Hydrobiologia

Phenotypic plasticity is an important adaptation to spatial and temporal environmental variations. For submerged macrophytes, adaptation to water depth and light variation is particularly important. To determine the morphological and physiological adaptive strategies of Vallisneria natans at different water depths and light conditions, we combined field investigation, light control experiment and in situ physiological response experiment. In the field investigation and the light control experiment, both water depth and light intensity had prominent effects on the morphological of V. natans, especially in fresh weight and leaf length. The leaf length elongated more rapidly at intermediate water depth sites with lower light intensity. In the in situ experiment, the survival boundary of V. natans is 5.5 m in Lake Erhai. Below this depth, the chlorophyll-a content increased gradually with increasing water depth. Our results demonstrated that V. natans can adapt to water depth and light availability by changing morphological, physiological and resource allocation. At low light condition, V. natans invested more resource for light acquisition, simultaneously, changing the photosynthetic pigment content to compensate for light attenuation; conversely, more resource was directed towards reproduction. These results will provide new insight for species selection when conducting aquatic plants restoration in freshwater ecosystem. HIGHLIGHTSO_LIWater depth and light availability affect the morphology, physiology, and resource allocation of V. natans. C_LIO_LIAn alternative resource allocation pattern of V. natans could shift between light acquisition and reproduction. C_LI

The Aral Sea was once the fourth-largest inland water body in the world. However, the lake rapidly shrank over the past six decades, mainly due to the loss of inflow from one of its tributaries, the Amu Darya River. Lakes and reservoirs are traditionally characterized by static chemical and morphological parameters, leaving untouched a dynamic impact of phytoplankton changes. We used an integrated approach combining traditional microscopy and FlowCam-based imaging flow cytometry to study phytoplankton communities during the 2018 and 2019 expeditions in the Aral Sea remnant lakes system. The residual Aral Sea water bodies experienced different environmental conditions, forming hypersaline South Aral, North Aral Sea that is constantly getting freshwater, and brackish Chernyshev Bay and Tushchybas Lake with 2-8 times amplitude of salinity changes attributed to the variability in the precipitation and periodical influx of freshwater. The salinity fluctuations had an impact on the phytoplankton communities in Chernyshev Bay, making it similar to the phytoplankton of North Aral in 2018 while resembling the hypersaline South Aral phytoplankton assemblages in 2019. Multivariate analysis revealed that salinity, water temperature, ammonium, and nitrates were major contributors to explaining the variance in the sampling data. We conclude that drastic phytoplankton fluctuations occur in the two brackish water bodies in the middle of the former Aral Sea, reflecting changes in salinity.

Rainbow trout, Oncorhynchus mykiss, is one of the most widely introduced fish species in the world, and its impacts on native fishes and ecosystems are of considerable concern. One of the rivers inhabited by rainbow trout in the Shiretoko Peninsula is the Chinishibetsu River, and the origin of rainbow trout in this river is thought to be Lake Chinishibetsu in the upper reaches of the system, where the private stocking of rainbow trout was conducted in the 1960s. However, the basic biology of rainbow trout in the Lake Chinishibetsu area is currently unknown. This study addresses this knowledge gap by examining the biology of rainbow trout in the inlet tributaries of Lake Chinishibetsu based on sampling conducted during the rainbow trout spawning season. A total of 104 rainbow trout, ranging in age from 1+ to 8+ years, were collected from the two inlet tributaries of Lake Chinishibetsu. White-spotted charr Salvelinus leucomaenis and Siberian stone loach Barbatula oreas, neither of which is native to the Shiretoko Peninsula, were also collected and had presumably invaded the area at the same time as the rainbow trout. The sampled rainbow trout included immature and mature males and females. The distribution of fork lengths of mature females was bimodal, and the sex ratio of mature rainbow trout was male-biased. Our results indicate that the rainbow trout population in the inlet tributaries of Lake Chinishibetsu is reproducing continuously and exhibits a dimorphic life history with river residents and lake migrants of both sexes. Additionally, rainbow trout continue to be collected downstream of the Chinishibetsu River, which is the primary habitat for this species in the Shiretoko Peninsula. Therefore, unless rainbow trout are eliminated from Lake Chinishibetsu, which serves as a source of non-native species upstream of the Chinishibetsu River, it will be difficult to control rainbow trout distributions and minimize population sizes on the Shiretoko Peninsula.

