Use of annular flumes to determine the influence of current velocity and bivalves on material flux at the sediment-water interface

A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m^?2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m^?2 h¹) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m^?2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s^?1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.     

Experimental studies of predation on polychaetes associated with seagrass beds

Predation on benthic polychaetes associated with seagrass beds was examined in laboratory and field predator inclusion experiments with one fish and three invertebrate predators. Predation had differential effects on polychaete taxa which depended on their microhabitat utilization patterns. The magnitude of predation effects strongly depended on the predator species, with the shrimpPenaeus duorarum having the greatest impact and the pinfishLagodon rhomboides the least. Abundance of spionid polychaetes, which are located near the sediment-water interface, was reduced most often by predation. Nereid and capitellid polychaete abundances were reduced by some predators and not by others. The results emphasize the need for more detailed natural history information on polychaete species in order to improve the interpretation of results from predation experiments.     

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian,SE France) evidenced by calcareous nannofossils

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.     

A multidisciplinary approach to evaluating impacts of shellfish aquaculture on benthic communities

The impact of suspended mussel culture (Mytilus edulis, M. trossulus) on the benthos of a small Nova Scotia cove (7 m depth) was assessed using meehods involving both benthic metabolism and community structure. Due to deposition of mussel feces and pseudofeces, sedimentation rate was higher under the mussel culture lines than at an adjacent reference site of similar sediment texture. Porewater profiles of sediment sulfate and sulfide indicated greater anaerobic metabolism at the mussel site than at the reference site, but sulfide was absent from the upper centimeters of sediments under the mussels. Seasonal measures of sediment oxygen demand showed little change between sites, but maximum rates of ammonium release at the mussel site were twice the highest rates measured at the reference site. Abundance of benthic macrofauna was higher at the reference site, but biomass was generally lower. Biomass at the mussel site was dominated by molluscs (Ilyanassa spp. andNucula tenuisulcata), that were attracted to mussels fallen from the culture and/or enriched organic matter due to biodeposition. Species diversity was lower at the reference site due to the dominance of the polychaeteNephtys neotena. Abundance-biomass comparisons (ABC method) of faunal analysis did not indicate any impact of biodeposition at this site: however, disturbance did not result in a typical assemblage of small opportunistic species anticipated with this method. Cluster analysis of macrofauna usually provided a clear separation between the sites. Since the contruction of a causeway (1968), foraminifera species composition showed a temporal response to temperature changes in the cove by shifting toward calcareous species, but assemblages downcore showed little or no relationship to aquaculture impacts. Although there is a shift toward anaerobic metabolism at the mussel lines, the impact of mussels falling to the sediments was more noticeable in benthic community structure than was any impact due to organic sedimentation or hypoxia. In general the impact of aquaculture on the benthos appeared to be minor. Furtyher assesment of these consequences may mandate both taxonomic and energetic approaches to impact assessment.     

Limited Consequences of Seagrass Decline on Benthic Macrofauna and Associated Biotic Indicators

Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.     

Trophic relationships of three sunfishes (Lepomis spp.) in an estuarine bayou

We examined ontogenetic, interspecific, and seasonal trophic patterns among sympatric sunfish species, redspotted sunfish,Lepomis miniatus; redear sunfish,Lepomis microlophus; and bluegill,Lepomis macrochirus, in an estuarine bayou. In particular we studied these feeding patterns in relation to relative abundances of prey from different benthic feeding habitats. All three sunfishes showed ontogenetic divergence in their trophic niches, reflecting different ecomorphological specializations. Small fishes depended on zooplankton, whereas larger fishes of all three species shifted their diets to benthic macrofauna. A potential for trophic resource partitioning was reflected by dietary differences among the three sunfish species. One impalied mechanism for resource partitioning was feeding habitat, as redear sunfish frequently used sediment-associated prey, while bluegill showed greater use of water-column-associated prey, and redspotted sunfish often used SAV-associated prey. However, all three sunfishes apparently used each feeding habitat to some degree; and, trophic differences were more clearly based on prey type than on feeding habitat. Redear sunfish, which can crush hard-shelled prey, exhibited the most distinctive diet. An apparent seasonal shift in feeding habitat occurred in autumn/winter, as indicated by increased overlap between diets and SAV. This shift was facilitated by changes in the relative abundances of several common prey types between benthic habitats. The relative abuandance and use of freshwater and estuarine-derived prey also varied seasonally, suggesting a possible trophic benefit of consistent prey availability in the estuarine bayou.     

