Brackish Lagoon Research Articles

Distribution of 210Po in the trophic levels of a brackish lagoon in Uruguay

Distribution of 210Po in the trophic levels of a brackish lagoon in Uruguay

Relationship between water quality and phytoplankton distribution of aquaculture areas in a tropical lagoon.

Aquaculture activities can affect water quality and phytoplankton composition. Our study estimated phytoplankton density and composition relating to aquaculture-impacted environmental factors. We analyzed water quality and phytoplankton at 35 sites in a tropical brackish lagoon, including inside aquaculture ponds (integrated farming of fish, shrimp, and crab), at wastewater discharge points, within 300m of these points, and farther out in the lagoon. Measurements were taken after aquaculture activities started in March and again in July. In both periods, total nitrogen (TN), total phosphorus (TP), chlorophyll-a (Chl-a), and turbidity decreased from the aquaculture ponds to the farther lagoon areas. Principal component analysis showed that nutrients, turbidity, and Chl-a were critical factors in aquaculture ponds, while salinity, temperature, pH, dissolved oxygen (DO), and water depth influenced water quality outside the ponds. Phytoplankton density was higher in July than in March due to aquaculture characteristics. Redundancy analysis indicated that phytoplankton, typical of inorganic, turbid, shallow lakes, was present throughout, whereas marine phytoplankton characterized the open water area (OWA). Marine phytoplankton caused a higher Shannon-Wiener index in July compared to March for OWA. Phytoplankton in aquaculture ponds was dominated by Oscillatoria spp., while Thalassiosira spp. dominated outside the ponds. We also identified indicator genera for two connected lagoons. Although constant water exchange prevented identifying specific indicator phytoplankton groups for aquaculture, this revealed the impact of wastewater from aquaculture ponds on the natural environment in the lagoons. Research on phytoplankton communities is necessary for the sustainable development of aquaculture and environmental management in coastal lagoons.

Variable habitat use supports fine-scale population differentiation of a freshwater piscivore (northern pike, Esox lucius) along salinity gradients in brackish lagoons.

In mobile animals, selection pressures resulting from spatio-temporally varying ecological factors often drive adaptations in migration behavior and associated physiological phenotypes. These adaptations may manifest in ecologically and genetically distinct ecotypes within populations. We studied a meta-population of northern pike (Esox lucius) in brackish environments and examined intrapopulation divergence along environmental gradients. Behavioral phenotypes in habitat use were characterized via otolith microchemistry in 120 individuals sampled from brackish lagoons and adjacent freshwater tributaries. We genotyped 1514 individual pike at 33highly informative genetic markers. The relationship between behavioral phenotype and genotype was examined in a subset of 101 pikes for which both phenotypic and genomic data were available. Thermosaline differences between juvenile and adult life stages indicated ontogenetic shifts from warm, low-saline early habitats towards colder, higher-saline adult habitats. Four behavioral phenotypes were found: Freshwater residents, anadromous, brackish residents, and cross-habitat individuals, the latter showing intermediary habitat use between brackish and freshwater areas. Underlying the behavioral phenotypes were four genotypes,putative freshwater, putativeanadromous, and two putativelybrackish genotypes. Through phenotype-genotype matching, three ecotypes were identified: (i) a brackish resident ecotype, (ii) a freshwater ecotype expressing freshwater residency or anadromy, and (iii) a previously undescribed intermediary cross-habitat ecotype adapted to intermediate salinities, showing limited reliance on freshwater. Life-time growth of all ecotypes was similar, suggesting comparable fitness. Bycombining genetic data with lifelong habitat use and growth as a fitness surrogate, our study revealed strong differentiation in response to abiotic environmental gradients, primarily salinity, indicating ecotype diversity in coastal northern pike is higher than previously believed.

