Showing papers on "Benthic zone published in 1981"

Remineralization and Nutrient Cycling in Coastal Marine Ecosystems

Abstract: Our views of remineralization and nutrient cycling in coastal marine ecosystems have changed considerably over the last 30 years. The major trend has been an increasing appreciation for the complexity of processes involved, including some marked changes in our assessment of the importance of bacteria with respect to smaller animals and in our perception of the association between bacteria and particulate matter in the sea. Among the more recent developments in this area is a growing awareness of the importance of the coupling between benthic and pelagic communities in coastal waters. There appears to be a strong linear correlation between the organic matter produced in the overlying water and the amount of organic matter consumed on the bottom in almost all of the coastal environments for which annual data are available. The large amount of organic matter consumed by the benthos (perhaps 25–50 percent of that produced) is associated with a large flux of inorganic nutrients from the sediments to the overlying water. The stoichiometry of net benthic nutrient regeneration differs from that of pelagic regeneration, however, and simple Redfield type models probably cannot be applied. The amount of fixed inorganic nitrogen returned to the water across the sediment-water interface appears to be about half of that expected on the basis of the flux of phosphorus. This behavior, along with the fact that an appreciable amount of organic matter in coastal waters gets remineralized on the bottom, contributes to the low N/P ratio that is characteristic of these areas and may be responsible for the observation that nitrogen is commonly the nutrient most limiting for primary production. Recent direct measurements of the flux of dissolved N2 across the sediment-water interface indicate that denitrification is probably responsible for the loss of fixed nitrogen during decomposition in the sediments. If this is a widespread phenomenon, estuaries, bays, and other coastal waters may be major sinks in the marine nitrogen cycle and important terms in the global nitrogen budget. However, the fact that eutrophication appears to be an increasing problem in many estuaries is dramatic warning that anthropogenic nutrient inputs can overwhelm the recycling and remineralization processes in coastal waters.

Characteristic Size Distributions of Integral Benthic Communities

Abstract: Uniform size spectra comprising bacteria through macrofauna characterize six intertidal communities when biomass concentration is expressed as a function of logarithmic intervals of organism size. ...

The ecology of marine sediments: an introduction to the structure and function of benthic communities

Abstract: The ecology of marine sediments: an introduction to the structure and function of benthic communities , The ecology of marine sediments: an introduction to the structure and function of benthic communitie... , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Variable effects of sediment addition on stream benthos

Abstract: Two upper Piedmont streams were studied to determine the effects of road construction, especially sediment inputs. Benthic macroinvertebrate data suggest that the stream community responded to sediment additions in two different ways. Under high flow conditions the benthic fauna occurs mainly on rocky substrates. As sediment is added to a stream the area of available rock habitat decreases, with a corresponding decrease in benthic density. There is, however, little change in community structure. Under low flow conditions, stable-sand areas may support high densities of certain taxa. Density of the benthic macroinvertebrates in these areas may be much greater than the density recorded in control areas, and there are distinct changes in community structure.

Resource Partitioning in a Mediterranean Demersal Fish Community

Abstract: Niche breadths and community matrices were examined for two guilds (benthic and epibenthic) on the western Meditemanean slope. There are a larger number of special~st species in the benthic than in the epibenthic guild. Selachians have broader niches than other species. Most species pairs with significant overlaps present high values in only a few size groups. some of them also showing seasonal or die1 patterns of resource partitioning. Analysis of covariance for each niche dimension shows that species are more closely packed with respect to depth distribution than to food. Covariance values of community matrices for each guild indicate that competition is more likely in the benthic than in the epibenthic guild.

Stability of sea urchin dominated barren grounds following destructive grazing of kelp in St. Margaret's Bay, Eastern Canada

Abstract: Kelp regeneration was observed for the first time in St. Margaret's Bay, Nova Scotia, Canada in an area known to have been devoid of macroalgae for several years. The regeneration was destroyed by sea urchins within 10 months. Experimentally induced kelp regeneration met a similar fate under normal grazing pressure. At the lowest sea urchin biomass and density encountered re-establishment of mature kelp stands seems highly unlikely. The sea urchin population required to suppress kelp regeneration is fed by benthic microalgae. Diatoms and other pioneer algal community species were found in the guts of sea urchins. The mean standing crop of benthic microalgae was found to be, 2.2 g C m-2 and production estimated as ca 15 g C m-2yr-1 at 8m depth. Most of the primary production of St. Margaret's Bay has been lost with the disappearing kelp populations.

