Benthic community response to a passive fishing gear in a coastal lagoon (South Brazil)

The influence of a passive shrimp fishing gear on benthic communities was studied at Laguna Estuarine System (South Brazil), a shallow choked coastal lagoon. The gear is composed by a group of fyke nets (25 mm mesh size) set in contact to the bottom, fixed with stakes forming a cage-like structure (around 30 m²). Samplings were conducted in the two main fishery areas of the estuarine system, Mirim (sand bottoms) and Imaruí (muddy bottoms) lagoon, in May 2005. In each area, 10 fyke net enclosures and 10 nearby sites without nets (control) were sampled. Microphytobenthos biomass (chlorophyll a and phaeopigments), number of taxa/species, density, Hill’s number N ₁ and N ₂, and estimated number of species (ES₁₀₀) were used as community attributes. For the nematodes, values of the maturity index and abundance of Wieser’s feeding type were used as well. The effects of the small-scale passive shrimp fishing gear on the coastal lagoon bottoms were dependent on the benthic component analyzed and the type of sediment. Whereas macrofauna was not affected by the net enclosures, meiofauna and nematodes, particularly from the mud sites were. At the sand site, the fyke net enclosures caused a decrease in the microphytobenthos biomass and changed the relative abundances of non-selective deposit feeding and epigrowth-feeding nematodes. The results indicated that small-scale static nets, such as the studied fyke enclosures, produced low intensity levels of disturbance. However, the enclosed area by nets at Laguna had already reached around 25,000 m². Given the large proportion of the coastal population involved and the area closed by nets, management policies should consider site-specific differences within the same estuarine system.     

Macrozoobenthic community structure in a poikilohaline Mediterranean lagoon (Laki Lagoon, northern Aegean)

The community structure of the macrobenthic fauna was studied in the overall area of Laki Lagoon in September 1997 (salinity 32–35 psu) and monthly from February 1998 to February 1999 in the innermost part of the lagoon (salinity 0.1–6.8 psu). Community structure was analyzed by means of uni- and multivariate methods. In September 1997, the macrofauna in the outer part of the lagoon was characterized by a higher diversity and the occurrence of both lagoonal and marine species, and in the innermost part by a higher total abundance and the occurrence of a few lagoonal species. The combination of distance from the sea, depth, salinity and sediment organic matter correlated best with the spatial distribution pattern of the macrobenthic fauna. Community structure in the innermost part of the lagoon showed a seasonal periodicity. Species composition during spring 1998, at 0.1–2.0 psu, was similar to that in September 1997. During summer the macrobenthic fauna became impoverished, but recovered from late summer onwards. The salinity increase during summer (up to 5–7 psu) was followed by the appearance of marine species in the innermost part of the lagoon. Total abundance displayed a peak in late spring and a lower one in mid-autumn. The seasonal dynamics of the faunal assemblage was mainly governed by water temperature. Predation pressure by Atherina boyeri may have contributed to quantitative community changes during autumn.     

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

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

Major benthic communities of the south-west lagoon of New Caledonia

A quantitative survey of the macrobenthos in the south-west lagoon of New Caledonia was carried out at 35 stations, sampled both with a grab and by diving. The stations were classified by multivariate analysis on the basis of their floral and faunal composition and three major communities, corresponding to muddy bottoms, grey sand bottoms and white sand bottoms, were identified. At the same time, grain-size analysis performed on sediment samples at each station enabled us to identify the most discriminating grain-size parameters for each type of bottom. Classification of stations with respect to the mud fraction and the very fine + fine sand fraction reproduced the groups identified on the basis of purely taxonomic criteria. Application of these results to the available sedimentological data allowed the main benthic communities in the investigation area to be mapped.     

