Effects of industrial outfalls on tropical macrobenthic sediment communities in Reunion Island (Southwest Indian Ocean)

Temporal changes in the composition of soft bottom macrobenthic assemblages at Reunion Island (Southwest Indian Ocean) were studied in the context of a long-term environmental monitoring programme studying the impacts of effluents of industrial sugar cane refineries that are transferred to shallow and deep coastal environments by different pathways: surface discharge and deep underground injection. Seven stations (between 20 and 160 m depth) were surveyed between 1994 and 2003 on the industrial zone. One additional station was surveyed on a reference site. Spatio-temporal changes in the composition of macrobenthic communities were assessed using several diversity indices, ABC curves, MDS and associated ANOSIM tests and biotic indices. Among the 171 taxa recorded, polychaetes were dominant (89 species), followed by crustaceans and molluscs. The analysis of spatial changes in the composition of macrobenthos showed the existence of distinct benthic communities along the depth gradient. Temporal changes in macrobenthos composition were most prominent at the shallowest station. They mainly corresponded to the decline of several initially dominant taxa and the increase of the Eunicid polychaete Diopatra cuprea. This station further showed increasing macrofaunal abundance, biomass and sediment organic content over time, concomitant with decreasing sediment grain sizes. In deeper environments, temporal changes were much smaller. Macrofaunal abundance and species richness increased progressively, suggesting a moderate impact on benthic ecosystems resulting from slight enrichments due to effluents rich in organic matter. Our results highlight an original response to disturbance pattern involving opportunistic Eunicidae species (D. cuprea) not previously described. Moreover, they allow for the comparison of the impact on macrofauna caused by industrial effluents exported by two distinct and different pathways in a tropical coastal high-energy marine environment.     

Macrobenthos habitat mapping in a tidal flat using remotely sensed data and a GIS-based probabilistic model

This paper proposes and tests a method of producing macrofauna habitat potential maps based on a weights-of-evidence model (a probabilistic approach) for the Hwangdo tidal flat, Korea. Samples of macrobenthos were collected during field work, and we considered five mollusca species for habitat mapping. A weights-of-evidence model was used to calculate the relative weights of 10 control factors that affect the macrobenthos habitat. The control factors were compiled as a spatial database from remotely sensed data combined with GIS analysis. The relative weight of each factor was integrated as a species potential index (SPI), which produced habitat potential maps. The maps were compared with the surveyed habitat locations, revealing a strong correlation between the potential maps and species locations. The combination of a GIS-based weights-of-evidence model and remote sensing techniques is an effective method in determining areas of macrobenthos habitat potential in a tidal flat setting.     

Decline in the species richness contribution of Echinodermata to the macrobenthos in the shelf seas of China

Echinoderms play crucial roles in the structure of marine macrobenthic communities. They are sensitive to excess absorption of CO₂ by the ocean, which induces ocean acidification and ocean warming. In the shelf seas of China, the mean sea surface temperature has a faster warming rate compared with the mean rate of the global ocean, and the apparent decrease in pH is due not only to the increased CO₂ absorption in seawater, but also eutrophication. However, little is known about the associated changes in the diversity of echinoderms and their roles in macrobenthic communities in the seas of China. In this study, we conducted a meta-analysis of 77 case studies in 51 papers to examine the changes in the contribution of echinoderm species richness to the macrobenthos in the shelf seas of China since the 1980s. The relative species richness (RSR) was considered as the metric to evaluate these changes. Trends analysis revealed significant declines in RSR in the shelf seas of China, the Yellow Sea, and the East China Sea from 1997 to 2009. Compared with the RSR before 1997, no significant changes in mean RSR were found after 1997, except in the Bohai Sea. In addition, relative change in the RSR of echinoderms and species richness of macrobenthos led to more changes (decrease or increase) in their respective biomasses. Our results imply that changes in species richness may alter the macrobenthic productivity of the marine benthic ecosystem.     