Species Composition of Benthic Diatoms and Distribution of Chlorophyll a on an Intertidal Flat in the Dutch Wadden Sea

Abstract: A linear transect with 12 sampling points was sampled in a tidal estuarine environment during 1973 for chlorophyll a and pheophytin, and for species composition of epipelic diatoms A gradual pattern in sediment from coarse to fine was found from the most seaward station towards the most landward station of the transect Differences in station level gave emersion times of 37 to 67 % of the tidal cycle In the course of the year, fluctuations in chlorophyll a content (mg chlorophyll a m-* in the top 2 cm of the sediment) appeared to be distinctly parallel at all stations However, mean yearly values differed widely from station to station, ranging between 20 and 100mg chlorophyll a m-2 Chlorophyll a concentration was positively related to the amount of particles < 16 pm in the sediment; this proportion was considered to relate negatively to the degree of exposure to currents and wave action It is likely that low daily winter irradiances limited diatom growth Heavy rain and strong wave action during storms suddenly reduced the chlorophyll a content considerably Species composition of epipelic benthic diatoms could partly be related to the sediment gradient and time of year It seems that high biomass values are formed almost exclusively by single species which are indifferent in their spatial distribution

Field Experiments on Responses of a Freshwater, Benthic Macroinvertebrate Community to Vertebrate Predators

Abstract: We examined the seasonal importance of vertebrate predators in potentially regulating the abundance and diversity of the benthic macroinvertebrates in the littoral zone of a soft-bottom reservoir that receives thermal effluent from a nuclear production reactor. Thirty-six predator (fish and turtle) exclusion cages (4 M2) were placed in shallow water at six locations along a thermal gradient in Par Pond, a 100-ha cooling reservoir on the Savannah River Plant near Aiken, South Carolina, USA. An additional 36 control plots (4 M2) were also set up. Cages were in place during three, 3-mo test periods beginning in September 1977. Estimates of benthic density, taxon richness, and distribution within functional groups (defined by feeding mechanism) were calculated for each test period. Effects of temperature on predator-prey relationships were also determined. Experimental results of this study suggest that vertebrate predation was not the fundamental parameter organizing the benthic macroinvertebrate community in the littoral zone of this reservoir. Neither taxon richness nor density of total macroinvertebrates was conclusively related to predator treatment. Relationships between predator treatment and community response (changes in density and taxon richness) were generally unaffected by either plot locality, temperature fluctuations from thermal effluent, or seasonal changes. When data from caged and control plots were pooled, however, both location and water temperature individually had direct impacts on the benthic community. From our results and other field studies we hypothesize that individual species of "keystone" benthic predators (Paine 1969h) do not occur in the littoral zone of freshwater lentic environments with soft bottoms. This hypothesis is based on the following four arguments. First, environmental heterogeneity should reduce predator efficiency relative to that found in rocky intertidal systems where keystone predation may be present. Second, relative food web complexity should reduce the community importance of an individual predator species. Third, the apparent relatively greater re- source partitioning of space and food in the freshwater littoral zone hinders monopolization of rate- limiting environmental resources by a single dominant prey species. Fourth, the effects of predation may not be extensive enough in time or area to provide sufficient resource space (and thus food) for exploitation by fugitive species. Possible regulation by a guild of predators and cases where the general hypothesis might be falsified are discussed.

Water Quality in Agricultural Watersheds: Impact of Riparian Vegetation during Base Flow

Abstract: Water quality was monitored for 17 months during base flow periods in six agricultural watersheds to evaluate the impact of riparian vegetation on suspended solids and nutrient concentrations. In areas without riparian vegetation, both instream algal production and seasonal low flows appeared to be major determinants of suspended solids, turbidity, and phosphorus concentrations. Peak levels of all parameters were reached during the summer when flows were reduced and benthic algal production was high. Similar summer peaks were reached in streams receiving major point inputs but peaks occurred downstream from the input. Instream organic production was less important in regulating water quality in areas with riparian vegetation and permanent flows. Concentrations of suspended solids remained relatively constant, while phosphorus and turbidity increased in association with leaf fall in autumn. Intermittent flow conditions in summer increased the importance of instream organic production in controlling water quality, even when riparian vegetation was present. Efforts to improve water quality in agricultural watersheds during base flow should emphasize maintenance of riparian vegetation and stable flow conditions.

