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The Harris mud crab Rhithropanopeus harrisii recently expanded into much of the Baltic Sea. This invasion is expected to have significant effects on the structure and functioning of benthic ecosystems due to the lack of native crabs. Habitat type potentially modulates the effects as crabs are expected to behave differently in different habitats. In this study we experimentally evaluated the effect of R. harrisii on the species composition and dominance structure of shallow water meiobenthos within common habitat types of the north-eastern Baltic Sea. Among the studied environmental variables R. harrisii had by far the strongest effects on meiobenthos. The effects of R. harrisii varied among different habitats with the crab mostly modifying taxonomic composition and species abundances of meiobenthic communities on unvegetated soft bottom sediments. Our experiment also showed that boulders provided shelter for R. harrisii and thereby reduced their burrowing activity and effects on the adjacent soft bottom meiobenthos. [ABSTRACT FROM AUTHOR]

Ecosystem engineers contribute to ecosystem functioning by regulating key environmental attributes, such as habitat availability and sediment biogeochemistry. While autogenic engineers can increase habitat complexity passively and provide physical protection to other species, allogenic engineers can regulate sediment oxygenation and biogeochemistry through bioturbation and/or bioirrigation. Their effects rely on the physical attributes of the engineer and/or its biogenic constructs, such as abundance and/or size. The present study focused on tube aggregations of a sessile, tube-building polychaete that engineers marine sediments, Lanice conchilega . Its tube aggregations modulate water flow by dissipating energy, influencing sedimentary processes and increasing particle retention. These effects can be influenced by temporal fluctuations in population demographic processes. Presently, we investigated the relationship between population processes and ecosystem engineering through an in-situ survey (1.5 years) of L. conchilega aggregations at the sandy beach of Boulogne-sur-Mer (France). We (1) evaluated temporal patterns in population structure, and (2) investigated how these are related to the ecosystem engineering of L. conchilega on marine sediments. During our survey, we assessed tube density, demographic structure, and sediment properties (surficial chl- a , EPS, TOM, median and mode grain size, sorting, and mud and water content) on a monthly basis for 12 intertidal aggregations. We found that the population was mainly composed by short-lived (6–10 months), small-medium individuals. Mass mortality severely reduced population density during winter. However the population persisted, likely due to recruits from other populations, which are associated to short- and long-term population dynamics. Two periods of recruitment were identified: spring/summer and autumn. Population density was highest during the spring recruitment and significantly affected several environmental properties ( i.e. EPS, TOM, mode grain size, mud and water content), suggesting that demographic processes may be responsible for periods of pronounced ecosystem engineering with densities of approx. 30 000 ind·m −2 . [ABSTRACT FROM AUTHOR]

Roots and rhizomes of seagrass play an important role in coastline zone by anchoring the substrate firmly which prevent resuspension and also controlling sediment biogeochemistry. The aim of this study was to compare the physical and chemical differences of sediments for 3 seagrass species, which have different root morphology between summer (February 2013) and the monsoon month (September 2013). Seven seagrass communities were studied and are: the mono stand of Halophila ovalis , Thalassia hemprichii , and Cymodocea rotundata , the mixed patches of H. ovalis with T. hemprichii , H. ovalis with C. rotundata , and T. hemprichii with C. rotundata and the mixed patches of 3 seagrass species. The roots of seagrasses were the main driver of differences in sediment properties; the branched, long root species, C. rotundata , showed an increasing redox potential by means of oxygen releasing from their roots. The unbranched, long root with dense root hair species, T. hemprichii , tended to cause more poorly sorted sediments. The carbon storage was also estimated and results showed a trend of higher organic carbon density was in the multispecific patches, the mono specific patches and bare sand, respectively. Season also influenced the sediment properties; high wave action in the monsoon stirred up the sediments, this led to lower organic carbon density and high redox potential. Our results suggest that the roots of seagrass species both increase and decrease sediment properties. [ABSTRACT FROM AUTHOR]

