Prey selection by the hogchoker, Trinectes maculatus (Pisces: Soleidae), along summer salinity gradients in Chesapeake Bay, USA

We investigated feeding by the hogchoker, Trinectes maculatus (Bloch and Schneider), in freshwater, oligohaline, mesohaline, and polyhaline regions of Chesapeake Bay, USA, and examined prey selection in relation to food availability. Otter trawling for fish and Van Veen grab sampling for benthic macrofauna occurred in July and August 1992 and August and September 1993. Hogchokers exhibited both opportunistic and selective feeding patterns along the estuarine salinity gradient in four tributaries (Potomac, Rappahannock, York, and James Rivers) and in the mainstem Chesapeake Bay. Major prey taxa included annelids, arthropods, and tellinid siphons. In polyhaline habitat, polychaetes dominated both the benthos and gut contents numerically and gravimetrically. On the other hand, oligochaetes were numerically dominant in freshwater/oligohaline areas but were rarely eaten, perhaps because of their burial depth. Arthropods (mostly amphipods) occurred at most salinities, were common in gut contents in low-salinity areas, and were replaced as prey by larger proportions of polychaetes in polyhaline regimes. Although hogchokers ate tellinid siphons, they rarely consumed whole bivalves or gastropods. These diet patterns (and especially the importance of siphon nipping) are similar to those of juvenile or small flatfish elsewhere in Europe, Africa, and North America. A size–salinity relationship for hogchokers occurred along the summer salinity gradient, with smaller fish predominating upstream and larger fish downstream. It was not clear from our data if variation in diet composition reflected changes in prey composition along the salinity gradient rather than changes in fish size. Received: 14 June 1997 / Accepted: 27 June 1997     

Interactions between mangroves and exotic Spartina in an anthropogenically disturbed estuary in southern China

Cordgrass (Spartina alterniflora) was introduced to China in 1979 from the United States for reducing coastal erosion. It grows vigorously in China and has spread over much of the Chinese coast, from Leizhou Peninsula to Liaoning, a range of more than 19 degrees of latitude. On the southern coast of China, S. alterniflora has invaded mangrove-dominated habitats during the last two decades, but little is known about interactions between native mangroves and invasive S. alterniflora. We studied the distribution and competitive interactions between native mangroves and S. alterniflora in the Zhangjiang Estuary at four tidal sites along a salinity gradient: oligohaline upstream, mesohaline, polyhaline, and euhaline downstream. S. alterniflora occurred at all four sites, and several mangrove species occurred at all but the downstream euhaline site. S. alterniflora has invaded the estuary widely and has spread to the lower tidal margins of mangroves. It has not invaded mangrove areas with a closed canopy but has established in the mangrove zone where the canopy was opened by human disturbance. Ramets of S. alterniflora transplanted into the understory of mangrove stands with closed canopies died within 10 weeks, but 37.5% survived and grew well on open mud flats. S. alterniflora had virtually no competitive effect on mangrove seedlings planted at the upstream oligohaline site. However, S. alterniflora competitively reduced biomass of mangrove seedlings to 33% over a period of 14 weeks at the mesohaline and polyhaline sites where human disturbance has opened the mangrove canopy. In contrast, S. alterniflora marginally facilitated growth and survival of experimental seedlings at the downstream euhaline site. In China, mangroves occur along the coastline south of Whenzhou, but they have been severely disturbed and removed widely, mainly by mariculture activities. Natural vegetation patterns and our experimental results suggest that, without intervention, S. alterniflora could gradually replace these mangroves in mid-salinity regions of Chinese estuaries.     

