Cold winter effects on benthic macrofauna communities in near- and offshore regions of the North Sea

In order to investigate the effect of severe winters on the long-term variability of benthic macrofauna communities four stations from the inner German Bight towards the Dogger Bank (North Sea) were sampled in March 1990 and from May 1995 to 2002. The stations were chosen to reflect a gradient in the hydrographic regime, temperature and organic matter supply. We initially hypothesized that the effect of severe winters on benthic communities will be more pronounced in the offshore more stable environment than in the nearshore regions. Our results clearly showed the opposite pattern. The benthic communities at the nearshore stations in the German Bight changed dramatically in species abundance and community structure after the severe winter 1995/1996. But the community structure in the German Bight returned to the previous stage within 2 years. In contrast, the offshore stations in the Oyster Ground and at the Dogger Bank remained rather unaffected by the severe winter and changed gradually during the study period. The results are discussed concerning the ecological importance of severe winters for benthic communities and the utility of our results for interpreting long-term changes.     

Macrofauna standing stock of the Dogger Bank. A comparison: III. 1950–54 versus 1985–87. A final summary

The macrofauna communities on the Dogger Bank in April/May 1985–87 were compared with those in April/May 1950–54 (Ursin, 1960). Unpublished data from Birkett on the central and western Dogger Bank from April/May 1952–54 were also used for the comparison. The changes in the communities from the fifties to the eighties were made clear by the increasing species numbers and in an increase or dominance of short-living opportunistic species. In contrast, a decrease in long-living bivalves was found. The total biomass in 1985–87 was 2.5 to 8 times higher than in 1950–54. Similarities between stations were below 20%. Some hypotheses concerning natural and anthropogenic impacts are given to interpret the observed changes.     

Benthic community structures in the North Sea

Coherent assemblages of marine benthic species have been recognized from the early twentieth century, and the classical papers of Petersen (1914, 1918) were based on studies of limited areas in the North Sea. In 1986, a synoptic survey of the North Sea north to 57°N was undertaken by a group of ten laboratories from seven North Sea countries. The results of this survey have recently been published (Heip et al., 1992a, b; Künitzer et al., 1992; Huys et al., 1992), and some of the results are summarized in this paper. The analysis of the macrofauna is based on slightly more than 700 taxa. In general, the North Sea macrofauna consists of northern species extending south to the northern margins of the Dogger Bank, and southern species extending north to the 100 m depth line. The central North Sea is an area of overlap of southern and northern species, especially around the 70 m depth contour. Consistent groupings of species are recognized that were summarized in seven faunal groupings. Macrofaunal body weight, density and diversity increase linearly towards the north. Macrofaunal biomass for the whole area averages 7 g adwt. m⁻² and decreases from south to north. Distribution patterns and trends within the meiofauna were very different. Nematodes, which are the dominant taxon overall, are least abundant in the sandy sediments of the Southern Bight, then increase to a maximum around 53° 30′ N and slowly decrease again towards the north. Copepod density and diversity are highest in the Southern Bight, due to the presence of many interstitial species. A large number of species new to science were recorded by the North Sea Benthos Survey and about 1500 species are expected to occur. Copepods show very distinct assemblages according to water depth and sediment type. The contrasting patterns in latitudinal gradients of body weight and number of species of macro- and meiofauna can be only partially explained. Latitude and sediment characteristics, such as grain size and content in plant pigments, and water depth, determine part of the variance in species composition, density and biomass of the benthic fauna, but the patterns that are observed are different for different benthic groups, requiring careful consideration as to their use in biological monitoring procedures. Distributions are related to current patterns in the North Sea, annual temperature variations and availability of food. However, large parts of the variance in many parameters remain unexplained.     

