Pelagic habitats in the Northeast Atlantic (NEA) have undergone substantial ecological change over the past six decades due to pressures such as climate change, overfishing, and nutrient pollution. To assess Good Environmental Status (GES; under the EU Marine Strategy Framework Directive) we present an integrated assessment of NEA pelagic habitat status using two plankton biodiversity indicators, representing community composition and plankton biomass/abundance, alongside an informative assessment of plankton diversity. We applied a stepwise approach, first combining component-level results across assessment units and fixed-point stations for four pelagic habitat types, then integrating status across indicators and habitat types to derive regional environmental status. Because operational thresholds are lacking, ‘Uncertain’ was the default status, while ‘Not Good’ required consistent, spatially representative biological change plausibly linked to anthropogenic pressures.Across the assessed indicators, we found regional and habitat-specific changes in plankton lifeform abundance, and general declines in phytoplankton biomass and zooplankton abundance. Six habitat-region combinations were assessed as ‘Not Good’, three as ‘Uncertain’, and one was ‘Unassessed’ due to lack of data. No pelagic habitats or regions were found to be in GES. It was only possible to designate ‘Not Good’ or ‘Uncertain’ status due to lack of suitable baseline data and uncertainty around what constitutes ‘Good’ status in the context of NEA pelagic habitats. Sea surface temperature and nutrients were the most important pressures associated with change. These results highlight the need to reduce nutrient pollution and meet international climate targets to conserve pelagic habitats and their ecosystem services.

Abstract Plankton monitoring is central to marine ecosystem research and policy, but the growing use of automated imaging systems must be assessed against established methods. Here, the Continuous Plankton Recorder (CPR) and the Plankton Imager (Pi-10) were compared during two transects in the North Sea. Copepod abundances recorded by the Pi-10 were much higher than those from the CPR, with mean values around 36 times greater, and no significant correlation was found between the two datasets. The CPR identified clear latitudinal shifts in copepod community composition, while the Pi-10 captured fine-scale spatial variation of total copepod abundances and size distribution within the population, both of which declined significantly with increasing latitude. The two instruments therefore offered different but complementary views of the plankton: the CPR delivered high taxonomic resolution, whereas the Pi-10 provided high-resolution measurements of abundance and size. Together, they improved characterization of plankton variability across spatial scales and underscored the value of overlapping deployments to support the integration of imaging technologies into long-term monitoring programmes.

Changes in plankton have important implications for ecosystem services, including supporting fish stocks, carbon sequestration, nutrient cycling, and oxygen production. Standard long-term plankton monitoring relies on light microscopy to identify and count plankton taxa, with methods fully supported by international standards, providing high quality trusted data. Novel methods, including imaging and molecular, offer means of collecting select types of plankton data efficiently, filling targeted knowledge gaps left by standard monitoring and generating a more complete picture of plankton dynamics. Standard and novel monitoring methods present different advantages and costs, positioning their suitability to address different management needs. Standard plankton monitoring time-series are unique in providing the long-term temporal coverage, and thus statistical power, needed to detect and understand climate change impacts. When explored in parallel with standard monitoring, novel methods open doors to observing our seas from complementary perspectives, but further work is necessary before data from standard and novel methods can be integrated to address policy needs. Marine management priorities are shifting, and novel methods are increasingly proposed as possible alternatives to standard monitoring. However, for a long-term taxonomic perspective it is still essential to retain the specialist skills and maintain standard monitoring time-series to inform policy assessments of important changes in pelagic biodiversity. This review aims to inform readers of the value of long-term data, the importance of retaining taxonomic skills and embracing novel methods for marine plankton monitoring to assess pelagic biodiversity. We recommend strategies to maintain long-term monitoring whilst incorporating novel methods.

