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1.
A benthic annular flume for both laboratory and in situ deployment on intertidal mudflats is described. The flume provides a means of quantifying material flux (i.e., biodeposition of suspended particulates, sediment resuspension, nutrients, oxygen, and contaminants) across the sediment-water interface in relation to changes in current velocity and benthic community structure and/or population density of key macrofauna species. Flume experiments have investigated the impact of the infaunal bivalveMacoma balthica and the epifaunal bivalveMytilus edulis on seston and sediment flux at the sediment-water interface. The bioturbatorMacoma was found to increase the sediment resuspension and/or erodability by 4-fold, at densities similar to those recorded at the Skeffling mudflat (Humber estuary) (i.e., >1000 individuals m?2). There was a significant correlation between sediment resuspension andMacoma density (r=0.99; p<0.001), which supported previous in situ field observations indicating bioturbation byMacoma enhanced sediment erodability. Biodeposition rates (g m?2 h1) ofMytilus edulis andCerastoderma edule were quantified and related to changes in population density in a mussel bed (Cleethorpes, Humber estuary). Biodeposition rates were up to 40-times the natural sedimentation rates. At the highest mussel bed densities (i.e., 50–100% cover or >1400 mussels m?2) the physical presence of this epifaunal bivalve on the sediment surface reduced erosion by 10-fold. The shift from net biodeposition to net erosion occurred at current velocities of 20–25 cm s?1. These results demonstrate that infaunal and epifaunal bivalves can have a significant impact on seston flux or sediment deposition and on sediment resuspension or erodability in estuaries where there are extensive mudflats.  相似文献   

2.
Early in 1976 benthic studies were initiated in a 20 kilometer long portion of the Western Sacramento-San Joaquin River Estuary. Water quality determinations indicated little vertical or horizontal differences in pH, temperature, or dissolved oxygen concentration within the study area. Low river outflows allowed the encroachment of seawater into the study area, an area normally exposed to fresh or slightly brackish water. The sediment composition changed dramatically at most stations during the year, being dominated by sands early in the year but by silts and clays in late summer. The shift in sediment composition was accompanied by an increase in grease and oilland metals content. The benthic community of the study area was generally dominated by the Asiatic clam (Corbicula manilensis), Macoma balthica, oligochaetes, the amphipods Corophium stimpsoni and C. spinicorne, nematodes, and a spionid polychaete, Boccardia ligerica. These taxa comprised 98% on average of the total benthic macroinvertebrates collected at each study site. The benthic assemblages of each of the stations were generally very similar to one another. Faunal similarities and changes in benthos composition were related to substrate composition and salinity incursion. In general, the upstream-channel stations had higher abundance of benthos than the other stations in the study area. Total benthic abundance was lowest at the downstream end of the study area. Total standing crop peaked in June and was lowest in November. Our studies indicate that the most important factors controlling the size and species composition of the benthos of the study area are salinity and sediment composition.  相似文献   

3.
A field experiment was carried out to investigate the patterns of macrobenthic recolonization and to determine the effects of biodeposition on benthic communities at an intertidal oyster culture site in New Brunswick, Canada. Total organic deposition in azoic organic-free sediment trays was generally higher within the farm compared to reference sites. Two weeks after deployment of trays, total organic content had reached 1.1%. The abundance, species number, and diversity of the macrobenthic community were positively correlated with the total organic content in the experimental trays, but the correlations between community parameters and organic content were negative in the ambient sediment. The results suggest that organic matter in sediment may have positive effects on macrobenthic infauna at low levels as an additional food source but may be harmful to benthic animals at high levels. This study also indicates that location in the intertidal zone is a major parameter affecting the community structure of macrobenthic colonization.  相似文献   

