Fecal pellets of benthic animals are important in sediment transport processes, yet few quantitat... more Fecal pellets of benthic animals are important in sediment transport processes, yet few quantitative data are available on their salient physical characteristics. We measured, directly and independently, the densities (specific gravities), sizes, and settling velocities of pellets produced by Amphicteis scuphobrunchiata, a deposit-feeding polychaete worm. Pellet density was measured by an isosmotic density gradient technique. Densities ranged from 1.086 to 1.282 gacm-3 and settling velocities from 3.03 to 5.94 cmes-I. Pellets transported as bedload for variable distances; the oldest pellets tested (6 h after production) traveled a median distance of 3.1 m, while freshly egested pellets traveled 9.5 m before disintegrating. Worms would reingest disaggregated pellets, but feeding rates correlated positively with pellet age, consistent with previous findings that this species feeds at a faster rate on energetically more profitable sediment. These results suggest substantial interactions among benthic animals, fecal pellets, and sediment transport processes.
Tht ampharetid polychaete Amphicteis scaphobranchiata is a marine, surfacedeposit feeder inhabiti... more Tht ampharetid polychaete Amphicteis scaphobranchiata is a marine, surfacedeposit feeder inhabiting cohesive sediments from continental shelf depths off British Columbia to abyssal habitats off southern California. It uses a previously undescribed method of removing fecal pellets from its feeding area via an elastic (Young's modulus = 7 MNm"-), mucous sling fashioned about the modified anterior median branchiae for which the species was named. This sling imparts a force of 4 x 10~' Pa, sufficient to ' Supported by contract NOOO14-80-C-0252 with the Office of Naval Research. Contribution 1339 from the School of Oceanography, University of Washington. yield a maximal pellet velocity of 27 cm • s ' and thereby to remove the pellet from the normal radius swept out by the animal's feeding tentacles. These observations indicate that this sedentary animal's food supply depends predominantly on the rate of sedimentation into the pit that is produced via its feeding and defecating activities, rather than on the rate of microbial regeneration or production that goes on within its feeding radius.
Woods I h)le ()ceanog i aphiic I istituti on Woods I ole, MIA (12543 (508) 457-2000 ext. 3427 Thi... more Woods I h)le ()ceanog i aphiic I istituti on Woods I ole, MIA (12543 (508) 457-2000 ext. 3427 Thisd f P Ub 10 120a beeni api~roved disiuibutioaI .ease axz d saJIG Long-Range Scientific Objectives 92-18145 9 2 7)3:Q0
ABSTRACT Laboratory flume experiments were conducted in order to test the influence on sediment c... more ABSTRACT Laboratory flume experiments were conducted in order to test the influence on sediment credibility of varying densities of the tube-building polychaete worm Owenia fusi/ormis. Ex-periments were performed on isolated individuals, in order to measure approximate spatial limits of ...
Short-term variations observed in the circulation, heat content, and surface mixed layer of an up... more Short-term variations observed in the circulation, heat content, and surface mixed layer of an upwelling plume off Cabo Nazca,
Http Dx Doi Org 10 1080 01490459009377874, Jan 28, 2009
Flail' velocity required to erode a bed of acid-washed sand is increased by intergranular adhesio... more Flail' velocity required to erode a bed of acid-washed sand is increased by intergranular adhesion resulting from growth of the benthic marine bacterium Alteromonas atlantica. In general. we find that either pure exopolymer alone or exopolymer generated during in situ growth increases erosion resistance of fine quartz sand. Moreover, the degree of erosion resistance increases in proportion to the concentration of exopolymer-component uronic acids, which in turn is dependent on relative nitrogen content of peptone-based growth media. Specifically, we observe that approximately 100 nmol of exopolymer or 1.5 nmol of component uronic acids generated by in situ bacterial growth under nitrogen-rich conditions per gram of dry sediment can effectively double seawater-flume flow velocity required for initiation of transport of otherwise noncohesive, 125-177/.1.,/11 quartz grains. This maximal effect corresponds 10 an estimated adhesive force that exceeds submerged particle weight by an order of magnitude and exceeds particle-specific uronic acids weight by seven orders of magnitude. Rapid analysis by gas chromatography/mass spectrometry of purified exopolvmer obtained from A. atlantica cultures shows it to be a polysaccharide containing approximately 20% uronic acids by weight. Maximal exopolymer and component uronic acid concentrations generated in these experiments are all order of magnitude less than values previously reported for estuarine sediments. These results are the first to correlate specific exopolymer components with sediment erosion resistance and further demonstrate the importance of microbial exudates ill sediment binding believed to occur in a wide range of marine environments.
