Biodeposition Rate Research Articles

Biogenic silica in sediment core indicates the historical development of off-bottom oyster farming

Sediment cores are commonly used for reconstructing historical events by determining the biogenic elements in sediment vertical profiles. The vertical flux of biogenic silica (BSi) can be enhanced by bivalve mollusks through biodeposition and can be subsequently recorded in the sediment core. However, whether BSi in sediment core can indicate the interactions between aquaculture farms and the ecosystem is unclear. In this study, sediment cores were collected from a typical off-bottom oyster farm in Sanggou Bay, China. Based on 210Pb chronology analysis of the sediment vertical profile, BSi content was determined to reflect the BSi burial flux during the farming history. The BSi biodeposition fluxes were estimated based on the biodeposition model, to identify the correspondence among BSi burial flux, BSi biodeposition flux, and annual oyster production during the historical development of the farm. The results show that the BSi density in the sediment increased obviously after 1980 when intensive oyster farming began, and reduced after 2000 when farming began to decline. Moreover, BSi burial flux had a corresponding relationship with oyster production and the simulated biodeposition rate, except for 1997–2001 when oyster production peaked. Our finding supported that the variation of BSi from biodeposition can be preserved and then recorded in the sediment, suggesting that BSi could be considered as an indicator to reconstruct the historical development of the oyster farm.

Quantification of the vertical transport of microplastics by biodeposition of typical mariculture filter-feeding organisms

The tremendous loss of microplastics from the sea surface and the low density of microplastics found in the water column and sediments indicate that the oceans have mechanisms capable of transporting microplastics from the surface to the seafloor. These include physicochemical processes and biological influences from marine organisms that drive the vertical migration of microplastics. Little is known, however, about the biological processes involved in the deposition of plastics in the marine environment. A considerable number of mariculture filter-feeding organisms can consume substantial amounts of suspended substances in the water column, and these organisms are ideal candidates for depositing microplastics. In this study, we analyzed microplastic abundance in typical mariculture filter feeders, i.e., ascidians (Halocynthia roretzi), oysters (Crassostrea gigas), scallops (Chlamys farreri) and clams (Ruditapes philippinarum), quantified the number and characteristics of the microplastics they deposited in situ, and further compared microplastic biodeposition rates. Microplastics were present in feces and pseudofeces and sank to form biodeposits rather than accumulating to significant levels in organisms. Microplastics were found in significantly higher numbers in the biodeposits of mariculture organisms than in the control deposits (p < 0.01). The shape and color of the microplastics in the sediments were not impacted by the presence of organisms (p > 0.05), but the deposition of <1000 μm and positive-buoyancy (less dense than seawater) microplastics was significantly increased in the biodeposits (p < 0.05). The highest microplastic biodeposition rate was found in scallops (1.14 ± 0.07 items·ind−1·d−1 or 0.5 ± 0.03 items·g−1·d−1). These results suggest that mariculture filter-feeding organisms have important biodepositional functions that influence the fate of microplastics through the transfer of microplastics from the surface to the seafloor. This study could contribute to a better understanding of the biological plastic pump mechanisms in oceans.

Hyriid mussels (Unionoida) enhance benthic organic matter and meiofauna densities in a temperate Australian river

