Kenneth D. Black

DEPOMOD-modelling the deposition and biological effects of waste solids from marine cage farms

Abstract To enable better predictive capability of the impact from large marine cage fish farms on the benthos and improved objectivity in the regulatory decision-making process, a computer particle tracking model DEPOMOD was developed. DEPOMOD predicts the solids accumulation on the seabed arising from a fish farm and associated changes in the benthic faunal community. The grid generation module allows the user to set up a grid containing information on depth, cage and sampling station positions for the area of interest. Given the information on wastage rates of fish food and faeces and hydrodynamics of the area, the initial deposition of particles on the seabed can then be predicted with the particle tracking model. The resuspension model then redistributes particles according to near-bed current flow fields to predict the net solids accumulated on the seabed within the grid area. From quantitative relationships between benthic community descriptors and solids accumulation, predictions of the level of benthic community impact can then be made. The particle tracking model was validated using sediment trap studies. Model predictions of flux (g/m 2 /day) generally agreed well with field data with an accuracy of ±20% and ±13% for a dispersive and depositional site, respectively. Using parameters from the validated resuspension model (rare among models in this field), semi-empirical quantitative relationships between predicted solids accumulation (g/m 2 /year) and observed Infaunal Trophic Index (ITI) and total individual abundance were established using data from numerous Scottish marine fish farms. A submodel was also validated for predicting feed input throughout a growing cycle for planning purposes. DEPOMOD may be used for assessing the potential impact of a farm throughout a growing cycle, or if the biomass consent is increased. It may also be used in the site selection process of a new farm to investigate the proposed farm position and biomass levels. Prediction of the dispersion of particulates during use of in-feed medicines may also be undertaken.

Growth of European sea bass (Dicentrarchus labrax L.) under hypoxic and oscillating oxygen conditions

Effects of moderate hypoxia and oscillating oxygen conditions on growth of European sea bass (Dicentrarchus labrax L.) were investigated. Groups of four to six sea bass (initial weights 40–90 g) were exposed to one of three oxygen regimes (40% air saturation; oscillations between 40–86% with a period of 770 min; 86% as a control) at 22°C and a salinity of 37 for 1 month. All fish survived and gained weight, but relative to the controls, the sea bass exposed to hypoxic conditions consumed significantly less food, exhibited a reduced growth, and had a lower condition factor. Oscillating groups were intermediate, and not statistically distinguishable from either normoxic or hypoxic treatments. Feed conversion efficiency and variation in body size were not significantly affected by oxygen conditions. Growth was correlated with feed intake, suggesting that reduced growth under moderate hypoxic or oscillating oxygen conditions is primarily due to reduced appetite and not a consequence of a decrease in feed conversion efficiency.

Bioturbation, sediment fluxes and benthic community structure around a salmon cage farm in Loch Creran, Scotland

Abstract This study examined bioturbation along an organic carbon gradient away from an Atlantic salmon farm and sought to determine relationships between benthic fluxes, mixing intensity and the infaunal community structure. Macrofaunal community structure, abundance and biomass were examined at stations with varying quantities and qualities of organic matter input. In situ benthic chambers were used to determine oxygen and nutrient fluxes and mixing parameters were derived from down core profiles of chlorophyll a (chl a ). Mean oxygen demand of sediments ranged between 8.8 and 467.8 mmol m −2 day −1 , being highest beneath the fish farm and indicating very high rates of community respiration and organic matter diagenesis. Oxygen and nutrient fluxes followed similar trends to community abundance and biomass, declining with increasing distance from the farm. Mixing intensity increased with distance from the farm until returning, at the farthest station, to values similar to those measured beneath the farm. The differences in the community structure between sediments beneath the farm and furthest from it suggest that similar diffusive mixing coefficients are generated by different mechanisms. These results generally follow the successional model of Pearson and Rosenberg [Oceanogr. Mar. Biol. Ann. Rev. 16 (1978) 229.], with the exception of the farthest station, but suggest that the bioturbation potential of the community over short time scales is greatest at stations with intermediate qualities and quantity of organic matter. However, the methods used here to assess mixing over short time scales (i.e. diffusive mixing coefficient and the mixed layer depth) do not account for the activities of deep burrowing infaunal animals, such as Maxmuelleria lankesteri , known to be present at the farthest station.