Diversity of larger consumers enhances interference competition effects on smaller competitors

Competition between large and small species for the same food is common in a number of ecosystems including aquatic ones. How diversity of larger consumers affects the access of smaller competitors to a limiting resource is not well understood. We tested experimentally how species richness (0–3 spp.) of benthic deposit-feeding macrofauna changes meiofaunal ostracods’ incorporation of fresh organic matter from a stable-isotope-labeled cyanobacterial bloom, using fauna from the species-poor Baltic Sea. Presence of macrofauna mostly decreased meiofaunal incorporation of bloom material, depending on the macrofauna species present. As expected, the species identity of macrofauna influenced the incorporation of organic matter by meiofauna. Interestingly, our results show that, in addition, species richness of the macrofauna significantly reduced meiofauna incorporation of freshly settled nitrogen and carbon. With more than one macrofauna species, the reduction was always greater than expected from the single-species treatments. Field data from the Baltic Sea showed a negative correlation between macrofauna diversity and meiofaunal ostracod abundance, as expected from the experimental results. We argue that this is caused by interference competition, due to spatial niche differentiation between macrofauna species reducing the sediment volume in which ostracods can feed undisturbed by larger competitors. Interference from macrofauna significantly reduces organic matter incorporation by meiofauna, indicating that diversity of larger consumers is an important factor controlling the access of smaller competitors to a limiting food resource.     

Bioavailability of lead in North Sea sediments

As part of an interdisciplinary research programme, lead contents were measured in the polychaeteNephtys spp. and in the sea-urchinEchinocardium cordatum as well as in the respective sediment fractions <20 μm taken from the Dogger Bank proper and the eastern coastal North Sea. A lower lead content was generally observed in the organisms taken from the German Bight than in those from the Dogger Bank, especially from its northeastern part. It is possible to divide both areas according to the slope found in the linear regression of lead versus total organic carbon contents in sediments, which is twice as steep for the Dogger Bank as for the eastern North Sea. This criterium points to a difference in sediment quality with regard to toxic metal contamination. The sediment quality of the Dogger Bank seems to be twice as bad compared with that of the eastern North Sea. This is in good agreement with the differences found in lead contamination of the sediment-dwelling polychaetes from both areas. The results indicate that lead is primarily accumulated by food ingestion.     

Structure and diversity of shallow soft-bottom benthic macrofauna in the Gulf of Lions (NW Mediterranean)

Samples of soft-sediment macrobenthos from 92 sites between 10 and 50 m depth were used to assess (1) the main soft-bottom macrofauna communities in the Gulf of Lions, (2) the different components of the diversity of benthic macrofauna in this area, and (3) the relevance of the use of major taxonomic groups as surrogates for the analysis of the structure and diversity of total macrofauna. Three main communities were identified by cluster analysis and associated procedures. These communities corresponded well to the assemblages recently identified on the basis of polychaete composition. The α-diversity indices were in accordance with those reported for similar communities in the Mediterranean. Conversely, the β-diversity value was higher than the few other data available in the literature for marine soft-bottom macrofauna. The total number of species in the studied area estimated by the “total species accumulation curve” (TS) method was 2,319, which was only 10% higher than the number obtained by extrapolation of the species–area curve. The similarity matrix based on polychaetes correlated best with the one based on total macrofauna. Polychaetes and crustaceans were also the best surrogates of total macrofauna when assessing α-diversity (except in the case of Δ*). Conversely, molluscs were the best surrogates of total macrofauna β-diversity. Our results show that the choice of an optimal surrogate for total benthic macrofauna depends on the characteristic of the benthic macrofauna to be studied. Moreover, this choice is also dependent on the environment to be studied.     

Use of benthic vs planktonic organic matter by sandy-beach organisms: A food tracing experiment with C labelled diatoms

Benthic diatoms are assumed to be of minor importance as food sources in sandy-beach food webs, since they are typically scarce in sandy-beach sediments; whereas organic matter derived from land and sea is known to be more important in sandy-beach food webs. In order to test if benthic and planktonic diatoms play a minor or major role, respectively, in sandy-beach food webs, a laboratory experiment was conducted. Labelled planktonic and benthic diatoms, enriched in the stable carbon ¹³C isotope, were offered as food sources to sandy-beach macrofauna and meiofauna communities. Uptake of both types of diatoms occurred with most of the species, but benthic diatoms were preferentially consumed by two macrofaunal species and all meiofaunal species. This result reveals the importance of benthic carbon sources in both macrofaunal and interstitial food webs, and suggests a link between both food webs through the common use of benthic diatoms.     

