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Deposit-feeding and suspension-feeding benthos in Buzzards Bay, Massachusetts, show marked spatial separation; suspension feeders are largely confined to sandy or firm mud bottoms while deposit feeders attain high densities on soft muddy substrata. Food source and bottom stability have been investigated as potential factors effecting this trophic-group separation. Between October 4, 1967 and August 22, 1969, observations were made at 11 stations in Buzzards Bay, Massachusetts, along two widely separated transects over bottoms ranging in texture from silt to fine and medium sand. Water depths at these stations ranged from 3 m to 20 m. Scuba divers made many of the field observations and collected most of the samples. This study included sampling of benthic macrofauna, taking bottom photographs, analyzing sedimentary structures, texture, organic content and water content of the sediments, and measuring both water currents and suspended sediment above the bottom. Laboratory experiments were also carried out to determine differential resuspension between burrowed and unburrowed muds. Intensive reworking of the upper few centimeters of a mud bottom by deposit feeders produces a fluid fecal-rich surface that is easily resuspended by low-velocity tidal currents. We suggest that the physical instability of this fecal surface tends to: (i) clog the filtering structures of suspension-feeding organisms, (ii) bury newly settled larvae or discourage the settling of suspension-feeding larvae, and (iii) prevent sessile epifauna from attaching to an unstable mud bottom. Thus suspension feeders are unable to successfully populate all areas of the bottom where a suspended food source is available, especially in areas where mud bottoms are intensively reworked by deposit feeders. Modification of the benthic environment by deposit feeders, resulting in the exclusion of many suspension feeders and sessile epifauna, is an example of trophic group amensalism. This biotic relationship appears to be important in shaping trophic-group distributions in embayments and basins on continental shelves.

A new sediment profile imaging (SPI) instrument, CHEM-SPI, was developed for in situ two-dimensional measurements of biogeochemical solutes using fluorosensor foils in sediments and overlying waters. The CHEM-SPI system was used to simultaneously measure vertical sections of pH, O2, and pCO2 distributions in subtidal, surface deposits of Long Island Sound, NY. Images are readily obtained in 5–15 min with inexpensive LED excitation and commercial grade digital cameras having typical pixel resolution of ~50–100 μm over areas >150 cm2 sediment. Seasonal examples of in situ deployments of the instrument revealed extensive horizontal and vertical heterogeneity of pH distributions. pH dynamics were associated with complex biogenic structures in the upper few centimeters of marine sediment and the pulsed input of organic matter during the spring bloom period. The pH beneath the sediment–water interface was dramatically depressed by the bloom input of organic matter but macrofaunal activity otherwise dominated pH variations in the bioturbated zone. The CHEM-SPI system allows direct quantitative confirmation of biogeochemical patterns previously inferred qualitatively from color patterns in visible SPI images. The instrument is sufficiently adaptable in design to accommodate new optical sensor foils for other chemical variables.

High resolution imaging of the seafloor has been limited to fixed sensors and/or limited field-of-view instruments. As a result, our ability to characterize large areas of benthic habitat has relied on acoustic maps and photomosaics combined with point sampling. In addition, the response of motile epibenthos and demersal fish to habitat patches, structure and disturbance has been largely inferred or based on disruptive sampling and manipulative experiments. Direct quantitative observation of large areal variation in these factors is possible through a combination of traditional video census techniques with high resolution optical imaging of the seafloor. Laser Line Scan Systems (LLSS) are capable of imaging continuous swaths of the seafloor from 3 to 15 m wide at speeds up to 5 km/h. Image quality is dependent on system performance and turbidity but can exceed limits required to distinguish benthic habitats and census undisturbed fish and epibenthos. This areal coverage rate (1 km/day) is several orders of magnitude higher than video sleds and can complement high resolution acoustic surveys (multibeam or side scan). We present results from several applications of these systems for assessment of benthic resources and disturbance in turbid estuarine environments.

