Phytoplankton Community Integrity Index (PCII) - A potential supplementary tool for evaluating nutrient enrichment status of Hong Kong marine waters.

Diagnosis of eutrophication requires evidence of disturbance to the balance of organisms. We describe a tool, the Plankton Community Integrity Index (PCII), derived from the Plankton Index (PI) for tracking change in the seasonal patterns of abundance of diatom and dinoflagellate lifeforms when plotted in state space. The tool uses a nutrient-minimum reference period to interpret PCII values as status indicators, with values close to 1 indicating "High" status and 0.6 a Biological Water Quality Criterion (BioWQC) target set at the "Fair"/"Good" status boundary. It has been applied to Hong Kong marine waters, using data from monthly samples from 1995 through 2021. A preliminary analysis, required for the PI method, confirmed monsoonal seasonality in the diatom lifeform. In 5 of the 9 water bodies examined, PCII time series correlated with those of Total Inorganic Nitrogen (TIN). Since 2020, all Water Control Zones met the operationally defined BioWQC target.

Major declines in NE Atlantic plankton contrast with more stable populations in the rapidly warming North Sea.

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.

Planning and licensing for marine aquaculture.

Marine aquaculture has the potential to increase its contribution to the global food system and provide valuable ecosystem services, but appropriate planning, licensing and regulation systems must be in place to enable sustainable development. At present, approaches vary considerably throughout the world, and several national and regional investigations have highlighted the need for reforms if marine aquaculture is to fulfil its potential. This article aims to map and evaluate the challenges of planning and licensing for growth of sustainable marine aquaculture. Despite the range of species, production systems and circumstances, this study found a number of common themes in the literature; complicated and fragmented approaches to planning and licensing, property rights and the licence to operate, competition for space and marine spatial planning, emerging species and diversifying marine aquaculture production (seaweed production, Integrated Multi-Trophic Aquaculture [IMTA], nutrient and carbon offsetting with aquaculture, offshore aquaculture and co-location and multiuse platforms), and the need to address knowledge gaps and use of decision-support tools. Planning and licensing can be highly complicated, so the UK is used as a case study to show more detailed examples that highlight the range of challenges and uncertainty that industry, regulators and policymakers face across interacting jurisdictions. There are many complexities, but this study shows that many countries have undergone, or are undergoing, similar challenges, suggesting that lessons can be learned by sharing knowledge and experiences, even across different species and production systems, rather than having a more insular focus.

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

Increasing direct human pressures on the marine environment, coupled with climate-driven changes, is a concern to marine ecosystems globally. This requires the development and monitoring of ecosystem indicators for effective management and adaptation planning. Plankton lifeforms (broad functional groups) are sensitive indicators of marine environmental change and can provide a simplified view of plankton biodiversity, building an understanding of change in lower trophic levels. Here, we visualize regional-scale multi-decadal trends in six key plankton lifeforms as well as their correlative relationships with sea surface temperature (SST). For the first time, we collate trends across multiple disparate surveys, comparing the spatially and temporally extensive Continuous Plankton Recorder (CPR) survey (offshore) with multiple long-term fixed station-based time-series (inshore) from around the UK coastline. These analyses of plankton lifeforms showed profound long-term changes, which were coherent across large spatial scales. For example, 'diatom' and 'meroplankton' lifeforms showed strong alignment between surveys and coherent regional-scale trends, with the 1998-2017 decadal average abundance of meroplankton being 2.3 times that of 1958-1967 for CPR samples in the North Sea. This major, shelf-wide increase in meroplankton correlated with increasing SSTs, and contrasted with a general decrease in holoplankton (dominated by small copepods), indicating a changing balance of benthic and pelagic fauna. Likewise, inshore-offshore gradients in dinoflagellate trends, with contemporary increases inshore contrasting with multi-decadal decreases offshore (approx. 75% lower decadal mean abundance), urgently require the identification of causal mechanisms. Our lifeform approach allows the collation of many different data types and time-series across the NW European shelf, providing a crucial evidence base for informing ecosystem-based management, and the development of regional adaptation plans.

The interplay between economics, legislative power and social influence examined through a social-ecological framework for marine ecosystems services.

In the last 15 years, conservation has shifted increasingly towards perspectives based on the instrumental value of nature, where what counts is what provides benefits to humans. The ecosystem services framework embraces this vision of nature through monetary valuation of the environment to correct market failures and government distortions that hinder efficient allocation of public goods, including goods and services provided by biodiversity and ecosystems. The popularity of this approach is reflected in different countries legislation; for instance, US, EU and UK have introduced economic criteria for comparing costs and benefits of environmental policies in protecting ecosystem services. From an operational perspective, the ecosystem services framework requires ecologists to estimate how the supply of services is affected by changes in the functionality and/or the extent of ecosystems; and economists to identify how changes in the supply affect the flow of direct and indirect benefits to people. However, this approach may be simplistic when faced with the complexity of social-ecological systems. We investigated this for three different marine services: assimilative capacity of waste, coastal defense and renewable energy. We find that economic valuation could provide efficient and fair allocations in the case of assimilative capacity, but leads to social clashes between outputs generated by cost benefit analysis and citizens' expectation in the case of coastal defense. In the case of renewable energy, controversies can be generated by regulatory mechanisms that are not necessarily aligned with the interests of industry or important social groups. We conclude that there is a need to integrate perspectives arising from utilitarian allocation of resources with those involving legislation and communal values in order to reconcile conflicting interests and better sustain marine social-ecological systems.

