Showing papers on "Benthic zone published in 2000"

Cenozoic deep-sea temperatures and global ice volumes from Mg/Ca in benthic foraminiferal calcite

Abstract: A deep-sea temperature record for the past 50 million years has been produced from the magnesium/calcium ratio (Mg/Ca) in benthic foraminiferal calcite. The record is strikingly similar in form to the corresponding benthic oxygen isotope (δ18O) record and defines an overall cooling of about 12°C in the deep oceans with four main cooling periods. Used in conjunction with the benthic δ18O record, the magnesium temperature record indicates that the first major accumulation of Antarctic ice occurred rapidly in the earliest Oligocene (34 million years ago) and was not accompanied by a decrease in deep-sea temperatures.

A quantitative analysis of fishing impacts on shelf-sea benthos

Abstract: 1. The effects of towed bottom-fishing gear on benthic communities is the subject of heated debate, but the generality of trawl effects with respect to gear and habitat types is poorly understood. To address this deficiency we undertook a meta-analysis of 39 published fishing impact studies. 2. Our analysis shows that inter-tidal dredging and scallop dredging have the greatest initial effects on benthic biota, while trawling has less effect. Fauna in stable gravel, mud and biogenic habitats are more adversely affected than those in less consolidated coarse sediments. 3. Recovery rate appears most rapid in these less physically stable habitats, which are generally inhabited by more opportunistic species. However, defined areas that are fished in excess of three times per year (as occurs in parts of the North Sea and Georges Bank) are likely to be maintained in a permanently altered state. 4. We conclude that intuition about how fishing ought to affect benthic communities is generally supported, but that there are substantial gaps in the available data, which urgently need to be filled. In particular, data on impacts and recovery of epifaunal structure-forming benthic communities are badly needed.

The fate of intertidal microphytobenthos carbon: An in situ 13C-labeling study

Abstract: At two intertidal sites (one sandy and one silty, in the Scheldt estuary, The Netherlands), the fate of microphytobenthos was studied through an in situ C-13 pulse- chase experiment. Label was added at the beginning of low tide, and uptake of C-13 by algae was linear during the whole period of tidal exposure (about 27 mg m(-2) h(-1) in the top millimeter at both sites). The C-13 fixed by microphytobenthos was rapidly displaced toward deeper sediment layers (down to 6 cm), in particular at the dynamic, sandy site. The residence times of microphytobenthos with respect to external losses (resuspension and respiration) were about 2.4 and 5.6 d at the sandy and silly stations, respectively. The transfer of carbon from microphytobenthos to benthic consumers was estimated from the appearance of C-13 in bacterial biomarkers, handpicked nematodes, and macrofauna. The incorporation of C-13 into bacterial biomass was quantified by carbon isotope analysis of polar lipid derived fatty acids specific for bacteria. The bacterial polar lipid-derived fatty acids (i14:0, i15:0, a15:0, i16:0, and 18:1 omega 7c) showed rapid, significant transfer from benthic algae to bacteria with maximum labeling after 1 d. Nematodes became enriched after 1 h, and C-13 assimilation increased until day 3. Microphytobenthos carbon entered all heterotrophic components in proportion to heterotrophic biomass distribution (bacteria > macrofauna > meiofauna). Our results indicate a central role for microphytobenthos in moderating carbon flow in coastal sediments. [KEYWORDS: Water marine habitats; microbenthic communities; westerschelde estuary; microbial biomass; epipelic diatoms; ecological role; organic-matter; grazing rates; chlorophyll-a; secret garden]

Trophic cascades in benthic marine ecosystems: Lessons for fisheries and protected-area management

