoparticles that are more bioavailable, utilized and absorbed by aquatic animals. However, this is still a new and emerging area of research in aquafeeds. This paper aims to review the effect of Se and Se nanoparticles (Se-NPs) application in aquafeeds on aquatic animals. Specifically, different compounds of Se, requirement levels by different species, effects on animal growth, physiology, antioxidant capacity and immune response have been highlighted. The review shows that the application of Se in aquafeeds could improve the growth performance, physiology, antioxidant enzymes, immunity and disease resistance in aquatic animals. However, the effectiveness could be highly influenced by the source of Se, aquaculture species and administration quantity. Through nanotechnology, the utilization and absorption of Se could be improved while reducing its toxicity. Therefore, Se-NPs present an efficient way to utilize nutrients in aquafeeds. Important gaps, however, exist in the current knowledge, particularly with regard to the response of shrimps and crustaceans to dietary supplementation of Se and Se-NPs as most of the existing studies have focused on fish species. Also, some species of economic importance and life stages have not been investigated, which hinders the embracement of nanotechnology in aquafeeds production.

Background Prebiotic feed additives aim to improve gut health by influencing the microbiota and the gut barrier. Most studies on feed additives concentrate on one or two (monodisciplinary) outcome parameters, such as immunity, growth, microbiota or intestinal architecture. A combinatorial and comprehensive approach to disclose the complex and multifaceted effects of feed additives is needed to understand their underlying mechanisms before making health benefit claims. Here, we used juvenile zebrafish as a model species to study effects of feed additives by integrating gut microbiota composition data and host gut transcriptomics with high-throughput quantitative histological analysis. Zebrafish received either control, sodium butyrate or saponin-supplemented feed. Butyrate-derived components such as butyric acid or sodium butyrate have been widely used in animal feeds due to their immunostimulant properties, thereby supporting intestinal health. Soy saponin is an antinutritional factor from soybean meal that promotes inflammation due to its amphipathic nature. Results We observed distinct microbial profiles associated with each diet, discovering that butyrate (and saponin to a lesser extent) affected gut microbial composition by reducing the degree of community-structure (co-occurrence network analysis) compared to controls. Analogously, butyrate and saponin supplementation impacted the transcription of numerous canonical pathways compared to control-fed fish. For example, both butyrate and saponin increased the expression of genes associated with immune response and inflammatory response, as well as oxidoreductase activity, compared to controls. Furthermore, butyrate decreased the expression of genes associated with histone modification, mitotic processes and G-coupled receptor activity. High-throughput quantitative histological analysis depicted an increase of eosinophils and rodlet cells in the gut tissue of fish receiving butyrate after one week of feeding and a depletion of mucus-producing cells after 3 weeks of feeding this diet. Combination of all datasets indicated that in juvenile zebrafish, butyrate supplementation increases the immune and the inflammatory response to a greater extent than the established inflammation-inducing anti-nutritional factor saponin. Such comprehensive analysis was supplemented by in vivo imaging of neutrophil and macrophage transgenic reporter zebrafish (mpeg1:mCherry/mpx:eGFPi114) larvae. Upon exposure to butyrate and saponin, these larvae displayed a dose-dependent increase of neutrophils and macrophages in the gut area. Conclusion The omics and imaging combinatorial approach provided an integrated evaluation of the effect of butyrate on fish gut health and unraveled inflammatory-like features not previously reported that question the usage of butyrate supplementation to enhance fish gut health under basal conditions. The zebrafish model, due to its unique advantages, provides researchers with an invaluable tool to investigate effects of feed components on fish gut health throughout life.

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Little is known about early coral settlement on shipwrecks with regard to their species and size compositions. Hurricanes in the Caribbean have a long history of sinking ships but a link with new coral settlement is understudied. In 2017, Hurricane Irma caused the sinking of over 300 vessels in the coastal waters of Saint Martin, eastern Caribbean. In 2021, coral settlement was studied on one of them, which included two native, one non-native, and two cryptogenic species. The corals were smaller than 8 cm in diameter. The invasive Tubastraea coccinea was the most abundant scleractinian and was predominantly represented by juveniles. A cryptogenic species, Stragulum bicolor, new for the Caribbean, was the most common octocoral. Because they can be harmful to the environment, shipwrecks should be monitored frequently for the occurrence of non-native species, especially when they are only a few years old.

