Midlittoral polychaete communities in the Eastern Mediterranean Sea: new information from the implementation of the Natural Geography in Shore Areas (NaGISA) protocol and comparisons at local and regional scales

The aim of this study was to attempt to fill current knowledge gaps on midlittoral Mediterranean biodiversity at local and regional scales, by using benthic polychaetes as a model taxon. Two different data sets were analysed: (i) a quantitative data set from the two Natural Geography in Shore Areas (NaGISA) study sites in Crete and (ii) a qualitative data set from multiple sites across the Mediterranean. At the local scale, the results provide evidence that (i) discrete species communities are formed in midlittoral Mediterranean habitats, which vary by geographical location and year, depending on the scale of observation; (ii) macrophyte coverage and Chl‐a are the only environmental variables associated, albeit weakly, with the above pattern; (iii) although naturally disturbed, the Cretan NaGISA sites do not seem to experience any anthropogenic stress; (iv) environmental heterogeneity and history seem to be much less important in shaping the polychaete communities than inter‐specific interactions; however, it is not possible to specify at this stage whether local or regional processes or even their interactions may shape the polychaete communities. At the regional scale, the results indicate that (i) the only factor that seems to be involved in the regional pattern is the identity of the study providing the data sets, which implies variability and bias in how research projects are carried out, from the sampling design through to data collection and analysis; (ii) the Cretan NaGISA sites may be considered as representative of the habitat in the Mediterranean, under certain conditions.     

Polychaete Fauna of Seagrass Beds (Halodule wrightii Ascherson) Along the Coast of Rio de Janeiro (Southeast Brazil)

Abstract.  The polychaete community structure from six Halodule wrightii seagrass beds along the Rio de Janeiro coast (Southeast Brazil) was investigated. Variations in species diversity, overall density and species composition in relation to sediment grain size, seagrass biomass and selected plant structural features such as root and shoot length from the study sites were analysed. Ten core samples (0.02 m²) were randomly collected from each site. Three additional samples were taken for grain size analysis of sediment. Sixty-eight species of polychaetes belonging to 24 families were found. The dominant species as well as species composition varied greatly among sites, showing that a typical polychaete community does not exist. The number of species was positively correlated with the silt-clay percent and sorting coefficient of the sediment. A positive correlation between polychaete density and plant biomass was also obtained. Multivariate analysis indicated that polychaete communities were influenced greatly by seagrass plant features: plants with longer shoots harbour mainly surface-deposit feeders such as Magelona papillicornis , whereas plants with a higher root-shoot length relation sheltered mainly suspension or interface feeders like Fabricia filamentosa . This study demonstrates that granulometric properties as well as plant architecture play an important role in structuring the polychaete community. As the community-level response can reflect changes in local seagrass beds, the structure of the polychaete community can be an important indicator for management plans and the restoration of seagrass ecosystems.     

Polychaete Communities Related to Plant Covering in the Médiolittoral and Infralittoral Zones of the Balearic Islands (Western Méditerranean)

Abstract. The polychaete fauna of the subtidal in the médiolittoral and the infralittoral hard bottom zones of the Balearic Islands at depths from 0 to 40m contained 220 species. Five different polychaete communities could be identified by changes in abundance, species richness, species composition, diversity, and trophic structure. In the very clear waters of these islands the infralittoral zone extends to a depth of 40 m and allows us to investigate whether former proposed models of polychaete distribution can be extended to this particular situation.     

