Loch Creran Research Articles

Stable isotope values (δ 13C, δ 15N) of macroalgal communities at Loch Creran and its relevance for elucidating sources of macroalgal organic carbon in fjordic sedimentary systems

Abstract Here, macroalgal isotopic values from Loch Creran, Western Scotland, were documented to determine the suitability of paired stable isotope analysis for identifying macroalgal-derived organic carbon sources in a fjordic sea loch. Variability in isotopic values (δ 13C and δ 15N) was evident within individual thalli of fucoid and kelp species, at the replicate level and between sampling localities. There were few consistent phylogenetic correlates in the isotopic values of macroalgae. The δ 13C ranges did, however, provide insight into differentiating between carbon sources more broadly, such as terrestrial from marine and between macrophyte lineages. As such, δ 13C could be indicative of the presence of macroalgal carbon sources within pools of organic matter but will likely be ineffective at separating these sources to lower taxonomic levels. Consequently, if these data are used alone to discriminate between macroalgal carbon sources and their relative contribution to a sedimentary pool of organic matter, the development of accurate conclusions will be challenging. The findings presented here demonstrate the need for complementary techniques or multi-tracer approaches to aid in the differentiation between macroalgal carbon sources to lower taxonomic levels rather than relying on stable isotopes as a biomarker alone.

Quantifying Marine Sedimentary Carbon: A New Spatial Analysis Approach Using Seafloor Acoustics, Imagery, and Ground-Truthing Data in Scotland

Marine sediments are important repositories of particulate organic matter, effectively burying organic carbon (OC) over geological timescales thus providing a climate regulation service. However, the spatial distribution of this marine sedimentary OC store is not well constrained. In this study we leverage a high resolution multibeam echosounder (MBES) survey taken at Loch Creran, a model fjordic site on the west coast of Scotland, to develop a new methodology for predicting the distribution of OC in surface sediments. Using an integrated approach, we combine use MBES survey, video imagery and ground-truthing data to produce a high-resolution (2 m x 2 m) map of surficial carbon and calculate a 10 cm stock. We find that the backscatter survey reliably uncovers a heterogeneous seabed and that OC correlates strongly with the MBES backscatter signal as a function of sediment composition. We estimate that there are approximately 12,346 ± 2,677 tonnes of OC held within the top 10 cm of mixed sediments across the MBES survey area (7.96 km2; 60% of the total area), upscaled to 20,577 ± 4,462 t of OC across Loch Creran (13.27 km2). Normalised by area, we find that mixed fine sediments with small fractions of sand and gravel are more effectivehold more carbon OC stores than homogenous fine sediments. This initial work proposes a novel methodological approach to using high resolution MBES surveys to improve the spatial mapping of sedimentary C carbon (C) and identification of C hotspots, enabling consideration of this resource in sedimentary carbon accounting, seabed management and climate mitigation strategies.

Tracking changes to a microplankton community in a North Atlantic sea loch using the microplankton index PI(mp)

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.

Can management effort be predicted for marine protected areas? New considerations for network design

This study examined the level of management complexity (simultaneously occurring licensed human activities) within the currently designated Marine Protected Areas (MPAs) in Scottish waters and through modelling and statistical analysis determined which variables play an important role in defining the level of management effort required for each MPA. This study utilised surveyed distribution data for Priority Marine Features and modelled distribution data showing potential “Most Suitable” Priority Marine Feature habitat through the species distribution model, Maxent. Prediction indicators were developed through Spearman׳s Rank coefficients and a linear regression model. Results showed that, (1) there was a significant negative correlation between the management complexity score within 5km of a MPA and the number of casework events (defined as any work or statutory consultation associated with an MPA, such as planning applications, discharges or new fisheries); and (2) a significant positive correlation between the number of casework events and location, number of features, and the type of features and most suitable scores. Calculations showed that Lochs Duich, Long and Alsh, Loch Sunart, Loch Sween and Loch Creran may potentially require most effort to manage once they are designated as MPAs. This study showed that it is possible to evaluate options within an MPA network to achieve cost effective options for the biodiversity and socio-economic objectives of MPA networks and that some MPAs are likely to be more efficient than others in terms of management time.