Tropicalization of the Northern Gulf of Mexico: Impacts of Salt Marsh Transition to Black Mangrove Dominance on Faunal Communities

The tropically associated black mangrove (Avicennia germinans) is expanding into salt marshes of the northern Gulf of Mexico (nGOM). This species has colonized temperate systems dominated by smooth cordgrass (Spartina alterniflora) in Texas, Louisiana, Florida and, most recently, Mississippi. To date, little is known about the habitat value of black mangroves for juvenile fish and invertebrates. Here we compare benthic epifauna, infauna, and nekton use of Spartina-dominated, Avicennia-dominated, and mixed Spartina and black mangrove habitats in two areas with varying densities and ages of black mangroves. Faunal samples and sediment cores were collected monthly from April to October in 2012 and 2013 from Horn Island, MS, and twice yearly in the Chandeleur Islands, LA. Multivariate analysis suggested benthic epifauna communities differed significantly between study location and among habitat types, with a significant interaction between the two fixed factors. Differences in mangrove and marsh community composition were greater at the Chandeleurs than at Horn Island, perhaps because of the distinct mangrove/marsh ecotone and the high density and age of mangroves there. Infaunal abundances were significantly higher at Horn Island, with tanaids acting as the main driver of differences between study locations. We predict that if black mangroves continue to increase in abundance in the northern GOM, estuarine faunal community composition could shift substantially because black mangroves typically colonize shorelines at higher elevations than smooth cordgrass, resulting in habitats of differing complexity and flooding duration.     

Did multiple sediment-associated stressors contribute to the 1999 lobster mass mortality event in Western Long Island Sound, USA?

Near-bottom hypoxia during summer months has been a documented recurring phenomenon for decades in western Long Island Sound (WLIS); this temperate estuary has also supported, until 1999, a substantial American lobster (Homarus americanus) fishery. In response to a dramatic mass die-off of lobsters that began in WLIS in the late summer of 1999, a benthic habitat survey using a sediment-profile imaging (SPI) camera was conducted in October 1999. Follow-up surveys involving SPI and simultaneous measurements of dissolved oxygen (DO), hydrogen sulfide and ammonia within 10 cm of the bottom were conducted in August, September and November 2000. The SPI images revealed black sediments at or just below the sediment-water interface at a high proportion of stations in both 1999 and 2000, suggesting strongly reducing conditions and elevated levels of sulfides and other reduced end-products in sediment pore-water. Visual redox depths were relatively shallow (less than 2 cm) and spatially variable, and benthic communities appeared to be dominated by small, surface-dwelling opportunists. In August 2000, near-bottom DO concentrations < 2 mg I⁻¹ coincided with shallow redox depths at stations in the Western Narrows region. As DO levels increased from August to November 2000, visual redox depths remained shallow. Both sulfide and ammonia were detected in samples of bottom water taken within about 10 cm of the seafloor in all three 2000 surveys. The results suggest that anaerobic decomposition processes within the organic-rich sediments of WLIS strongly influence conditions at the sediment-water interface during late summer-early fall, the time of year that the lobster mortality event of 1999 began. Releases of reduced end-products (e.g., sulfide and ammonia) into overlying waters, combined with low DO levels and abnormally high water temperatures, represent multiple environmental stressors that may have physiologically weakened the lobsters and increased their susceptibility to deadly pathogens.     

Do Spartina maritima Plantations Enhance the Macroinvertebrate Community in European Salt Marshes?