Abstract: An important principle of environmental science is that changes in single components of systems are likely to have consequences elsewhere in the same systems. In the sea, food web data are one of the few foundations for predicting such indirect effects, whether of fishery exploitation or following recovery in marine protected areas (MPAs). We review the available literature on one type of indirect interaction in benthic marine ecosystems, namely trophic cascades, which involve three or more trophic levels connected by predation. Because many indirect effects have been revealed through fishery exploitation, in some cases we include humans as trophic levels. Our purpose is to establish how widespread cascades might be, and infer how likely they are to affect the properties of communities following the implementation of MPAs or intensive resource exploitation. We review 39 documented cascades (eight of which include humans as a trophic level) from 21 locations around the world; all but two of the cascades are from shallow systems underlain by hard substrata (kelp forests, rocky subtidal, coral reefs and rocky intertidal). We argue that these systems are well represented because they are accessible and also amenable to the type of work that is necessary. Nineteen examples come from the central-eastern and north-eastern Pacific, while no well-substantiated benthic cascades have been reported from the NE, CE or SW Atlantic, the Southern Oceans, E Indian Ocean or NW Pacific. The absence of examples from those zones is probably due to lack of study. Sea urchins are very prominent in the subtidal examples, and gastropods, especially limpets, in the intertidal examples; we suggest that this may reflect their predation by fewer specialist predators than is the case with fishes, but also their conspicuousness to investigators. The variation in ecological resolution amongst studies, and in intensity of study amongst systems and regions, indicates that more cascades will likely be identified in due course. Broadening the concept of cascades to include pathogenic interactions would immediately increase the number of examples. The existing evidence is that cascade effects are to be expected when hard-substratum systems are subject to artisanal resource exploitation, but that the particular problems of macroalgal overgrowth on Caribbean reefs and the expansion of coralline barrens in the Mediterranean rocky-sublittoral will not be readily reversed in MPAs, probably because factors other than predation-based cascades have contributed to them in the first place. More cascade effects are likely to be found in the soft-substratum systems that are crucial to so many large-scale fisheries, when opportunities such as those of MPAs and fishing gradients become available for study of such systems, and the search is widened to less conspicuous focal organisms such as polychaetes and crustaceans.

Continental slope and deep-sea fisheries: implications for a fragile ecosystem

Abstract: Koslow, J. A., Boehlert, G. W., Gordon, J. D. M., Haedrich, R. L., Lorance, P., andParin, N. 2000. Continental slope and deep-sea fisheries: implications for a fragileecosystem. – ICES Journal of Marine Science, 57: 548–557.Exploited deepwater (>500 m) species generally exhibit clear ‘‘K-selected’’ life-history characteristics markedly different from most shelf species: extreme longevity,late age of maturity, slow growth, and low fecundity. Many also aggregate onrestricted topographic features such as seamounts, and as a consequence are notablyunproductive, highly vulnerable to overfishing, and have potentially little resilienceto overexploitation. Since 1964, deepwater fisheries have contributed 800 000–1 000 000 t annually to global marine fish landings. Underlying this apparent overallstability is the ‘‘boom and bust’’ cycle that has characterized many individualfisheries. The accumulated biomass of previously unfished stocks is typically fisheddown, often within 5–10 years, to the point of commercial extinction or very lowlevels. Most deepwater stocks are today overfished or even depleted. Depletion ofspecies from deep-sea environments that dominate mid to upper trophic levels mayhave long-term ecological implications, but the risks of reduced stock size and agestructure to population viability, the potential for species replacement, and theimpacts on prey and predator populations are not generally known. However, trawlfisheries have been shown to have potentially severe impacts on the benthic fauna ofseamounts, where these fish aggregate. This fauna, dominated by suspension feeders,such as corals, is typically restricted to the seamount environment and is character-ized by high levels of endemism, which suggests limited reproductive dispersal. Theability of the benthic community to recover, following its removal by trawling, is notknown.

