Eutrophication Of Coastal Waters Research Articles

Methane production in oxic seawater of the western North Pacific and its marginal seas

AbstractThe oceans are natural sources of atmospheric methane (CH4), but the origin of excess CH4 at the surface remains enigmatic. Incubation experiments were conducted in the western North Pacific (WNP) and its marginal seas (i.e., Yellow Sea and South China Sea [SCS]) to identify the degradation of methylphosphonate (MPn) to CH4 in the oceans and the microbes associated with MPn‐driven CH4 production. In the coastal seawater of the Yellow Sea, CH4 was observed to accumulate after MPn enrichment with a high MPn to CH4 conversion efficiency (approximately 60%). Dissolved inorganic phosphorus (Pi) did not effectively restrict the microbial utilization of MPn in the eutrophic coastal waters. The results of 16S rRNA gene sequencing showed that Vibrio spp. were the dominant bacteria in the MPn‐amended treatments. Moreover, several Vibrio isolates isolated from the coastal waters were found to produce CH4 while growing in culture using MPn as the sole P source, thereby indicating that Vibrio spp. might be the major contributors to MPn‐dependent CH4 production. In oligotrophic areas, such as the SCS and WNP, CH4 production from MPn metabolism was also observed in the surface seawater. In contrast to coastal waters, this pathway in oligotrophic areas is regulated by dissolved Pi availability. This work confirms that aerobic CH4 formation from MPn degradation can occur both in eutrophic coastal waters and oligotrophic oceans driven by MPn‐utilizing microorganisms (especially heterotrophic bacteria), which may have a significant impact on our understanding of the CH4 and P cycles in global oceans.

Getting the science right to protect and restore our environment. A critique of Lapointe et al. (2019) Nitrogen enrichment, altered stoichiometry, and coral reef decline at Looe Key, Florida Keys, USA: a 3-decade study

Eutrophication of coastal ecosystems and decline of essential benthic ecosystems are growing concerns globally. Understanding the drivers associated with a response of an indicator species at an ecosystem or even regional-scale hinges on a robust evaluation of data that spans both space and time. Consistent data, suitable and methodical data-handling procedures, appropriate statistical evaluation and logical assessment of hypotheses are essential. Lapointe et al. (Mar Biol 166:108, 2019) suggest that decline of stony coral at Looe Key reef is attributed to local and regional (i.e., discharge > 200 km away) nutrient discharges causing eutrophication of coastal waters and the degradation of essential habitat. Furthermore, Lapointe et al. (Mar Biol 166:108, 2019) posit that the restored freshwater flows to the Everglades ecosystem is a causative agent for the observed coral decline observed at Looe Key Reef. While the decline in coral coverage is alarming, rigorous statistical analysis is needed to attribute a true cause-and-effect relationship. This commentary discusses data handling techniques, the application of statistical methods, interoperability of data and evaluation of hypotheses presented by Lapointe et al. (Mar Biol 166:108, 2019) specific to Looe Key reef within the Florida Key Marine Sanctuary. This commentary is not merely a critique of the statistics used by the authors but rather the inappropriate statistical methods utilized and how it affects the acceptance or rejection of the authors’ hypotheses and the overall conclusions drawn.

A Dynamic Energy Budget model for the macroalga Ulva lactuca

Macroalgal blooms in eutrophic coastal waters around the globe constitute a rising issue for ecosystems and economic activities. Sometimes leading to anoxic events, a better understanding of its growth dynamics is necessary to develop mitigation strategies and inform policies on nutrient runoff management. The development of a Dynamic Energy Budget (DEB) model for the sea lettuce, Ulva lactuca, provides a generic mechanistic description of energy and matter fluxes within the macroalgae and between macroalgae and the environment. Forcing variables consist of seawater temperature, light intensity, and seawater concentrations of dissolved carbon and nitrogen. The model includes a self-shading module for light reduction under heavy biomass and simulation outputs consist of (but are not limited to) total algae biomass, nutrient uptake (carbon and nitrogen), photosynthetic rate, and state of nutrient reserve. Model parameters were estimated using data-sets from the literature and laboratory experiments, then validated using an independent field study in two estuaries with contrasting nutrient loads that feed into Malpeque Bay, PEI (Canada). The validation step yielded accurate temporal predictions of sea lettuce biomass in both of these estuaries. These results indicate that the present mechanistic modelling approach for predicting sea lettuce dynamics captures salient patterns along a spectrum of nutrient loading and could therefore be of use for managing across diverse ecological conditions, which is particularly relevant for a widespread species like Ulva lactuca.