Historically, advances in our knowledge of benthic community structure and functioning have necessarily relied upon destructive sampling devices (grabs, cores, anchor dredges, etc.) that lose valuable contextual information in the process of sampling. In the last 40 years, instrumentation capable of measuring dynamic events and/or processes within and immediately above the seafloor has been developed that facilitates the collection of ecological information. Of these, both acoustic and optical imaging devices have played a significant role in revealing much about the physiology and behaviour of, and interactions between benthic species, and the sedimentary habitat in which they reside. While a number of reviews have separately considered the methodological and technical aspects of imaging technologies, the collective contribution that imaging has made to benthic ecology has received less attention. In this short review, we attempt to highlight key instances over the last 40 years where either acoustic or optical-based imaging techniques have provided new ecological insights and information about fine-grained sedimentary environments. In so doing, we focus on the ecological advances that have formed the precursor to current research efforts and introduce some of the latest revelations from appropriate and emerging imaging applications.

The quantity, quality, and spatial distribution of particulate organic matter (POM) in the bioturbated zone of a sedimentary deposit are intimately related to the size and composition of the deposit-feeding community. Fresh allochthonous POM from the water column and autochthonous POM from epibenthic primary production are incorporated into the deposit by burial and through geophysical and biological mixing. Although the quality and quantity of organic materials produced at or settling onto the sediment surface determine benthic secondary production, subsurface particle transport determines how metabolizable POM is distributed within the deposit. Inasmuch as particle transport itself is often dominated by the mechanical activities of deposit-feeding macrofauna (Rhoads 1974; Aller 1982; Rice 1986), the biomass, species composition, and feeding depths of the deposit-feeding community and the standing crop and vertical distribution of metabolizable organic matter are fundamentally interdependent.

Even though the continental slope off Cape Hatteras has sediment accumulation rates on the order of 1 cm/year, large areas of soft sediment are intensively reworked by infaunal organisms. Primary sedimentary structures have been completely replaced with biogenic structures. Surface sedimentary structures are dominated by the bioturbational activities of a deep burrowing infauna (to at least 30 cm). The layer actively mixed by the benthos, as evidenced by sediment profile and X-ray images, is estimated to range from 5 to 20 cm, with the residence time for particles within the surface mixed layer ranging from about 4.5 to 18 years. The biological mixing parameter (G) ranges from 0.4 to 5.5, which indicates moderate to strong biological mixing relative to accumulation and strata formation. Bioturbation contributes to the dynamic forces affecting the surface sediments by decreasing compaction of sediment layers and dilating sediment fabrics by sediment mixing, and introducing large water-filled burrows and voids to subsurface sediments. The sediment profile images captured numerous subsurface feeding voids, and worms in the process of making deep burrows, many of which extended below the 5 to 10 cm average depth of the apparent color redoxpotential discontinuity layer. High rates of accumulation of organic-rich sediment lead to high standing stocks of benthos and intensive feeding/burrowing activity that result in organic rich stratagraphic sequences that are thoroughly mixed. Cape Hatteras is a apparent focusing point for the transport of shallow water sediments to the deep sea. Sediments across other areas of the continental slope just 100's of kilometers south of Cape Hatteras are not as thoroughly mixed or biologically active.

Historical data from the slope off Cape Hatteras show this environment to be atypical of the rest of the Atlantic slope in terms of high rates of sedimentation and high benthic/demersal standing stocks. This paper focuses on identifying potential sources for sediments and nutrients on the Hatteras slope and on likely transport mechanisms. Sediments consist mainly of subequal mixtures of sand, silt, and clay and contain an average of 1% carbon. This pool of carbon represents weathered organic matter containing polyunsaturated fatty acids (PUFA) and sterols typical of relatively refractory shelf/estuarine sediments. The labile organic fraction is derived from phytoplankton and zooplankton as reflected in short chain fatty acids (