Fatty acid compositions of gonadal material and diets of the sea urchin, Psammechinus miliaris: trophic and nutritional implications

The fatty acid compositions of gonadal material was examined for the sea urchin Psammechinus miliaris (Gmelin) held in aquaria and fed either salmon feed pellets or the macroalga, Laminaria saccharina for 18 months. Gonadal material was also examined from P. miliaris collected from four field sites, including commercial scallop lines encrusted with the mussel, Mytilus edulis, sea cages stocked with Atlantic salmon Salmo salar and two intertidal sea-loch sites, characterised by either a fine mud or a macroalgal substratum. The fatty acid compositions of known and potential dietary material was examined. The proportions of certain fatty acids in the gonads of P. miliaris were significantly affected by diet type and location. Docosahexaenoic acid (DHA) 22:6 n-3 was significantly higher in the gonads of the sea urchins fed salmon feed in aquaria and collected from the salmon cages and scallop lines than in the gonads of the sea urchins fed L. saccharina in aquaria and collected from the intertidal sea loch sites. The salmon feed and the mussel tissue also contained a high proportion of this fatty acid. Stearidonic acid 18:4 n-3 and arachidonic acid 20:4 n-6, however, were found in significantly higher proportions than DHA in the gonads of the sea urchins fed L. saccharina and collected from the two intertidal sea-loch sites. L. saccharina was also found to contain high proportions of stearidonic and arachidonic acid. The gonads of the sea urchins collected from the intertidal site, characterised by a mud substratum, and from the scallop lines were found to contain a lower 18:1 n-9/18:1 n-7 ratio and a higher proportion of branched and odd-chained fatty acids, signifying a high dietary bacterial input, than the sea urchins held in the aquaria and collected from the salmon cage. 20:2 and 22:2 non-methylene-interrupted dienoic fatty acids (NMIDs) were found in P. miliaris fed diets lacking these fatty acids suggesting de novo biosynthesis. These results, therefore, suggest that the proportions/ratios of certain fatty acids in the gonads of P. miliaris could be used to give an indication of the predominant diet type of this species in the wild.

Validation of a fish farm waste resuspension model by use of a particulate tracer discharged from a point source in a coastal environment

To validate a resuspension model of particulate material (salmonid farm wastes), a UV fluorescent particle tracer was selected with similar settling characteristics. Tracer was introduced to the seabed (water depth ≈30 m) and sediment samples taken on days 0, 3, 10, 17 and 30 to measure the horizontal and vertical distribution of tracer in sediments. A concentric sampling grid was established at radii of 25, 50, 100, 150, 200, 400, 700 and 1, 000 m from the source on transects 30° apart. The bulk of the deployed tracer was initially concentrated in an area 25 m radius from the release point; tracer was observed to steadily decrease to zero over a period of 30 days. In a 200 m region measured from the release point in the direction of the residual current, the redeposition of tracer was low. A Lagrangian particle tracking model was validated using these observed data by varying resuspension model parameters within limits to obtain the best agreement between spatial and temporal distributions. The validated model generally gave good predictions of total mass budgets (±7% of total tracer released), particulary where tracer concentrations were high near the release point. Best fit model parameters (critical erosion shear stress=0.018 N m−2, erodibility constan=60 g m−2 d−1) are at the low end of reported parameters for coastal resuspension models. Such a low critical erosion shear stress indicates that the frequency of resuspension and deposition events for freshly deposited material is high.

Glycoprotein emulsifiers from two marine Halomonas species: chemical and physical characterization

Aims:  To partially purify and characterize bioemulsifiers produced by two new marine Halomonas species, TG39 and TG67, and to compare their emulsifying activities with those of commercial emulsifiers.

The effects of hydrogen peroxide on the gill tissues of Atlantic salmon, Salmo solar L.

Abstract Atlantic salmon were exposed to hydrogen peroxide (1.37–2.58 g l−1) over a range of temperatures (10.4–16.0 °C) simulating treatment for sea lice. Gill tissues and behaviour were monitored. Exposure to 2.58 g l−1 for 20 min caused total mortality (n = 18) while a shorter exposure, 10 min, at the same temperature caused only one mortality. Exposure to 1.37 g l−1 for 20 min at 10.4 °C caused no significant damage to gill tissues. There is a significant correlation (r = 0.895, F = 24.13, P

