Lifeform indicators reveal large‐scale shifts in plankton across the North‐West European shelf

Desmit X., Nohe A., Borges A.V., Prins T., De Cauwer K., Lagring R., Van der Zande D., Sabbe K.

At least two major drivers of phytoplankton production have changed in recent decades in the North Sea: sea surface temperature (SST) has increased by similar to 1.6 degrees C between 1988 and 2014, and the nitrogen and phosphorus loads from surrounding rivers have decreased from the mid-1980s onward, following reduction policies. Long time series spanning four decades (1975-2015) of nutrients, chlorophyll (Chl), and pH measurements in the Southern and Central North Sea were analyzed to assess the impact of both the warming and the de-eutrophication trends on Chl. The de-eutrophication process, detectable in the reduction of nutrient river loads to the sea, caused a decrease of nutrient concentrations in coastal waters under riverine influence. A decline in annual mean Chl was observed at 11 out of 18 sampling sites (coastal and offshore) in the period 1988-2016. Also, a shift in Chl phenology was observed around 2000, with spring bloom formation occurring earlier in the year. A long time series of pH in the Southern North Sea showed an increase until the mid-1980s followed by a rapid decrease, suggesting changes in phytoplankton production that would support the observed changes in Chl. Linear correlations, however, did not reveal significant relationships between Chl variability and winter nutrients or SST at the sampling sites. We propose that the observed changes in Chl (annual or seasonal) around 2000 are a response of phytoplankton dynamics to multiple stressors, directly or indirectly influenced by de-eutrophication and climate warming.

McQuatters-Gollop A., Atkinson A., Aubert A., Bedford J., Best M., Bresnan E., Cook K., Devlin M., Gowen R., Johns D.G., Machairopoulou M., McKinney A., Mellor A., Ostle C., Scherer C., et. al.

Plankton are sensitive indicators of change and, at the base of marine food webs, they underpin important ecosystem services such as carbon sequestration and fisheries production. In the UK and the Northeast Atlantic region, change in plankton functional groups, or ‘lifeforms’, constructed based on biological traits, is the formally accepted policy indicator used to assess Good Environmental Status (GES) for pelagic habitats under the Marine Strategy Framework Directive (MSFD: 2008/56/EC). To identify changes in UK pelagic habitats, plankton lifeforms, were used from diverse UK data sets collected by different methods, including plankton sampling by nets, water bottles, integrating tube samplers, and the Continuous Plankton Recorder. A Plankton Index approach was used to identify change in plankton lifeforms. This is the first time that the pelagic plankton community has been assessed on a UK-wide scale and forms the foundation of the UK’s 2020 MSFD Assessment for pelagic habitat biodiversity and food webs. This approach revealed that some of the plankton lifeforms used in the assessment displayed spatially-variable changes during the past decade. Assessing plankton community change using a common indicator at the UK scale for the first time is a significant step towards evaluating GES for European seas. Determining GES for pelagic habitats, however, is a challenging process, with additional work required to interpret the assessment results and to identify causation of the changes observed.

Greenwood N., Devlin M.J., Best M., Fronkova L., Graves C.A., Milligan A., Barry J., van Leeuwen S.M.

The assessment of eutrophic conditions is a formal requirement of several European Directives. Typically, these eutrophication assessments use a set of primary indicators which include dissolved inorganic nutrients, chlorophyll, dissolved oxygen and secondary information which can include phytoplankton community data. Each directive is characterised by a different geographical or political boundary which defines the area under assessment. Several disparate sources of data from the Thames estuary and Liverpool Bay in the United Kingdom collected from different monitoring programs were combined to generate a fully integrated dataset. Data sources included remote sensing, ecosystem models, moorings, freshwater inputs, and traditional ship surveys. Different methods were explored for assigning ecologically relevant assessment areas including delineation of the assessment area based on salinity, extent of the river plume influence and ecohydrodynamic characteristics in addition to the traditional geographically defined typologies associated with the different directives. Individual eutrophication indicators were tested across these revised typologies and outcomes of the different metrics compared across the river to marine continuum for the two UK areas. There have been statistically significant decreasing trends in the loads of ammonium, nitrite and dissolved inorganic phosphorous between 1994 and 2016 to both the Thames estuary and Liverpool Bay study areas but no statistically significant trends in loads of nitrate or dissolved inorganic nitrogen. There have been statistically significant increases in riverine nitrogen:phosphorous between 1994 and 2016. Nutrient concentrations exceeded assessment thresholds across nearly all areas other than the large offshore assessment areas and outcomes of the chlorophyll metric were often below assessment thresholds in the estuarine based areas and the offshore areas, but exceedances of thresholds occurred in the near coastal areas. However, trait-based indicators of phytoplankton community using functional groups show changes in plankton community structure over the assessment period indicating that additional metrics which quantify community shifts would be a useful measurement to include in future eutrophication assessments.