Plankton, the primary energy resource in marine food webs, respond rapidly to environmental change, making them useful indicators of shifts in ecosystem structure or function. Categorising plankton into groups, or “lifeforms”, can be useful for understanding ecological patterns associated with environmental change. While the marine environment is changing rapidly due to anthropogenic pressures, the relative influence of these pressures across the plankton community remains uncertain, impacting our ability to account for changes in plankton in sustainable marine management. Using methodology developed for the 2023 OSPAR assessment of Pelagic Habitats, we analysed 29 years of Continuous Plankton Recorder data from the North-East Atlantic to examine how temperature, nutrients and background environmental variability impacted abundance. Variability was primarily explained by trends in other lifeforms, indicating shared responses to environmental pressures. Longitude, bathymetry, mixed layer depth, the nitrogen-to‑phosphorus ratio, and temperature were also significant predictors. However, contrasting influences of environmental drivers were detected. For example, small copepod abundance increased in warmer conditions whereas meroplankton, large copepods and fish larvae either decreased or were unchanged. Our findings highlight recent changes in stratification, reflected by variation in mixed layer depth, and imbalanced nutrient ratios are affecting multiple lifeforms, impacting the North-East Atlantic plankton community. To achieve environmental improvements in North-East Atlantic pelagic habitats, it is crucial that we continue to address climate change and reduce nutrient pollution.

Plankton monitoring datasets help inform indicators for marine biodiversity assessments under the European Union Marine Strategy Framework Directive and United Kingdom Marine Strategy. These indicators are used to assess long-term changes in the state of the pelagic habitats of the Northeast Atlantic which then guide policy formation and implementation to achieve Good Environmental Status. Across all ecosystems, environmental change has the potential to impact upon human wellbeing by changing the quantity and quality of ecosystem services. Here, we develop a socio-ecological assessment model that can describe how variations in pelagic habitat state, evidenced by plankton indicators, can impact human wellbeing. We show that pelagic habitat state can influence human wellbeing through changing the availability of 'goods and benefits' (as made available via ecosystem services), such as the contribution of phytoplankton to climate regulation, but also through mediating the risks of 'ecosystem hazards'. Importantly, changes to pelagic ecosystem state will also drive changes to ecosystem services and ecosystem hazards in the wider marine food web, supported by ecosystem processes associated with plankton, such as the rate of primary production. Applying the proposed assessment model to plankton monitoring data highlights the potential for a greater depth of understanding of the human wellbeing impacts driven by state changes in pelagic habitats. Alongside making best use of the available plankton monitoring data, quantifying the human wellbeing impacts arising from changes to pelagic habitat state increases the evidence base for decision makers.

The assessment of water quality, and in particular, of eutrophication, has been a core activity to establish, disseminate, and communicate the impact of anthropogenic influences on coastal and marine waters in the United Kingdom (UK) and globally. To date, the UK assessments of eutrophication have focused heavily on indicators, either singularly or in combination, associated with a numerical threshold, with supporting science concentrating on defining relevant thresholds and relating exceedances to management actions. However, as our understanding of the complexity of estuarine and coastal zone processes in terms of variability, time lags, ecological interactions and climate resilience has evolved, so too must the structure of our water quality assessments. This paper presents a review of existing UK eutrophication assessments, identifying what has worked and where gaps still exist, particularly as our ecosystems face rapid changes. From the gap analysis, we present a series of recommendations for future eutrophication assessments, assessing the feasibility of implementing those recommendations through consideration of effort, complexity and costs. This work presents a set of headline activities offering a renewed and revised approach to the structure of UK eutrophication assessments that will progress complex data flows, achieve enhanced alignment between directives, embed new indicators, greater understanding of ecosystem impacts and consideration of the shifting climate baseline.

This manuscript describes the collation of available water quality data from the freshwater reaches of surface streams within the Great Barrier Reef catchment area, northeastern Australia. This compilation represents one of the most comprehensive online datasets for historical tropical and subtropical freshwater quality around the world. We document the criteria for selection of the data and associated publications as well as the processes of data cleaning used to produce a qualitative assessment of the datasets. The final compilation includes 41 individual datasets that collectively report 466 sites and contain over 26,000 discrete water quality sample records totaling more than 350,000 unique water quality results. Finally, we outline the nuances of the data that end users need to take into account when combining them for spatial and temporal analyses. The dataset ensures that these valuable water quality data collected over the past four decades are preserved for the next generations of researchers, practitioners, management agencies and policy makers.

