There is an increasing concern that anthropogenic noise could have a significant impact on the marine environment, but there is still insufficient data for most invertebrates. What do they perceive? We investigated this question in oysters Magallana gigas (Crassostrea gigas) using pure tone exposures, accelerometer fixed on the oyster shell and hydrophone in the water column. Groups of 16 oysters were exposed to quantifiable waterborne sinusoidal sounds in the range of 10 Hz to 20 kHz at various acoustic energies. The experiment was conducted in running seawater using an experimental flume equipped with suspended loudspeakers. The sensitivity of the oysters was measured by recording their valve movements by high-frequency noninvasive valvometry. The tests were 3 min tone exposures including a 70 sec fade-in period. Three endpoints were analysed: the ratio of responding individuals in the group, the resulting changes of valve opening amplitude and the response latency. At high enough acoustic energy, oysters transiently closed their valves in response to frequencies in the range of 10 to <1000 Hz, with maximum sensitivity from 10 to 200 Hz. The minimum acoustic energy required to elicit a response was 0.02 m∙s-2 at 122 dBrms re 1 μPa for frequencies ranging from 10 to 80 Hz. As a partial valve closure cannot be differentiated from a nociceptive response, it is very likely that oysters detect sounds at lower acoustic energy. The mechanism involved in sound detection and the ecological consequences are discussed.
Implementation of an ecosystem approach to fisheries management (EAFM) for forage fish requires methods to evaluate tradeoffs associated with competing management objectives that focus on supporting fishery yields or providing food for predators. We developed an Ecopath with Ecosim ecosystem model of the U.S. Northwest Atlantic continental shelf (NWACS) for the period 1982–2013 to inform an EAFM for Atlantic Menhaden Brevoortia tyrannus. The model (with 61 trophic groups and 8 fishing fleets) was parameterized and fitted to time series using data from stock assessments, surveys, and literature. Fifty-year simulations evaluated how Atlantic Menhaden fishing mortality rates (F) influenced different ecosystem indicators, including population biomasses, fishery yields, prey-to-predator ratios, and the proportion of trophic groups that were positively or negatively affected. We quantified tradeoffs associated with a range of alternative ecosystem-based reference points for Atlantic Menhaden F and biomass (B), including F for maximum sustainable yield (FMSY), 0.5FMSY, proxies for current single-species Freference points, 75% of virgin unfished biomass (B0), and 40%B0. Striped Bass Morone saxatilis were most sensitive to increases in Atlantic Menhaden fishing, largely due to their strong dietary reliance on this prey species, but other higher-trophic-level groups (birds, highly migratory species, sharks, and marine mammals) were also negatively impacted. Other commercially important predators of Atlantic Menhaden (e.g., Bluefish Pomatomus saltatrix and Weakfish Cynoscion regalis) had moderate to negligible responses at the highest levels of Atlantic Menhaden F. The alternative reference points considered resulted in (1) variable Atlantic Menhaden biomasses (40–75% of B0) and yields (54–100% of MSY), (2) up to a 60% decline in Striped Bass B and yield, (3) negative impacts on the B of ≤13% of modeled groups, and (4) positive impacts on the B of ≤6% of modeled groups. Simulations demonstrated the varied responses, potential winners and losers, and tradeoffs resulting from alternative management strategies for Atlantic Menhaden. These results and the NWACS model can help to advance an EAFM for Atlantic Menhaden and other fishes.
Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) is an endangered species that migrate through, and occupy the coastal waters of the mid-Atlantic Bight where they interact with anthropogenic activities. Measures to understand and avoid Atlantic sturgeon that take into consideration the dynamic nature of their habitat may reduce harmful interactions. In this study, we matched fisheries independent biotelemetry observations of Atlantic sturgeon with daily satellite observations to construct a time resolved spatial distribution model of Atlantic sturgeon. We determined that depth, day-of-year, sea surface temperature, and light absorption by seawater were the most important predictors of Atlantic sturgeon occurrence. Demographic factors, such as sex and river-of-origin were of secondary importance. We found strong spatial differences in spring and fall migration patterns, when anthropogenic interactions peak. Our cross-validated models correctly identified > 88% of biotelemetry observations in our study region. Our models also correctly identified ∼64% of bycatch observations throughout the year. However, during their migrations, when harmful interactions were highest, our models correctly identified ∼90% of fisheries dependent observations. We suggest that this model can be used for guidance to managers and stakeholders to reduce interactions with this highly imperiled species, thereby enhancing conservation and recovery efforts.
Fishery species that reside in no-take, marine reserves often show striking increases in size and abundance relative to harvested areas, with the potential for larval spillover to harvested populations. The benefits of spillover, however, may not be realized if the populations or habitats outside of reserves are too degraded. We quantified oyster population density and demographics such as recruitment, growth, mortality, and potential larval output as a function of two types of oyster management strategies in Pamlico Sound, North Carolina, USA: (1) natural reefs + harvested and (2) restored reefs + harvested. We compared these data to demographic data collected as a function of a third type of management strategy, (3) restored reefs + protected from harvest. Mean oyster recruitment was ~12 times higher in restored + harvested reefs than in natural + harvested reefs. Mean total oyster density was ~8- to 72-times higher in restored + protected reefs than in restored + harvested or natural + harvested reefs, respectively. Moreover, harvested reefs exhibited truncated size structure, and few or no individuals greater than legal size (75 mm), whereas protected reefs typically had a polymodal size structure, including many large individuals. We estimate that restored + protected reefs have ~4 to 700 times greater potential larval output m−2 than restored + harvested or natural + harvested reefs, respectively. After accounting for total sound-wide areal coverage of each reef type, total potential larval output from restored + protected reefs was ~6 times greater than that from natural + harvested and restored + harvested reefs. Marine reserves can potentially subsidize harvested populations via larval spillover, however, in the case of oyster reefs in Pamlico Sound, the relatively degraded conditions of natural reefs (e.g., low vertical relief, low shell volume per square meter) may not provide much in the way of suitable settlement substrate to realize the benefits of larval spillover from reserves. Restoration of oyster reefs, even with a thin veneer of substrate, may improve settlement substrate to increase the benefits of larval spillover from reserves.
Vulnerable marine ecosystems (VMEs) are ecosystems at risk from the effects of fishing or other kinds of disturbance, as determined by the vulnerability of their components (e.g., habitats, communities, or species). Habitat suitability modeling is being used increasingly to predict distribution patterns of VME indicator taxa in the deep sea, where data are particularly sparse, and the models are considered useful for marine ecosystem management. The Louisville Seamount Chain is located within the South Pacific Regional Fishery Management Organization (SPRFMO) Convention Area, and some seamounts are the subject of bottom trawling for orange roughy by the New Zealand fishery. The aim of the present study was to produce high-resolution habitat suitability maps for VME indicator taxa and VME habitat on these seamounts, in order to evaluate the feasibility of designing within-seamount spatial closures to protect VMEs. We used a multi-model habitat suitability mapping approach, based on bathymetric and backscatter data collected by multibeam echo sounder survey, and data collected by towed underwater camera for the stony coral and habitat-forming VME indicator species Solenosmilia variabilis, as well as two taxa indicative of stony coral habitat (Brisingida, Crinoidea). Model performance varied among the different model types used (Boosted Regression Tree, Random Forest, Generalized Additive Models), but abundance-based models consistently out-performed models based on presence-absence data. Uncertainty for ensemble models (combination of all models) was lower overall compared to the other models. Maps resulting from our models showed that suitable habitat for S. variabilis is distributed around the summit-slope break of seamounts, and along ridges that extend down the seamount flanks. Only the flat, soft sediment summits are predicted to be unsuitable habitat for this stony coral species. We translated a definition for stony coral-reef habitat into a S. variabilis abundance-based threshold in order to use our models to map this VME habitat. These maps showed that coral-reef occurred in small and isolated patches, and that most of the seabed on these seamounts is predicted to be unsuitable habitat for this VME. We discuss the implications of these results for spatial management closures on the Louisville Seamount Chain seamounts and the wider SPRFMO area, and future modeling improvements that could aid efforts to use habitat suitability maps for managing the impact of fishing on VMEs.