ABSTRACT When measured or apparent yield stress of cohesive muds is assumed to reflect average pa... more ABSTRACT When measured or apparent yield stress of cohesive muds is assumed to reflect average particle-particle bond strength in network structures, critical bed shear stress required for grain-by-grain entrainment can be predicted from an analysis of the forces acting on component grains of geometrically-flat mud beds. Erosion resistance is then defined in terms of cohesive yield stress as well as nominal particle size, shape, relative density, and packing geometry. Predicted values of critical bed shear stress compare favorably with existing data from selected studies in which appropriate yield stress and hydrodynamic parameters have been reported.
Philosophical Transactions of the Royal Society B Biological Sciences, 1990
The concentration of fine 0(1pm) suspended sediment in deep-sea nepheloid layers is roughly 10 5 ... more The concentration of fine 0(1pm) suspended sediment in deep-sea nepheloid layers is roughly 10 5 particles cm -3 . Given this concentration, aggregation theory dictates that marine snow particles must remove fine particles at a rate of 3.5 x 10 -4 particles cm -3 s -1 for scavenging of small particles by large, fast-sinking ones to play a significant role in deposition from nepheloid layers. Assuming that one in every 10 fine particles that collide with a marine snow particle sticks to it, to achieve the above removal rate given a marine snow concentration of 10 -4 particles cm -3 requires contact efficiencies of 10 -1 to 10 -2 . Such values of contact efficiency are significantly larger than theoretical predictions of contact efficiency, but are supported by evidence from studies of radionuclide fluxes and particle size distributions. Discrepancies between inferred and predicted values of contact efficiency arise from differences in actual and model particle properties. Contact by direct interception potentially is enhanced by roughened particle surfaces and by wake capture. Wake capture is the process whereby fine particles are entrained in the recirculating eddies present behind settling particles with Reynolds numbers greater than one.
Eos, Transactions American Geophysical Union, 1988
The Oceanography Report The Oceanography Report: The focal point for physical, chemical, geologic... more The Oceanography Report The Oceanography Report: The focal point for physical, chemical, geological, and biological oceanographers.
Fecal pellets of benthic animals are important in sediment transport processes, yet few quantitat... more Fecal pellets of benthic animals are important in sediment transport processes, yet few quantitative data are available on their salient physical characteristics. We measured, directly and independently, the densities (specific gravities), sizes, and settling velocities of pellets produced by Amphicteis scuphobrunchiata, a deposit-feeding polychaete worm. Pellet density was measured by an isosmotic density gradient technique. Densities ranged from 1.086 to 1.282 gacm-3 and settling velocities from 3.03 to 5.94 cmes-I. Pellets transported as bedload for variable distances; the oldest pellets tested (6 h after production) traveled a median distance of 3.1 m, while freshly egested pellets traveled 9.5 m before disintegrating. Worms would reingest disaggregated pellets, but feeding rates correlated positively with pellet age, consistent with previous findings that this species feeds at a faster rate on energetically more profitable sediment. These results suggest substantial interactions among benthic animals, fecal pellets, and sediment transport processes.
Tht ampharetid polychaete Amphicteis scaphobranchiata is a marine, surfacedeposit feeder inhabiti... more Tht ampharetid polychaete Amphicteis scaphobranchiata is a marine, surfacedeposit feeder inhabiting cohesive sediments from continental shelf depths off British Columbia to abyssal habitats off southern California. It uses a previously undescribed method of removing fecal pellets from its feeding area via an elastic (Young's modulus = 7 MNm"-), mucous sling fashioned about the modified anterior median branchiae for which the species was named. This sling imparts a force of 4 x 10~' Pa, sufficient to ' Supported by contract NOOO14-80-C-0252 with the Office of Naval Research. Contribution 1339 from the School of Oceanography, University of Washington. yield a maximal pellet velocity of 27 cm • s ' and thereby to remove the pellet from the normal radius swept out by the animal's feeding tentacles. These observations indicate that this sedentary animal's food supply depends predominantly on the rate of sedimentation into the pit that is produced via its feeding and defecating activities, rather than on the rate of microbial regeneration or production that goes on within its feeding radius.
