Macrofaunal Community Structure Research Articles

Changes in Ecosystem Function Across Sedimentary Gradients in Estuaries

The input of terrestrial silt and clay (hereafter mud) into coastal environments can alter sediment grain size distribution affecting the structure and functioning of benthic communities. The relationship between sediment mud content and macrofaunal community structure has been well documented, but not the effects on ecosystem function. In 143 plots from the mid-intertidal sites in 9 estuaries, we measured sediment properties, macrofaunal community composition and fluxes of O2 and NH4+ across the sediment–water interface to derive process-based measures of ecosystem function across the sand–mud gradient. We observed reductions in measures of macrofaunal diversity and decreases in the maximum density of key bioturbating bivalves (Austrovenus stutchburyi and Macomona liliana) with increased mud content. Concurrently, the maximum rates of sediment oxygen consumption (SOC), NH4+ efflux (NH4+) and biomass standardized gross primary production (GPPChl-a) also decreased with increasing mud content. Environmental predictors explained 34–39% (P = 0.005–0.01) of the total variation in ecosystem function in distance-based linear models. After partitioning out the effect of mud, A. stutchburyi abundance was positively correlated and explained 25 and 23% (P = 0.0001) of the variation of SOC and NH4+, respectively. Also, mud content (negatively correlated) and temperature (positively correlated) explained 26% of variability in GPPChl-a (P = 0.0001). Our results highlight the importance of increased mud content and the associated reduction in the abundance of strongly interacting key species on the loss of ecosystem function in intertidal sand flats.

Interactions of habitat complexity and environmental characteristics with macrobenthic community structure at multiple spatial scales in the northeastern Chukchi Sea

Spatial trends in macrobenthic communities from the northeastern Chukchi Sea are evaluated to understand how ecological processes influencing macrofauna differ between small and large scales. Macrobenthos was sampled with a van Veen grab in a mesoscale study (distances ~10–200km) in 1986 and in a midscale study (distances ~2–20km) in 2008–2010. Common field and laboratory methods allowed for a direct comparison of the data sets. Environmental characteristics influencing spatial structures of macrobenthic communities varied with the scale of sampling. Midscale variations of macrofaunal community structure in the 2008–2010 study were associated with the local topographic variations resulting in an enhanced carbon deposition and a greater biological production; total density increased with the increasing water depth and organic carbon. Mesoscale environmental gradients in the 1986 study, reflecting physical dynamics, water mass movements, and oceanographic conditions, were associated with an inshore to offshore faunal gradient as density declined with greater water depth. Differences in environmental and biological community relationships between scales included shifts in the regression relationships between water depth and macrobenthic density with declining density at the mesoscale and the increasing density with greater depth at the midscale. Biomass declined more sharply with increased bottom-water temperature in the midscale study than in the mesoscale investigation. Multivariate analyses demonstrated similar shifts in the relationship between biotic summary measures and water depth. Increased benthic production is noted in other areas of the Chukchi Sea in association with topographic variations, and such variations may be predictive of increased benthic production. Ecologically significant changes in relationships of environmental and biological gradients between spatial scales indicate the need for small-scale sampling to detect long-term change in marine communities.

Benthic ecology of the northeastern Chukchi Sea. Part I. Environmental characteristics and macrofaunal community structure, 2008–2010