Strong impacts of grazing amphipods on the organization of a benthic community

Abstract: Large brown seaweeds dominate coastal hard substrata throughout many of the world's oceans. In coastal North Carolina, USA, this dominance by brown seaweeds is facilitated by omnivorous fishes, which feed both on red and green algae and on herbivorous amphipods that graze brown algae. When fish are removed in the field, brown seaweeds are replaced by red seaweeds, and herbivorous amphipods are more abundant. Using an array of large (;4000 L) outdoor mesocosms, we tested three mechanistic hypotheses for this pattern: fish feeding facilitates brown algal dominance (1) by removing red and green algal competitors, (2) by removing amphipods and reducing their feeding on brown sea- weeds, or (3) through an interaction of these mechanisms. Our experiments revealed strong impacts of both fish and amphipods, and a key role for the interaction, in structuring this community. When both fish and amphipods were removed (the latter with dilute insecticide), space was rapidly dominated and held for 17 weeks by fast-growing, primarily filamentous green algae. In contrast, when either fish, amphipods, or both were present, green algae were cropped to a sparse turf, and space was more rapidly dominated by larger macroalgae. The impacts of amphipods and fish on late-successional macroalgal assemblages were comparable in magnitude, but different in sign: red seaweeds prevailed in the amphipod- dominated treatment, whereas browns dominated in the presence of fish. Laboratory feeding assays and amphipod densities in the tanks suggested that the significant effects of am- phipods were attributable largely, if not exclusively, to the single amphipod species Am- pithoe longimana, which fed heavily on brown macroalgae. Our experimental removal of red and green algae failed to enhance cover of brown algae significantly; however, the latter reached substantially lower cover in the grazer-removal treatment, where green algae were very abundant, than in the fish-only treatment, where green algae were sparse. Thus, our results support the third hypothesis: fish-mediated dominance of brown algae involves both suppression of grazing amphipods and removal of algal competitors. Although collective impacts of fish and amphipods on this benthic community were generally comparable in magnitude, impacts normalized to each grazer's aggregate biomass were consistently higher for amphipods than for fish, sometimes by 1-2 orders of magnitude. Thus, the impacts of grazing amphipods (specifically A. longimana) on the benthic community were both strong and disproportionate to their biomass. These experimental results imply that grazing am- phipods, which are ubiquitous in marine vegetation but poorly understood ecologically, may play important roles in the organization of benthic communities, particularly where predation pressure is low.

Heavy metals structure benthic communities in colorado mountain streams

Abstract: The development of field sampling designs that employ multiple reference and polluted sites has been proposed as an alternative to the traditional upstream vs. down- stream approach used in most biomonitoring studies. Spatially extensive monitoring pro- grams can characterize ecological conditions within an ecoregion and provide the necessary background information to evaluate future changes in water quality. We measured physi- cochemical characteristics, heavy-metal concentrations, and benthic macroinvertebrate com- munity structure at 95 sites in the Southern Rocky Mountain ecoregion in Colorado, USA. Most sites (82%) were selected using a systematic, randomized sampling design. Each site was placed into one of four metal categories (background, low, medium, and high metals), based on the cumulative criterion unit (CCU), which we defined as the ratio of the instream metal concentration to the U.S. Environmental Protection Agency criterion concentration, summed for all metals measured. A CCU of 1.0 represents a conservative estimate of the total metal concentration that, when exceeded, is likely to cause harm to aquatic organisms. Although the CCU was less than 2.0 at most (66.3%) of the sites, values exceeded 10.0 at 13 highly polluted stations. Differences among metal categories were highly significant for most measures of macroinvertebrate abundance and all measures of species richness. We observed the greatest effects on several species of heptageniid mayflies (Ephemeroptera: Heptageniidae), which were highly sensitive to heavy metals and were reduced by .75% at moderately polluted stations. The influence of taxonomic aggregation on responses to metals was also greatest for mayflies. In general, total abundance of mayflies and abundance of heptageniids were better indicators of metal pollution than abundance of dominant mayfly taxa. We used stepwise multiple-regression analyses to investigate the relationship between benthic community measures and physicochemical characteristics at the 78 randomly se- lected sites. Heavy-metal concentration was the most important predictor of benthic com- munity structure at these sites. Because of the ubiquitous distribution of heavy-metal pol- lution in the Southern Rocky Mountain ecoregion, we conclude that potential effects of

Impact of cage farming of fish on the seabed in three Mediterranean coastal areas

Abstract: The impact of cage culture of marine fish on the benthic environment was investigated seasonally at three commercial fish farms (Cephalonia, Ithaki, and Sounion) established in coastal waters 20-30 m deep, with different types of sediment (from 80% silt to coarse sand) and varying current intensity. A transect of stations in the vicinity of the cages and a control station in each area were sampled for macrofauna and geochemical variables during July, October, and April. Redox potential in the sediment decreased under and near the cages but reached negative values only at the silty sediment site. Organic carbon and nitrogen content of the sediment near the cages increased by a factor of 1.5-5 and ATP content by 4-28 compared with the control. Azoic zones were not encountered, but the macrofaunal community was affected up to 25 m from the edge of the cages. At the coarse sediment sites, abundance and biomass under the cages were 10 times higher than at the control. Diversity indicated that the ecotone was in the vicinity of 25 m from the cages in all cases.Capitella cf. capitata dominated macrofauna up to 10 m from the cages in two fish farms, whereas the third was dominated by Protodorvillea kefersteini. Similar patterns of succession from the impacted to the normal zones were found, although macrofaunal composition differed among sites. Seasonal variability in geochemistry and macrofauna was higher in proximity of the cages. The results indicate that impacts of fish farming on benthos in the Mediterranean vary considerably depending on site characteristics.

