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1.
In an ecosystem-based resource management context, it is crucial to assess the relationships between community structure and ecosystem function and how those relationships change with resource extraction. To elucidate how changes in resource use can affect community structure and ecosystem function, we executed a comparative analysis of two different ecosystems subjected to notable fishing pressure. We contrasted the Northern Adriatic Sea (NAS) and Southern New England (SNE) ecosystems by examining outputs from comparable steady-state models. Both ecosystems have relatively high fishing pressure and a high biomass of benthic invertebrates. The basic structure of the food webs shows differences both in the number and definition of the functional groups, as described in the models. Fisheries, on the contrary, show similarities both in terms of catches and discards. Almost all statistics summarizing the structure and flows showed values three times higher in the SNE than in the NAS ecosystem, but despite this difference the two ecosystems exhibited similar, overall properties. Biomass ratios and the Mixed Trophic Impact (MTI) analysis showed that both ecosystems are dominated by the benthic compartment. Removing the biomass effect, however, shows a clear top-down effect, with a high rank achieved by fishing activities. In general terms, the low mean trophic level of catches and the high primary production required (PPR) values result in a high overexploitation level of the ecosystem, as highlighted by the L index. We conclude by exploring how comparative studies will continue to be valuable as ecosystem-based management is further implemented.  相似文献   

2.
Abstract. Three years of observations on a population of Notomastus latericeus Sars from Acquatina lagoon (Lecce, Italy) are reported. The population dynamics, life cycle, and reproduction were investigated in order to explain periodic density variations of this species. Some physical parameters of the water column were measured and sediment analyses were performed to characterize the environment. Secondary production was also estimated as part of a functional study of the benthic system in the Acquatina lagoon. The species is opportunistic; its density is apparently correlated to variation in salinity, but its presence in the lagoon is dependent on recruitment success and competition with other polychaete species.  相似文献   

3.
《Oceanologica Acta》1998,21(6):831-843
Shellfish farming leaves its mark on the environment in which it has developed, and the men who depend upon it. These changes have altogether balanced the lagoon cycle and have caused disastrous episodic events. Increased water clarity caused by the uptake of particulate material by shellfish farming allows seagrass to grow in deeper areas of the lagoon (down to five metres). Shellfish farming nutrient transformations increase ecosystem productivity, even if the filtration pressure keeps phytoplankton biomass at a low level. Storage of phosphorus and nitrogen in animal tissue limits eutrophication in this ecosystem. Transfer of oysters from growout facilities increases animal and vegetal specific diversity. The presence of large amounts of shellfish allows for the development of a masive benthos, while organic enrichment from biodeposition changes the specific composition of soft-bottom benthos. In the deeper areas, (less than six metres), where summer thermoclines limit oxygen transfer from surface water, the organically enriched substrate induces oxygen depletion and ammonium and nitrogen sulfide accumulation in the water column. This ecosystem dysfunction kills benthic populations, and sometimes reaches pelagic populations and affects the shellfish farming economy.  相似文献   

4.
Sponges are important components of coral reef fauna, although little is known of their temporal dynamics. Sponges dominate the lagoon system at Palmyra Atoll in the Central Pacific, which may not be its natural state. Here we examined the temporal variability and recruitment rates of these sponge assemblages to determine if they are stable and examined the evidence that a recent transition has occurred from a coral‐ to sponge‐dominated system. We found 24 sponge species in permanent quadrats in the lagoon between 2009 and 2011, and 11 species on our recruitment panels. The sponge assemblage composition and abundance did not vary significantly between years and appear stable. Many sponge recruits were found in both years that the panels were examined although higher rates were recorded in the second year of the study. While it seems very possible that a change to a sponge‐dominated lagoon is associated with declining environmental quality at Palmyra as a result of modifications over 70 years ago, without pre‐modification data on reef assemblage composition this remains speculative. Our observations of short‐term temporal stability in the sponge assemblages at Palmyra highlight the potential for sponge‐dominated reef states to be maintained in degraded reef environments that are seemingly unsuitable for coral survival.  相似文献   

