Jon Grant

Effects of suspended mussel culture (Mytilus spp.) on sedimentation, benthic respiration and sediment nutrient dynamics in a coastal bay

Many studies have shown that the pnmary effect of shellfish culture on nearshore manne systems is enhanced sedimentation T h ~ s tudy was d e s ~ g n e d to measure the effects of this enhanced sedimentation on the respiration and nutrlent fluxes of the benthic community and the coupling between the pelagic and ben th~c systems at a mussel culture s ~ t e (Mytllus edulls and M trossulus) In Upper South Cove, Nova Scotia, Canada There was a signif~cant association between chlorophyll In the water colun~n and sedimentation rate In Upper South Cove over the study year 1990, particularly under the mussel llnes, but the malority of the par t~cula te carbon and nitrogen whlch fell to the bottom was not Incorporated Into the sediments Suspended mussel culture had little Impact on sediment phosphorus dynamics The largest response of the sediment coinmunity to suspended mussel culture was ammonium release, whlch was higher under the mussel lines at all times of the year Over the year, the sedlments of the reference site were a net sink f o ~ total dissolved nitrogen, whlle the sediments under the mussel line were a source

The interaction between benthic diatom films and sediment transport

Abstract Field and laboratory flume studies were used to examine the stabilization of intertidal sands by diatom mucus films. Films were delineated by analyzing colloid carbohydrates, chlorophyll, and by scanning electron microscopy on intact sediment samples. In the field, diatom films were patchy on a scale of centimetres, corresponding to the structure of sand ripples. Films were present on the sediment surface after calm weather and absent after storms. Extracellular polysaccharides accounted for a maximum of 20% of microalgal carbon. Erosion of intact cores in the flume showed that although films stabilized local areas of the bed, portions of the film were also washed away or buried. Stabilized areas of the bed were transposed to new ripple locations as the bedform moved ‘through’ the film. This observation explained the heterogeneous distribution of films with respect to ripple topography in the field. SEM showed diatom cells attached between sand grains with mucus strands, particularly in samples from the films. Mucus attachment due to protozoa, fungi, and other organisms was also observed. In the flume, diatom cells were washed away leaving mucus strands behind. A flume core with diatom films lost smaller amounts of chlorophyll than a core without films, under similar stages of erosion. At the highest flow, many grains were cleaned of mucus coatings; the grains appeared similar to those from sites of active transport (crests) in the field. We conclude that sediment stabilization by biofilms must be studied on a spatial scale of centimetres, and a temporal scale of days to weeks. The most important effect of microbial binding of sediments may be their role in the transfer of organic matter between the sediment and the water column.

Sea Carousel—A benthic, annular flume

A benthic annular flume (Sea Carousel) has been developed and tested to measure in situ the erodibility of cohesive sediments. The flume is equipped with three optical backscatter sensors, a lid rotation switch, and an electromagnetic (EM) flow meter capable of detecting azimuthal and vertical components of flow. Data are logged at rates up to 10·66 Hz. Erodibility is inferred from the rate of change in suspended sediment concentration detected in the annulus. The energy-density/wave number spectrum of azimuthal flow showed peaks in the energy spectrum at paddle rotation wave numbers (k) of 14 and 7 m −1 (macroturbulent time scales) but were not significant. Friction velocity ( U *), measured (1) at 1 Hz using a flush-mounted hot-film sensor, and (2) derived from measured velocity profiles in the inner part of the logarithmic layer gave comparable results for Ū * −1 . At higher values of U*, method (2) underpredicted by up to 20%. Method (1) showed radial increases in Ū * in the annulus for Ū y > 0·32 m s −1 . Radial velocity gradients were proportional to ( Ū y − 0·32 m s −1 ). Maximum radial differences in U * were 10% for Ū y = 0·5 ms −1 . Suspended sediment mass concentration ( S ) in the annulus resulted in a significant decrease (10·5%) in Ū * derived by method (1) over the range 0 S −1 . These decreases were not evident in method (2). Method (1) may, therefore, be subject to changes in stress sensor calibration with changes in S . Subaerial deployments of Sea Carousel caused severe substrate disturbance, water losses, and aeration of the annulus. Submarine deployments produced stable results, though dispersion of turbid flume water took place. Results clearly demonstrated the existence of ‘Type I’ and ‘Type II’ erosion documented from laboratory studies.

