Mussel Aquaculture Research Articles

A Box Model for Ecosystem-Level Management of Mussel Culture Carrying Capacity in a Coastal Bay

The carrying capacity of shellfish aquaculture is determined by the interaction of cultured species with the ecosystem, particularly food availability to suspension feeders. A multiple box dynamic ecosystem model was constructed to examine the carrying capacity for mussel (Mytilus edulis) aquaculture in Tracadie Bay, Prince of Edward Island, Canada. Criteria for carrying capacity were based on chlorophyll concentration. The model was run in two different years (1998 and 1999) in which time series for three points inside the bay and a point outside the bay were available. This data set allows spatial validation of the ecosystem model and assessment of its sensitivity to changes in boundary conditions. The model validation process indicated that the differential equations and parameters used in the simulation provided robust prediction of the ecological dynamics within the bay. Results verified that mussel biomass exerts top-down control of phytoplankton populations. The model indicates that conditions observed during 1999 are more sensitive to grazing pressure from aquaculture than was observed during 1998, highlighting the importance of inter-annual variability in carrying capacity of the bay. This result is important from a management perspective because it emphasizes application of a precautionary policy and prediction in regulation of aquaculture activity in the bay. Retrospective scenarios showed that although the bay could yield greater mussel biomass production, stress on the environment would lead the ecosystem outside of its natural range of variation. Despite the spatial simplicity employed in the present model, it provides substantial management capability as well as an ecosystem-oriented approach to shellfish aquaculture.

Key parameters for the consumption suitability of offshore cultivated blue mussels (Mytilus edulis L.) in the German Bight

The occurrence and composition of toxic algae, and presence of viruses and other human microbial pathogens in production areas of mussels are factors determining suitability of mussel products for human consumption. As bivalves feed by filtering large volumes of water, potentially toxic viruses, algae, and bacteria as well as phytoplankton are ingested. With the expansion of mussel aquaculture and subsequent increase in human consumption of mussel products, improved risk management is required for consumer protection. For example, shifting production to offshore areas (e.g. wind farms) can decrease the hazards of infection due to dilution of contaminants, and increase overall health of mussels. In addition, the deployment of off-bottom cultivation methods such as longlines increases the condition index, growth, and aesthetic appearance of mussels. However, other hazards like algal toxins not yet monitored on a regular basis, may play a more important rule offshore. Here, we present an analysis of biological, economic, and consumer health-related aspects of mussel cultivation under near- and offshore conditions.

Biodeposit production and benthic loading by farmed mussels and associated tunicate epifauna in Prince Edward Island

An experimental study was done to evaluate the biodeposition dynamics associated with mussels and two fouling tunicates, Ciona intestinalis and Styela clava, in mussel aquaculture in Prince Edward Island (PEI), eastern Canada. The presence of C. intestinalis on small constructed mussel socks increased biodeposition by a factor of about 2 relative to mussel socks without tunicates. S. clava were small and had a negligible effect on total biodeposition from mussel socks although they increased sedimentation rates relative to that of abiotic control socks. Sinking rates of faecal pellets from large C. intestinalis varied between 1.39 and 6.54cm s−1 (LSMean=2.35cm s−1). Using biodeposit production and sinking rates and hydrological data obtained in the present study, footprints of benthic loading due to mussel and tunicate biodeposition for a typical mussel farm in PEI were modelled using Shellfish-DEPOMOD. The results show benthic loading below longlines with C. intestinalis to be ca. 2 times greater than those from lines with only mussels with rates of up to 15.2g m−2 d−1. However, given the greater settling rate of C. intestinalis biodeposits relative to mussel biodeposits, the extent of the footprint (≥1g m−2 d−1) is similar or even more restrained.