Beaugrand G., Conversi A., Atkinson A., Cloern J., Chiba S., Fonda-Umani S., Kirby R.R., Greene C.H., Goberville E., Otto S.A., Reid P.C., Stemmann L., Edwards M.

Impermanence is an ecological principle1 but there are times when changes occur nonlinearly as abrupt community shifts (ACSs) that transform the ecosystem state and the goods and services it provides2. Here, we present a model based on niche theory3 to explain and predict ACSs at the global scale. We test our model using 14 multi-decadal time series of marine metazoans from zooplankton to fish, spanning all latitudes and the shelf to the open ocean. Predicted and observed fluctuations correspond, with both identifying ACSs at the end of the 1980s4–7 and 1990s5,8. We show that these ACSs coincide with changes in climate that alter local thermal regimes, which in turn interact with the thermal niche of species to trigger long-term and sometimes abrupt shifts at the community level. A large-scale ACS is predicted after 2014—unprecedented in magnitude and extent—coinciding with a strong El Niño event and major shifts in Northern Hemisphere climate. Our results underline the sensitivity of the Arctic Ocean, where unprecedented melting may reorganize biological communities5,9, and suggest an increase in the size and consequences of ACS events in a warming world. Abrupt community shifts, for marine species from zooplankton to fish, are shown to occur with local climate changes in which warming pushes species beyond their thermal niche. This modelling approach suggests future events will be larger and have more broad-reaching impacts.

Tweddle J.F., Gubbins M., Scott B.E.

Phytoplankton are an extremely important component of the functioning of ecosystems and climate regulation. Because concentrations of phytoplankton are highly patchy in both space and time, it is proposed that more consideration concerning the potential impact from human developments and activities on the service provision afforded by phytoplankton should be accounted for in marine management processes. The multiple species of primary producers provide important provisioning and regulating ecosystem services (ES) and form the basis of marine food-webs, supporting production of higher trophic levels (a provisioning ES), and act as a sink of CO2 (a climate regulation ES). Spatial and temporal patchiness in the production of phytoplankton can be related to patchiness in the provision of these ES. Patches of naturally high phytoplankton productivity should be afforded consideration within processes to assess environmental status, within marine spatial planning (including marine protected areas) and within sectoral licensing, with marine planning and licensing acting at scales most in harmony with scales of phytoplankton heterogeneity (meters to tens of kilometres). In this study, consideration of phytoplankton in marine management decision making has been reviewed. This paper suggests that potential impacts of maritime developments and activities on the natural patchiness of phytoplankton communities be included in management deliberations, and mitigation be considered. This affords opportunities for researchers to engage with management authorities to support ecosystems-based management. Doing so will assist in maintaining or achieving good environmental status and support further, reliant, ES.

Kemp A.E., Villareal T.A.

Models used to predict future ocean ecosystem and biogeochemical behaviour depend on simplified ecological frameworks allowing the definition of plankton functional types. Foremost among such frameworks has been the mandala of Margalef. His 1978 paper has been increasingly referred to in the past decade as simplified ecological schemes have been sought to help predict the effect of climate change on phytoplankton. However, the mandala is based on an understanding of the subject that is over 40 years old, when observational studies were largely limited to the coastal ocean and to near surface waters. Furthermore, most recent reproductions of the mandala are significant oversimplifications of Margalef’s original. In these simplified mandala-type constructs, diatoms, in particular, have commonly been cast as a single plankton functional type that thrive in turbulent waters and decrease in abundance with increasing stratification. On this basis, it is widely predicted that diatom productivity and hence the effectiveness of the marine biological carbon pump will decrease with climate change that is driving increased stratification of the oceans. But Margalef’s original took a more refined approach and depicted diatom genera that were adapted to more stratified conditions such as those characteristic of the subtropical oligotrophic gyres. If we now draw on the vast advances in observational oceanography of recent decades it is evident that diatoms may thrive, bloom and generate significant export even in the most intensely stratified and apparently oligotrophic conditions. Indeed, some diatom species have unique adaptations to such environments. We therefore suggest that it is time to abandon oversimplified schemes and recognize the diverse ecology of diatoms.