Studying the distribution of organisms and their movements is fundamental to understand population dynamics. Most studies indicated that crocodilians do not move around much but several studies demonstrated that some species showed movement patterns. Detection of these movements along the individual life is still a challenge. In this study we analyzed the variation of strontium isotopic ratio (87Sr/86Sr) in the femur bones of 70 Caimanya care individuals caught in 16 sites located in five hydrological sectors of the Beni river floodplain in Bolivia. Our results demonstrated for the first time that such a methodology could yield indications about the capture sites and reconstruct individual life history. Analyses of the outer part of the femur of 70 individuals showed that capture sites could be differentiated between sectors and even between sites or groups of sites in each sector. Studies of complete 87Sr/86Sr profiles along the femur, representing the individuals entire life, were performed on 33 yacares. We found that most of the individuals did not show any significant isotopic variation throughout their lives. This absence of variation could result from a high fidelity to the birth site, and/or from an insignificant isotopic variation between the water bodies through which the animal has potentially moved. However, 24% of the analyzed individuals presented significant variations that can be considered as movements between different habitats. Based on the observed low proportion of moving yacares, we advocated that each water body should be considered an individual management unit.

Salt marshes are under high, and increasing, anthropogenic pressures that have notably been reported to affect the diet of several fish species, probably resulting in nursery function alterations. Most of the previous studies in Europe were yet based on gut content analysis of fish, which can be considered a snapshot of immediate impacts of salt-marsh changes, and hardly of long-term effects of disturbances. In this study, we investigated the impact of vegetation type (resulting from both plant invasion and sheep grazing) by assessing trophic network (and especially fish diet and position) of different salt-marsh conditions. Replicated samples of basic sources (particular organic matter and microphytobenthos), dominant vegetation, potential aquatic and terrestrial prey and fish of 3 main species were taken during summer 2010 in two bays from Western France (Mont -Saint-Michel Bay and Seine Estuary) and analysed using C and N stable isotope compositions. All response variables tested (overall trophic organization, trophic niche and trophic position) provided consistent results, i.e. a dominant site effect and a weaker effect of vegetation type. Site effect was attributed to differences in anthropogenic Nitrogen inputs and tidal regime between the two bays, with more marine signatures associated with a higher frequency of flooding events. A second hypothesis is that E. acuta, which has recently totally replaced typical salt-marsh vegetation in Mont Saint-Michel Bay strongly impacted the nursery function. The trophic status of dominant fish species was unchanged by local salt-marsh vegetation, and considered consistent with their diet, i.e. high for predatory species (the sea bass Dicentrarchus labrax and the common goby Pomatoschistus microps) and lower for biofilm grazing species (the thinlip mullet Chelon ramada). This study finally highlights the relevance of stable isotopes analyses for assessing long-term and integrative effects of changes in vegetation resulting from human disturbances in salt marshes. HighlightsO_LICross-ecosystem subsidies are of high functional importance, notably in salt marshes C_LIO_LIFish are vectors of exchanges, most European studies being based on their gut content C_LIO_LIUsing stable isotopes we analysed the effect of surrounding vegetation on food webs C_LIO_LISurprisingly we found weak vegetation and strong site effects on all metrics C_LIO_LINitrogen inputs, site accessibility and loss of nursery function can explain this fact C_LI O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=87 SRC="FIGDIR/small/222406v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@27b54borg.highwire.dtl.DTLVardef@ef583corg.highwire.dtl.DTLVardef@18a0303org.highwire.dtl.DTLVardef@1cbe5d4_HPS_FORMAT_FIGEXP M_FIG C_FIG

