Macrofaunal Species Research Articles

Indirect effects of Atrina zelandica on water column nitrogen and oxygen fluxes: The role of benthic macrofauna and microphytes

The effects of ecosystem engineers can be mediated by direct and indirect interactions. For suspension-feeding bivalves that contribute to benthic–pelagic coupling, indirect effects have been linked to hydrodynamics; however, the influence of these ecosystem engineers may also operate through interactions with surrounding sediments, microphytes and macrofauna that, in turn, affect nutrient and oxygen fluxes. This study investigated the indirect effects of an epibenthic suspension-feeding bivalve ( Atrina zelandica) on ammonium and nitrate–nitrite effluxes from the sediment, and oxygen consumption in the overlying waters, under dark conditions, at two sites with different environmental characteristics. Location-dependent effects were observed in the relative strength of the effect of Atrina on microphyte and macrofaunal abundance. The difference between the strength of the effect of Atrina on macrofauna between sites was not driven by a single species or type of species; rather all the species decreasing in abundance away from Atrina were small species that utilised the sediment water interface. Location-dependent effects were also observed in the relative strength of the effect of microphyte and macrofaunal abundance on oxygen and nutrient fluxes. While microphytes were an important consumer of oxygen at one site, at the other site, small infaunal macrofauna were important. Similarly, the strength of the effect of surrounding macrofauna on ammonium efflux varied between sites. These findings demonstrate the importance of natural history and species functions for understanding complex responses. They suggest that indirect effects by key benthic macrofaunal species in marine systems can also be important to benthic–pelagic coupling. In particular, while key species are often large, excretion and respiration of smaller macrofauna can be important to the exchange of nutrients near the seafloor and oxygen consumption in the benthic boundary layer.

Benthic Impacts of Intertidal Oyster Culture, with Consideration of Taxonomic Sufficiency

An investigation of the impacts from elevated intertidal Pacific oyster culture in a New Zealand estuary showed enhanced sedimentation beneath culture racks compared with other sites. Seabed elevation beneath racks was generally lower than between them, suggesting that topographic patterns more likely result from a local effect of rack structures on hydrodynamic processes than from enhanced deposition. Compared with control sites, seabed sediments within the farm had a greater silt/clay and organic content, and a lower redox potential and shear strength. While a marked trend in macrofaunal species richness was not evident, species composition and dominance patterns were consistent with a disturbance gradient, with farm effects not evident 35 m from the perimeter of the racks. Of the environmental variables measured, sediment shear strength was most closely associated with the distribution and density of macrofauna, suggesting that human-induced disturbance from farming operations may have contributed to the biological patterns. To evaluate the taxonomic sufficiency needed to document impacts, aggregation to the family level based on Linnean classification was compared with an aggregation scheme based on ;general groups' identifiable with limited taxonomic expertise. Compared with species-level analyses, spatial patterns of impact were equally discernible at both aggregation levels used, provided density rather than presence/absence data were used. Once baseline conditions are established and the efficacy of taxonomic aggregation demonstrated, a ;general group' scheme provides an appropriate and increasingly relevant tool for routine monitoring.

Feeding and territorial behavior of Paralvinella sulfincola, a polychaete worm at deep-sea hydrothermal vents of the Northeast Pacific Ocean

Behavioral adaptations to the severe nature and high faunal densities of hydrothermal vent habitats have received little attention from researchers. In this study, video and digital still imagery were analyzed to document the feeding and general behavior of the polychaete Paralvinella sulfincola at deep-sea vents on the Juan de Fuca ridge (North-East Pacific). This worm lives in mucous tubes on the actively growing portions of sulphide mineral chimneys and is considered to be the pioneering macrofaunal species in this habitat. We identified 6 recurrent behavior patterns, including antagonistic territoriality between neighboring conspecifics. The latter likely explains the regular spatial distribution of P. sulfincola populations on the substratum they colonize, and the observed confinement of feeding and exploration activities to a definable territory around the tube opening. Territory size, territorial overlap and density were significantly related to body weight, further supporting the importance of size and aggressive encounters in the maintenance of the worm's feeding area. During feeding, P. sulfincola uses its buccal tentacles to gather particles from the substratum using two different capture modes: seizing single macro-particles and aggregation of small particles.