Black shale deposition and faunal overturn in the Devonian Appalachian Basin: Clastic starvation, seasonal water-column mixing, and efficient biolimiting nutrient recycling

Abstract: Integrated geochemical data suggest that black shale deposition in the Devonian Geneseo Formation of western New York was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing. Once established, however, black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity. Recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced N and P regeneration from sediments, sustained high primary productivity by returning nutrients to the photic zone during mixing, and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification. This feedback was ultimately disrupted by rising siliciclastic influx, which diluted organic matter and restored benthic redox stability. The abrupt overturn of diverse, long-standing Appalachian basin marine communities may have been the result of trophic resource destabilization during Geneseo deposition.

Contributions of stable-isotope data to elucidating food webs of Mediterranean rocky littoral fishes.

Abstract: The food webs of rocky infra-littoral ecosystems in the Mediterranean have been little studied. In this investigation stable isotopes and dietary data were compared in an attempt to describe features of the food webs concerned. δ13C and δ15N were determined for plants, invertebrates and fishes from the Bay of Calvi, Corsica. Dietary data were derived from the literature. δ13C of plants ranged from –8.59‰ to –33.74‰, of benthic invertebrates from –17.0‰ to –20.52‰, of planktonic invertebrates from –20.08‰ to –22.34‰ and of fishes from –16.27‰ to –19.59‰. δ15N was generally greater at higher trophic levels. δ15N of plants was 0.95–2.92‰, of benthic invertebrates 1.69–6.54‰, of planktonic invertebrates 3.51–6.82‰ and of fishes 4.63–9.77‰. 13C enrichment tended to be associated with benthic food chains and 13C depletion with planktonic chains. Stable-isotope data suggested more varied diets for many species than implied by gut-contents data. Omnivory and trophic plasticity were widespread, and many consumers fed lower down the food chain than previous studies had suggested. Both stable-isotope and gut-contents analysis resolved differences between fishes feeding on planktonic and benthic prey and indicated that the herbivorous fish Sarpa salpa fed on a diet substantially different from that of other fishes. Zooplankton were important in the diets of several consumers (both primary and secondary), as was plankton derived detritus. One species of fish previously identified as planktivorous was shown to feed largely on benthic organisms, whilst several species of benthic invertebrates may feed on plankton-derived detritus. Although herbivores seemed to obtain most of their C from macroalgae, δ15N data suggested that many of these animals supplemented their intake of N, although gut-contents analysis did not provide evidence for such uptake. The isotopic data have elucidated several features of the food web which we would not otherwise have detected.

Chronic fishing disturbance has changed shelf sea benthic community structure

Abstract: Summary 1. Bottom fishing using towed nets and dredges is one of the most widespread sources of physical disturbance to the continental shelf seas throughout the world. Previous studies suggest that degradation and ecosystem changes have occurred in intensively fished areas. Nevertheless, to date it has been difficult to attribute habitat and benthic community changes to fishing effort at a spatial scale that is truly representative of commercial fishing activities. 2. In this study we present convincing evidence that chronic bottom-fishing disturbance has caused significant and widespread changes in the structure of two distinct soft-sediment benthic assemblages and habitats. 3. Our study compared the benthic fauna found in areas that have been exposed to either high or low levels of bottom-fishing disturbance over the past 10 years. We were able to validate the fishing effort data in some areas using scars in the shells of a long-lived bivalve mollusc (Glycymeris glycymeris) which result from fishing disturbance. Shell scars occurred most frequently in bivalves collected from the area of highest fishing effort. 4. Multivariate analyses and the response of abundance/biomass curves indicated that chronic fishing has caused a shift from communities dominated by relatively sessile, emergent, high biomass species to communities dominated by infaunal, smaller-bodied fauna. Removal of emergent fauna has thus degraded the topographic complexity of seabed habitats in areas of high fishing effort. The communities within these areas currently may be in an alternative stable state.

