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Effluents from land-based mariculture have a deleterious environmental impact by enriching littoral waters with particulate and dissolved nutrients. The use of suspension-feeders (e.g. bivalves) in biofiltration systems provides an inexpensive option for the biological removal of these nutrients from effluent water. Land-based facilities are safer because the quality of the incoming water can be controlled, and integrated polyculture systems can save resources, diversify the product, allow intensification, and are environmentally friendly, thus offering a valid alternative to open sea monoculture. Several approaches have been developed to reach this goal. These approaches are based on the use of algae and invertebrates as biofilters, which remove the dissolved and particulate nutrients from fishpond effluents. Sunlight-dependent assimilation turns excess nutrients into microalgae biomass, which is then consumed with other organic particulate matter by the invertebrates. These systems consist of three units: a) a fish or shrimp culture unit, b) an earthen pond that serves as both a microalgal production and a bivalve culture unit, and c) a seaweed biofilter unit. Microalgae, especially benthic diatoms, are responsible for most of the nutrient uptake. The main cultured herbivores are filter-feeding bivalves, which grow in the earthen pond. The seaweed biofilter strips the remaining dissolved nutrients from the effluents. The harvested yields (fish, bivalve and seaweed) contain 63% of the nitrogen introduced into the system, particulate matter (faeces and uneaten feed) contain 33%, and suspended and dissolved outflow, approximately 4% of the nitrogen budget. More complex systems require highly skilled operators and more sophisticated technology, but they provide increased product diversity. Depending on practical factors such as market prices, quality and cost of labor, seed and fingerlings supply, environmental conditions, market size and property cost, the operational protocol can be shifted between the three product types (fish, algae and invertebrates) to maximize profits.

The role of suspension—feeders varies according to the spatial and temporal scales at which assessments are made. In this paper, biodiversity, productivity, and filtration capacity are used to assess the influences of suspension-feeders at scales ranging from individual mussels to biogeographic regions. Quantitative comparisons based on the ‘catchment areas’ of single mussels, mussel beds and entire bays are used to illustrate how the role of these organisms varies as a function of the unit of measurement. One key factor influencing the relative importance of suspension-feeders at different scales is the rate of water movement and, thus, the volume of water available to the consumers. The biodiversity within suspension-feeder guilds is important because of the way it can affect the amount and sizes of particles removed from the spectrum of available food items. Variations in the role of these animals are also observed at time scales. The complexity of the scaling problem is illustrated using examples from the suspension-feeder guild in a tidal basin of the Wadden Sea (North Sea) where experiments and field measurements have provided insights into processes and mechanisms accounting for spatial and temporal variations.

Biological invasions increasingly alter taxonomical and functional structure of benthic communities. Among the invasive benthic invertebrates, the suspension-feeders are the most widespread type. Species belonging to that trophic group constitute from half to two thirds of total invasive species in various European seas. The importance of the alien suspension-feeders is particularly obvious in evolutionary young, species poor brackish water bodies, such as the Baltic Sea. We analyzed changes in suspension-feeder systems formed by both alien and native species along the salinity and depth gradients from a river mouth (the Curonian Lagoon) down to the halocline area of the Baltic Proper. There was a clear shift in the biomass dominance from the alien species in the lagoon to the native suspension-feeders in the sea. Both the native and alien obligatory suspension-feeders occupied shallow coastal marine and lagoon habitats and did not form stable communities below the 30 m depth.

Dreissena polymorpha and Corbicula fluminea are among the most aggressive freshwater invaders world wide, and often dominate water bodies they invade. They occur in similar habitats, however, their tolerance and preference for certain characteristics of freshwaters differ in important ways, and they can have different impacts on the environments they invade. We identify similarities and contrast differences between these species, and highlight important questions yet to be addressed, including: the ability to link short-term laboratory findings to large scale and long-term effects of invasion, the consequences of invasion by both species together rather than considering each in isolation, and identification of local versus system-wide effects when these non-native ecosystem engineers invade.