The community structure of recent ostracods in the Burullus lagoon, Egypt

This work concentrates on the recent ostracod community from the bottom sediments of Burullus lagoon (BuL), Egypt. It aims to identify the impacts of the environmental factors such salinity, substrate and pH on the ostracod community. Only four ostracod species are identified, Cyprideis torosa, Leptocythere castanea, Loxoconcha elliptica and Cypridopsis vidua. The results reflect the abundance of a sole tolerant species, C. torosa (79.59–100 %, with an average of 94.18 %), in all sites. Actually, this conclusion reflects the dominance of unfavorable conditions for increasing the biodiversity in the lagoon. Moreover, the associated benthic foraminiferal assemblage suffers from the rarity of species and the abundance of one tolerant species, Ammonia tepida. Therfore, there is an urgent need to understand the environmental conditions in the BuL. The measured low salinities are suitable for the survival of only brackish ostracod species. Moreover, the distribution and structure of the ostracod assemblage are mainly controlled by the type of bottom sediments. Actually, as the content of sand increases, particularly at sites near the connection to the sea, low numbers of individuals are recorded, whereas the number of living species increases in muddy substrate. Furthermore, the sites with sandy substrate display thick-walled carapaces, while the others with muddy substrate possess thin-walled carapaces. Also, the occurrence of Cypridopsis vidua is restricted only to the muddy substrate. In terms of the hydraulic conditions, the highest abundance of living species is recorded in the southern part, where the quiet conditions prevail. The lagoon water is alkaline, so pH has no observed effects on the ostracod community. Accordingly, salinity, sediment types and hydraulic conditions play the major role in controlling the abundabce, diversity and distribution of ostracods in the study area. Geographically, the identified ostracod species are broadly distributed in the brackish lagoons of the Mediterranean region.

European eel (Anguilla anguilla) survival modeling based on a 22-year capture-mark-recapture survey of a Mediterranean subpopulation.

Since the 1980s, the European eel (Anguilla anguilla) has declined by over 90% in recruitment across its European and North African distribution area. This diadromous fish spawns at sea and migrates into continental waters, where it grows for three to more than 30 years, depending on habitat conditions and location. During their growth, different habitat use tactics can locally influence the life-history traits of eels, including their survival rates. Thus, the spatio-temporal dimension of this species is crucial for management. Based on a rare Mediterranean long-term survey of more than 20 years (2001-2022) in an artificial drainage canal connected to a vast brackish lagoon (the Vaccarès lagoon), we aimed to study the dynamics of one subpopulation's life-history traits. We used Bayesian multistate capture-mark-recapture (CMR) models to assess the temporal variability in survival and abundance at both seasonal and inter-annual scales, considering life-stage structure. High survival rates and low detection probabilities were found for the undifferentiated and female yellow stages. In contrast, female silver eels exhibited lower survival rates and higher capture probabilities. Estimating detection probabilities and survival rates enabled accurate assessment of relative abundance across different life stages and time periods. Our findings indicated a substantial decrease in the abundance of undifferentiated and female yellow eels in the early 2000s, whereas the abundance of female silver eels remained consistently low yet stable throughout the study period. Considering the life stage seemed essential to study the dynamics of the eel during its continental growing period. The present results will provide key elements to propose and implement suitable sustainable environmental management strategies for eel conservation.

Classification of vegetation of the Barents Sea coast at the mouth of the Indiga River

Classification of coastal vegetation from the standpoint of the ecological-phytocoenotic approach at the estuary of the Indiga River, flowing into the southeastern part of the Barents Sea, is presented. On the base of 131 relevés of coastal vegetation, 23 associations in 18 formations were identified. The coastal vegetation in different biotopes differs in the structure and features of the phytocoenoses floristic composition. Based on the signs of vegetation cover, mesorelief, and hydrological features of the shores, the following biotopes were identified: saline and brackish marshes, beaches and dunes, tidal flats at the mouths of estuaries, saline and brackish lagoon lakes on marshes. The marches with 14 described associations have the highest phytocoenotic diversity. A phytocoenotic diversity of the beaches is noticeably less, 4 associations are described there. The vegetation background of the beaches is formed by the communities of the Leymeta arenarii formation, the vegetation background of the salty marshes is formed by the communities of the Cariceta subspathaceae, Cariceta glareosae, and Cariceta mackenziei formations. In saline lakes, large areas are occupied by communities of the Hippurideta tetraphyllae formation, and the communities of the Triglochineta maritimi and Plantagineta subpolaris formations are rare, the northern limit of their range runs approximately along the Indiga mouth. The vegetation of brackish marshes is mainly formed by the Cariceta salinae herbosum, Junceta gerardii, and Cariceta rariflorae communities. At the mouth of Indiga estuary, large areas are occupied by communities of the Magnocariceta formation. In the mouth of the Indiga, a little north of the range limit, communities of Eleocharis uniglumis, a rare species in the Nenets Autonomous Okrug, are described for the first time at the rank of association Eleocharitetum uniglumis. The aquatic vegetation of desalinated lagoon lakes is represented by the Myriophylleta sibirici formation. The halophyte vegetation of the Indiga River estuary is compared with the estuaries of the rivers of the Kanin Peninsula and the Pechora Bay. The ordination of geobotanical relevés shows a greater similarity of the coastal vegetation of the Indiga estuary with the estuaries of the rivers flowing on the Kanin Peninsula of the White and Barents Seas basins and with the vegetation of the rivers estuaries of the Pechora Bay coast. The article has an electronic appendix (https://journals.rcsi.science/0006-8136/issue/archive).