International audience; Alien fish substantially impact aquatic communities. However, their effects on trait composition remain poorly understood, especially at large spatiotemporal scales. Here, we used long-term biomonitoring data (1984-2018) from 31 fish communities of the Rhine river in Germany to investigate compositional and functional changes over time. Average total community richness increased by 49 %: it was stable until 2004, then declined until 2010, before increasing until 2018. Average abundance decreased by 9 %. Starting from 198 individuals/m(2) in 1984 abundance largely declined to 23 individuals/m(2) in 2010 (-88 %), and then consequently increased by 678 % up to 180 individuals/m(2) until 2018. Increases in abundance and richness starting around 2010 were mainly driven by the establishment of alien species: while alien species represented 5 % of all species and 0.1 % of total individuals in 1993, it increased to 30 % (7 species) and 32 % of individuals in 2018. Concomitant to the increase in alien species, average native species richness and abundance declined by 26 % and 50 % respectively. We identified increases in temperature, precipitation, abundance and richness of alien fish driving compositional changes after 2010. To get more insights on the impacts of alien species on fish communities, we used 12 biological and 13 ecological traits to compute four trait metrics each. Ecological trait dispersion increased before 2010, probably due to diminishing ecologically similar native species. No changes in trait metrics were measured after 2010, albeit relative shares of expressed trait modalities significantly changing. The observed shift in trait modalities suggested the introduction of new species carrying similar and novel trait modalities. Our results revealed significant changes in taxonomic and trait compositions following alien fish introductions and climatic change. To conclude, our analyses show taxonomic and functional changes in the Rhine river over 35 years, likely indicative of future changes in ecosystem services.

Aquaculture started in China some 5,000 years ago with carps in ponds fed with wastes from silk production and this form of local growth of low trophic fish on a natural food web still is very important. But to date high trophic species such as Atlantic salmon are the most traded, are typically kept at high stocking densities and require high-quality feed pellets. Balancing between a globally increasing demand for fish products, different forms of aquaculture, and the need to avoid feed-food competition, requires tailored formulations of aquafeed which includes by-products and novel ingredients.

Globally, aquaculture is one of the fastest growing animal protein sources. Not only will it continue to grow throughout the next decade, it will also increase its relative contribution to the human food system (Naylor et al., 2021). This growth will mainly be achieved from inland ponds as aquaculture production at sea faces limitations. However, conventional intensification of inland aquaculture will continue to exert pressure on the environment from land use competition, energy use, effluent discharge, and greenhouse gas (GHG) emissions. Therefore, the challenge is to enable growth of the aquaculture sector while still producing within planetary boundaries. Recent advances in feed formulation and technology, however, permit the recycling of agricultural and animal wastes through aquaculture. Natural production using the nutritious pond (NP) concept turns waste nutrients into aquafeed ingredients, raises protein use efficiency, and increases in-situ reuse and upgrading of waste nutrients. This chapter describes the underlying biological concepts and application strategies of the NP concept.

Aquaculture started in China some 5,000 years ago with carps in ponds fed with wastes from silk production and this form of local growth of low trophic fish on a natural food web still is very important. But to date high trophic species such as Atlantic salmon are the most traded, are typically kept at high stocking densities and require high-quality feed pellets. Balancing between a globally increasing demand for fish products, different forms of aquaculture, and the need to avoid feed-food competition, requires tailored formulations of aquafeed which includes by-products and novel ingredients.

Highlights •A solid knowledgebase and governance process is required to develop policies for sustainable growth of offshore aquaculture in the North Sea. •Environmental goals largely define maximum sustainable production levels. For seaweed culture this is limited to the scale of several hundred km2. •Definition of realistic ambitions is a process rather than a fixed value and greatly benefits from a ‘learning by doing’ approach.