Survey of mussel (Mytilus)species at Scottish shellfish farms

Mytilus trossulus and its hybrids with the native species Mytilus edulis and also Mytilus galloprovincialis have been recently detected in both farmed and natural populations of mussels in Scotland, adding complexity to the known M. edulis×M. galloprovincialis hybrid zone in Europe. Mytilus trossulus was first found in Scotland at aquaculture sites, where it was associated with significant losses in production and reductions in profitability. Mytilus trossulus and its hybrids have been identified at higher frequencies in farm stock than in natural intertidal populations, raising concerns about the potential wider impact of M. trossulus genotypes at mussel aquaculture sites in Scotland. The present study clarifies the composition of Mytilus species in cultivation at Scottish mussel aquaculture farms, by screening samples from 41 mussel aquaculture sites using a high-throughput real-time PCR methodology. Mytilus edulis alleles were detected at all sites. Mytilus galloprovincialis alleles were detected from samples collected at 39 sites, and M. trossulus alleles were found at five sites. Overall, M. trossulus genotypes were restricted in their geographical distribution. It is suggested that, in order to support the sustainability of the Scottish shellfish cultivation industry, the economic impact arising from the presence of M. trossulus could be limited through good management practice.

First evidence of fiberglass ingestion by a marine invertebrate (Mytilus galloprovincialis L.) in a N.W. Mediterranean estuary

Alfacs Bay is a N.W. Mediterranean estuary important for mussel (Mytilus galloprovincialis) aquaculture. During studies at the site, fiberglass particles were detected. The presence of fiberglass occurred naturally in the water throughout the study period (November 2006 to July 2007). An investigation was undertaken into its role in the feeding behavior of the local mussels. Fiberglass was present in all types of mussel samples. Rejection, which we would have expected for the whole study period, was only evident during the second season studied. To our knowledge, this is the first report of the ingestion of fiberglass by a marine organism. Our novel finding indicates the need to investigate fiberglass ingestion by marine organisms at different levels of the food web and the possible implications for human health and the health of the organisms themselves. In addition, we propose the use of mussels as sentinel organisms to monitor fiberglass contamination in marine ecosystems.

Preliminary evaluation of effects of invasive tunicate management with acetic acid and calcium hydroxide on non-target marine organisms in Prince Edward Island, Canada

The proliferation of invasive tunicates in Prince Edward Island (PEI) estuaries has necessitated the development of approaches for managing tunicates that foul aquaculture structures, especially Styela clava and Ciona intestinalis. Spraying or immersion with a saturated solution of hydrated lime (calcium hydroxide) or 5% acetic acid are effective against these tunicates, but are also biocidal to a variety of non-target organisms as demonstrated by bioassays with the bacterium Vibrio fischeri, sand shrimp Crangon septemspinosa and threespine stickleback Gasterosteus aculeatus. Both chemicals have the potential to alter estuarine pH, which should remain within the limits 7.0-8.7 mandated by federal water quality guidelines. Acetic acid is no longer used as a commercial treatment in PEI and currently poses no risk to the environment. The pH of saturated hydrated lime solutions used for immersing mussel socks reached 12.6, but the “pH footprint” in the estuarine water column was limited to a radius of 5 tonnes/ha) of quicklime (calcium oxide) pellets mainly converted to hydrated lime within minutes, but chemical conversion of hydrated lime to harmless calcium carbonate took up to 18 days depending on temperature, pellet size, and the amount of quicklime applied. Conversion of hydrated lime to calcium carbonate should be more rapid at the much lower daily application rates (<0.007 tonnes/ha) of hydrated lime in powdered form, which represented the maximum amount likely to be used in mussel aquaculture for tunicate management in PEI. In most PEI estuaries, dilution by tidal mixing alone is probably sufficient to return the pH to normal values within a tidal cycle at these relatively low inputs of hydrated lime, even without taking into account the chemical conversion which would be occurring simultaneously. Decisions about whether to use chemical treatments must balance economic and potential environmental costs of treatment against the known economic consequences of unmanaged tunicate biofouling. A recent shift to use of pressure washing will reduce the potential for impacts associated with chemical treatments, but may not be feasible in estuaries infested with Styela clava.