The use of tracers to evaluate the importance of bioturbation in remobilising contaminants in Baltic sediments

Large areas of the bottom sediments of the Baltic Sea are temporarily or permanently anoxic. These sediments are also an important sink for a variety of contaminants. Reoxygenation of bottom waters allows recolonisation by benthic infauna, which may have important implications for the fate of buried contaminants. This study used tracers to experimentally examine the role of bioturbation by benthic infauna in transporting sediment-associated contaminants in the Baltic Sea. Three different tracer methods were used in two experiments, using three key Baltic macrofaunal species: the amphipod crustacean Monoporeia affinis; the Baltic clam Macoma baltica; and the priapulid worm Halicryptus spinulosus. In the first experiment, a reoxygenation–recolonisation scenario was recreated in the laboratory, using hypoxic sediment cores collected in the field, to determine if there was remobilisation of buried 137Cs from the Chernobyl nuclear accident in 1986. The potential for the infauna to bury newly settled surface contamination was also investigated, using a fluorescent particle tracer. In the second experiment, artificially-created radiolabelled tracer layers ( 14C and 51Cr) were used to quantify both upward and downward movements of organic matter and sediment-associated contaminants by bioturbation. In both experiments there were clear visual differences between the sediment effects of the three species. Halicryptus spinulosus buried deepest into the sediment, creating a network of burrows, Monoporeia affinis burrowed actively in the upper few centimeters of the sediment, and Macoma baltica was quite stationary, but appeared to filter- and deposit feed at the sediment surface. Mixing depths in the hypoxic sediment varied from 4.0 ± 3.5 cm for M. baltica to 7.8 ± 2.1 cm for H. spinulosus. Biodiffusion rates ( D b) were similar for all treatments but biotransport rates ( r) were significantly different between treatments, mainly due to a high r value for H. spinulosus. In the experiment with radiolabelled tracer layers, 51Cr was transported more than 14C, and tracer originally at the surface transported more than tracer buried 4 cm below the surface. There was also transport of all tracers in treatments without added macrofauna. The most likely explanation is bioturbation by the meiofauna that were undoubtedly present in both experiments. Bioturbation by macrofauna both buries surface contaminants and remobilises those that are buried, but the effects are small and on a similar scale to transport caused by meiofauna. In addition, 137Cs profiles at the hypoxic site indicated that resuspension and redeposition of sediment by physical processes had occurred, and also showed that contaminants from the last 40 years were still present in the top 5–10 cm of the sediment, well within active mixing depths. At this site, as at many others in the Baltic, physical processes are likely to be far more important than biological processes in the redistribution of contaminants on a decadal timescale.

Mediterranean Lagoons Revisited: Weakness and Efficiency of the Rapid Biodiversity Assessment Techniques in a Severely Fluctuating Environment

The purpose of this paper is to test the performance of rapid biodiversity assessment techniques in the lagoonal environment at the pan-Mediterranean scale. The multivariate techniques can produce patterns of lagoonal biodiversity along the Mediterranean. Additionally, it is shown that the polychaete inventory can preferably be used rather than the aggregation of information at the family level for the purposes of rapid biodiversity assessment. These techniques, however, appear to be weak for the environmental assessment because they cannot detect differences between the naturally disturbed and the anthropogenically impacted lagoons. Both taxonomic distinctness indices are found to be robust in providing meaningful results for rapid biodiversity/environmental assessment when the crustacean inventory and the polychaete and molluscan ones are used for the estimation of the average taxonomic distinctness and of the variation in taxonomic distinctness values, correspondingly. Conversely, information on the distribution of the macrofaunal species to the Mediterranean lagoons appears to be inadequate for the needs of such rapid biodiversity assessment at a regional scale. It is suggested that information on ecological convergence of the macrofaunal species would probably provide biodiversity indices with additional power, at least in the lagoonal environment.

Does changing the taxonomical resolution alter the value of soil macroinvertebrates as bioindicators of metal pollution?