Chiba S., Batten S., Martin C.S., Ivory S., Miloslavich P., Weatherdon L.V.

Oceanographers have an increasing responsibility to ensure that the outcomes of scientific research are conveyed to the policy-making sphere to achieve conservation and sustainable use of marine biodiversity. Zooplankton monitoring projects have helped to increase our understanding of the processes by which marine ecosystems respond to climate change and other environmental variations, ranging from regional to global scales, and its scientific value is recognized in the contexts of fisheries, biodiversity and global change studies. Nevertheless, zooplankton data have rarely been used at policy level for conservation and management of marine ecosystems services. One way that this can be pragmatically and effectively achieved is via the development of zooplankton indicators, which could for instance contribute to filling in gaps in the suite of global indicators to track progress against the Aichi Biodiversity Targets of the United Nations Strategic Plan for Biodiversity 2010-2020. This article begins by highlighting how under-represented the marine realm is within the current suite of global Aichi Target indicators. We then examine the potential to develop global indicators for relevant Aichi Targets, using existing zooplankton monitoring data, to address global biodiversity conservation challenges.

Record N.R., Ji R., Maps F., Varpe Ø., Runge J.A., Petrik C.M., Johns D.

Bedford J., Johns D., Greenstreet S., McQuatters-Gollop A.

The Marine Strategy Framework Directive (MSFD) uses an indicator-based approach for ecosystem assessment; indicators of the state of ecosystem components ('state indicators') are used to determine whether, or not, these ecosystem components are at ‘Good Environmental Status’ relative to prevailing oceanographic conditions. Here, it is illustrated that metrics of change in plankton communities frequently provide indications of changing prevailing oceanographic conditions. Plankton indicators can therefore provide useful diagnostic information when interpreting results and determining assessment outcomes for analyses of state indicators across the food web. They can also perform a strategic role in assessing these state indicators by influencing target setting and management measures. In addition to their primary role of assessing the state of pelagic habitats against direct anthropogenic pressures, plankton community indicators can therefore also fulfil an important 'surveillance' role for other state indicators used to formally assess biodiversity status under the MSFD.

Capuzzo E., Lynam C.P., Barry J., Stephens D., Forster R.M., Greenwood N., McQuatters-Gollop A., Silva T., van Leeuwen S.M., Engelhard G.H.

Phytoplankton primary production is at the base of the marine food web; changes in primary production have direct or indirect effects on higher trophic levels, from zooplankton organisms to marine mammals and seabirds. Here, we present a new time-series on gross primary production in the North Sea, from 1988 to 2013, estimated using in situ measurements of chlorophyll and underwater light. This shows that recent decades have seen a significant decline in primary production in the North Sea. Moreover, primary production differs in magnitude between six hydrodynamic regions within the North Sea. Sea surface warming and reduced riverine nutrient inputs are found to be likely contributors to the declining levels of primary production. In turn, significant correlations are found between observed changes in primary production and the dynamics of higher trophic levels including (small) copepods and a standardized index of fish recruitment, averaged over seven stocks of high commercial significance in the North Sea. Given positive (bottom-up) associations between primary production, zooplankton abundance and fish stock recruitment, this study provides strong evidence that if the decline in primary production continues, knock-on effects upon the productivity of fisheries are to be expected unless these fisheries are managed effectively and cautiously.

Giron-Nava A., James C., Johnson A., Dannecker D., Kolody B., Lee A., Nagarkar M., Pao G., Ye H., Johns D., Sugihara G.

Chivers W.J., Walne A.W., Hays G.C.

The response of marine plankton to climate change is of critical importance to the oceanic food web and fish stocks. We use a 60-year ocean basin-wide data set comprising >148,000 samples to reveal huge differences in range changes associated with climate change across 35 plankton taxa. While the range of dinoflagellates and copepods tended to closely track the velocity of climate change (the rate of isotherm movement), the range of the diatoms moved much more slowly. Differences in range shifts were up to 900 km in a recent warming period, with average velocities of range movement between 7 km per decade northwards for taxa exhibiting niche plasticity and 99 km per decade for taxa exhibiting niche conservatism. The differing responses of taxa to global warming will cause spatial restructuring of the plankton ecosystem with likely consequences for grazing pressures on phytoplankton and hence for biogeochemical cycling, higher trophic levels and biodiversity. Marine plankton are the basis of the oceanic food chain. Here, Chivers and colleagues use ocean-basin wide plankton population data over six decades to show huge differences in the response of different plankton groups to climate change with major implications for the marine ecosystem and fisheries.