5.
Yellow Sea tidal flats are internationally recognised for their contribution to biological diversity and yet are under enormous pressure from reclamation, pollution and overexploitation. The benthic macroinfauna community is the dominant community on these tidal flats and a reliable indicator of benthic environmental changes. We surveyed the current benthic macroinfauna community of the Ganghwa Southern Tidal Flat, the largest remaining Korean mud flat in the Yellow Sea, in order to examine changes in the environmental situation of this benthic ecosystem. The results show a significant decline in species diversity from the last survey made in 2003, and a shift in species composition with appearances of polychaetes indicative of pollution and physical disturbances and other opportunistic species becoming dominant in both density and biomass. The benthic community shift observed during the two study periods may be associated with increased nutrient pollution as well as increased physical disturbances in this area. However, we recognise the limitations of the data both in frequency and scope but believe the significant changes to the composition of the benthic fauna are sufficient to warrant concern. Observations are required to examine the extent to which these human activities induce benthic community shift in this tidal flat.  相似文献   

6.
The aim of this work was to study the dispersion of particulate wastes derived from marine fish farming and correlate the data with the impact on the seabed. Carbon and nutrients were correlated with the physico-chemical parameters of the sediment and the benthic community structure. The sedimentation rates in the benthic system were 1.09, 0.09 and 0.13 g m?2 day?1 for particulate organic carbon (POC), particulate organic nitrogen (PON) and total phosphorus (TP), respectively. TP was a reliable parameter for establishing the spatial extent of the fish farm particulate wastes. Fish farming was seen to influence not only physico-chemical and biological parameters but also the functioning of the ecosystem from a trophic point of view, particularly affecting the grazers and the balance among the trophic groups. POC, PON and TP sedimentation dynamics reflected the physico-chemical status of the sediment along the distance gradient studied, while their impact on the benthic community extended further. Therefore, the level of fish farm impact on the benthic community might be underestimated if it is assessed by merely taking into account data obtained from waste dispersion rates. The benthic habitat beneath the fish farm, Ma?rl bed, was seen to be very sensitive to aquaculture impact compared with other unvegetated benthic habitats, with an estimated POC-carrying capacity to maintain current diversity of 0.087 g C m?2 day?1 (only 36% greater than the basal POC input). Environmental protection agencies should define different aquaculture waste load thresholds for different benthic communities affected by finfish farming, according to their particular degree of sensitivity, in order to maintain natural ecosystem functions.  相似文献   

7.
《Oceanologica Acta》2003,26(5-6):457-471
Merja Zerga lagoon, located on the Moroccan Atlantic coast, is a site of international value (Ramsar Site) in terms of its ornithological diversity. However, the lagoon is heavily exploited for its clams and fishes. In an effort to further understanding of lagoon ecosystems, and thus to facilitate the management and conservation of their resources, an ecological survey of its benthic component was carried out. Benthos is a valuable food source for birds, fishes and humans. This work involved identifying the macrozoobenthic communities in the lagoon and assessing their spatial distribution. The study was based on monthly sampling of the intertidal zone and seasonal sampling in subtidal zone, over a one-year period. In the intertidal zone, salinity and median diameter and silt content of the sediment exhibited a gradient extending from the entrance to the inner lagoon, according to tidal flow. Sediment grain size characteristics reflected a gradual decrease of tidal currents from the lagoon entrance towards the inner parts of the lagoon, i.e. silt content increased with distance from the entrance. In the subtidal zone, the tidal currents were fairly strong throughout the lagoon, leading to the presence of coarser sediments than in the intertidal zone. Based on these physical, chemical and substratum characteristics, three communities were identified: (i) Cerastoderma edule and (ii) Scrobicularia plana communities were located in both the intertidal and subtidal zones; and (iii) a Tapes decussata community that was only found in the subtidal zone. The assemblages in the subtidal zone were more diverse and the mean abundances of the constituent species were higher than in the intertidal zone, which is an interesting feature for a lagoon environment. Communities were distributed along an ecological gradient, without showing a discontinuity or ecotone. The lagoon functioned like an estuary in which the community structure was controlled by edaphic factors in the intertidal zone, and by the hydrological factors in the subtidal zone.  相似文献   

8.
The MoSE project (construction of mobile barrier to safeguard the Lagoon of Venice) entails changes to the structure of the lagoon's inlets. This could have consequences for the areas near the inlets and for the dynamics of the lagoon ecosystem as a whole. In order to predict the effects of the proposed alterations on the hydrodynamics of the lagoon, a well-tested hydrodynamic-dispersion model was applied. Simulations were carried out considering both idealised and realistic tide and wind scenarios.  相似文献   