Local enhancement of epibenthic macrofauna by aquaculture activities

Bivalve aquaculture can influence coastal marine ecosystems by increasing organic material deposition, which, in turn, can have multiple direct and indirect effects on the surrounding benthic community. We assessed the influence of blue mussel Mytilus edulis aquaculture on the epibenthic macrofauna at 4 sites in Prince Edward Island, eastern Canada. The abundance of macroinvertebrates and benthic fishes (>2 cm) was evaluated by visual counts using SCUBA within 4 mussel aquaculture facilities (‘farms’) and at locations at distances of 50, 100, 500 and 2000 m outside of them in June, August and November 2005. Benthic assemblages were dominated by seastars Asterias sp. (79%), rock crabs Cancer irroratus (8%), mud crabs Neopanope sayi (6%), moon snails Lunatia heros (2%), winter flounders Pleuronectes americanus (2%), American lobsters Homarus americanus (1%) and hermit crabs Pagarus sp. (1%). Although there was great variability among sites and sampling dates, mussel aquaculture had a clear effect on total abundance, which was generally greater within farms than at distances outside of them. These increases in abundance were mainly associated with increased numbers of seastars and rock crabs. Taxonomic richness and evenness differed among some mussel farms and distances outside of mussel farms, but there were no clear trends that suggested a negative influence of mussel aquaculture. Multivariate analyses indicated that communities within mussel farms differed from those at corresponding communities at distances outside of farms, but that the taxa that contributed to these differences varied among farms. Taxonomic assemblages for a specific farm and date were generally similar among distances outside of farms and increases in the abundance of epibenthic macrofauna appeared to be largely restricted to the immediate vicinity of mussel farms, i.e. <50 m. This increase in abundance probably reflected the attraction of mobile fauna due to increased food supply and possibly to the creation of a more heterogeneous habitat. These results suggest that large macroinvertebrates and benthic fishes, including ecologically and commercially important species, seem to respond positively to the presence of suspended mussel culture.

ENSO and riverine control of nutrient loading, phytoplankton biomass and mussel aquaculture yield in Pelorus Sound, New Zealand

Multi-year time-series were used to describe oceanic and riverine nutrient supply and primary biomass in Pelorus Sound, a 50 km long estuary supporting most of New Zealand's $200 mil- lion per annum mussel Perna canaliculus aquaculture industry. In the summer half-year (October to March), when the Southern Oscillation Index (SOI) was negative (El Nino), NNW along-shelf wind stress strengthened and sea surface temperature (SST) at the Sound entrance cooled, indicating upwelling. This triggered increases in phytoplankton biomass, particulate nitrogen (PN) and per capita yield of farmed mussels in the Sound. In the winter half-year (April to September), wind stress was unrelated to SOI, but during NNW winds Pelorus River flows increased, along with NO3 - , phyto- plankton biomass, PN and mussel yield. During an extended period of positive SOI (La Nina), SSE winds and drought during 1999 to 2002, seston (PN) abundance and its food quality decreased, con- comitant with a mussel yield decrease of ~25% throughout Pelorus Sound. Seston and mussel yield had recovered by 2003 without reductions in farming intensity, so over-grazing by mussels did not cause the yield minimum. Instead, climatic forcing of oceanic and riverine N supply and seston bio- mass underlay the inter-annual variation in mussel yield. As tracers of the relationship of nutrient loading and production, PN and mussel yield appeared more reliable than NO3 - or chl a concentra- tions. In Pelorus Sound, oceanic and riverine N supplies are seasonally complementary and sustain year-round mussel yield, although their inter-annual variability, linked to wider climate forcing, can drive considerable fluctuation in yield over the decadal scale.