4.
The goal of this paper is to find out whether suspended mussel culture affects the vertical fluxes of biogenic particles in the Ría de Vigo on a seasonal scale. With this aim, vertical fluxes of particulate organic carbon (POC) and the magnitude and composition of vertical export of phytoplankton carbon (Cphyto) collected in sediment traps were examined by comparing data obtained inside a mussel farming area (RaS) with those found at a reference station (ReS) not affected by mussels. Our results indicate that mussel farming has a strong impact on sedimentation fluxes under the rafts, not only increasing POC flux but also altering the magnitude and composition of Cphyto fluxes. Average POC flux at RaS (2564?±?1936 mg m?2 day?1) was four times higher than at ReS (731?±?276 mg m?2 day?1), and much of this increase was due to biodeposit fluxes (Cbiodep) which accounted for large proportion of POC flux (35–60 %). Indeed, because of this high Cbiodep flux, only a small proportion of the POC flux was due to Cphyto flux (3–12 %). At the same time, we observed an increased sedimentation of phytoplankton cells at RaS that could be explained by a combination of mechanisms: less energetic hydrodynamic conditions under mussel rafts, ballast effect by sinking mussel feces, and diatom aggregates. Moreover, mussel farming also altered the quality of the Cphyto flux by removing part of the predatory pressure of zooplankton and thus matching diatom composition in water column and sediment traps.  相似文献   

5.
Sediment toxicity and benthic macroinvertebrate community structure were measured as one component of a study cohceived to determine the distribution and effect of sediment contamination in tidal freshwater portions of the Potomac and Anacostia rivers in the Washington, D.C., area. Samples were collected at 15 sites. Analyses included a partial life cycle (28 d) whole sediment test using the amphipod Hyalella azteca (Talitridae) and an assessment of benthic community structure. Survival and growth (as estimated by amphipod length) were experimental endopoints for the toxicity test. Significant mortality was observed in 5 of 10 sites in the lower Anacostia River basin and at the main channel Potomac River site. Sublethal toxicity, as measured by inhibition of amphipod growth, was not observed. Toxicity test results were in general agreement with synoptically measured sediment contaminant concentrations. Porewater total ammonia (NH3+NH4 +) appears to be responsible for the toxicity of sediments from the Potomac River, while correlation analysis and simultaneously extracted metals: acid volatile sulfide (SEM∶AVS) results suggest that the toxicity associated with Anacostia River sediments was due to organic compounds. Twenty-eight macroinvertebrate taxa were identified among all sites, with richness varying from 5 to 17 taxa per site. Groups of benthic assemblages identified by group-average cluster analysis exhibited variable agreement with sediment chemical and sediment toxicity results. Integration of toxicological, chemical, and ecological components suggests that adverse environmental effects manifest in the lower Anacostia River benthos result from chemical contamination of sediment.  相似文献   

6.
The environmental impacts of salmon net-pen aquaculture on the benthic environment were investigated at a commercial fish farm located in coastal Maine waters. This site has a sandy mud bottom and low current velocities, is subjected to episodic sediment resuspension, and way in production for 3 yr prior to this study: We examined both the increase in carbon flux to the benthos caused by the net-pen and the effects of the elevated flux on sediment biogeochemistry and the microbenthic communities. The experimental design involved the establishment of two study sites, an ambient site ca. 100 m from the net-pen and a treatment site around the pen. Sediment traps deployed 1 m above the sediment-water interface indicated that carbon flux to the benthos was increased 1-fold to 6-fold (to a maximum of 5 g m?2d?1) at the edge of the net-pen with little or no increase in carbon flux 10 m from the pen. Unlike carbon flux rates, sediment organic matter inventories showed a complex pattern of change over time. Mineral surface area, organic carbon and nitrogen, digestible protein, and sterol content were initially (April 1991) lower beneath the pen than in ambient sediments. During 1991 ambient sediment accumulated organic matter until July after which it decreased, to a low during November. In contrast, organic matter inventories of sediment beneath the pen remained low until July and then increased to a high during November. These latter gains were associated with the development of bacterial mats at the sediment-water interface. Beneath the pen, microbial and macrofaunal communities were shifted toward those commonly associated with organic enrichment but seasonal trends and storm-related resuspension events also significantly affected these sediment communities. When abundant, most epibenthic organisms were more numerous near the pen than in adjacent ambient areas. These results suggest that net-pen aquaculture can alter the benthic ecosystem in Maine Coastal waters but indicate that the effects are spatially limited.  相似文献   

7.
Mussel populations (Mytilus edulis) in the Dutch Wadden Sea (intertidal mussel beds, subtidal beds and culture plots), the culture methods, the extent of mussel culture, and the ecology of the mussel are described. Mussels filter suspended matter from the water column and deposit it as feces and pseudofeces. Mussel beds consume large amounts of phytoplankton and speed up the cycle of production and breakdown of organic matter. There are indications that the consumption of phytoplankton can lead to food shortage for several animal groups. Mussels serve as an important food source for a wide range of organisms (e.g., starfish, eider ducks, and oystercatchers). Because mussel culture increased the mussel biomass in the Dutch Wadden Sea, the impact also increased. The most obvious impact of the culture is the dredging of seed mussels. Overexploitation of intertidal mussel and cockle beds and bad spatfall of both mussels and cockles since 1988 had a negative impact on bird populations. The extent of positive and negative aspects of mussel culture depends on natural and human influences. The negative aspects may (partly) be overcome by appropriate measures. *** DIRECT SUPPORT *** A01BY069 00007  相似文献   