The territorial waters of Hong Kong encompass extensive areas of shallow continental shelf affected by many activities including sand dredging for reclamation fill, disposal of dredged mud, disposal of sewage sludge, commercial fishing, and mariculture. The REMOTS sediment profile imaging camera has been used successfully since 1993 for rapid seafloor assessment to define baseline conditions and impacts on sediment duality during both wet (typhoon) and dry seasons. Several hundred stations have been occupied in a two week survey. Analysis of sediment profile images has allowed assessment of dredging and disposal effects and organic enrichment "hot spots". It appears that tropical storms may have a large effect on mobilization of soft sediments during the wet season, while anthropogenic factors (dredging, disposal, and seabed fishing activities) may assume greater relative importance in some areas during the dry season when severe storms are less common. The soft bottom benthic community consists of a few species of small invertebrates adapted to physical disturbance.

A synoptic reconnaissance survey was performed over a five-day period in August 1988 to assess benthic habitat quality throughout Narragansett Bay, Rhode Island, using REMOTS® sediment-profile photography and analysis in combination with measurements of the levels ofClostridium perfringens spores (a fecal indicator) in sediments. Three main areas of degraded benthic habitat quality related to either excessive organic enrichment or physical disturbance were identified based solely on the REMOTS® analysis: the Providence River Reach, Greenwich Bay and its associated coves and harbors, and an area located along the southwest side of Prudence Island. Sediments at many stations in these areas exhibited shallow apparent redox-potential discontinuity (RPD) depths, high apparent oxygen demand, and low-order benthic successional stages. ElevatedClostridium perfringens spore counts in surface sediments were attributed to inputs from wastewater treatment facilities. The highest spore counts occurred at the head of the bay, where wastewater treatment discharges and associated combined sewer overflows are numerous. Using data from the REMOTS® analysis and the sediment inventory ofC. perfringens spores, a distinction was made between organic enrichment of the bottom from sewage, versus nonsewage enrichment or physical disturbance. The combination of techniques employed in this investigation could be used to design more efficient monitoring programs to assess eutrophication effects in estuaries and determine the effectiveness of regulatory or management initiatives to reduce organic overenrichment of benthic habitats.

Microstructural growth increments within the shells of numerous Recent and fossil molluscs are interpreted as reflections of alternating periods of shell deposition and dissolution, occurring during aerobic and anaerobic respiration, respectively. The acidic end products of anaerobic metabolism are neutralized by calcium carbonate from the shell, leaving a relatively insoluble organic residue at the mantle-shell interface. With the return of oxygenated conditions and resumption of aerobic respiration, this organic material is reincorporated within the shell. Inasmuch as metabolic changes are often synchronized with lunar or solar cycles (or both), we are led to the nearly paradoxical conclusion that, as a result of shell destructive processes, a relatively complete and detailed record of both short- and long-term growth is often preserved within the molluscan exoskeleton. Analyses of relationships between ambient oxygen concentrations and shell structural types may eventually prove useful, in paleoecological studies, for determination of dissolved oxygen gradients in Phanerozoic marine environments.

Four distinctive benthic communities occur in the mid-shelf deltaic deposits of the Upper Devonian Sonyea Group: the Bellerophon Community, dominated by herbivorous gastropods and deposit-feeding bivalves; the Prodrtctella Community, dominated by brachiopods with adaptations for life on muddy substrata; the Cypricardella Community, dominated by bivalves and brachiopods with a variety of adaptations; and the Rhipidomella Community, dominated by brachiopods adapted for life on sandy substrata. The geographic and stratigraphic occurrence of the communities suggest that their distribution was controlled by two principal sets of environmental variables: (1) onshore to offshore gradients in salinity, dissolved oxygen concentrations, and sedimentary substrata, and (2) rate of delta progradation. A change in the rate of delta build-out during mid-Sonyea time led to a dramatic change in onshore to offshore community patterns. The change suggests that great care must be used in constructing generalized community models for longer intervals of Paleozoic time.

