Magnitude and Extent of Water Clarification Services Provided by Bivalve Suspension Feeding

Abstract

Studies in bivalve ecology have emphasized that phytoplankton dynamics in coastal regions may be strongly coupled with bivalve suspension feeding activity to the extent that the bivalves play a major ecological role in controlling phytoplankton biomass. The water clarification capacity of natural and cultured bivalve populations serves as the foundation for what is considered to be a manageable bioengineering tool for mitigating the major symptoms of eutrophication and thereby providing positive ecosystem-scale services. Although often predicted, suspended particle depletion by bivalve aggregations has only recently been measured directly. Field observations of food depletion by bivalve aggregations confirm the large capacity for water clarification. However, progressively increasing the standing stock of bivalves to achieve greater water clarification benefits eventually lead to inefficiencies in bivalve feeding related to increased flow reduction from structure drag, which facilitates an increase in water re-filtration. These physical and biological processes ultimately constrain the maximum water clarification capacity of the population to levels that can be substantially less than previously predicted. Positive ecosystem services from bivalve grazing are likely to occur in many coastal areas experiencing eutrophication (e.g. Lindahl 2011). However, it is important to take an ecosystem-based management approach that also considers the potential for adverse environmental interactions that may be associated with intensive and extensive suspended bivalve operations.

Comparing physical and biological impacts on seston renewal in a tidal bay with extensive shellfish culture

“…We estimated the refiltration ratio by comparing the bulk and realistic clearance rates. As an indicator of systemwide filtration capacity, the bulk CT is derived by dividing the water volume by the filtration rate (Dame & Prins, 1997), which, however, overlooks refiltration and overestimates the seston removal rate (Boegman et al, 2008;Cranford, 2019). In contrast, the CT calculated in our model accounts for refiltration by considering advection and dispersion of filtered water masses.…”

Production Characteristics and Optimization of Mitigation Mussel Culture

“…Basin-scale reduction in food supplies and quality will influence farm configuration, as the flux of food in a reduced gradient will support less biomass in upstream units if situated in close proximity. Furthermore, it has been demonstrated in heavily cultivated waters that ecological space is broadened for smaller phytoplankton classes (Froján et al, 2018;Cranford, 2019); however, in eutrophic or some extensively cultivated basins, smaller plankton classes may be increasingly utilized under field conditions (Sonier et al, 2016) or transported through the food chain to larger classes (Haraguchi et al, 2018). As of 2019, 7.34 km 2 of the Limfjorden are permitted for cultivation of mussels, where the overall surface area 1526 km 2 (Dinesen et al, 2011), or 0.5% of the fjord system; which suggests room for expansion in this highly productive system, in comparison with more extensively utilized areas (e.g., St.…”

Evaluating chlorophyll depletion in mitigation mussel cultivation at multiple scales

“…Chlorophyll is a principal indicator in many marine ecological assessment models (Ferreira et al 2011), and as a proxy for phytoplankton, the primary food source for bivalves. While the filtration of phytoplankton (or more generally, seston) has been recognized as an environmental service for some time (Officer et al 1982), more recently, bivalve cultivation for systemic environmental services (namely, nutrient reduction) in productive waters has become a prominent focus (Gren et al 2009, Petersen et al 2014, 2016, 2019, Rose et al 2014, Ferreira & Bricker 2016. Emerging mussel cultivation practices which prioritize nutrient extraction in strategic locations have been termed 'mitigation mussel culture', aiming to maximize nitrogen (N) removal from a given water body at the lowest possible operational costs.…”