Impact of eelgrass bed recovery and expansion on phytoplankton growth through nutrient competition

Eelgrass beds are highly productive and support diverse faunal assemblages; they also take in nutrients from the water and prevent excessive phytoplankton growth in eutrophic coastal waters through the reduction of available nutrients. Despite its importance, the global distribution of eelgrass has declined worldwide. In eutrophic areas with high chlorophyll a (Chl.a) concentrations, natural recovery of eelgrass beds after eutrophication is possible. To facilitate this, sufficient water clarity can be reached after a large enough decrease in phytoplankton concentration. In this study, we proposed a novel indicator for the maximum possible Secchi depth (MPSD), defined as the Secchi depth when the Chl.a concentration is equal to a reference Chl.a concentration. We applied the MPSD to evaluate water clarity improvements through the reduction of terrigenous anthropogenic nutrient loading. We found that phytoplankton did not control water clarity in the study area, which was instead controlled by background factors. Therefore, improvements in water clarity would not be expected after reducing terrigenous anthropogenic nutrient loading. The habitat of Zostera marina is determined by light availability, so we investigated a potential area with ≥20% surface irradiance and Z. marina existed in 27% of it (100 of 373 ha). The maximum further recovery of eelgrass by Secchi depth improvements to the MPSD was estimated at 36 ha. The impact of eelgrass recovery and expansion on phytoplankton growth from May to September was evaluated by a mathematical model under two scenarios: the current eelgrass distribution (100 ha) and potential maximum eelgrass distribution (373 ha). A Chl.a decrease of 1.0–3.0 μg l−1 from 4.0 to 7.0 μg l−1 was achieved in an area from May to July, and the improvement decreased with time. These evaluation methods and findings could help us gain a better understanding of the nutrient management in seagrass-vegetated semi-enclosed seas subjected to anthropogenic nutrient input.

ОЦЕНКА ЭКОЛОГИЧЕСКОГО СОСТОЯНИЯ ПРИБРЕЖНЫХ ВОД ЧЕРНОГО МОРЯ МЕТОДАМИ БИОИНДИКАЦИИ

Introduction. Using bioindication methods, the authors assessed the environmental state of water at the place where the Hadzhiyska River flows into the Black Sea (Slanchev Bryag / Sunny Beach resort, Bulgaria). Methods. The studies were carried out in the summer seasons of 2017–2019 during sea water “blooming”. The quality of river water was assessed by the state of the community of zoobenthic organisms using the Trent biotic index originally developed by Woodiwiss and the Mayer index, and the state of the coastal marine ecosystem was assessed by the species composition of the Black Sea macroalgae. Results. The waters at the mouth of the Hadzhiyska River can be classified as “polluted” and represent the main local source of biogenic elements entering the coastal sea waters. In the marine macrophytobenthos, representatives of green, brown and red algae were identified, including two species listed in the Red Book of the Black Sea — Cystoseira barbata and Zostera marina. The authors noted a displacement of native species — representatives of Cystoseira and Zostera genera — due to an increase in the number of associated algae from Ceramium, Cladophora and Ulva genera, which confirms organic pollution and eutrophication in coastal waters. The taxonomic structure of the macrophytes allows for the conclusion that the environmental state of the marine ecosystem in the area is satisfactory. The authors also provide a rationale for the use of benthic organisms in the express diagnostics of water environment quality in resort areas.

Viral Regulation on Bacterial Community Impacted by Lysis-Lysogeny Switch: A Microcosm Experiment in Eutrophic Coastal Waters.