Wetland Ramsar site in Tunisia (Soliman brackish lagoon): status, threats, and protection

Wetland Ramsar site in Tunisia (Soliman brackish lagoon): status, threats, and protection

Phytoplankton from a brackish lagoon in the central region of Veracruz, Mexico

Introduction: The brackish lagoons are ecosystems with great diversity and possibilities for human use. Therefore, the knowledge about phytoplankton needs to be improved to understand its real impact. Objective: To relate the Mandinga's Lagoon phytoplankton to the limnological conditions during the dry and wet seasons. Methods: The material was collected in three stations: Isla Conchas (ICO), Mandinga Chica (MCH) and Isla del Amor (IA) during the dry (March 2018) and wet (September 2017 and 2018) seasons. The limnological analysis included ten abiotic variables, and the phytoplankton was analyzed by the Utermöhl method. Data was analyzed with the Shannon index (H´) and Canonical Correspondence Analysis (CCA). Results: 136 species were identified: 68.4 % Heterokontophyta, 22.8 % Dinoflagellata, and 5.9 % Cyanobacteriota; with 40 euryhaline and 96 stenohaline. The most abundant species were: Bacillaria paxillifera, Chaetoceros compressus, Coscinodiscus rothii, and Chaetoceros atlanticus. The highest abundance was in ICO (dry) and the lowest in MCH (wet), with 307 x 103 and 76 x 103 cells/ml, respectively; the H´ ranged from 1.31 to 0.70 bits/ind. The CCA showed a relationship between salinity and dissolved oxygen with C. rothii and Ceratoneis closterium. The phosphates were associated with B. paxillifera, C. atlanticus, and Podosira stelligera. The nitrate, water temperature and pH were related to Tripos hircus, T. furca, Diploneis bombus, and Merismopedia elegans. In contrast, Skeletonema costatum, Cocconeis scutelum, and Nitzschia bicapitata did not correlate with the limnological variables. Conclusions: The Mandinga's Lagoon is a shallow, euryhaline and well-oxygenated ecosystem. The dominance of diatoms and dinoflagellates was evidenced by their ability to survive in different salinities and temperatures. It is recommended monitor phytoplankton, in particular Microcystis wesenbergii, B. quinquecornis, Pseudo-nitzschia cf. pungens, and P. cf. pseudodelicatissima as they are harmful algae.

Combining biotelemetry and genetics provides complementary insights relevant to the management and conservation of a freshwater predator (Esox lucius) living in brackish lagoons

To inform the management of wild fish populations, it is equally important to understand both the ecological connectivity of habitat patches, apparent at annual and seasonal scales, and the genetic connectivity, emerging at evolutionary scales across generations. Ecological connectivity indicates the potential for rapid recolonization upon local depletion, while genetic connectivity informs about the conservation needs related to the evolution of subpopulations and ecotypes in metapopulations. We combined acoustic biotelemetry and pooled-genome sequencing to study a northern pike (Esox lucius) population as a model of a freshwater piscivore that inhabits a network of shallow brackish lagoons in the southern Baltic Sea. We found limited ecological connectivity among genetically similar subpopulations of pike, suggesting a metapopulation structure characterized by discrete local subpopulations with infrequent migrations between them. Connectivity of different lagoons increased during spawning, suggesting directed spawning migrations to either freshwater rivers or low salinity patches in connected lake-like bays. Spawning site fidelity to either brackish or freshwater spawning sites was observed, further contributing to the reproductive isolation of certain subpopulations. The genetic population structure aligned with salinity gradients and geographical distance and was significant between pairs of rivers draining into the lagoon network, but it was unrelated to ecological connectivity. The results collectively suggest that local subpopulations may not rapidly replenish upon local depletion and that even weak connectivity among subpopulations was sufficient to maintain genetic homogeneity across lagoons with similar salinity levels. Effective management and conservation of species forming metapopulations, such as the coastal northern pike studied here, necessitate localized approaches that adapt fishing mortality to local abundance and promote access to specific habitats, especiallyrivers, during spawning to conserve the entire genetic biodiversity and foster resilience of the metapopulation.