Ecological indicators are taxa that are affected by, and indicate effects of, anthropogenic environmental stress or disturbance on ecosystems. There is evidence that some species of soil macrofauna (i.e. diameter >2 mm) constitute valuable biological indicators of certain types of soil perturbations. This study aims to determine which level of taxonomic resolution, (species, family or ecological group) is the best to identify indicator of soil disturbance. Macrofauna were sampled in a set of sites encompassing different land-use systems (e.g. forests, pastures, crops) and different levels of pollution. Indicator taxa were sought using the IndVal index proposed by Dufrêne and Legendre [Dufrêne, M., Legendre, P., 1997. Species assemblages and indicator species: the need for a flexible asymetrical approach. Ecological Monographs 67, 345–366]. This approach is based on a hierarchical typology of sites. The index value changes along the typology and decreases (increases) for generalist (specialist) faunal units (species, families or ecological groups). Of the 327 morphospecies recorded, 19 were significantly associated with a site type or a group of sites (5.8%). Similarly, species were aggregated to form 59 families among which 17 (28.8%) displayed a significant indicator value. Gathering species into 28 broad ecological assemblages led to 14 indicator groups (50%). Beyond the simple proportion of units having significant association with a given level of the site typology, the proportion of specialist and generalist groups changed dramatically when the level of taxonomic resolution was altered. At the species level 84% of the indicator units were specialist, whereas this proportion decreased to 70 and 43% when families and ecological groups were considered. Because specialist groups are the most interesting type of indicators either in terms of conservation or for management purposes we come to the conclusion that the species level is the most accurate taxonomic level in bioindication studies although it requires a high amount of labour and operator knowledge and is time-consuming.

Physico-chemical and biological sediment properties determining erosion resistance of contaminated riverine sediments – Temporal and vertical pattern at the Lauffen reservoir/River Neckar, Germany

In order to contribute to a reliable, easy-to-handle and economically viable erosion risk assessment of contaminated riverine sites, the present study aims to implement master-variables best characterising the sediment stability. Thus, a wide range of sediment properties was related to the critical shear stress for mass erosion, determined in the SETEG (Stroemungskanal zur Ermittlung der tiefenabhaengigen Erosionsstabilitaet von Gewaessersedimenten) pressurised channel, with special emphasis on vertical and temporal gradients in the Lauffen reservoir on the River Neckar. Over the course of 1 year, positive impacts of some macrofauna species and benthic diatoms on the sediment stability were detected for the sediment surface (0.5 cm). However, a high seasonal variability of biological parameters caused varying relations with erosion resistance in the upper sediment layers as shown for the colloidal carbohydrates. Considering only deeper sediment layers (5–35 cm), a more general pattern could be revealed with correlations between the critical shear stress and single sediment properties such as depth, grain size, total organic carbon (TOC), cation exchange coefficient (CEC), carbohydrates and proteins. Firstly, the influence of physico-chemical and biological properties on erosion resistance became evident, even over depths at 0–35 cm. Secondly, inter-particle forces are most important for erosion resistance. These are enhanced in fine-grained sediment layers, offering high binding capacities but also strengthened by polymeric substances permeating the void space and coating particles. These covariance patterns of sedimentological and biological parameters are addressed by multivariate statistical tests (principal component analysis), resulting in a higher magnitude of the correlation coefficient between critical shear stress and the master-variables in main component II (polymeric substances, grain size, TOC, CEC; R = 0.77 ) compared to single correlations.

