Richard F. Dame

A review of the feedbacks between bivalve grazing and ecosystem processes

This paper gives an overview of interactions betweenbivalve grazing and ecosystem processes, that mayaffect the carrying capacity of ecosystems for bivalvesuspension feeders. These interactions consist of anumber of positive and negative feedbacks.Bivalve grazing can result in local food depletion,which may negatively influence bivalve growth. On alarger scale, it may induce a top-down control ofphytoplankton biomasss, and structural shifts inphytoplankton composition. In the case of harmfulalgal blooms, phytoplankton may negatively affectbivalve grazing rates.The processing of large amounts of particulate mattermay change nutrient cycling on the scale of estuaries,and can result in changes in the inorganic nutrientpool available for phytoplankton, through regenerationand reduced storage of nutrients in algal biomass.This can reduce nutrient limitation of thephytoplankton and stimulate algal growth rates.Observations from mesocosm studies suggest that apositive feedback from bivalve grazing onphytoplankton growth may also change the physiologicalstate of the algae and improve food quality.

Bivalve carrying capacity in coastal ecosystems

The carrying capacity of suspension feeding bivalvesin 11 coastal and estuarine ecosystems is examined. Bivalve carrying capacity is defined in terms of watermass residence time, primary production time andbivalve clearance time. Turnover times for the 11ecosystems are compared both two and threedimensionally. Fast systems, e.g., Sylt and NorthInlet, have turnover times of days or less, while,slow systems, e.g., Delaware Bay, have turnover timesof months and years. Some systems,Marennes-Oléron, South San Francisco Bay and NorthInlet, require a net influx of phytoplankton in orderto support their bivalve populations. Three systems,Carlingford Lough, Chesapeake Bay and Delaware Bay,have very long bivalve clearance times due to small orreduced bivalve filter feeder populations. Carlingford Lough stands out because it is a naturallyplanktonic system now being converted to bivalveculture with an adherently stronger benthic-pelagiccoupling.Existing models of bivalve carrying capacity arereviewed. The Herman model is utilized as anappropriate ecosystem level model to examine carryingcapacity because it includes the three major turnovertime elements of water mass residence time, primaryproduction time and bivalve filter feeder clearancetime.The graphical analysis suggests that massive andsuccessful bivalve filter feeder populations are foundin systems with relatively short residence times(<40 days) and short primary production times (<4days) in order to sustain a high bivalve biomass withits associated rapid clearance times. Outliersystems are constrained by long water mass residencetimes, extended primary production times, and longclearance times.

Oyster reefs as processors of estuarine materials

Abstract Oyster reefs are dense concentrations of filter-feeding animals in estuarine ecosystems. A flow-through plastic tunnel is a feasible method of determining significant changes in material concentrations in tidal waters passing over an oyster reef. The oyster reef reduces the amplitude of the particulate organic carbon and chlorophyll a signals while increasing the amplitude, of the ammonia signal. The observations suggest that oyster reefs have one of the highest reported release rates of ammonia (1680–7250 μg at.·m −2 ·h −1 ), and thus are probably important in material cycles in marsh-estuarine ecosystems. The magnitude of particulate organic carbon removal by the oyster reef is many times greater than that expected from biofiltration alone, suggesting that removal due to physical factors may be important.

Estuaries of the South Atlantic Coast of North America: Their Geographical Signatures

Estuaries of the southeastern Atlantic coastal plain are dominated by shallow meso-tidal bar-built systems interspersed with shallow sounds and both low flow coastal plain and high flow piedmont riverine systems. Three general geographical areas can be discriminated: the sounds of North Carolina; the alternating series of riverine and ocean dominated bar-built systems of South Carolina, Georgia, and northeast Florida, and the subtropical bar-built estuaries of the Florida southeast coast. The regional climate ranges from temperate to subtropical with sea level rise and hurricanes having a major impact on the regions estuaries because of its low and relatively flat geomorphology. Primary production is highest in the central region. Seagrasses are common in the northern and southern most systems, while intertidal salt marshes composed ofSpartina alterniflora reach their greatest extent and productivity in South Carolina and Georgia. Nuisance blooms (cyanobacteria, dinoflagellates, and cryptomonads) occur more frequently in the northern and extreme southern parts of the region. Fishery catches are highest in the North Carolina and Florida areas. Human population growth with its associated urbanization reaches a maximum in Florida and it is thought that the long-term sustainability of the Florida coast for human habitation will be lost within the next 25 years. Tidal flushing appears to play an important role in mitigating anthropogenic inputs in systems of moderate to high tidal range, i.e., the South Carolina and Georgia coasts. The most pressing environmental problems for the estuaries of the southeastern Atlantic coast seem to be nutrient loading and poor land use in North Carolina and high human population density and growth in Florida. The future utilization of these estuarine systems and their services will depend on the development of improved management strategies based on improved data quality.

The influence of mussel beds on nutrients in the western Wadden Sea and eastern Scheldt estuaries

The uptake and release of materials by intertidal mussel beds were directly measured in two cultivated Dutch estuaries. Generally, chlorophylla, seston, and particulate organic carbon were taken up, while ammonium, orthophosphate, and silicate were released. The observed rates were higher than values computed from organismic observations and similar to those observed for intertidal oyster reefs in South Carolina. Specific estuarine material turnover rates varied from 1 week to 38 weeks when calculated with mussel bed fluxes. The fastest turnover rates were for chlorophylla and ammonium. These results support the idea that dense assemblages of bivalves are major components in the recycling of nutrients in estuaries.