8.
Concentrations of Fe, Mn, Cu, Zn, U and Pb, and stable Pb isotopes 206Pb, 207Pb and 208Pb were measured via inductively coupled plasma mass spectrometry in sediments, water and freshwater mussels (Velesunio angasi) from two catchments in the Alligator Rivers Region, Australia. Sediment U and Pb concentrations were higher in Magela Creek downstream than upstream of the Ranger U mine due to the mineralised nature of the catchment and potential local input of sediment from the mine site. Water metal concentrations were highest in Georgetown Creek, which is a tributary of Magela Creek and part drains the Ranger mine site, but there was little difference in concentrations between the Magela Creek upstream and downstream sites. Metal concentrations in mussels collected immediately upstream and downstream of the mine site also showed little difference, whereas Pb isotope ratios displayed a very distinct pattern. The 206Pb/207Pb and 208Pb/207Pb isotope ratios were more uranogenic downstream than upstream of the site and also more uranogenic than ratios measured in Sandy Billabong, a reference billabong in a catchment not influenced by U mineralisation. Isotope ratios were also more uranogenic in younger mussels, potentially due to the increasing footprint of the mine site over the past decade. The most uranogenic ratios were found in mussels from Georgetown Creek and at a site approximately 2 km downstream. At Mudginberri Billabong, approximately 12 km downstream of the Ranger mine, the relative contribution of uranogenic Pb to the total Pb concentration in mussels was small and overwhelmed by the input of industrial Pb with a Broken Hill type Pb signature. Whereas metal uptake by and thus concentrations in mussel flesh are influenced by water chemistry, mussel condition and metabolic rates, Pb isotope ratios are independent of these factors and provide a powerful means of source apportionment of contaminants in mussels and waterways, in particular in an U mining environment.  相似文献   

9.
The sedimentation pattern of organic material in the Greenland-Norwegian Sea is reflected in the surface sediments, although less than 0.5% of the organic matter is buried in the sediment. Maximum fluxes and benthic responses are observed during June and/or August/September, following the pattern of export production in the pelagial zone. The annual remineralization rate on the Vøring Plateau is 3.0 g C m–2 a –1 Freshly settled phytodetritus, as detected by chlorophyll measurements, is rapidly mixed into the sediment and decomposed. It stimulates the activity of benthic organisms, especially foraminifera. The mixing coefficient for this material is D b=0.2 cm2 d–1, which is two to three orders of magnitude higher than that estimated from radiotracer methods. The effect on the geological record, however, is likely to be small. Chlorophyll-containing particles are at first very evenly distributed on the seafloor. After partial decomposition and resuspension, a secondary redistribution of particles occurs which can result in the formation of a high accumulation area, with an up to 80-fold increase in the sedimentation rate by lateral advection. This is mainly due to physical processes, because biodeposition mediated by benthic animals increases sedimentation by only a factor of two or three.  相似文献   

10.
Net system production ranged from 13% to 29% of apparent system production in enclosures modelling coastal marine waters. Net production was measured by direct and indirect methods along with factors which impact its magnitude and fate. The direct measures of carbon, phosphorus, and nitrogen content of accumulating flocculent material in enclosures without sediment agreed with indirect measures by net system metabolism and by net sediment storage from nutrient mass balances. Increased nutrient supply, increased the absolute, but not relative, net system production ultimately stored in the sediment. Net production as dry weight of floc did not agree with that calculated from oxygen metabolism owing to a high silicon content of the organic matter. The presence of a benthic macrofauna decreased net system production storage by about 28–54%.  相似文献   