We report for first time about tropical seagrass meadows association with mangrove ecosystems and its effect on seagrass population dynamics off India in Andaman Sea. Two sites of Neil island, i.e. site 1, associated with mangroves and site 2 without mangroves were selected. Quadrat sampling (n=5) were used to collect sediment and seagrass samples. Reconstruction techniques were used to derive population age structure. T. hemprichii population was found mostly with sandy substrate at both sites, with silt consisting very low fraction at site 1. Density, biomass, productivity and morphometric features of T. hemprichii were significantly higher at site1. Reproductive density was higher at site 1, whereas reproductive effort to produce fruits were higher at site 2. The rhizome (vertical+ horizontal) production rates were higher at site 1 and the vertical elongation rate was higher at site 2. Plastochrome interval for site1 and 2 were 25.49 and 26.80 days respectively leading to formation of 14.31 and 13.62 leaves per year. T. hemprichii population at site 1 had four years of longevity and higher younger plants compared to site 2. The long-term average recruitment and present recruitment rate were higher at site 1 compared to site 2, resulting in steady state growth of the overall population at site 1. Higher number of younger plants suggests fitness of the T. hemprichii population at site 1, which increases the ecological significance of mangrove ecosystems have on seagrass population dynamics. This association should be considered for better management and conservation practices of coastal seascapes under global change scenarios.

In order to explore the physiological reaction to hyperosmotic environment, Solenaia oleivora were exposed to 2.23{per thousand} salinity. In 48h, the hemolymph osmolality kept increasing, and the hemolymph protein concentration increased in the first 6h and then decreased significantly, while the free amino acid content increased in the first 24h and then kept stable (P < 0.05). The activity of Na+/K+-ATPase at 0h was significantly higher than other times in most organs except intestine, which was highest at 3h (P < 0.05). The ions concentration were also influenced. The concentration of Na+ rose in haemolymph, axe foot and intestine, but decreased in gill and hepatopancreas. In hemolymph, gill, hepatopancreases and adductor muscle, the K+ concentration was the highest at 0h, while in axe foot and intestine, it showed a positive tendency. The concentration of Cl- in haemolymph, adductor muscle, intestine and axe foot were positively correlated with treatment time, while hepatopancreas showed opposite tendency. High salinity stress caused a difference in the gill histological structure, the gill structure shrunk, the gill lamellas space and shrinking degree showed an enlarging trend with salinity treatment time.

Globally estuaries are under increasing pressure from human development impacts as well as the growing effects of climate change that is already, and increasingly so, causing major changes in events such as droughts. Although droughts are regular occurrences and are projected to become progressively more significant in many parts of the world, their potential impacts on estuaries requires better understanding and quantification. This study aims to quantify environmental and phytoplankton parameter changes in two contrasting subtropical estuary types in South Africa; the temporarily closed uMdloti Estuary and the predominantly open to the sea uMlalazi Estuary during a hydrological drought event and subsequent non-drought period. Drought caused lower salinities, almost exclusively freshwater, throughout the temporarily closed estuarine type uMdloti. The marine-estuarine salinity environment of the predominantly open uMlalazi during drought expanded to include lower salinities in the non-drought period. Dissolved oxygen levels were more variable during drought conditions including periods of hypoxia, but more stable at elevated levels in both estuaries during the non- drought period. Temperature measurements included higher values during drought, especially in the dry season. Chl-a concentrations were overall higher and more variable during drought in uMdloti, with periods of bloom formation as well as decay. Drought-induced conditions can span several generations for estuarine and estuarine associated organisms. The results from the study provide quantitative support for the hypothesis that extended periods of drought conditions lead to a decrease in niche availability to estuarine organisms in a range of estuary types.