Bedload and water-column transport and colonization processes by post-settlement benthic macrofauna: Does infaunal density matter?

Copyright (c) 1997 Elsevier Science B.V. All rights reserved. In this study, we document dispersal and colonization by post-settlement benthic macrofauna on a large (250×500 m) area of intertidal sandflat at Wiroa Island in the Manukau Harbour, New Zealand, over a 2-week period in February 1994. We examine the effects of variation in the natural density of large (>15 mm) Macomona liliana Iredale (a tellinid bivalve) on these processes. Post-settlement transport was measured using cylindrical bedload and water-column traps positioned at 22 experimental sites within the study site. Macrofaunal colonization was documented using small pans of defaunated sediment deployed at each of the experimental sites. Greatest macrofaunal colonization of pans occurred in areas of greatest sediment reworking and deposition, suggesting transport and deposition of post-settlement stages may be passive processes. For some species [e.g. Austrovenus stutchburyi (Wood)] there was a significant positive relationship between their abundance and the weight of sediment in bedload traps, as well as wind conditions over the study period. This is consistent with passive transport processes, but does not exclude the possibility of active dispersal processes also being important. Differences in the hydrodynamic conditions (e.g. increased wind generated wave activity) over the 2-week study may have contributed to changes in abundance on the 2 sampling dates. For other species (e.g. Macomona liliana) the absence of significant positive relationships between abundance in either bedload or water-column traps and the weight of sediment retained in traps, as well as between ambient densities and the net flux of individuals across sites, is consistent with active dispersal and colonization. There was a negative relationship between background density of large Macomona liliana and numbers of smaller conspecifics (≤4 mm) and other bivalves [Austrovenus stutchburyi, Cyclomactra ovata (Gray) and Nucula hartvigiana Pfeiffer] colonizing pans of defaunated sediment. The results suggest that 10 to 100s m scale variation in the natural densities of an abundant siphonal surface deposit feeder may have a significant influence on dispersal and colonization and, thus, the spatial patterns of macrofauna on the tidal flat.

Scaling-up from experiments to complex ecological systems: Where to next?

a , b c d e * S.F. Thrush , D.C. Schneider , P. Legendre , R.B. Whitlatch , P.K. Dayton , a f a g h J.E. Hewitt , A.H. Hines , V.J. Cummings , S.M. Lawrie , J. Grant , a a i R.D. Pridmore , S.J. Turner , B.H. McArdle National Institute of Water and Atmospheric Research, P.O. Box 11-115, Hamilton, New Zealand Ocean Sciences Centre, Memorial University of Newfoundland, St. John’s, Canada ALC5S7 c ́ ́ ́ Departement de Sciences Biologiques, Universite de Montreal, C.P. 6128, succursale Centre-ville, ́ ́ Montreal, Quebec H3C 3J7, Canada Dept. Marine Sciences, University of Connecticut, Groton, CT 06340-6097, USA Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0201, USA Smithsonian Environmental Research Center, P.O. Box 28, Edgewater, MD 21037, USA Culterty Field Station, University of Aberdeen, Newburgh, AB40AA, Scotland Dept. of Oceanography, Dalhousie University, Halifax, Canada B3H 4JI Biostatistics Unit, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand

The relationship of bioenergetics and the environment to the field growth of cultured bivalves

