Shellfish farm-induced changes to tidal circulation in an embayment, and implications for seston depletion

Cultivated bivalves rely on natural seston for growth and metabolic processes. Because seston is a limited resource, there is a need to better understand its distribution and fluxes within culture embayments, so farms can be positioned optimally within these dynamic systems. In this study, a simple numerical tool was developed and implemented to address actual management issues related to the positioning of oyster Crassostrea virginica farms in the Richibucto Estuary (eastern Canada). The versatile procedure relied on hydrodynamic modelling and tracer advection−dispersion to reproduce the spatial and temporal dynamics of seston availability. The model identified 3 areas of interest within the estuary, each with unique water renewal rates and seston concentrations. The method also revealed major interactions between the different areas, and proved efficient in quantifying the effects of topographical alterations on seston availability. Our results suggest that such basic modelling tools produce relevant information in a timely manner, and thereby facilitate the necessary dialogue between science advisors, industry stakeholders and resource managers.

Section: Dynamics Of Organic Sestonmentioning

confidence: 80%

Spatially explicit seston depletion index to optimize shellfish culture

Guyondet¹,

Sonier²,

Comeau³

2013

“…By comparison, production of Laminaria hyperborea has been reported to be as high as 3000 g C m −2 (Abdullah & Fredriksen 2004). We have not taken into consideration the effects of the fish and kelp farms themselves on the water currents, which may reduce the fluxes of nutrients within the IMTA system (Grant & Bacher 2001, Plew 2011, Stevens & Petersen 2011. Neither have we considered small-scale reduction in DIN concentrations around single kelp ropes due to crowding of the plants.…”

Section: Simulation Experiments and Implications For Imtamentioning

confidence: 99%

Modelling the cultivation and bioremediation potential of the kelp Saccharina latissima in close proximity to an exposed salmon farm in Norway

Broch¹,

Ellingsen²,

Forbord³

et al. 2013

A 3-dimensional hydrodynamic−ecological model system (SINMOD) was used to estimate the full-scale cultivation potential of the brown alga Saccharina latissima in integrated multi-trophic aquaculture (IMTA) with Atlantic salmon Salmo salar. A previously developed model for the frond size and composition (carbon and nitrogen content) of S. latissima sporophytes was adjusted to data from an outdoor mesocosm growth experiment and then coupled and run online with the 3-dimensional model system. Results from simulations were compared with data from an IMTA field experiment, providing partial validation of the hydrodynamic-ecologicalkelp model system. The model system was applied to study the large-scale cultivation potential of S. latissima in IMTA with salmon and to quantify its seasonal bioremediation potential. The results suggest a possible yield of 75 t fresh weight S. latissima ha −1 in 4 mo (February to June) and about 170 t fresh weight ha −1 in 10 mo (August to June). The results further suggest that the net nitrogen consumption of a 1 ha S. latissima installation in the vicinity of a fish farm producing approximately 5000 t salmon in a production cycle is about 0.36 (0.15) t NH 4 + -N, or a removal of 0.34% (0.41%) of the dissolved inorganic nitrogen effluent with a cultivation period from August (February) to June. Due to the differing seasonal growth patterns of fish and kelp, there was a mismatch between the maximum effluent of NH 4 + -N from the fish farm and the maximum uptake rates in S. latissima.

“…Numerical modeling is the only tool available to look at such effects (e.g. Fan et al 2009, Plew 2011, but these models need some basis for their choice of scales and against which to be validated. For example, it is likely that the presence of the farm would influence the secondary flows (i.e.…”

Section: Farm-driven Flow and Stratification Variationmentioning

confidence: 99%

Turbulent, stratified flow through a suspended shellfish canopy: implications for mussel farm design

Stevens¹,

Petersen²

2011

Observations were used to quantify the influences of turbulent flow and mixing through the suspended canopy formed by a shellfish aquaculture farm in the microtidal Danish Limfjorden. Observations included current meter/profiler timeseries data and turbulence microstructure profiling. The influence was 2-way in that the turbulence is partially driven by the canopy and in turn the canopy is affected by the turbulence. The canopy reduced the flow speeds within its interior, which was sufficient to reduce levels of turbulent kinetic energy so that withincanopy rates of turbulent kinetic energy dissipation ε were between 10 −8 and 5 × 10 −6 m 2 s −3. Stratification and turbulence were generally inter-related. It was difficult to link the canopy effect to changes in stratification. This was partly due to a high degree of natural variability and partly because the canopy did not appear to generate that much mixing relative to background variability. Vertical diffusivities enabled estimates of the effect of mixing on nutrient depletion and suggest that in the investigated farm set-up vertical diffusivities are secondary in terms of contribution to this relationship but that they could play a dominant role in farms with a more spacious or compressed set-up of canopies. However, vertical flux estimates imply that there must be transverse fluxes of material. Results suggest several avenues for enhanced sustainable shellfish production. For example, canopy flushing can be enhanced with suitable arrangement of crop within a farmed area (heterogeneity). In addition, stratification persists within the canopy and so exposure to nutrient-deplete water can be minimized through staggered crop heights. However, to benefit from this knowledge, improved understanding of long-term variability in the background environment is required.