Response of intertidal macrobenthic communities to long term human induced changes in the Eo estuary (Asturias, Spain): implications for environmental management

Long term macrobenthos data together with physical habitat parameters were analysed to investigate spatial and temporal changes at an estuary under different anthropogenic pressures, mainly increasing shellfish farming. The aim was to assess the possible impacts of these pressures on the macrobenthic communities by comparing a period before and after changes in these pressures. Benthic samples were seasonally collected in 1990 (before major anthropogenic changes), 2000 and 2005 at the same sampling stations located on three different habitats in the Eo estuary (Northern Spanish coast). Multivariate and univariate methods were used to assess spatial variability of benthic assemblages and to compare community changes over time. Data from 1990 was assumed as the reference situation to appraise the subsequent impacts. We observed a significant spatial variability of the benthic assemblages in the system as a function of habitat heterogeneity in relation to sediment composition, presence/absence and density of seagrasses, and hydrodynamic regime. Changes were detected in the community composition at all sites during this 15 year period. The extent of changes was related to initial community conditions, rather than the intensity of the pressure. The results suggest that the responses of the benthic communities to human induced perturbations occurring in the system are largely dependent on its intrinsic buffer capacity, and that these communities have been able to cope with an increasing environmental stress (organic enrichment). In conclusion, to keep shellfish farming at a sustainable level without undesirable impacts, the disturbance intensity must be kept below the system carrying capacity. This will allow natural communities to cope with pressures and thus avoid further deterioration in ecological quality.     

Marine environmental quality assessment using polychaete taxocene characteristics in Vancouver Harbour

Polychaete taxocene characteristics from seven stations in Vancouver Harbour obtained during the PICES Practical Workshop are presented. Thirty families and 79 polychaete species were identified. Polychaete density ranged from 194.0 individuals m(-2) in Port Moody Arm to 846.0 individuals m(-2) in the Central Harbour, with a mean abundance over the seven stations of 428.9 individuals m(-2). Biomass varied from 3.0 g wet wt. m(-2) to 28.5 g wet wt. m(-2), with a mean biomass for the seven stations of 12.9 g wet wt. m(-2). High species diversity and richness of polychaete taxocene were observed at two stations, the West Vancouver Laboratory in the Outer Harbour and at a far field reference station in Thornborough Cannel. Sediment quality assessment indicated severe adverse effects at two sites in Port Moody Arm, where high concentrations of chlorinated hydrocarbons and some trace metals were found. A limited number of species, dominance of pollution-tolerant Tharyx multifilis, and the lowest values of polychaete biomass and indices of richness and diversity were detected in Port Moody Arm. Rich species composition and domination of pollution-sensitive species provided evidence of unstressed communities at the far field reference station. Sites in the Outer Harbour, Central Harbour and Indian Arm were characterised by intermediate pollutant exposure.     

The influence of geological, geochemical, and biogenic habitat heterogeneity on seep biodiversity

Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.     

Floating and fixed artificial habitats: Spatial and temporal patterns of benthic communities in a coral reef environment

While natural marine habitats with motion capabilities, e.g., kelps and seaweeds, have been studied alongside their associated fouling communities, little is known of the effect of motion on the communities of floating artificial habitats such as buoys, rafts, and pontoons, particularly in tropical systems. Hydrodynamic features greatly differ between floating and fixed artificial substrata, which in turn affect the structure of their associated communities. This study tested the hypothesis that floating and fixed artificial installations in a tropical reef system (Eilat, Red Sea) would support different benthic communities throughout space and time. Specifically, we examined differences in communities recruited onto settlement plates between floating and fixed installations deployed at three different sites, along a two-year monitoring period. The three sites exhibited distinct differences in species assemblages between the monitoring dates (6, 12, 18 and 24 months post deployment), mainly between the first and the last two dates. The average level of dissimilarity between floating and fixed installations increased over time at all sites. Over 50% of the dissimilarity between the floating and fixed installations resulted from five taxonomic groups i.e., bryozoans, bivalves, barnacles, sponges, including the amount of bare space on the settlement plates. The contribution of these groups to the dissimilarity changed both temporally within each site, and spatially among sites. The observed differences were related to the hydrodynamic characteristics of floating and fixed habitats, interacting with biotic features such as predation, successional processes and seasonality; and abiotic features including small-scale spatial changes, light, and position in the water column.     