Effects of reclamation on macrobenthic assemblages in the coastline of the Arabian Gulf: a microcosm experimental approach

Coastal reclamation and modifications are extensively carried out in Bahrain, which may physically smother the coastal and subtidal habitats resulting in changes to abundance and distribution of macrobenthic assemblages. A microcosm laboratory experiment using three common macrobenthic invertebrates from a proposed reclaimed coastal area was preformed to examine their responses to mud burial using marine sediment collected from a designated borrow area. Significant difference in numbers of survived organisms between control and experimental treatments with a survival percentage of 41.8% for all of the selected species was observed. The polychaete Perinereis nuntia showed the highest percentage of survival (57.1%) followed by the bivalve Tellinavaltonis (42.3%) and the gastropod Cerithidea cingulata (24.0%). Quantifying species responses to sediment burial resulted from dredging and reclamation will aid in predicting the expected ecological impacts associated with coastal developments and subsequently minimizing these impacts and maintaining a sustainable use of coastal and marine ecosystems in the Arabian Gulf.     

Numerical simulation of the impact of sediment supply and streamflow variations on channel grain sizes and Chinook salmon habitat in mountain drainage networks

Climatically driven changes in streamflow and hillslope sediment supply could potentially alter stream surface grain size distribution patterns and thereby impact habitat for a number of threatened and endangered in‐stream fish species. Relatively little is known about hydrograph (shape, peak flow) influence or the relative importance of chronic and episodic hillslope inputs on channel conditions. To better understand these external drivers, we calculated sediment routing through a gravel‐bedded river network using a one‐dimensional (1D) bedload transport model. We calculated changes in grain sizes and estimated Chinook salmon habitat suitability caused by a dry year and an extreme flood hydrograph, and chronic (diffusive, overland flow) or pulse (landslide, debris flow) hillslope sediment supplies. To obtain accurate channel conditions, a relatively high reference Shields stress, representative of steep mountain streams, was needed. An extreme event flood without any hillslope sediment inputs caused widespread bed coarsening and a decrease in aquatic habitat. Chronic sediment input combined with this hydrograph eliminated any changes in grain size and habitat, although when combined with a dry year flow, caused systematic bed fining. The influence of a given hydrograph therefore highly depends on the hillslope sediment supply. Regardless of the flow hydrograph or sediment pulse timing, grain size distribution or location, pulse sediment inputs did not cause widespread grain size changes despite being 100 times the total chronic input volume. Widespread and continuous hillslope sediment inputs may influence channel grain sizes and aquatic habitat more than a single discrete sediment pulse. Depending on the magnitudes of flow hydrograph and sediment supply alterations, climate change may induce no differences in grain sizes or very dramatic changes with significant consequences for long‐term sustainability. Copyright © 2013 John Wiley & Sons, Ltd.     

The role of biophysical interactions within the ijzermonding tidal flat sediment dynamics

This paper focuses on the importance of biophysical interactions on short-term and long-term sediment dynamics. Therefore, various biological (macrobenthos, photopigments, colloidal EPS) and physical parameters (grain size, water content, sediment stability, bed level) were determined (bi)monthly in nine sampling plots on the IJzermonding tidal flat (Belgium, 51°08′N, 2°44′E) during three consecutive years (July 2005–June 2008). Results showed that sediment stability varied on the short timescale and was directly influenced by biota, while bed level varied mainly on the long-term due to interannual variability. The short-term dynamic relationships between mud content, water content, fucoxanthin and macrobenthos density resulted in a seasonal mud deposition and erosion cycle, and directly influenced sediment stability. Moreover, macrobenthos was proven to be the most important parameter determining sediment stability. On the long-term, a shift was observed from high fucoxanthin/chla concentration, high mud content and zero to moderate densities of Corophium volutator towards low fucoxanthin/chl a and mud content and high Corophium densities, which resulted in a transition from net accretion to net erosion. However, most measured variables proved to be poor predictors for these long-term bed level changes, indicating that external physical forces, such as waves and storminess, probably were the most important factors triggering long-term sediment dynamics. Nevertheless, biota indirectly influenced bed level changes by mediating short-term changes in sediment stability, thereby influencing the erodability of the sediment. The macrobenthos, and especially the mud shrimp Corophium, was suggested as the (indirect) driving destabilising factor for the sampling plots in the IIzermonding when considering the long-term evolution.     