Marine viruses are major drivers of global biogeochemical cycles and energy fluxes, yet the importance of viral impacts on the succession and diversity of the bacterial community remains largely unexplored. Here, we explored viral life strategy and its potential effect on the bacterial community by experimental incubations of eutrophic coastal waters under lysogen-induced and non-induced treatments. The lysogen-induced treatment showed relatively constant viral and bacterial abundances, lytic and lysogenic viral production throughout the experimental period, together with the progressive declines in not only the relative abundances for SAR11, Rhodobacteraceae, Alteromonadaceae, and SAR86 but the bacterial community diversity. Conversely, the non-induced treatment observed the marked variation in the abundances of viruses, bacteria and cells with high nucleic acid content over the time course of incubation, which was congruent with the drastic shift in lytic and lysogenic viral production as well as the succession of bacterial community. Our results supported the hypotheses that a high level of lysogeny would occur with the increasing density of bacteria with rapid growth rate, which may contribute to a relatively lower host community diversity, whereas the lysogeny to lysis switching would fuel growth opportunities for less-active or initially rare bacterial taxa and generate a more diverse bacterial community. Altogether, the present study underscored the crucial regulatory role of the viral lysis-lysogeny pattern in bacterial community dynamics, composition and diversity, highlighting the viral impact on the microbial food web and biogeochemical processes.

Nitrogen enrichment, altered stoichiometry, and coral reef decline at Looe Key, Florida Keys, USA: a 3-decade study

Increased loadings of nitrogen (N) from fertilizers, top soil, sewage, and atmospheric deposition are important drivers of eutrophication in coastal waters globally. Monitoring seawater and macroalgae can reveal long-term changes in N and phosphorus (P) availability and N:P stoichiometry that are critical to understanding the global crisis of coral reef decline. Analysis of a unique 3-decade data set for Looe Key reef, located offshore the lower Florida Keys, showed increased dissolved inorganic nitrogen (DIN), chlorophyll a, DIN:soluble reactive phosphorus (SRP) ratios, as well as higher tissue C:P and N:P ratios in macroalgae during the early 1990s. These data, combined with remote sensing and nutrient monitoring between the Everglades and Looe Key, indicated that the significant DIN enrichment between 1991 and 1995 at Looe Key coincided with increased Everglades runoff, which drains agricultural and urban areas extending north to Orlando, Florida. This resulted in increased P limitation of reef primary producers that can cause metabolic stress in stony corals. Outbreaks of stony coral disease, bleaching, and mortality between 1995 and 2000 followed DIN enrichment, algal blooms, and increased DIN:SRP ratios, suggesting that eutrophication interacted with other factors causing coral reef decline at Looe Key. Although water temperatures at Looe Key exceeded the 30.5 °C bleaching threshold repeatedly over the 3-decade study, the three mass bleaching events occurred only when DIN:SRP ratios increased following heavy rainfall and increased Everglades runoff. These results suggest that Everglades discharges, in conjunction with local nutrient sources, contributed to DIN enrichment, eutrophication, and increased N:P ratios at Looe Key, exacerbating P limitation, coral stress and decline. Improved management of water quality at the local and regional levels could moderate N inputs and maintain more balanced N:P stoichiometry, thereby reducing the risk of coral bleaching, disease, and mortality under the current level of temperature stress.

Targeted set-aside: Benefits from reduced nitrogen loading in Danish aquatic environments