A box model of the seasonal exchange and mixing in Regions of Restricted Exchange: Application to two contrasting Scottish inlets

We present a time-dependent box model of exchange and mixing processes in Regions of Restricted Exchange (RREs). The model is applied to two contrasting Scottish inlets, but can potentially be applied to a wide range of stratified inshore water bodies. The model represents the vertical structure of the inlet using up to three horizontally uniform layers, representing surface, intermediate and deep basin water respectively, and calculates the daily volume, thickness, salinity and temperature of each layer over an annual cycle. The model is forced by observed time series of daily-mean wind stress, river discharge, surface heat flux, and depth-profiles of the external coastal temperature and salinity. Advective and diffusive fluxes between the layers, and between the inlet and adjacent coastal ocean, are calculated from parameterisations of known physical processes in inshore stratified waters, utilising published analytical solutions and empirically-based formulae. The goal is for the model to be generally applicable to RREs to support improved resource management. As such, the number of free parameters within the model has been kept to a minimum.The model predictions of layer temperature and salinity are quantitatively compared to observations from year-long sampling programmes in two contrasting Scottish inlets, Loch Creran and Loch Etive. The model showed good agreement with the observed data, reproducing the broad scale seasonal cycle and other shorter-term fluctuations. RMS errors for temperature were less than 1 °C, and for salinity typically of the order 1. The model results suggest that Loch Creran behaved as a well-mixed box, with weak stratification maintained by strong vertical diffusion, and volume exchange between the inlet and coastal waters dominated by tidal forcing. In contrast, Loch Etive exhibited classical fjordic three-layer hydrography and dynamics, with strong stratification, weak vertical diffusion and a density-driven circulation comparable in strength to tidal exchange. The effects of a deep water renewal event on water properties were successfully reproduced by the model. The potential for wider application of the model to resource management issues and to other types of RRE is discussed.

Spatial and Temporal Variability of Benthic Respiration in a Scottish Sea Loch Impacted by Fish Farming: A Combination of In Situ Techniques

The effects of fish farm activities on sediment biogeochemistry were investigated in Loch Creran (Western Scotland) from March to October 2006. Sediment oxygen uptake rates (SOU) were estimated along an organic matter gradient generated from an Atlantic salmon farm using a combination of in situ techniques: microelectrodes, planar optode and benthic chamber incubations. Sulphide (H2S) and pH distributions in sediment porewater were also measured using in situ microelectrodes, and dissolved inorganic carbon (DIC) fluxes were measured in situ using benthic chambers. Relationships between benthic fluxes, vertical distribution of oxidants and reduced compounds in the sediment were examined as well as bacterial abundance and biomass. Seasonal variations in SOU were relatively low and mainly driven by seasonal temperature variations. The effect of the fish farm on sediment oxygen uptake rate was clearly identified by higher total and diffusive oxygen uptake rates (TOU and DOU, respectively) on impacted stations (TOU: 70 ± 25 mmol O2 m−2 day−1; DOU: 70 ± 32 mmol O2 m−2 day−1 recalculated at the summer temperature), compared with the reference station (TOU: 28.3 ± 5.5 mmol O2 m−2 day−1; DOU: 21.5 ± 4.5 mmol O2 m−2 day−1). At the impacted stations, planar optode images displayed high centimetre scale heterogeneity in oxygen distribution underlining the control of oxygen dynamics by small-scale processes. The organic carbon enrichment led to enhanced sulphate reduction as demonstrated by large vertical H2S concentration gradients in the porewater (from 0 to 1,000 μM in the top 3 cm) at the most impacted site. The impact on ecosystem functions such as bioirrigation was evidenced by a decreasing TOU/DOU ratio, from 1.7 in the non-impacted sediments to 1 in the impacted zone. This trend was related to a shift in the macrofaunal assemblage and an increase in sediment bacterial population. The turnover time of the organic load of the sediment was estimated to be over 6 years.