AO_SCPLOWBSTRACTC_SCPLOWEmergent macrophytes are commonly used to control eutrophication in Constructed Floating Wetlands (CFW) systems. However, tropical emergent macrophyte species, particularly from South America, are underrepresented in these applications. This study aims to investigate the potential of five emergent macrophytes, Alternanthera philoxeroides, Ludwigia leptocarpa, Polygonum ferrugineum, Typha domingensis, and Urochloa mutica in controlling eutrophication and inhibiting cyanobacterial growth, compared to the floating macrophyte Pontederia crassipes, the most studied macrophyte for this purpose. Phytoremediation experiments were performed ex-situ in mesocosms (50 L) with high soluble reactive phosphorus (SRP) concentration (400 {micro}g L-1). Allelopathic effects of the macrophytes root exudates on cyanobacteria were tested in vitro using a strain of Microcystis aeruginosa. While P. crassipes reduced SRP concentration by 86% in 14 days, the tested macrophytes reduced SRP concentration by > 94%, except for T. domingensis, which showed a reduction of 64%. NH4+ and NO3- removal in 14 days were 96% and 62%, respectively, for P. crassipes. These values corresponded to 96% and 63% for the five tested macrophytes. Root exudates of A. philoxeroides, L. leptocarpa, and P. ferrugineum caused inhibition of M. aeruginosa growth with no detection of Chl-a after 7 days. Thus, three emergent macrophytes were more efficient in removing nutrients than P. crassipes. and showed allelopathic potential against cyanobacteria, indicating that using local emergent macrophytes in CFW systems can be a valuable and sustainable tool to mitigate eutrophication and its consequences in aquatic environments. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/603719v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@e09e31org.highwire.dtl.DTLVardef@b1d4a7org.highwire.dtl.DTLVardef@1003e0borg.highwire.dtl.DTLVardef@e97e22_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LIEmergent macrophytes were similarly efficient to P. crassipes in nutrient removal C_LIO_LILudwigia leptocarpa was the most efficient in SRP removal in 7 days C_LIO_LIAllelopathy on cyanobacterium M. aeruginosa by A. philoxeroides, L. leptocarpa, and P. ferrugineum root exudates C_LIO_LIAdapting emergent macrophytes in CFW structures can be helpful in in situ phytoremediation. C_LI SO_SCPLOWTATEMENTC_SCPLOWO_SCPCAP C_SCPCAPO_SCPLOWOFC_SCPLOW NO_SCPLOWOVELTYC_SCPLOWThis study lies in its comparative analysis of underrepresented tropical emergent macrophytes from South America against the widely studied floating macrophyte, Pontederia crassipes (water hyacinth). By focusing on these local emergent macrophytes, the research addresses a significant knowledge gap. It provides insights into their potential application in Constructed Floating Wetlands (CFWs) for nutrient removal and cyanobacteria control. Key findings demonstrate that the selected emergent macrophytes outperform P. crassipes in reducing soluble reactive phosphorus (SRP) concentrations and exhibit substantial nitrogen removal efficiencies. Furthermore, the allelopathic potential of A. philoxeroides, L. leptocarpa, and P. ferrugineum against the harmful cyanobacterium Microcystis aeruginosa showcases their dual functionality in mitigating eutrophication and inhibiting harmful algal blooms.

The common carp (Cyprinus carpio) is an important species in global aquaculture. To optimize its production, it is necessary to understand its behaviour in relation to environmental and management factors. This study investigated the spatial and temporal dynamics of carp behaviour in a semi-intensive aquaculture pond under controlled feeding regimes over two growing seasons (2022-2023). Using telemetry and stable isotope analysis, we investigated activity, depth utilisation and feeding behaviour in relation to growth and aquaculture practices. The activity of carp and their spatial use changed over time, influenced by temperature, food availability and stocking density. Activity peaked in spring and early summer and was highest at night and twilight. In the warmer months, shallow areas (<0.5 m) were favoured, probably due to thermoregulation, oxygen levels or access to prey. Individual variability in foraging site use and food composition correlated with growth, highlighting the importance of behavioural traits in resource acquisition. A flood-induced rise in stocking density in 2022 increased competition for food, resulting in higher activity and lower growth compared to 2023. Stable isotope analysis showed that benthic invertebrates were the main food source, supplemented by cereals, emphasising the importance of a balanced natural and artificial diet. Our results emphasise the value of telemetry and isotope analysis for improving aquaculture practises. Recommendations include adapting feeding to seasonal and individual behaviour, mitigating density effects and promoting sustainable practises to optimise carp production.