Algae, macrofaunal assemblages and temperature: a quantitative approach to intertidal ecosystems of Iceland

Algae and the associated macrofauna in two Icelandic intertidal ecosystems under cold and warm influence, respectively, were studied with respect to algae-macrofauna relationships and a possible effect of temperature on community structure. Two sites in Iceland were selected, Sandgerdi ligthhouse (64°8′N 22°40′W) on the southwestern coast, and Grimsey Island (66°33′N 18°04′W), in the north, on the Arctic Circle, where sea temperature is considerably lower (5° approximately). The biomass of algae and the number of species of algae and macrofauna were higher in Sandgerdi than in Grimsey, and the patterns of diversity, evenness, biomass and abundance also differed between the sites. In the intertidal zone of Sandgerdi, a total of 28 species of algae and 45 species of macrofauna were identified whereas only 16 algal species and 27 macrofaunal species were found in Grimsey. Canonical correspondence analysis (CCA) using algal biomass as the environmental variable were conducted, and revealed significant relationships between algae composition and the associated macrofauna; some macrofauna taxa showed specific trophic or refuge relationships with algal species. According to the CCA, Corallina officinalis showed the highest correlation with macrofaunal assemblages in both study sites. However, correlations between macrofauna and other algae differed between Grimsey and Sandgerdi. The present study, together with additional observations in Greenland waters, shows a general decrease of species richness and diversity towards the north which may primarily be due to the temperature regime.

Broad-scale effects of marine salmonid aquaculture on macrobenthos and the sediment environment in southeastern Tasmania

A comparison of sediments and associated macrobenthos at sites sampled within 20 fish farm leases distributed across southeastern Tasmania indicated major natural changes along a regional cline. Introduced taxa were strongly represented in the fauna, comprising 45% of total macrofaunal biomass. Large differences were evident between sites affected by different levels of organic farm waste. Sites located adjacent (< 10 m) to farm cages possessed significantly depressed sediment redox levels, a dominance of capitellid and dorvilleid polychaetes, and low macrofaunal species richness. Subtle impacts extended across farm lease areas in the form of depressed redox potential at 40 mm depth and changes to the macrobenthic community, including a prevalence of the dogwhelk Nassarius nigellus and a paucity of the heart urchin Brissus sp. and the maldanid polychaetes Asychis sp. and Rhodine sp. Minor farm effects were also evident at sites sampled 35 m outside farm lease boundaries, most notably as elevated population numbers of the polychaete Terrebellides sp., bivalve Mysella donaciformis and heart urchin Echinocardium cordatum. Amongst the univariate metrics examined, redox potential at 40 mm depth and the ratio of bivalves to total molluscs provided the most sensitive indicators of farm impacts, with the latter metric relatively insensitive to spatial variation between locations within the region studied.

Global Patterns in Sandy Beach Macrobenthic Communities

The data from 161 quantitative sandy beach transect surveys from a wide variety of locations were examined to identify trends and relationships between total marine macrofauna species richness, abundance, and biomass and physical variables. Several physical variables were correlated, especially sand particle size and beach face slope, and spring tide range and beach face slope. Higher latitudes experienced larger waves, and flatter beaches had finer sands, larger waves, and larger tides. Strong correlations were found between species richness and beach slope, tide range, and sand particle size, as well as various indices of beach state. Tropical regions harbored significantly more species than other regions. A new Beach index (BI), based on tide range, beach face slope, and sand particle size, correlated well with species richness, explaining 56% of the variability in the data without considering latitude. Abundance and biomass were best correlated with log(1/beach face slope) and tended to be higher in temperate regions. General patterns are discussed; the new index is evaluated; and the roles of sand, tide, slope, and latitude are considered. It is concluded that for regional studies log(1/beach face slope) is the most useful index to compare beaches, whereas for wider comparisons covering areas of differing tide range, BI might be most useful. These patterns have implications for global biodiversity management on sandy beaches.

Community structure in mussel beds at Logatchev hydrothermal vents and a comparison of macrofaunal species richness on slow‐ and fast‐spreading mid‐ocean ridges