Whyte C., Davidson K., Gilpin L., Mitchell E., Moschonas G., McNeill S., Tett P.

Microplankton plays a vital part in marine ecosystems, and its importance has been recognized by the inclusion of microplankton community composition in regulatory frameworks such as the European Water Framework Directive and the Marine Strategy Framework Directive as an indicator of ecological status. Quantitative techniques are therefore required to assess the environmental status of the microplankton in a water body. Here we demonstrate the use of a method known as the microplankton index PI(mp) to evaluate changes in the microplankton community of the west coast Scottish Sea Loch Creran. Microplankton in this fjord has been studied since the 1970s, providing a data set spanning four decades. Our analysis compares an arbitrarily chosen reference period between 1979 and 1981 with a period between 2011 and 2013 and demonstrates that between these two periods community structure has changed considerably with a substantial drop in the numbers of observed diatoms accompanied by a rise in the number of autotrophic/mixotrophic dinoflagellates as well as an increase in the potentially toxin producing genus Pseudo-nitzschia and that these are related to changes in both the intensity and timing of local patterns of precipitation. The PI(mp) is shown to be a useful and robust method to visualize and quantify changes in the underlying structure of the microplankton community and is a powerful addition to the toolbox of techniques needed to determine the health of our seas.

Burson A., Stomp M., Akil L., Brussaard C.P., Huisman J.

Measures to reduce eutrophication have often led to a more effective decline of phosphorus (P) than nitrogen (N) concentrations. The resultant changes in riverine nutrient loads can cause an increase in the N : P ratios of coastal waters. During four research cruises along a 450 km transect, we investigated how reductions in nutrient inputs during the past 25 yr have affected nutrient limitation patterns in the North Sea. This revealed a strong offshore gradient of dissolved inorganic N : P ratios in spring, from 375 : 1 nearshore toward 1 : 1 in the central North Sea. This gradient was reflected in high nearshore N : P and C : P ratios of particulate organic matter (mainly phytoplankton), indicative of severe P deficiency of coastal phytoplankton, which may negatively affect higher trophic levels in the food web. Nutrient enrichment bioassays performed on-board showed P and Si limitation of phytoplankton growth nearshore, co-limitation of N and P in a transitional region, and N limitation in the outer-shore waters, confirming the existence of an offshore gradient from P to N limitation. Different species were limited by different nutrients, indicating that further reductions of P loads without concomitant reductions of N loads will suppress colonial Phaeocystis blooms, but will be less effective in diminishing harmful algal blooms by dino- and nanoflagellates. Hence, our results provide evidence that de-eutrophication efforts in northwestern Europe have led to a large imbalance in the N : P stoichiometry of coastal waters of the North Sea, with major consequences for the growth, species composition, and nutritional quality of marine phytoplankton communities.

McQuatters-Gollop A., Edwards M., Helaouët P., Johns D.G., Owens N.J., Raitsos D.E., Schroeder D., Skinner J., Stern R.F.

Phytoplankton are crucial to marine ecosystem functioning and are important indicators of environmental change. Phytoplankton data are also essential for informing management and policy, particularly in supporting the new generation of marine legislative drivers, which take a holistic ecosystem approach to management. The Marine Strategy Framework Directive (MSFD) seeks to achieve Good Environmental Status (GES) of European seas through the implementation of such a management approach. This is a regional scale directive which recognises the importance of plankton communities in marine ecosystems; plankton data at the appropriate spatial, temporal and taxonomic scales are therefore required for implementation. The Continuous Plankton Recorder (CPR) survey is a multidecadal, North Atlantic–basin scale programme which routinely records approximately 300 phytoplankton taxa. Because of these attributes, the survey plays a key role in the implementation of the MSFD and the assessment of GES in the Northeast Atlantic region. This paper addresses the role of the CPR's phytoplankton time-series in delivering GES through the development and informing of MSFD indicators, the setting of targets against a background of climate change and the provision of supporting information used to interpret change in non-plankton indicators. We also discuss CPR data in the context of other phytoplankton data types that may contribute to GES, as well as explore future possibilities for the use of new and innovative applications of CPR phytoplankton datasets in delivering GES. Efforts must be made to preserve long-term time series, such as the CPR, which supply vital ecological information used to informed evidence-based environmental policy.

Tao Z., Wang S., Chi X., Zhang F., Sun S.

Chevassus E., Fossum K.N., Ceburnis D., Lei L., Lin C., Xu W., O'Dowd C., Ovadnevaite J.