Influence of mussel aquaculture on sediment organic enrichment in a nutrient-rich coastal embayment

Effects of mussel Mytilus edulis aquaculture on benthic organic enrichment were deter- mined in Tracadie Bay, a shallow, nutrient-rich embayment in Prince Edward Island, Canada. Water content (WC), inorganic grain size (GS), organic matter (OM), redox potentials (EhNHE) and free sul- fides (S) in the upper 2 cm of sediment were measured at 58 stations throughout the inlet to evaluate spatial variations between lease and non-lease locations. MANOVA results showed that mean (±SD) values for WC (64.8 ± 12.7%), OM (9.8 ± 4.3%), and S (1794 ± 771 µM) were significantly (p < 0.005) higher and EhNHE lower (-51 ± 78 mV) within mussel leases (n = 24) vs. non-lease areas (n = 34). Negative regressions between S and GS and positive regressions between EhNHE and GS at lease and non-lease locations had similar slopes but intercept values were significantly higher for S and lower for EhNHE (p < 0.007) for lease locations. EhNHE and a Benthic Enrichment Index derived from EhNHE, OM and WC were inversely related to S. K-means clustering and multi-dimensional scaling showed that geochemical variables could be used to group stations into categories of benthic organic enrich- ment within mussel lease and non-lease areas characteristic of oxic-hypoxic sediments described by measures of S and EhNHE.

Quantifying erosion rates and stability of bottom sediments at mussel aquaculture sites in Prince Edward Island, Canada

Downward fluxes of organic biodeposits under suspended mussel culture cause benthic impacts such as microbial mat production. Quantifying sediment erosion in these coastal ecosystems is important for understanding how fluxes of organic matter and particulates contribute to benthic–pelagic coupling. Critical shear velocity ( u⁎), erosion rates and particle size distributions of resuspended sediment were measured at two sites; an impacted muddy site with extensive mussel culture (site 1), and a coarser sandier site with less mussel influence (site 2), using a new method for assessing sediment erosion at Tracadie Bay, Prince Edward Island in August 2003. Shear forces were generated by vertically oscillating a perforated disc at controlled frequencies. These forces correspond to shear velocity, using a re-designed and calibrated Particle Erosion Simulator. Undisturbed sediment cores obtained by divers and grab (sub-cored using a Plexiglas™ cores) were exposed to shear stress to compare differences between collection methods. Microbial mats were present at site 1 which initially biostabilized sediment against erosion due to ‘armoring’ of the sediment, but onset of erosion was abrupt once these mats failed. Erosion sequences at site 2 (without mat cover) were smoother resulting in less material being eroded. Mean mass of material eroded was 47 and 23 g m − 2 min − 1 at sites 1 and 2 respectively. Mat area cover and shear velocity was strongly related. Critical shear velocities varied between 1.70 and 1.77 cm s − 1 , with no obvious differences between location or collection method, so sediments from these two contrasting sites had identical mean critical shear velocities. Significant differences existed in the concentrations of chlorophyll a, colloidal and bulk carbohydrates, between mats and bare sediment from site 1. Particle sizes measured by videography of resuspended sediment at different shear velocities ranged from 100 μm (the minimum diameter capable of being detected by the system), to large mat fragments of 1700 μm for both sites. These results provide evidence of the relevance of using a portable erosion device to indicate how sediment erodability is affected by mussel–microbial relationships.

A micro-dilution method for detecting oxytetracycline-resistant bacteria in marine sediments from salmon and mussel aquaculture sites and an urbanized harbour in Atlantic Canada

A micro-dilution technique with changes in optical density (OD) used to measure bacterial growth over 72 h in culture media containing 0, 5, 10, 20, 40, 80 and 160 μg OTC (oxytetracycline) ml −1 was applied to determine growth inhibition (GI) in mixed bacterial strains cultured from samples of marine sediments and salmon feed pellets. Growth of control cultures ( Aeromonas salmonicida) was inhibited at all OTC concentrations. Some feed pellet samples and under-cage sediments from salmon aquaculture sites in the Bay of Fundy showed GI up to ≥160 μg OTC ml −1. Lower values (40 to 80 μg OTC ml −1) occurred in subsurface (5–18 cm) sediments, >100 m from salmon pens and adjacent to sewage outfalls in Halifax Harbour. GI values <20 μg OTC ml −1 in sediment from reference locations in Halifax Harbour and mussel aquaculture sites are considered to reflect natural background levels for OTC resistance.