Abstract Studies in the Northern Hemisphere have shown that mussels play important roles as benthic‐pelagic couplers in freshwater systems, transferring filtered material, nutrients, and energy from the water column to sediments, through biodeposition and excretion. However, we know little of the functional roles of species of the Southern Hemisphere Hyriidae, the second most diverse family of the Unionoida. The aims of this study were to determine the biodeposition and excretion rates of nutrients and organic matter of the hyriid Alathyria jacksoni in an unregulated Australian river and test experimentally if the physical structure and biodeposition of A. jacksoni influenced sediment nutrients, organic matter, periphyton concentrations and meiofauna densities. In a lowland Australian river in late summer over 4 weeks, we measured biodeposition and excretion rates of A. jacksoni, and conducted a mesocosm experiment, during which we compared the effects of live mussels, dead mussel shells (shams), and controls without mussels on nutrients, organic matter, and meiofauna invertebrate densities in the sediment. Mean (± SE) mass of biodeposition was 70.85 ± 3.20 mg mussel−1 hr−1 and the relative rates of inorganic and organic biodeposition were 60.9 ± 3.1 and 9.9 ± 0.8 mg mussel−1 hr−1, respectively. Organic matter was significantly greater in the sediment of the mesocosms with live mussels than in that of the control mesocosms. There was also a trend of greater mean sediment chlorophyll‐a and total nitrogen concentrations in mussel treatments than in the controls. No significant difference was detected in sediment total phosphorous between mussel and control enclosures. The valves of live mussels had significantly higher amounts of organic material and chlorophyll‐a concentrations than the valves of sham mussels. There was a consistent trend of higher meiofauna densities collected in the benthos of the mussel enclosures than the control enclosures for total density and densities of Rotifera, Copepoda, Cladocera, Diptera, Oligocheata, Nematoda, and Ostracoda; this trend was near significant for total density; and significant for densities of Ostracoda, Rotifera, Cladocera, and Nematoda. Using our biodeposition and excretion rate estimates, and estimates of population size of A. jacksoni in the Lower Ovens River, we estimated that in a typical 1‐km reach in a month over summer, A. jacksoni would be biodepositing approximately 4.8 kg/day of organic matter (dry mass), 137 g N/day and 19 g P/day, and excreting 21 g N/day and 3.7 g P/day. Our findings are similar to those for Northern Hemisphere families of the Unionoida and serve to highlight the roles mussels play in processing of organic matter and cycling of nutrients in freshwater ecosystems.

Restoring tropical coastal wetland water quality: ecosystem service provisioning by a native freshwater bivalve

Freshwater bivalves can influence water quality by reducing phytoplankton levels through filter-feeding and altering nutrient levels through excretion and biodeposition. In northeast Australia, native freshwater bivalves (Corbicula australis) may help restore the water quality of coastal wetlands that receive high nutrient loads in runoff from nearby agricultural activity. We investigated the biofiltration and biodeposition capacity of C. australis and discuss their potential to provide an ecosystem service benefit of improved water quality to the Great Barrier Reef (GBR). The filtration and biodeposition rates of C. australis were measured in natural and artificial wetlands across: (1) the population’s size range; and (2) the temperature range of the wetlands they inhabit. High frequency water temperature loggers were deployed in wetlands throughout the year to determine water column temperature seasonality, population densities were measured to scale from individuals to ecosystem service provisioning potential. Bivalve filtration and biodeposition were quantified by measuring the rates of chlorophyll a removal and nutrient biodeposition, respectively. Biofiltration rates did not increase with size or differ between natural and artificial wetlands. In contrast, size was positively related to phosphorus (P) and nitrogen (N) biodepsoition rates, and N biodeposition rates differed between natural and artificial wetlands. Our results also suggest that biofiltration and biodeposition capacity of C. australis may be limited in high water temperatures only experienced in summer months. Overall, we demonstrate the importance of size, population density, and environmental context (i.e. wetland type and season) for the filtering capacity and biodeposition rate of C. australis. Larger individuals and denser populations mean that filtration and biodeposition rates are likely to be higher in artificial wetlands and may lead to greater processing of nutrient rich water.

Lake Characteristics, Population Properties and Invasion History Determine Impact of Invasive Bivalves on Lake Nutrient Dynamics

Invasive species can have large impacts on ecosystems, including the cycling and distribution of nutrients. To determine the whole-ecosystem effects of invasive zebra mussels on lake nutrient dynamics, we sampled 10 invaded Minnesota lakes spanning a broad trophic status gradient. We conducted N and P excretion and biodeposition rate measurements and determined the C, N and P composition of dreissenid soft tissues and shell material in the study lakes. We also estimated the whole-lake biomass of live dreissenid mussels and their dead shell material, constructing comprehensive nutrient budgets for dreissenid populations in the study lakes. We used the results of our measurements and published data to estimate the contribution of dreissenids to P budgets in 24 additional lakes in Europe and North America. Results show that nutrient cycling rates and composition of soft tissues and shells vary with mussel size and lake trophic status. Zebra mussels made variable, but often large, contributions to cycling and storage of water column standing stocks of POC, PON and TP in the study and literature lakes. In some lakes, the effects of zebra mussels on P dynamics were also considerable in the context of estimated P external and internal loading, sediment sequestration and effects of other biota. We show that the impact of zebra mussels on whole-lake nutrient budgets depends on lake properties, dreissenid population characteristics and invasion history. This information can be used by ecosystem managers to prioritize invasion prevention efforts toward lakes likely to be most strongly impacted by zebra mussel invasions.