The Marine Strategy Framework Directive (MSFD) aims to achieve “Good Environmental Status” (GES) in EU marine waters by 2020. This initiative started its first phase of implementation in 2012, when each member state defined the GES and environmental targets in relation to 11 descriptors and related indicators for 2020. In 2013, the EU Commission launched the reformed Common Fisheries Policy (CFP), which aims to achieve biomass levels capable of producing maximum sustainable yield (MSY) for all commercial stocks exploited in EU waters by 2020, as well as contribute to the achievement of GES. These two pieces of legislation are aligned since according to Descriptor 3 (commercial fish and shellfish), the MSFD requires reaching a healthy stock status with fishing mortality (F) and spawning stock biomass (SSB) compatible with the respective MSY reference limits for all commercial species by 2020. We investigated whether the two policies are effectively aligned in the Mediterranean Sea, an ecosystem where the vast majority of stocks show unsustainable exploitation. For this purpose, we assessed and compared the number and typology of stocks considered by the member states when assessing GES in relation to data on stocks potentially available according to the EU Data Collection Framework (DCF) and the proportion of landings they represented. The number of stocks considered by the member states per assessment area was uneven, ranging between 7 and 43, while the share of landings corresponding to the selected stocks ranged from 23 to 95%. A lack of coherence between GES definitions among the member states was also revealed, and environmental targets were less ambitious than MSFD and CFP requirements. This could possibly reduce the likelihood of achieving fishery sustainability in the Mediterranean by 2020. These conditions limited the envisaged synergies between the two policies and are discussed in consideration of the recent Commission Decision on criteria and methodological standards for GES.
The Canary Islands, as many islands and coastal regions, are characterized by no conventional energy sources (but renewable resources, mainly wind and solar), by a high population density and land scarcity. Taking into account this context, it is crucial to determine the offshore wind energy potential as a first step for the energy planning. For this purpose, a methodology adapted to islands’ and coastal regions’ requirements has been developed. The methodology is based on GIS (Geographical Information Systems), and takes into account technical, economic and spatial constrains. Wind turbines (bottom-fixed or floating according to the bathymetry) are placed within the resulting suitable areas, quantifying also the energy production and its cost. The economic analysis includes the calculation of the LCOE (Levelized Cost Of Energy), including integration costs, and the resulting resource cost curves. The methodology has been applied to a practical case, the Canary Islands. Results show that the electricity produced by offshore wind farms exceeds the yearly electricity demand. Moreover, the offshore wind energy cost is lower than the current electricity cost. The analysis provides further useful indicators such as percentage of suitable areas, surface covered by wind turbines, array density of turbines and marginal offshore wind energy cost.
- Reef sharks are declining world-wide under ever-increasing fishing pressure, with potential consequences on ecosystem functioning. Marine protected areas (MPAs) are currently one of the management tools used to counteract the pervasive impacts of fishing. However, MPAs in which reef sharks are abundant tend to be located in remote and underexploited areas, preventing a fair assessment of management effectiveness beyond remoteness from human activities.
- Here, we determine the conditions under which MPAs can effectively protect sharks along a wide gradient of reef accessibility, from the vicinity of a regional capital towards remote areas, using 385 records from baited remote underwater video systems and 2,790 underwater visual censuses performed in areas open to fishing and inside 15 MPAs across New Caledonia (South-Western Pacific).