A change in phytoplankton community index with water quality improvement in Tolo Harbour, Hong Kong.

Water quality in Tolo Harbour and Channel (Tolo) has been improved since 1998 after the diversion of sewage effluent. However, it remains poorly understood how nutrient loading reduction has impacted the phytoplankton community. To evaluate this, we applied a Phytoplankton Community Index PI(mp) to the 23-year data (1991-2013) at inner (TM4) and outer (TM8) sites in Tolo, with the former being more eutrophic than the latter. The results show that 1) the phytoplankton community changed with time after sewage diversion; 2) "diatoms and dinoflagellates" were better indicators of nutrient impact than "autotrophic/mixotrophic and heterotrophic dinoflagellates"; 3) the rate of recovery differed between the two stations, but both reached a similar state at a similar time; 4) seasonality of the phytoplankton community showed greater disturbance in spring than in other seasons. Our findings indicate that the nutrient reduction in the Tolo resulted in a positive change in the phytoplankton community.

Sediment and water nutrients and microalgae in a coastal shallow lagoon, Ria Formosa (Portugal): implications for the Water Framework Directive.

Coastal shallow lagoons are considered to be highly important systems, which have specific biogeochemical cycles and characteristics. The assessment of sediment-water interfaces is essential to understand nutrient dynamics and to evaluate the vulnerability to eutrophication, especially in regions of restricted water exchange (RRE), such as the Ria Formosa, which have natural conditions for the accumulation of nutrients. Water samples were collected during the years of 2006 and 2007-08 for nutrients, chlorophyll a and dissolved oxygen. Sediment samples were also collected for pore water nutrients and microphytobenthic chlorophyll a. Measurements of temperature, salinity and photosynthetic active radiation were also taken. The lagoon salinity is affected by occasional strong rainfall events. From comparison with previous work, a decrease in the nitrogen concentration in the water column can be observed, which may indicate an improvement of the water quality. Pore water nutrient concentrations were significantly larger than in the water column. Sediment-water exchanges are considered to be the most important processes in nutrient dynamics of the lagoon. Benthic microalgal biomass was also large compared with that of the phytoplankton. It represents about 99% of the total microalgal chlorophyll biomass of the system. The lagoon also contains (discontinuous) meadows of intertidal seagrass, but we did not study these. Due to the importance of sediments, the standard monitoring plans required by the Water Framework Directive may fail to track changes in the nutrient conditions and the microalgal responses to them.

Defining and detecting undesirable disturbance in the context of marine eutrophication.

An understanding of undesirable disturbance to the balance of organisms is needed to diagnose marine eutrophication as defined by EU Directives and OSPAR. This review summarizes the findings of the UK Defra-funded Undesirable Disturbance Study Team, which concluded that 'an undesirable disturbance is a perturbation of a marine ecosystem that appreciably degrades the health or threatens the sustainable human use of that ecosystem'. A methodology is proposed for detecting disturbance of temperate salt-water communities dominated by phytoplanktonic or phytobenthic primary producers. It relies on monitoring indicators of ecosystem structure and vigour, which are components of health. Undesirable disturbance can be diagnosed by accumulating evidence of ecohydrodynamic type-specific changes in: (i) bulk indicators; (ii) frequency statistics; (iii) flux measurements; (iv) structural indicators; and (v) indicator species. These are exemplified by (i) chlorophyll, transparency, dissolved oxygen, and opportunistic seaweed cover; (ii) HABs frequency; (iii) primary production; (iv) benthic and planktonic 'trophic indices'; (v) seagrasses and Nephrops norvegicus. Ecological Quality Objectives are proposed for some of these. Linking the diagnosis to eutrophication requires correlation of changes with nutrient enrichment. The methodology, which requires the development of a plankton community index and emphasizes the importance of primary production as an indicator of vigour, can be harmonized with the EU Water Framework Directive and OSPAR's Strategy to Combat Eutrophication.

Carbon and nitrogen fluxes across the Hebridean shelf break, estimated by a 2D coupled physical-microbiological model.

A two-dimensional coupled physical-biological model is described and used to compute the annual cycle of primary production across the Hebridean shelf and slope based on information collected during the Land Ocean Interaction Study (LOIS), with the focus on data for 1995. Calculations of modelled carbon and nitrate fluxes indicate an annual on-shelf near-surface flux of nitrate of 65 kmol N m(-1) year(-1) at the top of the slope (140 m deep) and an off-shelf near-bottom carbon flux of 23 kmol C m(-1) year(-1). Further down the slope (at 300 m deep) the on-shelf nitrate flux increased to 126 kmol N m(-1) year(-1) and the off-shelf carbon flux increased to 41 kmol C m(-1) year(-1). Carbon deposition to the sea floor was less than 0.4 mol C m(-2) year(-1) on the upper slope and 1.1 mol C m(-2) year(-1) lower down the slope, values which are four-fold lower than those inferred from benthic oxygen demand measurements made during the Shelf Edge Study but of similar magnitude to observations made during OMEX I.