This paper presents the outcomes of the fourth application of the Common Procedure for the Identification of the Eutrophication Status of the OSPAR Maritime Area (the “Common Procedure”), conducted for the period 2015–2020 for the North East Atlantic. Previously, OSPAR has assessed eutrophication based on national assessment areas and disparate approaches lacking a transparent and comparable basis. A more harmonized approach has now been achieved through development of ecologically relevant assessment areas defined by oceanographic criteria rather than international boundaries, allowing for consistent assessments across exclusive economic zones and acknowledging that eutrophication is a transboundary problem. Thresholds that were specific for those harmonized assessment areas and eutrophication parameters have been derived primarily from an ensemble modeling approach to determine pre-eutrophic conditions. Common assessment areas and harmonized thresholds have enabled, for the first time, an objective and comparable assessment of the eutrophication status of the whole OSPAR Maritime Area. This establishes a level playing field for managing eutrophication and a solid basis for deriving OSPAR nutrient reduction targets as a prerequisite for targeted and successful regional eutrophication management. This assessment shows that eutrophication problem areas persist, in particular along the continental coasts from France to Denmark/Sweden and in the Greater North Sea and the Bay of Biscay and Iberian coast. The main areas affected by eutrophication are the plumes and adjacent coastal areas in the Greater North Sea and Bay of Biscay/Iberian Coast, with riverine nutrient inputs remaining the major source of nutrient pollution. Approximately 6% (152,904 km 2 ) of the OSPAR Maritime Area is eutrophic, with the impacted area supporting many important ecosystem services. Fifty-eight percent of river plume areas (eight assessment areas out of 14), 22% (five of 27) of the coastal areas and 10% (three of 17) of the shelf areas were classified as problem areas. Application of the current assessment process to historical data from the previous three OSPAR assessment periods shows a gradual improvement since 2000. However, the OSPAR 2010 objective “to combat eutrophication, with the ultimate aim of achieving and maintaining a healthy marine environment where anthropogenic eutrophication does not occur” has not yet been fully achieved. Further measures to reduce nutrient loads are needed to ensure long-term sustainability of our coastal waters.

Anthropogenic pressures such as climate change and nutrient pollution are causing rapid changes in the marine environment. The relative influence of drivers of change on the plankton community remains uncertain, and this uncertainty is limiting our understanding of sustainable levels of human pressures. Plankton are the primary energy resource in marine food webs and respond rapidly to environmental changes, representing useful indicators of shifts in ecosystem structure and function. Categorising plankton into broad groups with similar characteristics, known as "lifeforms", can be useful for understanding ecological patterns related to environmental change and for assessing the state of pelagic habitats in accordance with the EU Marine Strategy Framework Directive and the OSPAR Commission, which mandates protection of the North-East Atlantic. We analysed 29 years of Continuous Plankton Recorder data (1993-2021) from the North-East Atlantic to examine how trends in plankton lifeform abundance changed in relation to one another and across gradients of environmental change associated with human pressures. Random forest models predicted between 57 % and 80 % of the variability in lifeform abundance, based on data not used to train the models. Observed variability was mainly explained by trends in other lifeforms, with mainly positively correlated trends, indicating bottom-up control and/or shared responses to environmental variability were prevalent. Longitude, bathymetry, mixed layer depth, the nitrogen-to-phosphorus ratio, and temperature were also significant predictors. However, contrasting influences of environmental drivers were detected. For example, small copepod abundance increased in warmer conditions whereas meroplankton, large copepods and fish larvae either decreased or were un- changed. Our findings highlight recent changes in stratification, reflected by variation in mixed layer depth, and imbalanced nutrient ratios are affecting multiple lifeforms, impacting the North-East Atlantic plankton com- munity. To achieve environmental improvements in North-East Atlantic pelagic habitats, it is crucial that we continue to address climate change and reduce nutrient pollution.