- We show that even one of the world's oldest (43 years), largest (172 km2) and most restrictive (no-entry) MPA (Merlet reserve) on coral reefs has between 17.3% and 45.3% fewer shark species and between 37.2% and 79.8% fewer shark abundance than remote areas in a context where sharks are not historically exploited.
- On coral reefs situated at less than 1 hr of travel time from humans, shark populations are so low in abundance (less than 0.05 individuals per 1,000 m2) that their functional roles are severely limited.
- Synthesis and applications. Remote areas are the last sanctuaries for reef sharks, providing a new baseline from which to evaluate human impacts on the species. However, there is no equivalent close to human activities even in large, old and strongly restrictive marine protected areas. As such sharks deserve strong protection efforts. The large, no-entry marine protected areas, close to humans, offer limited benefits for reef shark populations, but provide more realistic conservation targets for managers of human-dominated reefs. The exclusion of human activities on a sufficiently large area is key to protect reef shark populations. However, this strategy remains difficult to apply in many countries critically depending on reef resources for food security or livelihood.
The increasing amount of plastic littered into the sea may provide a new substratum for benthic organisms. These marine fouling communities on plastic have not received much scientific attention. We present, to our knowledge, the first comprehensive analysis of their macroscopic community composition, their primary production and the polymer degradation comparing conventional polyethylene (PE) and a biodegradable starch-based plastic blend in coastal benthic and pelagic habitats in the Mediterranean Sea. The biomass of the fouling layer increased significantly over time and all samples became heavy enough to sink to the seafloor. The fouling communities, consisting of 21 families, were distinct between habitats, but not between polymer types. Positive primary production was measured in the pelagic, but not in the benthic habitat, suggesting that large accumulations of floating plastic could pose a source of oxygen for local ecosystems, as well as a carbon sink. Contrary to PE, the biodegradable plastic showed a significant loss of tensile strength and disintegrated over time in both habitats. These results indicate that in the marine environment, biodegradable polymers may disintegrate at higher rates than conventional polymers. This should be considered for the development of new materials, environmental risk assessment and waste management strategies.
With the increasing demand for and reliance on plastics as an everyday item, and rapid increase in their production and subsequent indiscriminate disposal, the environmental implications of plastics are of growing concern. Given that plastic polymers are highly resistant to degradation, the influx of these persistent, complex materials is a risk to human and environmental health. Microplastics is described as a truly heterogeneous mixture of particles ranging in size form a few microns to several millimetres in diameter; including particles of various shapes from completely spherical to elongated fibres. Microplastic pollution has been reported on a global scale from the poles to the equator. The main route of concern is currently as a consequence of ingestion, which could lead to physical and toxicological effects on aquatic organisms.
To this end, in order to minimize the negative impacts posed by plastic pollution (microplastics), a plethora of strategies have been developed at various levels to reduce and manage the plastic wastes. The main objective of this paper is to review some of the published literatures on management measures of plastic wastes.
Estimates of fish biomass collated at the community level are reliable indicators of fish and ecosystem health. Data to calculate fish biomass is routinely collected using either underwater visual census (UVC) or stereo diver operated video (DOV), although the compatibility of UVC and DOV based estimates are yet to be assessed. Accordingly, we calculated and compared community level measures of coral reef fish biomass at Ningaloo reef (Western Australia) using both UVC and DOV. The UVC based biomass estimates were 788 kg/Ha, which was ∼50% greater than those from DOV (500 kg/Ha). Differences between the methods were primarily due to DOV measuring the length of only ∼40% of fish detected by video, preventing fish specific weight calculations for all fish encountered. When the size of unmeasured fish was assumed to be the median value of fish measured by DOV, revised DOV+ estimates of community biomass (778 kg/Ha) were similar to those from UVC. However, even when unmeasured fish were included in DOV calculations, biomass of some families (serranids) were still higher when using UVC. Conversely, DOV adjusted estimates of pomacentrid biomass were higher than those from UVC, due to DOV measuring fewer small bodied fish (<3 cm), thus having a larger median size for the high number of unmeasured pomacentrids compared to UVC. Our results suggest that community measures of fish biomass from DOV and UVC are broadly comparable once weights of unmeasured fish are incorporated into DOV estimates. This may increase the spatial and temporal scales at which fish biomass can be monitored, although compatibility of data will depend on the composition and size distribution of the fish assemblages.