Aquaculture production in extensive shrimp ponds along mangrove coasts may be influenced by many factors such as pond size, pond management, species diversity of mangroves and aquaculture species used, as well as the position and abundance of mangroves in the ponds. A growing number of studies indicate the potential positive effects of mangrove presence on pond productivity. In this study we aimed to assess the influence of mangrove presence on pond production characteristics as observed in the south-western coastal region of Bangladesh where mangroves grow largely naturally in aquaculture ponds. Using structured interviews we quantified a large number of pond production parameters from mangrove-associated shrimp aquaculture in ponds with a wide range of mangrove coverage (0% - >50%) including total costs, revenues and net profits. The 435 ponds for which data were collected were distributed among 61 villages in four regional clusters. The regions differed significantly in terms of the species present, the total coverage of mangroves, and their position in and around the ponds. Mangrove presence in the ponds correlated strongly with pond productivity and farm profits. Mangrove presence was significantly associated with smaller ponds which had higher input costs and revenue per unit pond area than larger ponds but lower net profitability. Notwithstanding our large sample size, and contrary to our expectations, this study was not able to identify clear profit benefits of the association of mangroves with shrimp ponds. Among various possible explanations, we suggest that, as currently observed in Bangladesh, the presence of mangroves in aquaculture ponds yields little or at most sub-optimal financial benefits. Hence, our results seem to indicate that there is great scope for improving of mangrove-use in shrimp aquaculture. In that, one can expect the largest potential benefit of associating mangroves with shrimp culture in large ponds (“scale benefit”) in which mangroves are presently not being used. The great potential for mangroves to help boost pond productivity and bolster farm economic and environmental resilience clearly remains largely untapped. Our results suggest that further work is needed to help farmers better select appropriate mangrove species, the most suitable locations for planting mangroves and the best percentage of mangrove pond coverage to boost shrimp production. As our cross-sectional study only provides a baseline of mangrove association with shrimp ponds additional,properly controlled experiments following the “Before-after-control-impact (BACI)” design are also needed in order to be able to discern the true causal effects of mangroves on aquaculture production.

Seven isonitrogenous (31.70% protein) and isolipidic (5.20%) experimental diets were made by supplementing a control diet (BA0) with 0.25, 0.50, 0.75, 1.0, 1.25, and 1.5 g bile acid (BA) kg−1 diet, respectively. The diets were fed to striped catfish (Pangasianodon hypophthalmus) to monitor the effects on the growth, non-specific immune response, gene expression of fatty acids metabolism, liver, and their intestinal morphology. The average initial fish weight was 10.3 ± 0.20 (SD) g. The diets were randomly assigned to 21 hapas, each stocked with 10 fish and fed for 70 days. Supplementing BA1.0 and BA1.25 significantly improved growth and nutrient utilization (P < 0.05) compared to BA0 and other treatments. Additionally, the hematological analyses red blood cell count (RBC), haemoglobin, packed cell volume (PCV) and white blood cell count (WBC) amplified in the subsequent order: BA1.0, BA1.25, BA0.75, BA1.50, and BA0.50 g kg−1 diet and finally BA0.25 g kg−1 diet compared to the control diet. The rates of serum lysozyme activity, biochemical parameters, phagocytic index, phagocytic activity, and antioxidants parameters were considerably improved (P ≤ 0.05) in fish fed diets BA1.0 and BA1.25. In the intestinal measurement and liver histomorphometricall, the highest values were observed on BA1.0 and BA1.25. Among the five genes assayed in the liver tissues, peritoneal fat, and musculature levels of ATGL, HSL, and CPT-1, genes expression increased in fish fed diets with increasing levels of bile acid added to the diet while, the expression of PPARα and FAS decreased. Consequently, bile acids are recommended at levels of 1.0–1.25 g kg−1 diet to improve the growth performance and immune status of striped catfish.

The relative influence of geography, currents, and environment on gene flow within sessile marine species remains an open question. Detecting subtle genetic differentiation at small scales is challenging in benthic populations due to large effective population sizes, general lack of resolution in genetic markers, and because barriers to dispersal often remain elusive. Marine lakes can circumvent confounding factors by providing discrete and replicated ecosystems. Using high-resolution double digest restriction-site-associated DNA sequencing (4826 Single Nucleotide Polymorphisms, SNPs), we genotyped populations of the sponge Suberites diversicolor (n = 125) to test the relative importance of spatial scales (1–1400 km), local environmental conditions, and permeability of seascape barriers in shaping population genomic structure. With the SNP dataset, we show strong intralineage population structure, even at scales

