Mussel Aquaculture Research Articles

Reproduction and early life history of an invasive ascidian Styela clava Herdman in Prince Edward Island, Canada

In the past decade, many aquatic invasive species have been introduced into Prince Edward Island, Canada, coastal waters, and they have had adverse effects on the aquaculture and fisheries industry. For instance, the mussel aquaculture industry has been overwhelmed by extremely high abundances of the invasive ascidian Styela clava in some areas. To understand and minimize the risk of spread of S. clava to other shellfish aquaculture sites, basic information on the reproductive biology of the ascidian is needed. This study investigated Styela gonad development, larval abundance and recruitment. Gonad development, using histological methods, indicated ovaries were ripe from late June through late October, 2004. Weekly water samples indicated larvae were present from 24 June to 29 October, with a distinct abundance peak in mid-August. Recruitment occurred from 24 June to 21 October. Timing of larval sampling was judged to be a crucial part of evaluating recruitment potential for monitoring purposes and a field experiment was carried out to document spatio-temporal larval concentrations. Data were gathered over 30 h sampling periods on 4 August and 14 September 2004. Water samples were taken simultaneously on an hourly basis at three depths: surface, 2 m and 4 m below the surface. Results indicated peaks in larval abundance were, in most cases, limited to a 3 h time interval in the early afternoon. Larval concentrations increased with water depth.

A box model of carrying capacity for suspended mussel aquaculture in Lagune de la Grande-Entrée, Iles-de-la-Madeleine, Québec

An object-oriented model of environment–mussel aquaculture interactions and mussel carrying-capacity within Lagune de la Grande-Entrée (GEL), Iles-de-la-Madeleine, Québec, was constructed to assist in development of sustainable mussel culture in this region. A multiple box ecosystem model for GEL tied to the output of a hydrodynamic model was constructed using Simile software, which has inherent ability to represent spatial elements and specify water exchange between modelled regions. Mussel growth and other field data were used for model validation. Plackett–Burman sensitivity analysis demonstrated that a variety of bioenergetic parameters of zooplankton and phytoplankton submodels were important in model outcomes. Model results demonstrated that mussel aquaculture can be further developed throughout the lagoon. At present culture densities, phytoplankton depletion is minimal, and there is little food limitation of mussel growth. Results indicated that increased stocking density of mussels in the existing farm will lead to decreased mass per individual mussel. Depending on the location of new farm emplacement within the lagoon, implementation of new aquaculture sites either reduced mussel growth in the existing farm due to depletion of phytoplankton, or exhibited minimum negative impact on the existing farm. With development throughout GEL, an excess of phytoplankton was observed during the year in all modelled regions, even at stocking densities as high as 20 mussels m −3. Although mussels cultured at this density do not substantially impact the ecosystem, their growth is controlled by the flux of phytoplankton food and abundance of zooplankton competitors. This model provides an effective tool to examine expansion of shellfish farming to new areas, balancing culture location and density.

Protective socking material for cultivated mussels: a potential non-disruptive deterrent to reduce losses to diving ducks

Predation of cultivated mussels by diving ducks can threaten the viability of mussel farms. Conventional scaring tactics have had limited success at deterring ducks from feeding on cultivated mussels, because of rapid habituation and 24-h feeding cycles of some waterfowl species. We tested a socking material containing a biodegradable protective layer against predation by diving ducks on experimental blue mussel (Mytilus edulis) aquaculture sites in Prince Edward Island, Canada. We also assessed the effect of this new socking material on mussel growth and survival. Results showed that the protective socking has the potential to reduce losses to ducks, but did not perform well for all mussel seed sizes used by the industry. The protective layer also did not biodegrade fast enough, trapping a portion of mussels inside the sock, affecting growth and survival of these mussels. Improvements are needed to make this solution effective for all mussel sizes used by the industry and to make its production more cost effective.

Chemical cues promote settlement in larvae of the green-lipped mussel, Perna canaliculus

The large (70,000 tonnes) mussel aquaculture industry for the endemic New Zealand green-lipped mussel, Perna canaliculus Gmelin, currently relies almost entirely (80%) on wild caught seed that is often harvested attached to great quantities of floating algae. Natural vagaries in catches of wild mussel seed frequently result in shortages of mussel seed that, at times, have severely affected commercial aquaculture production. Both field and laboratory experiments were used to establish that chemical cues derived from algae significantly increase settlement of mussel larvae on artificial substrates. This is the first time an algal chemical cue has been implicated in the settlement behavior of P. canaliculus larvae. These results have potential commercial implications for improving mussel seed supply through inducing higher or more reliable levels of mussel settlement for aquaculture seed collection.