Pyrolysis of Laminaria japonica with biochar production and its characteristics

In the present paper, biochar from the Laminaria japonica from brackish lagoons (Sea of Okhotsk, Sakhalin Island) was obtained by a stepwise pyrolysis at 500 °C. The properties of concerned biochar (elemental composition, specific surface area, particle size distribution) were studied. It was shown that the Laminaria japonica biochar has 0.2–18 μm particle sizes with a complex branched surface of high microporosity and a specific surface area of 38.6 m2g-1. Aforementioned biochar has the high content of carbon (~60 at%) and high content of oxygen (~34 at.%).

Using Aquatic Plant-Derived Biochars as Carbon Materials for the Negative Electrodes of Li-Ion Batteries

The current study focuses on the production of biochars derived from aquatic plants, specifically red seaweed Ahnfeltia and seagrass Zostera and Ruppia, found in brackish lagoons in the Sea of Okhotsk, Sakhalin Island. These biochars were obtained through a stepwise pyrolysis process conducted at temperatures of 500 and 700 °C. The characteristics of the biochars, including their elemental composition, specific surface area, and particle size distribution, were found to be influenced by both the type of biomass used and the pyrolysis temperature. The primary objective of this research was to investigate the potential of these biochars to be used as negative electrodes for lithium ion batteries. Among the various samples we tested, the biochar derived from the macroalgae Ahnfeltia tobuchiensis, produced at 700 °C, exhibited the highest carbon content (70 at%) and nitrogen content (>5 at%). The reversible capacity of this particular biochar was measured to be 391 mAh g−1 during the initial cycles and remained relatively stable at around 300 mAh g−1 after 25 cycles. These findings suggest that biochars derived from aquatic plants have the potential to be utilized as effective electrode materials in lithium ion batteries. The specific properties of the biochar, such as its elemental composition and surface area, play a significant role in determining its electrochemical performance. Further research and optimization of the pyrolysis conditions may lead to the development of biochar-based electrodes with improved capacity and cycling stability, thereby contributing to the advancement of sustainable and environmentally friendly energy storage systems.

Fish, Freshwater, and the Promise of Biodiversity History for Indonesian Studies

Freshwater fishes abound in Indonesia. They are everywhere in the archipelago—from rice fields and irrigation canals to brackish lagoons and highland rivers. They even populate the most unassuming bodies of water. Some species are found in the remotest of volcanic lakes while others call the blackest and most acidic peat swamps their home. Every island has its habitats and every habitat has its fishes, making Indonesia one of the world’s richest centers of ichthyofauna diversity. And yet, thinking with freshwater fishes—and their biodiversity history—has been largely absent from the field of Indonesian studies. A telling example of this biological blindspot can be found in the ways in which the Cornell Modern Indonesia Project (CMIP) has produced—and continues to constitute—Indonesia as an area of study and attachment. In CMIP’s Producing Indonesia: The State of the Field of Indonesian Studies, a landmark volume published in 2014, there were twenty-seven contributions that spanned the humanities and social sciences but none that looked at the role local scientists played in knowing the archipelago’s freshwater fauna or even broader the interplay between environment and society in shaping the study of modern Indonesia. In response, this essay centers the interplay between environment and society to show how it can open up new directions for future research and interdisciplinary collaboration. In doing so, and in particular, the paper argues that the story of fish and freshwater illustrates the promise of biodiversity history for the field of Indonesian studies in the age of environmental humanities and beyond.