A comparative analysis of three habitat suitability models for commercial yield estimation of Tapes philippinarum in a North Adriatic coastal lagoon (Sacca di Goro, Italy)

Habitat Suitability (HS) models have been extensively used by conservation planners to estimate the spatial distribution of threatened species and of species of commercial interest. In this work we compare three HS models for the estimation of commercial yield potential and the identification of suitable sites for Tapes philippinarum rearing in the Sacca di Goro lagoon (Italy) on the basis of six environmental factors. The habitat suitability index (HSI) is based on expert opinion while the habitat suitability conditional (HSC) is calibrated on observational data. The habitat suitability mixed (HSM) model is a two-part model combining expert knowledge and regression analysis: the first component of the model uses logistic regression to identify the areas in which clams are likely to be present; the second part applies the same parameter-specific suitability functions of the HSI model only in the areas previously identified as productive by the logistic component.The HS models were validated on an independent data set and estimates of potential yield of the Goro lagoon were compared. The effectiveness of the three approaches is then discussed in terms of predicted yield and identification of suitable sites for farming.     

Benthic community structure and sediment processes on an intertidal flat: results from the ECOFLAT project

Interactions between physical and biological processes in intertidal sediments have been the focus of studies in the framework of the ECOFLAT project. Process studies were focused on the Molenplaat, a 1.5 km² intertidal flat in the Westerschelde estuary, The Netherlands. Distinct spatial patterns in the biological community on the flat were found and related to patterns in bottom shear stress as derived from a hydrodynamic model. Based on these survey results five stations were selected with contrasting sediment composition and benthic communities.Long-term net sedimentation of mainly sand was deduced from radionuclide profiles. Sedimentation of mud on the surface of part of the intertidal flat was shown to be a seasonally cyclic process, with a magnitude sufficient to significantly affect the mud balance of the estuary. Measurements of erodability as a function of tidal current showed a biological control on this variable. Benthic microalgae stabilise the sediment surface, whereas the benthic macrofauna has a destabilising effect.Food web studies show that the contrasting biological communities (microbenthos, meiobenthos, macrobenthos) at muddy and sandy sites have substantial differences in the quantitative aspects of their food web. Turnover of microalgae is much lower at muddy than at sandy sites, and this is mostly related to a lower grazing pressure. It is hypothesised that high mud content decreases the availability of benthic microalgae to grazers.We demonstrate a positive feedback between benthic microalgae and mud sedimentation which may lead to the existence of different stable states. This may explain the existence of relatively sharp boundaries and strong community contrasts in the presence of weak and smooth environmental gradients.     

Ecological evaluation of an experimental beneficial use scheme for dredged sediment disposal in shallow tidal waters

An experiment was performed to test an alternative dredging strategy for the Westerschelde estuary. Clean sand dredged from the navigation channel was disposed seawards of an eroding intertidal flat in order to modify morphology and hydrodynamics, improving the multi-channel system with ecologically productive shallow water habitat. Five years of intensive monitoring revealed that part of the disposed sediment moved slowly towards the flat, increasing the very shallow subtidal and intertidal area, as planned. The sand in the impact zone became gradually finer after disposal, possibly due to reduced current velocities. Nevertheless, no changes in macrobenthic biomass, density, species richness and composition were detected in the subtidal zone, also demonstrating rapid macrobenthic recovery. In the intertidal zone, no ecological effects could be revealed superimposed on trends associated with long-term sediment fining. Thus, despite morphological success and absence of detected negative ecological impacts of the experiment, new beneficial habitat was not created.     

