Benthic infaunal community variability on the northern Svalbard shelf

Marine benthic communities are effective indicators of environmental change. Yet in the Arctic, there are few empirical tests of how sustained climatic change may influence community structure. Northern Svalbard is influenced by both warm Atlantic and cold Arctic water masses, providing an opportunity to assess potential effects of long-term environmental changes by examining spatial variation in community structure. We examined benthic macroinfaunal communities and sediment pigments under Atlantic and Arctic water masses on the northern shelf and fjords of Svalbard. We report on infaunal biomass, abundance, species composition, and diversity at 10 stations spanning 79°–81°N and ranging in depth from 200 to 500?m. Benthic biomass averaged 128?g?WW?m^?2 (48–253?g?WW?m^?2), mean density was 3,635?ind.?m^?2 (780–7,660?ind.?m^?2), and species richness varied from 45 to 136?taxa?stn.^?1. Abundance-based community structure clustered stations in groups related to water mass characteristics, with Atlantic and Arctic shelf stations being well distinguished from each other. Dominant taxa were different in Atlantic- and Arctic-influenced locations. Faunal biomass was highest in the Atlantic-influenced fjords, followed by Arctic fjords and Arctic shelf stations, with Atlantic shelf stations having the lowest biomass. Species richness and diversity were inversely related to biomass. Patterns in faunal biomass were strongly correlated with sedimentary pigments (R ²?=?0.74 for chl a and R ²?=?0.77 for phaeopigments), with large differences in sedimentary pigment concentration among stations. These relationships suggest that benthic fauna on the northern Svalbard shelf are food limited and dependent on predictable, albeit episodic, delivery of organic matter from the water column.     

Rapid recovery of benthic invertebrates downstream of hyperalkaline steel slag discharges

This study assesses the physical and chemical characteristics of hyperalkaline steel slag leachate from a former steelworks on two streams in England and their impacts on benthic invertebrate communities. Using multivariate methods (CCA), we related invertebrate richness and diversity with chemical parameters along the environmental gradient from point sources to less impacted sites downstream. Point discharges are characterised by high pH (10.6–11.5), high ionic strength (dominated by Ca–CO₃–OH waters), elevated trace elements (notably Li, Sr and V) and high rates of calcium carbonate precipitation. This combination of stressors gives rise to an impoverished benthic invertebrate community in source areas. The total abundance, taxonomic richness and densities of most observed organisms were strongly negatively correlated with water pH. Analysis using biological pollution monitoring indices (e.g. BMWP and Functional Feeding Groups) shows the system to be highly impacted at source, but when pH approaches values close to aquatic life standards, some 500 m downstream, complex biological communities become established. In addition to showing the rapid recovery of invertebrate communities downstream of the discharges, this study also provides a baseline characterisation of invertebrate communities at the extreme alkaline range of the pH spectrum.     

The response of two estuarine benthic communities to the quantity and quality of food

Experimental manipulations of food supply were performed on soft sediment cores from two European estuaries, the Westerscheldt and the Gironde, with a view to determining benthic macrofaunal community response. Over a period of twenty weeks in a laboratory mesocosm system, both communities showed losses in terms of numbers of individuals and small, but non-significant, losses in terms of numbers of species. Whereas no effect of the different types of foods or the dose levels at which they were supplied was detected for the Westerscheldt benthic community, that of the Gironde showed some significant response. This was largely attributed to the differential mortality of spionid polychaetes across the dose levels used, with the highest dose, equivalent to 200 g C m^–2 yr^–1, only just maintaining their initial population densities. The results are discussed in terms of the importance of lateral advection of food particles at the benthic boundary layer and the general insufficiency of many estimates of carbon input to shallow benthic systems.     