Dreissena is extremely abundant in waters it invades, and dramatically changes benthic invertebrate communities in terms of total biomass, species composition, and the relative abundance of functional groups. We analyzed the relative abundance of feeding functional groups of the benthic community before and after zebra mussel invasion in three Belarussian lakes, four lakes after invasion only, and one lake in the same region that has not been invaded. After invasion, benthic structure was dominated by one trophic group — filterers. This group accounted for greater than 96% of the total biomass of benthic invertebrates. We found that the relative abundance of feeding functional groups in the rest of the benthic community, without including Dreissena biomass, was also different in lakes examined before and after zebra mussel invasion. Before invasion and in the un invaded lake, planktonic invertebrates filtered a volume equivalent to the volume of the lake within few days, and were more than 200 times more effective than benthic filterers, which would take about 4 years to filter an equivalent volume. After Dreissena invaded the lakes, the total average biomass of all benthic invertebrates (including zebra mussels) increased more than 20 times. The filtration efficiency of the benthic community increased greater than 70 times, and the time required to filter the volume of the lake was not significantly different than that for zooplankton. These dramatic changes will alter the relative roles of the plankton and benthos in a variety of ecosystem functions, especially the movement of carbon from the plankton to the benthos.

Over centuries dramatic changes have occurred in the species composition of the Wadden Sea, a shallow coastal sea bordering the North Sea. Natural dynamics as well as direct and indirect anthropogenic influences have resulted in the introduction and the disappearance of important benthic populations. Historic records and extensive surveys show large variability in benthic suspension-feeder stocks. Infaunal species like the cockle ( Cerastoderma edule ) are extremely variable over time and space, hence show a typical resilient response. Mussel ( Mytilus edulis ) beds seem to be more stable over time. Once lost, mussel beds need more time to re-establish bed structures. It is hypothesized that infaunal populations have a high resilience, while epifauna species are characterized by resistance to changes as they form structures like reefs or beds. On the basis of this hypothesis the consequences of new introductions can be evaluated. It can be expected that the recent introduction of the resistant reef-building epifaunal Pacific oyster Crassostrea gigas , will lead to shifts in benthic suspension-feeder populations and eventually will develop a new stable state for the Wadden Sea that potentially offers less food for birds. This situation may deviate considerably from the actual nature conservation objectives that focus on the role of the Wadden Sea as one of Europe's most important wetlands for migratory bird populations.

Invasive suspension-feeding bivalves have reduced phytoplankton biomass in many aquatic systems, which has resulted in loss of trophic complexity in some systems. Using an example of one invasive bivalve in San Francisco Bay, Potamocorbula amurensis , the causes of differing system level responses are explored. San Francisco Bay, similar to of other shallow, turbid, non-nutrient limited, but low productivity systems, is likely to be most stressed by the loss of primary producers. While the northern bay has lost primary production following the invasion of P. amurensis , the southern bay (SB) has not and these differences are shown to be due to the different mechanisms responsible for the seasonal turbidity in the systems. Because the period of lowest turbidity in SB is coincident with the period of lowest bivalve grazing, the southern bay has not seen a reduction in its high magnitude but short spring bloom. A method for predicting if a shallow, turbid and nutrient replete estuary might lose phytoplankton production with a sudden increase in suspension-feeders is explored.

Suspension-feeding bivalves often may occur in large concentrations ('beds') on tidal flats. This makes them attractive for human consumers and the archaeological record shows collection of bivalves by coastal populations already tens of thousands of years ago. In modern time human interference with coastal stocks of bivalves intensified. This paper describes the successive steps in this development: 1. Local exploitation and local consumption, leading to reduction of average age, average size and small shifts in species composition. 2. Local exploitation coupled to remote markets. This leads to the same changes as at 1, but also may lead to extirpation of local populations. 3. Relaying of imported bivalves to restock overexploited beds. This may result in destruction of genetic adaptations, and it has been demonstrated that it results in the importation of parasites and diseases. 4. Cultivation of bivalves with either spat from natural sources or from hatcheries. Bivalve culture usually results in increased harvests compared to open fisheries; it may lead to overstocking with effects on the remainder of the ecosystem. 5. Introduction of new, exotic species, either to be cultivated or as an unplanned introduction of ‘weed’ species.

Aggregations of suspension-feeding organisms like oyster reefs, mussel beds and worm reefs are prominent systems in coastal environments. The fundamental properties of these systems are reviewed and indicate that they are complex systems that are highly optimized and evolutionarily selected for high productivity. Such systems are unstable when faced with a never experienced situation. In the case of oyster reefs, catastrophic collapse usually involves anthropogenic factors such as pollution, sediment loading, and over-harvesting. Strategies for examining these complex systems and developing compatible management approaches must include continued experimentation, learning, and adaptation by managers.