The hardness of marine sediments in the near-shore waters of Long Island Sound has been measured by penetration tests made both in situ and in the laboratory. Penetration of the sediment—water interface is found to be rate-insensitive and, for a given driving stress, independent of indentor size. Natural sediments in Long Island Sound show no measurable surface cohesion because of the effects of benthic animals, though artificial, azoic sediments prepared in the laboratory do. Hardness of marine mud is found to be sensitive to sand content. Analysis of penetration experiments in terms of punching a rigid-plastic material cannot account for these observations, but a model based on a description of the sediment as a locking material is successful. The observations are applied to defining the bearing capacity of the bottom and its resistance to burrowing by marine animals.

Documentation of long-term change in benthic ecosystems is important for assessing and managing the effects of such change on: 1) secondary production, particularly leading to commercially important food webs, 2) pollutant transfer within the food web, 3) the ability of the ‘new’ assemblage to metabolically burn-off labile detritus that might otherwise accumulate, contributing to long-term hypoxia, and 4) recyling of nutrients from the seafloor back to primary producers.

A rapid in-situ bottom survey technique is needed to provide information about sedimentary structures, boundary roughness and macrofaunal distributions in estuarine, continental shelf and deep sea sediments. We have made preliminary studies using ultrasound imaging as a possible means of providing this kind of information. Our laboratory studies have shown that a high-frequency acoustic backscattering system operated at 1.6 mHz can image the distribution of laminations and tubes in muddy sediments. We compare the acoustic images with radiographs taken from the same sections of the test sediment to demonstrate the accuracy and resolution of the acoustic record. This acoustic technique could be adapted to a towed sled vehicle to provide in-situ high-resolution (⩾ 1 cm) subbottom (0–10 cm) profiles of sedimentary fabrics and possibly biological structures.

The vertical distribution of macrobenthos and sedimentary structures in near-surface sediments of the East China Sea off the Changjiang has been assessed from analyses of boxcores. The geographic distribution of macrobenthos across the continental shelf reflects sediment type and sedimentation rate. In the rapidly accumulating silty-clays of the submarine delta, sparse populations of small polychaetes predominate. As sediment accumulation rate declines away from the river mouth, denser populations of more deeply burrowing polychaetes, crabs, and ophuroids occur. On the central and outer shelf, sparse populations of surface dwellers relect the sandy, mobile sediment conditions. Based on X-radiographs, five sedimentary facies are identified based on physical and biogenic sedimentary structures in the top 25 cm of sediment. These sedimentary fabrics reflect (1 and 2) high and low rates of accumulation on the submarine delta, in which physical and biogenic structures, respectively, predominate; (3) dynamic sands across the shelf; (4) a muddy, low-depositional environment south of Cheju Island; and (5) a shelf-break regime under the influence of the Kuroshio Current.

Biological and sedimentological samples were obtained in June 1980 from box cores taken in 100–200 m of water on sandy-mud sediments near the East and West Flower Garden Bank reefs, on the Texas-Louisiana Continental Shelf. The objective was to obtain baseline information about sedimentary parameters and organisms adjacent to the FGB environments in order to allow inferences to be made about potential effects of physical disturbance of the seafloor on the resident benthos. Most infaunal organisms are found in the upper 3–5 cm of the bottom. Permanent meiofauna dominate in both numbers and biomass. X-radiographs of sediment fabrics show all stations to be reworked by head-down deposit-feeders or errant bioturbators. Taxa responsible for this bioturbation were not quantitatively sampled. Macrofaunal densities range from 3000 to 25000 m−2 and total meiofauna from 221 to 892 × (10 cm)−2. Nematodes dominate followed in equal abundance by foraminiferans, polychaetes, and copepods. Seventy-five percent of the total sediment ATP in the top 3 cm is contributed by meiofauna. These benthic assemblages are hypothesized to represent a mixture of pioneering and high-order successional stages. Bacterial abundances are positively correlated with organic content and inversely correlated with macro- and meiofaunal densities. This inverse relationship may reflect consumer cropping intensities. Both microbial ATP and bacterial biomass are lower than reported for the Georgia Bight Shelf, Cape Blanc, West African Shelf, western coast of Norway, and Long Island Sound. Bacterial counts are lower than those recorded for the East China Sea and the Amazon River shelf. Moderate to low standing stocks of benthos, dominated by meiofaunal-sized taxa, further suggest that this area of the Gulf of Mexico is a relatively oligotrophic system for infaunal benthic consumers. Higher order successional stages are, in general, adversely affected to a greater extent than pioneering stages by physical disturbance. In the Texas-Louisiana shelf region, dilution of an already food limited system by inert barium sulphate would be expected to result in even lower standing stocks of benthic infaunal invertebrates.

