Showing papers on "Benthic zone published in 1985"

Microhabitats of benthic foraminifera within deep-sea sediments

Abstract: Benthic foraminifera are protozoans found throughout the deep-sea environment, secreting a test of calcium carbonate or constructing a test of cemented sediment particles (agglutinated or arenaceous foraminifera). In typical deep-sea sediments, the organic cement of agglutinated taxa degrades upon burial in the sediment and, consequently, few specimens survive in the fossil record. In contrast, calcareous species are well preserved in most oceanic sediments, except at abyssal depths where most carbonate sediment is dissolved because of high levels of carbonate under-saturation of the bottom waters. Although benthic foraminifera have been widely used in studies of Cenozoic palaeoceanography, little is known about the ecology of deep-sea species. I present here an analysis of living (stained) benthic foraminifera within the upper 15 cm of deep-sea sediments, which reveals species-specific microhabitat preferences, with distinct morphological features found with epifaunal and infaunal species. The existence of infaunal habitats suggests that the distribution of certain foraminifera is not directly controlled by overlying bottom-water conditions, but by physicochemical conditions within the sediments. The microhabitat preferences may also explain interspecific carbon isotope differences, as existing data show that infaunal foraminifera generally have lower δ13C isotope values than epifaunal species.

Evidence for the seasonal deposition of detritus to the deep-sea floor and its subsequent resuspension

Abstract: A free-fall benthic time-lapse camera and current meter system has been used to examine changes in the appearance of the sea bed in the Porcupine Seabight 50°N, 13°W — northeast Atlantic). Changes in the benthic environment due to rapid deposition of phytodetritus occur down to 4000 m. Photograhs taken every 8 h from 1 May to mid-August showed dramatic changes in the appearance of the sea bed between mid-June and mid-July. The sinking rate of the detritus was calculated from the time of the spring bloom until its arrival on the sea bed. In both 1982 and 1983, year which differed greatly in the timing of the spring bloom, the sinking rates were probably between 100 and 150 m d−1. Individual aggregates up to 12 mm diameter arrived between frames at all depths and up to 50 mm at 4000 m. Their subsequent disintegration was monitored over the few days following arrival on the sea bed. Some such aggregates were collected from the sea bed and a sinking rate experiment was carried out on them. Once on the sea bed, the detrital carpet moves over the sediment surface due to bottom currents; when currents exceed about 7 cm s−1 (at 1 m altitude), the material is resuspended. Increases in the quantity in suspension occur at the same time as decreases in the quantity visible on the sea bed. The tidal nature of the current gives a strong tidal component to the variation in suspended particles near the sea bed. The significance of a detrital critical erosion threshold to the structure of benthic and benthopelagic communities is discussed.

Long-Term Ecosystem Stress: The Effects of Years of Experimental Acidification on a Small Lake

Abstract: Experimental acidification of a small lake from an original pH value of 6.8 to 5.0 over an 8-year period caused a number of dramatic changes in the lake's food web. Changes in phytoplankton species, cessation of fish reproduction, disappearance of the benthic crustaceans, and appearance of filamentous algae in the littoral zone were consistent with deductions from synoptic surveys of lakes in regions of high acid deposition. Contrary to what had been expected from synoptic surveys, acidification of Lake 223 did not cause decreases in primary production, rates of decomposition, or nutrient concentrations. Key organisms in the food web leading to lake trout, including Mysis relicta and Pimephales promelas, were eliminated from the lake at pH values as high as 5.8, an indication that irreversible stresses on aquatic ecosystems occur earlier in the acidification process than was heretofore believed. These changes are caused by hydrogen ion alone, and not by the secondary effect of aluminum toxicity. Since no species of fish reproduced at pH values below 5.4, the lake would become fishless within about a decade on the basis of the natural mortalities of the most long-lived species.