Abstract A 3-month experiment was designed to investigate the effects of different stocking densities on growth, stress markers, intestinal digestive enzymes, hepatic antioxidant biomarkers, serum immunity, and survivability of striped catfish, Pangasianodon hypophthalmus. The relationship between fish stocking densities and water quality parameters was also assessed. Healthy fish (n = 1260 individuals, 17.52 ± 0.20 g) were raised in twelve fiberglass tanks. Triplicate fish groups with stocking densities of 60, 90, 120, or 150 fish per 1 m3 were designed, further referred to as SD60, SD90, SD120, and SD150 groups. Fish feeding was done using a commercially purchased well-balanced diet three times per day with a feeding rate of 3% of the wet fish weight. Results revealed that un-ionized ammonia, nitrite, and pH were significantly elevated, and dissolved oxygen levels were decreased significantly with increasing the stocking densities. The survival rates and growth significantly decreased with increasing fish stocking densities. The intestinal lipase, protease, trypsin, and amylase enzymes decreased significantly (P 3. Conversely, serum stress biomarkers (such as blood glucose and cortisol), transaminases, alkaline phosphatase, and blood urea nitrogen were significantly elevated with increasing stocking densities. Hepatic CAT, SOD, and T-AOC were decreased; meanwhile, hepatic MDA levels were significantly increased, together with the stocking rates. In the end, we found that the SD150 group recorded the lowest growth rates, immune responses, and antioxidant capacity and the highest stress markers as blood glucose and cortisol. In this context, we can conclude that the stocking 60 fish/m3 resulted in better growth, survival, immunity, antioxidant status, and overall performances of striped catfish. Graphical Abstract

Will the oceans feed the world? Optimistic views on a ‘Blue Revolution’ have recently been challenged and in particular the future role of marine fish culture is questioned. Important steps in raising global production of protein-rich animal seafood can only be expected from aquaculture of low-trophic organisms such as shellfish. Additional to the provisioning of healthy marine protein products, shellfish culture has many benefits as it causes little environmental impact, and provides the opportunity to contribute to ecosystem services.

A feeding trial was conducted to test the effect of dietary glutamate and glycine supplementation on growth potential, nutritional utilization and digestion, and energy metabolism of rainbow trout (Oncorhynchus mykiss). Four isonitrogenous and isolipidic diets (2 × 2 factorial design) were formulated with glutamate (Glu) and glycine (Gly) as the main factors. The protein source consisted mainly of black soldier fly larvae meal (40% inclusion in all diets) for its low-level content of glutamate and glycine. Triplicate groups of rainbow trout (30 fish/tank with mean initial body weight of 87.5 g ± 0.9) were restrictively fed by hand twice a day for 6 weeks. Dietary Glu and Gly supplementation did not affect feed intake, specific growth rate, or the feed conversion ratio. Whole body protein, lipid, amino acid and fatty acid composition were also unaffected by the supplementation of Glu and Gly in the diets. Dietary Gly supplementation increased the apparent digestibility of amino acids. Furthermore, supplementation with Gly, increased the concentration of serine, glycine, tryptophane, tyrosine and citrulline, while supplementation with Glu in the diets increased the concentration of hydroxy-proline and β-alanine in the serum of rainbow trout. Both dietary Glu and Gly supplementation improved the digestibility of the fatty acids. The expression of genes involved in the hepatic bile acid synthesis (e.g., apical sodium dependent bile acid transporter and organic solute transporter) were affected by supplementation of Gly in the diets. In general, this study showed that dietary supplementation with Gly and Glu improved the nutrient digestibility in rainbow trout.

Tidal sluices are a frequent element in the tidal regions of Europe's rivers and may hinder downstream migrating European eels Anguilla anguilla. Sea level rise will reduce the possibility for tidal sluices to freely discharge water, further compressing windows of opportunity for the passage of eels. Understanding how eels utilize the discharge events of tidal sluices and which conditions facilitate successful passage is pivotal for the design of effective fish migration measures. To investigate eel migration at a tidal sluice, acoustic receivers were placed at the tidal sluice Nieuwe Statenzijl and in its tributary of the Westerwoldse Aa, the Netherlands. Of the 30 tagged eels, 26 eels reached the tidal sluice and passage success was 100%. The mean migration speed of eels in the unobstructed part of the tributary was slow (0.14 m s−1). The eels were delayed in their migration by the sluice and delay was right-skewed distributed with most eels showing moderate delays (