A healthy marine ecosystem is a fully functioning system, able to supply ecosystem services whilst still maintaining resilience to human-induced environmental change. Monitoring and managing the health of resilient marine ecosystems requires indicators that can assess their biodiversity state and food web functioning. Plankton are crucial components of pelagic habitats, occupying the base of the pelagic food web. Larger plankton have long been used to monitor ecosystem productivity and biodiversity due to their identification via traditional light microscopy. In contrast, the regular monitoring of pico- and nanoplankton (<20 µm; hereafter called “tiny plankton”) only started with the development of flow cytometry techniques, which has limited their inclusion as ecosystem health indicators.Four UK plankton surveys have sampled and identified these tiny plankton for up to 14 years, providing an opportunity to test their suitability as indicators of ecosystem state. We investigated six groups of tiny plankton, including heterotrophic nanoeukaryotes, photosynthetic nanoeukaryotes, photosynthetic picoeukaryotes, and Synechococcus cyanobacteria, and two groups of heterotrophic bacteria. Flow cytometry and light microscopy data from an inshore Western English Channel station revealed that 99.98 % of plankton abundance and 71 % of plankton biomass was derived from tiny plankton cells too small to be quantified accurately under a light microscope and thus not adequately considered in assessments of pelagic habitats.Different UK marine and coastal regions showed consistency in peak abundances of these tiny plankton. We used a novel wavelet coherence method to identify time-based relationships between tiny plankton and environmental variables linked to human pressures. Relationships were found between nitrogenous nutrients and all tiny plankton groups, most commonly at sub-annual to annual time scales. Photosynthetic picoeukaryotes, heterotrophic nanoeukaryotes, and HNA-bacteria were associated with high sea surface temperatures. Given the here established relationship between tiny plankton and environmental variables, and their importance in the full plankton assemblage, we recommend that, alongside existing microplankton lifeforms, tiny plankton groups can be used as plankton lifeforms, either individually or in combination, to inform biodiversity indicators that meet policy obligations under the EU Marine Strategy Framework Directive (MSFD), (Oslo-Paris Convention) OSPAR strategies, and the UK Marine Strategy.

Plankton form the base of marine food webs, making them important indicators of ecosystem status. Changes in the abundance of plankton functional groups, or lifeforms, can affect higher trophic levels and can indicate important shifts in ecosystem functioning. Here, we extend this knowledge by combining data from Continuous Plankton Recorder and fixed-point stations to provide the most comprehensive analysis of plankton time-series for the North-East Atlantic and North-West European shelf to date. We analysed 24 phytoplankton and zooplankton datasets from 15 research institutions to map 60-year abundance trends for 8 planktonic lifeforms. Most lifeforms decreased in abundance (e.g. dinoflagellates: -5 %, holoplankton: -7 % decade-1), except for meroplankton, which increased 12 % decade-1, reflecting widespread changes in large-scale and localised processes. K-means clustering of assessment units according to abundance trends revealed largely opposing trend direction between shelf and oceanic regions for most lifeforms, with North Sea areas characterised by increasing coastal abundance, while abundance decreased in North-East Atlantic areas. Individual taxa comprising each phytoplankton lifeform exhibited similar abundance trends, whereas taxa grouped within zooplankton lifeforms were more variable. These regional contrasts are counterintuitive, since the North Sea which has undergone major warming, changes in nutrients, and past fisheries perturbation has changed far less, from phytoplankton to fish larvae, as compared to the more slowly warming North-East Atlantic with lower nutrient supply and fishing pressure. This more remote oceanic region has shown a major and worrying decline in the traditional food web. Although the causal mechanisms remain unclear, declining abundance of key planktonic lifeforms in the North-East Atlantic, including diatoms and copepods, are a cause of major concern for the future of food webs and should provide a red flag to politicians and policymakers about the prioritisation of future management and adaptation measures required to ensure future sustainable use of the marine ecosystem.

Assessments of the water quality in coastal zones often rely on indirect indicators from contributing river inputs and the neighbouring ocean. Using a novel combination of distance accumulation cost methods and an ocean-colour product derived from SENTINEL-3 data, we developed a probabilistic method for the assessment of dissolved inorganic nitrogen (DIN) in Liverpool Bay (UK) for the period from 2017 to 2020. Using our approach, we showed the annual and monthly likelihood of DIN exposure from its 12 major contributory rivers. Furthermore, we generated monthly risk maps showing the probability of DIN exposure from all rivers, which revealed a seasonal variation of extent and location around the bay. The highest likelihood of high DIN exposure throughout the year was in the estuarine regions of the Dee, Mersey, and Ribble, along with near-shore areas along the north Wales coast and around the mouth of the rivers Mersey and Ribble. There were seasonal changes in the risk of DIN exposure, and this risk remained high all year for the Mersey and Dee estuary regions. In contrast, for the mouth and near the coastal areas of the Ribble, the DIN exposure decreased in spring, remained low during the summer and early autumn, before displaying an increase during winter. Our approach offers the ability to assess the water quality within coastal zones without the need of complex hydrodynamic models, whilst still having the potential to apportion nutrient exposure to specific riverine inputs. This information can help to prioritise how direct mitigation strategies can be applied to specific river catchments, focusing the limited resources for coastal zone and river basin management.