Spatial variations of processes driving macrofaunal distributions can arise from interactions among topographic features and oceanographic patterns, and are not understood at small scales in the northeastern Chukchi Sea. Benthic macrofauna and environmental characteristics were measured to determine factors driving macrofaunal distributions as part of a multidisciplinary environmental program in the northeastern Chukchi Sea from 2008 to 2010. Macrofauna were sampled in three study areas, named Klondike, Burger, and Statoil, with a van Veen grab at up to 82 stations each year, as well as an area where marine mammals were seen feeding. The macrofaunal assemblages in all study areas were similar in species-composition with deposit-feeding polychaetes (53% of density and of 26% biomass) and bivalves (15% of density and 52% of biomass) collectively the most prominent groups. Maldane sarsi dominated the polychaetes in terms of both density and biomass, while bivalves were numerically dominated by Ennucula tenuis, but their biomass was dominated by larger species such as Macoma calcarea and Astarte borealis. Exceptions occurred in the marine mammal feeding area that was dominated by amphipods (71% of density and 30% biomass). Average densities were higher in Burger than in Klondike or Statoil, while biomass values were similar between Burger and Statoil, and higher in these two study areas than in Klondike. Overall, the distributions, biomass and density of benthic macrofauna reflect the high volume of production reaching the seafloor in the shallow waters of the Chukchi Sea. Variations in community structure among study areas were correlated with water depth and bottom-water temperature. Short-term temporal differences in community structure covaried with interannual oceanographic variations that may have altered food availability, macrofaunal survival, or larval recruitment. Topographic control over circulation appears to be a primary driver in structuring benthic communities within the present study region, as well as throughout the Chukchi Sea.

Effect of tropical rainfall in structuring the macrobenthic community of Mandovi estuary, west coast of India

Macrofaunal community structure is determined by a number of environmental variables. The riverine run-off during the monsoon brings about drastic changes in the physico-chemical parameters of a tropical estuary. The aim of the present study was to investigate the influence of rainfall in structuring the benthic macrofaunal community of a tropical estuary. The temporal dynamics of the macrobenthic community in the monsoon dominated Mandovi estuary (central west coast of India) was studied fortnightly from June 2007 to June 2009. A fixed location, downstream of the Madovi river, was sampled for benthic and water parameters. Ten replicates were collected during each sampling date using a Van Veen grab (0.04 m2). The macrofaunal abundance showed temporal fluctuation. The multivariate analysis showed the clustering of the samples linked to the environmental parameters (CCA and LINKTREE). The temporal variation observed in the macrofaunal abundance was basically due to changes in abundance of the dominant species. The variation in macrofaunal abundance was brought about by the recruitment and settling of re-suspended adults. It can be concluded that the macrofaunal structuring is influenced by temporal changes in the environment associated with the annual monsoon rainfall. Hence climate induced changes in the monsoonal pattern may affect the macrobenthic assemblages of tropical estuaries.

Role of the sandprawn Callichirus kraussi as an ecosystem engineer in a South African temporarily open/closed estuary

The role of the sandprawn Callichirus kraussi as an ecosystem engineer was experimentally assessed using caging experiments over a four-month period in 2010 in the temporarily open/closed Kasouga Estuary on the south-eastern coast of South Africa. The sandprawn contributed to a significant increase in bioturbation, associated with a decline in microphytobenthic algal concentrations which coincided with a significant decrease in the abundance of the gastropod Nassarius kraussianus. The presence of the sandprawn did not contribute to a significant decline in sediment organic content, or to the abundance, biomass and species composition of the infauna, which comprised mainly amphipods, isopods and polychaetes. Nor did it contribute to a change in the macrofaunal community structure. The absence of any significant differences between the various treatments appears to reflect the low densities of sandprawns in the estuary during the study period.

Meio- and macrofauna communities in three sandy beaches of the northern Adriatic Sea protected by artificial reefs

Interactions between meio- and macrofaunal assemblages and food availability were investigated in relation to tourism pressures on three beaches of the northern Adriatic Sea. All beaches were characterised by the presence of artificial reefs, freshwater inputs and tourism pressures. Beach sediments displayed high organic loads and low protein and chlorophyll a contributions to the bulk of the organic matter. Consequently, the organic matter was of mostly refractory composition and, thus, of scarce nutritional quality. Macrofaunal community structure and biomass were related to the quantity and nutritional quality of sedimentary organic matter, whereas meiofauna was apparently not. No relationships were found between physical variables and the metazoan communities. Most likely, the presence of artificial reefs reduced the physical impact of waves on the beach assemblages, whereas the presence of synergistic human impacts, including freshwater inputs and the tourism pressure, negatively influenced both the meio- and the macrofaunal assemblages.