Nitrogen (N) leaching from agricultural areas in the form of nitrate (NO3−) is one of the most dominant sources of eutrophication in coastal waters. This environmental pressure is expected to intensify with the predicted increase in food demand, highlighting the need for developing novel ways to reduce N loads from agriculture. This may be achieved by exploiting the spatial variation in N removal through denitrification in groundwater and surface water systems. Thus, agricultural intensification should occur in areas characterized by high N removal potential, whereas effective N-reduction measures such as setting aside agricultural land (set-aside) should be targeted towards areas characterized by low N removal. Simultaneously, setting aside agricultural land can potentially strengthen local nature areas. To reach the water quality targets defined by the EU Water Framework Directive (WFD), the Danish region has defined individual coastal N reduction goals for each of the existing Danish water catchments. With set-aside as an effective N-reduction measure the study aims were to: 1) evaluate the effect of targeting areas to set aside versus using no targeting and 2) evaluate whether different prioritization for targeting set-aside areas enhances multi-functionality of the landscape, while efficiently achieving the required N load reduction. Areas were selected according to three priority values: 1) high contribution to coastal N loads, 2) high nature value, and 3) low agricultural land rent. The combination of these three values per area defined three multifunctional scenarios: (GreenEnvi - N load dominates, TerreEco - nature dominates, AgroEcon - land rent dominates). Results indicate, that targeting areas with high N loads for set-aside is more beneficial (effective) for achieving multiple goals than blanket policies for entire countries (no targeting). Targeting requires only 23% of agricultural land compared to 35% when not targeting, leaving more land available for satisfying food demand. Moreover, multiple benefits can be achieved in surrounding environments by increasing set-aside to 25% according to the GreenEnvi scenario. The GreenEnvi scenario is also cheaper compared to targeting for only land rent.

Periphyton characteristics influence the growth and survival of Holothuria scabra early juveniles in an ocean nursery system

Floating hapas (fine mesh net enclosures) are a cost-effective ocean nursery system to culture post-metamorphic Holothuria scabra to release size. The growth of periphyton biofilm on hapas is a natural food source for early juveniles. This study investigated the effects of periphyton quality (i.e. chlorophyll-a, phaeopigment, total biomass, autotrophic index or AI), water quality (nutrients, chlorophyll-a) and environmental parameters (temperature, rainfall) on the temporal variation in the growth and survival of early juvenile (~3 mm) H. scabra reared in floating hapas. Five trials where the juveniles were reared for 60 days each in the eutrophic coastal waters of Bolinao, the Philippines were conducted during different months over 2 years. Significant differences in the growth and survival of juveniles among trials were found. Absolute growth rates (AGR) ranged widely (0.01–0.09 g/day). Trials with high AGR of juveniles (0.07–0.09 g/day) during the first 30 days of rearing had significantly higher chlorophyll-a (chl-a) in biofilm (15.9–27.5 mg/m2) and lower AI. Conversely, during the subsequent 30 days, trials with high AGR of juveniles (0.06–0.11 g/day) had significantly lower chl-a and higher AI. Multivariate analyses showed that chl-a in biofilm, AI and nutrients in the water column are good indicators of periphyton quality and juvenile growth rates in floating hapas. Further, this study validates the expansion of the feeding mode of juveniles from primarily grazing on microalgae, to feeding on detritus and heterotrophs as they grow. These results are important in optimizing ocean nursery systems.

Connectivity and Nitrate Uptake Potential of Intermittent Streams in the Northeast USA

Non-perennial streams dominate the extent of stream networks worldwide. Intermittent streams can provide ecosystem services to the entire network – including nitrate uptake to alleviate eutrophication of coastal waters – and are threatened by lack of legal protection. We examined 12 intermittent streams in the temperate, humid climate of the Northeast USA. Over three years of monitoring, continuous flow was observed a median of 277 d yr-1, with no-flow conditions from early summer into fall. Estimated median discharge was 2.9 L s-1 or 0.36 mm d-1. All intermittent streams originated from source wetlands (median area: 0.27 ha) and the median length of the intermittent stream from the source wetland to the downstream perennial stream was 344 m. Through regional geospatial analysis with high resolution orthophotography, we estimated that widely available, “high resolution” (1:24,000) hydrography databases (e.g., NHDPlus HR) only displayed 43% of the total number of intermittent streams. Whole-stream gross nitrate-N uptake rates were estimated at six intermittent streams during continuous flow conditions using pulse additions of nitrate and a conservative tracer. These rates displayed high temporal variability (range: no detect to over 6000 mg N m-1 d-1); hot moments were noted in nine of the 65 pulse additions. Whole-stream gross nitrate-N uptake rates were significantly inversely related to discharge, with no measurable rates above 7 L s-1. Temperature was significantly positively correlated with whole-stream gross nitrate-N uptake rates, with more hot moments in the spring. Microbial assays demonstrated that nitrate cycling in intermittent streams are consistent with results from low order, perennial forested streams and highlighted the importance of debris dams and pools – potential locations for transient storage. Our assessment suggests that intermittent streams in our region may annually contribute 24-47% of the flow to perennial streams and potentially remove 4.1 to 80.4 kg nitrate-N km-2 annually. If development in these areas continues, perennial streams are in danger of losing a portion of their headwaters and potential nitrate uptake areas may become nitrate sources to downstream areas. These results argue to manage fluvial systems with a holistic approach that couples intermittent and perennial components.