Importance of Snag Habitat for Animal Production in Southeastern Streams

Abstract: The Satilla River in southeastern Georgia is a low gradient coastal plain stream with large quantities of woody debris (snags) along its banks. The major objective of this study was to assess the relative importance of the snag habitat as a site of invertebrate production in comparison to benthic habitats. This was accomplished from quantitative sampling of invertebrate habitats, analysis of drifting organisms, and gut analyses of the major fish species. Invertebrate diversity, biomass, and production were considerably higher on snag surfaces than in either sandy or muddy benthic substrates. Although snags represented a relatively small habitat surface (4% of total habitat surfaces), snags supported 60% of total invertebrate biomass and 16% of the production for a stretch of river. Drift densities from night samples collected throughout the year were relatively high, and approximately 78% of drifting invertebrate biomass originated from the snags. Four of the eight major fish species obtained at ...

An Ecosystem approach to aquatic ecology: Mirror Lake and its environment

Abstract: I: An Ecosystem Approach.- A. Ecosystem Analysis.- 1. The Hubbard Brook Ecosystem Study.- 2. Other Interactions Between Ecosystems.- II: The Hubbard Brook Valley.- A. Environmental Parameters.- B. Biogeochemistry.- III: Mirror Lake and Its Watershed.- A. Physiographic Setting and Geologic Origin of Mirror Lake.- Location and General Physiographic Setting.- Geology.- Glacial History and Origin of Lake Basin.- Topography and Drainage Basin Characteristics.- Comparison of Mirror Lake and Hubbard Brook Drainage Basins.- B. Historical Considerations.- 1. History of the Vegetation on the Mirror Lake Watershed.- 2. Catastrophic Disturbance and Regional Land Use.- 3. Mirror Lake: Cultural History.- IV: Mirror Lake-Physical and Chemical Characteristics.- A. Importance of Perspective in Limnology.- B. Physical and Chemical Environment.- C. Stability, Circulation and Energy Flux in Mirror Lake.- D. Approaches to the Study of Lake Hydrology.- E. Flux and Balance of Water and Chemicals.- V: Mirror Lake-Biologic Considerations.- A. Species Composition, Distribution, Population, Biomass and Behavior.- 1. Bacteria.- 2. Phytoplankton.- 3. Periphyton.- 4. Macrophytes.- 5. Zooplankton.- 6. Benthic Macroinvertebrates.- 7. Benthic Microinvertebrates.- 8. Salamanders.- 9. Fishes.- B. Production and Limiting Factors.- 1. Bacteria.- 2. Phytoplankton.- 3. Macrophytes.- 4. Periphyton Production.- 5. Zooplankton.- 6. Benthic Macroinvertebrates.- 7. Vertebrates.- C. Organic Carbon Budget.- D. Decomposition.- VI: Mirror Lake-Ecologic Interactions.- A. The Littoral Region.- B. The Profundal Region.- C. The Pelagic Region.- D. The Lake-Ecosystem.- VII: Paleolimnology.- A. Sedimentation.- 1. Late-Glacial and Holocene Sedimentation.- 2. Contemporary Sedimentation.- B. Diatoms.- C. Animal Microfossils.- D. Fossil Pigments.- E. Chemistry.- F. Paleoecology of Mirror Lake and Its Watershed.- VIII: The Aquatic Ecosystem and Air-Land-Water Interactions.- A. Direct Atmospheric Input to Lakes.- B. Fluvial Input to Lakes.- C. Effects of Disturbance on the Land-Water Linkage.- D. Atmospheric Inputs to Watersheds Affecting Inputs to Lakes.- IX: Air and Watershed Management and the Aquatic Ecosystem.- A. Developmental State of the Forested Watershed-Ecosystem.- B. Forest Harvesting.- C. Highway Construction and Maintenance.- D. Air and Water Pollution.- E. Eutrophication Trends in Mirror Lake.- References.- Index of Genera and Species.- Index of Lakes and Streams.- General Index.

Bioavailability and biotransformation of aromatic hydrocarbons in benthic organisms exposed to sediment from an urban estuary.