Community structure and nutrition of deep methane-seep macrobenthos from the North Pacific (Aleutian) Margin and the Gulf of Mexico (Florida Escarpment)

Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200–3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep‐water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow‐seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane‐derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 ± 11,618 ind·m⁻²), the lowest in the Florida pogonophoran fields (926 ± 132 ind·m⁻²), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non‐seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (>60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H′) was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non‐seep sediments. Community composition differences between seep and non‐seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep δ¹³C and δ¹⁵N signatures were lighter for seep than non‐seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest δ¹³C values (average of species’ means) were observed at the Florida escarpment (−42.8‰). We estimated that on average animal tissues had up to 55% methane‐derived carbon in Florida mats, 31–44% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9–23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific δ¹³C variation (>30‰) between patch types. Overall we found few characteristic communities or features common to the three deep‐water seeps (>3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.     

Importance of seep primary production to Lophelia pertusa and associated fauna in the Gulf of Mexico

To investigate the importance of seep primary production to the nutrition of Lophelia pertusa and associated communities and examine local trophic interactions, we analyzed stable carbon, nitrogen, and sulfur compositions in seven quantitative L. pertusa community collections. A significant seep signature was only detected in one of the 35 species tested (Provanna sculpta, a common seep gastropod) despite the presence of seep fauna at the three sample sites. A potential predator of L. pertusa was identified (Coralliophila sp.), and a variety of other trophic interactions among the fauna occupying the coral framework were suggested by the data, including the galatheid crab Munidopsis sp. 2 feeding upon hydroids and the polychaete Eunice sp. feeding upon the sabellid polychaete Euratella sp. Stable carbon abundances were also determined for different sections of L. pertusa skeleton representing different stages in the growth and life of the aggregation. There was no temporal trend detected in the skeleton isotope values, suggesting that L. pertusa settles in these areas only after seepage has largely subsided. Isotope values of individual taxa that were collected from both L. pertusa and vestimentiferan habitats showed decreasing reliance upon seep primary production with average age of the vestimentiferan aggregation, and finally, no seep signature was detected in the coral collections. Together our data suggest that it is the presence of authigenic carbonate substrata, a product of past seep microbial activity, as well as hydrodynamic processes that drive L. pertusa occurrence at seep sites in the Gulf of Mexico, not nutritional dependence upon primary production by seep microbes.     

Biodiversity and community composition of sediment macrofauna associated with deep-sea Lophelia pertusa habitats in the Gulf of Mexico

Scleractinian corals create three-dimensional reefs that provide sheltered refuges, facilitate sediment accumulation, and enhance colonization of encrusting fauna. While heterogeneous coral habitats can harbor high levels of biodiversity, their effect on the community composition within nearby sediments remains unclear, particularly in the deep sea. Sediment macrofauna from deep-sea coral habitats (Lophelia pertusa) and non-coral, background sediments were examined at three sites in the northern Gulf of Mexico (VK826, VK906, MC751, 350–500 m depth) to determine whether macrofaunal abundance, diversity, and community composition near corals differed from background soft-sediments. Macrofaunal densities ranged from 26 to 125 individuals 32 cm⁻² and were significantly greater near coral versus background sediments only at VK826. Of the 86 benthic invertebrate taxa identified, 16 were exclusive to near-coral habitats, while 14 were found only in background sediments. Diversity (Fisher’s α) and evenness were significantly higher within near-coral sediments only at MC751 while taxon richness was similar among all habitats. Community composition was significantly different both between near-coral and background sediments and among the three primary sites. Polychaetes numerically dominated all samples, accounting for up to 70% of the total individuals near coral, whereas peracarid crustaceans were proportionally more abundant in background sediments (18%) than in those near coral (10%). The reef effect differed among sites, with community patterns potentially influenced by the size of reef habitat. Taxon turnover occurred with distance from the reef, suggesting that reef extent may represent an important factor in structuring sediment communities near L. pertusa. Polychaete communities in both habitats differed from other Gulf of Mexico (GOM) soft sediments based on data from previous studies, and we hypothesize that local environmental conditions found near L. pertusa may influence the macrofaunal community structure beyond the edges of the reef. This study represents the first assessment of L. pertusa-associated sediment communities in the GOM and provides baseline data that can help define the role of transition zones, from deep reefs to soft sediments, in shaping macrofaunal community structure and maintaining biodiversity; this information can help guide future conservation and management activities.     