Distribution and productivity of fish and macroinvertebrates in mussel aquaculture sites in the Magdalen islands (Québec, Canada)

Aquaculture structures may function in a manner analogous to artificial reefs, in that they provide a complex three-dimensional habitat for marine organisms and/or modify the surrounding environment. Further, aquaculture structures may increase the productivity of fish and macroinvertebrates similarly to natural complex habitats, such as seagrass beds. This research tested the general hypothesis that suspended bivalve culture increases the abundance and productivity of fish and macroinvertebrates. The study was done at two mussel farms in the Magdalen Islands, eastern Canada. Fish and macroinvertebrates were sampled in different areas within farms sites and in adjacent natural vegetated and unvegetated habitats. The instantaneous growth rates of winter flounder ( Pseudopleuronectes americanus), sand shrimp ( Crangon septemspinosa) and the rock crab ( Cancer irroratus) were estimated using physiological indicators (RNA/DNA ratios). The results demonstrated that mussel sites are not equivalent to natural structurally complex seagrass beds with respect to fish and macroinvertebrate assemblages. Several species were abundant in mussel farms, including winter flounder and rock crab. This work, however, provided little evidence to suggest that there was greater productivity of these fish and macroinvertebrates at mussel farms, as growth rates were usually equivalent in different habitats. This study, to our knowledge, is the first attempt to determine changes in productivity brought about by aquaculture. As future development of mussel aquaculture increases in many regions around the world, the methods presented here will provide baseline information on the abundance and productivity of fish and macroinvertebrates associated with aquaculture sites.

Evaluation of indicators used to detect mussel farm influence on the benthos: Two case studies in the Magdalen Islands, Eastern Canada

The aim of this study was to identify appropriate indicators to determine the influence of mussel aquaculture on the benthic environment. Both sediment [particle size, sediment profile imaging (SPI), % OM] and benthic community (abundance, biomass, number of species, Margalef’s species richness, Shannon–Weiner diversity, Pielou’s eveness, individual body mass, trophic group, a biotic index — AMBI, and community structure) characteristics were evaluated at two mussel farms in Great-Entry (GE) and Havre-aux-Maisons (HAM) lagoons in the Magdalen Islands (Quebec, Canada). Sampling stations were positioned directly beneath the outer-most mussel lines (0 m) and at distances of 3, 6, 9, 15, 30 m and at a control site (at either 300 or 500 m) along a transect leading from each farm. Contrasting patterns were observed. At GE, sediment characteristics and benthic communities did not vary among stations and were characterized by low diversity, abundance and biomass. At HAM, % OM decreased and macrofaunal diversity and abundance increased with increasing distance from the farm. Biomass was low under the mussel line, increased between 3 and 30 m and was low again at 300 m. This was explained by the abundance of the polychaete Pectinaria granulata, which seems to have benefited from a moderate organic loading associated with the mussel farm. The mean individual biomass of the second-order opportunistic deposit feeders P. granulata and Heteromastus filiformis decreased with distance from the farm, whereas that of the pollution-sensitive suspension feeder Ensis directus and deposit feeder Tellina agilis increased with increasing distance from the farm. At HAM, the effects of mussel farming were restricted to the vicinity of the farm, while at GE the pattern was less clear. The GE mussel farm had either little effect on the local environment or else larger-scale but diffuse effects. The study showed that the a priori choice of the sampling stations and indicators may influence the interpretation of the results. Community structure and SPI were the most efficient indices for detecting both small- and broader-scale influences at both studied mussel farms.