9.
The present work aimed to identify the main environmental drivers shaping temporal and spatial dynamics of macrobenthic communities within a eutrophic coastal lagoon. Sediments in the óbidos lagoon showed a gradient of increasing metal contamination from the inlet area to inner branches. The mid-lower lagoon area exhibited an intermediate contaminated condition between the inlet and upstream areas, suggesting that the effects of the organic loadings into the lagoon may be reflected until this area. This transitional feature was corroborated by biological data, with macrobenthic assemblages displaying characteristics of down- and upstream areas. Macrobenthic abundance peaked in winter, which was associated with a higher nutrient availability (mainly ammonium) and the proliferation of green macroalgae in mid-lower and inner lagoon areas. However, massive macroalgae growth resulted in a sharp decrease of macrobenthic diversity and abundance in spring, particularly where the higher amounts of decaying algae were detected. Higher dissimilarities between assemblages were detected during winter (and spring, for trophic composition), while in summer, differences were highly attenuated. The least contaminated area (close to the sea inlet) experienced smaller temporal variations for environmental variables, as well as the lowest temporal biological variability. This area was dominated by carnivores, which were related with increased salinity. Deposit-feeders were numerically dominant in the lagoon, being generally spread within organically enriched sandy and muddy areas. The high concentration of chlorophyll a and suspended particulate matter in water was reflected in the abundance of deposit-feeders/suspension-feeders, taking benefit of the high primary productivity. On the other hand, deposit-feeders/herbivores responded to the decay of macroalgae mats in the sediment. Biological associations varied with the biological data used (taxonomic versus trophic group composition; abundance versus biomass), highlighting the relevance of the combination of different data analysis' approaches. In general, BIOENV analysis indicated total phosphorus, biomass of Ulva, metals and organic carbon and nitrogen as being significantly influencing benthic patterns. On the other hand, discrepancies in ecological behaviours of some taxa were also detected in the present study stressing the need for additional studies on the relationships between macrobenthic communities and environmental variables. Implications of the present results for monitoring studies are discussed.  相似文献   

10.
大型底栖动物是河流生态系统中重要的生态类群,研究其群落组成及分布特征能为河流生态系统管理提供理论支撑。2018年6月(夏季)和11月(秋季),在崇明岛内河设置16个固定站点,开展了拖网和地笼相结合的大型底栖动物调查,分析研究了崇明岛内河大型底栖动物群落的组成与分布特征及影响因子。调查期间共采集到大型底栖动物14种,分属5目8科,主要为节肢动物。其中,淡水型10种,河口半咸水型3种,降海洄游型1种。从空间分布来看,北横引河记录12种,南横引河记录6种,竖河记录11种;不同河道大型底栖动物群落组成均以淡水型种类为主,主要优势物种为日本沼虾(Macrobrachium nipponense)和秀丽白虾(Exopalaemon modestus);北横引河大型底栖动物群落的物种数、多度及生物量均高于南横引河;而竖河介于两者之间。夏季大型底栖动物群落的物种数、多度和生物量均高于秋季,季节变化是崇明岛内河大型底栖动物群落组成变化的重要特征之一。综合来看,崇明岛内河大型底栖动物群落组成特征兼具内陆河流和河口区特点,它与崇明岛区位特征、河流水文及生境条件、水质特征及区域人类活动等多种因素有关。  相似文献   

11.
Although benthic macrophytes must be considered in monitoring programs to establish the ecological status of transitional and coastal waters in the European Union, the patterns of variability in species composition of macrophyte assemblages in Mediterranean coastal lagoons has scarcely been studied. In this work the spatial (both vertical and horizontal) and seasonal dynamics of macrophyte assemblages in a coastal lagoon (Mar Menor) are compared with those of open coastal assemblages in the SW Mediterranean to analyze any biological variability in lagoon assemblages and the factors that determine such variability. Different assemblages, characterized by well defined groups of species, can be described according to their isolation from the open sea and the type of substratum; at the same time, a vertical zonation pattern, similar to that found in all marine communities but more compressed, exists. This implies that when applying the EU Water Framework Directive or assessing environmental impact, a lagoon should not be considered spatially uniform and unique unit but as a mosaic of assemblages.  相似文献   

12.
Fish communities of the Ria Formosa coastal lagoon (south Portugal) were sampled on a monthly basis with a beach seine at 4 sites, during two different time periods: 1980–1986 and 2001–2002. Community indices, species ranking and multivariate analysis were used in order to identify changes in the fish community between the two time periods. A total of 153,511 fish representing 57 taxa were recorded. Although species composition was very similar for both sampling periods, multivariate analysis performed on annual species abundance in number and weight revealed differences in fish community structure between the two periods. Structural changes in fish community were related mostly to a sharp decrease in the abundance of Mugilidae from 1980–1986 to 2001–2002. These changes were probably associated to a decrease in organic matter contents and nutrients concentrations due to improvements in sewage treatment and better water circulation inside the lagoon. The changes in fish community structure are more evident in the inner areas of the lagoon than near the inlet. The association between changes in sewage patterns and changes in the ichthyofaunal community structure reinforces the importance of fish communities as a biological indicator of human induced changes in marine systems.  相似文献   

