In oceans and seas worldwide, an increasing number of end-of-life anthropogenic offshore structures (e.g., platforms, pipelines, manifolds, windfarms, etc.) are facing full or partial removal. As part of the decommissioning process, studies on potential importance of subsea infrastructure to marine megafauna (defined as: cetaceans, pinnipeds, sirenians, large fish – such as sharks, rays, billfishes, and tuna, as well as marine reptiles, and seabirds) are lacking. Dedicated scientific Remotely Operated Vehicle (ROV) surveys around offshore installations are rare, but there is a wealth of archived industrial data and noteworthy species sightings posted publicly on various social media platforms. This study used routine, incidentally collected ROV (n = 73) and commercial diver (n = 9) video recordings spanning 1998–2019 globally. Data were gathered directly from industrial partners (n = 36) and the public domain (YouTube; n = 46) to provide an account of marine megafauna presence and potential feeding behavior in the near-visible vicinity of subsea anthropogenic structures. A total of 79 video clips and 3 still images of marine megafauna near offshore structures were examined, resulting in 67 individual sightings and 16 sub-sightings (in which an individual was recorded within the same day). At least 178 individuals were identified to a minimum of 17 species of marine megafauna, amounting to a total (combined) sighting duration of 01:09:35 (hh:mm:ss). Results demonstrated proximate presence of marine megafauna (many of which are threatened species) to anthropogenic structures, with most animals displaying foraging or interaction behaviors with the structures. Observations included the deepest (2,779 m) confirmed record of a sleeper shark (Somniosus spp.) and the first confirmed visual evidence of seals following pipelines. These ROV observations demonstrate a latent source of easily accessible information that can expand understanding of marine megafauna interactions with offshore anthropogenic infrastructure. Consequently, other workers in this field should be encouraged to re-analyze archived datasets, commence further collaborative research projects with industrial partners, and/or expand Internet search terms to additional species assemblages, in a bid to quantitatively elucidate relationships between offshore infrastructure and marine species.
This study presents non-song vocalizations of humpback whales (Megaptera novaeangliae) from two migratory areas off the Western Australian coast: Geographe Bay and Port Hedland. A total of 220 sounds were identified as non-song sounds in 193 h of recordings reviewed. Of those, 68 were measured and qualitatively classified into 17 groups using their spectral features. One group (HW-02) had a high level of variation in terms of spectral slope. However, further classification using statistical classification methods was not possible because of the small sample size. Non-song sound frequencies varied from 9 Hz to 6 kHz, with the majority of sounds under 200 Hz. The duration of non-song sounds varied between 0.09 and 3.59 s. Overall, the use of spectral features allowed general classification of humpback whale sounds in a low sample size scenario that was not conducive to using quantitative methods. However, for highly variable groups, quantitative statistical classification methods (e.g., random forests) are needed to improve classification accuracy. The identification and accurate classification of a species’ acoustic repertoire is key to effectively monitor population status using acoustic techniques and to better understand the vocal behavior of the species. The results of this study improve the monitoring of humpback whales by standardizing the classification of sounds and including them in the species’ repertoire. The inclusion of non-song sounds in passive acoustic monitoring of humpback whales will add females and calves to the detection counts of otherwise only singing males.
An array of anthropogenic pressures is affecting tropical ecosystems, posing major conservation challenges for scientists, stakeholders and populations. Illegal cyanide fishing is one of the major threats to Indo-Pacific coral reefs, targeting a multitude of colorful species for the marine aquarium trade as well as large-sized groupers and wrasses for the food fish trade. Ultimately, the continued use of this destructive practice as oceans warm may overload tropical ecosystems and result in irreversible ecological damage. Here we show that the impact of cyanide poisoning in an ornamental tropical marine fish is magnified under increased temperatures. A sole pulse exposure of 60 s to 50 mg L–1 of cyanide under current temperature (26°C) caused substantial mortality (50–100%) in eight species of Pomacentridae. The clownfish Amphiprion ocellaris was the most resistant, especially medium-sized fish [average total length and weight of 38 mm and 1.12 g; LC50 (95% CI) = 50.00 (46.76 − 53.24) mg L–1] that showed shorter recovery times and higher survival rates (%) when compared to small-sized ones [average total length and weight of 25 mm and 0.30 g; LC50 (95% CI) = 28.45 (20.17 − 36.72) mg L–1]. However, when the most resistant size-class was concomitantly exposed to a sub-lethal dosage of cyanide (25 mg L–1 instead of 50 mg L–1) and ocean warming scenarios for 2100 (+3°C and heat wave +6°C), survival rates (%) decreased to 60 and 20%, respectively, and recovery times increased in the worst case scenario. Mortality outbreaks, as well as vulnerability to predation, will likely expand in fish inhabiting coral reefs exposed to cyanide fishing unless stronger conservation measures are taken in tropical reefs to limit this destructive practice now and in the oceans of tomorrow.