Effects of cold winters and regime shifts on macrofauna communities in shallow coastal regions

Several ecosystem components in the North Sea have undergone fundamental changes following climatic change and this paper aims to establish if these changes also have affected macrofauna communities in the southern North Sea. From 1978 to 2005, the macrofauna communities were sampled seasonally in the sublittoral zone off the island of Norderney, one of the East Frisian barrier islands. Abundance, biomass and species numbers of single species or larger taxonomic groups showed differences in long-term variability and eurytherm species dominated in the study area. After the cold winter of 1978/79 until the mid 1980s a higher percentage of arctic-boreal species were found, while after 1988 the percentage of species with a southern distribution in the North Sea increased in connection with a smooth biological regime shift and a positive North Atlantic Oscillation (NAO) index. Interface-feeders dominated the communities, followed by sand lickers and subsurface deposit-feeders. The latter were more abundant after cold winters, probably due to their ability to utilise dead buried faunal organic matter. Multivariate analyses revealed that cold winters affected the community structure more briefly, while a smooth biological regime shift in 1989/1990 and a climate regime shift induced abrupt biological regime shift in 2001/2002 caused longer-term progressive change in the macrofauna community structure. The significant correlation between macrofauna abundance, biomass and species number and the NAO index failed until 2001 due to a change in climate systems over the northern Atlantic hemisphere.

三种温带森林大型土壤动物群落结构的时空动态

Soil macro-faunas are important decomposers in ecosystem and play a significant role in nutrient cycling and energy flow. In Maoer Mountain,the soil macro-faunas were investigated in three typical forest types(Korean pine plantation forest,Hard-wood forest and Mongolian oak forest). Our object was to explore the community structure,spatial and temporal dynamic of soil macro-fauna,and its impact factors in temperate forest. Soil samples were collected from the litter layer and the soil layers at depth of 0—10 cm and 10—20 cm. Sampling was carried out continuously from May to October in 2012. A total of 3604 individuals,belonging to 3 Phyla,6 Classes,17 Orders and 50 families were extracted and identified. Among them,the Lumbricidae,Enchytraeidae and Lithobiomorpha were the dominant communities. The results showed that:(1) for horizontal distribution,the decreasing order of individual density and biomass was Korean pine plantation,Hard-wood forest and Mongolian oak. The group number of soil macro-faunas was the largest in Hard-wood forest,and the least in Mongolian oak forest. The Shannon and richness indices of soil macro-faunas were the highest in Mongolian oak forest and the lowest in Korean pine plantation forest,but the trend in the dominance index was opposite.The evenness index was the largest in Mongolian oak forest and the least in Hard-wood forest;(2) for vertical distribution,the individual density,group number,biomass and diversity of soil macro-fauna were significantly affected by the soil layer(P0.001). The individual density distribution appeared significant surface-aggregation,and the maximum biomass of soil macro-fauna was found at depth of 0—10 cm. The group number showed a decrease trend with the increasing layer in Korean pine plantation forest and that of highest value in both Hard-wood forest and Mongolian oak forest occurred at 0—10cm depth,not the litter layer. The Shannon index decreased with the increasing soil depth,while the dominance index appeared the opposite trend;(3) the Shannon and dominance index of soil macro-fauna were significantly different among different months(P0.01). Individual density and group number were higher in May and September than other months,and biomass of soil macro-fauna was the largest in September;(4) the correlation analysis showed that the individual density,group number and biomass of the soil macro-fauna were positively correlated with total organic carbon(P0.05),there was the significantly negative correlation between the Shannon index and soil bulk density(P0.01). It can be conclude that there was obviously spatial and temporal heterogeneity in soil macro-fauna community structure and the total organic carbon was one of the important impact factors.