In the North Atlantic, Area-Based Management Tools (ABMTs), including Marine Protected Areas (MPAs) and areas describing the inherent value of marine biodiversity, have been created in Areas Beyond National Jurisdiction (ABNJ). This deep-sea area (> 200 m) supports vitally important ecosystem services. Dealing with the multiple and increasing pressures placed on the deep sea requires adequate governance and management systems, and a thorough evaluation of cumulative impacts grounded on sound science. Notwithstanding the different objectives of various types of ABMTs, at an ocean scale it makes good sense to consider MPAs, Ecologically or Biologically Significant Areas (EBSAs) and other effective conservation measures, such as areas closed to protect Vulnerable Marine Ecosystems (VMEs), collectively to inform future systematic conservation planning. This paper focuses on climate change pressures likely to affect these areas and the need to evaluate implications for the state of biodiversity features for which they have been established. In a 20–50 year timeframe, virtually all North Atlantic deep-water and open ocean ABMTs will likely be affected. More precise and detailed oceanographic data are needed to determine possible refugia, and more research on adaptation and resilience in the deep sea is needed to predict ecosystem response times. Until such analyses can be made, a more precautionary approach is advocated, potentially setting aside more extensive areas and strictly limiting human uses and/or adopting high protection thresholds before any additional human use impacts are allowed.
Integrated management of multiple economic sectors is a central tenet of blue growth and socially optimal use of ocean-based natural resources, but the mechanisms of implementation remain poorly understood. In this review, we explore the challenges and opportunities of multi-sector management. We describe the roles of key existing sectors (fisheries, transportation, and offshore hydrocarbon) and emerging sectors (aquaculture, tourism, and seabed mining) and the likely synergistic and antagonistic inter-sector interactions. We then review methods to help characterize and quantify interactions and decision-support tools to help managers balance and optimize around interactions.
Ecosystem restoration aims to restore biodiversity and valuable functions that have been degraded or lost. The Coral Triangle is a hotspot for marine biodiversity held in its coral reefs, seagrass meadows, and mangrove forests, all of which are in global decline. These coastal ecosystems support valuable fisheries and endangered species, protect shorelines, and are significant carbon stores, functions that have been degraded by coastal development, destructive fishing practices, and climate change. Ecosystem restoration is required to mitigate these damages and losses, but its practice is in its infancy in the region. Here we demonstrate that species diversity can set the trajectory of restoration. In a seagrass restoration experiment in the heart of the Coral Triangle (Sulawesi, Indonesia), plant survival and coverage increased with the number of species transplanted. Our results highlight the positive role biodiversity can play in ecosystem restoration and call for revision of the common restoration practice of establishing a single target species, particularly in regions having high biodiversity. Coastal ecosystems affect human well-being in many important ways, and restoration will become ever more important as conservation efforts cannot keep up with their loss.