Inshore-offshore comparison of parasite infestation in Mytilus edulis: implications for open ocean aquaculture

Summary Offshore production offers a new perspective for mussel aquaculture in the German Bight (North Sea) as no expansion is possible in the intertidal and subtidal zone of the Wadden Sea because of restrictions on the number of licenses. The development of offshore wind farms offers a unique opportunity because of the associated infrastructure. Service platforms, as well as the pylons themselves, offer perfect structures for mooring longlines and other culture units. One of the advantages of offshore culture may be a lower parasite load in offshore mussels compared with mussels produced under traditional inshore bottom culture. By sampling mussel spat from offshore suspended buoys or collectors, we simulated an offshore culture situation and compared parasite infestation rates with those in mussel spat obtained from suspended inshore buoys or collectors, in mussels from inshore benthic subtidal beds and from inshore benthic intertidal mussel beds. Mussels from offshore sites were free of trematodes and shell-boring polychaetes. Parasitic copepods only occurred at a single offshore site, on a 20-year-old research platform, but not on buoys or collectors exposed for shorter time periods. All three monitored parasite taxa were present at all other sites. The highest prevalence was found for trematodes in inshore benthic intertidal mussels (78.7 ± 6.4%) and locally reached 100%. Through a variety of detrimental effects, trematodes, parasitic copepods and shell-boring polychaetes are known to affect growth performance and product quality. We therefore propose that offshore mussel production could be a promising culture procedure because it seems to result in lower parasite burden than at traditional culture sites. Whether offshore production also results in better survival and growth, compared with inshore mussel culture on a commercial scale, needs to be investigated further.

Acoustical and Sedimentological Characterization of Substrates in and Around Sheltered and Open-Ocean Mussel Aquaculture Sites and Its Bearing on the Dispersal of Mussel Debris

Side-scan sonar, camera observations, and sediment sampling are used to determine the seabed dispersal of mussel debris at three aquaculture farm sites in sheltered to exposed environments in the Marlborough Sounds, New Zealand. At the two sheltered farm sites, side-scan sonagraphs reveal high acoustic backscatter beneath culture sites and low backscatter in the immediate surrounds. This suggests a sharp contrast in seabed material around the edges of the farm. Photography and sediment samples reveal farms are underlain by mounds of shells with biodeposits infilling intershell voids and forming a veneer over entire mounds. In contrast, the surrounding seabed is naturally sedimented soft mud. Sediment from beneath the farms had total organic contents of 8%-19% decreasing sharply to natural levels of 4%-7%, 30 m from the farm's boundaries. The third site is exposed to energetic waves and currents, and exhibits low acoustic backscatter zones beneath the farm. Photographs show the seabed is predominantly clean sand with only scattered clumps of shells and no biodeposits visible. Sediments are typical of the natural setting. This lack of mussel debris indicates that there is sufficient energy to transport and dissipate the shell and biodeposits over a wide area with little impact on the natural sediment.

The effect of high air and water temperature on juvenile Mytilus edulis in Prince Edward Island, Canada

Mussel aquaculture on Prince Edward Island (PEI), Canada, is an important but relatively new industry. Although seed manipulation using hatcheries for mussel culture occurs on the west coast of North America, seed supply on the east coast of Canada, including Prince Edward Island (PEI), is based solely on wild collection. Two techniques for culling seed (<10 mm) were studied in this experiment to look at the effect on productivity, measured as size, growth and survival. The separate effects of air exposure or high water temperature treatments on a sample of Mytilus edulis spat were examined in the lab and in the field. The in vitro treatments resulted in a ∼50% mortality from an air exposure of 11 h at 27 °C and ∼75% mortality from a 6-h exposure to 33 °C water. Survivors of each treatment ( n=1152) were measured, along with controls ( n=2304) and randomly placed in compartmentalized (condo) cages. Cages were deployed on a mussel farm in each of three bays on Prince Edward Island, Canada. Size, growth and survival were monitored over a 10-month period. After the initial treatment, survivors of the air exposure treatment were significantly ( p<0.01) larger than the control. Survivors of the high water temperature treatment were smaller than the control ( p<0.01). Results from the field study showed that the treatments had a significant effect on size, growth and survival. These results suggest that relatively simple husbandry practices of weeding out weaker mussel seed can affect productivity. Given the limited availability for lease expansion in PEI bays, new husbandry practices are an important avenue to investigate, in order for the mussel industry to maximize production capability.