Abstract: Phylogenetically diverse benthic organisms [amphipods (Rhepoxynius abronius and Eohaustqrius washingtonianus); clams (Macoma nasuta); shrimp (Pandalus platyceros); fish (Parophrys vetulus)] were exposed to an urban estuarine sediment [ 16 ppm of two to six benzenoid ring aromatic hydrocarbons (AHs)] to which trace amounts of [3H]benzo[a]pyrene (BaP) were added. The techniques used to assess uptake and metabolism of AHs were gas chromatography/mass spectrometry (GC/MS) for AHs, high-pressure liquid chromatography/fluorescence spectrometry for AH metabolites in fish bile, and radiometric analyses for biotransformation of [3H]BaP. Generally, the extent of metabolism of [3H]BaP (M. nasuta < E. washingtonianus < R. abronius I P. platyceros N P. vetulus) was negatively correlated to tissue concentrations of AHs (three to six ring), except that amphipod species accumulated higher concentrations of AHs than did clams, indicating that other factors (e.g., feeding strategy and rate of excretion) also influenced accumulation of AHs. Radiometric and GC analyses for BaP in both sediment and tissues suggested that not all of the BaP (and presumably other AHs) extracted chemically from sediment was bioavailable.

Biological communities at vent sites along the subduction zone off Oregon

Abstract: An abundant deep-sea benthic community, dominated by the vestimentiferan tube worm, Lamellibrachia barhami, a giant white clam, Calyptogena sp., and a second clam, Solemya sp., was discovered along the northeast Pacific continental margin during dives of DSRV Alvin off Oregon. The localities are tectonically controlled and occur along submarine ridges that result from sediment deformation and accretion at the leading edge of plate subduction. Ancient sea-water buried with the sediment, dissolved methane and ammonia, and methane-derived carbonate are discharged to the ocean floor along this tectonically active margin. We hypothesize that the unusual benthic community is sustained by a chemosynthetic-energy metabolism based on the oxidation of methane by free living and symbiotic microbial populations. These organisms represent another significant adaptation of deep-sea biota to a site where the abundanc of food (in this case not directly related to particulate input from the sea surface but to tectonically generated methane), allows higher than normal levels of productivity and metabolism, despite the high pressures and low temperature of the deep-sea habitat. It is tempting to relate the global distribution of such faunas to chemosynthetic food sources generated by tectonic forces.

The effects of suspensoids on fish

Abstract: High suspensoid loads are a common feature of many Southern Hemisphere inland waters. Case studies on a natural lake (Chilwa), a man-made lake (Le Roux) and S.W. Indian Ocean estuaries reveal that the effects of turbidity on fish in these systems differ widely. In Lake Le Roux, high suspensoid loads influence fish by causing a reduced growth rate, a decrease in size at first maturity and maximum size, and a movement inshore by large fishes to feed on phytobenthos. High turbidities in Lake Chilwa sharply reduce food availability in benthic offshore zones, and restrict fishes to pelagic and inshore food resources. The resuspension of sediments by wind action may cause fish mortalities through deoxygenation of the water column. Moderate turbidity levels appear to be beneficial to fish in estuaries by affording protection from predators in shallow, food-rich areas. Turbidity gradients may also provide a navigational aid to fish entering estuaries.

Energy Flow Between the Pelagic and Benthic Zones: Factors Controlling Particulate Organic Matter Available to an Intertidal Mussel Bed

Abstract: Fluctuations and vertical gradients of particulate organic matter (POM, as indicated by chlorophyll a and phaeopigments) concentration over an intertidal mussel bed were studied over fortnightly ti...

Food-Limited Growth of Mytilus edulis L. in Relation to the Benthic Boundary Layer

Abstract: The hypothesis that depletion of organic particles near the sediment limits the growth of benthic suspension feeders was tested. In situ growth of Mytilus edulis L. was significantly depressed at t...

