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.

In this review, we briefly describe the two main techniques used to measure variable fluorescence in the aquatic environment, and show how the parameters derived from this technique can be used to estimate the rate of photosynthesis. The methods estimate the photochemical efficiency of photosystem II from ratios of fluorescence levels. Flashes of light that are transiently saturating for photochemistry (i.e. they are sufficiently bright to close all PSII reaction centres) are used to obtain the maximum fluorescence level. The type of saturating flash differs between methods. In one approach, single turnover (ST) flashes are applied. This allows only one charge separation during the flash and reduces only the primary acceptor of PS II, raising fluorescence to a level F_m(ST) . In a second approach the flashes are multiple turnover (MT), which allow repeated charge separation processes until all electron acceptors of PS II are reduced. A relaxation of quenching is induced by the longer flash, and this raises the maximum fluorescence to a higher level, F_m(MT) Application of the different approaches to an algal sample will result in differing F_m values and, as a result, different values for the photochemical efficiency of PS II, with the MT method giving higher values than ST. Several designs of equipment, based on MT or ST techniques, are available for use with phytoplankton or benthic algae. Both techniques measure variable fluorescence, but there are a number of important differences in the methods used to calculate photosynthetic rates. In our view, this necessitates the use of a different terminology in order to avoid confusion, until the underlying physiological differences are resolved. An example is given showing that combining terminology from the different approaches will result in calculation of erroneous photosynthetic electron transport rates.

Marine environmental monitoring has tended to focus on site-specific methods of investigation. These traditional methods have low spatial and temporal resolution and are relatively labour intensive per unit area/time that they cover. To implement the Marine Strategy Framework Directive (MSFD), European Member States are required to improve marine monitoring and design monitoring networks. This can be achieved by developing and testing innovative and cost-effective monitoring systems, as well as indicators of environmental status. Here, we present several recently developed methodologies and technologies to improve marine biodiversity indicators and monitoring methods. The innovative tools are discussed concerning the technologies presently utilized as well as the advantages and disadvantages of their use in routine monitoring. In particular, the present analysis focuses on: (i) molecular approaches, including microarray, Real Time quantitative PCR (qPCR), and metagenetic (metabarcoding) tools; (ii) optical (remote) sensing and acoustic methods; and (iii) in situ monitoring instruments. We also discuss their applications in marine monitoring within the MSFD through the analysis of case studies in order to evaluate their potential utilization in future routine marine monitoring. We show that these recently-developed technologies can present clear advantages in accuracy, efficiency and cost.

Although the terms 'health' and 'healthy' are often applied to marine ecosystems and communicate information about holistic condition (e.g. as required by the Ecosystem Approach), their meaning is unclear. Ecosystems have been understood in various ways, from non-interacting populations of species to complex integrated systems. Health has been seen as a metaphor, an indicator that aggregates over system components, or a non-localized emergent system property. After a review, we define good ecosystem health as: 'the condition of a system that is self-maintaining, vigorous, resilient to externally imposed pressures, and able to sustain services to humans. It contains healthy organisms and populations, and adequate functional diversity and functional response diversity. All expected trophic levels are present and well interconnected, and there is good spatial connectivity amongst subsystems.' We equate this condition with good ecological or environmental status, e.g. as referred to by recent EU Directives. Resilience is central to health, but difficult to measure directly. Ecosystems under anthropogenic pressure are at risk of losing resilience, and thus of suffering regime shifts and loss of services. For monitoring whole ecosystems, we propose an approach based on 'trajectories in ecosystem state space', illustrated with time-series from the northwestern North Sea. Change is visualized as Euclidian distance from an arbitrary reference state. Variability about a trend in distance is used as a proxy for inverse resilience. We identify the need for institutional support for long time-series to underpin this approach, and for research to establish state space co-ordinates for systems in good health. Changes in the northern North Sea, 1958-2008, plotted in a state space defined by the breeding success of kittiwakes, abundance of copepods Calanus spp., and simulated annual primary production.© Inter-Research 2013. www.int-res.com

We show how theoretical developments in macroecology, life-history theory and food-web ecology can be combined to formulate a simple model for predicting the potential biomass, production, size and trophic structure of consumer communities. The strength of our approach is that it uses remote sensing data to predict properties of consumer communities in environments that are challenging and expensive to sample directly. An application of the model to the marine environment on a global scale, using primary production and temperature estimates from satellite remote sensing as inputs, suggests that the global biomass of marine animals more than 10 ⁻⁵ g wet weight is 2.62×10 ⁹ t (=8.16 g m ⁻² ocean) and production is 1.00×10 ¹⁰ t yr ⁻¹ (31.15 g m ⁻² yr ⁻¹ ). Based on the life-history theory, we propose and apply an approximation for distinguishing the relative contributions of different animal groups. Fish biomass and production, for example, are estimated as 8.99×10 ⁸ t (2.80 g m ⁻² ) and 7.91×10 ⁸ t yr ⁻¹ (2.46 g m ⁻² yr ⁻¹ ), respectively, and 50% of fish biomass is shown to occur in 17% of the total ocean area (8.22 g m ⁻² ). The analyses show that emerging ecological theory can be synthesized to set baselines for assessing human and climate impacts on global scales.

Decreases in the concentration of ozone in the stratosphere are predicted to result in more biologically damaging ultraviolet-B radiation (UVBR) reaching the Earth's surface in the near future. The consequences for plant life of this small change in the solar spectrum are currently uncertain; this is particularly true for aquatic macrophytic algae. The aim of this review is to summarize the current knowledge of UVBR effects on macrophytes, and to highlight areas for future research. An overview of published underwater UVBR measurements shows that penetration of this waveband is low in the coastal waters where most macroalgae are found. Knowledge of UVBR targets in macroalgae is poor, and biological weighting functions have yet to be established. Studies of higher plants and phytoplankton are used to illustrate the many possible targets and effects of UVBR. The role of photosynthetically active radiation in causing dynamic and chronic photoinhibition in macroalgae and the interactions of PAR with UVR are examined in detail. These interactions are central to interpretation of field measurements of photoinhibition under natural solar radiation conditions. Potential strategies and mechanisms for repair of UVBR damage are discussed. Before the long-term effects of UVBR on macroalgal production and community structure can be determined, a greater knowledge of the specific targets of UVBR in macrophytes and the mechanisms of protection and repair must be determined. The ability of macrophytes to acclimate to higher UVBR and the interaction of UVBR with other stresses, such as high PAR, temperature and desiccation, must be assessed. Studies are needed which encompass effects on all stages of the macrophyte life cycle, from recruitment to maturity.