Potential methodological influences on the determination of particle retention efficiency by suspension feeders: Mytilus edulis and ciona intestinalis

The retention efficiency (RE) of suspension-feeding bivalve molluscs depends on particle size and is generally assumed to decline below a maximum retention of particles larger than 3 to 7 µm. Previous suggestions that the RE spectrum of mussels Mytilus edulis can exhibit variability, possibly as a result of physiological regulation, have been attributed to artifacts associated with the indirect method. The possibility that variable physical properties of seston particles and/or miscalculations can result in inaccurate RE measurements was examined using 3 methodologies (static, flow-through and a new approach based on the static method) and 3 particle sources (natural seston, algal cell monocultures and clay). Measurements obtained with the static method varied depending on the selected sampling interval. However, this artifact can be removed using frequent sampling and a regression analysis approach. Accurate RE measurements can be obtained with the flow-through method when feeding behaviour is flow independent. For all particle suspensions and methods, mussels from the study site in Lysefjord, Norway, had a maximum RE for particles >8–11 µm (1 to 5 September 2015). The RE for smaller particles declined gradually, with 50–60% retention of 4 µm particles and 30–40% retention of 2 µm particles. Differences in the RE size spectra of mussels and tunicates Ciona intestinalis, collected and measured at the same site, further indicated that RE was not influenced by potentially confounding methodological factors. Assumptions regarding the RE spectrum of bivalves have contributed to many conclusions on their ecosystem interactions. The reliability of clearance rate measurements obtained using the indirect method can only be assured if the effective retention of tracer particles is confirmed and not assumed.publishedVersio

Effect of Mytilus coruscus selective filtration on phytoplankton assemblages

The feeding selectivity of bivalves can play an important role in shaping the structure of phytoplankton communities of natural waters. This could be particularly true in waters with intensive bivalves farming, like Sungo Bay, Northern China. Understanding the role of bivalve feeding behavior is important for assessing how the dense cultivation of bivalves may affect phytoplankton community composition and food web structure in farm areas. In this study, we investigated the feeding selectivity of blue mussel Mytilus coruscus on natural phytoplankton assemblages in Sungo Bay using both optical microscopy and HPLC-pigment analysis. Results showed that cryptophytes dominated the phytoplankton community and made up 66.1% of the total phytoplankton abundance. A comparison of phytoplankton composition between natural and filtered seawater showed that M. coruscus preferred cryptophytes and dinoflagellates than Chaetoceros spp. and Skeletonema spp. Cryptophytes were not detected in gut contents by microscopic observation, while their marker pigment alloxanthin was present, suggesting they were also consumed by M. coruscus and can be readily digested. This highlights the shortcomings of microscopic methods and the significance of HPLC-pigment analysis in obtaining a comprehensive understanding of feeding selectivity of bivalves. The proportions of Chaetoceros spp. and Skeletonema spp. in gut contents were significantly lower than their proportions in the seawater, and contrastingly, the proportions of Cocconeis spp. and Pinnularia spp. showed opposite patterns. The marker pigments prasinoxanthin and zeaxanthin were detected in the gut of M. coruscus indicating that picophytoplankton (e.g., prasinophytes and Synechococcus) are also food sources for this bivalve. This information furthers our understanding of bivalve aquaculture and environment interactions.publishedVersio

Attraction and repulsion of mobile wild organisms to finfish and shellfish aquaculture: a review

Knowledge of aquaculture–environment interactions is essential for the development of a sustainable aquaculture industry and efficient marine spatial planning. The effects of fish and shellfish farming on sessile wild populations, particularly infauna, have been studied intensively. Mobile fauna, including crustaceans, fish, birds and marine mammals, also interact with aquaculture operations, but the interactions are more complex and these animals may be attracted to (attraction) or show an aversion to (repulsion) farm operations with various degrees of effects. This review outlines the main mechanisms and effects of attraction and repulsion of wild animals to/from marine finfish cage and bivalve aquaculture, with a focus on effects on fisheries-related species. Effects considered in this review include those related to the provision of physical structure (farm infrastructure acting as fish aggregating devices (FADs) or artificial reefs (ARs), the provision of food (e.g. farmed animals, waste feed and faeces, fouling organisms associated with farm structures) and some farm activities (e.g. boating, cleaning). The reviews show that the distribution of mobile organisms associated with farming structures varies over various spatial (vertical and horizontal) and temporal scales (season, feeding time, day/night period). Attraction/repulsion mechanisms have a variety of direct and indirect effects on wild organisms at the level of individuals and populations and may have implication for the management of fisheries species and the ecosystem in the context of marine spatial planning. This review revealed considerable uncertainties regarding the long-term and ecosystem-wide consequences of these interactions. The use of modelling may help better understand consequences, but long-term studies are necessary to better elucidate effects

Ecosystem models of bivalve aquaculture: Implications for supporting goods and services

In this paper we focus on the role of ecosystem models in improving our understanding of the complex relationships between bivalve farming and the dynamics of lower trophic levels. To this aim, we review spatially explicit models of phytoplankton impacted by bivalve grazing and discuss the results of three case studies concerning an estuary (Baie des Veys, France), a bay, (Tracadie Bay, Prince Edward Island, Canada) and an open coastal area (Adriatic Sea, Emilia-Romagna coastal area, Italy). These models are intended to provide insight for aquaculture management, but their results also shed light on the spatial distribution of phytoplankton and environmental forcings of primary production. Even though new remote sensing technologies and remotely operated in situ sensors are likely to provide relevant data for assessing some the impacts of bivalve farming at an ecosystem scale, the results here summarized indicate that ecosystem modelling will remain the main tool for assessing ecological carrying capacity and providing management scenarios in the context of global drivers, such as climate change