The comparative roles of suspension-feeders in ecosystems

Modeling particle selection efficiency of bivalve suspension feeders.- Field measurements on the variability in biodeposition and estimates of grazing pressure of suspension-feeding bivalves in the northern Baltic Sea.- Can bivalve suspension-feeders affect pelagic food web structure?- Motile suspension-feeders in estuarine and marine ecosystems.- Impact of suspension-feeding nekton in freshwater ecosystems: patterns and mechanisms.- Influence of eastern oysters on nitrogen and phosphorous regeneration in Chesapeake Bay, USA.- How does estimation of environmental carrying capacity for bivalve culture depend upon spatial and temporal scales?- Impact of increased mineral particle concentration on Acartia clausi (Copepoda) behaviour, suspension feeding and reproduction.- Suspension-feeders as factors influencing water quality in aquatic ecosystems.- Neoplasia in estuarine bivalves: effect of feeding behaviour and pollution in the Gulf of Gdansk (The Baltic Sea, Poland).- Bivalves as biofilters and valuable by-products in land-based aquaculture systems.- Significance of suspension feeder systems on different spatial and temporal scales.- Invaders in suspension-feeding systems: variations along the regional environmental gradient and similarities between large basins.- Contrasting distribution and impacts of two freshwater exotic suspension-feeders, Dreissena polymorpha and Corbiculafluminea.- Functional changes in benthic freshwater communities after Dreissena polymorpha (Pallas) invasion and consequences for filtration.- Does the introduction of the Pacific oyster Crassostrea gigas lead to species shifts in the Wadden Sea?- One estuary, one invasion, two responses: phytoplankton and benthic community dynamics determine the effect of an estuarine invasive suspension-feeder.- Development of human impact on suspension-feeding bivalves in coastal soft-bottom ecosystems.- Oyster reefs as complex ecological systems.- Synthesis/Conclusions.- Index .

Uptake and release of materials by a Wadden sea mussel bed

Abstract A flow-through plastic tunnel was used to determine the uptake and release of materials in the tidal waters passing over a mussel bed in the western Wadden Sea. There was significant uptake of total suspended sediments (4.4–7.2g · m−2 · h−1), Chl a (15.4–55.1 mg· m−2 · h−1), total organic C (0.8–1.1 g C· m−2· h−1) and nitrite + nitrate (0.02–0.08g N· m−2· h−1). There was a significant release of ammonium (0.04–0.11 g N· m−2· h−1) and o-phosphate (0.05–0.08 gP· m−2· h−1). The intertidal mussel bed removed particulate materials at high rates from the water column, transformed some of this material into biomass and released some constituents as dissolved waste products. This study supports the idea that mussel beds function as systems not just as populations of mussels which process estuarine materials. Even though the directions of material uptake and release on the mussel bed are similar to oyster reef systems, the magnitudes of material transports are generally higher on the mussel bed due to greater filter-feeder biomass, the existence of a substantial microbenthic algal component and a considerably different environmental setting.

Between estuaries and the sea

Dissolved and particulate materials and living organisms are exchanged between estuaries and the sea. Net material fluxes, import or export, appear to depend on physical and biological processes within both estuarine and coastal ecosystems. In temperate zone lagoonal systems, the marsh-estuarine continuum hypothesis can provide a reasonable synthetic explanation of transport based on the level of ecosystem maturity within the system. The relative importance of riverine and lagoonal material exchanges with the coastal ocean are at present entirely speculative and make the estimation of the regional influences of material transports between estuaries and the coastal ocean uncertain. Organismic exchanges depend on both passive and active behavior mechanisms and are species specific. Few quantitative estimates of organismic fluxes exist and the role of non-commercial invertebrates and fish in these fluxes are unknown.

The Role of Bivalve Filter Feeder Material Fluxes in Estuarine Ecosystems

Bivalve reefs and beds are a common feature of many estuarine and coastal environments. Bivalve filter feeders dominate these communities removing food from and releasing waste materials to the overlaying waters. The surrounding shallow tidal waters provide a habitat for growing phytoplankton and an environment for nutrient recycling. In essence, these systems are natural “feed lots” with the herbivorous bivalves playing the same role as large mammals in cultivated terrestrial systems. This feature of bivalves has been recognized and exploited through culture for millennia. With the application of modern technology to bivalve cultivation, many estuarine systems are approaching and even exceeding the capabilities of these ecosystems to maintain their environmental quality. In this paper, I will review modern ecosystem concepts with respect to material processing and nutrient cycling emphasizing the role bivalve filter feeders play in shallow estuarine and coastal ecosystems. In addition, the published evidence of bivalve filter feeder influence on these ecosystems will be examined, synthesized and potential areas of research identified.

Oyster reefs and nutrient retention in tidal creeks

The role of oyster reefs in nutrient cycling and grazing within an estuarine ecosystem was observed by experimentally manipulating six tidal creeks. Reactive nutrient concentrations were significantly different in creeks with oysters when compared to creeks from which oysters had been removed. This evidence supports the hypothesis that oyster reefs function as nutrient retention mechanisms in these systems. There were no significant differences in Chlorophyll a concentrations among the creeks. This suggests that despite the increased grazing pressure exerted by these filter feeders plankton productivity may be enhanced in creeks with oysters.