13.
The dynamics of benthic primary production and community respiration in a shallow oligotrophic, marine lagoon (Fællestrand, Denmark) was followed for 1·5 years. The shape of the annual primary production cycle was explained primarily by seasonal changes in temperature (r2 = 0·67-0·72) and daylength (r2 = 0·63), whereas temperature almost explained all variation in benthic community respiration (r2 = 0·83-0·87). On a daily basis the benthic system was autotrophic during spring and summer supplied by 'new' and 'regenerated' nitrogen and predominantly heterotrophic during fall and winter caused by light and nutrient limitation. The linear depth-relationship between porewater alkalinity and ammonium indicated that the C:N ratio of mineralized organic matter is low in spring and summer (3-6) and high in fall and winter (9-16). This is inversely related to net primary production and thus the input of labile, nitrogen-rich algal cells. Accordingly, mineralization occurred predominantly in the upper 2-5 cm of the sediment. The pool of reactive material (microalgal cells) was estimated to account for 12% of total organic carbon in the upper 3 cm, and had an average turnover time of less than 1 month in summer. Assimilation of organic carbon by benthic animals was equivalent to about 30% of the annual gross primary production. Grazing reduced chlorophyll a concentration in the sediment during summer and spring to values 30-40% lower than in winter, but maintained a 3-4 times higher specific microalgal productivity. The rapid turnover of organic carbon and nitrogen, and important role of benthic microalgae showed that the benthic community in this oligotrophic lagoon is of a very dynamic nature.  相似文献   

14.
Abstract. This study examines the variation in microphytobenthos structure and functioning in an intertidal lagoon during a macroalgal covering event. Multivariate techniques, applied on the recorded data, highlighted a clear seasonal pattern except for the July sample. The sudden macroalgae ( Cladophora sp.) development, which occurred in that month, enabled us to identify the massive covering as a disturbance factor on the benthic ecosystem. This biotic anomaly affected benthic microalgal production and community respiration, shifting the ecosystem from a highly photoautotrophic to an heterotrophic condition as shown by the BTS Index. This trophic index is therefore a useful tool for identifying episodic stress events mainly in intertidal habitats.  相似文献   

15.
《Oceanologica Acta》2003,26(1):67-75
The macrobenthic community structure of the Valli di Comacchio (northern Italy) was described in order to assess the ecological conditions of the main basins through 2001. In addition, the biotic data set gathered in 1997–1998 was compared to achieve an estimation of the eventual recovery of the lagoonal benthic assemblages. Four permanent sites (P1, M4, M5 and M6), located along a gradient of sediment texture and confinement, and representing four different areas of the lagoon, were sampled quarterly in 2001 for macrofauna and sedimentary variables (organic content, phytobenthic chlorophyll-a, depth of the redox potential discontinuity layer), and fortnightly for water variables (temperature, salinity, dissolved oxygen and planktonic chlorophyll-a). Water and sedimentary variables were typical of eutrophic areas. A total of 52 macrobenthic taxa were identified and, on the basis of the species collected, differences in faunal distribution among the four areas were recognized, although less marked than in previous studies. Sediment trophic status and its seasonal dynamics in the Valli were crucial in determining species distribution among the different areas. The comparison between 1997–1998 and 2001 biotic data indicated that conditions in the lagoon had improved, especially in the formerly most impaired, central area. In the Valli di Comacchio, the recovery of benthic communities after severe disturbance will probably take longer, even if sewage discharges have been removed 11 years ago. Secondary disturbance due to scarce water circulation, sharp temperature and salinity fluctuations, release of toxic substances from sediments influenced animal assemblages along spatial and temporal scales. The interplay of these variables probably caused deviations from the expected improvement in benthic conditions. Nevertheless, clear signs of amelioration, particularly at the previously most impaired area, were detectable.  相似文献   