Large grazers (megaherbivores) have a profound impact on ecosystem functioning. However, how ecosystem multifunctionality is affected by changes in megaherbivore populations remains poorly understood. Understanding the total impact on ecosystem multifunctionality requires an integrative ecosystem approach, which is especially challenging to obtain in marine systems. We assessed the effects of experimentally simulated grazing intensity scenarios on ecosystem functions and multifunctionality in a tropical Caribbean seagrass ecosystem. As a model, we selected a key marine megaherbivore, the green turtle, whose ecological role is rapidly unfolding in numerous foraging areas where populations are recovering through conservation after centuries of decline, with an increase in recorded overgrazing episodes. To quantify the effects, we employed a novel integrated index of seagrass ecosystem multifunctionality based upon multiple, well-recognized measures of seagrass ecosystem functions that reflect ecosystem services. Experiments revealed that intermediate turtle grazing resulted in the highest rates of nutrient cycling and carbon storage, while sediment stabilization, decomposition rates, epifauna richness, and fish biomass are highest in the absence of turtle grazing. In contrast, intense grazing resulted in disproportionally large effects on ecosystem functions and a collapse of multifunctionality. These results imply that (i) the return of a megaherbivore can exert strong effects on coastal ecosystem functions and multifunctionality, (ii) conservation efforts that are skewed toward megaherbivores, but ignore their key drivers like predators or habitat, will likely result in overgrazing-induced loss of multifunctionality, and (iii) the multifunctionality index shows great potential as a quantitative tool to assess ecosystem performance. Considerable and rapid alterations in megaherbivore abundance (both through extinction and conservation) cause an imbalance in ecosystem functioning and substantially alter or even compromise ecosystem services that help to negate global change effects. An integrative ecosystem approach in environmental management is urgently required to protect and enhance ecosystem multifunctionality.

Undersized European plaice dominate the discarded fraction of the catch of the beam trawl fisheries for sole in the Southern North Sea. Effects of environmental conditions at sea and of the use of a water-filled hopper on the survival of undersized European plaice discarded by pulse trawl fisheries were explored. During trips with commercial pulse-trawlers catches were discharged in either water-filled hoppers or conventional dry hoppers. For both hoppers, undersized plaice were sampled from the sorting belt. After assessment of vitality status, sampled fish were housed in dedicated survival monitoring tanks on board. Upon return in the harbour fish were transferred to the laboratory to monitor their survival for up to 18 days post-catch. Conditions at sea, such as wave height and water temperature, as prevailing during these trips were recorded or obtained from public data sources. The overall estimate for the survival probability for plaice discarded by pulse trawl fisheries is 12% (95% CI: 8% - 18%). Both water temperature and vitality status had strong effects on survival probabilities of discarded plaice. Increasing water temperature increased mortality. The vitality of the fish could be moderately increased by using a water-filled hopper to collect the fish on deck, but we found no significant direct effect of hopper type on plaice discard survival. It seems that to increase discards survival, fish need to be landed on deck in much better condition by a reduction of the impact of capture and hauling processes on fish condition

Marine lakes are bodies of seawater that are land-locked and maintain a subterranean connection to the surrounding sea. Here, we document the species diversity of benthic molluscs in 11 marine lakes in Raja Ampat, West Papua, Indonesia, using the roving diving survey method. We specifically tested for relationships between species richness and lake size and the degree of connection to the surrounding sea, and tested potential environmental drivers of community structure. We recorded 73 species, belonging to the classes Gastropoda (48 species, comprising 36 genera and 25 families), Bivalvia (24 species, consisting of 17 genera and 12 families), and Polyplacophora (one species). Molluscs from marine lakes are a subset of species also occurring in coral, seagrass, mangrove, and rocky shore habitats in the open sea. We found lake communities to mostly consist of grazers and filter feeders. The number of mollusc species significantly increased with increasing connection to the surrounding sea, but not with increasing surface area, indicating that dispersal potential may be the main driving force. Furthermore, we observed no significant influence of the environment on the variation in mollusc species composition among marine lakes. Still, we observed certain species to be exclusively present in either high or low-connected lakes, indicating a potential effect of environmental filtering. Marine lakes provide a unique ecosystem for diverse mollusc assemblages and as such should be protected.