Effects of simulated natural and massive resuspension on benthic oxygen, nutrient and dissolved inorganic carbon fluxes in Loch Creran, Scotland

The effect of repeated natural resuspension on benthic oxygen consumption and the effect of natural and massive resuspension on oxygen consumption and fluxes of phosphate, silicate, ammonium and dissolved inorganic carbon (DIC) were studied at two stations (S1 and S2) in a Scottish sea loch. Station S11 had organically enriched sediment and station S1 had lower organic content in the sediment. The fluxes were measured in situ using the Göteborg benthic lander. Natural resuspension, simulating resuspension events due to strong wind, waves or currents, and massive resuspension, simulating resuspension due to e.g. trawling or dredging, were created inside the incubation chambers by regulating the stirring of the incubated overlying water or by retracting and shaking the incubated sediment. Natural resuspension showed clear effects on the oxygen consumption at station S11, where it increased with an average of 12.8 (standard error (s.e.) 0.17) and 7.7 (s.e. 0.12) mmolm−2d−1 during the first and second incubations, respectively. At station S1 there was no clear effect of natural resuspension on the oxygen consumption. Massive resuspension increased the oxygen consumption on S1 with an average of 608 (standard deviation (sd) 366) mmolm−2d−1 and on S11 with an average of 2396 (sd 2265) mmolm−2d−1. The fluxes of ammonium, phosphate and silicate were affected by the massive resuspension in 50, 14 and 33% of the chambers, respectively, on station S11. However, in the majority of the cases there were no effects on the nutrient and DIC fluxes of massive resuspension. The absolute concentrations of DIC, ammonium and silicate did however instantly increase with an average of 419 (sd 297), 48 (sd 27) and 6.9 (sd 3.7) μM, respectively, at S11 upon massive resuspension. The concentrations of phosphate decreased instantly with an average of 0.2 (sd 0.1) μM. On station S1 there were effects only on the ammonium and silicate concentrations, which increased with 0.8 (sd 0.3) and 1.13 (sd 0.36) μM, respectively. The large increase in oxygen consumption due to massive resuspension indicates that activities like e.g. trawling and dredging that take place in areas where water exchange occurs infrequently may lead to oxygen depletion in bottom water, which in turn might affect the ecological balance. Silicate, ammonium and DIC can be released due to massive resuspension and contribute to increased algal blooms in surface waters.

The community associated with biogenic reefs formed by the polychaete, Serpula vermicularis

The study aims to provide the first detailed account of the diversity and composition of the community associated with biogenic reefs formed by serpulid worms. Ten reefs (aggregations of calcareous Serpula vermicularis tubes), spanning a broad size-range, were collected from Loch Creran, Scotland, a Special Area of Conservation designated principally for the protection of its biogenic reefs. Total faunal abundance was strongly linearly related to reef weight, whilst taxon richness exhibited a hyperbolic relationship with reef size. 278 taxa were recorded from the ten reefs, with a reef of 0.1 m2 area supporting 163 taxa and 12756 individuals, which appears to represent considerable augmentation of diversity and abundance for sedimentary areas of the loch where the reefs occur. The reef assemblage was dominated by polychaetes (94 taxa), molluscs (70 taxa) and crustaceans (45 taxa). Species composition varied with reef size, although reefs greater than 25 cm width exhibited relatively little variation. In comparison with other biogenic polychaete habitats, S. vermicularis reefs appear to support a highly diverse community, which exhibits a high degree of similarity with that found in association with aggregations of the horse mussel, Modiolus modiolus. The presence of the Connemara clingfish, Lepadogaster candollei, rarely recorded at such a northerly latitude, on several reefs, indicates that the reef habitat may provide a stronghold for this species at the edge of its biogeographical range.

Where’s the ‘reef’? A five year study of serpulid tube bioerosion in a Scottish sea loch