The considerable environmental benefits of seaweed aquaculture in China

Coastal water eutrophication and resource depletion have become serious issues in many coastal regions of the world. Seaweed aquaculture in Chinese coastal waters is a very important industry. This work assessed the major environmental benefits of seaweed cultivation, mapped the spatial distributions of various species and analyzed their environmental impacts during 2015 in China. This study found that seaweed aquaculture had brought in considerable environmental benefits, including the removal of about 75,563 t of nitrogen and 9592 t of phosphate from coastal waters, the sequestration of about 539,555 t of carbon, the absorption of 1,980,167 t of CO2, the release of 1,440,612 t of O2 into coastal waters, and the production of 5809 t of Iodine. In addition, seaweed cultivation saved approximately 29,313 t of chemical fertilizers, 1873 t of pesticide and 62,492 ha of farmland compared with terrestrial vegetable cultivation. These results demonstrate that Chinese seaweed aquaculture has turned the pollutants that cause eutrophication into nutrients, which generates considerable environmental benefits as well as socio-economic values. However, seaweed species, as well as coastal water qualities, vary by regions, spatial management of seaweed farms related to the coastal water quality is necessary. In the eutrophic coastal waters, more seaweed species that are highly capable of removing nitrogen and phosphate should be cultivated. Besides, the potentially negative effects of seaweed farming should also be considered before performing spatial management to ensure the healthy development of seaweed industry. As Chinese seaweed production continues to boom, it is a unique opportunity to strengthen the seaweed industry and to reach a win–win situation that both gains considerable environmental benefits and generates substantial socio-economic returns. This is also a promising way for other coastal developing nations/regions to follow.

Spatial and temporal variations of tintinnids (Ciliata: Protozoa) in the Bay of Mersin, Northeastern Mediterranean Sea

Seasonal variations in species composition and abundance of tintinnids were investigated in the eutrophic coastal and offshore waters of Mersin Bay. Twelve sampling cruises were performed from September 2008 to February 2011. A total of 85 tintinnid taxa were identified. Among the recorded genera, agglutinated Tintinnopsis had the largest number of species (12 species), followed by hyaline loricated Eutintinnius (9 species), and Proplectella (7 species). Stenosemella ventricosa, Tintinnopsis beroidea, T. compressa, Favella azorica, and Helicostemella subulata were the dominant species during the study period. There were clear seasonal variations in species composition and abundance of tintinnids. The highest number of tintinnid species occurred in January 2009 and November 2010 in the entire study area, while the lowest species number occurred in March 2009. Morever, species numbers were higher in offshore stations than coastal stations. Some species were present in the coastal area of the bay, and other species were present offshore. The highest tintinnid abundance values were found in September 2008 (820 ind L-1) and August 2009 (749 ind L-1) at coastal stations. The high abundance values in the coastal stations indicates that an increase of tintinnids is closely related to trophic status of the marine environment. In connection with these results, correlation analysis revealed that chlorophyll-a had an important effect on tintinnid abundance. Tintinnid communities may be used as a potential bio-indicator for assessing the trophic state of the coastal seas and bays.