AbstractSpecies lists for vent fields on the Mid‐Atlantic Ridge (MAR) from 14°N to 38°N suggest that there is a northern (&gt;27°N), shallow (&lt;2000 m) fauna and a southern (&lt;27°N), deeper (&gt;3000 m) endemic vent fauna, but little is known about how community structure varies along the ridge axis. In this study, quantitative samples of macrofaunal invertebrates associated with mussels (Bathymodiolus puteoserpentis) were collected at Logatchev (14°45′N), the southern‐most explored vent field on the MAR. Community structure (including species composition, species richness, diversity, and relative species abundances) in mussel beds at Logatchev was compared with that of Snake Pit (23°22′N) and Lucky Strike (37°17′N) mussel beds. The most striking feature of the Logatchev mussel‐bed macrofaunal invertebrate community was the tremendous abundance (up to 2390 individuals per liter of mussel‐volume sampled) and biomass of the ophiuroid, Ophioctenella acies. Logatchev and Snake Pit mussel beds share &gt;50% of their associated macrofaunal species; these two sites share only 20–25% of their macrofaunal species with Lucky Strike. Species–effort curves and univariate measures of diversity (H′, J′) do not support the claim that diversity of vent organisms on the MAR is highest at Logatchev, at least when one assesses this within a habitat type. Multivariate analysis readily differentiates the species‐abundance characteristics of Logatchev, Snake Pit, and Lucky Strike mussel‐bed macrofaunas. The relationship between sea‐floor spreading rate and diversity was explored through comparison of species richness in mussel‐bed habitats on slow‐spreading (MAR), fast‐spreading [northern East Pacific Rise (EPR)], and ultra‐fast‐spreading (southern EPR) mid‐ocean ridges. Species richness was greater in samples from the faster‐spreading ridge axes, where vents are more closely spaced but shorter lived, than on slow‐spreading centers, where vents are further apart but longer lived.

영암호 저서동물군집에 미친 하구둑 건설의 영향

To assess the macrobenthic community of oligohaline Youngam Lake, which is located at the Youngsan Watershed on the southwest part of Korea, macrobenthic fauna were collected at 45 stations during May, 2002. A total of 16 species of macrofauna were recorded with a mean density of 240 individuals per <TEX>$m^2$</TEX> and a mean biomass of 7.07 g wet weight per <TEX>$m^2$</TEX>. Major dominant faunal groups were crustacean arthropods in terms of the number of species and abundance, and polychaete annelids in terms of biomass. The mean grain size was <TEX>$5.7\;{\phi}$</TEX> which was dominated by silt fraction. The hydrological environment of the lake was characterised as an oligohaline environment with a mean surface water temperature of <TEX>$17.8^{\circ}C$</TEX> and a mean salinity of 2.08 psu. The major dominant species were amphipods, Corophium sp. (<TEX>$31\%$</TEX>) and Jesogammarus sp. (<TEX>$25\%$</TEX>). Lowe. values of species diversity (H') with a mean of 0.81 (less than 1.0 from most stations) reflected the overall poor faunal diversity in this area. Multivariate analysis suggested that this benthic faunal community could be divided into four sub-regions such as the area from lake proper to water channel to the south, the stations located at the entrance and northern water channel, the stations near the dike, and the lake proper area. Freshwater and brackish water species which occurred in each station group were corresponded to the oligohaline salinity regime. Bottom hypoxia appeared in the entrance part of the lake between dyke and lake proper on May, which was resulted from stratification from spring season. These facts imply that marine macrobenthos were severely impacted by low salinity and a consequent hypoxia after embankment of the lake due to the restriction of water circulation.

The relative importance of habitat complexity and surface area in assessing biodiversity: Fractal application on rocky shores

Theoretical work predicts that complex habitats allow more species to co-exist in a given area. However, more field studies are still needed to clarify this relationship, especially in intertidal habitats. Furthermore, the potential separate effects of surface complexity and area on species richness and abundance have rarely been addressed. We tested the hypotheses that a more complex substratum or larger surface area will support a greater number of individuals and species of mobile macrofauna on three rocky shores in Hong Kong. Surface complexity, assessed by using fractals, was an important factor in species–area relationships. The number of species increased proportionally to habitat complexity and this relationship was homogeneous among different shores. Total abundance of animals, however, was more dependent on the available surface area. The slope of the size–frequency distribution of animals in samples taken on surfaces with different fractal dimensions ( D) was significantly steeper with an increase in fractal dimension, showing that the relative abundance of small animals increased with surface complexity. Thus, surface complexity and area may be important in determining different aspects of the macrofaunal community structure on rocky shores. The resulting increase in surface area on more rough surfaces may introduce bias in density and species number assessments when two-dimensional sampling units (i.e., quadrats) are employed. It is necessary, therefore, to account for the surface complexity in the design and interpretation of the results of benthic studies. Using D as an index of surface complexity is very useful, but also involves some practical problems, e.g., surfaces may be anisotropic and different methods may give different estimates of D. Therefore, these different methods need to be calibrated before comparisons of D values between them are meaningful.