In the British Isles, aggregations of the tubicolous polychaete Serpula vermicularis L. occur only in a few localities in western Scotland and Ireland. In Loch Creran, Argyll, where written observations extend back to the 1880s, build-ups of skeletal debris constituting a true reef framework are notably absent. To investigate the taphonomic processes affecting the residence time of relict tube material, cleaned and weighed skeletal fragments were deployed on panels amongst living worm aggregations. Fragments were either open to the environment or enclosed in mesh cylinders to exclude grazing urchins. Panels were recovered and fragments re-weighed after 1, 2, 3 and 5 yr in situ. Caged fragments typically increased in dry weight over time, while most open fragments remained at steady-state or showed small weight decreases. Change in weight was correlated with the number of living tubeworms which had settled onto the skeletal fragments. Open fragments showed no consistent temporal trend in weight change, suggesting that urchin grazing was not a major bioerosive process over the 5 yr experimental timescale. Data from another locality where ser- pulid aggregations suffered mass mortality between 1984 and 1994 show that tube debris can persist for at least 15 yr in sea loch environments. S. vermicularis aggregations in sea lochs may be relatively transient features, appearing and disappearing over decadal timescales.

Sediment fluxes and carbon budgets in Loch Creran, western Scotland

Abstract Sea lochs are regions where riverine and marine organic carbon (OC) undergoes decomposition, deposition or transportation to shelf slopes and the deep sea. According to the OC budget presented here, discharge from River Creran (1.44×10 6 kg a −1 ) and phytoplankton material (0.89×10 6 kg a −1 ) make up a significant input of OC to Loch Creran while 0.67×10 6 kg a −1 OC is from other sources. A total of 1.28×10 6 kg a −1 OC is deposited in the loch and 1.14×10 6 kg a −1 OC is oxidized in the water column. Discharge to the Lynn of Lorn consists of 0.58×10 6 kg a −1 OC. Hence Loch Creran is a sink for OC where 42.7% of the total OC input is buried and 38% and 1.7% decomposed in the water column and subsurface sediments, respectively. River Creran contributes 63% labile and 37% refractory organic matter to the loch. More than 95% of each of the total OC, lignin and organic matter deposited onto the surface sediments is buried in the subsurface sediments. Seventy-five percent of the total organic matter decomposed in the water column is labile. Output to Lynn of Lorn consists of 54.6% refractory organic matter.

Description and sensitivity analysis for the LESV model: Water quality variables and the balance of organisms in a fjordic region of restricted exchange

In this paper we describe a new ecological model for Regions of Restricted Exchange (RRE), such as fjords, estuaries, rias and lagoons. The model is intended to simulate the impact of external nutrient input on microplankton (phytoplankton plus pelagic microheterotrophs) in RREs. We have implemented the model with the practical purpose of finding a safe limit to the capacities of RRE to assimilate fish-farm waste. Sea-cage farming of fish is increasing in fjords in northern and southern hemispheres, and its external nutrient input can lead to environmental problems such as eutrophication and deoxygenation. The model includes a physical system of three layers with exchanges driven by tidal movement, freshwater input, wind stirring. The biological part includes two microplankton compartments, each parameterizing a microbial loop and each containing chlorophyll. The first compartment represents diatoms and associated heterotrophs, and the second compartment represents flagellates and associated heterotrophs. As well as the balance of these organisms, the model simulates concentrations of nutrient N, P, and Si, dissolved oxygen, and water transparency. Chlorophyll and nutrient change are linked by yields ( q). Losses of microplankton to grazing by mesozooplankton or benthos are simulated by a temperature-dependent grazing pressure acting on a mean loss ( L 0 ) . The model also includes the ability to simulate point source inputs of nutrients or organic matter and a generic tracer with first order decay. Sea-cage fish-farms exemplify such point sources. In order to explore model behaviour, we included inputs from a 1500 tonnes salmon farm multiplied by a factor ( γ ) . We carried out sensitivity analysis to identify the most influential model parameters and forcing variables in the case of the shallow Scottish fjord, Loch Creran, in 1975 before the introduction of salmon farming. We tested the model fit to this pristine state ( γ = 0 ) , using Major Axis Regression of simulated variables on observed variables. The model successfully follows the seasonal cycles of chlorophyll (summer over both microplanktons) and the limiting nutrients (P, N). The sensitivity analysis identified three sets of key parameters: ( γ ) and other fish-farm coefficients, which control farm waste effects on an RRE; ( L 0 ) parameters for each microplankton, which link these to the rest of the ecosystem and which have implications for future inclusion of shellfish farming in the model and, chlorophyll yields from nutrients ( q), which are crucial for the predication of eutrophication and the ecological understanding of the model.