Potential role of scallops Argopecten irradians in deposition of particulate nutrient and trace elements in a eutrophic estuary, northern China

Anthropogenic inputs of nutrients and trace elements have globally significant impacts on coastal waters. In order to evaluate the effect of the filter-feeding bay scallop Argopecten irradians on benthic-pelagic coupling in a eutrophic estuary (Laizhou Bay), biodeposition of total suspended materials, particulate nutrient (C, N, P) and trace elements (Cu, Zn, Pb, Cr, Cd, Hg, As) were determined using modified sediment traps during autumn 2013. Results showed that biodeposition rates of the bay scallops were rather high compared with those reported for other bivalves. The allometric relationship between the biodeposition rate (BDR; g ind.(-1) d(-1)) and soft tissue dry weight (W; g ind.(-1)) was modeled (BDR = aW(b)) with the value of a being 1.24 in September and dropping to 0.96 in October. The biodeposition contributed to the enrichment of organic matter, C and N in the local sediment. Trace element concentrations in the scallop biodeposits were significantly higher than those of the natural surrounding sediments, especially during the months of October and November. A. irradians significantly increases the mass fluxes from the water column to the bottom, with estimated 1140 tonnes of total suspended material being deposited to the seabed each day in the culture zone. Results also suggest that biotransformation and biodeposition by such efficient filter-feeders may play a pivotal role in the fate and transportation of particulate nutrient and trace elements in aquatic ecosystems. In coastal waters and estuaries subject to anthropogenic inputs, suspended bivalve aquaculture could be environmentally advantageous via intense filtering and biodeposition, potentially mitigating eutrophication trace and element pressures.

Biologically induced deposition of fine suspended particles by filter-feeding bivalves in land-based industrial marine aquaculture wastewater.

Industrial aquaculture wastewater contains large quantities of suspended particles that can be easily broken down physically. Introduction of macro-bio-filters, such as bivalve filter feeders, may offer the potential for treatment of fine suspended matter in industrial aquaculture wastewater. In this study, we employed two kinds of bivalve filter feeders, the Pacific oyster Crassostrea gigas and the blue mussel Mytilus galloprovincialis, to deposit suspended solids from marine fish aquaculture wastewater in flow-through systems. Results showed that the biodeposition rate of suspended particles by C. gigas (shell height: 8.67±0.99 cm) and M. galloprovincialis (shell height: 4.43±0.98 cm) was 77.84±7.77 and 6.37±0.67 mg ind−1•d−1, respectively. The total solid suspension (TSS) deposition rates of oyster and mussel treatments were 3.73±0.27 and 2.76±0.20 times higher than that of the control treatment without bivalves, respectively. The TSS deposition rates of bivalve treatments were significantly higher than the natural sedimentation rate of the control treatment (P<0.001). Furthermore, organic matter and C, N in the sediments of bivalve treatments were significantly lower than those in the sediments of the control (P<0.05). It was suggested that the filter feeders C. gigas and M. galloprovincialis had considerable potential to filter and accelerate the deposition of suspended particles from industrial aquaculture wastewater, and simultaneously yield value-added biological products.

