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Crowding conditions in bivalve populations cause intraspecific competition processes, resulting in individual growth reduction. In aquaculture, density is usually maximized to obtain a greater commercial yield. Commercial farms provide an ideal scenario for studying the effect of density on mussel growth in suspended culture systems. In this study, different growth indicators for Mytilus galloprovincialis (growth rates, length and weight growth curves and size frequency distributions) were measured along a cultivation density gradient. Ropes cultured at different densities (220, 370, 500, 570, 700, 800 and 1150 ind/m) were hanged from a commercial raft and growth indicators were monitored monthly over the second phase of traditional culture in Galicia, from thinning-out to harvest (April to October 2008). A negative effect of density on individual growth was observed. Individuals cultured at lower densities presented higher growth rates and consequently reached greater weight and length values at the end of the experimental period than those cultured at higher densities. Differences in growth related to the cultivation density may suggest differences in intraspecific competition for limiting resources (space/food). Effects of density on growth started after 4 months of culture (August) when individuals reached sizes around 66 ± 1.3 mm. The increase in size of individuals in a population implies an increment of their food and space requirements, which in turn intensifies intraspecific competition. This fact should be considered in aquaculture management, since higher densities could be supported without effects on growth performance if cultured mussels are limited to a lower size.

Kreiss et al. Future Socio-Political Scenarios Aquaculture returns, and marketing options as opposed to the direct effect of climate-driven changes in the environment. These results can inform adaptation planning by the European aquaculture sector. Moreover, applying consistent scenarios including societal and economic dimensions, facilitates regional to global comparisons of adaptation advice both within and across Blue Growth sectors.

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Bivalve molluscs are characterized by high morphological plasticity in response to variations in local environmental conditions. In the present study, we evaluate this capacity in the mussel Mytilus galloprovincialis with regard to intra-specific competition caused by cultivation density. Suspended cultivation ropes at different initial densities (220, 370, 500, 570, 800 and 1150 individuals per meter of rope) were placed on a raft in the Ría Ares-Betanzos, following standard cultivation techniques. From May to October, covering the period from thinning out to harvest, various morphological indicators (length/width, length/height and height/width ratios) and allometric relationships (Volume-Length and Projected area-Length) in addition to energy distribution (dry tissue weight/dry valve weight) were analyzed. Differences in morphological indicators due to cultivation density were observed while no influence on the energy distribution was detected. From the second cultivation month (June), a decrease was recorded in the length/height ratio of individuals due to cultivation density. Similarly, there was also a decrease in the length/width ratio, although this decrease only became statistically significant from September. In addition, the allometric relationships studied (Volume-Length and Projected area-Length) suggested asymmetric competition processes. Differences in volume or projected area between densities were only detected at the end of the experimental culture (October) and only in the smaller individuals. These morphological adaptations can be understood as a strategy to mitigate the effects of intra-specific competition, palliating the consequences of physical interference at high densities.

We present an on-line early warning system that is operational in Scottish coastal waters to minimize the risk to humans and aquaculture businesses in terms of the human health and economic impacts of harmful algal blooms (HABs) and their associated biotoxins. The system includes both map and time-series based visualization tools. A "traffic light" index approach is used to highlight locations at elevated HAB/biotoxin risk. High resolution mathematical modelling of cell advection, in combination with satellite remote sensing, provides early warning of HABs that advect from offshore waters to the coast. Expert interpretation of HAB, biotoxin and environmental data in light of recent and historical trends is used to provide, on a weekly basis, a forecast of the risk from HABs and their biotoxins to allow mitigation measures to be put in place by aquaculture businesses, should a HAB event be imminent.

Abstract. Self-thinning (ST) models have been widely used in the last decades to describe population dynamics under intraspecific competition in plant and animal communities. Nevertheless, their applicability in animal populations is subjected to the appropriate inclusion of space occupancy and energy requirements. Specifically, the disposition of gregarious sessile animals in complex matrices hampers the application of classical ST models. This paper reviews the self-thinning models, regression methods (central tendency and frontier techniques) and discrimination criteria currently applied for gregarious sessile species through application to the analysis of mussel populations (Mytilus galloprovincialis) grown in suspended culture. In addition, we propose to model the temporal evolution of site occupancy in the stochastic frontier function (SFF). Our results confirm that the number of layers should be included in the classical bidimensional ST model for the analysis of multilayered populations. The estimated parameters obtained by the different fitting techniques depended on the measurement method of the variables in the model. This, together with the proximity between the space and food selfthinning theoretical exponents (SST and FST, respectively) highlights the difficulty in discriminating the competition limiting factor (space/food) from the self-thinning exponent. On the other hand, the SFF provided congruent results for biomass and individual mass analysis, in contrast to the lack of robustness observed for the central tendency regression methods. Furthermore, the SFF approach allowed a dynamic interpretation of the ST process providing insight into the temporal evolution of site occupancy. These results highlight the suitability of the stochastic frontier approach in the analysis of self-thinning dynamics in sessile animal populations.

Fish farming releases extensive amounts of particulate organic waste that can be exploited by bivalves in integrated culture. We tested if mussels Mytilus galloprovincialis cultured at two depths (1 and 6 m) in a raft, moored 170 m from a fish farm had greater growth than bivalves held 550 m from the fish cages. Mussel growth was monitored monthly, covering the second phase of the culture, from thinning-out to harvest (March to November 2011). We also studied if fish solid and dissolved nutrients increased the organic content of the seston and chlorophyll-a levels near the fish cages through weekly samples. Results showed no differences in seston, chlorophyll and physiochemical characteristics of the water among rafts. Maximum growth and Condition Index (CI) occurred during springsummer (April-August), when mussels had access to greater food quality and quantity. Mussels cultivated close to the cages showed similar shell length, weight and CI compared with mussels distant from the fish farm. Average shell length, meat dry weight and CI at harvest were 76.31 mm, 2.51 g and 23%. Bivalves cultured distant from the fish cages displayed 26% higher biomass than the other raft at the end of the experiment. Differences in biomass were explained by the significantly higher recruitment of mussel seed observed at the raft distant from the fish cages from June to November. The lack of a significant enhancement in growth of the bivalves cultured next to finfish is discussed.