Sedimentation, suspension, and resuspension in Tasman Bay and Beatrix Bay, New Zealand, two contrasting coastal environments which thermally stratify in summer

The influence of density stratification on sedimentation, suspension, and resuspension in Tasman Bay and Beatrix Bay, New Zealand, two contrasting coastal environments, was studied with specific reference to the implications for modelling aquaculture sustainability. Tasman Bay, an enhanced scallop (Pecten novaezelandiae Reeve) fishery, is a very large coastal indentation gently shelving to c. 20 m deep c. 10 km from shore and open to the Tasman Sea, whereas Beatrix Bay, an area of intense Greenshell™ mussel (Perna canaliculus Gmelin) aquaculture, is a small (22 km2 × 30–40 m deep) enclosed embayment off the side of the nearby Pelorus Sound. Sediment trap arrays were used to determine the vertical fluxes of suspended solids and the associated chlorophyll component. Benthic chambers were used to investigate sediment nutrient regeneration. In summer, salinity gradients in both bays are minimal or non‐existent because of low inputs of fresh water and density stratification is mainly controlled by water temperature. The data from mid summer exhibited different spatial distribution patterns for detritus and phytoplankton biomass (as indicated by chlorophyll) in these two very different bays, although they had similar turbulent environments. The density discontinuity at the thermocline had a strong influence on settling of phytoplankton. There was evidence of upwards entrainment of suspended paniculate matter into the upper water column from the thermocline in Beatrix Bay. Benthic resuspension was estimated to contribute up to 90% of the suspended solids caught in sediment traps near the sea floor in both bays. The trapping rate of phytoplankton was thought to be dependent on species dominance. Possible mechanisms of resuspension included turbulence in the benthic boundary layer, and high velocities below the thermocline associated with internal seiches. The presence of a mid water column chlorophyll maximum in Beatrix Bay is discussed in terms of nutrient and light regimes at the thermocline, and species composition. In Tasman Bay, the chlorophyll maximum was thought to be caused by resuspension of benthic microphytes and their subsequent confinement in a thin layer (2–4 m thick) of high turbulence between the thermocline and the seabed.

Fatty acid composition of phytoplankton, settling particulate matter and sediments at a sheltered bivalve aquaculture site

Fatty acid biomarkers were used to investigate the biogeochemistry of a former blue mussel ( Mytilus edulis ) aquaculture site in a shallow, sheltered cove in northeastern Newfoundland. High levels of polyunsaturated fatty acids (PUFA) in net-tow and sediment trap samples indicated a substantial phytoplankton source of organic matter, and fluctuations in specific fatty acid biomarkers reflected the changing abundances of diatoms and dinoflagellates . In comparison, sediments contained very low levels of PUFA (<15%) and were dominated by terrestrial and bacterial markers. In a separate study, blue mussels were grown at this closed site, providing the opportunity to examine the relationship between lipid supply, as recorded by net-tow and trap samples, and bivalve requirements. The average plankton fatty acid composition throughout the year agreed well with that of the adult blue mussels, suggesting that fatty acids were provided in proportions very similar to the bivalves' requirements. The fatty acid composition of the blue mussels was typical of those collected elsewhere, with PUFA proportions near 50%. However, examination of fatty acid data of plankton sampled in other areas revealed that the plankton in the current study may have been unusual in providing fatty acids at levels required by the bivalves.

Fouling Communities of Mussel Aquaculture Installations in the White Sea

We have classified fouling communities developing on artificial substrates of mussel mariculture plants in Kandalakshskii Bay of the White Sea. Several major types of fouling have been distinguished: mussel fouling; fouling similar to the epifauna of the benthos biocenosis of Laminaria saccharinadominated by the ascidian Styela rusticaor sponges Halichondria paniceaand Halisarca dujardini; young fouling developed by algae and the ascidians of the genus Molgula; and ecotone communities in-between these types of fouling. The characteristics of the distinguished communities are provided.

MUSMOD ©, a production model for bottom culture of the blue mussel, Mytilus edulis L.