16.
台湾海峡生态系统对海洋环境年际变动的响应分析   总被引：13，自引：2，他引：13  
通过比较1985~2001年的海表温度与其间收集的现场营养盐、浮游植物和浮游动物丰度及群落结构变动信号,以及1971~1998年的中上层鱼类渔获量变动信息,发现了台湾海峡生态系统对物理环境年际变动产生的响应迹象.1997 年夏季台湾海峡处于偏冷状态,南部近岸上升流强度减弱;1997年冬季正值一个较强的暖事件发展到顶峰,北上入侵暖水强度增强、浙闽沿岸冷水强度减弱.导致这两个时期营养盐分布特征改变,发生了一系列从浮游植物到浮游动物,从生物量到群落结构的异常响应,暖水性中上层鱼类渔获量则似乎呈现出El Niño年偏高的趋势.根据有限的辅助证据推测,El Niño很可能不是控制台湾海峡海洋环境年际变动的强信号,而台湾海峡的气候海洋生态长期低频变动可能更多地受到东亚季风中国边缘海系统的控制.  相似文献   

17.
Abstract. Polychaete community structure in Valle Magnavacca, the largest basin of the Valli di Comacchio (Northern Adriatic Sea) lagoonal ecosystem, was analyzed in a three‐year study. Three shallow‐water stations were sampled at about 3‐month intervals. Univariate and multivariate analyses were utilized to investigate community structure changes in relation to natural and man‐induced disturbance. The polychaete community at station 3, in the central area of the lagoon, was the most disturbed, while that of station 2 was the most well structured. We hypothesize that polychaete community structure results from regular seasonal disturbances which lead to almost predictable fluctuations in species abundance. Superimposed on these regular cycles are acute disturbance events that further reduce species abundance or exclude species from the habitat.  相似文献   

18.
《Oceanologica Acta》1999,22(6):705-720
The importance of habitat to fisheries production on Australia's southeast continental shelf is part of a five-year study of ecosystem functioning and its implications for a sustainable fishery. Benthic habitats from 40 m to ∼200 m were studied, based on identification of suitable sites from local fishers' information. Results presented here concentrate on data from a single mesohabitat at 40–60 m depth collected over two days. Macrohabitats within this mesohabitat were discriminated as soft, hard and rough from visual inspection of acoustic echograms. Subsequent analysis of the return echoes using roughness and hardness indices did not significantly improve real-time visual discriminations. Macrohabitats were sampled with an underwater video camera, sediment sampler, benthic sled, demersal trawl, gillnets and fish traps to relate the acoustic classifications to biological habitats. There were distinct differences in the benthic and fish communities between macrohabitats discriminated by acoustics. We concluded that discrimination of habitats from visual inspection of echograms, plus limited verification with physical sampling, could provide sufficient information for spatial management. However, successful management of individual species, the fish community and the ecosystem requires an understanding of the association of fishes with habitat at the macrohabitat and mesohabitat level, and its variability through time.  相似文献   

19.
The coastal waters of Peru and Chile are among the most productive of the world's oceans. A striking source of interannual variability in this upwelling ecosystem, El Niño, results in large population and community variations. During El Niño the seasonal upwelling ceases and warm, clear oceanic waters occur close inshore, setting a unique oceanographic scenario in which the performance of populations and communities can be studied. While most attention has been focused on the pelagic components of such systems, numerous changes occur in inshore, benthic populations. Likewise, little attention has been paid to the critical role of humans as predators or active users of inshore, benthic resources. Humans as components of the ecosystem can impose significant alterations on population and community structure. In this paper the fishery statistics of three economically important inshore, benthic resources (the gastropod Concholepas concholepas, the cephalopod Octopus vulgaris and the kelp Lessonia nigrescens) are analysed in relation to the strong 1982/83 El Niño event. In particular, trends are described for landings in the far northern regions of Chile, where the marked effect of El Niño was concurrent with high levels of exploitation of C. concholepas and L. nigrescens.  相似文献   

20.
长江河口生态系统鱼类浮游生物生态学研究进展   总被引：12，自引：0，他引：12  
鱼类浮游生物群落结构的时空分布和动态变化与其所处水域的环境因子有密切的关系，它的变动受环境因子的变化和时空异质性的制约，而其鱼类浮游生物群落结构的变动最具代表性。研究证明，鱼类浮游生物群落结构对鱼类资源的补充，延续和维持生态平衡具有重要的意义，但尚无系统报道。本文就长江口鱼类浮游生物群落的研究做了阐述。三峡工程建设之后，通过改变长江径流来改变长江口水域的温度、盐度及其他非生物因子，同时由于非生物因子的变化，也引起生物因子的改变，从而使鱼类浮游生物优势种的组成和群落结构的生态性质发生了一定的变化，可以影响到长江口鱼类资源的补充，进一步改变长江口水域生态系统的平衡。  相似文献   

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