Ecological restoration of salt marshes using plantations may enhance the macroinvertebrate community, but little is known about the development of benthic macroinvertebrates after ecological engineering projects in European salt marshes. This study analyzed the environment and the macroinvertebrate community in European salt marshes 3 years after restoration using Spartina maritima plantations in comparison with non-restored and preserved marshes in Odiel Marshes (Southwest Iberian Peninsula). We hypothesized that planting Spartina maritima on intertidal mudflats would increase species richness and diversity (Shannon–Weaver index) of the benthic macroinvertebrate community by increasing environmental heterogeneity, providing feeding resources and improving sediments characteristics. Benthic macrofauna samples (composed mainly of annelids, crustaceans, and mollusks) were sampled in plots of 20 cm?×?25 cm to 5 cm depth between +1.8 and +3.0 m above Spanish Hydrographic Zero. Sediment organic matter content, bulk density, pH, and redox potential were the variables that best explained macroinvertebrate distribution. Restored marshes achieved similar diversity and even higher specific richness than preserved marshes, although with differences in species composition. Non-restored marshes showed the lowest diversity. Restored and preserved marshes did not differ in total abundance or biomass of macroinvertebrates, both being higher than in non-restored marshes. The macroinvertebrate communities in preserved and non-restored marshes showed the largest difference in taxa composition, with restored marshes occupying an intermediate position. Salt marsh restoration using S. maritima increased the complexity (ecological diversity and species richness) and abundance of the benthic macroinvertebrate community. Our study offers new information about the role of salt marsh plants in mediating faunal communities via ecological engineering projects.     

REE patterns of eucrites and their genetic implications

Rare earth element (REE) abundances in eucrites were precisely determined on Juvinas, Pasamonte, Cachari, Stannem and Antarctic eucrites Y-74450,63,D+G; Y-75015,20,E+F; Y-75011,73; Y-790007,61,F; Y-75011,84,D-1 and Y-790007,61,E-4. The last two samples are eucrite clasts from polymict eucrites. The other Antarctic eucrite samples are matrix from polymict eucrites.Like the Stannern eucrite, all of the Antarctic eucrites have relatively high REE abundances. REE abundances in two clast samples are higher than those in the Stannern and matrix samples of the Antarctic eucrites. When REE abundances in the Antarctic eucrites and the Stannem eucrite are normalized by the REE abundance suite of the Juvinas or Pasamonte eucrites, highly linear REE patterns are obtained. For the Juvinas- or Pasamonte-normalized REE patterns of the Antarctic and Stannern eucrites, the inclination of the linear REE patterns increases with increasing REE abundances. These observations suggest that the eucrites with larger REE abundances such as the Stannern and Antarctic eucrites were produced as residual liquid in a fractional crystallization process from the main group of eucrites (e.g., the Juvinas eucrite). On the other hand, the Moore County cumulate eucrite is considered to be a solid phase formed in this process.     

Diverse Dietary Responses by Saltmarsh Consumers to Chronic Nutrient Enrichment

We examined the effect of whole-ecosystem nutrient enrichment on herbivory in saltmarsh creek-wall habitats in the Plum Island Estuary (Massachusetts, USA). Located between the macrophyte-dominated high marsh and adjoining mudflats, creek walls are steep vertical habitats vegetated with productive filamentous algae and associated epiphytes. Annual nitrate and phosphate loading rates were increased approximately ×10–15 in creeks mimicking short-term (2-month) and chronic (6-year) eutrophication. We assessed the diets of epifaunal invertebrates (three gastropods and one amphipod species) that potentially graze on benthic algae using natural isotope abundance data and per capita grazing rate measurements derived from ¹³C prelabeled algae. Substantial dietary contributions from benthic algae were observed in all consumers even though previous research has indicated most rely on Spartina detritus as the principal food resource. The amphipod Orchestia grillus and the snail Melampus bidentatus grazed benthic algae in excess of 500 μg algal C g C^?1 h^?1, whereas the snail Nassarius obsoletus and hydrobiid snails grazed at lower rates. Few dietary changes were detected with short-term enrichment. Algal grazing rates of N. obsoletus and M. bidentatus increased with chronic enrichment probably as a functional response to increased algal productivity. O. grillus grazed at a high rate and parasitic infection did not affect its consumption of benthic algae. The abundance and frequency of occurrence of O. grillus on creek-wall habitats increased with chronic nutrient enrichment suggesting amphipods contribute to top–down control on benthic algae and slow algal growth as nutrient enrichment occurs.     