Spatial and temporal variation of resource limitation in Chesapeake Bay

We report nutrient addition bioassays at 18 stations in Chesapeake Bay (USA) to assess resources limiting phytoplankton growth. Data were pooled from several sampling programs conducted from 1989 to 1994. Spatially, light and P limitation declined from low salinity regions to high salinity regions, as N limitation increased. This spatial pattern was driven primarily by freshwater inflows with high N/P and seawater inflows with low N/P. Seasonally, there was a marked progression of winter light limitation, spring P limitation, and summer N limitation at mesohaline and polyhaline stations. The seasonal pattern appeared to be caused by temperature, mixing, river discharge, and sediment P fluxes. At high salinity stations, we also observed winter N limitation (caused by DIN depletion prior to spring nitrate delivery), and at lower salinity stations there was fall P limitation (caused by reaeration of bottom sediments). At tidal fresh stations, turbidity and nutrient concentrations resulted in continuous light limitation, except at some stations in summer. Interannual decreases in light limitation and increases in N and P limitation appear to represent improvements in water quality. Received: 31 October 1997 / Accepted: 18 December 1998     

Detection of pollution effects on marine macrobenthos: further evaluation of the species abundance/biomass method

Further empirical data are presented to evaluate the method of detecting pollution-induced disturbance in marine benthic communities by a comparison of the distribution of numbers of individuals among species with the distribution of biomass among species. A suggested abbreviated name for the technique is the ABC method (abundance biomass comparison). Application of the technique to new data shows that it is a sensitive indicator of natural physical and biological disturbance as well as pollution-induced disturbance over both spatial and temporal scales. Changes in the configuration of ABC plots during ecological succession are the reverse of those resulting from increased pollution levels. The technique should also be applicable to intertidal sediments, where physical disturbance of the sediment by waves does not appear to preclude its utility.     

Untersuchungen zum ökotoxikologischen Schädigungspotenzial und Erosionsrisiko von kontaminierten Sedimenten in staugeregelten Flüssen

Particle-bound pollutants accumulate in river-bottom sediments, a process which results in a significant decrease in the ecotoxicological availability of toxicants for the majority of aquatic organisms. Under normal hydrologic conditions, the release of contaminants from bottom sediments is usually of minor importance. In contrast, flood events may remobilize highly contaminated sediments via in-stream erosion. The objective of this study was to develop a combined ecotoxicological and hydraulic approach to elucidate the ecotoxicological implications associated with the risk of erosion of contaminated sediments. This integrated strategy was applied to the lock-regulated Neckar river in Southern Germany. Both the bottom-sediment cores and suspended matter from two intensive flood events were investigated. Sediment samples below an erosional unconformity showed a sharp increase in the ecotoxicological load. Moreover, it was found that major flood events (HQ₅ and higher) could possibly erode even very old, well-consolidated and highlycontaminated sediments. The suspended matter of the high discharge events investigated (return periods of 15 to 20 years) exerted significantly higher cytotoxicity and mutagenicity than a moderate flood with a 1-year return period. These findings support the conclusion that the observed ecotoxicological effects during major floods may at least in part be due to the in-stream erosion of highly contaminated bottom sediments.     

Assessment of enrichment,geo-accumulation and ecological risk of heavy metals in surface sediments of the Msimbazi mangrove ecosystem,coast of Dar es Salaam,Tanzania

Results of the assessment of enrichment, accumulation and the ecological risk associated with three heavy metals (Cd, Cu and Pb) and one metalloid (As) in surface sediments of Msimbazi estuary are presented. Surface sediment samples (0–5 cm) were collected from Msimbazi River estuary in September 2016 using handheld PVC short corers. Long-sediment cores from the site were also collected using PVC pipes and their vertical profiles of metals concentrations assessed with the aim of establishing site-specific baseline metals concentrations. The established site-specific baseline values were used for the determination of normalised enrichment factors (EF) and geoaccumulation (Igeo) of metals instead of using average crustal values. Iron-based enrichment factors show that the sediments of Msimbazi have experienced enrichment of metals that originate from anthropogenic sources of pollution (EF > 1). Geo-accumulation results indicate that Msimbazi sediments can be designated as uncontaminated to moderately-contaminated with As, Cd and Pb (class 1–2). Geoaccumulation indices for Cu indicate that sediment can be designated as uncontaminated to moderately contaminated (class 1) and moderately to strongly contaminated (class 3). Results show further that the Ecological Risk associated with the accumulation of these metals in Msimbazi sediments was low based on Hakanson approach.     