Effects of oil spill on seawater infiltration and macrobenthic community in tidal flats

Tidal flat ecosystem simulators are used to clarify the effects of stranded fuel oil on tidal flat ecosystems. Results show that oil spills increase the periphyton on sediment by decreasing the predation stress caused by deposit feeders. About a month after an oil spill, the total population density of the macrobenthos recovered. The oxidation-reduction potential in the surface sediment drops to a negative value after the oil spill, and the anaerobic condition throughout the sediment seems to be responsible for the decrease in the population density of the macrobenthos. The infiltration volume of seawater into the oil-stranded sediment decreases to a third of that without the oil spill. The recovery of infiltration volume after about a month coincides with the recovery of the population density of the macrobenthos. This result suggests that the macrobenthic population is highly dependent on the infiltration of seawater.     

Amelioration of marine farming impact on the benthic environment using artificial reefs as biofilters

An in situ monitoring of the sediment characteristics and macrobenthic communities was undertaken at a marine fish culture site in subtropical waters of Hong Kong before and after the deployment of biofilters which were made of cement concrete artificial reef (AR) structures. According to the distance to the boundary of the fish cages, 6 points were selected as sampling stations: 2 at the fish cages, 2 near the boundary of the fish culture area, and 2 reference sites further away from the culture area. Bimonthly sediment samples were collected for analysis of silt-clay fraction (SCF), moisture content (MC), total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP). The macrobenthos (>0.5mm) present in the sediment were sorted, identified and enumerated. TOC, TKN and TP levels at the fish cage stations were consistently higher than those at the reference stations over the 1-year pre-AR and 2-year post-AR deployment monitoring period. The diversity of macrofauna was significantly reduced at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Over the 2-year post-AR deployment period, TOC, TKN and TP showed a decreasing trend at the fish cage and intermediary stations. More diverse macrofaunal communities were recorded at the fish cage stations, with species diversity H'increasing from 0-1 at the beginning of the AR deployment to H'>2 at the end of the study. The present results demonstrated that artificial reefs can improve the benthic abiotic environment and biotic conditions beneath fish rafts which are deteriorated due to farming activities.     

Status of Macrobenthic Community and Its Relationships to Trace Metals and Natural Sediment Characteristics

Laizhou Bay, located in the northwest of Shandong Peninsula, has complex transitional environments between terrestrial and marine ecosystems. In the present study, a total of 122, 131, and 139 species were collected in spring, summer, and autumn 2011, respectively. Species constitutions of macrobenthos were grouped into four phyla, of which annelida were the most abundant phylum, the average biomass proportion of echinodermata was the lowest, and the proportion of important species for mollusca was the highest. The structure of the macrobenthic community showed significant differences between sites, and greater divergence was observed between the third site (S03) and other stations. The ABC plots showed that the biomass curve lay below the abundance curve, and the W‐statistic value was negative. The result of the BOPA index showed that two stations had moderate ecological status in spring and that there were two heavily polluted sites and one moderately polluted site in summer. The BIO‐ENV analyses indicated that the grain‐size fractions together with trace metals (Hg, Pb, Zn, Cu, and Cr) could be considered as the major environmental variables influencing the macrobenthic patterns. The results together demonstrated that the macrobenthic communities in Laizhou Bay were negatively affected, perhaps by the tremendous impact of heavy metals in the sediments.     

Offshore macrobenthic recovery in the Murchison field following the termination of drill-cuttings discharges

The effects of discharged drilling cuttings contaminated with oil-based drilling fluids on the macrobenthos surrounding several North Sea oil-production platforms have been well documented. Areas of biological effect ranging from highly modified benthic communities, through transitional zones to undisturbed zones have been identified and characterized. Results are presented from a series of studies at the Murchison oil field which indicate partial recovery of macrofaunal communities around the production platform after cuttings discharges had ceased. Eventual rates of recovery of affected macrobenthic communities around production platforms are discussed in terms of persistence of oil in the drilling cuttings and the rates of degradation of the oil and its toxic components.     