Woods I h)le ()ceanog i aphiic I istituti on Woods I ole, MIA (12543 (508) 457-2000 ext. 3427 Thi... more Woods I h)le ()ceanog i aphiic I istituti on Woods I ole, MIA (12543 (508) 457-2000 ext. 3427 Thisd f P Ub 10 120a beeni api~roved disiuibutioaI .ease axz d saJIG Long-Range Scientific Objectives 92-18145 9 2 7)3:Q0
ABSTRACT Laboratory flume experiments were conducted in order to test the influence on sediment c... more ABSTRACT Laboratory flume experiments were conducted in order to test the influence on sediment credibility of varying densities of the tube-building polychaete worm Owenia fusi/ormis. Ex-periments were performed on isolated individuals, in order to measure approximate spatial limits of ...
Short-term variations observed in the circulation, heat content, and surface mixed layer of an up... more Short-term variations observed in the circulation, heat content, and surface mixed layer of an upwelling plume off Cabo Nazca,
Http Dx Doi Org 10 1080 01490459009377874, Jan 28, 2009
Flail' velocity required to erode a bed of acid-washed sand is increased by intergranular adhesio... more Flail' velocity required to erode a bed of acid-washed sand is increased by intergranular adhesion resulting from growth of the benthic marine bacterium Alteromonas atlantica. In general. we find that either pure exopolymer alone or exopolymer generated during in situ growth increases erosion resistance of fine quartz sand. Moreover, the degree of erosion resistance increases in proportion to the concentration of exopolymer-component uronic acids, which in turn is dependent on relative nitrogen content of peptone-based growth media. Specifically, we observe that approximately 100 nmol of exopolymer or 1.5 nmol of component uronic acids generated by in situ bacterial growth under nitrogen-rich conditions per gram of dry sediment can effectively double seawater-flume flow velocity required for initiation of transport of otherwise noncohesive, 125-177/.1.,/11 quartz grains. This maximal effect corresponds 10 an estimated adhesive force that exceeds submerged particle weight by an order of magnitude and exceeds particle-specific uronic acids weight by seven orders of magnitude. Rapid analysis by gas chromatography/mass spectrometry of purified exopolvmer obtained from A. atlantica cultures shows it to be a polysaccharide containing approximately 20% uronic acids by weight. Maximal exopolymer and component uronic acid concentrations generated in these experiments are all order of magnitude less than values previously reported for estuarine sediments. These results are the first to correlate specific exopolymer components with sediment erosion resistance and further demonstrate the importance of microbial exudates ill sediment binding believed to occur in a wide range of marine environments.
ABSTRACT When measured or apparent yield stress of cohesive muds is assumed to reflect average pa... more ABSTRACT When measured or apparent yield stress of cohesive muds is assumed to reflect average particle-particle bond strength in network structures, critical bed shear stress required for grain-by-grain entrainment can be predicted from an analysis of the forces acting on component grains of geometrically-flat mud beds. Erosion resistance is then defined in terms of cohesive yield stress as well as nominal particle size, shape, relative density, and packing geometry. Predicted values of critical bed shear stress compare favorably with existing data from selected studies in which appropriate yield stress and hydrodynamic parameters have been reported.
Philosophical Transactions of the Royal Society B Biological Sciences, 1990
The concentration of fine 0(1pm) suspended sediment in deep-sea nepheloid layers is roughly 10 5 ... more The concentration of fine 0(1pm) suspended sediment in deep-sea nepheloid layers is roughly 10 5 particles cm -3 . Given this concentration, aggregation theory dictates that marine snow particles must remove fine particles at a rate of 3.5 x 10 -4 particles cm -3 s -1 for scavenging of small particles by large, fast-sinking ones to play a significant role in deposition from nepheloid layers. Assuming that one in every 10 fine particles that collide with a marine snow particle sticks to it, to achieve the above removal rate given a marine snow concentration of 10 -4 particles cm -3 requires contact efficiencies of 10 -1 to 10 -2 . Such values of contact efficiency are significantly larger than theoretical predictions of contact efficiency, but are supported by evidence from studies of radionuclide fluxes and particle size distributions. Discrepancies between inferred and predicted values of contact efficiency arise from differences in actual and model particle properties. Contact by direct interception potentially is enhanced by roughened particle surfaces and by wake capture. Wake capture is the process whereby fine particles are entrained in the recirculating eddies present behind settling particles with Reynolds numbers greater than one.
Eos, Transactions American Geophysical Union, 1988
The Oceanography Report The Oceanography Report: The focal point for physical, chemical, geologic... more The Oceanography Report The Oceanography Report: The focal point for physical, chemical, geological, and biological oceanographers.
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