Situated to the south of New Zealand in the Southern Ocean are the New Zealand Subantarctic Islands, comprising the Auckland, Campbell, Antipodes, Snares and Bounty Islands. Sometimes referred to as the ‘Forgotten Islands’, these island groups are among the most remote and hostile within New Zealand waters. Yet, as they harbour some of the country’s most unique biodiversity and contain some of the world’s least modified landforms, they were recognized in 1998 with the designation of World Heritage Area status. It is not surprising therefore that the Islands have long appealed to visitors wishing to explore and understand the Islands’ rich natural and cultural environments. Typically, fare-paying tourists arrive by sea in small- to medium-sized expedition-style cruise vessels, although in recent years, the number of small vessels, such as yachts and sail boats, has increased. The most recent Conservation Management Strategy (2016) proposes developing and implementing a visitor monitoring programme to determine the effects of visitors on the natural and cultural environment, as well as on the visitor experience itself. However, there is only piecemeal data published on visitor numbers (especially since the mid-1990s) upon which to base visitor monitoring, and there is only limited evidence regarding the range of possible impacts visitors may have, including direct and indirect impact on wildlife, soils, and vegetation. In order to address this gap in knowledge, this case study draws on stakeholder interviews (n = 4), and a range of secondary sources (including visitor statistics from the Department of Conservation, tour operators and other published works) to provide an overview and update on visitation to the Islands, including site-specific data, an assessment of tourist impacts, and how impacts are currently monitored and managed.
Electronic tags are significantly improving our understanding of aquatic animal behavior and are emerging as key sources of information for conservation and management practices. Future aquatic integrative biology and ecology studies will increasingly rely on data from electronic tagging. Continued advances in tracking hardware and software are needed to provide the knowledge required by managers and policymakers to address the challenges posed by the world's changing aquatic ecosystems. We foresee multiplatform tracking systems for simultaneously monitoring the position, activity, and physiology of animals and the environment through which they are moving. Improved data collection will be accompanied by greater data accessibility and analytical tools for processing data, enabled by new infrastructure and cyberinfrastructure. To operationalize advances and facilitate integration into policy, there must be parallel developments in the accessibility of education and training, as well as solutions to key governance and legal issues.
As the environmental issues facing our planet change, scientific efforts need to inform the sustainable management of marine resources by adopting a socio-ecological systems approach. Taking the symposium on “Understanding marine socio-ecological systems: including the human dimension in Integrated Ecosystem Assessments (MSEAS)” as an opportunity we organized a workshop to foster the dialogue between early and advanced-career researchers and explore the conceptual and methodological challenges marine socio-ecological systems research faces. The discussions focused on: a) interdisciplinary research teams versus interdisciplinary scientists; b) idealism versus pragmatism on dealing with data and conceptual gaps; c) publishing interdisciplinary research. Another major discussion point was the speed at which governance regimes and institutional structures are changing and the role of researchers in keeping up with it. Irrespective of generation, training or nationality, all participants agreed on the need for multi-method approaches that encompass different social, political, ecological and institutional settings, account for complexity and communicate uncertainties. A shift is needed in the questions the marine socio-ecological scientific community addresses, which could happen by drawing on lessons learnt and experiences gained. These require in turn a change in education and training, accompanied by a change in research and educational infrastructures.
Anthropogenic impacts on coastal areas have led to an increased degradation of marine environments globally. Eelgrass ecosystems are particularly susceptible to human induced stressors as they are sensitive to low light conditions and usually grow in shallow protected areas where pressure from coastal development is high. The extensive decline in coverage of eelgrass along the Swedish Northwest coast since the 1980s has largely been attributed to the effects of coastal eutrophication and overfishing. However, the impact on eelgrass from small-scale coastal development (docks and marinas) has never been investigated in this area. The aim of this study was to assess the local and large-scale effect of shading by docks and marinas on eelgrass habitats along the Swedish NW coast and to investigate the decision process behind small-scale exploitation to identify problems with the current legislation, which allows for continued exploitation of eelgrass. Through field assessments of eelgrass around docks and analysis of available data on eelgrass and dock distribution along the coast, the present study demonstrates that shading from docks reduced eelgrass coverage with on average 42–64% under and adjacent to the docks, and that floating docks affected larger areas and caused a much stronger reduction in eelgrass coverage (up to 100% loss) compared to docks elevated on poles (up to 70% reduction in coverage). The total eelgrass area negatively affected by docks and marinas along the NW coast was estimated to approximately 480 ha, an area corresponding to over 7% of the present areal coverage of eelgrass in the region. The analysis of decisions for dock construction showed that eelgrass was generally not assessed or considered in the decision process and that 69–88% of the applications were approved also in areas where eelgrass was present. Furthermore, marine protected areas only marginally reduced the approval of applications in eelgrass habitats. The continued small-scale development along the Swedish NW coast constitutes a significant threat to the already decimated coverage of eelgrass along the coast and changes in the management practices are needed in order to achieve both national and international goals on environmental status.