Sediment quality assessment of Santos shoreline trough toxicity assays and characterization of macrobenthic community structure

This study evaluated the toxicity of the sediment on 7 points located in front of drainage canals river on the beaches of Santos-SP, together with the characterization of the community structure of benthic macrofauna. Were performed campaignsummer (February 2008) and the campaign winter (July 2008). The toxicity tests with sea-urchin Lytechinus variegatustreatments were performed in elutriate and sediment-water interface, as ABNT NBR 15350/2006. The benthic macrofaunawasidentified as Mollusca, Crustacea and Polychaeta, and it was calculated mean density (ind/0,026m²) and Polychaetadominance. In campaigns for summer and winter treatment sediment-water interface showed toxicity at all points, whilethe treatment elutriate showed toxicity at points 6 and 7. Polychaeta dominance was negatively correlated (r = -0,56) withgranulometry and positively correlated with organic matter for the winter campaign, being some of these species indicators.of polluted and anoxic environments

Effects of coal mining subsidence on the community structure of soil macro-fauna in central China

为了解不同沉陷程度农田土壤生态系统中大型土壤动物群落结构, 于2007年夏季对我国中部潞安集团井工开采区沉陷农田生态系统中不同等高线处大型土壤动物群落组成进行了调查, 采用野外手捡法共采集大型土壤动物477只, 隶属于3门7纲15目22科。其中, 蜘蛛目、鞘翅目、直翅目和膜翅目为优势类群, 占总捕量的83.64%; 常见类群4类, 占总捕量的13.22%。研究结果表明: 不同沉陷程度对农田大型土壤动物个体数、类群数均有不同程度影响, 农田大型土壤动物个体密度随着沉陷深度的增加呈现增加趋势, 沉陷区土壤生态环境的变化引起大型土壤动物的局部迁移。Jaccard相似性系数表明沉陷区中部(2 m、4 m和6 m等高线处)三者间相似程度较高, 正常农田(CK)与沉陷区底部(7 m等高线处)之间相似程度最低, 达到极不相似程度。研究认为不同沉陷程度对大型土壤动物的群落结构有明显影响, 将大型土壤动物作为沉陷区农田土壤质量评价中生物性状指标具有重要意义。

Environmental effects on the structure of polychaete feeding guilds on the beaches of Sepetiba Bay, south-eastern Brazil

Several studies have been conducted to explain patterns of the abundance, richness and diversity of sandy-beach macrofauna; however, such analyses have ignored the overall functional structure of macrofauna communities. Few studies have examined polychaete feeding guilds on sandy beach environments. To examine the effects of environmental factors on polychaete feeding guilds on sandy beaches, 12 sandy beaches from five islands in Sepetiba Bay were sampled. A total of 24 polychaete morphospecies, grouped among 21 families, were identified in these sandy beaches. The polychaete species were classified into 10 feeding guilds, and the SDT guild (suspended-deposit feeders, discretely motile, with tentacles) was the most abundant feeding guild, with 34.2% of total number of organisms. The highest trophic importance index and index of trophic diversity values were recorded on the sheltered beaches. A canonical correspondence analysis showed that the exposure rate, beach length, and grain size of the beach sediment significantly affected the polychaete feeding guild distribution and abundance. We can conclude that sheltered beaches have a higher diversity of feeding guilds than exposed beaches and that the biological descriptors of the feeding guilds are directly associated with the grain size of the sediment.

Does the diversity of kelp forest macrofauna increase with wave exposure?

Kelp (Laminaria hyperborea (Gunn.) Foslie) forests support a diverse community of invertebrates. The aim of the present study was to test if the abundance, diversity (measured as average species number) and community structure of macrofauna associated with epiphytic algae on kelp stipes depend on physical stress from wave surge and habitat diversity, or if differences simply result from differences in habitat size. Results show that faunal diversity increased with wave exposure, mainly due to increasing wave stress and habitat diversity. Abundance was highest at medium wave exposed stations, and lowest at low exposure stations. However, the habitat structural diversity is high in kelp forests regardless of wave exposure, and a typical kelp forest fauna is associated with functional groups of epiphytic algae across different levels of wave exposure.