Benthic invertebrates living in low oxygen regions of the Black Sea, Gulf of California, and basins off Southern California form three major biofacies associated with the following concentrations of dissolved oxygen: (1) an azoic region (≤ 0.1 ml/1), (2) a low diversity, small, soft-bodied infauna (0.3–1.0 ml/1), and (3) a diverse calcareous fauna (2 1.0 ml/l). These biofacies recapitulate the chronologic appearance of Pre-Cambrian trace fossils followed by a diverse calcified fauna in the Cambrian. The basin model has been used to reconstruct a Lower Cambrian oxygen level of 0.1 P.A.L. (present atmospheric level). This value is ten-fold that proposed in the Berkner-Marshall hypothesis.

Water depth does not directly control the distribution of marine bivalve molluscs, but bathymetric inferences may sometimes be made by relating water depth to environmental variables known to limit bivalve distribution, such as temperature, salinity, and nature of the substratum. When contemporaneous stenothermal and eurythermal (or stenohaline and euryhaline) bivalve associations are found in the same general area , the more tolerant associations (eurythermal or euryhaline) will usually be found in shallower water than less tolerant (stenothermal or stenohaline) associations. Similarly, associations dominated by epifaunal and boring bivalves would normally be expected in relatively shallow water where hard substrata are most abundant. Burrowing infaunal bivalves are present at all depths, but infaunal deposit-feeding bivalves are most common in subtidal, quiet water muds. Observations on Recent infaunal benthonic associations suggest that organisms adapted for deep vertical burrowing are common only in intertidal and shallow subtidal environments where stress conditions at the sediment-water interface are most severe. In contrast, infaunal organisms adapted for horizontal burrowing just below the sediment surface predominate in deeper subtidal environments. In situ associations of fossil bivalves adapted for these two modes of burrowing should therefore be reliable indicators of relative water depth. These burrowing patterns may also be determined directly from biogenic sedimentary structures, and thus this paleobathymetric tool may be applied to many unfossiliferous sedimentary rocks.

Biogenic reworking of marine sediments is described from intertidal deposits in Barnstable Harbor and subtidal sediments of Buzzards Bay, Massachusetts. Reworking activities of three polychaete species were studied in Barnstable Harbor: Clymenella torquata, Pedinarla goiddii, and Amphitrite ornata. Sediment reworking by these tube-dwelling annelids is primarily a vertical and lateral size-sorting process. The selective ingestion and transportation of sand and smaller-sized particles leads to the formation of biogenically graded deposits. Clymenella is estimated to ingest 274 ml. of sediment per worm per year. Pectinaria ingests 400 ml. of sediment per worm per year according to Gordon (1966). The annual reworking rate of Amphitrite remains unknown, but probably exceeds that of Clymenella and Pectinaria. Five stations in Barnstable Harbor were artificially laminated with colored sand horizons to observe biogenic reworking at depth within the sediment. After 2 months, differences in intensity of reworking b...

Light from a tungsten filament source is passed through sections of sediment 1 to 6 mm thick. Transmitted infrared radiation is recorded by an ordinary camera loaded with infrared sensitive film. Sediments are generally more transparent to infrared radiation than to white light. For this reason, infrared photographs reveal sedimentary structures that are difficult or impossible to resolve with the visible spectrum. Infrared film can detect subtle differences in density, composition, and texture. This technique is best applied to relatively clean, sand-sized sediments because of their high infrared transparency.