In order to assess future sea level rise and its societal impacts, we need to study climate change pathways combined with different scenarios of socioeconomic development. Here, we present sea level rise (SLR) projections for the Shared Socioeconomic Pathway (SSP) storylines and different year-2100 radiative forcing targets (FTs). Future SLR is estimated with a comprehensive SLR emulator that accounts for Antarctic rapid discharge from hydrofracturing and ice cliff instability. Across all baseline scenario realizations (no dedicated climate mitigation), we find 2100 median SLR relative to 1986–2005 of 89 cm (likely range: 57–130 cm) for SSP1, 105 cm (73–150 cm) for SSP2, 105 cm (75–147 cm) for SSP3, 93 cm (63–133 cm) for SSP4, and 132 cm (95–189 cm) for SSP5. The 2100 sea level responses for combined SSP-FT scenarios are dominated by the mitigation targets and yield median estimates of 52 cm (34–75 cm) for FT 2.6 Wm−2, 62 cm (40–96 cm) for FT 3.4 Wm−2, 75 cm (47–113 cm) for FT 4.5 Wm−2, and 91 cm (61–132 cm) for FT 6.0 Wm−2. Average 2081–2100 annual SLR rates are 5 mm yr−1 and 19 mm yr−1 for FT 2.6 Wm−2 and the baseline scenarios, respectively. Our model setup allows linking scenario-specific emission and socioeconomic indicators to projected SLR. We find that 2100 median SSP SLR projections could be limited to around 50 cm if 2050 cumulative CO2 emissions since pre-industrial stay below 850 GtC, with a global coal phase-out nearly completed by that time. For SSP mitigation scenarios, a 2050 carbon price of 100 US$2005 tCO2 −1 would correspond to a median 2100 SLR of around 65 cm. Our results confirm that rapid and early emission reductions are essential for limiting 2100 SLR.
Microplastic is considered a potential threat to marine life as it is ingested by a wide variety of species. Most studies on microplastic ingestion are short-term investigations and little is currently known about how this potential threat has developed over the last decades where global plastic production has increased exponentially. Here we present the first long-term study on microplastic in the marine environment, covering three decades from 1987 to 2015, based on a unique sample set originally collected and conserved for food web studies. We investigated the microplastic concentration in plankton samples and in digestive tracts of two economically and ecologically important planktivorous forage fish species, Atlantic herring (Clupea harengus) and European sprat (Sprattus sprattus), in the Baltic Sea, an ecosystem which is under high anthropogenic pressure and has undergone considerable changes over the past decades. Surprisingly, neither the concentration of microplastic in the plankton samples nor in the digestive tracts changed significantly over the investigated time period. Average microplastic concentration in the plankton samples was 0.21 ± 0.15 particles m− 3. Of 814 fish examined, 20% contained plastic particles, of which 95% were characterized as microplastic (< 5 mm) and of these 93% were fibres. There were no significant differences in the plastic content between species, locations, or time of day the fish were caught. However, fish size and microplastic in the digestive tracts were positively correlated, and the fish contained more plastic during summer than during spring, which may be explained by increased food uptake with size and seasonal differences in feeding activity. This study highlights that even though microplastic has been present in the Baltic environment and the digestive tracts of fishes for decades, the levels have not changed in this period. This underscores the need for greater understanding of how plastic is cycled through marine ecosystems. The stability of plastic concentration and contamination over time observed here indicates that the type and level of microplastic pollution may be more closely correlated to specific human activities in a region than to global plastic production and utilization as such.