Intertidal meiofauna of a high-latitude glacial Arctic fjord (Kongsfjorden, Svalbard) with emphasis on the structure of free-living nematode communities

Meiofauna communities of four intertidal sites, two sheltered and two more exposed, in Kongsfjorden (Svalbard) were investigated in summer 2001 at two different tidal levels (i.e. the low-water line and close below the driftline, referred to as mid-water (MW) level). A total of seven meiofaunal higher taxa were recorded with nematodes, oligochaetes and turbellarians being numerically dominant. Mean total meiofaunal densities ranged between 50 ind. 10 cm⁻² and 903 ind. 10 cm⁻². Our data showed a clear decrease in total meiofaunal densities with increasing coarseness of the sediment. Total meiofaunal biomass varied from 0.2 g dwt m⁻² to 2 g dwt m⁻² and, in general, was high even at low meiofaunal densities, i.e. larger interstitial spaces in coarser sediments supported larger meiofauna, especially turbellarians. The results on the vertical distribution of meiofauna contrasted sharply with typical meiobenthic depth profiles on other beaches, probably in response to ice-scouring and concomitant salinity fluctuations. Oligochaetes were the most abundant taxon, with a peak density of 641 ind. 10 cm⁻² at Breoyane Island. They were mainly comprised of juvenile Enchytraeidae, which prohibited identification to species/genus level. Nematode densities ranged between 4 ind. 10 cm⁻² and 327 ind. 10 cm⁻². Nematodes were identified up to genus level and assigned to trophic guilds. In total, 28 nematode genera were identified. Oncholaimus and Theristus were the most abundant genera. The composition of the nematode community and a dominance of predators and deposit feeders were in agreement with results from other arctic and temperate beaches. Nematode genus diversity was higher at the more sheltered beaches than at the more exposed ones. Low-water level stations also tended to harbour a more diverse nematode communities than stations at the MW level. Differences in nematode community structure between low- and MW stations of single beaches were more pronounced than community differences between different beaches and were mainly related to resources quality and availability.     

Carbon cycling by seafloor communities on the eastern Beaufort Sea shelf

Tight pelagic-benthic coupling on Arctic shelves suggests that resident benthic communities may be particularly important in the cycling of carbon and regeneration of nutrients. We sampled 16 stations in the eastern Beaufort Sea during Autumn 2003 and Summer 2004 to determine spatial patterns in sediment community carbon demand, and the manner in which that demand was partitioned among epifauna, macroinfauna, and meio-/microfauna. Sediment carbon demand in this relatively oligotrophic area was similar to that measured in more productive Arctic shelf sites, and was largely related to the distribution of phytodetritus in surface sediments. Epibenthic megafaunal communities were dominated by echinoderms and exhibited peak abundance (up to 240 ind. m^− 2) and biomass at stations in the 60-90 m depth range. Partitioning of the carbon demand revealed the local importance of megafauna, accounting for up to 41% of the community demand. Macrofauna accounted for on average between 25 and 69% of the carbon demand, while meio-/microfauna were responsible for 31-75% of the demand. Total community carbon demand by the benthos is estimated to account for approximately 60% of the annual new production in the region, suggesting the great ecosystem importance of benthic communities on the Beaufort shelf, and potentially across the Arctic. Our study region is strongly influenced by the Mackenzie River, and ongoing climate change is likely to result in altered productivity regimes, changes in quality and quantity of available food, and higher levels of sediment deposition. Impacts of these events on benthic community structure and function will likely have repercussions throughout the ecosystem.     

Response of invertebrates to lotic disturbance: is the hyporheic zone a patchy refugium?

1. Natural experiments, in the form of disturbance from spates, were used to study the resistance and resilience of interstitial communities. Investigations were conducted in a by-passed section of the Rhône River characterized by an artificial hydrology with frequent spates separated by regular minimum discharge of 30 m³ s^–1. 2. Three areas of a bar were studied, upwellings at the head of the bar (stations 1 and 2), and downwelling at the tail of the bar (station 3). In the head of the bar the substratum was characterized by stable cobbles, while mobile gravels dominated in the tail of the bar. At each station, samples were derived from four depths (0.5, 1.0, 1.5 and 2.0 m below the surface of the substratum). Fifteen spates occurred during the study period whose peak discharge ranged from 50 to 1640 m³ s^–1. Temporal variations of the fauna were studied by comparing the spate effect observed 1 day (resistance), 7 days (resilience) and 17 days after the spate. Within-class correspondence analysis was used to compare the temporal variability of the fauna within each class {station/depth}. 3. The fauna differed markedly between the three stations, and the relative density of stygobionts (i.e. hypogean fauna) decreased from 55% at station 1 to 4% at station 3. The spatio-temporal variability increased dramatically from station 1 to station 3. 4. The results suggest that the hyporheic zone acts as a patchy refugium: the stations were more or less active refugial zones, depending on hydrology (upwelling or downwelling), substratum stability and spate amplitude. 5. The downwelling station was the main refugium area for benthic taxa. Important migrations of benthic groups (e.g. Gammarus, Cladocera) or hyporheic taxa (e.g. Cyclopoida and Harpacticoida) were observed deep into the sediment (2 m). Vertical movements of stygobionts (Niphargus, Niphargopsis) were also observed at high amplitude spates. These movements were very important (great numbers of individuals migrated) at low and medium magnitude spates, but were unimportant at high discharge, when the threshold of sediment instability was exceeded. In this case the substratum became mobile and induced drift of benthic organisms. 6. Conversely, in the upwelling stable stations, accumulation was less important (lower number of species and lower densities) but more constant with increasing discharge, suggesting that substratum stability is also a key factor. 7. Generally recovery was rapid at all stations (within 7 days) but no relationships were found between resilience (rate of recovery) and the amplitude of spates.     