Cold-water corals are habitat-forming species that are also classified as indicators of vulnerable marine ecosystems (VMEs) due to the threat of various anthropogenic impacts, e.g., fisheries and oil/mineral exploration. To best protect VMEs, knowledge of their habitat requirements and distribution is essential. However, comprehensive sampling of the deep sea is difficult due to access and cost constraints, so species distribution modeling (SDM) is often used to predict overall distributions and ecological preferences of species based on limited data. We used Maximum Entropy (Maxent) modeling to predict the probability of presence of the reef-building scleractinian Lophelia pertusa and the octocorals Paragorgia arborea and Primnoa resedaeformis using a total of 2149 coral presence points and 15 environmental predictor variables. The environmental variables used in the analysis were processed to 176 m resolution and included bathymetry, depth, geomorphometric characteristics [slope, aspect, and bathymetric position index (BPI)], oceanography (temperature, salinity, current directions, and speed), surface chlorophyll a concentration, sediment type, and marine landscape type. Comparing presence points with environmental data showed that the temperature and depth range for Lophelia was narrower compared to the gorgonians, and it occurred in shallower, warmer water. Observations showed that Lophelia had a broad, bimodal response to Broad BPI, while the predicted model indicated a more narrow response. Paragorgia tolerated the greatest range of sloping according to the model. All three species were observed with a bimodal pattern along a wide range of mean current speed, while the models indicated a high response to faster current speed. Jackknife tests showed that sediment type was an important predictor for gorgonian corals, while BPI and minimum temperature were more important for Lophelia. The spatial precision of the models could be further increased by applying environmental layers with a higher and uniform spatial resolution. The predicted distribution of corals and their relation to environmental variables provides an important background for prioritizing areas for detailed mapping surveys and will aid in the conservation efforts for these VMEs in Norwegian waters and beyond.
Global habitat deterioration of marine ecosystems has led to a need for active interventions to halt or reverse the loss of ecological function. Restoration has historically been a key tool to reverse habitat loss and restore functions, but the extent to which this will be sufficient under future climates is uncertain. Emerging genetic technologies now provide the ability for restoration to proactively match adaptability of target species to predicted future environmental conditions, which opens up the possibility of boosting resistance to future stress in degraded and threatened habitats. As such, the choice of whether to restore to historical baselines or anticipate the future remains a key decision that will influence restoration success in the face of environmental and climate change. Here, we present an overview of the different motives for restoration – to recover or revive lost or degraded habitats to extant or historical states, or to reinforce or redefine for future conditions. We focus on the genetic and adaptive choices that underpin each option and subsequent consequences for restoration success. These options span a range of possible trajectories, technological advances and societal acceptability, and represent a framework for progressing restoration of marine habitat forming species into the future.
As a hotspot of species diversity and fishing pressure, Indonesia is a global priority for the conservation of sharks, rays and their cartilaginous relatives (herein “sharks”). The high value marine tourism industry in Indonesia can create economic incentives for protecting and sustainably managing marine ecosystems and species, including sharks. This study estimates the economic value of shark and ray tourism in Indonesia and explores tourist preferences and local community perceptions of the tourism industry to understand the current and potential future role of this industry in shark and ray conservation. We identified 24 shark tourism hotspots across 14 provinces, with primary data collected from 365 tourists and 84 local community members over six case study sites. We use Purchasing Power Parity (PPP) and travel efforts to extrapolate expenditures to other tourism sites. We estimate that at least 188,931 dedicated or partially dedicated shark tourists visit Indonesia each year. The median annual expenditures of these shark tourists is estimated at USD 22 million (for 2017), accounting for at least 7% of the total USD 1 billion marine tourism revenue in Indonesia in 2017 and 1.45× the value of annual shark exports in the country (inflation-adjusted to 2017 values). If sharks were absent from the surveyed sites, Indonesia’s tourism industry could lose ∼25% of these dive tourist expenditures. Despite this considerable value, our study indicates a mismatch between the absolute economic value of shark and ray tourism and its role in providing an incentive for conservation. Results from interviews with local communities in or near shark and ray tourism sites indicate that shark fishers are not well placed to receive direct economic benefits from shark and ray tourism. Since overfishing is the primary threat to shark populations, failure to engage with and appropriately incentivize these stakeholders will be detrimental to the success of Indonesia’s shark conservation efforts. If shark populations continue to decline due to insufficient conservation actions, the tourism industry could suffer economic losses from shark and ray tourism of more than USD 121 million per annum by 2027, as well as detrimental impacts on species, marine ecosystems, fisheries and people.