An evaluation of benthic community structure in and around the Sackville Spur closed area (Northwest Atlantic) in relation to the protection of vulnerable marine ecosystems

Abstract Barrio Froján, C. R. S., MacIsaac, K. G., McMillan, A. K., del Mar Sacau Cuadrado, M., Large, P. A., Kenny, A. J., Kenchington, E., and de Cárdenas González, E. 2012. An evaluation of benthic community structure in and around the Sackville Spur closed area (Northwest Atlantic) in relation to the protection of vulnerable marine ecosystems. – ICES Journal of Marine Science, 69: 213–222. The benthic macrofaunal community structure is investigated within and around a closed area at Sackville Spur in the Northwest Atlantic to ascertain whether continued exclusion of bottom fishing can be justified. This and other similar closed areas have been introduced by the Northwest Atlantic Fisheries Organisation (NAFO) to protect areas of likely occurrence of taxa that are indicative of vulnerable marine ecosystems (VMEs) from the damaging effects of bottom-contact fishing gear. Results reveal subtle yet significant differences in macrofaunal assemblage composition and community structure between inside and outside the closed area, between above and below the 1200-m depth contour (i.e. the historical depth limit of fishing), and between areas where dense sponge spicule mats are either present or absent. Differences were observed in many assemblage metrics; however, the most revealing was the greater abundance, biomass, diversity, and number of VME indicative taxa inside the closed area than outside. Overall community composition is also significantly different between treatments. Depth, sediment temperature, and the proportion of clay within sediments are important in shaping the faunal assemblage. The importance of the effects of fishing is discussed, although it is not possible to ascertain if fishing is the direct cause behind observed differences in the macrofaunal assemblage. A continued closure of the area is recommended, as well as options for streamlining the evaluation process of other closed areas.

Ecosystem Engineering Effects of Aster tripolium and Salicornia procumbens Salt Marsh on Macrofaunal Community Structure

This paper examines how perennial Aster tripolium and annual Salicornia procumbens salt marshes alter the biomass, density, taxon diversity, and community structure of benthic macrofauna, and also examines the role of elevation, sediment grain size, plant cover, and marsh age. Core samples were collected on a fixed grid on an intertidal flat in the Westerschelde estuary (51.4° N, 4.1° E) over 5 years (2004–2008) of salt marsh development. In unvegetated areas, macrobenthic biomass, density, and taxon diversity were highest when elevation was highest, benthic diatoms were most abundant, and sediment median grain size was smallest. In contrast, in salt marsh areas, macrobenthic biomass and taxon diversity increased with median grain size, while the effects of elevation and diatom abundance on macrobenthic biomass, density, and diversity were not significant. In fine sediments, macrofaunal community structure in the salt marsh was particularly affected; common polychaetes such as Nereis diversicolor, Heteromastus filiformis, and Pygospio elegans had low abundance and oligochaetes had high abundance. Marsh age had a negative influence on the density of macrofauna, and A. tripolium stands had lower macrofaunal densities than the younger S. procumbens stands. There were no significant effects of marsh age, plant cover, and vegetation type on macrobenthic biomass, taxon diversity, and community structure. The results highlight that ecosystem engineering effects of salt marsh plants on macrofauna are conditional. Organic enrichment of the sediment and mechanical hindering of macrofaunal activity by plant roots are proposed as plausible mechanisms for the influence of the salt marsh plants on macrofauna.