Preservation effects on wet weight, dry weight, and ash-free dry weight biomass estimates of four common estuarine macro-invertebrates: no difference between ethanol and formalin

Two preservative treatments traditionally used in aquatic sciences, formalin (4%) and ethanol (70%), were compared for their effects on biomass estimations. The effects of both preservatives on wet weight, dry weight, and ash-free dry weight were determined for samples preserved for 10, 21, and 90 days. The effects were studied in four different macrofauna species commonly found in German estuaries: Heteromastus filiformis (Capitellidae, Polychaeta), Hediste diversicolor (Nereididae, Polychaeta), Corophium sp. (Amphipoda, Crustaceae), and Gammarus spp. (Amphipoda, Crustacea). The biomass estimates of preserved samples were compared with those of unpreserved samples. In all four species the loss in wet weight, dry weight, and ash-free dry weight was most pronounced within the first 10 days, and an additional weight loss was recorded between days 10 and 21. However, there was no further loss in weight for samples kept for as long as 90 days in the preservatives. In general, crustaceans exhibited higher weight loss than polychaetes, and smaller species (H. filiformis and Corophium sp.) showed higher weight loss and a higher variability than larger species. As our main result, significant differences between the two preservative treatments did never occur. Our results contradict some earlier investigations on this matter where formalin has been reported to be superior to alcoholic preservatives because weight loss was less pronounced than in ethanol. Factors affecting biomass estimates are discussed and we conclude that, for the macrofauna groups tested, the use of the toxic formalin solution is not justified when the major intent is biomass estimation.

Macrofauna diversity in Posidonia oceanica detritus: distribution and diversity of mobile macrofauna in shallow sublittoral accumulations of Posidonia oceanica detritus

The mobile macrofauna in submerged detritus accumulations (SDAs) of the seagrass Posidonia oceanica was investigated in the Bay of Calvi, Corsica, Mediterranean Sea. The distribution of the macrofauna was related to the exposure of the habitat and to the degree of packing and decomposition of the SDAs. In the less decomposed, younger SDAs, the number of individuals per species, but also species richness, was relatively low. In the more decomposed, older SDAs, the abundance and number of species increased, showing predominance of a few crustacean taxa such as gammaridean amphipods, shrimps and the leptostracan Nebalia bipes. Many of the macrofaunal species in the SDAs are members of the animal communities of surrounding seagrass meadows or adjacent hard or soft bottoms, while others, like N. bipes, apparently live in closer association with the SDAs.

Relative influences of bioturbation and physical mixing on degradation of bloom-derived particulate organic matter: Clue from microcosm experiments

Chloropigment profiles observed in coastal marine sediments imply that the fate of bloom-derived organic matter is simultaneously affected by physical and biological mixing processes, but these influences are poorly differentiated by field measurements. To test relative influences of biological versus physical mixing processes on organic matter degradation, we conducted a series of microcosm experiments in three simulated mixing regimes: bioturbated, episodically physically mixed, and unmixed. Algal materials (uniformly 13C and 15N-labeled) were added on the surface of homogenized (pre-sieved) sediment cores as a simulation of natural deposition of bloom-derived organic matter (with an increase of 30–40 nmol chlorophyll- a in 1 g of dry sediment). Biological mixing was initiated by adding a group of macrofauna or individual species into the sediment cores while physical mixing was manipulated by mechanically stirring the surface sediment at variable frequency. We followed the time-dependent and depth-dependent variations of algal organic matter ( 13C-POC and 15N-PON) and chloropigments in simulated mixing regimes over 1-month incubations. The analytical results showed that algal organic matter and chlorophyll- a (Chl- a) degraded coincidentally but the degradation rates varied in different mixing regimes, which was likely related to variable redox conditions created by different mixing processes. In general, physical mixing immediately transported the fresh particulate organic matter from the oxic surface to the deep anoxic sediments, where 13C-POC, 15N-PON and Chl- a degraded at a 3–5× slower rate than those in the unmixed and bioturbated sediments. No matter how frequently the sediments were stirred, similar amounts of 13C-POC, 15N-PON, and Chl- a remained in all physically mixed cores after 1 month. On the other hand, biological mixing created an oscillating oxic/anoxic environment for degradation of algal organic matter through irrigation to deepen dissolved oxygen penetration and via reworking to mix particles between oxic and anoxic sediments. However, the influences of biological mixing on organic matter degradation varied with macrofaunal species and their behaviors. In the unmixed regime, 13C-POC, 15N-PON, and Chl- a from the added algal materials degraded under continuous oxic conditions on the sediment–water interface at similar rates to those in the bioturbated sediments.