Spatial dispersion of an estuarine benthic faunal community

By means of a box-sampler 20 moderately undisturbed sediment samples were obtained, which were subsampled on board the ship. The fauna in the upper 0–5 cm of the sediments was compared to that in the 5–10 cm layer; almost all species collected in both strata were found in the upper 0–5 cm. About 64% of the individuals and 74% of the biomass were restricted to this upper layer. A sample area of 0.5 m² (depth 0–10 cm) was found to be sufficient to make a quantitative evaluation of the benthic community. The horizontal dispersion of the macrobenthic community was studied using the variance/mean ratio and its dependence on sample size is discussed. The abundant species occurred in patches larger than 0.06 m² and high densities were correlated with aggregation.     

Impact of iceberg scouring on macrobenthic communities in the high-Antarctic Weddell Sea

UW-video guided multibox corer sampling in- and outside iceberg scours provided quantitative macrozoobenthos samples for analyses of effects of grounding icebergs on infaunal benthic communities. These studies were performed on the southeastern Weddell Sea shelf off Kapp Norvegia and Austasen. Based on the UW-video sequences, stations were grouped a priori into two different "disturbance categories" and into undisturbed areas.Average biomass of major taxa in the cores of undisturbed areas was significantly higher (14,716.5 g wet weight m^-2) than in old (405.3 g w. wt. m^-2) or in young scour marks (9.2 g w. wt. m^-2). The habitat taxon richness, too, was highest in undisturbed areas (on average, 11.8 taxonomic units occurred per core), decreased in old scour marks (9.0) and was lowest in young scours (6.8). In undisturbed areas, a higher developed community structure was reflected by a greater variety of taxonomic groups, some of which were principally absent in scours.In young scours, the number of taxa was significantly reduced. Motile forms such as echinoderms and crustaceans, mainly amphipods, and juvenile polychaetes, in particular pioneering species of the family Spionidae, started the recolonization of the devastated areas. Burrowing organisms occurred in older scours where the initially overcompacted sediment had softened. In the course of the re-establishment of macrofaunal communities (after some years/decades), the faunal composition is expected to change towards a "normal" dominance of suspension-feeding organisms, mainly sponges and bryozoans, being typical for wide areas on the southeastern Weddell Sea shelf.A more detailed taxonomical approach, using 167 polychaete species as representatives of the macrozoobenthos, also revealed significant differences between undisturbed and affected areas. The mean abundances (784, 389, and 242 ind. m^-2, respectively), as well as habitat species richness (11.6, 5.5, and 3.1, respectively), decreased from undisturbed areas to old to young iceberg scours. Similarly, a large variety of motile and sessile forms was encountered among the polychaetes at undisturbed sites, whereas in scours, the polychaete fauna was impoverished in terms of species richness, abundance and variety of feeding types and lifestyles.     