The socio-cultural, economic, and environmental conditions of the world are changing rapidly and recreational fisheries will have to adapt to the uncertain future. Key research areas include assessing the sustainability of recreational fishing in response to climate change, ongoing biodiversity decline and changing social values. In this context, technological advances and digitalization can play a major role in advancing recreational fisheries. We evaluated the contributions of research that was presented at the 9th World Recreational Fishing Conference relative to 100 key research questions identified for recreational fisheries in 2020. Given that the 9th WRFC happened in the midst of the COVID-19 pandemic, we additionally synthesise impacts of COVID-19 on recreational fisheries. We found that the majority of contributions focused on resource monitoring and catch and release, while less attention was dedicated to governance, management-stock and habitat enhancement, and threats to sustainability. Rapid technological advances represent both a challenge (e.g., difficulty in management response), but also an opportunity for recreational fisheries (e.g., hyper connectivity of digital platforms for communication). Science is helping recreational fisheries to adapt and remain resilient to rapid social and environmental uncertainties, but this knowledge must be incorporated into governance structures and resource allocation strategies to ensure effective implementation.

Shrimp culture rearing systems are dynamic with numerous processes influencing system performance. This research investigated the effects of stocking density, feeding level and C:N ratio on shrimp production, water quality and microbial community composition in a biofloc shrimp rearing system, using a 3 × 3 factorial design. Pacific white shrimp (Litopenaeus vannamei) were stocked at 27, 120, or 300 individual m−3 and fed 100, 80 or 60% of the recommended daily feed ration. For each combination of stocking density and feeding level, C:N ratios of 7.4, 12 or 16 were created by feeding a mixture of casava and rice bran besides the daily pelleted feed input to culture tanks. After 12 weeks of culture, the harvested shrimp biomass was the highest in the rearing tanks with the highest stocking density, feeding level and C:N ratio (P < 0.05), while the individual shrimp size at harvest decreased with increasing stocking density (P < 0.05). Biofloc biomass (e.g. total suspended solids TSS, volatile suspended solids VSS) and, to a lesser degree, water quality (total ammonia nitrogen TAN, NO2-N) were affected by 2 and 3-way interactions of the main tested factors. The ash, protein, fat and nitrogen free extract (NFE) content in biofloc were affected by stocking density (P < 0.05), and ash and NFE content by C:N ratio (P < 0.05). Regarding the microbial community composition in the biofloc at the highest stocking density, increasing feeding level and C:N ratio led to an increasing microbial richness and diversity (P < 0.05) as a result of nutrient input. Overall, the shrimp production and biofloc biomass were influenced in a similar way by the stocking density, feeding level and C:N ratio applied in the biofloc system. Future research should focus on how the type of carbohydrates and methods of administration affect shrimp growth and biofloc formation, and how this may promote health benefits through the microbial community manipulation.

This study assessed the effect of different dietary ingredients on the quantity and characteristics of faecal waste produced by rainbow trout (Oncorhynchus mykiss). Seven ingredients were tested: fish meal (FM), mussel meal (MM), poultry meal wet rendered (PM-W) or dry rendered (PM-D), insect meal (IM), single cell protein (SCP) and brewers grain protein (BGP). Eight experimental diets were formulated: a control diet (CON) being predominantly plant-based and seven test diets, which contained 70% of the CON diet and 30% of one of the test ingredients. Rainbow trout juveniles (65 g, 30 fish/tank) were fed the experimental diets at satiation for six weeks, in triplicate groups. Dry matter (DM) and nutrient digestibility of diets and the test ingredients were measured. Furthermore, to estimate the faecal characteristics, particle size distribution (PSD) and removal efficiency of the faecal waste were determined. Nutrient digestibility of diets and ingredients differed significantly. Growth did not differ between the experimental diets, but DM digestibility was affected by the diet. Diets affected the amount of faecal waste produced, its removal efficiency (%) and the amount of non-removed faeces (g DM/kg DM feed). The highest and lowest removal efficiency were observed at FM and BGP diets, respectively. Accordingly, FM diet resulted in the lowest (37 g DM/kg DM feed), while BGP diet resulted in the highest (125 g DM/kg DM feed) amount of non-removed faeces. Further, it was also observed that differences in faecal removal efficiency can compensate for the variation in the quantity of faecal waste produced. Consistent with the faecal removal efficiency data, faeces PSD was also influenced by diets. FM and MM diets resulted in faeces with lowest proportion of particles of