亚热带养殖海湾皱瘤海鞘生物沉积的现场研究

A worldwide increase in farming of filter feeding bivalves and a growing awareness of the likely environmental impacts stem from biodeposition lead to extensive and well recognized studies.Whereas the suspended longline culture with massive and intensive facilities built(e.g.,buoys,anchors and ropes) and bivalve shells in the farming area supply the footstone for the fouling organisms such as the ascidians and large number of breeding depended on them,which can be extremely abundant in areas of large-scale bivalve culture.Therefore,the fouling organisms may also influence the environment by remarkably increasing their amounts.There is an urgent need to examine the possible effects of biodeposition from the fouling organisms.The ascidian Styela plicata is one of the most predominant fouling species in tropical and subtropical bays.S.plicata is a filter feeding species like the bivalves.However,untill recently,the biodeposition of S.plicata was unknown.In order to evaluate the influence of S.plicata on the coastal environment,the biodeposition rate of ascidian S.plicata was investigated in Dapeng Cove,located in the southwest of the Daya Bay,a subtropical bay in southern China.Intensive oyster Crassostrea gigas longline culture activities were conducted there.The ascidians were sampled from the culture facilities and shells of the oyster Crassostrea gigas.The biodeposition rate was measured in situ in suspended culture areas by sediment traps from January to July,2012.The contents of organic matters(OM),total carbon(TC),total nitrogen(TN),organic carbon(OC) and organic nitrogen(ON) in biodeposits and in natural sediments were analyzed and compared. Results showed that the biodeposition rate of S.plicata ranged from 145.5 to 1011.8 mg·ind-1·d-1,with an average of 516.0 mg·ind-1·d-1.The mean contents of OM,TC,OC,TN and ON in the biodeposits was 14.38%,10.80%,2.87%,3.06% and 0.86%,respectively,and were higher than those of 13.39%,7.36%,2.32%,2.29% and 0.67% respectively,in natural sediments.In particular,the contents of TC and ON in the biodeposits were significantly higher than those in the natural sediments(P0.05).The biodeposition rate of OM,TC,OC,TN and ON by S.plicata were 74.20,55.73,14.80,15.79 and 4.43 mg·ind-1·d-1,respectively.The density of S.plicata in the longline culture area ranged from 54.9 to 222.1 ind/m2,with an average of 147.5 ind/m2.The OM,TC,OC,TN and ON deposited by S.plicata was 10.94,8.21,2.18,2.32 and 0.65 g·m-2·d-1,respectively.The average biodeposition rate of ascidian S.plicata in the farming area was 76.1 g·m-2·d-1,1.21 times higher than the natural sedimentation rate(62.7 g·m-2·d-1) in the longline culture area.An estimated amount of 29000 t of biodeposits,4100 t of OM,3100 t of TC,820t of OC,870 t of TN and 240 t of ON can be produced by all the ascidians in suspend culture area in Dapeng Cove in one year. The results indicated that S.plicata has a high biodeposition rate and the species can be an important contributor to aggregating mineral and organic matter from water column to surface sediment,which may impact the physical,chemical and biological conditions of benthic environment.Therefore,when assessing the effects of suspended longline culture of bivalves on the coastal ecosystem,not only the farming bivalves,but also the fouling organisms especially the ascidians should be considered.

Zebra mussels mediate benthic–pelagic coupling by biodeposition and changing detrital stoichiometry

Summary1. The zebra mussel (Dreissena polymorpha) is one of the most successful invasive species; it has colonised many aquatic systems in Europe and North America with strong impacts on various ecosystem processes. The effect of D. polymorpha filtration on pelagic seston concentrations has been quantified in several studies, but the magnitude and stoichiometry of the transfer of sestonic biomass into benthic detritus by D. polymorpha and the accompanying enrichment of the benthic habitat is still under‐investigated.2. We studied biodeposition by zebra mussels in two series of laboratory experiments with the food algae Cryptomonas erosa and Scenedesmus obliquus. We also measured the year‐round biodeposition rate under natural conditions in the oligotrophic Lake Constance.3. In all experiments, zebra mussel biodeposition was linearly related to seston concentration. In the field, the relationship changed with a seasonal shift in algal composition and lower biodeposition rates during the spring algal bloom.4. For both algal species in laboratory experiments, biodeposited material was depleted in phosphorous at an algal concentration ≤0.6 mg ash‐free dry mass L−1, but not at higher concentrations. This effect was not observed in the field, probably because of high variation in C : N : P stoichiometry.5. By mediating the transfer of pelagic resources into the benthos zebra mussels provide a sufficient amount of detritus for benthic invertebrates, especially during summer. Thus, material biodeposited by the mussels might increase benthic secondary production from pelagic resources, and zebra mussels are important mediators of this flux of organic matter from the pelagic zone into the benthos.