Relative importance of macrofaunal burrows for the microbial mineralization of pyrene in marine sediments: impact of macrofaunal species and organic matter quality

The significance of macrofaunal burrows for microbial organic matter mineralization is well recognized. However, despite the importance of marine sediments as main sinks for organic particle-reactive contaminants such as polyaromatic hydrocarbons (PAHs), the significance of biogenic structures for microbial pollutant mineralization is largely unknown. We measured microbial mineralization of the PAH pyrene in different sediment compartments (surface, burrow and reduced bulk sediments) as a function of contamination history (uncontaminated and pyrene-exposed), macrofaunal species (Amphiura filiformis and Nereis diversicolor) and sediment organic matter quality (labile Tetraselmis sp. and refractory lignin). Sediments were exposed to combinations of the 3 factors for 43 d, after which sediment samples from the 3 compartments were incubated for radio-respirometric measurements in 1 4 C-pyrene-coated flasks to monitor 1 4 CO 2 production (i.e. pyrene mineralization) for 128 d. Pyrene exposure enhanced microbial pyrene mineralization (MPM) rates by an order of magnitude in all compartments, signifying MPM as inducible. MPM rates increased successively from reduced bulk to burrow and surface sediments in uncontaminated treatments, while MPM rates were highest in burrows when exposed to pyrene. This emphasizes the oxygen dependence of MPM and pinpoints burrows as MPM hot spots. Enrichment with labile organic matter doubled MPM rates in pyrene-exposed surface sediment, likely fertilizing MPM where oxygen is readily available. Burrow sediment MPM rates were doubled with A. filiformis, suggesting species-specific stimulation of the microbial community within the burrows. In conclusion, burrow sediment appears to be at least as important as surface sediment for microbial PAH degradation in marine sediments. Furthermore, macrofaunal biodiversity, sedimentation events and the trophic state of the system should be taken into account when the fate and effects of organic contaminants are assessed in marine systems.

Processing of 13C-labelled phytoplankton in a fine-grained sandy-shelf sediment (North Sea): relative importance of different macrofauna species

On-board and in situ experiments with 13 C-labelled diatoms were carried out to investigate the processing of algal carbon by the macrofauna community of a fine sandy-shelf site in the southern German Bight (North Sea). The time series (12, 30, 32 and 132 h incubations) was supplemented by additional laboratory experiments on the role of the dominant macrofauna organism, the bivalve Fabulina fabula (Bivalvia: Tellinidae), for particulate organic matter subduction to deeper sediment layers. The specific uptake of algal 13 C by macrofauna organisms was visible after 12 h and constantly increased during the incubation periods. F. fabula, a facultative (surface) deposit- and suspension-feeder, Lanice conchilega (Polychaeta: Terebellidae), a suspension-feeder and the (surface) deposit-feeder Echinocardium cordatum (Echinodermata: Spatangidae) were responsible for the majority of macrofaunal carbon processing. Predatory macrofauna organisms like Nephtys spp. (Polychaeta: Nephtyidae) also quickly became labelled. The rapid subduction of fresh organic matter by F. fabula down to ca. 4 to 7 cm sediment depth could be demonstrated, and it is suggested that entrainment by macrofauna in this fine-grained sand is much more efficient than advective transport.