Relationships between benthic community condition, water quality, sediment quality, nutrient loads, and land use patterns in Chesapeake Bay

Abstract: Associations between macrobenthic communities, measures of water column and sediment exposure, and measures of anthropogenic activities throughout the watershed were examined for the Chesapeake Bay, U.S. The condition of the macrobenthic communities was indicated by a multimetric benthic index of biotic integrity (B-IBI) that compares deviation of community metrics from values at reference sites assumed to be minimally altered by anthropogenic sources of stress. Correlation analysis was used to examine associations between sites with poor benthic condition and measures of pollution exposure in the water column and sediment. Low dissolved oxygen events were spatially extensive and strongly correlated with benthic community condition, explaining 42% of the variation in the B-IBI. Sediment contamination was spatially limited to a few specific locations including Baltimore Harbor and the Southern Branch of the Elizabeth River and explained about 10% of the variation in the B-IBI. After removing the effects of low dissolved oxygen events, the residual variation in benthic community condition was weakly correlated with surrogates for eutrophication—water column concentrations of total nitrogen, total phosphorus, and chlorophylla. Associations between benthic conditions and anthropogenic inputs and activities in the watershed were also studied by correlation analysis. Benthic condition was negatively correlated with measures of urbanization (i.e., population density, point source loadings, and total nitrogen loadings) and positively correlated with watershed forestation. Significant correlations were observed with population density and nitrogen loading below the fall line, but not above it, suggesting that near-field activities have a greater effect on benthic condition than activities in the upper watershed. At the tributary level, the frequency of low dissolved oxygen events and levels of sediment contaminants were positively correlated with population density and percent of urban land use. Sediment contaminants were also positively correlated with point source nutrient loadings. Water column total nitrogen concentrations were positively correlated with nonpoint nutrient loadings and agricultural land use while total phosphorus concentrations were not correlated with land use or nutrient loadings. Chlorophylla concentrations were positively correlated with nitrogen and phosphorus concentrations in the water column and with agricultural land use but were not correlated with nutrient loads.

Seasonality in coastal benthic ecosystems

Abstract: For historical reasons, knowledge about seasonality in the dynamics of marine benthic suspension feeders from temperate areas comes mainly from studies of cold temperate seas. Recent surveys of Mediterranean taxa show different patterns from those observed in cold temperate seas, which are characterized by winter dormancy. In the Mediterranean, summer dormancy predominates among taxa and appears to be related to energetic constraints. Temperature and food availability are crucial to the dynamics of benthic suspension feeders. However, because these factors tend to be positively correlated in cold temperate seas, it is difficult to distinguish between their effects. Such correlation does not occur in Mediterranean ecosystems. The contrast between recent studies in the Mediterranean and in other areas can help to disentangle confounded environmental controls.

Stable isotopes' as trophic tracers: combining field sampling and manipulative labelling of food resources for macrobenthos

Abstract: We combined 3 different approaches to determine the relative importance of micro- phytobenthos production as food for intertidal macrobenthic animals: (1) the natural abundance of stable-isotope ratios of carbon and nitrogen, (2) an in situ deliberate tracer addition of 13 C-bicarbonate, which was transferred through the benthic food chain after its incorporation by benthic algae, and (3) a dual labelling experiment in a flume, where pelagic and benthic algae were labelled with 15 N and 13 C, respectively. The results of the 3 approaches confirmed the high importance of microphytobenthos as a food source for (surface) deposit feeders. Despite the clearly demonstrated resuspension of benthic algae at high current velocities, suspension feeders appeared to depend almost exclusively on pelagic algae (and possibly detrital carbon) as a food source. Based on the results of the experiments, we determined an approximate degree of dependence on microphytobenthos for different species of intertidal macrobenthos. The macrobenthic biomass at 5 study locations, when weighted by these coefficients, correlated very well with measured productivity of the microphytobenthos.