A mussel production model, MUSMOD © was developed to seed bottom culture lease sites in Maine to their carrying capacity. The process of model development is demonstrated with three models: (a) an initial conceptual model, (b) an aggregated model driven by the tidal exchange of food particles and (c) MUSMOD ©, the final model driven by food supplied in the tidal flow of water across a site. The final model predicts mussel production using the concentrations of phytoplankton and detritus in the surface water, detritus quality, tidal current speed, water depth and temperature. Field measurements of several quantities (e.g., clearance, respiration, growth rates for shell and meat, food concentration gradient, and temporal feeding pattern, (Newell et al., 1997, Development of the mussel aquaculture lease site model, MUSMOD ©: a field program to calibrate model formulations, J. Exp. Mar. Biol. Ecol., this volume) were obtained to evaluate and calibrate the final model. Model refinement using iterations of modeling and field work demonstrated the importance of food quantity and quality in explaining the observed patterns of mussel growth. Food quantity explained the first-order growth pattern, but it was necessary to account for the quality of the food to explain the second-order details of growth. Vertical mixing supplied the majority of new food particles, however, particles settling over the mussel bed during slack water accounted for 33% of the phytoplankton and 45% of the detritus entering the feeding layer from above. A sensitivity analysis of the effects of seed density on mussel growth using MUSMOD © identified the optimum carrying capacity for three Maine lease sites. Seeding mussels during the optimum time period (May to early July) resulted in the harvest of marketable mussels from 40 mm seed in 8 months for a high food year and in 13 months when the food supply was low. Characterizing the food supply using particulate organic matter, POM, alone was not sufficient to explain mussel growth in the detail necessary to answer many farm management questions.

Development of the mussel aquaculture lease site model MUSMOD ©: a field program to calibrate model formulations

Field observations were used along with mathematical modelling to develop model formulations to represent mussel ( Mytilus edulis) growth at several shallow subtidal study sites along the Maine coast, USA. In order to match predicted growth from the model MUSMOD © (D.E. Campbell, C.R. Newell, 1997. MUSMOD ©: A mussel production model for use on bottom culture lease sites. J. Exp. Mar. Biol. Ecol., in press.) with observed growth rates in the field, modifications were made in the model with respect to: (a) factors affecting the supply of food to the mussel feeding zone (vertical mixing, settling, resuspension and particle depletion); (b) short-term variability in mussel feeding and respiration over a tidal cycle; (c) the effects of seasonal variations in food quality on assimilation, scope for growth, and observed growth. Surface and bottom water samples taken from 1989 to 1991 revealed daily fluctuations in SPM, POM, chlorophyll a, particulate carbon and nitrogen, and phytoplankton carbon which were similar to annual ranges. Maine waters are typified by a spring diatom bloom, followed by a rise in detritus in early summer. Successful representation of mussel growth was obtained when food concentration was expressed as phytoplankton and detrital carbon, and assimilation was modelled as a function of food type (phytoplankton or detritus), and detritus quality (as percent of maximum annual N/C ratio of the detritus). By expressing particle depletion as a percent reduction from conditions at the edge of the lease site, scope for growth was modelled over an annual period. Observations with a time-lapse benthic video monitor (TLBVM) and flow-through physiological chambers demonstrated tidal variations in filtration rate, respiration rate and shell gape in subtidal mussels, with periods of valve closure correlated with low particle concentrations. These observations support the hypothesis that mussel energy gain is maximized during fluctuating food availability by the control of pumping rate via the shell gape response. This may explain why field observations of filtration rate are sometimes lower than maximum published values, and allows the mussels to maintain a slightly positive scope for growth by reducing respiratory losses when food particles are limiting. The settling flux of phytoplankton and detritus, while poorly characterized in coastal New England waters, provides over 30% of the estimated food supply to subtidal mussel cultures and may explain, in part, the patterns of shell gape observed in this study.

Simultaneous occurrence of diarrhetic and paralytic shellfish poisoning toxins in Spanish mussels in 1993.

Mussel aquaculture is an important industry for the Galician Rias, located in northwestern Atlantic coast of Spain. Since 1976 this region has been seriously affected by incidents of paralytic and diarrhetic shellfish poisoning (PSP and DSP). A particularly bad episode occurred in 1993, when the toxic event lasted for an unusually long period. Many people were stricken ill with unusual symptoms. In this paper we report on the chemical analysis of toxic 1993 mussel samples, using the techniques of liquid chromatography and capillary electrophoresis coupled with mass spectrometry. These analyses revealed a very complex toxin profile, with both PSP and DSP toxins present. Two DSP toxins, okadaic acid and DTX2, were observed, while the primary PSP toxins were B1 and the decarbamoylated derivatives of saxitoxin, GTX2 and GTX3. Small amounts of saxitoxin and other as yet unidentified PSP toxins were observed.

Influence of stock and culture site on growth rate and mortality of mussels ( Mytilus galloprovincialis Lmk.) in Galicia, Spain

The influence of stock and culture site on growth rate and mortality was investigated in populations of Mytilus galloprovincialis Lmk. cultivated in the area of greatest mussel production in the world (Galicia, N.W. Spain). The experimental results indicate that variations in mortality, from May to August, of mussel seed are mostly determined by the populations selected as source of seed. On the other hand, differences in growth rate over this 3-month period are mainly explained by two components of spatial variation; a site component (variation among rafts) and a micro-site component (variation within raft). In addition, differences in growth rate between the fore and the aft part of the rafts (micro-site component) were clearly higher than differences among rafts placed in distinct growing sites (site component). These results are discussed in connection with the role of both the selection of the source of seed and the management of rafts in the improvement of mussel aquaculture in Spain.