Production of bioavailable and refractory dissolved organic matter by coastal heterotrophic microbial populations

Production of dissolved organic matter (DOM) by heterotrophic microbial communities isolated from Loch Creran (Scotland) was studied in time course incubations in which cells were re-suspended in artificial seawater amended with variable proportions of glucose, ammonium and phosphate. The incubation experiments demonstrated that microheterotrophs released part of the substrate as new DOM, with a production efficiency of 11 ± 1% for DOC, 18 ± 2% for DON and 17 ± 2% for DOP. Estimating the impact of this production in Loch Creran, showed that from 3 ± 1% (DOC) to 72 ± 16% (DOP) of DOM could originate from the heterotrophic microbial community. The produced DOM (PDOM) was both bioavailable (BDOM) and refractory (RDOM). Bioavailability as assessed by the difference between the maximum and the end DOM concentration, was generally higher than found in natural systems, with DOP (73 ± 15%, average ± SD) more bioavailable than DON (70 ± 15%), and DON than DOC (34 ± 13%). The stoichiometry of PDOM was linked to both nutrient uptake and BDOM ratios. Absorption and fluorescence of DOM increased significantly during the incubation time, indicating that microheterotrophs were also a source of coloured DOM (CDOM) and that they produce both bioavailable protein-like and refractory humic-like fluorophores.

Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

The bioavailability and bacterial degradation rates of dissolved organic matter (DOM) were determined over a seasonal cycle in Loch Creran (Scotland) by measuring the decrease in dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) concentrations during long-term laboratory incubations (150 days) at a constant temperature of 14 °C. The experiments showed that bioavailable DOC (BDOC) accounted for 29 ± 11% of DOC (average ± SD), bioavailable DON (BDON) for 52 ± 11% of DON and bioavailable DOP (BDOP) for 88 ± 8% of DOP. The seasonal variations in DOM concentrations were mainly due to the bioavailable fraction. BDOP was degraded at a rate of 12 ± 4% d – 1 (average ± SD) while the degradation rates of BDOC and BDON were 7 ± 2% d – 1 and 9 ± 2% d – 1 respectively, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentration and degradation rate of DOM suggested that the higher the concentration the faster DOM would be degraded. On average, 77 ± 9% of BDOP, 62 ± 14% of BDON and 49 ± 19% of BDOC were mineralized during the residence time of water in Loch Creran, showing that this coastal area exported C-rich DOM to the adjacent Firth of Lorne. Four additional degradation experiments testing the effect of varying temperature on bioavailability and degradation rates of DOM were also conducted throughout the seasonal cycle (summer, autumn, winter and spring). Apart from the standard incubations at 14 °C, additional studies at 8 °C and 18 °C were also conducted. Bioavailability did not change with temperature, but degradation rates were stimulated by increased temperature, with a Q 10 of 2.6 ± 1.1 for DOC and 2.5 ± 0.7 for DON (average ± SD).

Analysis of coastal and offshore aquaculture: Application of the FARM model to multiple systems and shellfish species