O_LIGlacial relict mysid and amphipod crustaceans are characterised by their affinity for cold and well-oxygenated waters and inability to disperse upstream or by external agents. These crustaceans occur in large and deep lakes of Northern and Central Europe and North America, their distributions shaped by glaciation events. In Europe, along the southern edge of their distribution (Germany, Poland, Lithuania, Belarus), glacial relict crustaceans are threatened by eutrophication and global warming. C_LIO_LIThis study assesses the status of three glacial relict malacostracan species in Lithuania; the amphipods Monoporeia affinis and Pallaseopsis quadrispinosa, and mysid Mysis relicta, and models their abundance as a function of environmental variables and the presence of invasive Ponto-Caspian mysids and amphipods. C_LIO_LIOur results revealed that M. affinis is likely extinct in the country, whereas M. relicta was found in only 9 out of 16 locations from which it was previously recorded. The distribution of P. quadrispinosa appears to be shrinking. C_LIO_LILake depth and water flowthrough intensity were significantly and positively associated with the relative abundance of relict mysids and amphipods, but no association was found with lake size or the presence of invasive Ponto-Caspian crustaceans. C_LIO_LIWe conclude that urgent action to mitigate the effects of nutrient run-off is needed to improve the status of glacial relict and other species that require good water quality. We also propose the re-introduction of glacial relict species in Lake Dr[u]k[s]iai, where they went extinct during the operation of the Ignalina nuclear power plant that heated the lake, but where deep-water environmental conditions have improved following the powerplant closure in 2010. C_LI

Understanding the mechanisms that generate organism distribution patterns from the beta diversity perspective can assist in environmental monitoring strategies. In this study, we emphasized the limnic zooplankton due to the ability of these organisms to respond quickly to environmental variations. Therefore, we evaluated the following questions: (i) Do different regions of the same lake have the same importance in contributing to beta diversity? (ii) Do beta diversity and its components vary over the hydrological cycle? (iii) What is the importance of local and spatial predictors in beta diversity and its components? (iv) Do beta diversity and its components show a consistent pattern throughout the hydrological cycle? We found that the contribution of different sites to diversity was more associated with regions with low abundance and richness of organisms values, such as the littoral and igarapes, which shows the relevance of these areas for biological monitoring and for the delimitation of priority areas for the zooplankton diversity conservation. Despite the peculiarities of each hydrological period and regarding beta diversity components, we verified a species substitution and differences in abundance pattern in the lake. We also found low concordance patterns between the periods and low environmental and spatial variables prediction on beta diversity patterns.

Anthropogenic stressors, including restoration activities, can have ecosystem wide impacts, reflecting in various biotic components, particularly the basal levels in the trophic webs. Functional traits link taxonomic diversity to ecosystem function, thereby enabling a better ecological assessment of ecosystem health. We studied the effects of restoration activities on the community structure and functional diversity of freshwater cladoceran zooplankton in an urban water reservoir. Samples were taken in the early and late phases of the restoration work. Cladoceran species community and functional composition was significantly different between the two phases. There was a considerable reduction in taxonomic richness, functional richness and redundancy in the late phase. Taxonomic beta diversity between the two phases was explained more by nestedness. Habitat degradation due to haphazard restoration measures such as destruction of littoral zone and arbitrary desilting in addition to the dumping of untreated sewage could have contributed to the decrease in species and functional richness within the reservoir.

Salinity is an environmental factor that strongly characterizes the habitat use patterns of aquatic organisms. However, knowledge is biased toward the effect of differences in osmotic pressure among salinity habitats; how ambient specific gravity (SG) differences determine species distribution is scarcely understood. Diadromous fish, which migrate between marine and freshwater habitats, may encounter this SG problem when they are unexpectedly landlocked in or colonize freshwater areas with low environmental SG. This is particularly serious for planktonic larval fish, which must maintain neutral buoyancy for foraging and passive locomotion, although their swimbladders are generally underdeveloped. Then, we hypothesized that the SG problem limits the establishment of freshwater resident populations in marine-originated diadromous fishes. To test this hypothesis, the SG modulation ability of newly hatched larvae was compared among three closely related diadromous goby species in Gymnogobius, one of which has freshwater resident populations. The aquarium experimental results did not support that only the species deriving freshwater residents can maintain neutral buoyancy even in freshwater conditions; that is, all three species could modulate their body SG almost equally to those of both fresh and sea waters. This suggests that the ability to maintain neutral buoyancy in freshwater had been pre-adaptively acquired prior to larval freshwater colonization. On the other hand, it is highly noteworthy that the early larvae of the target group maintained neutral buoyancy in various SG environments using swimbladders, which is the first such evidence in teleosts.