Trophic Ecology and Structure of Coastal Antarctic Fish Communities

Abstract: The trophic ecology and structure of 5 benthic Antarctic fish communities were studied. Two locations at South Georgia Island, one at the South Sandwich Islands, and two at the South Orkney Islands were sampled using a bottom trawl. Specles diversity was low with 13 or fewer species in each community and a pronounced dominance of 3 or fewer species per community. H' diversity values were < 1.3 in all cases and < 0.8 in 3; e evenness values were < 0.6 in all cases and < 0.3 in 3. The South Sandwich Island community had the lowest species diversity (H' = 0.2), likely due to a very limited prey spectrum, geographic isolation, geologically recent formation, and volcanic origin which formed only a narrow shelf zone where coastal fish communities could develop. The dominant species in all communities were one or more of the nototheniid fishes Notothenia larseni, N. gibberifrons, N. nudifrons, and N. angustifrons. Food resource partitioning was evident within communities at a general taxonomic category level of prey identification. Dominant species within communities generally are morphologically and behaviorally adapted to feed at different levels along a vertical prey-distribution axis. N. larseni feeds above the bottom. N. gibberifrons and N. nudifrons feed on benthos, N. gibberifrons preys more on infauna, and N. nudifrons more on epifauna. N. angustifrons is also a benthos feeder but takes somewhat different prey than the other two species. Low fish species diversity precludes the necessity for fine division of food resources within vertical habitat zones. Feeding niche differences, likely evolved by nototheniids as an adaptation to avoid competition for prey, may contribute to the success and dominance of nototheniid species in these communities. Nearly all cases of high prey overlap were cases involving non-dominant species, and in which krill (Euphausia superba) was important for both species. Krill is a very abundant prey resource in the Antarctic, particularly during austral summer and fall, minimizing competition for this prey among channichthyids and nototheniids. The South Sandwich Island community had a prey spectrum consisting almost entirely of only 3 gammaridean amphipod species. This lowdiversity prey spectrum is probably due to the unstable volcanic rock and cinder bottom type, which does not support a well developed benthic invertebrate fauna. Competition for amphipods likely was great and low fish diversity reflects the low prey resource diversity. Daily rations, calculated in terms of dry prey biomass, for N. angustifrons, N. gibbenfrons, and N. larseni were between 0.24 and 2.03 % dry body weight, depending on mean prey weight in stomachs and gastric evacuation rate for each species. Krill was an important food resource for N. larseni, Champsocephalus gunner], Trernatomus newnesi, and Chaenocephalus aceratus. Based on small sample sizes, T hansoni, Champsocephalus esox, and Pseudochaenichthys georgianus also appear to prey heavily on E. superba. At one South Georgia Island community essentially all fishes preyed substantially on krill, suggesting that even fishes with benthic feeding modes take advantage of abundant krill resources when available close to the bottom.

Energy flow in the Ythan Estuary, Aberdeenshire, Scotland

Abstract: A steady-state energy flow model has been constructed for the Ythan estuary. Nutrient and particulate organic carbon flux has been described in relation to freshwater drainage and tidal action. No rates of retention however, could be provided. Organic C to organic N ratios of detritus vary from 1:14 to 1:200 in the water column, whilst this ratio is 1:8 in the sediments of the mudflats. Primary production by benthic macrophytes, benthic algae and phytoplankton amounts to 631 g C m −2 year −1 whilst the production for zooplankton is 0·8 g C m −2 year −1 , for meiofauna 19·5 g C m −2 year −1 and for macrofauna 48·8 g C m −2 year −1 . The efficiency of energy transfer between the invertebrate macrofauna and vertebrate predators approximates to 54·2% which is higher than that recorded hitherto in various aquatic ecosystems.

Chromatic adaptation of photosynthesis in benthic marine algae: An examination of its ecological significance using a theoretical model

Abstract: All available action spectra of photosynthesis for benthic marine algae have been multiplied by the spectral distribution of the light at different depths in all Jerlov water types to predict the photosynthesis per unit quantum irradiance of each species in each habitat. Comparison of the predictions indicates that red algae are best adapted chromatically to photosynthesize at all depths (including 0 m) in all except the clearest oceanic waters. The results show little correlation with the patterns of vertical distribution of green, brown, and red algae in benthic marine habitats, and suggest, therefore, that light quality is not a major factor in the control of that distribution. A review of physiological evidence supports the hypothesis that the changes in pigment composition that are observed with increasing depth in marine algae are largely adaptations to low irradiance, and not to the spectral composition of underwater light.