The relationship between acoustic backscatter, sediment grain size and benthic community structure is examined using three different quantitative methods, covering image- and angular response-based approaches. Multibeam time-series backscatter (300 kHz) data acquired in 2008 off the coast of East Anglia (UK) are compared with grain size properties, macrofaunal abundance and biomass from 130 Hamon and 16 Clamshell grab samples. Three predictive methods are used: 1) image-based (mean backscatter intensity); 2) angular response-based (predicted mean grain size), and 3) image-based (1st principal component and classification) from Quester Tangent Corporation Multiview software. Relationships between grain size and backscatter are explored using linear regression. Differences in grain size and benthic community structure between acoustically defined groups are examined using ANOVA and PERMANOVA+. Results for the Hamon grab stations indicate significant correlations between measured mean grain size and mean backscatter intensity, angular response predicted mean grain size, and 1st principal component of QTC analysis (all P < 0.001). Results for the Clamshell grab for two of the methods have stronger positive correlations; mean backscatter intensity (r ² = 0.619; P < 0.001) and angular response predicted mean grain size (r ² = 0.692; P < 0.001). ANOVA reveals significant differences in mean grain size (Hamon) within acoustic groups for all methods: mean backscatter (P < 0.001), angular response predicted grain size (P < 0.001), and QTC class (P = 0.009). Mean grain size (Clamshell) shows a significant difference between groups for mean backscatter (P = 0.001); other methods were not significant. PERMANOVA for the Hamon abundance shows benthic community structure was significantly different between acoustic groups for all methods (P ≤ 0.001). Overall these results show considerable promise in that more than 60% of the variance in the mean grain size of the Clamshell grab samples can be explained by mean backscatter or acoustically-predicted grain size. These results show that there is significant predictive capacity for sediment characteristics from multibeam backscatter and that these acoustic classifications can have ecological validity. [ABSTRACT FROM AUTHOR]

Abstract: Spatio-temporal changes in macrozoobenthic assemblage structure were monitored at 8 stations in a river-affected temperate lagoon (Idoura Lagoon, Japan) from May 1997 to May 1998 to assess animal–environment relationships in estuarine soft-bottom habitats. A total of 29 taxa occurred with a predominance of a few polychaete species including Heteromastus cf. similis, Hediste spp., Pseudopolydora cf. kempi and Prionospio japonica. The community structure differed significantly among four habitat types that were characterized by different salinity, sediment characteristics, and/or bottom elevation. For each habitat, macrozoobenthic community structure changed significantly with time, which was discriminated mostly by the lower density of polyhaline opportunistic species such as P. cf. kempi in warmer period. The salinity in the study area was much lower from May to September, mainly due to irrigation discharge from paddy fields, which seemed to be a lethal factor for the polyhaline species. C/N ratio and δ13C value of the sediment implied the accumulation of river-derived organic matters during the high river flow period. Present results showed the significant effects of fluctuating river discharge on the estuarine soft-bottom habitats, suggesting a linkage among terrestrial, riverine and estuarine ecosystems. [Copyright &y& Elsevier]

Abstract: The spatial distribution, abundance, and assemblage structure of macrozoobenthos were examined at 45 stations in a brackish lagoon (Idoura Lagoon, Japan) to examine the animal–environmental relations in estuarine soft-bottom habitats. We found a total of 23 taxa; the polychaetes Heteromastus sp., Hediste spp., and Prionospio japonica and the isopod Cyathura muromiensis numerically dominated the community. Cluster analysis and one-way analysis of similarity (ANOSIM) identified seven groups of stations that had significantly different macrozoobenthic communities; these were subsequently consolidated into five habitat groups according to their association with environmental characteristics. Canonical correspondence analysis (CCA) showed that salinity, silt-clay content, and the oxidation–reduction potential (ORP) of the sediment strongly affected the macrozoobenthos distribution pattern in the lagoon, whereas other factors (e.g., relative elevation of the habitat and sediment organic content) had much weaker effects. Similarity percentages (SIMPER) procedures indicated that the polychaete Notomastus sp. and the bivalve Macoma contabulata were specific to habitats with low salinity and reduced mud, whereas the bivalve Nuttallia olivacea was specific to sandy bottoms. Heteromastus sp. and Hediste spp. achieved their highest densities in rather oxidized sediments. The acid-volatile sulfide (AVS) content in the sediment was suggested as another possible factor affecting macrozoobenthic density. Our results clearly demonstrate that macrozoobenthic assemblages in estuarine soft-bottoms have high spatial heterogeneity on a small scale (e.g., hundreds of meters) related to physical and chemical environmental changes. Our data also suggested the importance of sediment redox condition (e.g., ORP and AVS content) and sediment grain size as structuring factors in estuarine soft-bottom communities as well as the salinity in the habitat. [Copyright &y& Elsevier]