The focus of this study was to assess the potential of otolith microchemistry as a fishery management tool for different European freshwater fish species in an Alpine foreland with a diverse range of different water bodies but low geological variation. 87Sr/86Sr isotope and Sr/Ca ratios in water samples from 26 habitat sites in a pre-alpine catchment region around lake Chiemsee, Germany, an important region for recreational and economic fisheries, were analysed. 87Sr/86Sr isotope ratios and the Sr mass fractions in otoliths of 246 fish out of 16 species were determined using (laser ablation) inductively coupled plasma mass spectrometry ((LA)-ICP-MS). Habitats could be discriminated into three distinct strontium isotope regions (SIGs) and seven clusters with characteristic 87Sr/86Sr isotope and Sr/Ca ratios. The direct comparison of 87Sr/86Sr isotope ratios in water and otolith samples allowed to identify fish that might have been a) migrating b) transferred from other water bodies or c) stocked from fish farms. Sr/Ca ratios in water and the Sr mass fraction in otoliths were highly correlated, although significant differences between species from the same environment could be documented. Sr mass fractions in sagittae of Perca fluviatilis were about 60 % of those in sagittae of Coregonus spp and of lapilli of roach Rutilus rutilus from the same habitats. Different partition factors for water to otolith Sr/Ca mass fractions were determined for different species. Discrimination of fish otoliths by 87Sr/86Sr isotope ratios and Sr mass fractions according to habitat clusters was possible with success rates ranging from 92 % to 100 % for cyprinids, European perch Perca fluviatilis, whitefish Coregonus spp. and European grayling Thymallus thymallus, and was 74 % for salmonids. Otolith microchemistry proved to have great potential to serve as a fishery management tool at smaller spatial scales such as in the studied Alpine foreland when considering the limited variation of 87Sr/86Sr isotope and Sr/Ca ratios, the type and spatial distribution of habitats, and the species and question under investigation. HighlightsO_LIOtolith microchemistry applied in in area with limited geological variability C_LIO_LIFish transferred, stocked or migrated were identified C_LIO_LIRegressions between Sr/Ca ratios in water predict Sr mass fractions in otoliths C_LIO_LISpecies specific Sr discrimination from water into otoliths C_LIO_LIEuropean freshwater fish species assigned to habitat clusters of origin C_LI

Sockeye salmon (Oncorhynchus nerka) is a traditional object of fishery in the northern Pacific, but its island populations now face emerging threats from territories development and escalating risks of unregulated fishing. The present study aims to assess the current status of Kuril island populations associated with the biogeographical processes in the past. We analyzed diversity distribution of the D-loop sequence and three mtSNPs localized in the Cytb and COI genes in sockeye salmon populations across the North Pacific. mtDNA variants were grouped into two distinct lineages: haplogroups 10T and 13T. Their distribution suggests an Asian origin for the 10T lineage and a North American origin for the 13T haplogroup. Testing the biogeographical scenarios support recurrent postglacial expansions of North American strains into the southernmost territories of the Asian range during the last two glacial cycles. Concurrently, during the Holocene transgression, there were two centers of sockeye salmon radiation in Asia associated with the refugium in the Kamchatka River basin and a minor cryptic refugium in the Hokkaido region. We also propose an island bridge hypothesis to explain dispersal of 10T-lineage from the Kamchatka River basin into Cook Inlet and Alaska Peninsula watersheds via the Aleutian Islands.