Impacts of the 2011 Tsunami on Sediment Characteristics and Macrozoobenthic Assemblages in a Shallow Eutrophic Lagoon,Sendai Bay,Japan

A huge tsunami is one of the greatest disturbance events in coastal benthic communities, although the ecological consequences are not fully understood. Here we examined the tsunami-induced changes in the sediment environment and macrozoobenthic assemblage in a eutrophic brackish lagoon in eastern Japan. The 7.2-m-high tsunami completely replaced muddy sediment with drifting sea sand throughout the lagoon, leading to the drastic changes in quantity and quality of sedimental organic matters, sulfide contents, and sediment redox condition. Intensive physical stress devastated the benthic community, but the disappearance of sulfidic muddy bottoms significantly improved the habitat quality for macrozoobenthos. The re-established macrozoobenthic community after 5 months was characterized by (1) a 2-fold higher total density, but sharp declines in species richness, diversity, and evenness; (2) an increased density of opportunistic taxa (e.g., polychaete Pseudopolydora spp. and amphipod Monocorophium uenoi) in newly created sandy bottoms; and (3) disappearance of several dominant taxa including bivalves and chironomid larvae. These findings indicate that the sensitivity and recovery potential of macrozoobenthos were highly taxa-specific, which was closely related to the taxa’s ecological characteristics, including tolerance to physical disturbance, life-history traits, and life form. Our data revealed the rapid recolonization of opportunistic macrozoobenthos after a huge tsunami, which would contribute to the functional recovery of estuarine soft-bottom habitats shortly after a disturbance event.     

Benthic zonation of the Eastern Gotland Basin, Baltic Sea

In this paper recent benthic biological studies in the Eastern Gotland Basin area of the Baltic Sea are summarised. A general pattern of vertical distribution of macrofauna is presented and special reference is made to sharp temporal changes in macrofauna of deeper, subhalocline areas of the basin. Information on faunal sediment reworking ability is compiled. The environmental factors driving benthic zonation are discussed and the vertical benthic zones are defined on the basis of their major biological and abiotic features. This analysis shows that due to sharp gradients in environment and clear differences in composition of macrofauna, the ecological functioning of the Eastern Gotland Basin benthic zones is clearly different. Therefore, in the biogeochemical models of benthic-pelagic interaction, these zones (together with water layers they underlie) should be treated separately, as different sub-systems.     

Patterns in pelagic and benthic nanoflagellate densities in the coastal upwelling system along the Banc d'Arguin,Mauritania

We studied spatial variation in abundance of marine benthic and pelagic heterotrophic nanoflagellates in relation to abundances of autotrophic flagellates, bacteria and cyanobacteria in an upwelling area off the Banc d'Arguin, Mauritania.There was enormous spatial variation in densities. In the sediments these ranged from 8–219 × 10³ cm^–3 for heterotrophic flagellates. Maximum values are in the range of those for temperate shallow marine bottoms. Low densities (< 20 × 10³) were confined to the deep stations (> 1000 m). Over the shelf (10–100 m depth) densities were high but related to grain size rather than to concurrent upwelling phenomena or to the abundance of benthic macrofauna.Pelagic flagellate abundance appeared to be more indicative of contemporary hydrographic conditions, most obvious by an increase in the ratio heterotrophic/autotrophic nanoflagellates away from the area of most intense upwelling.     

Oligochaetes in the southern basin of the Venetian Lagoon: community composition, species abundance and biomass

The oligochaete community of the Chioggia Lagoon (southern basin of the Venetian Lagoon) has been studied from May 1992 to May 1994, at ten fixed sampling stations, distributed across the lagoon. Numerous data regarding composition, abundance, biomass and the breeding periods of the species in the community have been obtained. Nine tubificid species, recently reported for the Mediterranean and Ponto-Caspian areas have been collected. Among them only three were abundant everywhere, except in the innermost part of the lagoon, and throughout the year: Tubificoides vestibulatus, T. swirencowi and Limnodriloides maslinicensis. Only one enchytraeid genus, Grania, has been found restricted to an area near the connection with the sea. The values for the Shannon Diversity Index for the community never exceeded 0.8 and were mainly between 0.4 and 0.7. The most interesting result was the decrease of abundance and biomass, proceeding from the sea mouth (about 6000 ind m^–2) towards the innermost part of the lagoon (less than 100 ind. m^–2). Correlations are suggested with the different grain size of the sediment.     