This paper proposes institutional innovations to advance a transparent monitoring system for the environmental impacts from mineral development on the deep seabed beyond national jurisdictions managed by the International Seabed Authority (ISA). Using a literature review, ISA’s regulations, and five cases of other environmental monitoring of the deep sea, this study observes that ISA’s environmental monitoring system for exploration and exploitation currently lacks critical elements to facilitate transparency. Insufficient compliance reporting and review systems, as well as limited access to information by stakeholders, lower the system’s effectiveness. ISA has not developed adequate mechanisms to support effective multinational collaboration in monitoring. The ISA monitoring system without these characteristics may not be sufficiently adaptive to allow detection and management of environmental changes in the deep seabed. This study suggests 15 institutional recommendations to ISA in order to enhance transparency for monitoring nodule mining in the Central Pacific deep seabed. Principal recommendations include establishing compliance review committees independent of ISA governing bodies, implementing collective monitoring and reporting by adjacent contractors, and reconsidering the centralized decision-making authority by the Secretary-General to improve confidentiality.
Seagrass beds provide nursery habitats for marine species. Seagrass leaves, in particular, are used as spawning grounds and as a food source for fish and invertebrates, but direct evidence of spawning in seagrass leaves is rare. It is also very challenging to identify eggs through morphological analysis, since the eggs of many marine species appear similar. To accurately identify the eggs on the leaves of the dominant seagrass species in the South China Sea, and evaluate seasonal contribution of seagrass leaves as a food source, DNA barcoding and stable isotope technique were conducted. Interestingly, Monetaria annulus was found to spawn on the leaf sheath of Thalassia hemprichii in Li’an gang, Hainan Island. This choice of oviposition site might increase embryo survival compared to the other parts of the seagrass leaves. Meanwhile, the eggs of Stethojulis trilineata were deposited on the entire leaf of Halophila ovalis in Liusha Bay, Guangdong Province. The small fingernail-shaped leaves of H. ovalis might be beneficial for S. trilineata to lay eggs as they are closer to the sediment surface than other seagrass leaves. Based on the stable carbon and nitrogen isotope analyses, the primary food source of M. annulus in summer and in winter were particulate organic matter and seagrass, respectively. The results suggest that seagrass leaves are not only important for fish and invertebrates as a spawning site, but also as a food source. The findings of the present study may support the urgent requirement of the conservation of seagrass beds for sustaining the productivity of marine fisheries.
There is a reluctance to incorporate Fishers’ Ecological Knowledge (FEK) into the evidence base used to underpin marine management decisions. FEK has proved to be useful as an alternative reference of biological changes in data-poor scenarios. Yet, recreational fisher knowledge has rarely been included in scientific studies despite being a source of FEK. Here, the use of recreational FEK to assess the conservation status of marine ecosystems in Galicia (NW Spain) was evaluated. Galicia has a highly complex marine socioecological system that includes both a large global commercial fleet and a powerful recreational sector, alongside other important stakeholders (e.g., tourism, aquaculture). Anglers and spear fishers were asked to provide their perceptions of the conservation status of fish stocks and the impacts on marine ecosystems. Face-to-face interviews were transcribed into text and analyzed using text mining tools. Key concepts were used to quantify fishers’ perceptions of changes in their target fish stocks and quantify the main impacts on marine ecosystems. Overfishing and habitat loss, followed by reduction in biodiversity, pollution, and warming temperatures were considered to be the main drivers of the poor status of cephalopods and finfish stocks. Perceived temporal declines in fish stocks were consistent with available biological data, highlighting the potential for recreational FEK to be used to assess long-term ecological changes. It was important to seek opinions from different users, including fishers from traditional commercial and recreational fisheries, as these groups had good knowledge of the impacts on natural and cultural community heritage. The poor status of ballan wrasse (Labrus bergylta) and kelp beds was identified, which was of concern due to it being a key species in coastal ecosystems. Use of FEK is a good approach to develop knowledge of these systems, but broader monitoring programs are needed to protect the future of these ecosystems.