Feeding responses of the gastropod Crepidula fornicata to changes in seston concentration

We investigated the response of the suspension-feeding activity of the prosobranch gastropod Crepidula fornicata (L.) to changes in seston abundance and composition, characteristic of the natural particle variability experienced by suspension-feeding organisms as a consequence of tidal resuspension. The experimental conditions were characterized by seston concentrations (12.2 to 196.0 mg 1 -1 ) inversely related to the organic content of particulate matter (56 to 6%). The organic fraction was composed of 2 benthic diatoms, Entomoneis pseudoduplex (Smith) and Nitzschia aurariae (Cholnoky). Inorganic matter was composed of 2 to 3 μm diameter kaolinite particles. The functional unit used for determination of ecophysiological responses was a chain of 6 individuals with mean chain dry tissue weight of 1.05 g. The efficiency of particle retention as a function of particle size increased with increasing particle size from 2 to 4 μm (equivalent spherical diameter). Above 4 μm, all particles were cleared from suspension with 100% efficiency, but retention efficiencies of smaller particles significantly declined with increasing seston loads. A constant clearance rate (CR) was found throughout the seston range, with a mean of 0.76 ± 0.05 1 h -1 g -1 (±SE). Filtration rate increased linearly with seston concentration from a minimum value of 10 mg h -1 g -1 to a maximum of 42.8 mg h -1 g -1 at the highest concentration. The total biodeposition rate (sum of pseudofaeces and faeces) followed a similar linear trend, with an increase from 3.8 to 41.6 mg h -1 g -1 at the highest concentration. Absorption rate was very stable throughout the range of suspended particulate matter concentrations tested with a mean of 4.9 ± 0.5 mg h -1 g -1 (±SE). It was not possible to ascertain pre-ingestive selection, even though the organic content of biodeposits and diet was very similar. The low retention efficiency of small inorganic particles at high seston loads was the sole mechanism that was clearly identified in this study as counteracting food dilution by inorganic material, through the enrichment of the organic content of filtered matter. The absence of pre-ingestive selection in C. fornicata would increase the physiological significance of this process in turbid environments.

Density-dependent effects on seston dynamics and rates of filtering and biodeposition of the suspension-cultured scallop Chlamys farreri in a eutrophic bay (northern China): An experimental study in semi-in situ flow-through systems

Effects of stocking density on seston dynamics and filtering and biodeposition by the suspension-cultured Zhikong scallop Chlamys farreri Jones et Preston in a eutrophic bay (Sishili Bay, northern China), were determined in a 3-month semi-field experiment with continuous flow-through seawater from the bay. Results showed that the presence of the scallops could strongly decrease seston and chlorophyll a concentrations in the water column. Moreover, in a limited water column, increasing scallop density could cause seston depletion due to scallop's filtering and biodeposition process, and impair scallop growth. Both filtration rate and biodeposition rate of C. farreri showed significant negative correlation with their density and positive relationship with seston concentration. Calculation predicts that the daily removal of suspended matter from water column by the scallops in Sishili Bay ecosystem can be as high as 45% of the total suspended matter; and the daily production of biodeposits by the scallops in early summer in farming zone may amount to 7.78 g m − 2 , with daily C, N and P biodeposition rates of 3.06 × 10 − 1 , 3.86 × 10 − 2 and 9.80 × 10 − 3 g m − 2 , respectively. The filtering and biodeposition by suspension-cultured scallops could substantially enhance the deposition of total suspended particulate material, suppress accumulation of particulate organic matter in water column, and increase the flux of C, N and P to benthos, strongly enhancing pelagic–benthic coupling. It was suggested that the filtering-biodeposition process by intensively suspension-cultured bivalve filter-feeders could exert strong top-down control on phytoplankton biomass and other suspended particulate material in coastal ecosystems. This study also indicated that commercially suspension-cultured bivalves may simultaneously and potentially aid in mitigating eutrophication pressures on coastal ecosystems subject to anthropogenic N and P loadings, serving as a eutrophic-environment bioremediator. The ecological services (e.g. filtering capacity, top-down control, and benthic–pelagic coupling) functioned by extractive bivalve aquaculture should be emphasized in coastal ecosystems.