Deep-sea habitat heterogeneity influence on meiofaunal communities in the Gulf of Guinea

To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200 km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150–4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes. The meiofaunal communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with the different identified habitats. The two control sites, located at >100 km away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The remote operated vehicle (ROV) Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of S. mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone.     

Does beach seine fishery permanently alter macroinvertebrate communities and sediment characteristics in the Southern Caspian Sea?

The impacts of a beach seine fishery on macroinvertebrate communities and sediment characteristics were investigated in the Southwest Caspian Sea. Samples from a single impacted site that was regularly seined were compared with two control sites outside the fishing area. Benthic macroinvertebrates were sampled on four occasions: 6 months prior to the opening of the beach seine fishery (Time 1), 1 day immediately after the closing of beach seining (Time 2), 1 week after closing (Time 3), and 1 month after closing (Time 4). No significant differences were detected in total density, Shannon diversity, or evenness of the macroinvertebrate assemblages between impact and control sites. Unlike density, species richness increased significantly immediately after fishery closure at all sites. A significant difference was detected in the number of species between Time 2 and Time 3 at all sites and the number of species was reduced at Time 4 in all sites. Pontogammarids increased by twofold in the impact site 1 day immediately after closing beach seine fishery and leveled off toward the end of the closed season. The amplified density of pontogammarids 1 day after fishery closing at the impact site might be driven in part by an increase in sediment oxygen content resulting from disturbance of the sea floor. An alternative explanation is that the effect of fish predation on pontogammarids has largely been minimized at the impact site after 6 months of continuous fishing activity. No significant changes in the sedimentary organic content and chlorophyll‐a between the impact and control sites were observed during the courses of sampling; however, a significant change occurred between the average sedimentary pheopigment content of the control sites and that of the impact site. The conclusion from the present study is that beach seine fishery does not harm to benthic communities. The closed season also seemed to allow recovery to pre‐season levels of macroinvertebrate richness and sedimentary chlorophyll‐a.     

More about taxonomic sufficiency: a case study using polychaete communities in a subtropical bay moderately affected by urban sewage

The taxonomic sufficiency approach has been proposed as a surrogate for the typical analysis of speciesabundance data, especially in conditions involving prominent pollution gradients. Here, we evaluate the use of taxonomic sufficiency with infralittoral macrobenthic data derived from samples taken in a moderate polluted subtropical environment in southeastern Brazil, analysing five taxonomic levels and including two functional levels throughout polychaete feeding guilds and trophic groups. The data were collected seasonally at nine stations and studied for two abundance data series (0.5 and 1.0 mm sieve mesh-size). The results showed a similar ordination pattern between the two sieve mesh-size, but with the 0.5 mm sieve data a different pattern was observed during austral summer. A slight loss of information was detected using genus, family, polychaete species and their feeding guilds as taxonomic/ functional units. These results together with those of the cost/ benefit ratio, suggested that the family level seemed to be sufficient to detect the impact caused by moderate pollution in this shallow-water, subtropical environment. In additional, through the use of feeding guilds, similar patterns are obtained. Correlation analysis showed that chlorophyll a, total organic matter, zinc, and chromium sediment content were the variables that best explained the biological pattern observed and not always the best correlation coefficient occurring at the species level. The feeding guild approach seems to be useful and generates interpretable results similar to those obtained with the species level of the whole macroinfauna. The results showed an important cost reduction in the sample processing, suggesting that it is possible to adopt a coarser taxonomic level monitoring program even in species-rich communities.     