Abstract The field culture of bivalve molluscs is dependent on the production and supply of phytoplankton and other food sources, its consumption by these suspension feeders, and its transformation into bivalve tissue. An understanding of the processes by which food is captured and utilized is fundamental to prediction of bivalve growth and management of shellfish aquaculture. The following perspective considers the role of food quality and quantity in the ingestion and absorption of food particles, as well as the influence of temperature, water circulation and other environmental variables on bivalve energy budgets and growth rate. A particular focus is the role of simulation modelling in quantifying the influence of these variables on scope for growth. Seston depletion is a major influence on cultured animals such that bivalves are limited by both food quality and quantity. Seston depletion can be managed by taking advantage of particle maxima (e.g. resuspension), matching culture species to turbidity gradients, and arranging hanging culture to take advantage of seston renewal in oblique flow. Food limitation interacts with temperature in cold temperate areas where high primary production occurs at low temperatures. Model simulations of mussel growth demonstrate the importance of temperature acclimation of filtration and its relationship to the timing and magnitude of the spring bloom. In addition to the energetics of individual animals, energy flow through culture ecosystems is considered in terms of bivalve processing of organic matter and competition with Zooplankton and fish. Because bioenergetics is at the root of all of these issues, simulation modelling of scope for growth and related components of the ecosystem is a vital tool in prediction and management of commercial bivalve aquaculture.

Modelling the effect of food depletion on scallop growth in Sungo Bay (China)

Sungo Bay (China) has a mean depth of 10 m, a total area of 140 km 2 and is occupied by several types of aquaculture, whilst opening to the ocean. The production of scallops (Chlamys farreri) cultured on long lines is estimated to exceed 50 000 tonnes (total weight) per year. Selection of sites for scallop growth and determination of suitable rearing densities have become important issues. In this study, we focused on the local scale (e.g. 1000 m) where rearing density, food concentration and hydrodynamics interact. We have developed a depletion model coupling a detailed model of C. farreri feeding and growth and a one-dimensional horizontal transport equation. The model was applied to assess the effect of some environmental parameters (e.g. food availability, temperature, hydrodynamism) and spatial variability on growth, and to assess the effect of density according to a wide range of hydrodynamical and environmental conditions. In the simulations, food concentrations always enabled a substantial weight increase with a final weight above 1.5 g dry weight. Compared to a reference situation without depletion, a density of 50 ind m –3 decreased growth between 0% and 100%, depending on current velocity when maximum current velocity was below 20 cm s –1 . The mean ratio between food available inside and outside the cultivated area (depletion factor) varied with the percentage of variation in scallop growth that was due to density. Our model suggests that scallop growth was correlated with maximum current velocity for a given density and current velocity below 20 cm s –1 . The model was integrated within a Geographical Information System (GIS) to assist in making decisions related to appropriate scallop densities suitable for aquaculture at different locations throughout the bay. Concepts (depletion), methods (coupling hydrodynamics and growth models), and the underlying framework (GIS) are all generic, and can be applied to different sites and ecosystems where local interactions must be taken into account.

Comparative models of mussel bioenergetics and their validation at field culture sites