11.
The study was performed between March 2009 and March 2010 at the Sinop Inner Harbor on cultured mussels at the offshore submerged longline system. The samples of mussels, sediment and suspended particulate matter were seasonally taken for the purpose of monitoring differences of metal contents. In addition, burnable organic matter, contamination factors (CF), pollution load index (PLI) in sediment samples, meat yield of mussels were seasonally determined. All metals in suspended particulate matter were found to be above the national limit. Cd concentration in sediment was above the limit according to sediment quality guidelines, and Cd concentration in mussel was above both national and international limit values. According to CF and PLI identified in sediment, it was found that Inner Harbor was under the effect of anthropogenic pollution in terms of Cd accumulation. Provisional tolerable weekly intake calculated in mussel did not exceed the tolerable consumption values. In conclusion, it can be said that this region considered for commercial mussel cultivation is not a suitable area.  相似文献   

12.
In coastal ecosystems, suspension-feeding bivalves can remove nitrogen though uptake and assimilation or enhanced denitrification. Bivalves may also retain nitrogen through increased mineralization and dissimilatory nitrate reduction to ammonium (DNRA). This study investigated the effects of oyster reefs and clam aquaculture on denitrification, DNRA, and nutrient fluxes (NO x , NH4 +, O2). Core incubations were conducted seasonally on sediments adjacent to restored oyster reefs (Crassostrea virginica), clam aquaculture beds (Mercenaria mercenaria) which contained live clams, and bare sediments from Smith Island Bay, Virginia, USA. Denitrification was significantly higher at oyster reef sediments and clam aquaculture site than bare sediment in the summer; however, DNRA was not enhanced. The clam aquaculture site had the highest ammonium production due to clam excretion. While oyster reef and bare sediments exhibited seasonal differences in rate processes, there was no effect of season on denitrification, or dissimilatory nitrate reduction to ammonium (DNRA) or ammonium flux at the clam aquaculture site. This suggests that farm management practices or bivalve metabolism and excretion may override seasonal differences. When water column nitrate concentration was elevated, denitrification increased in clam aquaculture site and oyster reef sediments but not in bare sediment; DNRA was only stimulated at the clam aquaculture site. This, along with a significant and positive relationship between denitrification and sediment organic matter, suggests that labile carbon limited nitrate reduction at the bare sediment site. Bivalve systems can serve as either net sinks or sources of nitrogen to coastal ecosystems, depending mainly on the type of bivalve, location, and management practices.  相似文献   

13.
The feeding behavior of three species of mussels, the native Ischadium recurvum and the invasives Mytella charruana and Perna viridis, was studied in an invaded ecosystem in Florida (USA). In situ feeding experiments using the biodeposition method were performed along a salinity gradient in four different locations along the St. Johns River. Water characteristics, such as salinity, temperature, dissolved oxygen, and seston loads, were recorded to identify relationships between these variables and the feeding behavior of the mussels. Feeding behavior of the species varied by study site. Clearance, filtration, organic ingestion, and absorption rates of I. recurvum were negatively affected by salinity. For the invasive mussel, M. charruana, rejection was positively related to salinity while total ingestion, organic ingestion, and absorption rates were positively related to the percentage of organic matter in the seston. For P. viridis, total and organic ingestion rates were negatively affected by salinity but positively affected by total particulate matter. Condition indices for P. viridis and M. charruana were 13.16?±?0.64 and 6.63?±?0.43, respectively, compared to 4.82?±?0.41 for the native species I. recurvum, indicating that these mussels are well adapted to the environmental conditions in the area. This study indicates that the three species have different preferred habitats because of their specific responses to water characteristics. Thus, the invasive mussels will not totally occupy the niche of the native mussel in Florida despite overlapping zones. These data may help identify potential invaded areas and understand the extent of the invasion.  相似文献   

14.
Several tidal flats in both Estero de Punta Banda and Bahia de San Quintín, Baja California, and one in Mission Bay, southern California, were sampled for macrofaunal properties (taxonomic composition, density, species richness, and functional groups for animals ≥0.3 mm) and associated environmental variables (sediment properties, salinity, plant belowground biomass, and cover ofZostera marina) in order to establish a benchmark data set for these areas. The grouping of macrofauna into higher taxonomic or functional groups for these comparisons reduced variability and revealed stronger relationships. Each estuary had a fairly distinct macrofaunal assemblage, with that of Estero de Punta Banda being different from Bahia de San Quintín and Mission Bay primarily due to dominance by a capitellid polychaete, lower proportions of surface deposit feeders, and higher proportions of fauna with a planktonic stage. The flats in Mission Bay and Bahia de San Quintín were dominated by peracarid crustaceans, oligochaetes and polychaetes and had higher proportions of direct developers and macrofauna with mobile adult stages than did Estero de Punta Banda. There was an overlap of the environmental characteristics among estuaries, with more variability of sediment and vegetation properties within than among estuaries. Within Bahia de San Quintín, there was an oceanic to back-bay distribution gradient of macrofauna that was similar to that found in estuaries in wetter climates, despite the lack of a salinity gradient in San Quintín. A decoupling of the benthos and the assumed anthropogenic stresses was observed with the degraded site, Mission Bay, being most similar to the relatively pristine Bahia de San Quintín. Selection of reference sites and sampling variables should be made cautiously because effects of disturbance factors on the benthos may be site-dependent, scale-dependent, or negligible.  相似文献   