Responses of Benthic Infauna to Large-Scale Sediment Disturbance in Corpus Christi Bay, Texas

Responses of benthic infauna to large scale disturbance by dredged material placement were studied at eight paired (placement and reference) areas in Corpus Christi Bay, Texas in 1995 and 1996. Total infaunal abundance, taxa richness, and the biomass of annelids and molluscs in placement areas no longer differed from that of reference areas approximately one year after placement. Annual secondary production for annelids and molluscs did not differ between placement and reference areas, however mean (± standard error) total annual secondary production at reference areas (53.6 ± 5.8 g AFDW/m²/yr) was greater than that of placement areas (26.2 ± 2.5 g AFDW/m²/yr) due to higher brittle star densities in reference areas. Differences in community structure between placement and reference areas returned to pre-placement levels one year after disturbance. The magnitude of changes in sediment grain size related to disturbance was positively correlated with the degree of convergence of placement area communities with pre-placement and reference communities. Sediment compaction was consistently associated with infaunal taxonomic composition (BIOENV) and increased linearly with time after disturbance. The use of the term “recovery” with reference to recolonization of dredging-related disturbance implies a return to pre-placement ecological conditions that are frequently neither a reality nor a practical expectation for areas that are subject to repeated disturbances. Our characterization of biological responses to dredged material disturbance targeted benchmarks that were linked to both pre-disturbance conditions and differences between disturbed and neighboring undisturbed areas and indicate that impacts persisted less than one year.     

MMHg production and export from intertidal sediments to the water column of a tidal lagoon (Arcachon Bay,France)

Hg cycling in biologically productive coastal areas is of special importance given the potential for bioaccumulation of monomethylmercury (MMHg) into aquatic organisms. Field experiments were performed during three different seasons in Arcachon Bay, a mesotidal lagoon (SW France), to assess the variability of the water column concentrations, sediment–water exchanges and potential formation and degradation of MMHg. The objectives were to evaluate the contribution of intertidal mudflats to MMHg production and the various pathways of Hg species export. Dissolved and bulk concentrations of Hg species in the water column downstream of tidal flats were measured throughout several tidal cycles. The Hg benthic fluxes at the sediment–water interface were determined by means of benthic chambers for three different stations. Hg methylation and demethylation potentials were determined in surficial sediments and the water column using isotopic tracers. The tidal surveys demonstrated that benthic remobilization of Hg occurs primarily in association with sediment erosion and advection during ebb tide. However, elevated dissolved Hg concentrations observed at low tide were found to be caused by a combination of pore-waters seeping, benthic fluxes and methylation in the water column. Benthic fluxes were more intense during late winter conditions (median MMHg and inorganic Hg (IHg) fluxes: 64 and 179 pmol m^?2 h^?1, respectively) and subsequently decreased in spring (median 0.7 and ?5 pmol m^?2 h^?1, respectively) and fall (median ?0.4 and ?1.3 pmol m^?2 h^?1, respectively). The trends in methylation and demethylation potentials were at the opposite of the fluxes, two times lower during winter than for spring or fall conditions. In this tidal environment, MMHg production in surface sediments and its subsequent release is estimated to be the major source of MMHg to the water column during winter and spring time. However, during the more productive summer period, the Hg methylation extent in the water column may be very significant and equivalent to the sediment contribution.     

Secondary Production of Macrobenthic Invertebrates from Delaware Bay and Coastal Waters

Secondary production of benthic invertebrates was estimated for Delaware Bay and coastal Delaware. Production and turnover ratios were highest in Delaware Bay (P = 46,572 mg AFDW m⁻² yr⁻¹, P:B = 6,O) and progressively lower at two coastal stations (P = 7,501 to 30,124 mg AFDW m⁻² yr⁻¹, P:B = 2.3 to 5.3, and P = 4,485 to 4,492mg AFDW m⁻² yr⁻¹, P:B =2.3 to 4.8). Production was inversely related to sediment particle size. Production in Delaware Bay was relatively evenly distributed between deposit feeding polychaetes and suspension feeding molluscs with a definite shift in production dominance to suspension feeding molluscs at the coastal stations. Moreover, crustaceans and echinoderms played a larger role in production at the coastal stations than in Delaware Bay. Concerns about the health of soft-bottom communities in Delaware Bay expressed earlier were not supported here. Finally, it was concluded that P and P: B from the Delaware Bay area were very similar to those obtained from other areas in the North Atlantic which agrees with estimates for other estuaries in the northern hemisphere.     