Food for the deep sea: utilization, dispersal, and flux of nekton falls at the Santa catalina basin floor

Abstract: The role of large food falls in the ecology of deep-sea benthos has been the topic of much speculation and little direct study. The submersible Alvin and free vehicles were used to assess experimentally the fate and flux of nekton falls at a depth of 1310 m in the Santa Catalina Basin. Parcels of dead fish (1 to 40 kg) placed on the basin floor rapidly attracted large aggregations of fish and invertebrate scavengers, which consumed the bulk of the carrion within hours to days. The most strongly attracted megafaunal scavenger was the ophiuroid Ophiophthalmus normani , the dominant megabenthic species in the background epifaunal assemblage. O. normani attained densities of 700 m −2 in aggregations containing thousands of individuals, and remained at elevated abundance around baitfalls for weeks. Six other megafaunal species also appeared to feed directly on carrion, including two of the next ten most abundant megabenthic organisms. Several of these species exhibited roosting behavior near baitfalls; this is probably an adaptation for exploiting rich but unpredictable food resources. Scavengers consumed bait parcels so rapidly and then dispersed so broadly that energy from nekton falls apparently reaches infaunal benthos only in very attenuated form, yielding at most minor community enhancement. Necrophagy was not the sole cause of megafaunal attraction to bait parcels; there is evidence that three predacious species were drawn to high concentrations of their ophiuroid prey. Benthic standing-crop and turnover-rate estimates for nekton falls suggest that perhaps 11% of benthic community respiratory requirements are met by nekton carcasses reaching the basin floor; the flux of energy to the deep sea through such fall events thus merits further study. These energy bonanzas occur frequently enough that O. normani , and other common necrophages, are likely to encounter at least one nekton fall per year. Such windfalls thus could influence the life histories of several dominant megafaunal species in Santa Catalina Basin.

Catastrophic anoxia in the chesapeake bay in 1984.

Abstract: In 1984, four climatic sequences combined to produce what may be a major anoxic catastrophe in the northern Chesapeake Bay, sufficient to severely threaten the major benthic species. These sequences are (i) the highest late-winter streamflow on record from the Susquehanna River watershed; (ii) streamflows from the Susquehanna River for the consecutive months of June, July, and August that are higher by 2 standard deviations than the respective monthly mean values measured over the last 34 years; (iii) a stationary high in August off the Atlantic Coast; and (iv) an absence of strong storm events in summer. An empirical equation is proposed for the prediction of the monthly trend of dissolved oxygen decrease in terms of a temperature-dependent subpycnoclinal respiration and a modified estuarine Richardson number. As of 23 August 1984, the summer pycnocline of the northern bay had eroded upward from its historically recorded depth below 10 meters to an abnormally shallow 5 meters, with higher stratification than in earlier years. Dissolved oxygen concentrations directly below the pycnocline decreased to zero during June, 2 months earlier than for previous wet years. At present, oxygen-deficient waters containing significant concentrations of hydrogen sulfide have penetrated into Eastern Bay and the Choptank and Potomac rivers. Because most remaining shellfish-spawning and seed-bed areas in these tributaries are located at depths between 4 and 8 meters, the continued absence of major destratifying events will prolong the present anoxic trend and may result in high benthic mortalities.

Oxygen-minimum zone edge effects: Evidence from the central California coastal upwelling system

Abstract: Geologic and biological data from box cores, gravity cores, and bottom photographs across the modern coastal upwelling system of central California reveal that biogeochemical activity increases along the edges of the oxygen-minimum zone (OMZ; <0.5 ml/1 O2). Macrofauna and benthic foraminifers, as well as relative concentrations of calcium carbonate, glauconite, and fecal pellets, all display edge effects. The major controls appear to be a combination of dissolved oxygen concentration of near-bottom waters, bottom currents, and possibly bacterially mediated nutrient recycling, as well as food supplies. OMZ edge effects should be recognizable in the rock record and may prove to be powerful paleoenvironmental/paleoecological indicators.

Eutrophication and management initiatives for the control of nutrient inputs to Rhode Island coastal lagoons

Abstract: An assessment of developing eutrophic conditions in small temperate lagoons along the coast of Rhode Island suggests that in such shallow, macrophyte based systems the response to nutrient enrichment differs from that described for plankton based systems. The nitrogen loadings per unit area of the salt ponds are 240–770 mmol N per m2 per year. Instead of the high nutrient concentrations, increased phytoplankton biomass and turbidity, leading to eventual loss of benthic macrophytes described for such systems as the Chesapeake, Patuxent and Appalachicola Bay, nutrient enrichment of the Rhode Island lagoons has led to increased growth of marine macroalgae. The increased macroalgal growth appears to alter the benthic habitat and a shift from a grazing to detrital food chain appears to be impacting important shellfisheries. As more extensive areas of organic sediments develop, geochemical cycling changes, resulting in higher rates of nitrogen remineralization and accelerated eutrophication. The major sources of nitrogen inputs to the salt ponds have been identified and a series of management initiatives have been designed to limit inputs from present and potential development within the watersheds of the lagoons.