Models of bioenergetics of the blue mussel (Mytilus edulis) were constructed to simulate growth in suspended culture at field sites in Upper South Cove (Nova Scotia) and Marennes-Oleron Bay (France). Two models with contrasting complexity of feeding behaviour were used to test whether simple empirical formulations of the energy budget (statistical model) were adequate to simulate growth compared to a more fully mechanistic model. In the statistical model, ingestion was related to a single food source (particulate organic matter, POM) and absorption efficiency via laboratory feeding studies from the literature. In the mechanistic model, filtration, particle rejection and selection, and absorption efficiency were related to phytoplankton, detrital food and total particulate load. Respiration terms were identical between models to facilitate comparisons between feeding behaviour. Measured tissue trajectories of cultured mussels were used to groundtruth model predictions. The Nova Scotia grow-out site was characterized by low turbidity and particulate organic matter (POM), and seasonally high chlorophyll, while the Marennes-Oleron site had high turbidity (up to 180 mg l−1) and POM, but similar chlorophyll to the Nova Scotia site. Results of the simulations indicated that for Nova Scotia, the statistical model provided a realistic growth trajectory, whereas the mechanistic model underpredicted growth during the first half of the year due to low phytoplankton biomass. Use of fluorometer records rather than water samples as a measure of chlorophyll improved the accuracy of the growth prediction. For Marennes-Oleron, the statistical model was unsuccessful since its POM-ingestion relationship did not allow for limitation by turbidity. The mechanistic model applied to this site was reasonable in predicting a growth trajectory, but it was sensitive to the functional curve of particle rejection as well as the maximum daily ingestion. Simulations at both sites were sensitive to the POC content of POM and the absorption efficiency of detritus. These simulations demonstrate that simple formulations of food and feeding will suffice in predicting growth where seston values are not extreme (e.g., high turbidity). Although the separation of suspended food source into POM and chlorophyll may be convenient, it is not clear how organic particle selection occurs, considering the aggregated nature of particles in the field, and the close association of POM with silt grains. The sensitivity of models to both food quality and feeding formulation requires better knowledge of variance in suspended food sources and the ability of bivalves to deal with natural particle mixtures.

Sensitivity of benthic community respiration and primary production to changes in temperature and light

In-situ measurements of benthic community respiration and primary production on an intertidal sandflat in Nova Scotia, Canada were used to test the hypothesis that community responses to light and temperature were similar within and between seasons. Multiple regression indicated that mean incubation temperature explained 57% of the variance in total sediment oxygen demand (TOD). The logarithmic relationship between TOD and temperature (Q10=6.5) was not significantly different between fall and spring, suggesting no acclimation within season. Chemical oxygen demand measured in formalin-poisoned cores averaged 30% of TOD. Microalgal gross primary production (GROSS) was measured as oxygen production in light cores. Mean incubation temperature and sediment chlorophylla explained 56% of the variance. The linear relationship between GROSS and temperature had Q10=2.0. When production was normalized to chlorophylla [GROSS(SP)], seasonal production-temperature curves were significantly different. The spring curve had Q10=3.3; in the fall, production and temperature were not related. GROSS(SP)-light curves derived from Plexiglas shade experiments in the field were linear and not significantly different between fall and spring. Temperature alone was a better predictor of GROSS(SP) than light, even when P/I curves were adjusted for temperature. One can therefore model community respiration and photosynthesis at this site using daily averages in temperature, which are then summed over longer time scales to estimate monthly or seasonal rates.

Resuspension and growth ofOstrea edulis: A field experiment

Field experiments withOstrea edulis L. were conducted to examine the effects of resuspension on subtidal oyster growth in a small cove in malifax County, Nova Scotia. Removable racks with strips of fixed juvenile oysters were placed at 4 and 30 cm above a coarse sandy bottom (2 m depth). Summer growth was assessed weekly for 7 wk (July to August 1985) using silhouette images to follow individual change in shell area, a correlate of change in wet weight. Daily measurements of temperature, erosion/deposition (buried plate depth) and sediment chlorophyll suggested that sediment transport partially controlled the standing stock of benthic microalgae. Relative oyster growth per week was positively correlated with temperature. In addition, relative growth initially increased as the transport regime went from erosional to depositional (maximum growth near zero net transport) but growth rate declined with continued deposition. The relationship of oyster growth to gross changes in sediment chlorophyll showed a similar parabolic trend. The shape of these curves is similar to those obtained in published laboratory feeding experiments, which suggest beneficial effects of resuspension as a bivalve food supplement, but inhibition at higher levels due to decreased ingestion or dilution of food with inorganics. It is postulated that sand bottoms may provide more suitable resuspension environments than mud due to lower suspended loads over coarse sediments. Resuspension may be a valuable supplement to water column production as food for cultured bivalves, a factor of value in grow-out site selection.