Spectral discrimination of coral reef benthic communities

Abstract: Effective identification and mapping of coral reef benthic communities using high-spatial and -spectral resolution digital imaging spectrometry requires that the different communities are distinguishable by their spectral reflectance characteristics. In Kaneohe Bay, Oahu, Hawaii, USA, we collected in situ a total of 247 spectral reflectances of three coral species (Montipora capitata, Porites compressa, Porites lobata), five algal species (Dictyosphaeria cavernosa, Gracilaria salicornia, Halimeda sp., Porolithon sp., Sargassum echinocarpum) and three sand benthic communities (fine-grained carbonate sand, sand mixed with coral rubble, coral rubble). Major reflectance features were identified by peaks in fourth derivative reflectance spectra of coral (at 573, 604, 652, 675 nm), algae (at 556, 601, 649 nm) and sand (at 416, 448, 585, 652, 696 nm). Stepwise wavelength selection and linear discriminant function analysis revealed that spectral separation of the communities is possible with as few as four non-contiguous wavebands. These linear discriminant functions were applied to an airborne hyperspectral image of a patch reef in Kaneohe Bay. The results demonstrate the ability of spectral reflectance characteristics, determined in situ, to discriminate the three basic benthic community types: coral, algae and sand.

A Trophic Flow Model of the Caeté Mangrove Estuary (North Brazil) with Considerations for the Sustainable Use of its Resources

Abstract: The Caete Estuary lies within the world's second largest mangrove region, 200 km south-east of the Amazon delta. It has an extension of about 220 km 2 and is subjected to a considerable human impact through intensive harvest of mangrove crabs ( Ucides cordatus ) and logging of mangroves. In order to integrate available information on biomass, catches, food spectrum and dynamics of the main species populations of the system, a trophic steady state model of 19 compartments was constructed using the ECOPATH II software (Christensen & Pauly, 1992). Ninety-nine percent of total system biomass is made up by mangroves ( Rhizophora mangle , Avicennia germinans and Laguncularia racemosa ), which are assumed to cover about 45% of the total area and contribute about 60% to the system's primary production. The remaining biomass (132 g m −2 ) is distributed between the pelagic and benthic domains in proportions of 10% and 90% respectively. Through litter fall, mangroves inject the main primary food source into the system, which is either consumed directly by herbivores (principally land crabs, Ucides cordatus ) or, when already metabolized by bacteria, by detritivors (principally fiddler crabs, Uca spp.). These two groups are prominent in terms of biomass (80 g and 14·5 g m −2 ), and food intake (1120 g m −2 yr −1 and 1378 g m −2 yr −1 respectively). According to the model estimates, energy flow through the fish and shrimp compartments is of relatively low importance for the energy cycling within the system, a finding which is contrary to the situation in other mangrove estuaries reported in the literature. The dominance of mangrove epibenthos is attributed to the fact that a large part of the system's production remains within the mangrove forest as material export to the estuary is restricted to spring tides, when the forest is completely indundated. This is also the reason for the low abundance of suspension feeders, which are restricted to a small belt along the Caete River and the small creeks which are watered daily. Phytoplankton, temporarily refloating benthic diatoms, neritic zooplankton and small pelagic fish dominate the (low) pelagic biomass. Total system throughput (10 559 g m −2 yr −1 ) and mean transfer efficiency between trophic levels (9·8%) calculated by the model fit well into the range reported for other tropical coastal ecosystems. The very high gross efficiency of the fishery (catch/net primary production) of 8·6% and its low trophic level (2·1) is explained by a high harvesting rate of mangroves and the fact that the main animal resource in the system are the mangrove crabs ( Ucides cordatus ), which feed at the first trophic level. The model was balanced asuming a turnover rate for the land crabs of P / B =0·25 ( P / B : production per unit of biomass) which is possibly too high. If this value was replaced by a (possibly more realistic) lower value, the model would not balance, suggesting a situation in which more biomass is being harvested than produced, which hints to an overexploitation of this resource A ranking of the various system components in terms of their contribution to the system function (ascendency sensu Ulanowicz, 1997) revealed that detritus and associated bacteria contribute 34%, mangroves 19%, fiddler crabs 13%, phytoplankton and microphytobenthos 10%, mangrove crabs 10%, and the remaining 14 groups 14% to the total ascendency. Summary statistics of the model are given and compared with those of other coastal ecosystems.