Shallow-water benthic and pelagic metabolism: evidence of heterotrophy in the nearshore Georgia Bight

Abstract: Pelagic primary production and benthic and pelagic aerobic metabolism were measured monthly at one site in the estuarine plume region of the nearshore continental shelf in the Georgia Bight. Benthic and water-column oxygen uptake were routinely measured and supplemented with seasonal measures of total carbon dioxide flux. Average respiratory quotients were 1.18:1 and 1.02:1 for the benthos and water column, respectively. Benthic oxygen uptake ranged from 1.23 to 3.41 g O2 m-2 d-1 and totalled 756 g O2 m-2 over an annual period. Water column respiration accounted for 60% of total system metabolism. Turnover rates of organic carbon in sediment and the water column were 0.09 to 0.18 yr-1 and 6.2 yr-1, respectively. Resuspension appeared to control the relative amounts of organic carbon, as well as the sites and rates of organic matter degradation in the benthos and water column. Most of the seasonal variation in benthic and pelagic respiration could be explained primarily by temperature and secondarily by primary productivity. On an annual basis, the shelf ecosystem appeared to be heterotrophic; primary production was 73% of community metabolism, which was 749 g C m-2 yr-1. The timing of heterotrophic periods through the year appeared to be closely related to both river discharge and the periodicity of growth and death of marsh macrophytes in the adjacent estuary. The results of this study support the estuarine “outwelling” hypothesis of Odum (1968).

Mediterranean Marine Ecosystems

Abstract: Ecological Factors and their Biogeographic Consequences in the Mediterranean Ecosystems.- The Mediterranean Benthos: Reflections and Problems Raised by a Classification of the Benthic Assemblages.- On the Biogeography of the Benthic Algae of the Mediterranean.- Distribution and Ecology of Endemic Elements in the Mediterranean Fauna (Fishes and Echinoderms).- Mediterranean Sea Meiobenthos.- The Deep Mediterranean Benthos.- The Eastern Mediterranean Shelf Ecosystem in Global Connexion Including some Biological and Geological Implications.- Effects of Pollution and Man-Made Modifications on Marine Benthic Communities in the Mediterranean: A Review.- The Effects of the Geological and Physico-chemical Factors on the Distribution of Marine Plants and Animals in the Mediterranean.- Environmental Control of the Mesoscale Distribution of Primary Producers and its Bearing to Primary Production in the Western Mediterranean.- Phytoplankton Production in Oligotrophic Marine Ecosystems: the Mediterranean Sea.- Deep Phytoplankton and Chlorophyll Maxima in the Western Mediterranean.- Features and Peculiarities of Zooplankton Communities from the Western Mediterranean.- The Zooplankton Communities of the Eastern Mediterranean (Levantine Basin, Aegean Sea): Influence of Man-Made Factors.- Processes of Differentiation Between Mediterranean Populations of the Super-Species Tisbe clodiensis Battaglia and Fava (1968) (Copepoda).- Evolutionary and Zoogeographical Remarks on the Mediterranean Fauna of Brachyuran Crabs.- The Impact of the Lessepsian (Suez Canal) Fish Migration on the Eastern Mediterranean Ecosystem.- Mediterranean Marine Ecosystems: Establishment of Zooplanktonic Communities in Transitional and Partly Isolated Areas.- Contributors.- Species Index.