Abstract. Organic aerosol (OA) is recognized as a significant component of particulate matter (PM), yet their specific composition and sources, especially over remote areas, remain elusive due to the overall scarcity of high-resolution online data. In this study, positive matrix factorization was performed on organic aerosol mass spectra obtained from high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurements to resolve sources contributing to coastal PM. The focus was on a summertime period marked by enhanced biological productivity with prevailing pristine maritime conditions. Four OA factors were deconvolved by the source apportionment model. The analysis revealed primary marine organic aerosol (PMOA) as the predominant submicron OA at Mace Head during summertime, accounting for 42 % of the total resolved mass. This was trailed by more oxidized oxygenated organic aerosol (MO-OOA) at 32 %, methanesulfonic acid organic aerosol (MSA-OA) at 17 %, and locally emitted peat-derived organic aerosol (peat-OA) at 9 % of the total OA mass. Elemental ratios (O:C–H:C) were derived for each of these factors: PMOA (0.66–1.16), MO-OOA (0.78–1.39), MSA-OA (0.66–1.39), and peat-OA (0.43–1.34). The specific O:C–H:C range for MO-OOA hints at aliphatic and lignin-like compounds contributing to more oxidized organic aerosol formation. The total mass concentrations of primary organic aerosol and secondary organic aerosol were overall equal and almost exclusively present in the marine boundary layer, in agreement with previous findings. This study reveals that OA not only reflects atmospheric chemistry and meteorology – as evidenced by the significant ageing of summertime polar air masses over the North Atlantic, driven by ozonolysis under Greenland anticyclonic conditions – but also serves as an indicator of marine ecosystems. This is evident from MSA-OA being notably associated with stress enzyme markers and PMOA showing the typical makeup of largely abacterial phytoplankton extracellular metabolic processes. This study also reveals distinct source regions within the North Atlantic for OA factors. MSA-OA is primarily associated with the Iceland Basin, with rapid production following coccolithophore blooms (lag of 1–2 d), while diatoms contribute to a slower formation process (lag of 9 d), reflecting distinct oceanic biological processes. In contrast, PMOA is sourced from more variable ecoregions, including the southern Celtic Sea, western European Basin, and Newfoundland Basin, with additional contributions from chlorophytes and cyanobacteria at more southerly latitudes. Overall, these findings emphasize the need for longer-term investigations to further map the influence of phytoplankton taxa variability on aerosol composition and the broader impacts on aerosol–climate interactions.

Xu X., Luo W., Ren Z., Song X.

The detection, observation, recognition, and statistics of marine plankton are the basis of marine ecological research. In recent years, digital holography has been widely applied to plankton detection and recognition. However, the recording and reconstruction of digital holography require a strictly controlled laboratory environment and time-consuming iterative computation, respectively, which impede its application in marine plankton imaging. In this paper, an intelligent method designed with digital holography and deep learning algorithms is proposed to detect and recognize marine plankton (IDRMP). An accurate integrated A-Unet network is established under the principle of deep learning and trained by digital holograms recorded with publicly available plankton datasets. This method can complete the work of reconstructing and recognizing a variety of plankton organisms stably and efficiently by a single hologram, and a system interface of YOLOv5 that can realize the task of the end-to-end detection of plankton by a single frame is provided. The structural similarities of the images reconstructed by IDRMP are all higher than 0.97, and the average accuracy of the detection of four plankton species, namely, Appendicularian, Chaetognath, Echinoderm and Hydromedusae,, reaches 91.0% after using YOLOv5. In optical experiments, typical marine plankton collected from Weifang, China, are employed as samples. For randomly selected samples of Copepods, Tunicates and Polychaetes, the results are ideal and acceptable, and a batch detection function is developed for the learning of the system. Our test and experiment results demonstrate that this method is efficient and accurate for the detection and recognition of numerous plankton within a certain volume of space after they are recorded by digital holography.

Lu Y., Jin L., Chen H., Luo A., Ehrlich E., Li S., Wilkinson D.M., Sha Z., Yang J.

Holland M.M., Artigas L.F., Atkinson A., Best M., Bresnan E., Devlin M., Eerkes-Medrano D., Johansen M., Johns D.G., Machairopoulou M., Pitois S., Scott J., Schilder J., Stern R., Tait K., et. al.

Johnston D., Humphreys E., Davies J., Evans T., Howells R., Pearce-Higgins J.