The biology and ecology of lotic microcrustaceans

Abstract: SUMMARY 1. Copepoda, Ostracoda and ‘Cladocera‘ are important meiobenthic Crustacea which can be both numerically abundant and species rich in running waters. Harpacticoids and ostracods are well adapted to benthic life because they are typical crawlers, walkers, and burrowers. Many cladocerans are substratum dwellers, but most benthic species among these can also swim. Cyclopoids which are generally good swimmers are nevertheless often bottom frequenters and actively colonise sediment interstices (the hyporheic zone). 2. The subclass Copepoda includes 10 orders. With 53 families, the order Harpacticoida dominates the benthos. Only five of these families are represented in fresh waters (ca. 1 000 species and subspecies). The order Cyclopoida includes 12 families of which the Cyclopidae is well represented in freshwater habitats with 900 species and subspecies. Freshwater Ostracods belong to the order Podocopida (5 000 species) with three superfamilies occurring in running fresh waters. The group ‘Cladocera‘ contains four orders, 12 families, more than 80 genera, and 450‐600 freshwater species. Most of the benthic species are found in the families Chydoridae (39 genera), Macrothricidae, Ilyocryptidae and Sididae. 3. For each of the three major taxa, morphological characteristics are presented, specimen collection and preparation are described and references to available taxonomical keys are provided. 4. Biological characteristics are extremely diverse among and within the three taxa, resulting in a great variety of strategies in meiobenthic crustaceans. Characteristics of reproduction, sexual dimorphism, cyclomorphosis and population parameters (i.e. clutch size, lifespan, growth, moulting) are provided for some of the most common species. 5. Important differences between the three main taxa were found at the species level. Ecological requirements such as hydraulic microhabitats and geomorphologic features of the streambed are the major determinants of species diversity and abundance for benthic microcrustacea of lotic habitats. Many studies on the ecology of these communities are limited by a lack of knowledge of the life history characterisitics of lotic (especially interstitial) crustacean populations.

Traits of benthic macroinvertebrates in semi‐natural French streams: an initial application to biomonitoring in Europe

Abstract: 1. The methods used to indicate the biological state of streams are often based on taxonomic composition, and the abundance of species or other taxa. This 'taxonomic structure' varies among ecoregions and cannot be applied to wider geographical areas. Therefore, we assessed the species traits of benthic macroinvertebrates from semi-natural reference sites as a potential benchmark for large-scale biomonitoring. Our purpose was to assess the stability of community structure, based on the representation of taxa and of traits, across large gradients of geology (sedimentary to granitic), altitude (65-1982 m), geographical coordinates (0° 48' W to 7° 20' E and 42° 52' to 48° 44' N), stream order (1-5) and slope (0.5-60‰). 2. We used invertebrate abundance data from the 62 most natural French stream sites available. These abundance data served to weight the occurrence of 'biological' traits, such as reproductive characteristics, mobility, resistance forms, food, feeding habits, respiration, and 'ecological' traits, such as preferences for temperature, trophic level, saprobity, biogeographic distribution, longitudinal zonation, substratum and current velocity. 3. Multivariate analyses of taxonomic composition demonstrated a clear site gradient from lowlands to uplands and from calcareous to granitic geology. In contrast, community structure based on both biological and ecological traits was stable across environmental gradients. 4. The frequency distribution of biological traits indicated that the stream benthos of the 'reference sites' had a mixture of categories which confirmed theoretical predictions for temporally stable and spatially variable habitats. A mixture of ecological trait categories also occurred at our reference sites. Thus, semi-natural benthic macroinvertebrate communities are functionally diverse. Moreover, we included an initial application of these traits to a case of slightly to moderately polluted sites to show that the impact of humans significantly changes this natural functional diversity. 5. Future studies should focus on the potential for various biological and ecological traits to discriminate different human impacts on the benthic macroinvertebrates of running waters, and on the integration of this functional application into a general 'reference-condition' approach.

Succession in marine benthic habitats and fauna in response to oxygen deficiency: analysed by sediment profile-imaging and by grab samples

Abstract: This study shows, for the first time, in situ images of changes in marine benthic habitats in response to oxygen deficiency. Tight coupling is demonstrated between gradual degradation of benthic habitat and faunal behaviour, species richness, abundance and biomass. The critical oxygen level that forced changes in the benthic faunal successional stages was ∼10% that of air saturation (∼0.7 ml 02 l -1 ). Before this critical saturation level was reached, tube-building polychaetes their tubes extended higher into the water column, the width of the sub-oxic sediment layer decreased, and vertical animal burrows (formerly oxidised and brown in colour) became sulphidic and black. Over a 10 mo hypoxic period (June 1997 to April 1998) in the Gullmarsfjord (Swedish west coast), benthic community successional stages declined from equilibrium to virtually azoic conditions. As normoxic conditions returned, pioneering stages gradually recolonised the area.