Effect of sediment copper on benthic fauna

Abstract: Relations between species diversity in benthic-fauna communities and sediment concentration of heavy metals (Cu, Pb, Zn) and organic matter were tested by correlation and regression analyses on data from Norwegian fjords. Diversity and Cu showed a strong negative correlation. A moderate negative correlation was found for Pb and a weak negative correlation for Zn. Diversity and organic matter showed a moderate negative correlation. The negative correlation between diversity and Cu is interpreted as a cause-effect correlation, with high copper concentrations being toxic to a number of species, thus lowering diversity. Correlation plots were made between Cu and occurrence of selected species. Among the 50 most frequently occurring species, 20 were significantly missing from more copper-polluted (Cu > 200 ppm) stations.

Comparability of introduced tiles and natural substrates for sampling lotic bacteria, algae and macro invertebrates

Abstract: SUMMARY. 1 Benthic microflora (bacteria and algae) and macro invertebrates on two types of introduced substrates, unglazed clay tiles and sterilized rocks, were compared quantitatively with natural rocks in a third-order stream. Big Sulphur Creek, California, U.S.A. 2 Exposure periods ranging from 28 to 153 days for introduced substrates indicated that tiles accurately represented bacterial density, chlorophyll a, and macro invertebrate density and species composition of natural rocks within 28 days; phaeophytin and total organic material (as ash-free dry weight) were accurately represented within 63 days. In contrast. sterilized rocks required a 63 day exposure to simulate most of the above natural-rock features. 3 Tiles reduced sampling variability (i.e. increased precision) when compared with either natural or sterilized rocks, especially the variability associated with algal measurements. In benthic studies where a sufficiently long exposure period is possible (1-2 months), introduced substrates can reduce the effort and cost of benthic sampling while minimizing habitat disruption.

Increased benthic grazing: An alternative explanation for low phytoplankton biomass in northern San Francisco Bay during the 1976–1977 drought

Abstract: Among the consequences of extremely low river flow into northern San Francisco Bay during a two-year drought were (1) a gradual increase in salinity, (2) an unusual decline in chlorophyll a concentration, and (3) the upstream migration of estuarine benthic invertebrates to the normally brackish area of the bay. Total abundance in the benthos at a shallow monitoring site increased from a normal 2000 to greater than 20 000 individuals m −2 during the summer of 1977, presumably in response to the increased salinity. Estimated filtration rates derived from equations in the literature for one of the species, the suspended-feeding bivalve Mya arenaria ranged from 1 to 4 m 3 m −2 day −1 during 1977 depending on abundance and mean size on sampling dates. Because water depth at this site is less than 2 m, Mya could have filtered all of the particles (including diatoms) from the water column on the order of once per day. Several other immigrant species undoubtedly contributed to the removal of particles from the near-bottom water as well. Increased benthic grazing, therefore, could have accounted for the anomalously low phytoplankton biomass observed during the drought. These results suggest that during periods of prolonged low river flow and increased salinity benthic food webs could become more important than planktonic food webs in the upper part of the estuary.

Response of global deep-water circulation to Earth's climatic change 135,000–107,000 years ago

Abstract: The response of deep ocean circulation to major climatic events of the past 135,000 years is inferred using carbon-13 analyses of benthic foraminifera from the major ocean basins. The results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions.

Meiofaunal prominence and benthic seasonality in a coastal marine ecosystem.

Abstract: The muds of a shallow (7 m) site in Narragansett Bay, Rhode Island contained higher abundances of meiofauna (averaging 17×106 individuals per m2 and ash free dry weight of 2.9 g/m2 during a 3 year period) than have been found in any other sediment. The majority of sublittoral muds, worldwide, have been reported to contain about 106 individuals per m2. This difference is attributed primarily to differences in sampling techniques and laboratory processing.Extremely high meiofaunal abundances may have also occurred because Narragansett Bay sediments were a foodrich environment. While the quantity of organic deposition in the bay is not unusually high for coastal waters, this input, primarily composed of diatom detritus, may contain an unusually high proportion of labile organics. Furthermore, meiofauna could have thrived because of spatial segregation of meiofauna and macrofauna. While meiofauna were concentrated at the sediment-water interface, most macrofauna were subsurface deposit feeders. Macrofaunal competition with, and ingestion of meiofauna may thus have been minimized.The seasonal cycles of meiofauna and macrofauna were similar. Highest abundances and biomass were observed in May and June and lowest values in the late summer and fall. Springtime increases of meiofaunal abundance were observed in all depth horizons, to 10 cm. We hypothesize that phytoplankton detritus accumulated in the sediment during the winter and early spring, and that the benthos responded to this store of food when temperatures rose rapidly in the late spring. By late summer, the stored detritus was exhausted and the benthos declined.