Climate change is regarded as a major threat to seabird populations globally. While the impacts on certain species are well-studied, the majority remain understudied, which may limit our understanding of the key mechanisms linking climate change to population dynamics. This information is important to identify vulnerable species and inform potential conservation responses. To address this gap, we reviewed literature on the impacts of climate change on the demography of 25 seabird species breeding in the UK and Republic of Ireland from relevant studies conducted within the wider North-East Atlantic. We found regional and species-specific variations in research effort, with the North Sea being the most studied area. The most frequently studied species were common guillemot Uria aalge (n = 35), black-legged kittiwake Rissa tridactyla (n = 29), and European shag Gulosus aristotelis (n = 25). Breeding productivity and population abundance were the primary demographic parameters investigated. The North Atlantic Oscillation and sea surface temperature were commonly used to describe climate influences, often linked to bottom-up mechanisms affecting demography through changes in prey availability. Breeding productivity was the most monitored demographic rate across species; this may lead to important mechanisms affecting other demographic rates, such as survival, being overlooked. Regional and species-specific disparities in research could bias the identification of key mechanisms. Despite these uncertainties, current literature highlights the importance of climate impacts through the food chain and severe storm events affecting seabirds. In response, climate change adaptation should prioritise management of fish stocks near breeding colonies and coastal management to protect vulnerable colonies from storm events.

Börner G., Frelat R., Akimova A., van Damme C., Peck M., Moyano M.

Plankton dynamics in temperate ecosystems have mainly been studied during productive seasons, with comparatively less research conducted during the winter, particularly on microplankton. We implemented plankton sampling during a regular fishery cruise to investigate North Sea micro- and mesozooplankton community composition, abundance, and size structure (55-2000 µm) during autumn (Buchan/Banks area) and winter (Downs area) between 2013 and 2019. Samples were analyzed using image-based techniques. Community diversity (broad taxa) was relatively similar across years in both areas, with diatoms and tripos taxa sets dominating the microplankton community and gastropods and copepods dominating the mesozooplankton group. The average micro- to mesozooplankton ratio (in abundance) was 90:1 for Buchan/Banks, resulting in an average (±SD) normalized abundance size spectra (NASS) slope of -1.45 ± 0.18. For Downs, the micro- to mesozooplankton ratio was 235:1 with a steeper NASS slope of -1.67 ± 0.20 due to fewer large organisms. Interannual changes in the planktonic community for each area and their potential environmental drivers were examined using redundancy analysis (including taxonomy and size) and correlation analysis using NASS slopes (size only). Both approaches highlighted the importance of water mass properties (e.g. salinity, temperature, turbidity) in shaping plankton dynamics, although the amount of explained variance differed between approaches (11 vs. 46%). Our results contribute to a better understanding of standing stocks of plankton and their environmental drivers. Specifically, novel insights were gained into microplankton dynamics, which play an important role in supporting the growth and survival of winter-spawned fish larvae in the North Sea.

Pearce R. ., Selley H.

ABSTRACTFor the two European seahorse species, the short‐snouted Hippocampus hippocampus and the long‐snouted Hippocampus guttulatus, there are knowledge gaps that need further research. These research gaps become increasingly pressing under climate change, where uncertainty in how coastal ecosystems will change is compounded by uncertainty in how these seahorses will respond to changing pressures. Under climate change, these species could experience northward range shifts, expanding their range in United Kingdom (UK) coastal waters, potentially requiring the UK to take a leadership role in European seahorse conservation in the future. This review aims to synthesise current scientific research to provide an overview of how these seahorse species are likely to respond to climate change. Using the most recent Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (AR6), predictions for future change along with the likelihood and severity of seahorse species response are combined to provide a confidence ranking in the climate change risk for these species in the UK. When considering individual factors, such as sea surface temperature, these seahorse species show some resilience, but climate change is the cumulative impact of multiple stressors, which existing research has not been able to capture. Overall, further research on seahorse response to environmental variables is needed across Europe.

Kimmel D., Crouser D., Harpold C., Lamb J., Spear A.