Biogeochemical cycling in an organic-rich coastal marine basin—I. Methane sediment-water exchange processes

Methane produced in anoxic organic-rich sediments of Cape Lookout Bight, North Carolina, enters the water column via two seasonally dependent mechanisms: diffusion and bubble ebullition. Diffusive transport measured in situ with benthic chambers averages 49 and 163 μmol · m ^?2 · hr ^?1 during November–May and June–October respectively. High summer sediment methane production causes saturation concentrations and formation of bubbles near the sediment-water interface. Subsequent bubble ebullition is triggered by low-tide hydrostatic pressure release. June–October sediment-water gas fluxes at the surface average 411 ml (377 ml STP: 16.8 mmol) · m^?2 per low tide. Bubbling maintains open bubble tubes which apparently enhance diffusive transport. When tubes are present, apparent sediment diffusivities are 1.2–3.1-fold higher than theoretical molecular values reaching a peak value of 5.2 × 10^?5 cm² · sec^?1. Dissolution of 15% of the rising bubble flux containing 86% methane supplies 170μmol · m^?2 · hr^?1 of methane to the bight water column during summer months; the remainder is lost to the troposphere. Bottom water methane concentration increases observed during bubbling can be predicted using a 5–15 μm stagnant boundary layer dissolution model. Advective transport to surrounding waters is the major dissolved methane sink: aerobic oxidation and diffusive atmospheric evasion losses are minor within the bight.     

Modeling CO2 chemistry, δC, and oxidation of organic carbon and methane in sediment porewater: Implications for paleo-proxies in benthic foraminifera

I present a numerical diffusion-advection-reaction model to simulate CO₂ chemistry, δ¹³C, and oxidation of organic carbon and methane in sediment porewater. The model takes into account detailed reaction kinetics of dissolved CO₂ compounds, H₂O, H⁺, OH⁻, boron and sulfide compounds. These reactions are usually assumed to be in local equilibrium, which is shown to be a good approximation in most cases. The model also includes a diffusive boundary layer across which chemical species are transported between bottom water and the sediment-water interface. While chemical concentrations and δ¹³C_TCO2 at these locations are frequently assumed equal, I demonstrate that they can be quite different. In this case, shells of benthic foraminifera do not reflect the desired properties of bottom water, even for species living at the sediment-water interface (z = 0 cm). Environmental conditions recorded in their shells are strongly influenced by processes occurring within the sediment. The model is then applied to settings in the Santa Barbara Basin and at Hydrate Ridge (Cascadia Margin), locations of strong organic carbon and methane oxidation. In contrast to earlier studies, I show that a limited contribution of methane-derived carbon to porewater TCO₂ in the Santa Barbara Basin cannot be ruled out. Simulation of methane venting shows that at oxidation rates greater than , the δ¹³C of porewater TCO₂ at z > 1 cm is depleted by more than 15‰ relative to bottom water. Depletions of this magnitude have not been observed in living benthic foraminifera, even at methane vents with much higher oxidation rates. This suggests that foraminifera at these sites either calcify at very shallow sediment depth or during times when oxidation rates are much lower than ∼50 μmol cm⁻² y⁻¹.     

Densities ofPenaeus aztecus,Penaeus setiferus,and other natant macrofauna in a Texas salt marsh