The Farm Aquaculture Resource Management (FARM) model has been applied to several shellfish species and aquaculture types. The performance of the FARM model, developed to simulate potential harvest, key financial data, and water quality impacts at the farm-scale, was tested in five systems in the European Union: Loch Creran, Scotland (Pacific oyster), Pertuis Breton, France (blue mussel), Bay of Piran, Slovenia (Mediterranean mussel), Chioggia, Italy (Mediterranean mussel) and Ria Formosa, Portugal (Manila clam). These systems range from open coasts to estuaries, and are used for shellfish aquaculture by means of different cultivation techniques (e.g. oyster bottom culture in Loch Creran and mussel longlines and poles in Pertuis Breton). The drivers for the FARM model were supplied by measured data, outputs of system-scale models or a combination of both. The results (given in total fresh weight) generally show good agreement with reported annual production (shown in brackets) at each farm: simulated production of 134 tons of Pacific oyster in Loch Creran (150 tons, − 10%), 2691 tons of blue mussel in Pertuis Breton (2304 tons, + 17%), 314 tons of Mediterranean mussel in the Bay of Piran (200 tons, + 57%), 545 tons of Mediterranean mussel in Chioggia (660 tons, − 17%) and 119 tons of Manila clam in Ria Formosa (104 tons, + 15%). The nitrogen mass balance for each farm was also determined with the FARM model. The net removal of nitrogen (N) by the farms was estimated to correspond to 1206 population equivalents per year (PEQ y − 1 ) in Loch Creran, 93503 PEQ y − 1 in Pertuis Breton, 9196 PEQ y − 1 in the Bay of Piran, 97916 PEQ y − 1 in Chioggia and 8613 PEQ y − 1 in Ria Formosa. The aggregate income due to both the shellfish sale and substitution value of land-based fertilizer reduction or nutrient treatment was estimated to be about 700 k€ y − 1 in Loch Creran, 30,706 k€ y − 1 in Pertuis Breton, 3000 k€ y − 1 in the Bay of Piran, 30,000 k€ y − 1 in Chioggia, and 5000 k€ y − 1 in Ria Formosa. Outputs of FARM may be used to analyse the farm production potential and profit maximization according to seeding densities and/or spatial distribution. Results of a marginal analysis for all the study sites were determined. As an example, profit maximization in Loch Creran was obtained with 97 tons of seed, resulting in a total production of 440 tons (profit of 2100 k€ for a culture period of about 2 years). FARM additionally integrates the well-known ASSETS model, for assessment of farm-related eutrophication impacts. The assessment results for the five study sites show that water quality is either maintained or improved in all farms under standard conditions of culture practice. FARM results may be used by farmers to analyse farm production potential and by managers for environmental assessment of farm-related water quality impacts, whether positive or negative. It is a useful tool for all stakeholders for the valuation of nitrogen credits, which may be traded as part of an integrated catchment management plan. The FARM results were scaled up to determine a net value of 11–17 billion € y − 1 of ecosystem goods and services, provided by shellfish culture towards reducing eutrophication in the coastal waters of the European Union. These numbers highlight the role that extractive organic aquaculture plays in integrated coastal zone and nutrient emissions management.

Mapping serpulid worm reefs (Polychaeta: Serpulidae) for conservation management

Abstract This study describes investigations into mapping of the biogenic reefs produced by the polychaete worm, Serpula vermicularis, for the purposes of conservation management. Reef distribution throughout Loch Creran, Scotland, was mapped using a diver transect technique and was found to be restricted to a peripheral band, with a mean upper limit of distribution of 2.7 m. The mean lower limit was found to decrease with distance from the mouth of the loch, with a lower limit of 9.3 m in the lower basin rising to 6.6 m in the upper basin; the likely influence of a corresponding decrease in the upper depth distribution of muds is discussed. Through determination of the mean width of the reef band and coastline length, the areal extent of the reef band was estimated as 108 ha, revealing Loch Creran to harbour the most extensive known development of S. vermicularis reef habitat in the world. The utility of sidescan sonar in mapping serpulid reefs was examined in four of the major embayments. Reef material appeared as characteristic patterning on the sonargrams, with the morphology of individual larger reefs being discernible. Sidescan sonar was found to be particularly valuable for the identification and monitoring of threats to the conservation of serpulid reefs. Sidescan sonar surveying was found to facilitate identification of loss of habitat extent resulting from anthropogenic activities such as moorings, aquaculture installations and dredging and can also be used to monitor the potentially damaging activity of otter trawling. Further improvements in the mode of deployment of sidescan sonar are discussed. Copyright © 2008 John Wiley & Sons, Ltd.