Early chemical diagenesis, sediment-water solute exchange, and storage of reactive organic matter near the mouth of the Changjiang, East China Sea

Abstract: A substantial proportion of the material delivered to the modern oceans is supplied by a few large rivers such as the Changjiang. Early diagenetic reactions in surficial bottom sediments determine in large part both the eventual influence of these rivers on the sea and the nature of sedimentary deposits formed. The region off the mouth of the Changjiang exemplifies the interplay between physical, chemical, and biological factors which can produce particular spatial patterns of diagenesis and sediment-water exchange. To examine these patterns measurement of pore water solute profiles, sediment-water solute fluxes, and solute reaction rates in the upper few decimeters of sediment were made at 27 stations near the Changjiang in the East China Sea. Direct measurements of dissolved Si(OH)4, NH4+, and NO3−, fluxes from or into bottom sediments made during summer and autumn periods (15 to 24°C) range from 0.13 to 13.2, −2.6 to 3.4, and −1.4 to 3.2mmol m−2 day−1, respectively. Net solute flux from the sea floor is often lowest from deposits having the highest interstitial solute concentrations. In addition, bottom regions having the highest build up of reaction products or depletion of reactants in pore waters (with respect to overlying water) actually have the lowest rates of reaction. These same areas of elevated (products) or depleted (reactants) pore water solute concentrations, low reaction rates, and low net rate of solute exchange which are located near the mouth of the Changjiang are sites of high sedimentation rates and depauperate benthic communities. High water turbidity and resuspension apparently hinder water column production and input of reactive organic matter or other biogenic material which drive many diagenetic reactions. Rapid sedimentation or disturbance hinders benthic community development, lowers biogenic reworking, and allows build up or depletion of reaction products or reactants in bottom sediments. Offshore areas of lower sedimentation, higher productivity, and active bottom communities are sites of high initial reaction rates and increased sediment-water solute exchange compared with rapid sedimentation regions. A diagenetic paradox resulting from the interaction between benthic communities and the physical environment of sedimentation is that proportionally the greatest storage of diagenetic products related to organic matter decomposition can occur in sediments that are initially the least diagenetically reactive.

The occurrence of ‘epipsammic’ diatom populations: A result of interaction between physical sorting of sediment and certain properties of diatom species

Abstract: The role of ‘sand’ (particles >55 μm) as a substratum for benthic diatoms was investigated, using sediments collected from tidal flats and main channels in the Ems estuary. On average, 13% of the sand grains were occupied by one or more diatom cells. It appeared that 80% of the diatom cells in this fraction were present in or on mud coating the sand grains. Of the sand grains in the water, 7% were occupied by diatom cells. The preference of benthic diatoms for the mud coatings rather than the bare parts of the sand grains stresses the importance of ‘mud’ (particles Of the sand grains with attached diatoms, the mean number of diatom cells per grain in the water was similar to that on the tidal flats. This indicates a large exchange of sand between tidal flats and channels. A similar exchange between tidal flats and possibly a shift in the species composition. These processes suggested by the striking similarities in cell number distribution and species composition in samples from these two habitats. However, on exposed tidal flats certain species were present in lower numbers than in the channels, indicating that loosely attached diatoms can be scoured off their substratum. Consequently, two factors are assumed to contribute to the dynamics of the species composition of benthic diatoms. The first is the adhesion capacity of diatoms and the second is sediment sorting by currents and waves. These factors cause a differential but significant flux of benthic diatoms to and from the channels, followed by changes over time in the diatom populations on the tidal flats and possibility a shift in the species composition. These processes show that the terms ‘epipelic’ and ‘epipsammic’ are not helpful to classify the main components of the diatom flora in this estuary.