Sedimentary Pigments and Organic Matter in Relation to Benthic Fauna in the Tan-Shui Estuary,Taiwan

The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary.

The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas.

Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments.     

Sedimentary Pigments and Organic Matter in Relation to Benthic Fauna in the Tan-Shui Estuary, Taiwan

The benthic ecological structure of the Tan-Shui estuary, Taiwan is changed due to long term effects of dumping of urban wastewater and of engineering actions. to monitor these changes, we sampled and analyzed benthos and sediment from 12 stations on the estuary.

The composition of the dominant species of benthos varied seasonally, with molluscan and crustacean species having greater numbers and higher frequencies of occurrence than other species. the dominant taxa during winter were Nassarius sp. and Maldanidae at two stations. Analysis using Simpson's index and Shannon's index showed the benthic community varied more in coastal areas than in offshore areas.

Physicochemical analysis showed that most of the Tan-Shui estuary consisted of sandy sediment. the variations in concentrations of organic carbon and total nitrogen at each station were small. Although the concentrations of chlorophyll-a and carotenoid at all stations were generally low, the two stations had the highest concentrations, and we concluded that the concentration of pigments in these sediments was related to the abundance of benthos. the community structure of the benthos reflected the characteristics of the sediments, and benthic species exhibited selection of and adaptation to specific sedimentary environments.     

An integrated investigation of biomarkers’ response in crabs (Liocarcinus depurator) and benthic indices at a metalliferous waste discharge area in North Evoikos gulf,Greece

This study applied biomarkers and benthic indices at an area in North Evoikos Gulf, Greece, affected by metalliferous slag disposal. Biomarkers of antioxidant defense (catalase, glutathione S-transferase), and neurotoxicity (acetylcholinesterase) were measured in crabs Liocarcinus depurator. Iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), and zinc (Zn) concentrations in sediments and crabs were also measured. High levels of all metals were found in sediments at the disposal area. Metal levels in the crabs were also higher in the disposal area although spatial differences were not as marked as in the sediments. Accordingly, biomarker responses of crabs in the disposal area were also noted suggesting impact on the antioxidant defense of the organisms against oxidative stress. Benthic indices showed disturbance in the disposal area. The combined approach of measuring biomarkers and contaminant levels in the crabs and sediment was complementary to the benthic indices approach providing indications of metal exposure related effects. Our results support the idea that a twofold monitoring approach of assessing both the benthic community structure shifts and the biomarkers and metal accumulation levels may integrate and capture both the structural and the toxicological effects of dumping onto the benthic communities.     

Atmospheric dinitrogen fixation by benthic communities of Tikehau Lagoon (Tuamotu Archipelago, French Polynesia) and its contribution to benthic primary production

Acetylene reduction rates were measured in lagoonal sediments, cyanobacterial mats and limestone surfaces between 1991 and 1995 at many sites, depths and seasons; all the studied substrata contained cyanobacteria. The acetylene reduction/¹⁵N₂ fixation ratio was measured for the different communities and varied between 1.8 and 4.8, depending on substratum. Fixation rates were 1.7 to 7 times higher during daylight compared to night-time rates. N₂ fixation rates ranged from 0.4 to 3.9 mg N m^-2 day^-1 for the lagoonal sediment/mat communities, and the rate was about 2 mg N m^-2 day^-1 for the lagoonal limestone substrata. Total lagoonal benthic N₂ fixation contributed 24.4% of the total nitrogen requirement for the benthic primary production of benthic communities of the lagoon. The input of N₂ fixation by the microbial planktonic communities (including cyanobacteria) of the lagoon, which are highly productive, is unquantified but is likely to be large.     