Use of a Phytoplankton Community Index to assess the health of coastal waters

AbstractTett, P., Carreira, C., Mills, D. K., van Leeuwen, S., Foden, J., Bresnan, E., and Gowen, R. J. 2008. Use of a Phytoplankton Community Index to assess the health of coastal waters. – ICES Journal of Marine Science, 65: 1475–1482. Monitoring of marine-ecosystem status and health requires indicators of community structure and function. As a structural indicator, we propose a Phytoplankton Community Index (PCI) based on the abundance of “life-forms” such as “pelagic diatoms” or “medium-sized autotrophic dinoflagellates”. To calculate the PCI, data showing seasonal variation in these abundances are plotted in “life-form space” of two or more dimensions. Data from a “type-specific reference condition” are then enclosed within a reference envelope. Comparison data are plotted into the same coordinate system, and the PCI is the proportion (between 0 and 1) of these new data that fall within the reference envelope. Results from initial applications of this method are shown for UK coastal waters in the northern North Sea (near Stonehaven), a Scottish fjord (Loch Creran), and the eastern Irish Sea (including Liverpool Bay). The Stonehaven data (1997–2005) were used to compare values obtained from weekly sampling with those from monthly sampling. A spatial comparison between more- and less-nutrient-enriched waters in the eastern Irish Sea (1991–2003) showed little difference in phytoplankton community structure. Loch Creran has experienced a large change in the “balance of organisms”, and hence a reduction in the PCI, between 1979–1981 and 2006/2007, associated with a decrease in chlorophyll but no apparent change in nutrients. These results are discussed in relation to the intended uses of the PCI as an index of biological quality for the Water Framework Directive (WFD) and an index of ecosystem health in the context of eutrophication. Although the method only measures change, it can also be used as an indicator of biological quality if the reference conditions are those defined for a WFD waterbody, and as an indicator of health if appropriately calibrated. Suggestions are made for further development.

Assessing the biodegradability of terrestrially-derived organic matter in Scottish sea loch sediments

Abstract. Lignin oxidation products, oxygen uptake rates, molar organic carbon to nitrogen (OC/N) ratio (from bulk elemental analysis) and Rp values (from loss on ignition experiments, the ratio of the refractory to total organic matter, OM) were determined for sediments along transects of Loch Creran and Loch Etive. Lignin data indicated the importance of riverine inputs contributing to land-derived carbon in the lochs as total lignin (Λ, mg/100 mg organic carbon, OC) decreased from 0.69 to 0.45 and 0.70 to 0.29 from the head to outside of Loch Creran and Loch Etive, respectively. In addition, significant correlations of lignin content against total OM and OC (p<0.05) also suggested a distinct contribution of terrestrial OM to carbon pools in the lochs. The general trend of decreasing oxygen uptake rates from the head (20.8 mmole m−2 day−1) to mouth (9.4 mmole m−2 day−1) of Loch Creran indicates decomposition of OM. Biodegradability of the sedimentary OM was also characterized by the increase of Rp values from the head to mouth of the lochs: 0.40 to 0.80 in Loch Etive and 0.43 to 0.63 in Loch Creran. Furthermore, the molar OC/N ratio decreased from 11.2 to 6.4 in Loch Creran, and from 17.5 to 8.2 in Loch Etive. Derived rate constants for OM degradation were found to decrease from LC0 to LC1, and increase from RE5 to RE6. This work demonstrates that oxygen uptake rates, Rp values and molar OC/N ratio are able to serve as useful proxies to indicate the biodegradability of sedimentary OM.

Small-scale variation within a Modiolus modiolus (Mollusca: Bivalvia) reef in the Irish Sea. II. Epifauna recorded by divers and cameras

The spatial heterogeneity of epifauna on a Modiolus modiolus reef off north-west Wales was investigated using divers. The community associated with these horse mussels was similar to that described previously from Loch Creran and the north basin of Strangford Lough. Some differences in epifauna may be attributable to the less sheltered nature of the site. Modiolus modiolus numbers and the associated epifaunal community were significantly different between ridge and trough sub-habitats. Troughs can be considered ‘reduced’ ridge communities whereas ridges have high densities of horse mussels and certain sessile taxa were correlated with their abundance. Modiolus modiolus aggregation as a competitive response to the feeding environment, enhanced food availability on ridges and sediment deposition amongst mussel clumps may start to explain the undulating bed-form. Patchiness in community composition and periodic cover by ophuroids has implications when considering the monitoring of the horse mussel community. Stratified, in situ recording of the highly populated ridges could improve the statistical sensitivity of monitoring horse mussel reefs whilst simultaneously focusing on the more sensitive indicators of fishing threats.