Marine ecosystems are being continually impacted by human activities and, among these, fisheries have been one of the most damaging. Fisheries modify the structure and functioning of food-webs through biomass removal and physical damage to the seabed, leading to loss of biodiversity and ecosystem services provided by the oceans. The ecosystem-based approach to fisheries is considered the most efficient way to achieve the goal of sustainable use of marine resources while allowing for biodiversity protection. The Strait of Sicily is a biologically important area of the central Mediterranean Sea characterized by high habitat complexity and rich biodiversity, however, due to the multispecific nature of local fisheries and weak implementation of the adopted management plans, this region is particularly vulnerable. We used fishery independent time series (1994–2016) to identify the main demersal assemblages and map their spatial distribution. The pressure of fishing effort on each of these defined assemblages was then quantified in order to evaluate the impact of bottom trawling on demersal communities. Our results showed four spatially distinct and temporally stable assemblages of the Strait of Sicily. These have a clear spatial distribution, different species composition and biodiversity values and are driven primarily by environmental gradients (i.e., mainly depth and, to a lesser extent, surface salinity). The demersal assemblages were subsequently grouped in homogeneous areas characterized by specific communities of commercial and non-commercial species and response to trawling impacts. These areas are proposed as Spatial Managements Units to evaluate and manage demersal mixed fisheries, while also considering biodiversity conservation in the central Mediterranean Sea.
The direct and indirect impact of fish farms, shellfish aquaculture, and extensive forms of aquaculture such as seeding of juvenile sea urchins, on macrophytes (seaweeds and seagrasses), is reviewed in Mediterranean benthic ecosystems. Fish farms constitute a source of organic matter and nutrients (food and fecal pellets) that causes the extirpation of Posidonia oceanica seagrass meadows beneath and near to farm facilities. In addition to direct effects, the nitrogen enrichment of macrophytes tissues increases the grazing pressure by herbivorous fishes and sea urchins. In some cases, the impact can continue to increase several years after the cessation of farming activities. Natural restoration of extirpated seagrass meadows is generally unlikely at the human time scale. Shellfish aquaculture is the cause of the main flow of introduced macrophytes in the Mediterranean; the main vector is the importation of oyster spat from Japan and Korea. North-eastern Pacific seaweeds are now the dominant biotic component of some Mediterranean lagoons (e.g., Thau, Mar Piccolo, and Venice lagoons). In addition to direct effects, mussel aquaculture can constitute a source of larvae that flow with currents, the adults of which can overwhelm seaweed forests (e.g., Carpodesmia mediterranea). Shellfish aquaculture is also a source of fecal pellets, resulting in changes in bottom macrophytes, and a vector of diseases of metazoans, the extirpation of which may change the functioning of recipient macrophyte ecosystems. The edible sea urchin Paracentrotus lividus is sometimes erroneously considered as in decline due to over-harvesting. However, its abundance in the second half of the 20th century was probably a consequence of human impact (overfishing of its predatory fish, organic pollution. This man-induced proliferation resulted in the extirpation of seaweed forests (e.g., Carpodesmia spp., Treptacantha spp. – formerly Cystoseira spp. – Sargassum spp.; many species are endemic), which play a key role in Mediterranean coastal ecosystems. Therefore, the attempts to restore sea urchin abundance, via seeding of juveniles from hatcheries, has further artificialized the habitats rather than contributing to the restoration of natural ecosystems. Good practices guidelines are proposed aimed at minimizing the impact of aquaculture on macrophytes.
Significant population declines in Acropora cervicornis and A. palmata began in the 1970s and now exceed over 90%. The losses were caused by a combination of coral disease and bleaching, with possible contributions from other stressors, including pollution and predation. Reproduction in the wild by fragment regeneration and sexual recruitment is inadequate to offset population declines. Starting in 2007, the Coral Restoration Foundation™ evaluated the feasibility of outplanting A. cervicornis colonies to reefs in the Florida Keys to restore populations at sites where the species was previously abundant. Reported here are the results of 20 coral outplanting projects with each project defined as a cohort of colonies outplanted at the same time and location. Photogrammetric analysis and in situ monitoring (2007 to 2015) measured survivorship, growth, and condition of 2419 colonies. Survivorship was initially high but generally decreased after two years. Survivorship among projects based on colony counts ranged from 4% to 89% for seven cohorts monitored at least five years. Weibull survival models were used to estimate survivorship beyond the duration of the projects and ranged from approximately 0% to over 35% after five years and 0% to 10% after seven years. Growth rate averaged 10 cm/year during the first two years then plateaued in subsequent years. After four years, approximately one-third of surviving colonies were ≥ 50 cm in maximum diameter. Projects used three to sixteen different genotypes and significant differences did not occur in survivorship, condition, or growth. Restoration times for three reefs were calculated based on NOAA Recovery Plan (NRP) metrics (colony abundance and size) and the findings from projects reported here. Results support NRP conclusions that reducing stressors is required before significant population growth and recovery will occur. Until then, outplanting protects against local extinction and helps to maintain genetic diversity in the wild.
