Sessile biota can compete with or facilitate each other, and the interaction of facilitation and competition at different spatial scales is key to developing spatial patchiness and patterning. We examined density and scale dependence in a patterned, soft sediment mussel bed. We followed mussel growth and density at two spatial scales separated by four orders of magnitude. In summer, competition was important at both scales. In winter, there was net facilitation at the small scale with no evidence of density dependence at the large scale. The mechanism for facilitation is probably density dependent protection from wave dislodgement. Intraspecific interactions in soft sediment mussel beds thus vary both temporally and spatially. Our data support the idea that pattern formation in ecological systems arises from competition at large scales and facilitation at smaller scales, so far only shown in vegetation systems. The data, and a simple, heuristic model, also suggest that facilitative interactions in sessile biota are mediated by physical stress, and that interactions change in strength and sign along a spatial or temporal gradient of physical stress.

Effects of excess loading of nutrients to the marine environment can be mitigated by mussel cultures, basically through nutrient removal from the marine environment when shellfish are harvested. Shellfish farming also provide other goods and services to the marine environment primarily through the impact on water transparency caused by shellfish filtration. There is an increasing awareness of the mitigation potential in mussel culture in relation to eutrophication, but so far practical examples of culture on full scale devoted to mitigation are few. Further, impact of mussel farming on nutrient cycling, e.g. in the sediments below the culture units, has raised concerns. In this review, we clarify concepts in relation to nutrient mitigation and discuss goods and services delivered by mussel mitigation cultures and their impact on an ecosystem scale based primarily on results from studies in heavily eutrofied estuaries. A multi-criteria approach for site selection is presented based on experiences from Danish waters, and economic aspects of mitigation cultures are analysed in relation to use of the produced mitigation mussels. Future perspectives for extractive cultures are discussed in relation to source of excess nutrients.

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41Land-based management has reduced nutrient discharges, however, many coastal waterbodies waterbodies without circulation models. The value of removed nitrogen was estimated using

Feeding behavior of mussels (Mytilus edulis) was measured in situ using a video camera and expressed as the mean percentage of valve gape aperture (VA), concomitant with environmental and biological parameters over two tidal cycles. Mussel feeding behavior and the physical parameters responded to three primary tidal components, of which semidiurnal was dominant (12.42 h). VA was synchronized with chlorophyll a (Chl a) concentration (proxy for food) with a strong positive correlation (r 5 0.72, p , 0.001). Chl a and suspended particulate matter (SPM) were dependent on tidal advection. The combination of the reconstructed tidal constituents derived from harmonic analysis were used to successfully model mussel feeding behavior (r 5 0.90, p , 0.001). In this concentration range (0.6 to 2.5 mg L 21 ), Chl a, measured at 1 m above the mussel bed, regulates mussel feeding behavior irrespective of the presence of predators, changes in SPM, or flow velocity.

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Bivalve environmental services have become a focal point for their inherent role in the management of eutrophication, while active cultivation has become increasingly acknowledged as a mechanism for integrated nutrient reduction. In recent years, cultivation practices designed specifically for nutrient extraction have emerged; "mitigation culture." While modeling efforts have been able to describe expanded potential of these services, only a single commercial pilot scale, realworld demonstration, has been documented. Over two production seasons (2017-2018), the optimization of nutrient extractive potential of mussels (Mytilus edulis) at full commercial-scale was evaluated by first testing multiple density configurations of conventional longline-spat collector setups and potential harvest times, then by comparing different cultivation technologies at three farms. Potential biomass volumes of 770-1700 t with longlines and 2100-2600 t on nets was demonstrated in fullscale production (18.8 ha), yielding 0.6-1.27 t N ha −1 and 0.04-0.1 t P ha −1 , and 1.63-2.0 t N ha −1 and 0.1-0.12 t P ha −1 respectively. In general, 1 t of harvested mitigation mussels will yield 13.7 kg N and 0.9 kg P. Winter harvests exhibited higher yields (103-124%) than early spring harvests on optimized configurations, favoring an abbreviated production season. Production potential was similar between sites, despite differing environmental conditions, indicating eutrophic waters are suitable for expanded mitigation production. This study presents for the first-time production data of mitigation mussels utilizing different configurations and technologies to maximize yield and nutrient extraction potential.