Abstract: Sediment destabilization by sediment-reworking organisms is common in coastal aquatic environments, but the potential of bioturbation to inhibit shoreline succession has not been suggested previously. The lugworm Arenicola marina is a widespread and dominant large burrower at European Atlantic shores, and a major source of bioturbation and bioirrigation on the extensive intertidal flats in the Wadden Sea (eastern North Sea). The hypothesis that lugworm activities inhibit the successive development from sandy to muddy sediments in depositional embayments has been tested by a large-scale exclusion field experiment. Changes in sediment properties indicate a progressive clogging of interstices with fine particles and organic matter, resulting in lower sediment permeability in exclusion areas compared to lugworm inhabited control areas. Chlorophyll content in the surface layer was consistently higher in the absence of lugworms. Lack of sub-surface irrigation in the absence of lugworms combined with reduced sediment permeability resulted in increased concentrations of ammonium, phosphate, silicate, and sulphide in the pore-water. Concentrations >100μM of sulphide gave rise to toxic conditions for macrofauna. The effects of lugworms on sediment characteristics were more conspicuous in fine than in medium sand. It is concluded that A. marina contributes to the maintenance of permeable sand and thereby sustaining suitable conditions for the lugworm population itself. Without this “ecosystem engineer” mud flats would greatly expand at the expense of sand flats in the Wadden Sea. [Copyright &y& Elsevier]

Marine sediment properties were quantified along SE Asian siltation gradients and across different habitat types to assess the extent of terrestrial sediment influence and derive indicators of of terrestrial sediment input. Three sites in the Andaman Sea (Ranong, Phuket and Trang; Thailand), one site in the Gulf of Thailand (Pak Phanang; Thailand) and three sites in the South China Sea (Bolinao at the Luzon Island, Puerto Galera at the Mindoro Island and El Nido at the Palawan Island, all in the Philippines) were studied. The following main habitat types were covered: mangroves, seagrass beds, coral reefs, mud flats, river mouths and deep channels.Particularly in Bolinao and El Nido, distinct fronts in siltation were identified at about 7 km from the source. Mud (<63 μm), water content, organic matter, total nitrogen, total phosphorus and iron co-varied along the first axis of a principal components analysis, which correlated negatively with the pattern in medium to coarse sand (>250 μm), total and inorganic carbon as well as calcium. Interstitial ammonia and phosphate varied with the fine sand fraction along the second axis. Two-way analysis of variance showed that water depth, distance from silt source, site and habitat type all contributed to the variance, but site explained most. Linear regressions showed positive correlations between silt and water content, organic matter, total nitrogen, total phosphorus and iron, but negative correlations with calcium suggesting iron and calcium as markers for terrigeneous and marine origin, respectively. The composition of the sediment particulate matter groups the habitat types in two clusters: (1) silty types as river mouths, shallow mud bottoms, deep channels and mangrove stands with high contents of organic matter and nutrients versus (2) non-silty types as seagrass beds and coral reefs with low contents of nutrients and organic matter.Median settling velocities of the silt loads varied from 0·6 m d−1to 27 m d−1. Experimentally determined susceptibility to resuspension identified a critical water content of 50%. [Copyright &y& Elsevier]

Bioturbating benthic organisms have typically been characterised by how they modify the vertical sediment erosion thresholds. By means of several annular flume experiments, we aimed to understand how benthic organisms may affect grain-size sediment properties over time, and how this depends on the sediment type and the sediment loading of the water column. We compared the effect of two bioturbating macroinvertebrate species: a local dominant species, the cockle Cerastoderma edule and a spreading non-indigeneous species, the clam Ruditapes philippinarum. Our results indicate that the effect of benthic organisms on sediment dynamics is strongly dependent on both the prevailing environmental conditions and the benthic species present. If sediment is sandy, the benthos can gradually enhance the silt content of the sediment by mixing in part of the daily tidal sediment deposition. In contrast, if sediment is muddy, benthos can gradually decrease the silt content of the sediment by specifically suspending the fine fraction. Moreover, we observed that the native cockles had a stronger impact than invasive clams. Therefore, bioturbating benthos can have an important effect in determining the local sediment properties, with the outcome depending both on the species in question and the environmental conditions the bioturbator lives in. Our findings show that sediment bioturbation may have strong implications for tidal flat stability undergoing major changes from natural or anthropogenic sources. Image 1 • Flumes are used to understand how benthic organisms modify sediment properties. • Bioturbating benthic organisms have an effect on sediment dynamics and properties. • This effect depends on the benthic species and local environmental conditions. • If sediment is sandy, benthos enhance sediment silt content. • If sediment is muddy, benthos decrease sediment silt content through resuspension. [ABSTRACT FROM AUTHOR]