Causes and consequences of salt-marsh erosion in an Atlantic estuary in SW Spain

This study reports on the quantification of horizontal erosion by undermining of slopes in the atlantic mesotidal salt marshes of Odiel, SW Spain, and analyses its causes and consequences. Horizontal erosion has produced considerable losses of salt marsh area, including zones of mature salt marsh. Human pressure, such as from water-borne traffic or the exploitation of the slopes for the capture of bait, increases the natural erosion processes. The role of vegetation in protecting the slopes against erosion is studied. Channel banks covered with plants, many of which belong to species with long-living, above-ground creeping stems, were less eroded than those without vegetation cover. The enormous volume of sediments moved (ca. 7000m³ in one year) could contribute to the silting-up of the navigable channels of the estuary, so that continual dredging is necessary to allow access to shipping. These sediments are highly contaminated, and dredging exposes them more directly to the trophic network of the estuary. There is a considerable loss of natural resources. Finally, the integrated management of this coastal ecosystem is discussed.     

Benthic community response to petroleum-associated components in Arctic versus temperate marine sediments

We assessed the effects of crude oil and drill cuttings on sediment oxygen demand (SOD) of marine benthic communities from Arctic (Barents Sea) and temperate (Oslofjord) areas of the Norwegian continental shelf. Field-collected cores in both areas were subjected to three different treatments: two concentrations of hydrocarbon-contaminated sediments, and drill cuttings (DC). Cores were incubated for 21 days at 5°C (Barents Sea) and at 10°C (Oslofjord) during which SOD was measured five times. We observed significantly higher SOD in the high oil concentration (HOC) and DC treatments compared to control cores from the Arctic, but not in the temperate Oslofjord. No difference was observed between the low oil concentration (LOC) and control at either location. The clear differences in the response of Arctic benthic communities to petroleum compounds compared to temperate benthic communities is likely related to differences in community structure, sensitivity of individual taxa to petroleum-related compounds and different contamination history of the two study areas.     

广东清远电子垃圾处理地沉积物对伸展摇蚊的慢性毒性效应

电子垃圾拆解引起的环境污染和生态风险已成为全球关注的热点问题,不适当的电子垃圾拆解过程造成处理区水体沉积物受到多类有机化合物和重金属污染,直接威胁生活在沉积物中的底栖动物。在典型电子垃圾处理地广东清远采集沉积物,测定样品中以烃类为主的色谱难分离混合物(unresolved complex mixture,UCM)的含量,开展伸展摇蚊全生命周期慢性毒性测试。结果表明,清远沉积物中的UCM浓度(0.08±0.01)%接近于这类污染物对伸展摇蚊的慢性半致死性效应浓度(0.073±0.022)%。同时发现清远沉积物对以摇蚊为代表的底栖无脊椎动物具有显著慢性毒性效应,且可通过测定UCM含量初步估算。这为开展以电子垃圾处理地沉积物为代表的,受到以麻醉作用为主要致毒机制的混合物污染的沉积物的毒性评价提供了一种有效方法。     