ABSTRACTEcosystem‐based fisheries management (EBFM) remains an aspirational goal for management throughout the world. One of the primary limitations of EBFM is the incorporation of basic lower trophic level information, particularly for zooplankton, despite the importance of zooplankton to fish. The generation of zooplankton abundance estimates requires significant time and expertise to generate. The rapid zooplankton assessment (RZA) is introduced as a tool whereby nontaxonomic experts may produce rapid zooplankton counts shipboard that can be applied to management in near real time. Zooplankton are rapidly counted shipboard and placed into three broad groups of zooplankton relevant to higher trophic levels: large copepods (> 2 mm), small copepods (< 2 mm), and euphausiids. A Bayesian, hierarchical linear regression modeling approach was used to validate the relationship between RZA abundances and laboratory‐processed abundances to ensure the rapid method is a reliable indicator. Additional factors likely to impact the accuracy of the RZA abundance predictions were added to the initial regression model: RZA sorter, survey, season, and large marine ecosystem (Bering Sea, Chukchi/Beaufort Sea, and Gulf of Alaska). We tested models that included the random effect of sorter nested within survey, which improved fits for both large copepods (Bayes R2 = 0.80) and euphausiids (Bayes R2 = 0.84). These factors also improved the fit for small copepods when the fixed effect of season was also included (Bayes R2 = 0.65). Additional RZA data were used to predict laboratory‐processed abundances for each zooplankton category and the results were consistent with model training data: large copepods (Bayes R2 = 0.80), small copepods (Bayes R2 = 0.64), and euphausiids (Bayes R2 = 0.88). The Bayesian models were therefore able to predict laboratory‐processed abundances with an associated error when accounting for these fixed and random effects. To demonstrate the utility of zooplankton data in management, zooplankton time series from the Bering Sea shelf were shown to vary in relation to warm and cold conditions. This variability impacted commercially important fish, notably Walleye Pollock (Gadus chalcogrammus), and these time series were used by managers using a risk table approach. The RZA method provides a rapid zooplankton population estimation in near real time that can be applied to the management process quickly, thus helping to fill a gap in EBFM.

Holland M.M., Atkinson A., Best M., Bresnan E., Devlin M., Goberville E., Hélaouët P., Machairopoulou M., Faith M., Thompson M.S., McQuatters-Gollop A.

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 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.

Neven C.J., Giraldo C., Girardin R., Lefebvre A., Lefebvre S., Loots C., Meunier C.L., Marchal P.

Although zooplankton were extensively studied in the North Sea, knowledge about winter zooplankton assemblages is still scarce, despite potential influence of zooplankton overwintering stocks on seasonal plankton succession and productivity. Furthermore, several economically and ecologically important fish species reproduce during winter contributing to the zooplankton community as passive members (eggs) or predators (larvae). To elucidate on winter zooplankton distribution, abundance and composition in the Southern North Sea and Eastern English Channel, we defined assemblages based on mesozoo- and ichthyoplankton data sampled between January and February 2008 using fuzzy-clustering and indicator species. Mesozoo- and ichthyoplankton (eggs+larvae) were integrated in a common analysis by using a spatial grid adapted to the datasets and defined by means of a geostatistical method developed in agronomics. Potential environmental drivers of assemblage distribution were evaluated by means of GLMM and comparison with data from 2022 facilitated insight about the inter-annual representativeness of the assemblages. Five zooplankton assemblages were found varying with regard to total zooplankton abundance, dominant and indicator taxa. Spatial variability of abiotic (dissolved nutrients, salinity, depth, temperature, organic matter in suspension, chlorophyll a), biotic variables (phyto- and microplankton composition), water masses and fish spawning grounds were revealed as potential drivers of assemblage distribution. Assemblages off the Rhine-Scheldt estuary and in the German Bight harbored the biggest zooplankton overwintering stocks that might influence the grazing pressure on phytoplankton spring production. Assemblages off the Rhine-Scheldt estuary and covering the English Channel and the Southern Bight were found to be of high importance for herring and plaice larvae. Although further analyses suggested inter-annual representativeness of the assemblages found (2008 vs 2022), the assessment of further years would be necessary to account for potential inter-annual variability. Future studies could profit from the assessment of microzooplankton facilitating insight in fish larvae feeding potential and zooplankton overwintering strategies.

Kordubel K., Martínez-Rincón R.O., Baschek B., Boersma M., Hieronymi M., Johns D.G., Kirstein I.V., Voynova Y.G., Möller K.O.

To assess the spatiotemporal evolution of the heterotrophic dinoflagellate Noctiluca scintillans in the North Sea, the Helgoland Roads time series and Continuous Plankton Recorder survey were analysed using generalized additive models. Over the last decades, blooms of N. scintillans have occurred more frequently and intensively in many regions. This harmful algal bloom forming species can alter food webs, reduce ecosystem productivity, and lead to economic losses while causing lower aquacultural yields. After the 1990s, N. scintillans abundances have significantly increased by 1.65-fold and a significant prolongation of the bloom window was found (from 27.5 to 98 days in recent decades) off the island of Helgoland, Germany. Significant correlations were found between bloom initiation and nutrients, as well as light availability since these factors lead to increased prey availability. Highest abundances of N. scintillans were associated with water temperatures around 17 °C and wind speed below 6 ms

Tyldesley E., Banas N.S., Diack G., Kennedy R., Gillson J., Johns D.G., Bull C.