Macroparasite Communities with Special Attention to Invasive Helminths in European Eels Anguilla anguilla from Freshwaters and Brackish Lagoons of a Mediterranean Island

An extensive survey of macroparasites in 320 European eel Anguilla anguilla (Linnaeus, 1758) was conducted in two brackish lagoons and eleven freshwater localities in the Mediterranean island of Corsica (France) between spring 2021 and winter 2021–2022. It resulted in the identification of nineteen parasites: two Monogea, four Digenea, one Copepoda, four Acanthocephala, three Cestoda, and five Nematoda, including the first geographical records, as Corsican freshwater sites were studied for the first time. The silvering stage was determined, and the eels were aged through otolithometry to compare parasite communities. Classic parasitology indices, a multivariate analysis, and an analysis of indicator values (IndVal) showed clear preferences towards the host’s habitat and salinity. Seasonal variations were shown for several parasites. A dataset from the same two coastal lagoons was used to study the changes in the parasite communities over the last decade, and this showed an increase in the prevalence and abundance of three invasive helminth species: the Monogenea Pseudodactylogyrus bini (Kikuchi, 1929), Pseudodactylogyrus anguillae (Yin and Sproston, 1948) Gusev, 1965 and the Nematoda Anguillicola crassus Kuwahara, Niimi, and Itagaki, 1974. These pathogenic parasites were found in all sampled localities, except for the two Monogenea in the polyhaline-to-euhaline Urbino lagoon. It is thus advised that future management measures take into account the environmental preferences of the most concerning parasites.

Holocene relative shore‐level changes and development of the Ģipka lagoon in the western Gulf of Riga

Holocene relative shore‐level changes and development of the Ģipka palaeolagoon in the western Gulf of Riga are reconstructed using multiproxy analyses by combining litho‐, biostratigraphical and chronological data with remote sensing and geophysical data. The results show the development of the Ģipka basin from the Ancylus Lake/Initial Litorina Sea coastal zone (before c. 9.1 cal. ka BP) to coastal fen (c. 9.1 to 8.4 cal. ka BP) and gradual development of the Litorina Sea lagoon (c. 8.4 to 4.8 cal. ka BP) and its transition to a freshwater coastal lake (c. 4.8 to 4.6 cal. ka BP), fen (c. 4.6 to 4.2 cal. ka BP), and river floodplain (since c. 4.2 cal. ka BP). The highest shorelines of the Ancylus Lake and Litorina Sea were mapped at an elevation of 12–11 and 9 m a.s.l., respectively. A new relative shore level (RSL) curve for the western Gulf of Riga was constructed based on RSL data from the Ģipka area and from nearby Ruhnu Island studied earlier. The reconstruction shows that the beginning of the last marine transgression in the western Gulf of Riga started at c. 8.4 cal. ka BP, and concurred with the 1.9 m RSL rise event recorded from the North Sea basin. Diatom analysis results indicate the existence of the Ģipka lagoon between c. 7.7 and 4.8 cal. ka BP, with the highest salinity c. 6.1 cal. ka BP. During the existence of the brackish lagoon, settlement sites of the Neolithic hunter–gatherer groups existed on the shores of the lagoon in the period c. 6.0 to 5.0 cal. ka BP.

At the edge of the desert: The evolution of the Holocene environment in Lake Rkiz, Senegal River valley

The analysis of faunal remains, pollen grains and other palynomorphs from a 4 m long core recovered at Lake Rkiz, Mauritania (16.911420 N, −15.172668 W, 0 m asl) documents the major phases of marine intrusion in the Senegal River system during the Holocene. Lake Rkiz was exposed to marine waters from 10 to 4 ka: a brackish lagoon developed at 10 ka, followed by a mangrove between 8.7 and 7 ka both in a calm environment. Rhizophora populations were never developed, however, either because they did not reach the core site at the northern extremity of the lake, or because they were restricted to the Senegal River bed. After 7 ka, the environment became increasingly unstable and the mangrove was replaced by a more clearly marine environment. During the last two millennia, a new, discrete phase of marine intrusion is recorded at Lake Rkiz. Contemporary to that already noted in the Ferlo River valley which feeds the Senegal River through Lake Guiers to the south, it also testifies to a positive oscillation of the sea level. The evolution of the regional vegetation of Lake Rkiz follows that of North tropical Africa with the expansion of a gallery forest of tropical humid affinity dominated by Celtis during the AHP. As elsewhere in the Sahara and Sahel, tropical plant types co-occurred with Saharan ones attesting to a mosaic-like landscape.