Barriers and Bridges in Abating Coastal Eutrophication

Over the past 30 years concerted campaigns have been undertaken to reverse nutrient-driven eutrophication in coastal waters in Europe, North America, Asia and Australia. Typically, eutrophication abatement has proven a more recalcitrant challenge than anticipated, with ecosystem improvements only recently beginning to emerge or falling short of goals. Reduction in nutrient loads has come mainly from advanced treatment of wastewaters and has lagged targets set for diffuse agricultural sources. Synthesis of the major campaigns—varying in terms of physical settings, ecosystem characteristics, nutrient sources, socio-economic drivers, and governance—identified barriers inhibiting eutrophication abatement and potential bridges to overcome them. Actionable science can be advanced by: application of the well-established and emerging knowledge and experience around the globe, client-responsive strategic research, and timely and conclusive adjudication of scientific controversies. More accountable governance requires: enduring engagement of high-level officials of the responsible governments; effective communication of the causes, risks and benefits to the public and stakeholders; quantitative and accountable allocation of responsibility for nutrient load reductions; and binding requirements, as opposed to simply voluntary actions. Effective reduction in nutrient loads requires: reduction strategies for both nitrogen and phosphorus; inclusion of actions that reduce atmospheric emissions of nitrogen in addition to direct inputs to waterways; efficacious regulations; public subsidies based on performance; limitations on biofuel production that increases nutrient loads; and enhancing the sinks and losses for legacy nutrients retained in soils and groundwater. Outcomes must be measured and strategies appropriately adjusted through: sustained monitoring of essential indicators and processes, the use of multiple models, truly adaptive management, and the precautious interventions within the coastal ecosystem. The changing climate must be taken into account by reassessing achievable future conditions and seeking alternatives for mitigating and adapting to climate change that also reduce nutrient loads.

Effect of invasive ctenophores Mnemiopsis leidyi and Beroe ovata on low trophic webs of the Black Sea ecosystem

The study focuses on the impact of life excretion and mucus released by the “biological pollutants” invasive ctenophore Mnemiopsis leidyi and its predator Beroe ovata on the marine environment and lower trophic levels of the Black Sea ecosystem (bacteria, pico-phytoplankton, nano-autotrophic/heterotrophic flagellates, micro-phytoplankton, chlorophyll a, primary production (PP), micro-zooplankton). The chemical and biological variables were analysed in two sets of lab experiments with natural communities from mesotrophic (Gelendzhik) and eutrophic (Varna) coastal waters. While both species altered the chemical properties of experimental media, exerting structural and functional changes in the low food-web biological compartments, the results showed a stronger effect of B. ovata, most likely related to the measured higher rate of excretion and amount of released mucus. In addition the alterations in the Gelendzhik experiment were more pronounced, indicating that environmental implications on lower food-web are more conspicuous in mesotrophic than in eutrophic coastal waters.

Sources and sinks of dissolved inorganic carbon in an urban tropical coastal bay revealed by δ13C-DIC signals

Dissolved inorganic carbon (DIC), its stable isotope composition (δ13C-DIC) and ancillary parameters of the water column were investigated in a eutrophic tropical marine-dominated estuary surrounded by a large urban area (Guanabara Bay, Rio de Janeiro, Brazil). Most negative δ13C-DIC signatures (down to −6.1‰) were found in polluted regions affected by direct sewage discharges where net heterotrophy induces high partial pressure of CO2 (pCO2) and DIC concentrations. Keeling plot was applied to this polluted region and determined the δ13C-DIC sewage signature source of −12.2‰, which is very consistent with isotopic signature found in wastewater treatment plans. These negative δ13C-DIC signatures (i.e., DIC depleted in 13C) were restricted to the vicinity of urban outlets, whereas in the largest area of the bay δ13C-DIC signatures were more positive (i.e., DIC enriched in 13C). The most positive δ13C-DIC signatures (up to 4.6‰) were found in surface waters dominated by large phytoplankton blooms, with positive correlation with chlorophyll a (Chl a). In the largest area of the bay, the preferential uptake of the lighter stable carbon isotope (12C) during photosynthesis followed the Rayleigh distillation, and appeared as the most important driver of δ13C-DIC variations. This reveals an important isotopic fractionation (ε) by phytoplankton due to successive algal blooms that has turned the remaining DIC pool enriched with the heavier stable carbon isotope (13C). The calculated diel apparent ε showed higher values in the morning (18.7‰–21.6‰) and decreasing in the afternoon (6.8‰–11.1‰). ε was positively correlated to the pCO2 (R2 = 0.88, p = 0.005) and DIC concentrations (R2 = 0.73, p = 0.02), suggesting a decline in carbon assimilation efficiency and decreasing uptake of the lighter carbon under CO2 limiting conditions. The eutrophic coastal waters of Guanabara Bay have δ13C-DIC signatures well above that found in estuaries, shelf and ocean waters worldwide.