Effects of mussel aquaculture on the nitrogen cycle and benthic communities in Kenepuru Sound, Marlborough Sounds, New Zealand

Nitrogen pools and transformations and benthic communities at a Perna canaliculus farm and a nearby reference site without direct influence of marine farming in Kenepuru Sound, New Zealand, were compared on four dates between September 1982 and May 1983. The organic nitrogen pool in the top 12 cm sediment was 7.4 to 10.8 mol m-2 at the mussel farm and 6.1 to 8.9 mol m-2 at the reference site. The nitrate and nitrite pools were similar in both sediments, but the ammonium pool in the mussel farm sediment was about twice as high as in the reference sediment. In January, the sediment ammonium concentrations ranged from 418 nmol cm-3 (surface) to 149 nmol cm-3 (12 cm depth) at the mussel farm and from 86 to 112 nmol cm-3 at the reference site. The molar C:N ratio of the sediment organic matter was 6.2 to 7.2 at the mussel farm and 7.9 to 10.0 at the reference site. The molar N:P ratio of the sediment organic matter was 4.3 to 7.2 and 3.3 to 6.1 at mussel farm and reference site, respectively. The total nitrogen mineralisation rate in the top 12 cm sediment ranged from 21.7 to 37.1 mmol m-2 d-1 at the mussel farm and from 8.5 to 25.0 mmol m-2 d-1 at the reference site. Ammonium excretion by mussels was about 4.7% (January) and 7.4% (May) of the combined nitrogen mineralisation by mussels and sediment. The sediment-denitrification rate was 0.7 to 6.1 mmol m-2 d-1 at the mussel farm and 0.1 to 0.9 mmol m-2 d-1 at the reference site. In January, 76 and 93% of the nitrate reduced in the sediments were denitrified at the mussel farm and reference site, respectively. The denitrification rate on the mussel lines (determined on detritus-covered mussels) was twice the mussel farm sediment-denitrification rate and 10 times the reference sediment-denitrification rate. Total denitrification at the mussel farm was 21% higher than at the reference site. The loss of nitrogen through mussel harvest and denitrification was 68% higher at the mussel farm. The surface layers of both sediments contained about 75 mg m-2 chlorophyll a. Sediment phaeophytin levels were 52 mg m-2 at the reference site and 137 mg m-2 at the mussel farm. While the benthic infauna of the mussel-farm sediment consisted only of polychaete worms, the reference sediment contained also bivalve molluscs, brittle stars and crustaceans.

EXPERIMENTAL CULTURE OF Mytilis edulis (L.) IN A NORTHERN ESTUARINE GRADIENT: GROWTH, SURVIVAL, AND RECRUITMENT

AbstractMussels (Mytilus edulis L.) were experimentally cultured at 12 sites (1.5 km intervals) in an estuarine gradient on the Damariscotta River, Maine. Growth, survival, and recruitment of mussels were monitored and hydrographic data were collected. Peak growth of mussels occurred in May and June. The 4 upper‐estuarine sites were characterized by (1) earlier timing of peak growth, (2) suppressed growth in June and July relative to lower estuary mussels, and (3) marked mortality in September. Mussels grew rapidly in the lower 10 km of the estuary, exhibiting different temporal patterns of growth, but achieving comparable seasonal growth and survival. Seed mussels used for the growth experiments had settled on collectors during the previous summer and, accordingly, grew to 50 mm length in approximately 12 months: 15 months of growth yielded 57–71 mm mussels. Recruitment varied considerably, but was consistently high throughout the middle estuary, where settlement densities of 5–8 seed mussels per cm2 were observed. A 5‐year record of spatfall at one site in the middle estuary indicated that recruitment there was relatively consistent from year to year. The high mortality of mussels in the upper estuary of the Damariscotta River was associated with temperatures of 20°C and above, but may be related to factors other than temperature stress per s***a. Reduced ration during periods of warm temperature and increased metabolism may be responsible for these mortalities. Dense populations of newly‐settled mussels survived at some locations where temperatures exceeded 20°C and adult mortalities were high, indicating that high settlement densities and the existence of extensive populations of very young mussels do not, by themselves, provide enough information to adequately assess the potential of a site for mussel aquaculture. This potential may be meaningfully assessed by the use of a small experimental mussel raft and the collection of temperature and salinity data. Our results indicate that extensive areas of estuaries similar to the Damariscotta may be utilized for the culture of mussels.