Ocean acidification (OA) is a global problem with profoundly negative environmental, social and economic consequences. From a governance perspective, there is a need to ensure a coordinated effort to directly address it. This study reviews 90 legislative documents from 17 countries from the European Economic Area (EEA) and the UK that primarily border the sea. The primary finding from this study is that the European national policies and legislation addressing OA is at best uncoordinated. Although OA is acknowledged at the higher levels of governance, its status as an environmental challenge is greatly diluted at the European Union Member State level. As a notable exception within the EEA, Norway seems to have a proactive approach towards legislative frameworks and research aimed towards further understanding OA. On the other hand, there was a complete lack of, or inadequate reporting in the Marine Strategy Framework Directive by the majority of the EU Member States, with the exception of Italy and the Netherlands. We argue that the problems associated with OA and the solutions needed to address it are unique and cannot be bundled together with traditional climate change responses and measures. Therefore, European OA-related policy and legislation must reflect this and tailor their actions to mitigate OA to safeguard marine ecosystems and societies. A stronger and more coordinated approach is needed to build environmental, economic and social resilience of the observed and anticipated changes to the coastal marine systems.
Their availability, low cost, applicability in virtually any industrial sector and any household have not only resulted in plastics becoming an everywhere used material, but owing to its specific structure resulting in an issue pertaining to environmental pollution. There are 13 monitoring stations within research area to include recreational and industrial areas differing in hydrodynamic behaviour. The research geography bearing in mind the Russia's scale is not vast so far, yet it is being expanded yearly. Research was done at seven Vladivostok beaches, two beaches at the head of the Amur Bay and three beaches of the Posyet Bay. All the samples taken at the western side of the bay at the depths of 2-6m contained microplastic particles. Quality analysis of all the samples collected was carried out using mass-spectrometric method and that of infrared microscopy. It has been found that the chemical constitution of the samples studied is represented mostly by polyethene, polypropylene, particles of polystyrene and polyvinylchloride. Coastal samples frequently contain cellulose. A certain amount of methylaniline, formaldehydes, and monocarbozides was detected. All the said gives ground for ascertaining harmful influence of microplastics not only on sea water quality but on the state of marine biota.
The Magellan Strait is a narrow passage connecting the Pacific and Atlantic oceans in South America. An average of 2023 ships per year transit this corridor with 80% representing the international fleet. The southwestern part of the Strait in Chile is an important summer feeding area for humpback whales. Considering the risk to whales of feeding among dense ship traffic, the movements of 25 satellite-tagged whales relative to vessel density were analyzed, to provide policy recommendations for protecting the species from vessel collisions. A total of 3694 filtered whale positions from 21 individuals were obtained along the southwest passage. The daily range covered by individual whales was 8.8 km, and <25 km on 90% of all days. Ship density in the same square kilometers where whales were encountered was 0.27 per week, slightly more often than once per month, however this encounter rate varied by 100-fold between individuals, depending on how often animals were in the central shipping lane. One of the tagged whales stopped transmitting and washed up dead suggesting a ship strike. In the last decade, four other humpback whales and three sei whales were killed by probable ship strikes, all near Isla Carlos III, the core of the humpback feeding area. A 10-knot speed restriction and onboard observers are recommended during the five months of maximum whale abundance, applying to all merchant vessels traveling through the Strait, between Cabo Holland and Isla Bonete north of Carlos III Island, for a distance of 28 nautical miles (52 km).