Land Uses Simplified Index (LUSI): Determining Land Pressures and Their Link With Coastal Eutrophication

Human activities on land result in the high-level production of nutrients. When these nutrients reach coastal waters, they could drive the eutrophication process. Here we present the Land Uses Simplified Index (LUSI), an easy-to-use tool for assessing continental pressures on coastal waters. This assessment is done by indirectly estimating continental nutrient loads and concentrations and their influence on coastal waters. LUSI is based on systematic information describing both the land uses that influence coastal waters by providing nutrient-rich freshwater inflows (urban, industrial, agricultural, and riverine) and the coastline morphology, which can modify this influence, as it determines the degree of coastal water confinement and therefore the likelihood that these inflows will be diluted. A low LUSI value indicates that coastal waters are not or only slightly influenced by continental pressures and/or that these pressures are diluted. On the contrary, a high LUSI value indicates that coastal waters are strongly influenced by continental pressures and/or that these pressures are not diluted. LUSI fulfils a methodological gap, as a simple method to assess coastal pressures when there is a lack of information. Furthermore, it fulfils the requirement of the Water Framework Directive for a true pressure assessment (i.e. not confounded with impact), which for coastal waters imply using pressure data from land. An additional and important feature of LUSI is that it allows the establishment of pressure-impact relationships with impact indicators, such as those related to the Biological Quality Elements of the above Directive. For example, a relationship based on LUSI, as a proxy of pressure, and on the chlorophyll-a concentration, as a proxy of phytoplanktonic biomass and, thus, of the eutrophication impact. By providing insights into the land uses that trigger eutrophication in coastal waters, LUSI aids in the design of measures aimed at remediating anthropogenic damage caused to the environment.

Corrigendum: Hypoxic Induced Decrease in Oxygen Consumption in Cuttlefish (Sepia officinalis) Is Associated with Minor Increases in Mantle Octopine but No Changes in Markers of Protein Turnover

[This corrects the article DOI: 10.3389/fphys.2017.00344.].

Harmful phytoplankton diversity and dynamics in an upwelling region (Sagres, SW Portugal) revealed by ribosomal RNA microarray combined with microscopy

The study region in Sagres, SW Portugal, is subject to natural eutrophication of coastal waters by wind-driven upwelling, which stimulates high primary productivity facilitating the recent economic expansion of bivalve aquaculture in the region. However, this economic activity is threatened by harmful algal blooms (HAB) caused by the diatoms Pseudo-nitzschia spp., Dinophysis spp. and other HAB dinoflagellates, all of which can produce toxins, that can induce Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (DSP) and Paralytic Shellfish Poisoning (PSP). This study couples traditional microscopy with 18S/28S rRNA microarray to improve the detection of HAB species and investigates the relation between HAB and the specific oceanographic conditions in the region. Good agreement was obtained between microscopy and microarray data for diatoms of genus Pseudo-nitzschia and dinoflagellates Dinophysis spp., Gymnodinium catenatum and raphidophyte Heterosigma akashiwo, with less effective results for Prorocentrum. Microarray provided detection of flagellates Prymnesium spp., Pseudochattonella spp., Chloromorum toxicum and the important HAB dinoflagellates of the genera Alexandrium and Azadinium, with the latter being one of the first records from the study region. Seasonality and upwelling induced by northerly winds were found to be the driving forces of HAB development, with Pseudo-nitzschia spp. causing the risk of ASP during spring and summer upwelling season, and dinoflagellates causing the risk of DSP and PSP during upwelling relaxation, mainly in summer and autumn. The findings were in agreement with the results from toxicity monitoring of shellfish by the Portuguese Institute for Sea and Atmosphere and confirm the suitability of the RNA microarray method for HABs detection and aquaculture management applications.