The Great Barrier Reef (GBR) is a marine protected area subject to natural and anthropogenic disturbances. Water quality is critical for the health and protecting resilience of GBR coral ecosystems against the synergistic and cumulative pressures of tropical cyclones, marine heat waves, and outbreaks of crown-of-thorns starfish. The concentration of Total Suspended Solids (TSS) is a key water quality parameter measured at multiple spatio-temporal scales from in situ probes to satellite observations. High TSS concentrations can adversely impact coral and seagrasses on the inshore GBR. We present diurnal TSS derived from Himawari-8 Geostationary satellite observations at 10 min frequency and demonstrate its applicability for improved monitoring of GBR water quality. Diurnal TSS obtained from Himawari-8 observations were compared to TSS computed from in situ bio-optical measurements at the Lucinda Jetty Coastal Observatory (LJCO). The coastal waters at LJCO experience diurnal variability of TSS (~7 mg L−1), where magnitude peaks followed the slack tides, and the largest diurnal changes were associated with freshwater discharge residuals from the wet season. Exceedance maps revealed that TSS is above guideline thresholds in the open coastal and mid-shelf waters for ~60% of the valid monthly observations, including during dry season months.

Major planktonic lifeforms such as diatoms, dinoflagellates, meroplankton and holoplankton have recently shown significant and alarming changes in abundance - mainly downwards trends - around the northwest European shelf. This has major implications for food web connections and for ecosystem services including seafood provision and carbon storage. We have quantified these changes in abundance for 2006–2019/20 using a Plankton Index (PI) and show that the scale of spatial aggregation is critical to the ability of the PI to detect change, understand causal mechanisms, and provide advice to policymakers. We derived PI statistics in the Celtic and North Seas from data from the Continuous Plankton Recorder survey offshore and England’s Environment Agency inshore using three sets of spatial units: (i) Ecohydrodynamic (EHD) units based on hydro-biogeochemical modelling, (ii) ‘COMP4′ areas based on cluster analysis of satellite data for chlorophyll a and primary productivity, and (iii) English coastal and estuarine Water Framework Directive (WFD) waterbodies. For the largest scale areas, the EHD units (median size 87,000 km2), we find greater change in plankton communities than previously reported, suggesting that these shifts have continued and possibly intensified in recent years. The smaller-scale COMP4 areas (median size 6,700 km2) appear to encompass more spatially coherent changes in plankton community structure than EHD units; at this scale PI values indicate community shifts of greater magnitude. These COMP4 areas provide a reasonable compromise scale for linking offshore plankton communities to large-scale drivers of change such as climate warming. For inshore plankton communities, larger changes are detected at the smaller WFD waterbody scale (median size 11 km2). This scale allows direct links to coastal management measures and is more suitable for linking to land-sourced pressures. Recent integration of the UK’s OSPAR and WFD plankton monitoring data management enables the exploration of changes across spatial scales to develop a holistic understanding of ecosystem health. Regional-sea scale derivation of the PI for coastal waters provides a clear indication that changes are occurring, at least in phytoplankton communities, while localised PI statistics offer an additional layer of information which can be an important tool for linking to localised drivers of change including coastal anthropogenic pressures. Broadscale inshore zooplankton monitoring is needed to evaluate the coastal plankton community holistically; zooplankton communities offshore are also changing but these changes cannot currently be linked to coastal processes. Layering information across spatial scales provides a breadth of system-level understanding beyond what any one typology can provide.