Impact of a low salinity year on the metabolism of a hypersaline coastal lagoon (Brazil)

Araruama Lagoon is a large, continuously hypersaline coastal lagoon (mean salinity 52 g l^-1). However, during certain years the evaporation-precipitation balance is modified and results in lower salinity conditions, e.g. 1989–1990 when the mean salinity measured 41 g l^-1. These atypical conditions are responsible for a different behavior of the system, normally characterized by the presence of extensive microbial algal mats, low pelagic primary production compared to benthic primary production, and low turbidity. However, during this study (1989–1990), the presence of microbial algal mats was restricted to the shallow eastern embayment of the lagoon representing c.a. 8% of the total area, the mean concentration of suspended matter was relatively high (21.2 mg l^-1) when compared with a typical year, and primary production measured was 447 mg C m^-2 d^-1, higher than benthic primary production during hypersaline years. These conditions therefore influence the trophic state of the system, during low salinity conditions, the lagoon was meso-eutrophic.     

Distribution and abundance of demersal fishes and of some other marine benthic organisims on the continental shelf (0-60 m) of French Guiana

In order to establish the distribution and abundance of demersal fishes and of some other benthic organisms on the continental shelf of French Guiana (western central Atlantic), ninety-five bottom trawls were effected at depths ranging from 0 to 60 m in October 1993. A total of one hundred and ten different species were identified including eight decapod crustaceans, two cephalopods, one sea turtle and ninety-nine fishes. Despite the high species richness in benthic macrofauna, most species showed a low count, and only twelve of them comprised more than 80% of total captures. This study has mainly highlighted the existence of a well-pronounced bathymetric zonation. This phenomenon would appear to be linked to environmental factors, especially salinity and substrate granulometry, which are greatly conditioned by fresh water and sediment flowing in large rivers such the Amazon River. The results revealed three distinct faunistic assemblages: a littoral (or shallow-water) community (0-30 m) distributed in coastal estuarine waters characterized by muddy bottoms, a middle-shelf community (30-50 m), and a lower-shelf community (depths > 50 m) distributed in deeper marine waters characterized by sandy bottoms.     

Caging experiment: Relationship between mesh size and artifacts

In marine sediments, cages are widely used to detect effects of predation on infauna. Artifacts due to the use of cages have been, instead, poorly estimated. In this study we have analysed the changes in macrofauna and in sediment composition when cages of different mesh sizes are used to exclude predators. In a shallow micro-tidal flat, the effect of three mesh sizes (2, 6 and 18 mm) was tested on sediment and macrofauna, using cages that excluded predators (EC), partial cages (PC) and natural sediment (un-caged plots, UC). PC allowed the predators to feed on the sediment, but modified the sediment similarly to the complete cages. Changes were measured for the abundance and species composition of macrofauna and for sediment total organic matter (TOM), chlorophyll-a, proteins and water content.The use of cages did not alter TOM and water content, whereas chlorophyll-a and phaeopigments were more abundant under the cages. The deep-burrowing shrimp Upogebia pusilla also increased under cages of any mesh-size. There was, instead, an effect on the abundance of macrofauna only when the smallest mesh size was used. Surprisingly, the exclusion of predators decreased the abundances of Tanais dulongii, Oligochaetes, Brania oculata, whereas the abundance of Aphelochaeta marionii changed when both PC and EC were put in the sediment. Collectively, all these findings indicated that for surface animals the use of small mesh sizes can bias the interpretation of results.     