Coral mortality following extreme low tides and high solar radiation

Extreme tidal events are one of the most predictable natural disturbances in marine benthic habitats and are important determinants of zonation patterns in intertidal benthic communities. On coral reefs, spring low tides are recurrent disturbances, but are rarely reported to cause mass mortality. However, in years when extremely low tides coincide with high noon irradiances, they have the potential to cause widespread damage. Here, we report on such an event on a fringing coral reef in the central Great Barrier Reef (Australia) in September 2005. Visual surveys of colony mortality and bleaching status of more than 13,000 corals at 14 reef sites indicated that most coral taxa at wave-protected sites were severely affected by the event. Between 40 and 75% of colonies in the major coral taxa (Acropora, Porites, Faviidae, Mussidae and Pocilloporidae) were either bleached or suffered partial mortality. In contrast, corals at wave-exposed sites were largely unaffected (<1% of the corals were bleached), as periodic washing by waves prevented desiccation. Surveys along a 1–9 m depth gradient indicated that high coral mortality was confined to the tidal zone. However, 20–30% of faviid colonies were bleached throughout the depth range, suggesting that the increase in benthic irradiances during extreme low tides caused light stress in deeper water. Analyses of an 8-year dataset of tidal records for the area indicated that the combination of extended periods of aerial exposure and high irradiances occurs during May–September in most years, but that the event in September 2005 was the most severe. We argue that extreme low-tide, high-irradiance events are important structuring forces of intertidal coral reef communities, and can be as damaging as thermal stress events. Importantly, they occur at a time of year when risks from thermal stress, cyclones and monsoon-associated river run-off are minimal.     

Macrozoobenthic community structure in the Ría de Foz,an intertidal estuary (Galicia,Northwest Spain)

The community structure of the macrobenthic (>1 mm) fauna of an intertidal soft-bottom estuary, the Ría de Foz (Galicia, Northwest Spain) was investigated on 99 occasions during June, September and December 1984 and March 1985. The infaunal data were subjected to classification and ordination techniques. The analyses indicated that sediment characteristics (grain size, percentage silt-clay and organic-matter content) and tidal height are the most important factors governing the distribution and abundance of the intertidal communities. Three faunal assemblages were identified and examined in terms of species dominance, constancy and fidelity. In the clean sands of the outer estuary two main assemblages were distinguished; one, corresponding to the boreal LusitanianTellina community, inhabited the middle and lower tidal levels; the other, typical of a biocoenosis of sands and slightly muddy mediolittoral sands, inhabited the upper tidal level. The third benthic assemblage occupied the muddy sands and mud of the inner estuary and displayed some features in common with theCardium edule-Scrobicularia community described by Thorson.     

Modelling the effects of green macroalgae blooms on the population dynamics of Cyathura carinata (Crustacea: Isopoda) in an eutrophied estuary

A population dynamics model was developed to simulate the effects of benthic macroalgae blooms (mostly Enteromorpha spp.) on the productivity of Cyathura carinata (Crustacea: Isopoda), a possible keystone species in the benthic communities of the Mondego estuary. The model describes C. carinata population dynamics, as well as the relationships between Enteromorpha biomass, Enteromorpha decaying rates, organic matter content in the sediments and detritus consumption by C. carinata, a detritic feeder. Model results support the idea that seasonal blooms of Enteromorpha determine a significant increase of organic matter content in the sediments, due to macroalgae decay, which initially contributes to enhance C. carinata consumption and growth rates, determining a significant increase in the biomass. Nevertheless, later, following the algae bloom, C. carinata biomass decreases, and reaches its lowest value, close to 0, when the algae crash. This effect is probably related with strong anoxic conditions, especially during night, due to high algal decomposition rates. In accordance with the model, migration of new individuals from adjacent areas must occur in order to recolonise the area affected by the algae bloom. Therefore, it seems reasonable to conclude that macroalgae blooms that are limited in space may favour C. carinata populations, but extensive blooms affecting the whole area of distribution of this species will determine its disappearance.     

Methodological approach for metal pollution evaluation in sediments collected from the Taranto Gulf