Oil refineries: a review of their ecological impacts on the aquatic environment

Pollution of the aquatic environment occurs from many different sources including from oil refineries. Oil refinery effluents contain many different chemicals at different concentrations including ammonia, sulphides, phenol and hydrocarbons. The exact composition cannot however be generalised as it depends on the refinery and which units are in operation at any specific time. It is therefore difficult to predict what effects the effluent may have on the environment. Toxicity tests have shown that most refinery effluents are toxic but to varying extents. Some species are more sensitive and the toxicity may vary throughout the life cycle. Sublethal tests have found that not only can the effluents be lethal but also they can often have sublethal effects on growth and reproduction. Field studies have shown that oil refinery effluents often have an impact on the fauna, which is usually restricted to the area close to the outfall. The extent of the effect is dependent on the effluent composition, the outfall's position and the state of the recipient environment. It is possible to detect two effects that oil refinery effluent has on the environment. Firstly it has a toxic effect close to the outfall, which is seen by the absence of all or most species. Secondly there is an enrichment effect which can be distinguished as a peak in the abundance or biomass. These effects are not limited to just oil refinery effluents, which makes it difficult to distinguish the effects an oil refinery effluent has from other pollution sources. The discharge from oil refineries has reduced in quantity and toxicity over recent decades, allowing many impacted environments in estuaries and coasts to make a substantial recovery.     

Metazoan meiofaunal communities at cold seeps along the Norwegian margin: Influence of habitat heterogeneity and evidence for connection with shallow-water habitats

Cold-seep environments and their associated symbiont-bearing megafaunal communities create islands of primary production for macro- and meiofauna in the otherwise monotonous and nutrient-poor deep-sea environment. To examine the spatial variation and distribution patterns of metazoan meiobenthos in different seepage-related habitats, samples were collected in two regions off Norway: several pockmarks associated with the Storegga Slide including the Nyegga pockmark area (730 m; 64°N), and the active, methane-venting Håkon Mosby Mud Volcano (HMMV) west of the Barents Sea (1280 m; 72°N). Based on sediment geochemistry and associated epifauna, three different habitat types were distinguished across the two regions: (1) reduced sediment with suboxic conditions, sometimes covered by bacterial mats, (2) sediment colonised by chemosynthetic, siboglinid tubeworms, and (3) sediment outside the influence of seepage and without a large chemosynthetic fauna. Meiofaunal communities varied strongly in terms of generic diversity and dominance among the different habitat types. Control sites and Siboglinidae polychaete fields both supported high nematode genus richness similar to normal deep-sea sediments, whereas the reduced sediments yielded a genus-poor nematode community dominated by one or two successful species. Meiofaunal densities in the different habitats were negatively correlated with macrobenthic densities. An extremely dense (>11,000 ind. 10 cm^–2), mono-specific nematode population appeared to be restricted to the bacterial mats at HMMV. It consisted of a new cryptic species of the Halomonhystera disjuncta complex, which has been described from intertidal habitats in the North Sea. The reduced seep sediments at Nyegga did not yield H. disjuncta but were dominated by Terschellingia longicaudata, another cosmopolitan nematode species known to be abundant in organic-rich, oxygen-poor, shallow-water environments. These observations point to a past or recent connection between margins and shallow-water habitats.     

Polychaete Associations in a Subtropical Environment (São Sebastião Channel, Brazil): A Structural Analysis

Abstract. Analysis of polychaetes from 60 quantitative soft bottom samples (November 1993 – August 1994) from the São Sebastião Channel at 10 to 45 m yielded 126 species from a total of 12,003 individuals. The distribution of both the bottom sediment type and species was patchy. Abundance data were analysed with multivariate techniques and revealed a strong correlation between species and sediment variables. Polychaetes were more diverse, abundant and richer in species number in those sites with higher sandy fractions. On the other hand, sites where silt, clay and organic carbon predominated showed a poor annelid fauna. Here, pollution by the sewage discharge of a submarine pipe, the oil terminal activities and the clandestine oil tank washing have an important impact on the bottom fauna. Only little temporal variation in the composition of the polychaete associations was found during the study period.     