15.
Monitoring of small-scale distribution patterns of benthic invertebrates has demonstrated distinct trends in faunal abundances with position relative to individual culms of saltmarsh cordgrass,Spartina alterniflora, at Tar Landing Bay Marsh, near Morehead City, North Carolina. Samples containing culms ofSpartina yielded significantly higher abundances (at least three times) than did samples without them. Among common species, onlyNereis succinea did not show this effect. Matrix-arranged and randomly placed sets of samples have confirmed a positive relationship between cross-sectional area of culms in a sample (at the sediment-water interface) and contained numbers of macrofauna, juvenile macrofauna and meiofauna. These patterns occurred despite a decreased volume of sediment in samples containing culms. Heightened abundances of benthic invertebrates associated with structural elements at the sediment-water interface may result from either nonrandom recruitment (either active via recruit selectivity or passive through hydrogeographic effects of culms) or differential post-recruitment mortality (resulting from inhibition of epibenthic predators or from variable habitat quality).  相似文献   

16.
The role of labile organic material and macrofaunal activity in benthic respiration and nutrient regeneration have been tested in sublittoral fine sand sediments from the Gulf of Valencia (northwestern Mediterranean Sea). Three experimental setups were made using benthic chambers. One experiment was performed in-situ through the annual cycle in a well-sorted fine sand community. The remaining experiments were carried out with mesocosms under laboratory conditions: one with different concentrations of organic enrichment (mussel meat and concentrated diatoms culture), and the other adding two different densities of the endofaunal bivalve Spisula subtruncata. Biochemical variables in surface sediment and changes in oxygen consumption and nutrient fluxes throughout incubation period were studied in each experiment. In the in situ incubations, dissolved oxygen (DO) fluxes showed a strong correlation with sedimentary biopolymeric fraction of organic carbon. Organic enrichment in the laboratory experiments was responsible for increased benthic respiration. However, sediment response (expressed as DO uptake and dissolved inorganic nitrogen—DIN—release) between oligotrophic and eutrophic conditions was more intense than between eutrophic and hypertrophic conditions. S. subtruncata abundances close to 400 and 850 ind m?2 also intensified benthic metabolism. DO uptake and DIN production in mesocosms with added fauna were between 60 and 75 % and 65–100 % higher than in the control treatment respectively. The results of these three experiments suggest that the macrobenthic community may increase the benthic respiration by roughly a factor of two in these bottoms, where S. subtruncata is one of the dominant species. Both organic enrichment and macrobenthic community in general, and S. subtruncata in particular, did not seem to have a relevant role in P and Si cycles in these sediments.  相似文献   

17.
We reared larval zebra mussels,Dreissena polymorpha, and quagga mussels,D. bugensis, through and beyond metamorphosis (settlement) at salinities of 0–8‰. Juvenile zebra mussels gradually acclimated to 8‰ and 10‰ have been reared at these salinities for over 8 mo. Tolerance to both higher temperatures and higher salinities increases with larval age in both species (though zebra mussel embryos and larvae have a greater degree of salinity tolerance than quagga mussel embryos and larvae). Thus, only 6% of 3-day-old zebra mussel veligers survived after exposure to 4‰ for 8 additional days, whereas there was 22% survival of veligers placed in 4‰ at day 13 and grown to settlement 11 d later. Zebra mussel pediveligers, acclimated to increasing salinity in 2‰ increments beginning at day 23, continued to survive and grow in 8‰ after 5-mo exposure, though the growth rates of these juveniles were significantly less than those of juveniles reared in lower salinities. Quagga mussels did not metamorphose and settle as quickly as zebra mussel pediveligers. No quagga mussel pediveligers had settled before exposure to artificial fresh water (AFW), 2‰ 4‰, 6‰, and 8‰ on day 30. Percent settlement of these quagga mussel juveniles (based on 100% survival at the start of experiments on day 30) was 90% in AFW, 67% at 2‰, 69% at 4‰, 46% at 6‰, and 0.1% at 8‰.  相似文献   