Characterization of benthic habitat settings in a lagoonal ecosystem using free-living nematodes as proxy

Free-living nematodes are sensitive to most of the disturbances and therefore have ability to reflect direct structural and functional changes in an ecosystem. We studied nematode assemblages of Chilika Lagoon, the largest lagoon of Asia, across spatio-temporal scales in link with environmental variables and evaluated nematode assemblages as a proxy to characterize lagoonal benthic habitat settings. Our results revealed that nematode communities showed significant variation spatially and temporally in terms of mean density (16–854/10 cm²) and mean number of species (7–74). Salinity is the key factor that controls nematode community structure across this lagoon and was strongly supported by statistical analyses. The observed nematode assemblages were further used as a proxy to assign benthic habitats of Chilika into distinct biological, topographical and hydrological settings. This study showed that nematode assemblages could be effectively used for long term ecological monitoring of dynamic sedimentary environment of lagoons globally.     

Stabilizing properties of a high-biomass benthic community in a fluctuating ecosystem

The shallow Northern Adriatic Sea is subject to strong seasonal and short-time fluctuations in climatic parameters and production. A high-biomass benthic epifauna community on sublittoral soft bottoms with biomass values of 370±73 g wet weight m^–2, which consists of almost 90% filter feeders provides a storage compartment. This storage compartment exerts a regulatory effect on the total system metabolism through controlling watercolumn biomass and converting it to macrofauna biomass with a lower respiration: biomass ratio. Special adaptations of the brittle starOphiothrix quinquemaculata, the dominant species, to strong and rapid changes in temperature and oxygen saturation are discussed.     

Spatial and inter-annual variability of the macrobenthic communities within a coastal lagoon (Óbidos lagoon) and its relationship with environmental parameters

The present work aims to analyse spatial and inter-annual variability in the benthic environment within the Óbidos lagoon, assessing the relationships between environmental characteristics and macrobenthic distribution patterns. Sediment samples were collected in February 2001 and 2002 for the study of macrofauna and biogeochemical parameters (sediment grain size, organic matter, organic carbon, chlorophyll a, and phaeopigments). Comparing 2001 to 2002, a general increase in the number of species, diversity and equitability indices was observed throughout the study area. Likewise, there was an increase of phytopigments and organic matter contents in the upper sediment layer. Based on the macrobenthic community patterns and environmental variables three main areas could be distinguished in both years: an outer area near the inlet mostly influenced by the sea, with very depressed number of species and abundance, and dominated by Saccocirrus papillocercus, Lekanesphaera levii, Microphthalmus similis and Nephtys cirrosa; an intermediate area located in the central part of the lagoon characterized by sandy sediment and low organic carbon, and colonized by a high diverse community with Hydrobia ulvae, Cerastoderma edule and Abra ovata as the most characteristic species; and the innermost area of the lagoon with muddy enriched sediments dominated by Heteromastus filiformis, oligochaetes, Scrobicularia plana, Cyathura carinata, Corophium acherusicum, phoronids, insect larvae and Corbula gibba. Deposit-feeders were dominant in the muddy sediments from the inner area, where suspension-feeders were also abundant. Carnivores were associated with clean sandy sediments from the inlet area and herbivores were more abundant within the central area.     

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

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

Influence of benthic macrofauna on microbial production of methylmercury in sediments on the New England continental shelf

Microbial methylation processes in sediment are an important source of toxic monomethylmercury (MMHg) to aquatic ecosystems. Although bioturbation activities (feeding, digging of galleries, excavations, bioirrigation) by benthic fauna are known to affect many biogeochemical processes, their influence on benthic MMHg production is poorly understood. We investigated the effect of benthic fauna on the microbial production of MMHg in sediments on the continental shelf of the northwest Atlantic Ocean in September 2009. Replicate cores of sieved (control) and unaltered sediment containing native macrofauna were incubated to examine the influence of benthic macrofauna on net MMHg production, potential gross rates of Hg methylation, sediment reworking, dissolved oxygen and organic carbon concentrations, and microbial metabolic activities. The presence of macrofauna stimulated aerobic microbial respiration and net MMHg production, but had no observed effect on short-term gross rates of Hg methylation. This suggests that bioturbation may promote net MMHg production by inhibiting demethylating microorganisms, although overall community metabolism was increased. Results from this work emphasize the need to enhance our knowledge and understanding of the interactions among benthic fauna, microorganisms, and geochemistry in affecting MMHg production.     