Macrobenthic community response to copper in Shelter Island Yacht Basin, San Diego Bay, California

We examined Cu contamination effects on macrobenthic communities and Cu concentration in invertebrates within Shelter Island Yacht Basin, San Diego Bay, California. Results indicate that at some sites, Cu in sediment has exceeded a threshold for “self defense” mechanisms and highlight the potential negative impacts on benthic faunal communities where Cu accumulates and persists in sediments. At sites with elevated Cu levels in sediment, macrobenthic communities were not only less diverse but also their total biomass and body size (individual biomass) were reduced compared to sites with lower Cu. Cu concentration in tissue varied between species and within the same species, reflecting differing abilities to “regulate” their body load. The spatial complexity of Cu effects in a small marina such as SIYB emphasizes that sediment-quality criteria based solely on laboratory experiments should be used with caution, as they do not necessarily reflect the condition at the community and ecosystem levels.     

Detection of anthropogenic Cu, Pb and Zn in continental shelf sediments off Sydney, Australia--a new approach using normalization with cobalt.

Concentrations of Co, Cu, Pb and Zn were determined in 107 surficial sediment samples from the continental margin adjacent to Sydney, Australia. The spatial distributions of trace metals in the sediments and the mud content are similar and increase with greater distance from the coast. In contrast, normalization of the concentrations of Cu, Pb and Zn in the total sediment with Co enables a coastal anthropogenic source to be identified. The spatial distribution of Co-normalized concentrations of Cu, Pb and Zn in total sediment is similar to the distribution of these trace metals in the fine fraction of sediment (<62.5 microm), indicating that Co may be used as a normalizing element for determining contaminant sources in the marine environment near Sydney.     

Distribution and ecological relevance of fine sediments in organic-enriched lagoons: the case study of the Cabras lagoon (Sardinia, Italy)

In organic-enriched sedimentary systems, like many Mediterranean coastal lagoons, a detailed analysis of sediment grain size composition and partitioning within the muds is crucial to investigate sedimentological trends related to both hydrodynamic energy and basin morphology. In these systems, sediment dynamics are particularly important because the partitioning and transport of fine sediments can strongly influence the redistribution and accumulation of large amounts of organic matter, and consequently the distribution of benthic assemblages and the trophic status and functioning of a lagoon. Nevertheless, studies on benthic-sediment relationships have been based mainly on a rather coarse analysis of sediment grain size features. In muddy systems, however, this approach may impede a proper evaluation of the relationships and effects of the distribution of fine sediment and organic matter on the biotic benthic components. Here we show that the distribution of sedimentary organic matter (OM) and total organic carbon (TOC) in the Cabras lagoon (Sardinia, Italy) can be explained (i.e., predicted) as a function of a nonlinear increase in the amount of the cohesive fraction of sediments (< or = 8 microm grain size particles) and that this fraction strongly influences the structure, composition and distribution of macrobenthic assemblages. Even in such a homogeneously muddy system, characterized by "naturally" occurring impoverished communities, impaired benthic assemblages were found at < or = 8 microm, OM, TOC contents of about 77%, 11% and 3.5%, respectively. A review of studies conducted in Mediterranean coastal lagoons highlighted a lack of direct integrated analysis of sediment features and the biotic components. We suggest that, especially in organic-enriched coastal lagoons, monitoring programs should primarily investigate and consider the cohesive fraction of sediments in order to allow a better assessment of benthic-sediment relationships and ecological quality of the system.     