Lead and cadmium contents in selected macrofauna species from the Dogger Bank and the eastern north Sea

Lead and cadmium concentrations were measured in the polychaetesNephtys hombergi andN. caeca, in the sea-urchinEchinocardium cordatum, and in the bivalveVenus striatula obtained from the Dogger Bank and the eastern North Sea. The cadmium concentrations determined in all four species from these areas were relatively equal, except for an increase in concentration found in those species from the northeastern part of the Dogger Bank. A lower lead content was generally observed in the individuals taken from the German Bight than in those from the Dogger Bank, especially from its northeastern part. In the case of lead, it is possible to divide the southern North Sea into three regions according to the different concentration levels by statistical treatment: the less contaminated German Bight, the more contaminated central Dogger Bank and the highly affected northeastern Dogger Bank. The results obtained contradict the prevailing opinion that offshore invertebrate populations are, in comparison to individuals from coastal regions, less affected by contaminants such as heavy metals.     

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.     

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.     

Breaking the boundary — The key to bottom recovery? The role of mysid crustaceans in oxygenizing bottom sediments

Large areas of the Baltic Sea bottoms suffer from low oxygen conditions and anoxia, impoverishing the benthic macrofauna. The important macrofaunal function bioturbation, which improves the transport of oxygen into the sediment does not occur in an absence of benthic macrofauna. The objective of this study was to investigate if a semi-pelagic species, like the mysid crustacean Mysis relicta, is able to improve the oxygen conditions of the sediment and thereby acts as a facilitator for re-colonization of azoic sediments by benthic species. We also wanted to study the potential of M. relicta in breaking the diffusive boundary layer under varying degrees of oxygen deficiency. Three types of sediment qualities were used to mimic the severity of oxygen deficiency. Under normoxia, moderate hypoxia (40% O₂) and hypoxia, (20% O₂) M. relicta's bioturbation activity was studied by recording oxygen profiles in sediments with and without mysids. In normoxia the mysids were able to oxygenize the sediment independent of sediment quality. The results show that mysids are able to bioturbate the sediment to some extent in hypoxia independent of the sediment quality. In all treatments with mysids the diffusive boundary layer was more or less completely broken down. In normoxia treatment with sediment of very low quality the mysids prevented growth of the sulphur bacteria Beggiatoa spp. which usually occurs on anoxic bottoms. The ability of this semi-pelagic species to improve benthic oxygen conditions can be seen as an important first step in re-colonization by real benthic species.     

Functional Role of Large Organisms in Intertidal Communities: Community Effects and Ecosystem Function

In marine soft sediments, large organisms are potentially important players in the nonlinear interactions that occur among animals, their food, and their chemical environment, all of which influence the contribution of benthos to ecosystem function. We investigated the consequences of removing large individuals of two functionally contrasting benthic communities on nutrient regeneration, microphyte standing stock, and macrobenthic community composition. The experiment was conducted at two adjacent sites that were physically similar but biologically different, one dominated by large deposit feeders and the other by large suspension feeders. Chemical fluxes were measured in experimental plots, and sediments were sampled to assess changes in macrofauna, sediment grain size, organic content, and microphyte standing stock. Our results demonstrate that the removal of large suspension feeders or deposit feeders influenced the flux of nitrogen and oxygen, surficial sediment characteristics, and community composition. In the deposit-feeder community, interactions between nutrient regeneration and grazing highlight important feedbacks between large macrofauna and biogeochemical processes and production by microphytes, indicating that the loss of large infauna driven by increased rates of anthropogenic disturbance may lead to functional extinction and cause shifts in community structure and ecosystem performance.     

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.     