18.
Filter-feeding bivalves, like oysters, couple pelagic primary production with benthic microbial processes by consuming plankton from the water column and depositing unassimilated material on sediment. Conceptual models suggest that at low to moderate oyster densities, this deposition can stimulate benthic denitrification by providing denitrifying bacteria with organic carbon and nitrogen (N). While enhanced denitrification has been found at oyster reefs, data from oyster aquaculture are limited and equivocal. This study measured seasonal rates of denitrification, as well as dissimilatory nitrate reduction to ammonium (DNRA), and dissolved inorganic N fluxes at a rack and bag eastern oyster (Crassostrea virginica) aquaculture farm. Consistent with models, denitrification was enhanced within the farm, with an average annual increase of 350% compared to a reference site. However, absolute denitrification rates were low relative to other coastal systems, reaching a maximum of 19.2 μmol m?2 h?1. Denitrification appeared to be nitrate (NO3 ?) limited, likely due to inhibited nitrification caused by sediment anoxia. Denitrification may also have been limited by competition for NO3 ? with DNRA, which accounted for an average of 76% of NO3 ? reduction. Consequently, direct release of ammonium (NH4 +) from mineralization to the water column was the most significant benthic N pathway, with seasonal rates exceeding 900 μmol m?2 h?1 within the farm. The enhanced N processes were spatially limited however, with significantly higher rates directly under oysters, compared to in between oyster racks. For commercial aquaculture farms like this, with moderate oyster densities (100–200 oysters m?2), denitrification may be enhanced, but nonetheless limited by biodeposition-induced sediment anoxia. The resulting shift in the sediment N balance toward processes that regenerate reactive N to the water column rather than remove N is an important consideration for water quality.  相似文献   

19.
Benthos cannot survive in strongly reduced sediments, in which the redox potential is around ?400 mV. Such sediments are typically found in inner harbors that are exposed to wastewater discharges. Field experiments were conducted to investigate the potential of sediment microbial fuel cells (SMFCs) for improving the benthic environment in such sediments. To the best of our knowledge, this has not been reported in any previous literature. Bottom sediment was collected and used to fuel an SMFC suspended 500 mm below the water surface. The sediments then were collected one year after installation, and their benthos environment was investigated. The most remarkable results are that the diversity and growth of benthos were higher in the SMFC-applied sediment than in a control sediment. The results have further strengthened that the sediment remediation was enhanced, in which the oxygen consumption rate of the sediment was reduced, and the mineralization of the organic matter was increased. Our findings suggest that SMFCs are a promising technology for the remediation of strongly reduced sediment and for the improvement of the benthic environment.  相似文献   

20.
Marine phanerogams are ecosystem engineers, as their presence induces major environmental changes that impact on the benthic fauna. Consequently, modifications to the structure of benthic communities would be expected to be associated with seagrass decline. Since 2005, Zostera noltii seagrass beds in Arcachon Bay (France), the largest in Europe, have undergone a severe decline. Twelve stations distributed throughout the lagoon were sampled in 2002, and all were found to be densely planted at that time. Subsequently, the same stations were revisited in 2010 and seagrass cover had drastically decreased by that time. Based on benthic macrofauna, multidimensional scaling (MDS) analysis identified four groups. Years were separated. In 2002, two groups were distinct in relation to the water body, since in 2010 separation between the two other groups was related to seagrass occurrence. When looking at community structure and dominant species there were moderate differences within and between years, independent of seagrass decline. Seagrass loss did not drastically modify the species composition as they were preserved in the remaining seagrass patches. However, there was a drop in macrofauna abundance in unvegetated muddy compared with abundance in the remaining seagrass areas. Epifauna was particularly affected by seagrass decline. Among biotic indicators based on macrofauna, multivariate indicator MISS (Macrobenthic Index in Sheltered Systems) was in agreement with the similarity of macrofauna structure among groups, while other tested indicators performed badly in relation to seagrass occurrence. However, no index detected seagrass loss, highlighting the necessity of maintaining a separate survey on seagrass cover.  相似文献   

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