The effects of benthic organisms on the physical properties of granular substrata are well documented. The range of effects has been presented in H. B. Moore (1931, 1939), Schwartz (1932), Dapples (1942), D. G. Moore and Scruton (1957), McMaster (1967), Rhoads (1974), Rowe (1974), Powell (1974), Richards and Park (1976), Myers (1977a,b), Self and Jumars (1978), Lee and Swartz (1980), and Carney (1981). These papers relate the effects of benthic species to changes in grain size, sorting, fabric, water content, compaction, shear strength, and bottom stability. Those autecologic parameters that appear to be most highly correlated with physical modifications of sediments include: method of feeding, feeding selectivity, feeding level relative to the sediment—water interface, degree of mobility, organism size and population density, burrowing depth, and, if the organism is a tube dweller, the density, spacing, and length of tubes.

Trace fossils have great paleoecologic utility because they are (1) widespread in space and time, (2) found in place, and (3) largely the record of animal behavior and response, making them ideal indicators of environmental conditions.

The Rhoads-Cande profile photographic camera and its updated version, the video REMOTS (Remote Ecological Monitoring of the Seafloor) system, are described for in situ remote monitoring of the seafloor. These systems allow one to identify temporal and spatial changes in both the benthic fauna and physical-chemical aspects of the sedimentary environment. Image interpretation is based on a model which allows one to deduce the stage of infaunal succession from observed organism-sediment relations. The REMOTS system was developed because existing methods of obtaining ecological information are labor intensive, expensive, and data return is slow. The REMOTS system may be used for efficient monitoring of dredge-spoil activities and as a reconnaissance mapping tool for detecting change in benthic habitats in the region of outer continental shelf drilling fields.

This preliminary study documents temporal changes in seafloor erodibility at a 14-meter-deep mud bottom station in central Long Island Sound over a 29-month period. The mean critical rolling and saltation velocities of the bottom were determined in the laboratory with a specially constructed flume containing salt water. A removable 45-cm length of the 10 cm by 10 cm closed flume channel was used as a box core. A removable bottom on the core box allowed scuba divers to obtain relatively undisturbed samples of the seafloor. Samples were returned to the laboratory in thermally insulated containers and critical erosion velocities were determined within a few hours. In 1974 and 1975, minimum annual mean rolling velocities were measured in July (16–19 cm sec -1 at z = 100 cm). Maximum mean rolling velocities were recorded in November 1974 and October 1975 (respectively 28 cm sec -1 and 23 cm sec -1 at z = 100 cm). The observed change in mean critical velocities in 1976 was different from that observed in 1974 and 1975. The minimum mean rolling velocity in 1976 was recorded in October (19 cm sec -1 at z = 100 cm) and the peak threshold velocity was measured in July (28 cm sec -1 at z = 100 cm). We propose tentatively that two opposing biogenic processes influence the observed changes in critical velocities; stabilization by sediment binding and destabilizaton by bioturbation. An estimate of the influence of microbial growth and mucus binding on bottom erodibility was obtained by culturing microorganisms on beds of glass beads of various sizes in the flume. Critical rolling velocities of glass beads increased 25% to 60% after 3–15 days related to mucus production and binding of the beads. Seafloor stabilization by sedentary polychaetes was also studied in the laboratory by comparing mean critical rolling velocities of natural sediment without tube-forming polychaetes with mean rolling velocities of the same sediment after introducing dense aggregations of Heteromastus filiformis. Critical rolling velocities increased by 80% over a period of 11 days.