Optimised recovery of lignin-derived phenols in a Scottish fjord by the CuO oxidation method

Lignin is found only in vascular plant tissues, hence monitoring of lignin in aquatic environments is important in the determination of the sources and fate of terrestrial organic matter (OM). Concentrations of lignin-derived phenols provide an estimate of the amount of terrestrial OM in a system. Other lignin parameters such as the ratios of syringyl to vanillyl (S/V) and cinnamyl to vanillyl (C/V) phenols provide information on vegetation sources; and the ratios of vanillic acid to vanillin, (Ad/Al)v, and syringic acid to syringaldehyde, (Ad/Al)s, indicate the degradation stage of lignin materials. Concentrations of lignin-derived phenols were determined for the surface and subsurface sediments of a Scottish sea loch, Loch Creran, using a CuO oxidation method. In order to achieve the highest methodological efficiency, a series of validation experiments for each procedural step were carried out. As a result, several procedural steps were optimized. It was found that a lower oxidation temperature resulted in higher product yield and the duration and temperature of the silylation step have no effect on the outcome of the process. Studies of seasonal variations of lignin parameters showed that the occasional increase in lignin content in sediment trap samples was attributable to materials discharged from River Creran and the incoming water from the direction of Creagan bridge. The flow regime caused resuspension of surface sediments and entrainment of lignin materials into the water column. Lignin parameters exhibited more significant trends across an axial transect of the loch (from the head to mouth). Total lignin content decreased and the C/V ratios increased from upper to lower Loch Creran as these lignin materials were transported further down the loch and were subjected to hydrodynamic sorting processes.

Trade-offs between shellfish aquaculture and benthic biodiversity: A modelling approach for sustainable management

This paper presents an ecosystem modelling approach aimed at improving shellfish aquaculture management by explicitly considering natural benthic biodiversity. This methodology uses a combination of benthic field survey data, sediment and bathymetric mapping, physiological models and dynamic ecosystem modelling. The Wild species Integration for Shellfish Ecoaquaculture (WISE) approach helps to understand the baseline food requirements for maintaining natural benthic biodiversity of suspension-feeding organisms, thus informing managers on potential upper thresholds for shellfish aquaculture. WISE was tested in four coastal systems in Europe and China, including bays, estuaries and sea loughs with widely differing aquaculture activities. In the European systems, where the aquaculture industry is developing, species diversity and abundance are much higher and suspension-feeding wild species play an important role in the consumption of food resources. Densities of wild individuals were estimated to be 13 ind m−2 in Sanggou Bay (total: 2×109), 33 ind m−2 in Xiangshan Gang (total: 122×109), 95 ind m−2 in Carlingford Lough (total: 4.62×109) and 175 ind m−2 in Loch Creran (total: 2.62×109). Total clearance rates by wild populations were calculated as 5% of the total volume d−1 in Sanggou Bay (75×106 m3 d−1), 11% d−1 in Xiangshan Gang (434×106 m3 d−1), 40% d−1 in Loch Creran (93 – 99×106 m3 d−1) and 45% d−1 in Carlingford Lough (170–250×106 m3 d−1). In relative terms, wild populations play a more important role than cultivated shellfish in clearing suspended particles from the European systems due to the much lower aquaculture activity. 56% and 76% of total primary production in Loch Creran and Carlingford Lough, respectively, are consumed annually by wild organisms, while less than 50% is consumed in Chinese systems (45% in Sanggou Bay and 2.9% in Xiangshan Gang). Integration of the WISE approach within broader ecological modelling illustrates some of the trade-offs between commercial aquaculture and the conservation of biodiversity, showing that rates of and capacities for shellfish culture are reduced when both wild and cultured suspension-feeding species are considered in relation to the available seston. When food resources are partitioned between wild and cultivated species, there is a decrease in individual length and weight (9 to 22% reduction in shell length and 24 to 52% reduction in total fresh weight for the Pacific oyster; reductions of 6% in length and 20% in weight for blue mussel; reductions of 4% in length and 13% in individual weight for bivalves in Xiangshan Gang), resulting in a lower aquaculture production (e.g. for Pacific oyster, a reduction of 12.5% in Carlingford Lough, 34% in Loch Creran and of 9% for bivalves in Xiangshan Gang).