The human dimensions of harmful algal blooms (HABs) are becoming increasingly apparent as they grow in frequency and magnitude in some regions of the world under changing ocean conditions. One such region is the U.S. West Coast, where HABs of toxigenic species of Pseudo-nitzschia have been found to coincide with or closely follow periods of warming. In 2015, the region experienced a massive HAB of Pseudo-nitzschia that was associated with the 2014-16 Northeast Pacific marine heatwave. The HAB event delayed the opening of the lucrative commercial Dungeness crab fishery for up to 5 months and closed the popular recreational razor clam fishery, resulting in fishery failures and disaster declarations and causing significant sociocultural and economic impacts to coastal communities. Here, management actions are examined that were taken by federal and state government agencies and responses of coastal residents to this extreme HAB event using a disaster risk management framework consisting of four phases: 1) prediction and early warning, 2) event response, 3) recovery and reconstruction, and 4) mitigation and prevention. Clear differences in management actions at the state level were evident in California, Oregon, and Washington during every phase, producing vastly different perceptions of management by coastal residents. A history of trusted relationships and coordination among agencies and with the fishing industry in Washington State was associated with more transparent and accepted management responses. The examination found that additional education, outreach, and trust-building exercises would provide benefits to communities affected by extreme HAB events. Our findings contribute to an understanding of climate change adaptation in coastal communities dependent on fishery resources.
In this paper we outline the stakeholder-led approaches in the development of biological data products to support effective conservation, management and policy development. The requirements of a broad range of stakeholders and iterative, structured processes framed the development of tools, models and maps that support the FAIR (Findable, Accessible, Interoperable, Reusable) data principles. By structuring the resultant data products around the emerging biological Essential Ocean Variables, and through the engagement with a broad range of end-users, the EMODnet (European Marine Observation and Data Network) Biology project has delivered a suite of demonstration data products. These products are presented in the European Atlas of Marine Life, an online resource demonstrating the value of open marine biodiversity data and help to answer fundamental and policy-driven questions related to managing the natural and anthropogenic impacts in European waters.
The polluting of marine ecosystems with plastics is both a global and a local problem with potentially severe consequences for wildlife, economic activity, and human health. It is a problem that originates in countries’ inability to adequately manage the growing flow of waste. We use an impact pathway framework to trace the flow of plastics through the socio-ecological system and identify the role of specific policy instruments in achieving behavioral changes to reduce marine plastic waste. We produce a toolbox for finding a policy that is suitable for different countries. We use the impact pathway and toolbox to make country-specific recommendations that reflect the reality in each of the selected countries.
Over the past decade, coastal communities and ecosystems in the Northeast United States have begun to face acute and chronic impacts of climate change. Extreme events such as Superstorm Sandy caused stakeholders in this region to examine what information is needed to implement adaptation and mitigation plans to prepare for the next major storm. The objective of this study was to determine research needs identified by stakeholders in the Northeast needed for decision-support and policy creation so that scientists can target future research efforts to fill gaps. Modeled after document analysis methods in Dilling et al. (2014), this study examines documents sourced from local and regional organizations in both the public and private sectors to determine gaps in information necessary for climate resilience planning. Stakeholders throughout the Northeast expressed a need for solution-based research, in particular natural and nature-based solutions such as wetlands. Additionally, there was a need to better understand the economic impacts of climate change on key industries in the region as well as cost-benefit analyses of different adaptation options. It was also determined that government organizations, such as Sea Grant, play a crucial role in supporting stakeholder needs assessments both in terms of funding and providing necessary expertise. This study provides a baseline of stakeholder-expressed research needs in the Northeast to start the conversation between communities and researchers interested in conducting useable science.
Over two million leisure boats use the coastal areas of the Baltic Sea for recreational purposes. The majority of these boats are painted with toxic antifouling paints that release biocides into the coastal ecosystems and negatively impact non-targeted species. Regulations concerning the use of antifouling paints differ dramatically between countries bordering the Baltic Sea and most of them lack the support of biological data. In the present study, we collected data on biofouling in 17 marinas along the Baltic Sea coast during three consecutive boating seasons (May–October 2014, 2015 and 2016). In this context, we compared different monitoring strategies and developed a fouling index (FI) to characterise marinas according to the recorded biofouling abundance and type (defined according to the hardness and strength of attachment to the substrate). Lower FI values, i.e. softer and/or less abundant biofouling, were consistently observed in marinas in the northern Baltic Sea. The decrease in FI from the south-western to the northern Baltic Sea was partially explained by the concomitant decrease in salinity. Nevertheless, most of the observed changes in biofouling seemed to be determined by local factors and inter-annual variability, which emphasizes the necessity for systematic monitoring of biofouling by end-users and/or authorities for the effective implementation of non-toxic antifouling alternatives in marinas. Based on the obtained results, we discuss how monitoring programs and other related measures can be used to support adaptive management strategies towards more sustainable antifouling practices in the Baltic Sea.