O_LIEnvironmental conditions bottlenecking species population demographics are less known in cold regions with harsh winters despite of global concerns of declining freshwater mussels (Unionidae). Few studies examined both cold and summer environments in attempts to promote habitat conservation of Unionidae species. C_LIO_LIWe identified the taxonomically confused Unionidae species using phylogenetic analysis with mtDNA (COI region) and tested the hypothesis that winter mortality is the main cause of contrasting population demographics and structures in floodplain lakes in northern Japan. Demographic surveys were conducted in two lakes, which contrasted in recruitment rates, over one year including 4-month ice-covered periods C_LIO_LIAlthough previous studies have identified freshwater mussels as introduced Anemina arcaeformis (Heude 1877) based on morphology, this study confirmed the focal species as potentially native Buldowskia iwakawai (Suzuki, 1939). High winter mortality (30-40%) of adult mussels was found, although the mortality did not significantly differ between the populations with contrasting recruitment. C_LIO_LISurprisingly, the annual mortality was much lower in juveniles (10%) than in gravid and nongravid adult individuals (40-75%). The main inter-population difference was attributed to the higher summer mortality of gravid females, but not juveniles and non-gravid individuals, in the population with low recruitment. C_LIO_LIThese results collectively suggest that summer hypoxia combined with physiological stresses on females in winter is a likely population growth-limiting mechanism. To prevent a chain of adult abundance decreases in winter and high mortality of gravid mussels and newly born juveniles in summer, improvements in summer habitat conditions are necessary, while winter conditions need to be considered simultaneously. Increases in water circulation rates and alleviations of hypoxic conditions is an option for short-term habitat improvement approach. The current study sheds light on the winter-mediated mortality of freshwater mussels in shallow eutrophic floodplain lakes and contributes to improved management strategies for degraded floodplain waterbodies. C_LI

Interannual fluctuations in the abundance of young-of-the-year (YOY) European perch (Perca fluviatilis) were studied in two large French peri-alpine lakes. Using a 12-year dataset of late-summer hydroacoustic surveys, we quantified YOY perch densities and explored their relationship with environmental drivers through Generalized Additive Models (GAMs). Our analysis revealed a strong link between surface temperature during the embryonic phase and YOY recruitment success. Embryonic thermal conditions alone explained 44 to 88% of the variability in YOY density across lakes, confirming temperature as a key predictor of perch recruitment. In contrast, trophic factors and adult stock showed no consistent trends. These findings validate in natura the central role of spring thermal regimes in shaping recruitment and provide a framework to better understand recruitment variability under ongoing climate change.

The increased intensity, frequency and duration of extreme climatic events (ECEs) in the context of climate change have been recognised as additional pressures for seagrass habitat in lagoon ecosystems. Among these ECE, this study focuses on the impact of marine heatwaves (MHWs) on seagrass species in Mediterranean coastal lagoons, i.e., the seagrasses Cymodocea nodosa, Nanozostera noltei, and Ruppia cirrhosa. We experimentally assessed with a near-natural mesocosm, the effects of a 20-day heatwave at three intensities (+2, +4, +6{degrees}C above control near-natural conditions) in spring and summer on these seagrass species and quantified changes in growth performance, respiration, and gross primary production. Responses to these MHW varied by species and season. C. nodosa responded differently to MHWs in spring and summer, its net foliar growth rate being stimulated and maintained, respectively. N. noltei responded positively to moderate MHWs (+2, +4{degrees}C) in spring but showed vulnerability to the high-intensity MHWs (+6{degrees}C) in summer. R. cirrhosa remained resilient in spring and benefited from MHWs in summer, particularly at +4{degrees}C intensity, to stimulate growth. Hence, all three species were able to tolerate a single 20-day MHW with the species being increasingly better adapted in the following order N. noltei, R. cirrhosa, and C. nodosa. Increase of the initiation and growth of new leaves was a common phenological response observed in all three species, albeit at a lesser extent for R. cirrhosa. Our near-natural experimental approach reveals species- and season-dependent responses to MHWs, highlighting the complexity of seagrass resilience in lagoon ecosystems. These findings provide valuable insights to inform conservation strategies and improve the management of coastal habitats under future climate scenarios.

We characterized how land use influenced dissolved nutrients and periphytic algal biomass in an Andean basin from Northwest Patagonia. Nutrient export, especially dissolved inorganic nitrogen increased with human population density. However, no correlation between nutrient concentration and algal biomass was found, which could instead be limited by light availability. Our results suggest that local N-limited ecosystems are liable to eutrophication by increased demographic pressure and that alternative wastewater treatment strategies are necessary for sustainable growth.