Ecological significance of benthic foraminifera: 13C labelling experiments

Abstract: We examined the ability of foraminifera in taking up freshly deposited algal carbon in intertidal estuarine sediments. Lyophylized C-13-labelled axenic Chlorella was added to intact sediment cores containing natural benthic biota. The response of the system as a whole was rapid; similar to 5% of the added carbon was respired to CO2 within 6 h. Bacteria assimilated similar to 2 to 4 % of the added carbon within 12 h. Among the foraminifera, the dominant foraminifer Ammonia exhibited rapid uptake and it is estimated that similar to 1 to 7% of the added carbon was ingested within 3 to 53 h. This rapid, substantial uptake by Ammonia and the significant contribution of foraminifera to meiobenthic abundance and biomass (37 and 47% respectively) suggest that foraminifera play an important role in the carbon cycle in these sediments. [KEYWORDS: meiobenthos; benthic foraminifera; bacterial biomarkers; algal carbon; carbon cycle; CO2; C-13 labelling Deep-sea; organic-carbon; sedimentation event; metazoan meiofauna; adriatic sea; fatty-acid; phytodetritus; community; microalgae; deposition]

Distribution of benthic algae in the upper Illinois River basin in relation to geology and land use

Abstract: SUMMARY 1 Benthic-algal distributions in the upper Illinois River basin, IL, U.S.A., were examined in relation to geology, land use, water chemistry and stream habitat using (detrended) (canonical) correspondence analysis, autecological metrics and indicator-species analysis in order to identify the major environmental gradients influencing community variation. 2 Ionic composition and major nutrient [i.e. nitrogen (N) and phosphorus (P)] concentration of surface waters, salinity (Na-Cl type), substratum type and physiognomic form of dominant species were primary factors contributing to variation in benthic-algal assemblages of the basin. Basin geology was a significant contributing factor, but the explained variance associated with this factor was less than that related to land use. 3 Proportions of algal biomass consisting of cyanophytes, filamentous chlorophytes, halophilic diatoms and diatoms which utilize nitrogen heterotrophically were greater in eutrophic river segments than in less nutrient-enriched segments. Composition of the benthic flora indicated meso-eutrophic or eutrophic conditions throughout the basin; there were few diatoms indicative of hypertrophic waters. Shifts in diatom-assemblage structure in response to nutrient loading provided an incomplete representation of the community-response curve. 4 A weighted-averages regression model based on total P and benthic-algal abundances (all divisions included) yielded a highly significant correlation (r2 = 0.83) between species-inferred [WA(tol)] and observed total P, with systematic bias (increased deviation of residuals) occurring only at concentrations greater than ∼ 1.0 mg L−1 total P. This result indicates that total P regression and calibration models can be predictable for a river basin receiving excessive loadings of phosphorus.

Benthic flux of biogenic elements on the Southeastern US continental shelf: influence of pore water advective transport and benthic microalgae

Abstract: In situ, paired light and dark benthic flux chamber incubations were used to estimate the exchange of nutrients, oxygen and inorganic carbon across the sediment – water interface of the South Atlantic Bight (SAB) continental shelf. The results indicate that physically forced non-diffusive pore water transport and benthic primary production (BPP) by sea floor microalgae exert a major influence on benthic exchange rates on the mid- and outer-continental shelf (depths of 14–40 m). Light fluxes to the sea floor and sediment photosynthetic pigment distributions determined on two, widely spaced cross-shelf transects suggest that BPP may occur over 84% of the SAB continental shelf area. Microalgal gross BPP rates at all study sites averaged 400±260 mg C m−2 d−1 between May and September 1996 while water column primary productivity averaged 682±176 mg C m−2 d−1, implying a total primary productivity for this region of approximately 1100 mg C m−2 d−1 (1.6 times the water column productivity alone). The results are also consistent with the advective transport of pore waters. Benthic flux chambers appear to retard this exchange, affecting the accuracy of derived net fluxes. Given our inability to relate pore water gradients to fluxes in non-diffusive regimes and to mimic natural advective transport in intact core incubations, traditional techniques such as pore water gradient diffusion calculations or shipboard core incubations also may not provide accurate flux estimates. Because of these limitations, fundamental questions remain concerning the processes that control nutrient inventories in pore waters and the magnitude of the net benthic flux of nutrients on the sandy SAB shelf.