In January 2013, tropical cyclone Oswald caused widespread flooding in the North-East coast of Australia, and large and highly episodic inputs into Princess Charlotte Bay (PCB, northern Great Barrier Reef). Freshwater outflows from the Normanby and Kennedy rivers, the two main rivers draining the adjacent catchments, resulted in drastic changes in physical, biogeochemical and optical properties within PCB. On 31 January, 2 days after the peak riverine discharge from the Normanby river, nutrients and dissolved organic matter contents peaked under the influence of large outflows from the Kennedy river into the western section of the bay (5.8 μM for dissolved inorganic nitrogen, 6.9 g m−3 for dissolved organic carbon and 6.1 m−1 for the colored dissolved organic matter absorption coefficient at 412 nm). In the eastern section of the bay, the situation appeared more ‘mixed’, with a suspended solids concentration reaching 23.1 g m−3 close to the Normanby river mouth. The main phytoplankton bloom occurred in the transition zone between the Kennedy and Normanby flood plumes, and was dominated by diatoms with a chlorophyll a concentration reaching 14.6 mg m−3. This study highlights the need to better describe the critical spatial and temporal scales of variability of key biogeochemical and optical properties after a major flood event. The data collected is key to improve the accuracy of ocean color remote sensing algorithms and regional biogeochemical budgets following highly episodic inputs.

Seagrass beds provide a range of ecosystem services but are at risk from anthropogenic pressures. While recent progress has been made, the distribution and condition of South Pacific seagrass is relatively poorly known and selecting an appropriate approach for mapping it is challenging. A variety of remote sensing tools are available for this purpose and here we develop a mapping toolbox and associated decision tree tailored to the South Pacific context. The decision tree considers the scale at which data are needed, the reason that monitoring is required, the finances available, technical skills of the monitoring team, data resolution, site safety/accessibility and whether seagrass is predominantly intertidal or subtidal. Satellite mapping is recommended for monitoring at the national and regional scale, with associated ground-reference data where possible but without if time and funds are limiting. At the local scale, satellite, remotely piloted aircraft (RPA), kites, underwater camera systems and in situ surveys are all recommended. In the special cases of community-based initiatives and emergency response monitoring, in situ or satellite/RPA are recommended, respectively. For other types of monitoring the primary driver is funding, with in situ, kite and satellite recommended when finances are limited and satellite, underwater camera, RPA or kites otherwise, dependent on specific circumstances. The tools can be used individually or in combination, though caution is recommended when combining tools due to data comparability.

Marine coastal waters of Bahrain are under pressure due to human activities and climate change. We used marine monitoring data (2005-2020) from 27 sites to establish baseline conditions and develop standards for assessments of water quality. Five hydrodynamic regions were identified: Oyster Beds, North, West, East, East (Coastal). Data from Oyster Beds sites, likely to be less impacted by human activities, were used to determine baseline conditions. For most parameters, candidate thresholds were based on 50 % and 100 % variation from baseline and 95th percentiles. Comparisons of data against different thresholds showed different outcomes. Overall, results indicate good water quality, with potential concerns in East (Coastal). Trend analyses showed some significant trends in all regions: downward (favourable) for some parameters (e.g. turbidity: North) and upward for others (e.g. nitrate: Oyster Beds, East and East (Coastal)). Future work requires greater understanding around optimum guidelines that protect and mitigate any adverse ecological impacts.

Modern-day coral reef conservation requires connections between researchers, decision-makers and stakeholders to achieve holistic ecosystem-based management (EBM), rooted in and supported by local communities. However, the COVID-19 pandemic, global political and financial instability and growing concerns over emissions from air travel have meant that face-to-face meetings and in-person fieldwork are increasingly difficult for many researchers at distant institutions. In this paper we discuss how to achieve EBM remotely, using a combination of freely available online data, remote fieldwork techniques and virtual communication and engagement tools. We highlight resources that have been useful in our work for components of overseas EBM and discuss lessons learned from those experiences. There are benefits to remote working, including reduced carbon emissions and travel costs, the ability to record and re-use electronic training materials, the ability to reach a wider audience than through face-to-face meetings and an increased reliance and division of labour with local researchers and stakeholders. However, developing new relationships and gaining a deeper contextual understanding of the local site and culture is not easily replaced by online or remote methods. Post-COVID-19, it is likely that some aspects of remote working within coral reef conservation will continue, as in many other aspects of global collaboration. We propose a blended approach where much of the work and collaboration is conducted online, but with some in-person visits to develop the key relationships or decisions are needed.