Differences in the benthic-pelagic particle flux (biodeposition and sediment erosion) at intertidal sites with and without clam (Ruditapes philippinarum) cultivation in eastern China.

An annular flume or flux system (AFS) was deployed to measure the biodeposition and sediment resuspension processes at four stations in the mid-shore and low-shore zones along both natural and Manila clam (Ruditapes philippinarum) farming transects in Xuejiadao intertidal area located in Jiaozhou Bay, eastern China. The results showed that there was a significant correlation between biodeposition rates and the density (r=0.984, P<0.05) and biomass (r=0.977, P<0.05) of the suspension feeding Manila clam. The effect of biodeposition at the farming transect was more intensive than at the natural transect where the biodeposition effect was lower than that resulting from natural sedimentation. In contrast, the biodeposition rate at the culture site with the high density of Manila clams was four times the sedimentation rate. Following the addition of Manila clams to increase their density in natural sediments, there was a marked increase in both clearance and biodeposition rates at all four sites. At the site with the highest natural bivalve biomass, the biodeposition rate increased 1.5-fold, while at the site with the least bivalve biomass, it increased by 40 times compared with the biodeposition rate by natural biota. The mean clearance rate of Manila clam was 0.90+/-0.34 l h(-1) ind.(-1) and the biodeposition rate was calculated to be 0.06+/-0.01 g h(-1) ind.(-1). The critical erosion velocities of intertidal sediment at Xuejiadao were from 17.4 to 20.4 cm s(-1). Relationships describing suspended particulate matter (SPM) vs. current velocity were analysed by linear regression following log transformation of the SPM. Statistical analysis of the slopes of the regression lines revealed that there were distinct differences between the low-shore and mid-shore (P<0.05) at both transects, respectively. There was also distinct difference between the two mid-shore stations (P<0.05) possibly due to differences in the densities of bioturbators (e.g. Macoma incongrua etc.), however, there was no significant difference between the two low-shore stations (P>0.05). Furthermore, it was found that the site differences in sediment erodibility were not significantly correlated with measured physical properties of sediments and biota factors such as total macrofauna biomass, total abundance and macrofauna densities, Chl-a and Ph-a (P>0.05). However, there was a significant correlation between sediment erodability and both median grain size (P<0.01) and the density of the bioturbator M. incongrua (P<0.05). There was also evidence of a slight increase in sediment stability after 3 h of air exposure, but the effect was not overcome following the addition of Manila clams. It is hypothesised that the lower stability of sediments at the mid-shore level was probably associated with higher densities of bioturbators and with disturbance by shrimp farming near the high-shore.

Role of filtering and biodeposition by Adamussium colbecki in circulation of organic matter in Terra Nova Bay (Ross Sea, Antarctica)