Habitat-related densities of natant macrofauna were compared between vegetated and nonvegetated areas in aSpartina alterniflora marsh on Galveston Island, Texas. The most abundant macrofauna were crustaceans,Palaemonetes pugio, Penaeus aztecus, Penaeus setiferus, andCallinectes sapidus, and small fish,Gobiosoma bosci, Lagodon rhomboides, Leiostomus xanthurus, Fundulus similis andMicropogonias undulatus. Excluding residentsP. pugio, G. bosci andF. similis, most of the macrofauna were transient juveniles of estuarine-dependent species. Among crustaceans,P. pugio, P. aztecus, andC. sapidus were significantly more dense in vegetated habitat, butP. setiferus was not consistently more abundant in either vegetated or nonvegetated habitat. Of 29 species of fishes, 14 were usually in vegetation, 11 were more often on nonvegetated bottom, and 5 were indifferent to either habitat. Much seasonal variability in abundances ofP. aztecus, P. setiferus, andC. sapidus, but notP. pugio, could be attributed to changes in temperature, salinity and water-level. Strong selection for vegetated habitat byP. aztecus was related to the historical water-level pattern coinciding with seasonal periods of marsh flooding. Apparently, high seasonal tides during the spring and fall facilitated access to vegetated habitat in the marsh and exploitation by transientP. aztecus. In contrast, strong selection for vegetation byP. pugio, abundant year-around in the marsh, was not similarly influenced by seasonal changes in water-level. Overall, habitat-related densities and physical interactions suggest that marsh physiography together with differences in tides may greatly determine the extent to which certain estuarine macrofauna utilize marsh habitats.     

Benthic macrofaunal communities in partially impounded salt marshes in Delaware: Comparisons with natural marshes and responses to sediment exposure

This two-part study examined the benthic macrofaunal community in Delaware salt marsh impoundments having partial tidal restriction. The first part compared abundance, diversity, and taxonomic composition in three habitat types in impoundments—creeks, vegetated creek banks, and ponds—to those found in natural marshes. Impoundment effects were present but were habitat-specific. Abundances were higher in natural marsh creeks than in impoundment creeks, and diversities were higher in impoundment ponds than in natural marsh ponds. Vegetated bank communities in impoundments were about 50% insects and arachnids and 50% oligochaetes, while natural bank communities were primarily oligochaetes and the polychaeteManayunkia aestuarina. This is likely due to the decrease in flooding of the vegetated high marsh caused by partial impoundment. Pond and creek community composition also showed impoundment effects: in comparison with natural marshes, impoundments had higher proportions of the burrowing anemoneNematostella vectensis, nemerteans, andTubificoides sp. oligochaetes and lower proportions of the oligochaeteClitellio arenarius. The second part of the study compared benthic macrofauna in an impoundment before, during, and after the water level was lowered so that some bottom sediments were exposed and some covered with just a few centimeters of water for several weeks. During this event, macrofaunal abundances were reduced and the community shifted from being dominated by annelids, anemones, and nemerteans toward one dominated by annelids and insects. About 6 wk after reflooding, persistent effects of this disturbance were still suggested by greatly increased abundances and 96% dominance by one species of oligochaete,Paranais litoralis. Impoundment management plans calling for periods of sediment exposure or very low water may want to consider the potential for strong and persistent effects on the macrofaunal community.     

Ammonium excretion by benthic invertebrates and sediment-water nitrogen flux in the Gulf of Mexico near the Mississippi River outflow

Benthic macroinvertebrate biomass and ammonium excretion rates were measured at four stations in the Gulf of Mexico near the Mississippi River mouth. Calculated areal excretion rates were then compared to sediment-water nitrogen fluxes measured in benthic bottom lander chambers at similar stations to estimate the potential importance of macroinvertebrate excretion to sediment nitrogen mineralization. Excretion rates for individual crustaceans (amphipods and decapods) was 2–21 nmoles NH₄ ⁺ (mg dry weight)^?1 h^?1. The mean excretion rates for the polychaetes, Paraprionaspio pinnata [6–12 nmoles NH₄ ⁺ (mg dry weight)^?1h^?1] and Magelona sp. [27–53 nmoles NH₄ ⁺ (mg dry weight)^?1h^?1], were comparable or higher than previous measurements for similar size benthic or pelagic invertebrates incubated at the same temperature (22±1°C). Although the relatively high rates of excretion by these selective feeders may have been partially caused by experimental handling effects (e.g., removal from sediment substrates), they probably reflected the availability of nitrogen-rich food supplies in the Mississippi River plume. When the measured weight-specific rates were extrapolated to total areal biomass, areal macroinvertebrate excretion estimates ranged from 7 μmole NH₄ ⁺ m^?2h^?1 at a 40-m deep station near the river mouth to 18 μmole NH₄ ⁺ m^?2h^?1 at a shallower (28-m deep) station further from the river mouth. The net flux of ammonium and nitrate from the sediments to the water measured in bottom lander chambers in the same region were 15–53 μmole NH₄ ⁺ m^?2h^?1 and ?25–21 μmole NO₃ ^? m^?2h^?1. These results suggest that excretion of NH₄ ⁺ by macroinvertebrates could be a potentially important component of benthic nitrogen regeneration in the Mississippi River plume-Gulf shelf region.     