Interrelationships of bacteria,meiofauna and macrofauna in a Mediterranean sedimentary beach (Maremma Park,NW Italy)

Collelungo beach (Maremma Park, NW Italy), was sampled quantitatively for macrofauna, meiofauna and bacteria in May 2003; several physicochemical variables and variables associated with food availability and sediment structure were also measured. Replicated samples were collected from three sites representing natural conditions, an erosion regime, and the influence of the Ombrone River, respectively, as well as from four stations each located in the surf and sublittoral zones. Both uni- and multivariate techniques were used to assess the benthic community structure and the associated environmental variables. Different diversity indices revealed no pattern; in contrast, multivariate techniques applied on the macrobenthic fauna and the polychaete taxocommunity distinguished between the sites located in natural and eroding conditions from the one located nearby the discharges of the Ombrone river. Τhe community patterns deriving from meio- and macrofauna are clearly divergent. The overall benthic faunal community appears to be influenced by both groups of organisms. The patterns of the meio- and macrofaunal communities seem to be affected synergistically by a number of environmental variables, in accordance with the multicausal environmental severity hypothesis. Meiofaunal patterns are more often correlated with bacteria and the protein concentration than are macrofaunal patterns, indicating a potential utilization of bacteria as a food source by the meiofaunal organisms. Total bacterial numbers are associated with the macrofaunal pattern under the erosion regime, probably as a consequence of competition for food between macrofauna and meiofauna.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

The role of waves in the colonisation of terrestrial sediments deposited in the marine environment

Elevated rates of sediment run-off, as a result of changes in land-use and climate, are a significant threat to marine coastal communities, with a potential to cause broad-scale, long-term alteration of habitats. Individual sedimentation events can smother estuarine flats with terrigenous sediments, creating a significant disturbance to local benthic communities. Variations in the degree to which a habitat is altered, the rate at which mixing occurs, and species-specific dispersal and responses to the altered habitat, suggest that colonisation of terrestrial sediment depositions will vary with location, both between and within estuaries. This study was designed to explore the effect that variations in wave-induced hydrodynamics would have on long-term colonisation of terrestrial sediment depositions on intertidal flats. Sites for the experimental deposition of terrestrial sediment were located along a gradient in wave exposure, with only limited variation in immersion times (30 min) and ambient sediment particle sizes (predominantly fine sand). Over 20 months, periodic measurements were made of factors predicted to affect colonisation: the sediment characteristics of the deposited sediment; local-scale wave climate; bioturbation of the deposited sediment; and local populations of benthic invertebrates. Neither opportunistic use of the new resource, progressive recovery or facilitation by colonising macrofauna was observed. Little vertical mixing of the deposited and existing sediment by either waves or bioturbators occurred; instead bedload transport was the dominant process. Local differences in hydrodynamic conditions and macrobenthic communities resulted in site-specific colonisation of the experimental plots. The strength and duration of the macrofaunal response to deposited sediment observed in this study suggest that chronic small-scale (m's) patchy deposition of terrestrial sediment in the intertidal marine environment has a strong potential to alter both habitats and communities.     

Benthic fauna affects recruitment from sediments of the harmful cyanobacterium Nodularia spumigena

Physical disturbance and feeding by macrofauna in the sediment can potentially affect bloom initiation of phytoplankton species that have benthic stages in their life cycle. In this experimental study, we investigated how different species of macrozoobenthos can affect the recruitment of Nodularia spumigena from the sediment to the water column. N. spumigena is a toxic, nitrogen-fixing filamentous cyanobacterium, which forms large summer blooms in the Baltic Sea. Benthic recruitment from resting stages (akinetes) and vegetative cells deposited on the seafloor have long been suspected to initiate the blooms. We found that, depending on species-specific traits, deposit-feeding macrofauna (an amphipod, Monoporeia affinis, a bivalve, Macoma balthica and an invasive polychaete, Marenzelleria cf. arctia) has the potential to either reduce or facilitate recruitment of this cyanobacterium. Shorter filament length in treatments with fauna than in the treatment without indicates feeding on or mechanical destruction of N. spumigena by the animals. Our results show the importance of an often overlooked aspect of phytoplankton bloom initiation, the role of macrozoobenthos.     