Composition and Abundance of Benthic Macrofauna of a Tropical Sea-Grass Bed in North Queensland, Australia

The aims of this study were to characterize the functional composition of benthic macrofauna of a tropical sea-grass bed and to determine temporal variations in abundance of benthic macrofauna in relation to environmental factors such as sea-grass biomass, temperature, salinity, and sediment type. Benthic macrofaunal composition and abundance were investigated by core sampler during April 1999, October 1999, March 2000, and August 2000 at three stations within a sea-grass bed at Cockle Bay in North Queensland, Australia. A total of 110 species of benthic macrofauna was collected. Polychaetes were the most abundant group (37 species; 52% of total macrofaunal numbers; 47% of biomass) followed by amphipods (27 species; 35% of total numbers). Decapods were also important, with 28 species contributing 31% of total macrofaunal biomass. Other miscellaneous groups were tanaids, isopods, and ophiuroids. Most amphipods (65%) and decapods (90%) were epifaunal, but polychaetes were equally represented by epifauna and infauna. Temporal variation in both species composition and abundance was large: the peak number of benthic macrofauna occurred in April 1999 and March 2000, and biomass was highest in April 1999. Benthic macrofauna numbers as well as biomass were lowest in August 2000. These temporal patterns of abundance of benthic macrofauna appeared to correlate closely with temporal variation of sea-grass biomass. In addition, the factors of life cycle and predation by common fish species may be indirectly associated with these patterns of macrofaunal abundance.

Immediate impacts and recovery trajectories of macrofaunal communities following hydraulic clam dredging on Banquereau, eastern Canada

Abstract A hydraulic clam dredging experiment, designed to mimic offshore commercial dredging practices, was carried out at a depth of approximately 70 m on a sandy seabed on Banquereau, on the Scotian Shelf, eastern Canada. The experiment was designed to study the separate and combined effects of dredging through three treatment boxes (Dredging Only, Dredging and Discarding, Discarding Only) and two spatially separated reference boxes. In all, 270 taxa were identified from grab samples. Of these, four bivalves are targeted in the commercial fishery (Arctica islandica, Cyrtodaria siliqua, Mactromeris polynyma, and Serripes groenlandicus) while 266 taxa were non-target species. Sample biomass was dominated by the propellerclam, C. siliqua, and the echinoderm, Echinarachnius parma, while the polychaete, Spiophanes bombyx, was the numerical dominant. The dredges captured 33 invertebrate and two fish taxa, although &gt;80% of the catch biomass comprised propellerclams and echinoderms. Immediately after dredging, most macrofaunal species decreased in abundance, with the greatest declines inside dredge furrows (which covered 53–68% of the area inside the dredged boxes). Large numbers of propellerclams were excavated to the seabed surface, with a large proportion showing massive damage. There were few signs of discards on the sediment surface. Recovery trajectories of target and non-target species were followed for 2 years. Following initial declines in abundance and biomass of most taxa immediately after dredging, there were marked increases in abundance of polychaetes and amphipods after 1 year. Two years after dredging, abundances of opportunistic species were generally elevated by ≫100% relative to pre-dredging levels. Two years after dredging, average taxonomic distinctness had decreased (i.e. taxonomic relatedness between species had increased) due, in part, to increased numbers of species of certain polychaetes and amphipods, while communities had become numerically dominated (50–70%) by S. bombyx. It is concluded that the disturbed community was still in the colonizing phase 2 years after dredging. The mobile brittlestar, Ophiura sarsi, displayed increases in abundance ranging from 200% to 300% in the dredged and reference boxes over the 2-year post-dredging. A similar response of non-target macrofauna in the reference boxes suggests, possibly, a coincident natural recruitment pulse. Dredging resulted in pronounced, sustained reductions in biomass (up to 67%) of the target bivalves with no signs of recovery after 2 years. Recruitment of target bivalves (&gt;1-mm shell length) was very low throughout the experimental area during this interval.