Palaeoecology, facies and stratigraphy of shallow marine macrofauna from the Upper Oligocene (Palaeogene) of the southern Pre-North Sea Basin of Astrup (NW Germany)

The 22 meter thick marine carbonate Upper Oligocene series of Astrup (NW Germany) is correlated with the Chattian type section of Doberg. It indicates a more constrained palaeogeographical and biostratigraphical position ranging from the biozones of Chlamys (C.) decussata (upper Chattian A) to Chlamys (C.) semistriatus (lower Chattian C). The macrofauna can be subdivided into three main benthic communities: A. the ?coarse gravel spondylid beach fauna?? of the shore zone with ?pebble beach facies?? dominated by sessile brachiopods, large balanids, spondylids, oysters or small regular echinoids. Borings are common in pebbles; B. the ?glauconite fine gravel brachiopod-bryozoan littoral fauna?? of the shallow subtidal zone where a terebratulid/lithothamnid dominated fauna/flora is present. The rhodophyceans were most possibly anker stones and substrates for cirripeds and serpulids; C. the ?glauconite carbonate sand phytal fauna?? of the shallow subtidal zone with a rich benthic mollusc dominated fauna. Indirect evidence for seagrass and macroalgae occurs on the attachment negatives of balanids and oysters, and also on Cibicides foraminifera or bryozoans like Cellepora. The facies types along the Wiehengebirge Island and Teutoburger Wald Peninsula coasts of the southern Pre-North Sea Basin differ with respect to their benthic communities to that of the siliciclastic Leipziger and the Rhenish Bay facies.     

Environmental impact of salmon net-pen culture on marine benthic communities in Maine: A case study

The environmental impacts of salmon net-pen aquaculture on the benthic environment were investigated at a commercial fish farm located in coastal Maine waters. This site has a sandy mud bottom and low current velocities, is subjected to episodic sediment resuspension, and way in production for 3 yr prior to this study: We examined both the increase in carbon flux to the benthos caused by the net-pen and the effects of the elevated flux on sediment biogeochemistry and the microbenthic communities. The experimental design involved the establishment of two study sites, an ambient site ca. 100 m from the net-pen and a treatment site around the pen. Sediment traps deployed 1 m above the sediment-water interface indicated that carbon flux to the benthos was increased 1-fold to 6-fold (to a maximum of 5 g m^?2d^?1) at the edge of the net-pen with little or no increase in carbon flux 10 m from the pen. Unlike carbon flux rates, sediment organic matter inventories showed a complex pattern of change over time. Mineral surface area, organic carbon and nitrogen, digestible protein, and sterol content were initially (April 1991) lower beneath the pen than in ambient sediments. During 1991 ambient sediment accumulated organic matter until July after which it decreased, to a low during November. In contrast, organic matter inventories of sediment beneath the pen remained low until July and then increased to a high during November. These latter gains were associated with the development of bacterial mats at the sediment-water interface. Beneath the pen, microbial and macrofaunal communities were shifted toward those commonly associated with organic enrichment but seasonal trends and storm-related resuspension events also significantly affected these sediment communities. When abundant, most epibenthic organisms were more numerous near the pen than in adjacent ambient areas. These results suggest that net-pen aquaculture can alter the benthic ecosystem in Maine Coastal waters but indicate that the effects are spatially limited.