Eutrophication Leads to Accumulation of Recalcitrant Autochthonous Organic Matter in Coastal Environment

AbstractAnthropogenic nutrient enrichment is changing the structure and the function of coastal ecosystems. These coastal zones are transitions between freshwater and marine systems where multiple biogeochemical processes remove, produce, and transform organic matter. The extent to which the coastal zone is merely a conduit for terrestrial (allochthonous) organic matter versus a distinct source of autochthonous organic matter fueled by eutrophication is unclear. To address this issue, we characterized the freshwater and marine dissolved organic matter (DOM) pools in a eutrophic estuary with a long water residence time (Roskilde Fjord, Denmark) over an annual cycle. We combined elemental, optical (absorbance and fluorescence), and isotopic analyses to obtain insight about the bulk properties of the DOM pool during this period. We also used sediment traps to analyze the changes related to the exchange of organic matter between the particulate organic matter and DOM fractions. The results showed that labile autochthonous DOM from in situ primary production was rapidly transformed to more recalcitrant DOM that accumulated in the estuary despite continuous exchange with the open sea. Also, parts of the particulate organic matter pool were degraded rapidly (within 24 hr) and transformed into the DOM pool. Accumulated DOM was characterized by relatively low molecular size and stable carbon isotopic value and by high protein‐like fluorescence. These results indicate that autotrophic material can be a major source of specific recalcitrant DOM in eutrophic coastal waters, contributing significantly to the flux of organic carbon to the ocean.

Ulvan lyase from Formosa agariphila and its applicability in depolymerisation of ulvan extracted from three different Ulva species

Members of green macroalgae cause green tides in eutrophicated coastal waters. These green tides pose an environmental issue and an economic burden on coastal municipalities. The biomass from these green tides has a potential to be used as feedstock in biorefinery due to the content of interesting biomacromolecules. Ulvan, an anionic water-soluble polysaccharide, is one of such components, and its depolymerisation to high-value oligosaccharides or fermentable monosaccharides would bring value to green tide biomass which is otherwise left to decompose. However, only a few ulvan depolymerising enzymes are studied to date. Ulvan lyases depolymerise ulvan, via the β-elimination mechanism, leading to release of oligosaccharides with an unsaturated 4‑deoxy‑l‑threo‑hex‑4‑enopyranosiduronic acid at the non-reducing end. In this study, we have identified the presence of two different domains, a catalytic and a non-catalytic, in a putative ulvan lyase from Formosa agariphila KMM 3901. We overexpressed, purified, and biochemically characterised the full-length ulvan lyase, which was found to be most active at a temperature of 45 °C and pH 8.5. It exhibited high specificity for ulvan and did not degrade heparan sulphate, chondroitin sulphate, alginate, pectin or xanthan. Detailed analyses of end products of the enzymatic degradation of ulvan using 1H NMR and LC-MS revealed a disaccharide with an unsaturated uronic acid (∆) linked to 3‑sulphated rhamnose (Rha3S), trisaccharide with xylose (Xyl) flanked by Rha3S (Rha3S-Xyl-Rha3S), tetrasaccharide with an unsaturated uronic acid at the non-reducing end (∆Rha3S-Xyl-Rha3S) and pentasaccharides (Rha3S-Xyl-Rha3S-Xyl-Rha3S and branched ∆Rha3S-Xyl-(∆)Rha3S) as the principal end products. We also found that the catalytic domain that lacks the non-catalytic carbohydrate binding module exhibited higher affinity for the soluble ulvan and efficiently depolymerised it. This study reveals the characteristics of the endolytic ulvan lyase, which is a member of the ulvan utilisation loci in Formosa, and points towards the potential ulvan depolymerisation applications in Ulva biorefinery.