An integrated GIS approach for sustainable aquaculture management area site selection

Within New Zealand, growth in the aquaculture industry has led to the diversification of aquaculture sites from more sheltered bays and harbours toward open coast locations. Coastal zone managers, along with the aquaculture industry, aim to ensure the long-term sustainability of any ‘new’ sites selected. Through targeted data collection programmes and the subsequent implementation of Geographic Information System (GIS) based models, the most suitable and sustainable locations for Aquaculture Management Areas (AMAs) can be identified. This approach is applied within the Bay of Plenty, New Zealand, with specific reference to suspended mussel ( Perna canaliculus) aquaculture. Within the region, areas where maximum sustainability may be achieved make up 18% of the total area considered, with conflicting uses and other constraints accounting for 46%. Whilst further site and development specific studies are required to determine explicit carrying capacities, the effort required has been considerably reduced by eliminating unsuitable locations and identifying those where sustainability can be maximised.

Growth and condition index of mussel Mytilus galloprovincialis in experimental integrated aquaculture

Integrating mussel and finfish aquaculture has been recognized as a way to increase profits and decrease environmental impacts of finfish aquaculture, but not enough is known about the effects of finfish aquaculture on mussel growth. Here we present a pilot study aimed at determining how distance from finfish aquaculture affects mussel growth. To this end, we measured growth and condition index of mussel (Mytilus galloprovincialis) at three different distances (0, 60 and 700 m) from finfish aquaculture in the eastern Adriatic Sea. There was a statistically significant difference in growth of tagged mussels with respect to site. Average measured lengths of mussels at sites 1, 2 and 3 after the 10 months of the experiment were 57.60, 62.73 and 58.66 mm. Mussels grew fastest from March to May, and slowest from July to September, regardless of their position. Condition index showed spatial and temporal variations with higher values during fall and winter (∼23), and lower values during spring and summer (∼20). Our results show that production cycle in areas traditionally considered suboptimal for aquaculture can be equivalent to the cycle in areas traditionally considered optimal for mussel aquaculture if mussel aquaculture is integrated with finfish aquaculture.

Multi-scale spatial variations in benthic sediment geochemistry and macrofaunal communities under a suspended mussel culture

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 348:103-115 (2007) - DOI: https://doi.org/10.3354/meps07034 Multi-scale spatial variations in benthic sediment geochemistry and macrofaunal communities under a suspended mussel culture Myriam D. Callier1,2, Christopher W. McKindsey1,2,*, Gaston Desrosiers2 1Ocean and Environmental Sciences Division, Maurice Lamontagne Institute, Fisheries and Oceans Canada, PO Box 1000, Mont Joli, Quebec G5H 3Z4, Canada 2Institut des Sciences de la Mer, Université du Québec à Rimouski, 310 allée des Ursulines, CP 3300, Rimouski, Quebec G5L 3A1, Canada *Corresponding author. Email: mckindseyc@dfo-mpo.gc.ca ABSTRACT: The chemical and biological effects of biodeposition from a mussel culture were evaluated at multiple spatial scales during the summer of 2003 in Great-Entry Lagoon, eastern Canada. Sediment samples were collected directly under and between mussel lines (positions 10 m apart: 10 m scale) from multiple sites (located ca. 100 m apart: 100 m scale) in each of 3 zones: reference (R), 0+ and 1+ mussel cohort zones (located at least 500 m apart: km scale). In general, redox potential decreased and sulphide concentration increased with sediment depth but did not differ among zones or positions. A clear difference in macrofaunal community structure was observed among R, 0+ and 1+ zones, as well as between the positions directly under mussel lines in 1+ sites (1+under) and those between 1+ mussel lines (1+between). The benthic community at 1+under positions was dominated by an opportunistic species (Capitella capitata) and had the lowest diversity and biomass. 0+ sites were characterised by the greatest number of species and biomass, suggesting that some species have benefited from a moderate organic loading from the 0+ mussels. Historical data indicate that the deeper part of the lagoon was a naturally enriched environment. The mussel farm probably contributes to local organic enrichment. Comparison of benthic communities from the present study (>20 yr after the initiation of mussel aquaculture) in the site to similar historical data from 3 periods (1975 and 1978, before mussel farming; 1982, at the start of farming activities; and 2004, after the 1+ mussel harvest) showed that community structure differed largely because of the greater abundance of deposit feeders in 2003. However, among these 3 periods the differences in benthic community structure were no greater than differences observed between years within the periods. KEY WORDS: Aquaculture · Biodeposition · Organic enrichment · Redox potentials · Sulphide · Macrofaunal community structure · Spatial scale Full text in pdf format PreviousNextCite this article as: Callier MD, McKindsey CW, Desrosiers G (2007) Multi-scale spatial variations in benthic sediment geochemistry and macrofaunal communities under a suspended mussel culture. Mar Ecol Prog Ser 348:103-115. https://doi.org/10.3354/meps07034 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 348. Online publication date: October 25, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Influence of mussel aquaculture on nitrogen dynamics in a nutrient enriched coastal embayment