Productivity of bacteria and microalgae and the effect of grazing by holothurians in sediments on a coral reef flat

Abstract: Bacterial productivity in sandy sediments on reef flats at Lizard Island, Great Barrier Reef was determined from the rate of incorporation of tritiated thymidine into DNA The study was conducted during January 1982 and July 1983 A small diurnal increase occurred in sediments having a dense population of microalgae Bacterial production was 120 to 370 mg C m-2 d-1 in summer on reef flats, which was equivalent to 30–40% of primary production by benthic microalgae In winter, rates of primary production by benthic microalgae and secondary production by bacteria were about one-half to one-fifth of those in summer There was much variation in production, due to patchiness in the distribution of benthic microbes, especially microalgae Doubling times for the bacteria in surface sediment were 1 to 2 d in summer and 4 to 16 d in winter on the reef flats These high productivity values for bacteria indicated that a net input of organic matter to the sediment was needed to support the growth of bacteria Sediment bacteria thus have a very important role in transforming organic matter on the reef flats Grazing by Holothuria atra depressed both primary production and bacterial production It was estimated that these holothurians ate about 10 to 40% of bacterial carbon produced each day in summer, and thus have an important role in the carbon cycle Harpacticoid copepods were numerically important components of the benthic meiofaunal community and probably had a significant impact on bacterial density as grazers

Benthic faunal energy flow and biological interaction in some shallow marine soft bottom habitats

Abstract: Infauna, including macrofauna and temporary meiofauna, and mobile epibenthic fauna have been quantitatively investigated in more than 15 shallow (0 to 1.5 m) soft bottom areas from 1977 to 1982 on the Swedish west coast. The areas are grouped into 3 types of habitats having little or no vegetation: (1) exposed, (2) semi-exposed, (3) sheltered, and 1 habitat (4) where vegetation dominates. Results are presented mainly from 4 intensively studied areas, representative of each of the habitats. Infaunal annualproduction varies between and within habitats depending on temperature, recruitment strength, available space and predation pressure. Comparisons with lower salinity areas in the Baltic show lower infaunal production and production/biomass ratios there than on the Swedish Skagerrak coast. Epibenthic faunal annualproduction is similar within habitats; highest in vegetated areas (about 6 g AFDW m-2) followed by semi-exposed areas (4 to 5 g AFDW m-2). It is suggested that each habitat has a carrying capacity for epibenthic faunal production. Epibenthic faunal production is 5 to 10 times higher in semi-exposed habitats on the Skagerrak coast than in similar habitats on the Baltic coast. As production of the epibenthic fauna is similar between years within habitats despite significant interannual variations of infaunal production, food is not likely to be a limiting factor for epibenthic faunal production in summer-autumn in Swedish Skagerrak shallow waters. In most years 51 to 75 % of production o f dominant infaunal prey organisms is consumed by epibenthic carnivores in semiexposed unvegetated habitats. However, in years with heavy infaunal settlement the percentages are much lower. In an exposed area consumption exceeds infaunal production and epibenthic carnivores also prey upon semi-pelagic mysids. In a sheltered area about 10 % of the infaunal production is eaten and the fate of the remainder is unknown. In a vegetated area the epibenthic faunal consumption is about 4 times that of infaunal production. Here about 75 % of the food consumed by the dominant carnivore Palaemon adspersus is non-carnivorous epifauna, mainly amphipods. Thus, infauna is the quantitatively most important food category for epibenthic carnivores in exposed, semi-exposed and sheltered habitats with little or no vegetation, while in vegetated habitats non-carnivorous epifauna is the dominant prey. Energy flow through the 4 different shallow habitats is discussed in general terms and presented diagramatically for 2 of them. Exposed and semi-exposed shallow unvegetated habitats are largely fuelled by phytoplankton produced offshore, utilized by suspension feeders. In vegetated habitats the primary food is largely produced within the area and detritus and 'small' herbivores are important in this energy flow. Sheltered unvegetated habitats are largely based on detritus as food. In all these habitats a significant part of the animal production during summer and autumn is later transferred to deeper waters by migration and there constitutes a valuable food resource for coastal fish populations.