Habitat heterogeneity influences cold‐seep macrofaunal communities within and among seeps along the Norwegian margin. Part 1: macrofaunal community structure

AbstractHåkon Mosby mud volcano (HMMV) is one of the most active and most studied seep sites in European waters. Many authors have described its thermal activity, dynamic of mud flows, and geochemical and microbial processes. It is characterised by a concentric zonation of successive biogenic habitats related to an activity and geochemical gradient from its centre to its periphery. Around the central area covered by mud flows, white and grey microbial mats occur among areas of bare sediment, whereas siboglinid tubeworm fields of Sclerolinum contortum and/or Oligobrachia haakonmosbiensis colonise the peripheral areas. The meiofaunal community is known to be structured among habitats, but the macrofauna has rarely been investigated and has never been sampled in situ. As part of the European project HERMES, using the ROVs Victor 6000 and Quest 4000, we sampled quantitatively the different habitats of the volcano for macrofauna sensus lato, retained on a 250‐ or 500‐μm sieve. We also sampled a newly discovered pockmark on Storegga slide (cne 5.6) and two pockmarks (G11, G12) in the Nyegga area. Macrofauna was identified and counted from phylum to family level. Our results on HMMV showed a gradient of increasing density and diversity from the volcano centre (1–3 taxa; 260 ind·m−2) to the peripheral siboglinid fields (8–14 taxa, 93,000 ind·m−2), with an intermediate situation for microbial mats. For macrofauna ≥500 μm, non‐siboglinid polychaetes dominated the communities of the central mud volcano area, white mats and S. contortum fields (83, 89 and 37% of the total, respectively), whereas gastropods dominated grey mats and O. haakonmosbiensis fields (89 and 44% of the total, respectively). Polychaete families followed the same pattern of diversity according to habitats within HMMV. Of 23 polychaete families identified, only one occurred in the centre, and three in the microbial mats. Capitellidae and Dorvilleidae (typical of organically and sulphide‐enriched areas) occurred at remarkably high densities in white microbial mats and in O. haakonmosbiensis fields. The S. contortum fields were the most diverse habitat with 12 polychaete families. The 250‐μm fraction showed similar taxa dominating the habitats, but taking meiofauna into account, nematodes became the major taxon in white mats and in S. contortum fields, where they were particularly large in size, whereas copepods dominated in other habitats. Meiofauna and macrofauna did not show the same patterns of density according to habitats. Using principal components analysis the habitats at HMMV were clearly distinct, and clustered according to dominant species of siboglinids and type of microbial mats. Pockmarks at Nyegga showed a similar concentric pattern of habitats around fluid sources as on the volcano, which seemed similarly to influence macrofauna composition, but at a much smaller scale. Total taxa and polychaete diversity are high in the S. contortum fields in these pockmarks as well. Regional‐scale comparisons including HMMV and Storegga suggested a higher influence of habitat‐type than seep‐site on the community structure.

Effects of thermal pollution on the soft-bottoms surrounding a power station in the Canary Islands (NE Atlantic ocean)

The spatial and temporal effects of hot seawater (60–70°C) from a power station on nearby soft-bottom communities were analyzed in the protected area “Sebadales del sur de Tenerife” (SE coast of Tenerife, Canary Islands, NE Atlantic Ocean). The samples were taken during summer 2003 and winter 2004 from 12 to 20 m depth. The highest macrofaunal abundance and species diversity were found in the turbines. A specific community, characterized by the polychaetes Aponuphis bilineata and sabellids of the genus Chone and the amphipod Photis longicaudata, inhabited the surroundings of the power station turbines. Permanent current from sea effluent had majok impact over the macrofaunal community structure of the neighbouring bottom where no measurable responses to thermal disturbance were detected.

Seagrass colonization: Knock-on effects on zoobenthic community, populations and individual health

This study provided evidence that Zostera noltii presence affects macrofauna community structure independently from median sediment grain-size and that the notion of ecosystem health is rather subjective: in the present case, we recorded “good health” in terms of seagrass development, “no impact” in terms of macrobenthic biotic indices and “negative effect” for a given key-population. The occurrence and development of a Z. noltii seagrass bed was surveyed at Banc d’Arguin, Arcachon Bay (France), to estimate the modification of the macrozoobenthic community and of the dynamics of a key-population for the local ecosystem, – the cockle Cerastoderma edule. Even though median grain-size of the sediment decreased only at the very end of the survey, i.e. when seagrass totally invaded the area, most of the macrofauna community characteristics (such as abundance and biomass) increased as soon as Z. noltii patches appeared. The structure of the macrofauna community also immediately diverged between sand and seagrass habitats, without however modifying the tested biotic indices (BENTIX, BOPA, AMBI). The health of the cockle population (growth, abundance, recruitment) was impacted by seagrass development. Related parasite communities slowly diverged between habitats, with more parasites in the cockles from seagrass areas. However, the number of parasites per cockle was always insufficient to alter cockle fitness.