Phytoplankton depletion by mussel aquaculture: high resolution mapping, ecosystem modeling and potential indicators of ecological carrying capacity

Mussels held in suspended culture have an exceptional capacity to filter the water column and reduce suspended particle concentrations. However, seston depletion is only of concern if the phytoplankton are cleared faster than they can be replaced by tidal exchange and primary production. The occurrence of significant phytoplankton depletions over extended periods and different spatial scales is directly linked to concepts of production and ecological carrying capacity owing to food limitation and alterations in ecosystem structure, material fluxes and pathways and nutrient cycling. Knowledge on ecosystem interactions with shellfish aquaculture supports the growth of a sustainable industry and the development of an ecosystem-based management approach. The scale and magnitude of phytoplankton depletion was documented at mussel aquaculture farms in Canada and Norway using a computer controlled, towed undulating vehicle (BIO-Acrobat) that collects geo-referenced CTD and chlorophyll a data. Rapid synoptic surveys with intensive horizontal and vertical sampling permitted high resolution 3-D mapping of phytoplankton variations over farm to coastal ecosystem scales. Phytoplankton depletion by mussels is size-specific and it is expected that in areas where mussels control phytoplankton biomass, that picophytoplankton (0.2 to 3.0 ìm) will dominate. This hypothesis was tested, and confirmed, by measuring total and picophytoplankton biomass in Prince Edward Island embayments, where the risk of phytoplankton depletion varies greatly owing to regional differences in water flushing, bay volume and culture biomass. Key words: mussel culture; phytoplankton depletion; picophytoplankton; carrying capacity; ecosystem models; indicator

Temporal variations in suspended particulate waste concentrations at open-water fish farms in Canada and Norway

The co-cultivation of finfish and bivalve filter feeders, with the purpose of recycling solid waste effluents and enhancing aquaculture revenues, has stimulated efforts to characterize particulate waste dynamics at open-water fish farms. Temporal variability in waste concentrations in the water column was studied at Atlantic salmon Salmo salar farms in eastern Canada and Norway, and at a sablefish Anoplopoma fimbria farm in western Canada. Turbidity and chlorophyll a (chl a) sensors were used to continuously monitor suspended particulate matter (SPM) and chl a concentrations at various depths and distances to the net-pens. Time-series analysis of these data indicated that SPM fluctuations at the study sites corresponded largely with tidal periodicity and variations in phytoplankton biomass (chl a). ANOVA comparisons of mean SPM levels in water flowing from the direction of net-pens (potential farm influence) and towards the farm (control) generally indicated insignificant effects of fish wastes on SPM levels at the farms (p > 0.05). A significant effect of the farm was detected by an ANOVA comparison of SPM concentrations collected at 5 m depth at farm and reference stations in an oligotrophic fjord, but the calculated level of waste enhancement over the sampling period was extremely small (0.02 mg l−1). Results indicate that temporal variations in SPM concentrations around the open-water fish farms were largely driven by natural processes and that the addition of fish wastes had a negligible effect. Consequently, there is little rationale for introducing commercial extractive species (e.g. bivalves) in open-water integrated multi-trophic aquaculture systems to mitigate the horizontal flux of particulate fish wastes

Effects of seasonal variations in phytoplankton on the bioenergetic responses of mussels (Mytilus galloprovincialis) held on a raft in the proximity of red sea bream (Pagellus bogaraveo) net-pens

13 páginas, 7 tablas, 5 figurasThe seasonal variability of the physiological components of the Scope for Growth (SFG) of mussels Mytilus galloprovincialis was investigated in a raft adjacent (170 m) to fish net-pens and compared with a raft 550 m distant from the cages in Ría Ares-Betanzos (Galicia, Spain). Chlorophyll and phytoplankton size-classes were determined in the field, simultaneously with SFG. Average chlorophyll-a was 0.65 ± 0.24 μg l− 1, while nanophytoplankton (2–20 μm) was the most abundant size-class, ranging from 50 to 70% of the total chlorophyll. The temporal pattern found for chlorophyll-a and phytoplankton size-classes reflected the upwelling–downwelling events and were correlated with the feeding, digestive and metabolic rates. Nanophytoplankton and microphytoplankton were preferentially cleared and ingested by mussels. There were no significant differences between the chlorophyll and phytoplankton size-classes among rafts. The lack of any enhancement in food availability resulted in no significant increase in the SFG of mussels beside the fish cages. Maximum SFG corresponded with the autumn (16.60 ± 7.90 J h− 1) and spring (12.72 ± 9.32 J h− 1) chlorophyll maximums. An abnormally hot summer and reduced chlorophyll levels resulted in lower energy intake, significantly higher metabolic expenditure and a negative SFG (− 34.57 ± 12.55 J h− 1). Any particulate wastes and potential fish-derived chlorophyll enhancement would be rapidly diluted by the currents, while the placement of bivalves too distant from the fish farm in an environment with high supplies of natural seston may explain the lack of an augmented SFG of the co-cultured musselsThis study was sponsored by the project Ecological Sustainability of Suspended Mussel Aquaculture (ESSMA) (ACI2008-0780) and the PROINSA-CSIC contract project (CSIC 0704101100001). Jade Irisarri is supported by JAE-Predoc CSIC-FSE 2012–2015 scholarship.Peer reviewe