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 347:61-78 (2007) - DOI: https://doi.org/10.3354/meps06997 Influence of mussel aquaculture on nitrogen dynamics in a nutrient enriched coastal embayment Peter J. Cranford1,*, Peter M. Strain1, Michael Dowd2, Barry T. Hargrave1, Jonathan Grant3, Marie-Claude Archambault3 1Ecosystem Research Division, Fisheries and Oceans Canada, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada 2Department of Mathematics and Statistics, Dalhousie University, Halifax, Nova Scotia B3H 3J5, Canada 3Department of Oceanography, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada *Email: cranfordp@mar.dfo-mpo.gc.ca ABSTRACT: The combined influences of intensive mussel aquaculture and watershed nutrient inputs on nitrogen dynamics in Tracadie Bay, Prince Edward Island, Canada, were examined using a nitrogen budget and an ecosystem model. Budget calculations, and inputs and parameters for the model were based on extensive field data. Both approaches showed that mussel aquaculture has a dominant influence on all aspects of the nitrogen cycle and dramatically alters pathways by which nitrogen reaches the phytoplankton and benthos. A large proportion of phytoplankton production is supported by land-derived nitrogen and this anthropogenic input is important for sustaining existing levels of mussel production. The amount of nitrogen removed in the mussel harvest is small compared with agricultural nitrogen inputs and the amounts excreted and biodeposited on the seabed. Mussel biodeposition greatly increases the flux of nitrogen to the benthos, with potentially serious eutrophication impacts. Results from the observation-based nitrogen budget and dynamic model were compared and both support the above conclusions. However, the ability of the model to test different scenarios and to provide additional information (e.g. fluxes) over a finer spatial scale led to insights unattainable with a nitrogen budget. For example, food appears to be less available to mussels at the head of the Bay than at the mouth, despite the lower density of grow-out sites in the former location. The number of fundamental ecosystem processes influenced by the mussels and the complexity of their interactions make it difficult to predict the effects of mussels on many ecosystem properties without resorting to a model. KEY WORDS: Eutrophication · Nitrogen cycling · Nitrogen budget · Ecosystem model · Ecophysiology · Biodeposition · Excretion Full text in pdf format PreviousNextCite this article as: Cranford PJ, Strain PM, Dowd M, Hargrave BT, Grant J, Archambault M (2007) Influence of mussel aquaculture on nitrogen dynamics in a nutrient enriched coastal embayment. Mar Ecol Prog Ser 347:61-78. https://doi.org/10.3354/meps06997 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 347. Online publication date: October 11, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Hydrodynamic Forcing of Long-Line Mussel Farms: Observations