Tube-forming polychaetes enhance invertebrate diversity and abundance in sandy sediments of Mozambique,Africa

In marine soft-bottom systems, polychaetes can increase habitat complexity by constructing rigid tubes (e.g. several onuphid species) that contrast with surrounding topographically flat sediments. These structures can provide predation refuges and increase larval settlement and thereby increase the richness and abundance of fauna. We collected invertebrate samples from an intertidal flat with low onuphid tube density (2.7 m^–2) in Mozambique and document that more organisms (70 times higher mollusc abundances) and more species (15 times more mollusc species) were found associated with solitary tubes of an onuphid polychaete compared with surrounding sand habitats. These results are in agreement with tube versus sand comparisons from soft-bottom systems in the North Atlantic where polychaete tube densities are often much higher.     

Changes in Irish Sea Benthos: Possible Effects of 40 years of Dredging

From 1946 to 1951 Dr N. S. Jones sampled the benthos around the south of the Isle of Man from over 200 sites. Multivariate methods have been used here to compare subsets of this historical data with recent data from the same locations: of these locations some have been subject to heavy scallop dredging over the intervening 40 plus years and some to little dredging. Clear changes were apparent regardless of scallop dredging intensity. Some of the changes in the heavily dredged areas were those expected to result from extreme physical disturbance—an increased polychaete mollusc ratio, loss of some fragile species, and an increase in the predominance of scavenger/predator species. However, changes in the lightly dredged areas also included the loss of a number of species including some potentially fragile tube-dwellers. Reasons for these changes were not apparent.     

Polychaete Depth Distribution in a Posidonia oceanica Bed (Rhizome and Matte Strata) and Neighbouring Soft and Hard Bottoms

Abstract. The study was carried out in a Posidonia oceanica bed and in the neighbouring sandy and rocky bottoms, at Ponza Island (Central Tyrrhenian Sea), in order to investigate the distributional pattern of the polychaete community at different depths. A total of 15232 individuals of polychaetes belonging to 218 species was collected and three new species of Syllidae were found. The polychaete community of the matte can be clearly distinguished from the neighbouring communities; this is due to the high species richness in Posidonia , which is related to the heterogeneity of the biotope. In the Posidonia bed the shallow stations (1 m and 5 m depth) were the richest in terms of species numbers and individuals due to the high shoot density of the seagrass bed. In the shallow waters polychaete community structure changed according to the different exposure to water movement. Rocky bottom species, which preferentially inhabit crevices, were more abundant in the matte exposed to water movement (5–10 m depth). In contrast, soft-bottom species were more abundant in the sheltered zone (1 m depth) as well as in the deeper zone due to the reduction of the Posidonia bed.     

Polychaete tubes create ephemeral community patterns: Lanice conchilega (Pallas, 1766) associations studied over six years

On intertidal sandflats spatial patterns of benthic communities are influenced by biogenic habitat structures such as mussel beds or seagrass meadows. These structures represent ecological islands hosting a different and often more diverse and abundant community than surrounding sandflats. However, few studies have been carried out on tube aggregations of the polychaete Lanice conchilega, although its tube tops are conspicuous habitat features on European intertidal coasts with densities reaching several thousand per m².The aim of this study was to determine differences between benthic communities associated with tube aggregations and tube-free areas, and to investigate the longevity of community patterns around L. conchilega tubes. From 1995 to 2000, the L. conchilega population of an intertidal sandflat off the Eastern Friesian coast was sampled annually. Multivariate analysis showed significant differences between the L. conchilega and reference communities. Species diversity and abundance were higher among tube aggregations. This pattern developed rapidly after L. conchilega colonisation but was also readily destroyed, mainly due to dynamic changes of the L. conchilega population.Five species of benthic macrofauna were exclusively found among L. conchilega tubes, and four species were more abundant in tube aggregations than in reference areas. Only one species, the polychaete Aphelochaeta marioni, was found in lower numbers in dense L. conchilega aggregations.Hence, it is concluded that L. conchilega is a habitat engineer, which alters the composition of the benthic community and contributes to its patchy distribution pattern. However, this pattern is dynamic and ephemeral. Effects of tube aggregations depend on the population dynamic of L. conchilega itself and the species composition in the surrounding sands.