Empirical Evidence Reveals Seasonally Dependent Reduction in Nitrification in Coastal Sediments Subjected to Near Future Ocean Acidification

Research so far has provided little evidence that benthic biogeochemical cycling is affected by ocean acidification under realistic climate change scenarios. We measured nutrient exchange and sediment community oxygen consumption (SCOC) rates to estimate nitrification in natural coastal permeable and fine sandy sediments under pre-phytoplankton bloom and bloom conditions. Ocean acidification, as mimicked in the laboratory by a realistic pH decrease of 0.3, significantly reduced SCOC on average by 60% and benthic nitrification rates on average by 94% in both sediment types in February (pre-bloom period), but not in April (bloom period). No changes in macrofauna functional community (density, structural and functional diversity) were observed between ambient and acidified conditions, suggesting that changes in benthic biogeochemical cycling were predominantly mediated by changes in the activity of the microbial community during the short-term incubations (14 days), rather than by changes in engineering effects of bioturbating and bio-irrigating macrofauna. As benthic nitrification makes up the gross of ocean nitrification, a slowdown of this nitrogen cycling pathway in both permeable and fine sediments in winter, could therefore have global impacts on coupled nitrification-denitrification and hence eventually on pelagic nutrient availability.     

Estimation of bottom ammonium affinity in the New Caledonia lagoon

Ammonium affinity of New Caledonia lagoon benthic communities was measured during the course of 33 in situ enrichment experiments, in order to estimate the contribution of benthos to ammonium fluxes. Ammonium chloride was injected into enclosures pushed into the sediment, in order to obtain a concentration of 20–22 mol l^-1 in the enclosed water which approximated the interstitial water content. Ammonium kinetic uptake was then followed for two hours. Grey-sand bottom displayed the highest affinity for ammonium, but white-sand and muddy bottom affinity was of the same order of magnitude. Macrophytes, and microphytes (when macrophytes are absent), account for the bulk of ammonium bottom uptake. As a result, grey-sand bottoms with their dense macrophyte cover represent a sink for water column nitrogen and play a key role in nutrient cycling of the lagoon. Correspondence to: G. Boucher     

Short Term Bioturbation Activity in the Lagoonal Sediments of Tikehau Atoll (Tuamotu Archipelago,French Polynesia)

To quantify bioturbation activity in Tikehau lagoon, a tracer made of black basaltic sand was poured over the natural white calcareous sediment surface. Three stations respectively located on the inner flat (-3m), the inner slope (-9m), and the lagoon floor (-19m), were studied for short periods of time (48 hours). Bioturbation by macrofauna was quantified by volume of sediment ejected onto the experimental surface and by volume of tracer incorporated into sediment. The results showed a rapid incorporation of sedimented particles at the interface by way of the funnels and burrows of surface deposit feeders and carnivores. Expelled quantities varied with respect to site location: 213 cm³ · m⁻² · 24 h⁻¹ in the inner flat; 98.9 cm³ · m⁻² · 24 h⁻¹ in the inner slope; 7.9 m³ · m⁻² · 24 h⁻¹ in the lagoon floor. Bioturbation by decapod megafauna appeared to be important in the dynamics of the sediments in the deepest areas of the lagoon. In these areas, with almost no hydrodynamical impacts on sediments, bioturbating events were responsible for sediment mixing (despite lower absolute rates than in shallow area). Hydrodynamics controlled the spatial distribution of macroinvertebrate trophic groups by its effects on sedimentation.