The concentrations of Hg, Cd, Pb, Cu, Ni, V, and Sn were determined in marine sediments collected from Taranto Gulf (Ionian Sea, Southern Italy). The aim of this article is to study the methodological approach in order to evaluate total metal levels determined in marine sediments of a contaminated area (Taranto Gulf, Southern Italy), to identify contaminated areas and to predict adverse biological effects based on Sediment Quality Guidelines (SQGs). The results are discussed in relation to geological characteristics of sediments in order to define background levels and anthropogenic input. Experimental results were elaborated by multivariate statistical techniques and Geographical Information System (GIS) software. The geoaccumulation index I _geo and two sets of SQGs (in particular (a) the threshold effect level (TEL), the probable effect level (PEL) and (b) the effect range-low (ERL) and the effect range median (ERM)) have been used for environmental evaluation of metal concentrations. Results show that in Taranto coastal area, Mar Piccolo basin represents the most contaminated area. A comparison with results from other Mediterranean areas demonstrates that for some metals (such as Cd, Pb, and Hg) Taranto seas represent one of the most polluted areas in the Mediterranean Sea. A comparison of metal levels with SQGs also suggests an ecotoxicological risk for benthic organisms mainly in the first inlet of Mar Piccolo.     

Study on polychlorinated dibenzo‐p‐dioxins and dibenzofurans in rivers and estuaries in Osaka Bay in Japan

In order to search the source of polychlorinated dibenzo‐p‐dioxins (PCDDs) and dibenzofurans (PCDFs) in blue mussel in Osaka bay, sediments from Osaka bay and from rivers running near an urban municipal incinerator were analysed for PCDDs, PCDFs and PCBs. The river and estuary sediments were all found to be contaminated with PCDDs at average levels of 9.8 and 12ppb on the dry basis, PCDFs of 7.8 and 5.1 ppb, and PCBs of 1600 and 1300ppb, respectively. The two sediments contained similar profiles of specific isomers and congeners of PCDDs and PCDFs with each other. In addition, there was observed positive close correlations between PCDD and PCDF levels in the two specimens as well as fly ash from urban municipal incinerators. These allow the conclusion that the main source of the two chemicals in Osaka bay is fly ash from waste incineration.     

Type of disturbance and ecological history determine structural stability.

This study aims to reveal whether complexity, namely, community and trophic structure, of chronically stressed soil systems is at increased risk or remains stable when confronted with a subsequent disturbance. Therefore, we focused on a grassland with a history of four centuries of patchy contamination. Nematodes were used as model organisms because they are an abundant and trophically diverse group and representative of the soil food web and ecosystem complexity. In a field survey, a relationship between contaminants and community structures was established. Following, two groups of soil mesocosms from the field that differed in contamination level were exposed to different disturbance regimes, namely, to the contaminant zinc and a heat shock. The zinc treatment revealed that community structure is stable, irrespective of soil contamination levels. This implies that centuries of exposure to contamination led to adaptation of the soil nematode community irrespective of the patchy distribution of contaminants. In contrast, the heat shock had adverse effects on species richness in the highly contaminated soils only. The total nematode biomass was lower in the highly contaminated field samples; however, the biomass was not affected by zinc and heat treatments of the mesocosms. This means that density compensation occurred rapidly, i.e., tolerant species quickly replaced sensitive species. Our results support the hypothesis that the history of contamination and the type of disturbance determine the response of communities. Despite that ecosystems may be exposed for centuries to contamination and communities show adaptation, biodiversity in highly contaminated sites is at increased risk when exposed to a different disturbance regime. We discuss how the loss of higher trophic levels from the entire system, such as represented by carnivorous nematodes after the heat shock, accompanied by local biodiversity loss at highly contaminated sites, may result in detrimental effects on ecosystem functions.     

土壤和沉积物中非水解有机碳对菲的吸附

采用改进的酸水解方法对土壤和沉积物中的有机质组分进行了分离和提取,用固体13C核磁共振（13CNMR）表征了非水解有机碳（NHC）,同时研究了不同有机质组分对菲的吸附行为,结果表明,菲的吸附等温线都呈现出明显的非线性,能很好地拟合Freundlich方程;而且NHC和碳黑（BC）比其原始和去矿样品的吸附容量都有明显提高.这些结果揭示了NHC和BC主要控制着菲在土壤和沉积物中的吸附行为.沉积物及其NHC对菲的吸附容量要高于土壤及其NHC,这与土壤和沉积物中有机质的不同来源有关.