The Population Development of the Invasive Round Goby Neogobius melanostomus in Latvian Waters of the Baltic Sea

The invasive round goby (Neogobius melanostomus) was established in the coastal waters of the Baltic Sea in the early 1990s. The first observation of the species in Latvian waters was in 2004. In the intervening period, the population grew, the species became of significance for local fisheries, and it likely impacted the local ecosystem in the Baltic Sea. In this study, we characterize the spatial-temporal population development of round goby in Latvian coastal waters using data from three different scientific and fisheries-independent surveys. We also include data from commercial fisheries landings to describe the fisheries targeting the species. Our results suggest an exponential increase in population numbers of round goby in Latvian waters, peaking in 2018, followed by a sharp decline. This observation is also supported by data from commercial fisheries landings. We suggest that intensive commercial fishing had a considerable impact on the rapid decline of the species, but that the decline was potentially amplified through a wider scale decline, as observed in many areas of the Baltic Sea. The results of this study contribute to the knowledge base on the species and how fisheries can aid in limiting the development of invasive fish populations. Based on the results of the study, we also provide recommendations for better future monitoring of the species in the coastal waters of the Baltic Sea

Temporal development of coastal ecosystems in the Baltic Sea over the past two decades

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Hidden variables in a Dynamic Bayesian Network identify ecosystem level change

EU; The Academy of Finland; Projektträger Jülich (PtJ); Germany; The State Education Development Agency of Latvia; The National Centre for Research and Development, Poland; The Swedish Research Council Formas; BalticEye Stockholm University; foundation BalticSea202

Baltic herring prey selectively on older copepodites of Eurytemora affinis and Limnocalanus macrurus in the Gulf of Riga

Zooplankton availability is a major factor affecting herring body condition that in turn describes its well-being. As herring feeding is known to be selective, it is relevant to access its preferences upon zooplankton species and particular copepod developmental stages to forecast possible intraspecific competition for resources in the species scarce environment of the Gulf of Riga where herring stock size due to successful recruitment has almost doubled since 1989. This study tries to answer whether the small-sized plankters dominated zooplankton community permits herring to be a selective eater. Also how herring body condition has changed in connection to environment driven zooplankton community changes. The time series of zooplankton abundance and herring condition from 1995–2012 were studied; and a detailed study of herring diet was performed monthly by stomach content analysis during the main feeding season in 2011 and 2012. We found that herring selectively prey on Limnocalanus macrurus and older copepodite stages of Eurytemora affinis, and moreover these were species of whose selected copepodite stages explained most of variation in herring condition factor. The found relationship between herring feeding selectivity and long-term variation of herring condition allows applying spring zooplankton abundance of E. affinis and L. macrurus to estimate favourable feeding conditions for herring, and could also require the revision of currently used model for herring recruitment estimations, where only biomass of E. affinis is taken into account. In recent years, the high condition of herring can be associated with a considerable increase of lipid-rich copepod species L. macrurus

Multidecadal dynamics of the Arctic copepod <i>Limnocalanus macrurus</i> in relation to environmental variability in the Baltic Sea

The Arctic Limnocalanus macrurus is a prominent representative of large copepods which performs several essential functions in freshwater and marine ecosystems. Being a cold stenotherm species, its distribution is primarily confined to deeper water layers. Based on the long-term observations from one of the largest spatially confined natural populations of this species in the Baltic Sea, we detected profound long-term variability of L. macrurus during 1958–2016: high abundances before the 1980s, then nearly disappearance in the 1990s and recovery in the 2000s. The main environmental parameters explaining the interannual variability of L. macrurus in spring were herring spawning stock biomass in preceding year, winter severity, and bottom water temperature in preceding summer. The effect of winter severity and water temperature was also non-linear. The sliding window correlation analysis pointed to a non-stationary relationship between the abundance of L. macrurus and the key variables. Given the observed pronounced seasonality in the population structure of L. macrurus (young stages dominated in the beginning of the year and only adults were left in the population in summer and autumn) we identified the dynamics of key environmental variables to understand this species under different ecosystem configurations and different combinations of drivers of change