Temporal development of fish communities in brackish lagoons of the Baltic Sea considering the invasion of the non-indigenous round goby (Neogobius melanostomus)

Globally, successful invasions of non-indigenous species affect biodiversity and can push ecosystems beyond tipping points. This study aimed to identify factors that influence round goby (Neogobius melanostomus) abundances and distribution pathways along the eastern German coast of the Baltic Sea over a 12year period. The study further explored how the invasion of round goby affected the local fish and benthos assemblages in terms of species numbers and diversity. Round goby invaded various areas and estuaries and has established self-sustaining populations at low densities with further westward spread along the coast appearing to be ongoing. Salinity emerged as the most important predictor for overall round goby abundance, while the influence of macrozoobenthos abundance, vegetation cover, oxygen concentration, and water temperature were comparably low, indicating that round goby have a high tolerance in this regard. Negative impacts of round goby on benthic organisms and indigenous fish species, such as native gobiids, flounder (Platichthys flesus), ruffe (Gymnocephalus cernua), perch (Perca fluviatilis), pikeperch (Sander lucioperca), and cod (Gadus morhua), were not observed. This could be attributed to the comparably low densities of round goby at the sampling areas (0.0001 to 0.2 fish per m2) in combination with a potential surplus of benthic resources counteracting negative effects of predation and competition. The results suggest that its broad environmental adaptability could have enabled round goby to occupy a vacant ecological niche in coastal areas of the south-western Baltic Sea, which is generally considered to be species-poor due to strong environmental gradients. However, it cannot be excluded that certain effects of the round goby invasion may be too subtle to be detected. Thus, the results of our study underline the need for a specific long-term monitoring of the round goby invasion across taxa and habitats.

Synthesizing historic and current evidence for anadromy in a northern pike (Esox lucius L.) meta-population inhabiting brackish lagoons of the southern Baltic Sea, with implications for management

Pike (Esox lucius) populations across the central and southern Baltic Sea have undergone declines in recent decades. The underlying reasons are not fully understood but the loss of access to freshwater habitats in tributaries to brackish lagoons may be one important factor in some localities. Our objective was to synthesize evidence for the presence of historic and contemporary anadromy in pike from the brackish lagoon systems around the Fischland-Darß-Zingst peninsula and the islands of Hiddensee, Rügen and Usedom (Germany) by combining a review of grey literature, interviews with local citizens with knowledge tracing back to the mid-20th century, and field studies based on a range of methods, including telemetry, fyke netting and electrofishing of tributaries during the spawning seasons in the years 2020–2022. Genetic analyses were used to validate the existence of reproductively isolated subpopulations among pike migrating into different streams. The collective findings confirm the existence of freshwater spawning activity and genetic subpopulations across the entire study system in a multitude of tributaries, streams and ditches, but many populations appear to be small. The prevalence of anadromy across tributaries has likely suffered from water management activities in the 1970s and 1980s that blocked access to many rivers, ditches, streams and wetlands. Reduced access to freshwater streams through migration barriers associated with wetland management and agriculture could have fostered selection pressures to fully recruit in brackish environments, at the cost of declines and perhaps even local extinctions of once abundant anadromous subpopulations, most likely reducing stock resilience through the loss of genetic diversity and biocomplexity. Restoration of wetlands and access to freshwater spawning sites to recover subpopulations and anadromy can be recommended.

Distinct community assembly processes and habitat specialization driving the biogeographic patterns of abundant and rare bacterioplankton in a brackish coastal lagoon