Macrofaunal community structure in the littoral zone of a freshwater-deprived, permanently open Eastern Cape estuary

Spatial patterns in the macrofauna community structure within four distinct zones of the permanently open, freshwater-deprived Kariega Estuary on the southeastern coastline of southern Africa were investigated in March–May 2010. The zones within the littoral zone comprised a band of Zostera capensis (Setchell) exposed at spring low tide and comprising Zone I; a band of mud or sand, lacking vegetation, corresponded to Zone II; stands of Spartina maritima (Curtis) formed Zone III and a belt of Sarcocornia perennis (Miller) constituted Zone IV. Total macrofauna abundance and biomass during the study ranged from 16–816 ind/m2 and from 0.032–390.76 mg wwt/m2 and demonstrated no significant horizontal or vertical patterns (P > 0.05 in both cases). Multidimensional scaling (MDS) indicated that there were no significant spatial patterns in the macrofaunal community structure within the four zones which could be related to the predominance of euryhaline species, including Marphysa sanguinea (estuarine wonder worm), Arcuatula capensis (estuarine mussel), Macoma litoralis (littoral tellin) and Nassarius kraussianus (tick shell) throughout the estuary. The absence of any distinct spatial patterns in the community structure of the macrofauna appears to be related to the virtual absence of any horizontal patterns in selected physico-chemical variables and availability of submerged macrophytes along the length of the estuary. Comparisons with historical data indicate that while there have been no significant changes in the estimates of the total macrofauna abundance and biomass within the estuary over the past three decades, abundances of selected species have declined by as much as 80%. The decline in the abundances of these species appears to reflect the predominance of hypersaline conditions within the upper reaches of the estuary and intense fishing activities in the lower reaches of the system.

Macrofaunal Community Structure in the Littoral Zone of a Freshwater-Deprived, Permanently Open Eastern Cape Estuary

Spatial patterns in the macrofauna community structure within four distinct zones of the permanently open, freshwater-deprived Kariega Estuary on the southeastern coastline of southern Africa were investigated in March–May 2010. The zones within the littoral zone comprised a band of Zostera capensis (Setchell) exposed at spring low tide and comprising Zone I; a band of mud or sand, lacking vegetation, corresponded to Zone II; stands of Spartina maritima (Curtis) formed Zone HI and a belt of Sarcocornia perennis (Miller) constituted Zone IV Total macrofauna abundance and biomass during the study ranged from 16–816 ind/m2 and from 0.032–390.76 mg wwt/m2 and demonstrated no significant horizontal or vertical patterns (P > 0.05 in both cases). Multidimensional scaling (MDS) indicated that there were no significant spatial patterns in the macrofaunal community structure within the four zones which could be related to the predominance of euryhaline species, including Marphysa sanguinea (estuarine wonder worm), ...

Implications of dredging induced changes in sediment particle size composition for the structure and function of marine benthic macrofaunal communities

A meta-analysis approach was used to assess the effect of dredging induced changes in sediment composition, under different conditions of natural physical disturbance, for the structure and function of marine benthic macrofaunal communities. Results showed the sensitivity of macrofaunal communities increased as both the proportion of gravel increased and the level of natural physical disturbance decreased. These findings may be explained by the close association of certain taxa with the gravel fraction, and the influence of natural physical disturbance which, as it increases, tends to restrict the colonisation by these species. We conclude that maintaining the gravel content of surface sediments after dredging and, where practicable, locating extraction sites in areas of higher natural disturbance will minimise the potential for long-term negative impacts on the macrofauna.