The paleoenvironmental significance of spatial distributions of grain size in groundwater‐recharged lakes: A case study in the hinterland of the Badain Jaran Desert,northwest China

For lakes in desert hinterlands that are not recharged by river runoff, sediment input solely comes from wind transport. While the processes of sediment transport and deposition in these lakes differ significantly from those with river discharge, the spatial distribution of sediment grain size in these groundwater‐recharged lakes remains largely unknown. Moreover, whether the grain size distribution in these lake sediments can be used as a proxy in the study of past climatic change and environmental evolution studies is unclear. In this study, five lakes with a range of surface areas that had no runoff recharge were selected from the hinterland of the Badain Jaran Desert of north‐western China, and a total of 108 samples of lake surface sediments were collected to examine the spatial distribution of grain size. Moreover, an end‐member‐modeling algorithm was used to calculate end members from all grain size measurements. Our results showed that both the median and mean grain sizes in the lake sediments decreased from the nearshore to the offshore, deep‐water zone. However, the lowest median and mean grain sizes were not found in the center of the lakes, in contrast to lakes recharged by surface runoff. The median grain size of sediment in the lake center was negatively correlated with lake level, and thus could help reveal lake evolution at low resolutions. Moreover, EM1 and EM2 were interpreted as wind transported sediment, and sediment perturbed by lake waves after wind transport, respectively. The modal grain size of EM1 varied slightly between lakes, while changes in the modal grain size of EM2 were related to lake area. Given the positive relationship found between EM2 content and lake level, changes in the EM2 content (%) can serve as a rough indicator of lake level fluctuations at low temporal resolutions. Copyright © 2017 John Wiley & Sons, Ltd.     

Macrobenthic associations in a South Atlantic Brazilian enclosed bay: the historical influence of shrimp trawling

This study characterized the macrobenthos of Tijucas Bay and related the distribution and dominance patterns with historical trawling activities. Fifteen sampling sites were established in the bay and were sampled in summer and winter for the characterization of the macrobenthos. To evaluate the trawling effects, three passages were established at each site with control and impacted areas analyzed before and after trawl-net action in impacted area. Seasonal differences occurred in macrobenthos, possibly influenced by rainfall where the relative water level of the Tijucas River was directly associated with the discharge of freshwater and particulate matter. The associations identified in the bay were distinct in comparison with the Zimbros Embayment. The trawling assessment showed no significant variation in the macrobenthos after the trawl, possibly due to decades of shrimp exploitation in the bay. Trawling and instable environmental conditions inside the bay make the establishment of a stable macrobenthic community difficult.     

Effects of nutrient enrichment derived from fish farming activities on macroinvertebrate assemblages in a subtropical region of Hong Kong

To study the correlation between nutrient enrichment derived from fish farming activities and changes in macrobenthic assemblages, a one-year field study was conducted in Kau Sai Bay marine fish culture zone of Hong Kong. Bimonthly sediment samples were collected at six stations: two at the fish cages, two near the boundary of the fish culture area, and two reference sites further away from the culture area. Sediment physico-chemical characteristics in terms of silt/clay fraction, moisture content, total organic carbon (TOC), total Kjeldahl nitrogen (TKN) and total phosphorus (TP) were analyzed. The macrobenthos (>0.5 mm) present in the sediment were sorted, identified and enumerated. On average, TOC, TKN and TP levels at the fish cage stations were 82.8%, 128.5% and 1315.7% higher than those at the reference stations, respectively. As a result, the N:P molar ratio was greatly reduced from 8.75 at the reference stations to 1.83 at the fish cage stations. Univariate and multivariate analyses revealed that diversity of macrofauna was significantly reduced and community structure differed at the fish cage stations relative to the reference sites. The intermediary stations near the fish culture area showed a transitional state of disturbance. Faunal diversity was negatively correlated with nutrient level, reflecting the adverse impacts of nutrient enrichment derived from fish farming activities on the benthic assemblages. Whilst in subtropical Asia-Pacific trash fish is the major feed for fish culture resulting in a higher nutrient loading and nutrient ratio accumulated in the sediment beneath the fish rafts, the effects of nutrient enrichment on macrobenthic assemblages are comparable to that in temperate waters owing to relatively high sediment metabolism rate and smaller fish culture scale in Hong Kong.