Organically enriched terrigenous marine sediments are commonly associated with near-bottom waters containing low concentrations of dissolved oxygen, as well as with sediment pore waters high in dissolved sulfides. Today such habitats are typically dominated by dense aggregations of opportunistic polychaetes which intensively pelletize surface sediments while deposit-feeding. Laboratory study of one such species, Capitella sp. I, indicates that these polychaete aggregations and their associated agglutinated tubes have a low probability of direct preservation in the sedimentary column. Synthetic lutites prepared from these sediments, however, contain pelletal sedimentary fabrics indicative of the former presence of polychaetes. To evaluate the effectiveness of these criteria for paleoecological reconstructions of OMZs, we undertook a study of the Sonyea Group (Upper Devonian Catskill Shelf and Basin). Wedge-shaped thin sections of rocks from a range of environments in the Upper Devonian Catskill Shelf and Basin Complex were examined. Only sections from the slope facies fulfilled the necessary criteria for postulating the presence of an OMZ. Methods are given for the preparation of synthetic lutites in order to identify these cryptic, yet paleocologically important, sedimentary fabrics. Recognition of such fabrics in otherwise "barren" shales may allow for more detailed reconstructions of ancient hypoxic and anoxic basins.

Mobile infauna are prominent members of modern benthic communities inhabiting granular substrata. In settings below normal wavebase, the benthic fauna is dominated by infaunal deposit-feeders (McCall, 1977; Rhoads et al., 1978), and the substratum is characterized by bioturbated sedimentary fabrics (Moore and Scruton, 1957; Rhoads, 1974). Habitats subjected to wave reworking contain fewer deposit-feeders and retain physical sedimentary fabrics. The increase of biogenic sediment-reworking on an onshore-to-offshore gradient is widespread on modern marine shelves dominated by detrital clastics (Moore and Scruton, 1957; Reineck, 1967; Howard and Reineck, 1972, 1981) or carbonates (Ginsburg and James, 1974; James and Ginsburg, 1979) and has proven useful in reconstructing bathymetric gradients in ancient sedimentary basins (Byers, 1977; Byers and Larson, 1979).

Direct measurements of shell growth of an unclassified mussel from active hydrothermal vents along the Galapagos Rift reveal growth rates of approxmately 1 centimeter per year for mature specimens. The largest mussel collected (with shell length of 18.4 centimeters) was estimated to be 19 ± 7 years old at the time of sampling. Recorded growth rates are among the highest documented for deep-sea species .

Graded beds may be produced by deposit-feeding organisms in intertidal and shallow subtidal environments. Barnstable Harbor, Cape Cod, Massachusetts, contains intertidal populations of Clymenella torquata, a sedentary polychaete. Clymenella selectively ingests specific size fractions of sediment at a depth of 10-30 cm within the tidal flats. Sand and silt are transported vertically through the gut and egested as uncompacted feces on the sediment surface. Size fractions too coarse for ingestion ( > 1.0 mm) are concentrated at the lower end of worm tubes producing a well graded stratum. Laboratory measurements indicate that Clymenella is capable of displacing 87 liters of sediment per m2 per year at the mean annual water temperature of Barnstable Harbo (11°C). The thickness of a graded bed, limited by feeding depth, is less than 30 cm. Maximum and average grain size decrease in regular fashion from the base to the top of the bed. Sorting is poor and values vary irregularly in the bed. The size distribution curves are strongly to moderately fine-skewed in samples at the base of beds; curves become more nearly symmetrical at the top of graded beds. Biogenically graded beds may be distinguished from physically deposited graded beds by textural properties, associated sedimentary structures, geometry of the deposits, and lithology of interfingering facies. The best development of biogenic graded bedding occurs in sites of slow hysical sediment accretion and relatively weak bottom currents.

Yoldia limatula is a deposit-feeding pelecypod. In Buzzards Bay, Massachusetts, and Long Island Sound it comprises less than 10 percent (by number) of the total bottom fauna, yet is probably capable of entirely reworking the sediment. Yoldia reworks the sediment by ejecting it several centimeters into the water from its excurrent siphon. Measurements of hourly reworking rates were made under controlled temperature conditions. Extrapolations of yearly reworking rates were determined to be 5-6 liters per square meter per year in Buzzards Bay and 23-51 liters per square meter per year in Long Island Sound. This study suggests that great numbers of organisms may not be required to account for extensive sediment reworking.