Quantitative differences between benthic algal communities along a depth gradient in lake michigan1,2

Abstract: This study analyzes the impact of conditions associated with depth upon benthic algal communities in Lake Michigan. Diatom abundance was greater at 9.1 and 14.6 m depths than 6.5, 22.6 and 27.4 m. Shallow (6.5 m), mid-depth (9.1 and 14.6 m) and deep (22.6 and 27.4 m) zones were distinguishable on the basis of community composition, structure and abundance. Dominance of benthic species, high diversity and low abundance in shallow communities probably resulted from substantial substrate disturbance by wave action in this productive zone. Dominance of benthic species, high diversity and high abundance characterized mid-depth communities where less wave disturbance enabled algal accumulation. Preponderance of living planktonic taxa, low diversity and low abundance delineated deep communities where planktonic algae accumulated and low light levels reduced growth of benthic species.

Dispersal of Benthic Meiofauna by Wave and Current Action in Bogue Sound, North Carolina, USA

Abstract: . Results from sediment trap experiments in Bogue Sound, North Carolina, indicate that meiofauna from a wide variety of taxa and benthic habitats are regularly suspended in the subtidal water column. Interstitial species are estimated to account for 10–30 % of the suspended meiofauna. Measurements of suspended nematode concentrations, when compared with wind and current velocity records, suggest that in Bogue Sound, shoaling and breaking waves are more important than tidal currents in controlling meiofauna erosion and deposition. Linear regression analysis indicates that 80% (r = 0.907) of the variation in suspended nematode density is correlated with changes in the mean onshore-offshore component of local wind velocity. Nematode turnover associated with spring and summer coastal wind patterns is estimated to be several hundred animals per m2per day. Once suspended, meiofauna may be carried up to 10 km per day by residual currents in the Sound. Although erosion, transport and deposition of benthic nematodes by wave and current action appears to provide an effective means of dispersal along continental coastlines, the high settling velocity of nematodes suspended in Bogue Sound (on the order of 10-4m s-1) suggests that net downward flux in shelf and slope waters probably prevents their dispersal across ocean basins by surface currents.

The effect of drought on benthic invertebrate communities in a lowland river

Abstract: Benthic macroinvertebrates were sampled at regular intervals from rural and urban sections of the River Roding, Essex, England, in 1975 and 1976. During the latter year a severe drought led to a marked decline in flows and to desiccation of parts of the river bed. In general, drought conditions resulted in an increase in invertebrate populations and possible reasons for this are presented. A considerable number of individuals of certain groups such as cased caddisfly larvae and prosobranch molluscs were, however, eliminated from the river at this time, mainly as a result of stranding and chemical changes in the environment. The effect of reduced flows on river faunas is briefly discussed.

Plankton Metabolism and Carbon Processes in the Amazon River, Its Tributaries, and Floodplain Waters, Peru‐Brazil, May‐June 1977

Abstract: A synoptic study of photosynthetic and respiratory activity of plankton communities in different Amazon surface waters indicates that large—scale events such as flooding can have a major impact upon the cycling of carbon and nutrients in these aquatic ecosystems. During high water, the major factors influencing primary production appeared to be nutrient concentrations in the mouthbays and varzea (floodplain) lakes and high levels of suspended matter in the Amazon mainstem. In riverine systems, plankton primary production (PPP) averaged 4.04 mg C°m—3°h—1, and measures of respiration (Re) averaged 0.67 mg C°m—3°h—1. In the more productive varzea lakes and mouthbays, PPP averaged 26.37 mg C°m—3°h—1 and Re averaged 2.30 mg C°n—3°h—1. Bacterial densities, 14 C—acetate rate constants for uptake, and plankton carbon: ATP ratios implied that heterotrophic microbiota were important components of the plankton communities in riverine waters. The importance of terrestrial organics to metabolic activity in all waters was implied by high particulate carbon: nitrogen ratios (20:1). These features were especially evident in riverine surface waters where integrated respiration rates exceeded those of plankton primary production. Riverine respiratory levels may be attributed to several factors: adequate supplies of terrestrial organic carbon, sufficient dissolved nutrient concentrations, increased surface area of suspended matter for microbial attachment and growth, and shading of phytoplankton by suspended matter which reduces photosynthetic activity. Observed supersaturation of Amazon waters by carbon dioxide was similar to observations for other rivers of the world. Shifts of CO2 solute components to CO2 in surface waters of varzea lakes and mouthbays and of some tributaries implied high partial pressures of carbon dioxide (°500—1500 Pa). The primary source of CO2 is most likely decomposing organic matter in planktonic and benthic environments of the rivers, lakes, and flooded terrestrial lowlands. The hypothesis that respiratory input of CO2 balanced by evasion (gas lost to atmosphere) is sufficient to explain high CO2 vapor pressures in the Amazon River appeared true from our calculations but needs further examination. Particular attention should be given to periods of rising water, when planktonic respiration appears to be two orders of magnitude greater than at periods of high water. Subsequent seasonal studies of the Amazon and other large rivers are needed to determine how the plankton community, the chemistry of terrestrially derived organics and their biological oxidation in water, and inorganic factors control CO2 supersaturation and exchange with the atmosphere.