Abstract Return rates of Atlantic salmon (Salmo salar) from the sea to European rivers have declined in recent decades. The first months at sea are critical for growth and survival; recent evidence suggests that reduced food availability may be a contributory factor to the observed declines. Here, zooplankton abundance data are used to derive a measure of prey energy available to forage fish prey of salmon during early marine migration. This zooplankton prey energy has significantly and dramatically declined over much of the northeast Atlantic, and specifically within key salmon migration domains, over the past 60 years. Marine return rates from a set of southern European populations are found to exhibit clustering not entirely predictable from geographical proximity. Variability in grouped return rates from these populations is correlated with zooplankton energy on a range of scales, demonstrating the potential use of zooplankton energy as an indicator of salmon marine survival. Comparison with environmental variables derived from ocean model reanalysis data suggests zooplankton energy is regulated by a combination of climate change impacts on ecosystem productivity and multi-decadal variability in water mass influence along the migration routes.

Guzzi A., Schiaparelli S., Balan M., Grillo M.

The Mediterranean Sea, as one of the world’s most climate-sensitive regions, faces significant environmental changes due to rising temperatures. Zooplankton communities, particularly copepods, play a vital role in marine ecosystems, yet their distribution dynamics remain poorly understood, especially in the Ligurian Sea. Leveraging open-source software and environmental data, this study adapted a methodology to model copepod distributions from 1985 to 1986 in the Portofino Promontory ecosystem using the Random Forest machine learning algorithm to produce the first abundance and distribution maps of the area. Five copepod genera were studied across different trophic guilds, revealing habitat preferences and ecological fluctuations throughout the seasons. The assessment of model accuracy through symmetric mean absolute percentage error (sMAPE) highlighted the variability in copepod dynamics influenced by environmental factors. While certain genera exhibited higher predictive accuracy during specific seasons, others posed challenges due to ecological complexities. This study underscores the importance of species-specific responses and environmental variability in predictive modeling. Moreover, this study represents the first attempt to model copepod distribution in the Ligurian Sea, shedding light on their ecological niches and historical spatial dynamics. The study adhered to FAIR principles, repurposing historical data to generate three-dimensional predictive maps, enhancing our understanding of copepod biodiversity. Future studies will focus on developing abundance distribution models using machine learning and artificial intelligence to predict copepod standing crop in the Ligurian Sea with greater precision. This integrated approach advances knowledge of copepod ecology in the Mediterranean and sets a precedent for integrating historical data with contemporary methodologies to elucidate marine ecosystem dynamics.

Scherer C., Ludlow F., Matthews A., Hayes P., Klais R., Holm P.

The North Sea region boasted one of the world’s most important fisheries for many centuries. Climate directly and indirectly influences the development and survival of many important pelagic fish in the North Sea ecosystem. One indirect influence is the food availability in the form of phyto- and zooplankton abundance, which is strongly controlled by environmental factors. One of these environmental factors is local sea surface temperatures. A negative correlation between zooplankton abundance and sea surface temperature is well established for the epeiric sea on the European continental shelf. Continuous temporal observations of North Sea zooplankton production only exist since 1958. Therefore we developed a Historical Plankton Index (HPI) from 800 CE onwards to extend our record of temperature-driven zooplankton abundance in the North Sea over a multi-centennial time scale. For this we used the North Atlantic temperature reconstructions and associations between zooplankton abundance and contemporary sea surface temperatures established applying a General Additive Modelling (GAM) approach. We then examined the association between the HPI and historical landings from the Dutch commercial herring fishery in the 17th century to test the utility of our HPI. We examine the potential influence of food availability (in terms of zooplankton abundance) on the fishery, the evolution of which is often only considered in terms of human influences such as conflict, fishing gear and demand for fish as a commodity. We find that under certain conditions the HPI can explain 20% of the variability in Dutch herring landings. This highlights the importance of developing long-term and large-scale indices of natural marine ecosystem dynamics to understand the historical fortunes of the commercial fishing industry. The results are directly relevant to the United Nations’ sustainable development goal 14 – life below water.