Effects of fine sediment inputs from a logging road on stream insect communities:a large-scale experimental approach in a Canadian headwater stream

A forest headwater stream was manipulated (logging road-crossing amended) to induce fine sediment inputs. Benthic inorganic sediment concentrations .particles 1.5–250 μm increased from a 2-year pre-disturbance average of about 800 g m^–2 to over 5000 g m^–2 that persisted for 3 years. Aquatic insect communities were examined over the 5-year study period in the manipulated and nearby reference streams. Overall, the effects of the fine sediment increases on aquatic insect communities were minimal. There were no significant effects of sedimentation on total aquatic insect abundance or biomass. An index of multivariate dispersion gave no evidence of community stress at the manipulated site. Multivariate ordination plots and time trends among univariate community metrics indicated only subtle changes in community structure. Among the univariate metrics (16 time series analyses in total), six gave evidence of a sediment impact on aquatic insect communities. Of those, the clearest indications of an effect were small reductions in diversity and richness of spring communities. These resulted from a significant decline in the proportion of spring shredders, accompanied by a significant increase in the percent Chironomidae. This large-scale experimental approach integrated the realism of a whole-stream study with the control of a manipulative study by including pre-manipulation measurements and excluding other confounding catchment disturbances. In this regard, it may provide a more realistic measure of benthic community level responses to sedimentation in streams at a magnitude associated with logging activity than many previous studies.     

The soft-bottom macrobenthos of Gray's Reef National Marine Sanctuary and nearby shelf waters off the coast of Georgia, USA

As part of an ongoing ecological assessment of the Gray's Reef National Marine Sanctuary (GRNMS), a 58-km² marine protected area 32 km off the coast of Georgia, USA, surveys of benthic macroinfaunal communities, contaminant levels in sediments and biota, and general habitat conditions were conducted during 2000-2002 at 20 stations within the sanctuary and along three cross-shelf transects in nearby shelf waters. Macroinfaunal community structure and composition exhibited distinct cross-shelf patterns associated with sediment granulometry, depth and possibly other factors related to shoreline proximity (e.g., erosional effects, recruitment of estuarine species). Finer-scale spatial patterns of benthic fauna among stations within the sanctuary appear to be related to proximity to live-bottom habitat and other features of seafloor structure (e.g., rippled vs. flat sand). Population densities of dominant fauna within the sanctuary also varied considerably among years, resulting in shifts in the ranking of dominants at most stations. Chemical contaminants generally were at low background concentrations below probable bioeffect levels and thus are not a likely cause of the observed spatial patterns of benthic fauna. However, trace concentrations of pesticides, PCBs, and PAHs were detectable in sediments and biota throughout the study area, demonstrating that chemicals originating from human activities are capable of reaching the offshore sanctuary environment, possibly from atmospheric deposition or cross-shelf transport of materials outwelled through coastal sounds. Highly diverse infaunal assemblages also were observed within the sanctuary and nearby sites of similar depth, suggesting that the sanctuary is an important reservoir of marine biodiversity. Results of this study should be useful in addressing long-term science and management needs of the GRNMS and in furthering our understanding of broader ecological patterns and dynamics of the surrounding South Atlantic Bight (SAB) ecosystem.     

Spatial variability in structural and functional aspects of macrofauna communities and their environmental parameters in the Jade Bay (Wadden Sea Lower Saxony, southern North Sea)

Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences.     

Quantification of biogenic 3-D structures in marine sediments

Burrow and tube structures of marine infauna were quantified in sediments from cores obtained at 3 depths (75, 95 and 118 m) at 3 occasions over a 1-year period. The benthic communities at the two deeper stations were re-establishing subsequent to re-oxygenation after hypoxic conditions; the shallow station was a reference station unaffected by hypoxia. The benthic macrofauna was simultaneously quantified from sieved grab samples. The sediment cores were frozen and later sliced with a plane in horizontal layers. Biogenic structures in these sections were digitally analysed for numbers, area and volume. Number of tubes and burrows showed a general decline with depth in the sediment. The biogenic structures in the sediment at the reference station increased the sediment-water interface about 1.5 times compared to the surface area. The surface areas of burrows and tubes were 2 to 3 times larger at the reference station than at the deeper stations. The benthic fauna at the 95-m and 118-m stations showed a temporal increase in density and number of species. In contrast, development of biogenic surface areas in the sediment at these stations showed no significant temporal trend during the benthic faunal succession. Relic tubes of Melinna cristata were found throughout the sampling period at the 118-m station. The ecological importance of bioirrigation for biogeochemical processes is discussed.     