At Terra Nova Bay, the scallop Adamussium colbecki (Smith, 1902) characterises the soft and hard bottoms from 20 to 80 m depth, constituting large beds and reaching high values of density (50–60 individuals/m 2) and biomass (120 g/m 2 DW soft tissues). To assess its role in the organic matter recycling in the coastal ecosystem, its filtering and biodeposition rates were evaluated in laboratory experiments during the austral summer 1993/94. Filtration rates, measured in a flow-through system, were calculated from the difference in particulate organic carbon (POC), nitrogen (PON) and chlorophyll- a (Chl- a) concentration in inflow and outflow water. Experiments were performed using natural sea water with POC, PON and Chl- a concentrations of about 450 μg/l, 90 μg/l and 2 μg/l, respectively. The biodeposition rate and the biochemical composition of the biodeposits were studied in order to detect how the organic matter is transformed through feeding activity of A. colbecki. At +1°C temperature, the average filtering rate was about 1 l h −1 g −1 (DW soft tissues) in specimens ranging in body mass from 2 to 3 g (DW soft tissues) and 6–7 cm long. The biodeposition rate in 3–8 cm long specimens, ranging from 0.4 to 5.7 g (DW soft tissues), was about 5.65 mg DW/g DW/day, leading to an estimate of Corg flux, through biodeposition by A. colbecki, of about 21 mg C m −2 day −1 at in situ conditions. Comparison between the biochemical composition of seston and biodeposits shows a decrease of the labile compounds, of the Chl- a/phaeopigments ratio in the biodeposits. The recorded C/N ratio decrease suggests a microbial colonisation in the biodeposits. This study suggests that Adamussium colbecki plays an important role in coupling the material fluxes from the water column to the sea bed, processing about 14% of total Carbon flux from the water column to the sediments, with an assimilation efficiency of 36%.

Use of in situ flume to quantify particle flux (biodeposition rates and sediment erosion) for an intertidal mudflat in relation to changes in current velocity and benthic macrofauna

Abstract A portable in situ annular flume was deployed on eight occasions at five stations along a shore normal transect from immediately below the saltmarsh to the mid-tide level of the Skeffling mudflat in the Humber estuary. Both large scale (km) and small scale (m) spatial differences (i.e. between ridges, gullies and pools on ridges) were examined. Biodeposition rates were measured at low current velocities (5 cm s −1 ), while sediment resuspension and erosion rates were determined in response to step-wise increases in current velocities between 10 and 50 cm s −1 (equivalent to a range in shear stress from 0.02 to 1.6 Pa). Maximum biodeposition rates (6.6 g m −2 h −1 ) were more than an order of magnitude higher than the mean sedimentation rate in the absence of sediment and biota. There was a significant correlation between biodeposition rate and the density of the suspension feeder Cerastoderma edule ( r = +0.90; P &lt; 0.05). The intertidal sites could be separated into three distinct groups on the basis of sediment stability/erodibility. Upper shore sites had the highest stability with critical erosion velocities ( u crit ) of 30 cm s −1 , whereas the pools and gullies were the most easily eroded with u crit of 15 cm s −1 . Site differences in sediment erodibility were not significantly correlated with measured physical properties of the sediment (bulk density, moisture content, % POM, % sand). However, there was a significant correlation between sediment erodibility and the density of Cerastoderma ( r = +0.89; P &lt; 0.01) and an index of the bioturbation activity of Macoma balthica ( r = +0.96; P &lt; 0.001).

Biodeposition by the horse mussel Modiolus modiolus (Dillwyn) during the spring diatom bloom

The production and nutritional quality of faeces and pseudofaeces from the horse mussel Modiolus modiolus (Dillwyn) was measured during the spring diatom bloom in Logy Bay, Newfoundland. Chloropigments, organic carbon, organic nitrogen and biogenic silica were determined in faeces and pseudofaeces, and compared with values from seston samples. The biodeposition rate of a horse mussel (faeces and pseudofaeces) of 5 g dry meat weight varied from 40.9 mg dry weight · day −1 at the peak of the bloom to 4–8 mg · day −1 at the end. The concentrations of organic carbon and organic nitrogen were lower in the faeces and pseudofaeces than in the seston, but chlorophyll a levels were greater in the pseudofaeces than in the seston or faeces. In terms of dry weight, faeces production was five or more times greater than pseudofaeces production, but the latter were more important in recycling chlorophyll a, especially during the peak of the diatom bloom. Microscopic analysis of the biodeposits showed that chains and large diatoms were very abundant in the pseudofaeces, whereas the faeces contained only frustules of small cells and of short chains, indicating that M. modiolus concentrates the large diatoms contained in the seston and rejects them in the pseudofaeces. The rejection of organic-rich diatoms by M. modiolus during the spring bloom provides a mechanism for the recycling of nutrients to suspension-feeders and deposit-feeders.