The lipid composition of sealoch sediments underlying salmon cages

Abstract The lipid composition of sediments underlying salmon cages in a Scottish sealoch was determined along with that of the diet supplied to the fish to examine the influence of lipids originating from fish farm wastes. Sediments were taken at regular intervals along a transect line perpendicular to the line of cages and extending 50 m on either side. Lipids were extracted from regions of the sediment cores corresponding to different depth layers of sediment and analyzed for lipid class and fatty acid composition. The lipid content of the surface layer of sediment (0–5 mm) directly under the cages (2 mg/g sediment) was substantially higher than that of the deeper layers of sediment. The amount of lipid in the surface sediment decreased markedly with the distance from the cages, with the decrease being more rapid on one side of the fish farm than the other. At the 50-m sampling sites, the lipid content of the surface sediment layer (0.4 mg/g sediment) was closer to that of the underlying layers. Triacylglycerols, the main lipid class present in the diet fed to the salmon, were present in sediments in highest concentration (0.44 mg/g sediment) in surface sediments directly beneath the cages. Free fatty acids, sterols, polar lipids and a combined hydrocarbons/wax esters/cholesterol esters fraction were all present at similar levels to those of triacylglycerols in sediments beneath the cages. The distribution pattern of the amounts of individual lipid classes in sediments followed that of total lipid and showed a decrease with the distance from the cages. The lipid component of the fish feed contained a higher level of polyunsaturated fatty acids, particularly 20:5( n − 3) and 22:6( n − 3), than lipid extracted from the sediments, while branched chain and odd-chain length fatty acids were more abundant in the latter. The principal fatty acid of the fish diet, 22:1( n − 11) (14.7% total fatty acids) comprised around 9% of the fatty acids of surface sediment layer directly under the cages, but less than 5% of those at 50 m. The proportions of the other characteristic fatty acids of the diet, 20:1( n − 9), 20:5( n − 3) and 22:6( n − 3), showed a similar decrease with distance. The results show that the lipid composition of sediments underlying marine fish cages is influenced by that of waste material from the cages.

Unlocking nature’s treasure-chest: screening for oleaginous algae

Micro-algae synthesize high levels of lipids, carbohydrates and proteins photoautotrophically, thus attracting considerable interest for the biotechnological production of fuels, environmental remediation, functional foods and nutraceuticals. Currently, only a few micro-algae species are grown commercially at large-scale, primarily for “health-foods” and pigments. For a range of potential products (fuel to pharma), high lipid productivity strains are required to mitigate the economic costs of mass culture. Here we present a screen concentrating on marine micro-algal strains, which if suitable for scale-up would minimise competition with agriculture for water. Mass-Spectrophotometric analysis (MS) of nitrogen (N) and carbon (C) was subsequently validated by measurement of total fatty acids (TFA) by Gas-Chromatography (GC). This identified a rapid and accurate screening strategy based on elemental analysis. The screen identified Nannochloropsis oceanica CCAP 849/10 and a marine isolate of Chlorella vulgaris CCAP 211/21A as the best lipid producers. Analysis of C, N, protein, carbohydrate and Fatty Acid (FA) composition identified a suite of strains for further biotechnological applications e.g. Dunaliella polymorpha CCAP 19/14, significantly the most productive for carbohydrates, and Cyclotella cryptica CCAP 1070/2, with utility for EPA production and N-assimilation.

Comparisons of fatty acid and stable isotope ratios in symbiotic and non-symbiotic brittlestars from Oban Bay, Scotland

The bed-forming brittlestars Ophiothrix fragilis , Ophiocomina nigra and Amphiura chiajei from Oban Bay, Scotland were studied using methods previously employed to study chemoautotrophic symbioses. Ophiothrix fragilis and A. chiajei both contain symbiotic bacteria (SCB) while Ophiocomina nigra is non-symbiotic. Samples were taken of Ophiothrix fragilis at approximately two-week intervals for one year. Symbiotic bacteria numbers were determined by direct counting of homogenates of the arms of 50 individual brittlestars. Water samples were analysed for chlorophyll content. Stable isotope ratios for carbon and nitrogen were determined for each homogenate sample. Regular SCB counts were made on the infaunal brittlestar A. chiajei . Homogenate samples of Ophiothrix fragilis , A. chiajei and the non-symbiotic Ophiocomina nigra were analysed to produce fatty acid profiles for each species. Symbiotic bacteria count varied by up to one order of magnitude in both Ophiothrix fragilis and A. chiajei with no evidence of seasonality in this variation. Symbiotic bacteria number was inversely correlated with δ 15 N but no relationship was established with δ 13 C. 16:1ω7 and 18:1.ω7 fatty acids were used as putative bacterial markers. Both symbiotic species had higher percentages of 16:1ω7 than the non-symbiotic Ophiocomina nigra . However, only Ophiothrix fragilis appeared to receive appreciable quantities of 18:1ω7 from its SCB. The SCB are heterotrophic and may contribute to the nitrogen budget of the host. The two symbiotic species studied here derive the bulk of their nutrition from conventional feeding but SCB make significant, additional contributions.