Large Spatial Scale Variability in Bathyal Macrobenthos Abundance,Biomass, α- and β-Diversity along the Mediterranean Continental Margin

The large-scale deep-sea biodiversity distribution of the benthic fauna was explored in the Mediterranean Sea, which can be seen as a miniature model of the oceans of the world. Within the framework of the BIOFUN project (“Biodiversity and Ecosystem Functioning in Contrasting Southern European Deep-sea Environments: from viruses to megafauna”), we investigated the large spatial scale variability (over >1,000 km) of the bathyal macrofauna communities that inhabit the Mediterranean basin, and their relationships with the environmental variables. The macrofauna abundance, biomass, community structure and functional diversity were analysed and the α-diversity and β-diversity were estimated across six selected slope areas at different longitudes and along three main depths. The macrobenthic standing stock and α-diversity were lower in the deep-sea sediments of the eastern Mediterranean basin, compared to the western and central basins. The macrofaunal standing stock and diversity decreased significantly from the upper bathyal to the lower bathyal slope stations. The major changes in the community composition of the higher taxa and in the trophic (functional) structure occurred at different longitudes, rather than at increasing water depth. For the β-diversity, very high dissimilarities emerged at all levels: (i) between basins; (ii) between slopes within the same basin; and (iii) between stations at different depths; this therefore demonstrates the high macrofaunal diversity of the Mediterranean basins at large spatial scales. Overall, the food sources (i.e., quantity and quality) that characterised the west, central and eastern Mediterranean basins, as well as sediment grain size, appear to influence the macrobenthic standing stock and the biodiversity along the different slope areas.     

Documentation of the presence of Gmelinoides fasciatus (Stebbing, 1899) and the native benthic fauna in the Volga River at Tver (Tver Region,Russia)

In the Volga Basin, the small Baikalian amphipod Gmelinoides fasciatus was introduced in 1965 into the Gorky reservoir in order to enhance fish production; it appeared in 1986 in the Rybinsk reservoir and we recorded it during monitoring activities in 2006 at Tver. In total, at the monitoring site Tver/Migalovo 69 benthic invertebrate taxa were identified. We compared data from three summer seasons. During summer low flow period Gmelinoides fasciatus did not exceed a share of 12.6% considering individual (ind) densities (mean abundance 165 ± 104 ind m^?2) and 14.2% considering biomass (mean biomass 0.39 ± 0.44 g m^?2). Abundances and biomass of G. fasciatus were shown to be stable over three years and no increase was observed. The monthly dataset (March–November 2008) revealed dynamics in relation to the native benthic communities and it was shown that the maximal densities of Gmelinoides did not exceed 587 ind m^–2. Understanding the effects on benthic communities caused by the invasive amphipod Gmelinoides fasciatus is crucial in order to predict further developments in European inland waters and to establish management strategies.     

Macroinvertebrate communities in Wheeler Reservoir (Alabama) tributaries after prolonged exposure to DDT contamination