Ingestion rate, assimilation efficiency and energy balance in Mytilus chilensis in relation to body size and different algal concentrations

Basing on a quantification of filtration, ingestion, assimilation, biodeposition, excretion and respiration rate, energy budgets were established in Mytilus chilensis Hupe in relation to body size and three different food concentrations of the unicellular green alga Dunaliella marina. The present quantifications revealed that in M. chilensis the ingestion rate only increases slightly with an increase in food concentration which, however, is counterbalanced by a significant decrease in assimilation efficiency in such a way that assimilation rate finally is nearly constant and independent of the food concentrations tested. The quantifications of these results are given by the a-values of the general allometric growth equation P=aWb relating the energy disposable for growth and reproduction (P; cal d-1 to body size (W; dry-tissue wt, g). The best energy budget was obtained at the lowest food concentration tested (0.8 mg algal dry wt l-1; at 12°C and 30‰ S) with an a-value of 58.8, while the energy budget at the highest food concentration (2.14 mg l-1) was only slightly lower with an a-value of 49.8; the b-values were 0.49 and 0.51, respectively. The net growth efficiencies (K2) decreased with increasing body size (from 20 mg to 3 000 mg drytissue wt) from 76.7 to 47.9% at the lowest food level and from 72.6 to 44.0% at the highest food level tested. These relatively high net growth efficiencies seem to reflect optimal experimental conditions. Furthermore, by a comparison of estimated growth (calculated on the basis of the best energy budget) with growth actually quantified in culture raft mussels in the south of Chile during the highest production period of the year, it is obvious that the energy budgets established really reflect the conditions experienced by the mussels in their natural environment.

Biodeposit production by the mussel Mytilus edulis L. on rocky shores

Seasonal changes in the amount of biodeposit (faeces and pseudofaeces) produced by the mussel Mytilus edulis L., which is one of the representative suspension-feeders in the rocky intertidal and shallow subtidal regions of Mutsu Bay, were studied in the laboratory. The effects of water temperature, light, food concentration, flow rate, body size, age, and spawning on biodeposit production were investigated. More biodeposit was produced in summer than in other seasons. Throughout the year, the amount of biodeposit was positively correlated with body size. Relatively more biodeposit was produced by smaller than by larger individuals. A M. edulis population living in one square meter was estimated to produce 9.20 kg of faeces and 2.71 kg of pseudofaeces per year (dry wt). More biodeposit was produced at water temperatures of 17.6–20.2° C than at 4.5–7.6° C and 25.2–26.0° C. The optimum temperature for biodeposit production was found to be ≈ 20.0 °C. When kept in the dark, M. edulis produced more biodeposit than in the light. When food concentration is increased, more psuedofaeces are produced; the amount of faeces, however, remains constant. With increasing flow rate, the amount o f biodeposit per h increased but the biodeposition rate decreased. Larger amounts of faeces and smaller amounts of pseudofaeces were produced by younger mussels than by older ones of a similar size. Spawning also affected biodeposit production.

Comparison of feeding and biodeposition of three bivalves at different food levels

Experiments on the edible mussel Mytilus edulis, the American oyster Crassostrea virginica, and the hard clam Mercenaria mercenaria, using flowing systems, showed that the feeding and biodeposition rates were affected by food concentration. At all levels of food concentration, the order of increasing feeding rate (both the percent of available particulate carbon and the actual amount of carbon removed) was: clam < oyster < mussel. All bivalves exhibited lower feeding rates (both precent and actual) at low food concentrations. However, the precent of available food removed quickly increased to a maximum at food concentrations typical for the natural environment. This maximum remained constant for the mussel and oyster, but declined with increasing food concentration for the clam. However, because this percentage was for increasing levels, the actual carbon removed continued to increase up to the highest food level for all three bivalves. In increasing order of biodeposition rate, the bivalves were: clam < oyster < mussel. The biodeposition rates of the three bivalves increased logarithmically with increased food concentration as a result of the production of pseudofeces. The feeding and biodeposition data were used to calculate assimilation rates, and this pointed out the higher efficiency of the oyster compared to the mussel and clam.