Reproductive Strategies of Marine Benthic Invertebrates: A Settlement-Timing Hypothesis

Abstract: Evidence for nudibranch molluscs is presented which shows a clear relationship between egg-size and developmental mode (planktotrophic, lecithotrophic and direct development), egg-size and development time, and thereby larval strategy and development time. Egg-to-juvenile periods differ significantly according to strategy, with lecithotrophic pelagic development being the briefest, and planktotrophic development the longest. In addition, support of the lecithotrophic strategy necessitates a greater absolute calorific threshold on the part of the adult than does the planktotrophic strategy. It is proposed that for a given species there is an optlmal time to spawn (when standing crop IS at a peak) and an optimal time for the larva to settle. While accepting that in selecting for a particular strategy a compromise must be struck between such mediating factors as total and relative energy demand on the adult, egg numbers, individual probabilities of larval survival, and especially dispersal requirements, the settlement-timing hypothesis may be instrumental in resolving some paradoxical situations. Thus, for example, a species in which two or more alternative strategies appear supportable, in energetic terms, may select that strategy which appropriately 'bridges' the period between the optimal time to spawn and to settle.

Benthic Storms: Temporal Variability in a Deep-Ocean Nepheloid Layer

Abstract: Time series measurements of light scattering were made for 2½ months at 20 meters above the bottom in the western North Atlantic. The highest values recorded with the nephelometer exceeded all previous measurements worldwide. Rapid changes indicated a high degree of activity near the sea floor, and some increases may have been related to atmospheric storms.

Modern Deep-Water Coral Mounds North of Little Bahama Bank: Criteria for Recognition of Deep-Water Coral Bioherms in the Rock Record

Abstract: Deep-water, ahermatypic coral mounds are present at water depths of 1,000-1,300 m on the lower slope north of Little Bahama Bank. The mounds are patchily distributed over a minimum area of 2,500 km2 and typically display 5-40 m of relief above the surrounding sea bottom. A diverse benthic community exists on these apparently unlithified mounds, including l 1 genera and 16 species of ahermatypic coral (Bathypsammia, Caryophyllia, Deltocyathus, Desmophyllum, Enallopsammia, Javania, Madrepora, Polymyces, Solenosmilia, Stephanocyathus, and a previously undescribed genus), alcyonaceans, gorgonians, antipatharians, hydroids, ophiuroids, crinoids, barnacles, galatheid crabs, polychaetes, gastropods, bivalves, and sponges. Conspicuously absent from the coral fauna are Lop elia and Dendrophyllia, common deep-water corals in other parts of the Atlantic. Radiocarbon dates on fresh coral and gorgonian fragments of 940 ± 40 and 860 ± 50 years indicate the mounds are at least in part Recent and are probably actively forming today. Bored and stained corals date at around 22 10314C years B. P., which establishes a minimum age for these mounds. We speculate that the mounds develop on sea-floor perturbations in areas where strong bottom currents provide needed oxygen and nutrients to the fauna. The mounds may have undergone multi-stage evolution from colony to thicket to coppice to bank. This evolution may be accomplished through the in situ contribution of skeletal material along with the baffling and trapping of fine-grained carbonate sediment winnowed from adjacent areas by bottom currents. If found in the rock record, the coral mounds north of Little Bahama Bank would probably be considered bioherms. Geologists should thus be aware that scleractinian bioherms are not uniquely shallow-water in origin. The distinction between ancient deep- and shallow-water coral buildups involves using multiple recognition criteria, including: 1) presence or absence of algae; 2) diversity of corals; 3) coral morphology and microstructure; 4) abundance of planktonic/benthonic components; 5) microborings; 6) surrounding litho- and biofacies; 7) stable isotopes of carbon and oxygen; and 8) trace element geochemistry, particularly Sr and U concentrations. The distinction between deep- and shallow-water bioherms is crucial to regional paleoenvironmental and stratigraphic interpretations.