Quarterly measurements were conducted of the structure, abundance, and diversity of macroinvertebrates comprising two distinct, but overlapping zoobenthic communities in backwaters to Wheeler Reservoir Alabama. The study area included portions of Huntsville Spring Branch (HSB) and Indian Creek (IC) which contain massive quantities of DDT residues (DDTR = DDT, DDD, DDE). Additionally, sewage effluents entering HSB just upstream from the study area have resulted in nutrient enrichment, especially at the two uppermost stations. Herpobenthos (burrowed in bottom sediments) and haptobenthos (attached to substrates) were collected at seven stations along an east-west gradient including a control site above the DDT contamination, and sites with mean sediment residues ranging from 2,730 ppm DDTR in HSB down to 12 ppm DDTR at the mouth of IC.Fifty taxa were collected from dredge samples of the herpobenthos; Tubificid oligochaetes and chironomid larvae comprised 97% of the herpobenthos. At the two uppermost stations in HSB, the control site and the site with the highest sediment DDTR, oligochaete density averaged twice that of chironomids. Downstream, densities of both groups were similar. Mean density at the upper two stations was 9431 and 10 644 organisms m^–2, respectively, significantly (P < 0.05) higher than downstream stations. Herpobenthos was dominated by detrital-algal feeders in HSB while in IC, predaceous chironomids were more numerous. Taxa diversity was also lowest (P < 0.05) at the two upper sites.Forty-five taxa were collected from artificial substrate (Hester-Dendy multiplate samplers) samples of the haptobenthos. Naidid oligochaetes and chironomids dominated the haptobenthos, although nematodes were occasionaly abundant. Chironomids were more abundant than oligochaetes at all sites except the control station, which received the greatest nutrient enrichment from sewage effluents. Mean haptobenthic density in the middle portion of the study area ranged from 31 163 to 37 310 organisms m^–2 and was diferent (P < 0.05) from upper and lower stations. Taxa diversity was lowest at the upper-most station, but no trends were evident among stations.Nutrient enrichment from sewage effluents apparently had greater impact on zoobenthic communities in the HSB-IC System than did DDT contamination. However, the presence of DDTR undoubtedly contributed, in part, to the few Ephemeroptera, Plecoptera, and Trichoptera collected at contaminated stations. Based on the density of oligochaetes and chironomid larvae at station 2 (highest DDTR), macroinvertebrates in this system are resistant to DDTR.     

Effects of sediment properties on benthic primary production in the Columbia River estuary

Effects of sediment properties on benthic primary production were investigated along transects in the intertidal regions of the Columbia River estuary. On the tidal flats, benthic diatoms were the most abundant plants, while microalgae and submergent vascular macrophytes were relatively rare. At five intensive study sites, mean rates of benthic primary production varied between 5 mg C m⁻² h⁻¹ at Clatsop Spit and 84 mg C m⁻² h⁻¹ at Youngs Bay. A regional analysis of data from these sites and from 31 less intensively studied survey sites indicated that Youngs Bay and Baker Bay were more productive than Grays Bay, Cathlamet Bay and the tidal flats in the upper estuary above these bays. This pattern corresponded to the stability and particle size distribution of the sediment in these areas. Benthic gross primary production for the total estuarine area of 410 km² was estimated to be 4895 t carbon per year and represents a mean rate of 72 g C m⁻² year⁻¹. Of the total net primary production in the estuary, benthic plants accounted for about 7%, while phytoplankton and emergent vascular plants in the marshlands contributed approximately 56% and 37%, respectively. Data from this study also suggested that physical processes related to estuarine circulation can ultimately determine the productivity of benthic plant assemblages, and minimize the regulatory and limiting effects of temperature, nutrient supply and consumption by benthic animals.     

Bathymetric distribution and diversity of deep water polychaetous annelids in the Sigsbee Basin, northwestern Gulf of Mexico

The deep water polychaete fauna is analyzed in this study particularly regarding its composition and variations with depth in the Sigsbee Basin, northwestern region of the Gulf of Mexico. Samples were taken at 10 stations along a bathymetric gradient with depth ranges from 200 to 3760 m with a USNEL (0.25 m²) corer. A total of 287 individuals were identified, from 21 families and 65 species. The most important families, both in terms of abundance and species richness, were: Paraonidae (65.4 ind./0.25 m², 9 spp.), Cirratulidae (28.93 ind./0.25 m², 7 spp.) and Spionidae (18.07 ind./0.25 m², 7 spp.). In general, density tended to decrease with depth with minima at around 2000 m, although two abundance peaks were detected at 3700 and 3760 m, making the pattern seem an inverted parabolic curve. The Shannon-Wiener diversity values varied from 0.54–0.92 at around 2000 m to 3.39 at 3620 m and 3.34 at 3760 m. These results contrast with what is already reported from the North Atlantic and the Tropical Pacific deep benthic communities, where highest diversities are found at 2000 m. Faunal changes evaluated through Beta Diversity (0.08–0.1) and the low similarity found between the stations, emphasized the high variability in the composition of the fauna in the Sigsee Basin, meaning that the faunal composition is practically different at all the sampling stations. Ten species are newly recorded for the Mexican fauna.