The ecological diversity patterns and community assembly processes along spatio-temporal scales are least studied in the bacterioplankton sub-communities of brackish coastal lagoons. We examined the biogeographic patterns and relative influences of different assembly processes in structuring the abundant and rare bacterioplankton sub-communities of Chilika, the largest brackish water coastal lagoon of India. Rare taxa demonstrated significantly higher α- and β-diversity and biogeochemical functions than abundant taxa in the high-throughput 16S rRNA gene sequence dataset. The majority of the abundant taxa (91.4 %) were habitat generalists with a wider niche breadth (niche breadth index, B = 11.5), whereas most of the rare taxa (95.2 %) were habitat specialists with a narrow niche breadth (B = 8.9). Abundant taxa exhibited a stronger distance-decay relationship and higher spatial turnover rate than rare taxa. β-diversity partitioning revealed that the contribution of species turnover (72.2–97.8 %) was greater than nestedness (2.2–27.8 %) in causing the spatial variation in both abundant and rare taxa. Null model analyses revealed that the distribution of abundant taxa was mostly structured by stochastic processes (62.8 %), whereas deterministic processes (54.1 %) played a greater role in the rare taxa. However, the balance of these two processes varied across spatio-temporal scales in the lagoon. Salinity was the key deterministic factor controlling the variation of both abundant and rare taxa. Potential interaction networks showed a higher influence of negative interactions, indicating that species exclusion and top-down processes played a greater role in the community assembly. Notably, abundant taxa emerged as keystone taxa across spatio-temporal scales, suggesting their greater influences on other bacterial co-occurrences and network stability. Overall, this study provided detailed mechanistic insights into biogeographic patterns and underlying community assembly processes of the abundant and rare bacterioplankton over spatio-temporal scales in a brackish lagoon.

Co-designing management recommendations with stakeholders: A case study about northern pike (Esox lucius) in the southern Baltic Sea

Involving all interest groups, often called stakeholders, is increasingly recognized as a key part of sustainable natural resource management, promoting acceptability and compliance with management decisions. However, there is the difficulty of how to build trust, integrate diverse knowledge bases and account for varying objectives of different stakeholders. We present insights from a fisheries stakeholder process that used structured decision making and participatory modelling in a workshop series over the course of three years to develop management advice for a northern pike (Esox lucius) meta-population inhibiting brackish lagoons of the southern Baltic Sea in Germany. The stock is co-exploited by commercial and recreational fisheries who are in conflict over space and fish and vary in values. We formed and professionally facilitated a stakeholder group composed of 15 representatives of all main interest groups. The workshops generated a shared vision and seven mutually agreed management objectives that combined aspects of biological, ecological, economic, and social sustainability. To meet objectives, the group identified more than 40 management options, revolving around stock monitoring, control and surveillance, knowledge transfer, harvest regulations, habitat management, predator control and pike stocking. Participatory model building provided forecasts on the impacts of selected management options, allowing to transparently examine trade-offs based on quantitative criteria matched to objectives. The process overall led to stakeholder consensus about multiple management tools that the group recommended to government officials for future management reform. Challenges remain as to the communication of irreducible ecological and social uncertainties associated with quantitative predictions. In this context, cognitive maps about cause-and-effect relationships affecting pike were found useful to integrate knowledge and remind about uncertainties. Our case study shows that stakeholder-inclusive approaches using structured decision making and participatory modelling with professional facilitation are time- and planning-intensive, but can promote common system understanding and development of mutually agreed management advice also in heterogeneous stakeholder groups that are often in severe conflict with each other.

Length-based assessment of an exploited coastal pike (Esox lucius) stock (Rügen, southern Baltic Sea) underscores the crucial relevance of growth and natural mortality for assessment outcomes

Many capture fisheries are considered data-poor, including the northern pike (Esox lucius) fishery in brackish lagoons in the southern Baltic Sea of Germany. The objective of our work was to assess the exploitation status of this stock, which is perceived by stakeholders to be in decline. Size structure data collected via rod-and-reel-angling, fyke nets, and gill nets, and empirical estimates of growth, maturation, and fecundity from the lagoon stock were used to fit the Length-Based Spawning Potential Ratio (LB-SPR) model. Parameter uncertainty in von Bertalanffy growth estimates and natural mortality in the Baltic Sea pike stock was considered in sensitivity analyses. Assessment outcomes were sensitive to estimates of growth rate, particularly asymptotic length L∞, instantaneous natural mortality M, and gear selectivity. Under-aging of old fish in scale-based age estimates overestimated terminal length and generated negative bias in the estimated stock status. Despite the sensitivity of assessment outcomes to life-history parameter choice, the stock status for the Baltic Sea consistently indicated a fully exploited situation with SPRs robustly above 0.4 and current fishing mortality rates between 0.2 and 0.4 yr−1. This result agreed with previous assessments using catch-only models. Our work serves as a reminder, that when using length-based methods, unbiased growth, and natural mortality estimates are critical for robust assessment outcomes.