The first detailed observations of the motion and loading of a mussel (shellfish) aquaculture long-line are described in order to identify the dominant modes of flow-structure interaction and provide a baseline for prediction of future structures. A long-line is typically a 120m long sequence of surface floats beneath which is looped rope bearing the mussel crop. Accelerometer and load cell data from sensors mounted on the structure along with remote radar data are examined in the context of wave and current measurements. The mussels comprise the largest mass and drag element of the structure, and the tidally affected pretensioning of the mooring lines dominates the background load. However, waves and currents increase the maximum load by potentially 100% over this value. The floats at each end of the long-line follow the wave orbital motion reasonably well, more so than the floats in the middle of the backbone. The mussel-laden loops of rope (droppers) clearly respond differently to the floats, implying flexibility in the vertical dimension. This suggests that flow around the droppers, which influences mussel feeding ability and hence production, is complex and highly three-dimensional.

The effect of anti-fouling treatments for the clubbed tunicate on the blue mussel, Mytilus edulis

A major problem for the mussel aquaculture industry on Prince Edward Island, Canada surfaced in the late 1990s with the introduction of a fouling organism commonly known as the clubbed tunicate, Styela clava. This organism has the ability to infest mussel cultivation equipment to the point where productivity is severely compromised. This study examined the effects two anti-fouling treatments, air exposure and acetic acid, had on experimental mussel populations. Socked mussel seed obtained from a mussel farm on Prince Edward Island was exposed to three treatment regimes and subsequently placed on a long-line in New London Bay, P.E.I. The treatments were a 40-h air exposure, 30-s 5% acetic acid immersion and a 2-min 5% acetic acid immersion. Treatment effects on mussels were measured after seven months in the field, along with untreated controls. Mussel quality was assessed using mussel sock weights, length, condition index and changes in genetic characteristics measured at allozyme loci. A significant decrease in mean sock weights was found for all three treatments compared to control sock weights ( p < 0.05). Sock weights for the air exposure, 30-s acetic acid dip and 2-min acetic acid dip were reduced by 38%, 67%, and 74% respectively compared to control sock weights. This revealed a significant loss in productivity (incl. mortality and loss of attachment) in the treated mussel populations. However, results on the other characteristics used to assess mussel fitness found no long-term effects on the health or genetic structure of the mussel populations that survived the treatment regimes. Although air exposure is now considered an inefficient method to kill post-larval Styela clava, the results provide preliminary evidence regarding the safe use of the acetic acid treatment regimes tested in terms of long-term mussel population health.

Behavioural interactions of seabirds with suspended mussel longlines

Increased abundances of a number of seabird species have been found in areas of mussel longline aquaculture (compared to control sites) in a recent study at Bantry Bay, southwest Ireland. The aim of this study was to investigate whether this form of mussel aquaculture also affects the activity budgets and foraging behaviour of these seabirds. Scan-sampling was used to compare seabird activity budgets between three areas of mussel longline aquaculture and three control sites. Foraging activities of Great-Northern Divers Gavia immer, an Annex 1 species under the Euopean Union's Birds Directive, were also compared between sites using focal sampling. The behaviour of gulls (Larus sp.), Cormorants Phalacrocorax carbo, Shags Phalacrocorax aristotelis and Great-Northern Divers (but not auks, Alcidae) differed significantly between areas of mussel aquaculture and control sites in this study. Mussel suspension buoys were heavily utilized by gulls, cormorants and shags as safe perching platforms for preening activities. Gulls also fed extensively on epifauna attached to the buoys. Great-Northern Divers spent more time snorkelling (head submerged in search of food) in mussel sites than in the control sites, however dive duration and visible foraging success rates did not differ significantly between sites. Overall, the environmental impact of mussel suspension culture appears to be positive or neutral on marine bird species occurring at this study site.