The Population Development of the Invasive Round Goby <i>Neogobius melanostomus</i> in Latvian Waters of the Baltic Sea

The invasive round goby (Neogobius melanostomus) was established in the coastal waters of the Baltic Sea in the early 1990s. The first observation of the species in Latvian waters was in 2004. In the intervening period, the population grew, the species became of significance for local fisheries, and it likely impacted the local ecosystem in the Baltic Sea. In this study, we characterize the spatial–temporal population development of round goby in Latvian coastal waters using data from three different scientific and fisheries-independent surveys. We also include data from commercial fisheries landings to describe the fisheries targeting the species. Our results suggest an exponential increase in population numbers of round goby in Latvian waters, peaking in 2018, followed by a sharp decline. This observation is also supported by data from commercial fisheries landings. We suggest that intensive commercial fishing had a considerable impact on the rapid decline of the species, but that the decline was potentially amplified through a wider scale decline, as observed in many areas of the Baltic Sea. The results of this study contribute to the knowledge base on the species and how fisheries can aid in limiting the development of invasive fish populations. Based on the results of the study, we also provide recommendations for better future monitoring of the species in the coastal waters of the Baltic Sea

Application of the marine ecosystem services approach in the development of the maritime spatial plan of Latvia

The Maritime Spatial Plan for Internal Waters, Territorial Waters and Economic Exclusive Zone of the Republic of Latvia is a long-term spatial planning document, which defines the permitted uses of the sea and conditions for development. Work on maritime spatial planning (MSP) in Latvia was a novel process from different aspects including incorporation of the concept of ecosystem services (ES) into MSP. In the course of the MSP process, marine ES were mapped and assessed, and impacts of proposed spatial solutions for the use of the sea were assessed. The scope of mapping and assessment of ES was limited by data availability and expert knowledge on marine ecosystems. MSP in Latvia was an open and transparent process with an active involvement of different stakeholder groups. Marine ES assessment results were visualized and used during the public consultations to highlight the marine areas providing the most significant social benefits as well as to facilitate debate about potential impacts arising from proposed uses of the sea. The marine ES approach, in a spatially explicit manner, provided stakeholders and policymakers with a strategic framework to address a complex social–ecological system.EDITED BY Joao Rodrigue

Spatio‐temporal dynamics of multi‐trophic communities reveal ecosystem‐wide functional reorganization

Large‐scale alterations in marine ecosystems as a response to environmental and anthropogenic pressures have been documented worldwide. Yet, these are primarily investigated by assessing abundance fluctuations of a few dominant species, which inadequately reflect ecosystem‐wide changes. In addition, it is increasingly recognized that it is not species identity per se, but their traits that determine environmental responses, biological interactions and ecosystem functioning. In this study, we investigated long‐term, spatio‐temporal variability in trait composition across multiple organism groups to assess whether functional changes occur in a similar way across trophic levels and whether shifts in trait composition link to environmental change. We combined extensive trait datasets with long‐term surveys (30–40 yr) of four organism groups (phytoplankton, zooplankton, benthic invertebrates and fish) in three environmentally distinct areas of a large marine ecosystem. We found similar temporal trajectories in the community weighted mean trait time‐series of the different trophic groups, revealing ecosystem‐wide functional changes. The traits involved and their dynamics differed between areas, concurrent with climate‐driven changes in temperature and salinity, as well as more local dynamics in nutrients and oxygen. This finding highlights the importance of considering both global climate, as well as local external drivers when studying ecosystem changes. Using a multi‐trophic trait‐based approach, our study demonstrates the importance of integrating community functional dynamics across multiple trophic levels to capture ecosystem‐wide responses which could, ultimately, help moving towards a holistic understanding, assessment and management of marine ecosystems