Species identity, diversity and microbial carbon flow in reassembling macrobenthic communities

Intense disturbance may locally destroy patches of habitat and shape the landscape into a mosaic of reassembling communities. The development of ecosystem properties during such community reassembly is poorly understood. In intertidal bare sediments, trophic relations between microphytobenthos or heterotrophic bacteria and macrofauna invertebrates may guarantee fundamental ecosystem properties such as carbon flow through the food web. We studied the dynamic relation between reassembling macrofauna communities and such microbial carbon flow during recovery after severe disturbance. We deliberately induced prolonged hypoxia in winter and early summer and allowed recolonisation for periods of two and five months. Carbon flow was quantified from basal resources (microphytobenthos and bacteria) to intermediate consumers using ¹³C as a tracer. Within the period of study (5 months), microbial carbon flow fully recovered, although macrofauna diversity was still very low compared to the natural communities (ranging from 6 to 17 species). More than 90% of microbial carbon flow to macrofauna was due to the consumers that recolonised within two months. Two of these species were dominant contributors to microphytobenthos carbon transfer to fauna. Furthermore, at an early stage of reassembly, this ecosystem property was remarkably similar when disturbance took place at different times of the year (winter or early summer), although there were differences in assemblage composition and functional diversity. We conclude that species assemblages and ecosystem function developed relatively independently in this benthic system. We discuss which ecological factors may have caused such non-parallel development of macrofaunal communities and carbon flow.     

Influence of the mode of macrofauna-mediated bioturbation on the vertical distribution of living benthic foraminifera: First insight from axial tomodensitometry

We investigated the influence of bioturbation by macrofauna on the vertical distribution of living (stained) benthic foraminifera in marine intertidal sediments. We investigated the links between macrofaunal bioturbation and foraminiferal distribution, by sampling from stations situated on a gradient of perturbation by oyster-farming, which has a major effect on benthic faunal assemblages. Sediment cores were collected on the French Atlantic coast, from three intertidal stations: an oyster farm, an area without oysters but affected by oyster biodeposits, and a control station. Axial tomodensitometry (CT-scan) was used for three-dimensional visualization and two-dimensional analysis of the cores. Biogenic structure volumes were quantified and compared between cores. We collected the macrofauna, living foraminifera, shells and gravel from the cores after scanning, to validate image analysis. We did not investigate differences in the biogenic structure volume between cores. However, biogenic structure volume is not necessarily proportional to the extent of bioturbation in a core, given that many biodiffusive activities cannot be detected on CT-scans. Biodiffusors and larger gallery-diffusors were abundant in macrofaunal assemblage at the control station. By contrast, macrofaunal assemblages consisted principally of downward-conveyors at the two stations affected by oyster farming. At the control station, the vertical distribution of biogenic structures mainly built by the biodiffusor Scorbicularia plana and the large gallery-diffusor Hediste diversicolor was significantly correlated with the vertical profiles of living foraminifera in the sediment, whereas vertical distributions of foraminifera and downward-conveyors were not correlated at the station affected by oyster farming. This relationship was probably responsible for the collection of foraminifera in deep sediment layers (> 6 cm below the sediment surface) at the control station. As previously suggested for other species, oxygen diffusion may occur via the burrows built by S. plana and H. diversicolor, potentially increasing oxygen penetration and providing a favorable microhabitat for foraminifera in terms of oxygen levels. By contrast, the absence of living foraminifera below 6 cm at the stations affected by oyster farming was probably associated with a lack of biodiffusor and large gallery-diffusor bioturbation. Our findings suggest that the effect of macrofaunal bioturbation on the vertical distribution of foraminiferal assemblages in sediments depends on the effects of the macrofauna on bioirrigation and sediment oxidation, as deduced by Eh values, rather than on the biogenic structure volume produced by macrofauna. The loss of bioturbator functional diversity due to oyster farming may thus indirectly affect infaunal communities by suppressing favorable microhabitats produced by bioturbation.