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1.
Tuna farming is based on fishing bluefin tuna in their natural habit of the western Mediterranean and fattening them in floating cages. Although this type of aquaculture is expanding rapidly in the Mediterranean Sea, very little information is available for an environmental impact assessment and environmental monitoring of tuna ranching. Spatial and temporal scales of impact need to be established before the norms and regulations affecting this new branch of aquaculture can be properly implemented. The biotic indices measured pointed to detectable impact only under the cages, although multivariate techniques defined an environmental gradient of stressed macrofaunal assemblages. The benthic surveys carried out indicated that high impact was restricted to a radius of roughly 5 m from the cages with a transitional radius at 35 m. This zone was characterized by high densities of opportunistic species. There was a further zone of moderately stressed benthic environment extending to about 180–220 m from the cages. This moderately stressed zone exhibited slight changes in community structure, because the densities of some species were stimulated. At distances greater than 220 m from the tuna farm, the system apparently returned to normal conditions. The fallow period produced partial remediation of the area affected, except in the sediment underneath the cages where even a 6‐month fallow period was not sufficient for the community to totally recover.  相似文献   

2.
ABSTRACT: Fish cage farming generates large amounts of organic waste in the form of unconsumed feed and fecal matter, resulting in sediment deterioration and a threat to its own sustainability. Field studies analysed the scale of the impact of fish cage farming on sediment quality, variability of impact and spread of sediment enrichment in the vicinity of a fish farm. Two fish culture sites near the Fukuyama area of the Seto Inland Sea of Japan were chosen for the study. There was a significant difference between the quality of the sediment in aquaculture and non-aquaculture areas. The sediment underlying the fish cage farms was found to be extremely reducing, acidic and sulfidic. Sediment ignition loss did not vary markedly with the season. However, the redox potential and acid volatile sulfide content of aquaculture areas did show some seasonal variation. Sediment encircling a 165 m radius from the center of a farm in Yokota was judged as organically enriched by fish farming. A variation in sediment quality within the two sites and also within the stations was observed. Based on sediment quality, the stations could be categorized as less affected, highly affected or moderately affected.  相似文献   

3.
1. The impact of land-claim on the intertidal areas of the Forth estuary, eastern Scotland is described. It is shown that in recent times almost 50% of the intertidal area has been destroyed for a variety of purposes, including agriculture, harbours and industrial development. 2. The loss of infaunal invertebrate biomass and production from the intertidal habitat has been calculated for each part of the estuary, and by summation for the whole estuary. The loss is discussed in relation to the total biomass and production, both intertidally and subtidally, of the estuary. It is shown that proportionately more biomass and production may have been lost than area. 3. The impact of land-claim on estuarine fish is calculated. Land-claim has removed 24% of the natural fish habitats in the Forth estuary, and thereby removed 40% of their food supply. 4. The impact of habitat loss on birds was observed for one area where observations continued throughout a period of land-claim. For individual bird species at Torry Bay, land-claim had consequences ranging from neutral to substantially negative. Significant declines were found for overwintering populations of dunlin and bar-tailed godwit. Comparisons of pre- and post-land-claim bird feeding usage of this area, showed that the impact of land-claim on local bird populations differed between species. The large scale loss of habitat on the Forth seems likely to have reduced the size of some shorebird populations which overwinter on the estuary. 5. It is concluded that when considering the impact of land-claim on estuaries that, as found in some previous studies, a simple consideration of area lost may be inadequate to describe the effects of land-claim, and the consequences for animals living within the estuary may differ considerably amongst themselves and from area to area.  相似文献   

4.
In a large marine lagoon (Thau lagoon, southern France) with a shellfish farming dominant eutrophication, the macrophyte communities were sampled by six transects of three depths (1.5, 2.5 and 5 m) and their characteristics (species composition, diversity and biomass) were described in relation to environmental and sediment parameters. With increasing eutrophication (total inorganic nitrogen, 0.140-0.295 mg l-1; dissolved reactive phosphorus, 0.045-0.110 mg l-1; and N/P atomic ratio, 3-22), silt fraction and shell fragments in sediments increased (12-93 and 0-65% dry wt respectively). Different types of macrophytic communities could be defined in the shallow zone (1.5-2.5 m) corresponding to four main and successive stages of degradation. A pure eelgrass stand (Zostera marina and Z. noltii) and an eelgrass community colonized by macroalgae were observed in SW sites and could be distinguished by their sedimentary features. In sites (NE) more affected by eutrophication (fine-textured sediment), available incident light determined two main seaweed communities: an Ulva rigida community, outside the shellfish tables, and a Gracilaria bursa-pastoris community in the shellfish tables (lower incident light).  相似文献   

5.
Mytilus trossulus and its hybrids with the native species Mytilus edulis and also Mytilus galloprovincialis have been recently detected in both farmed and natural populations of mussels in Scotland, adding complexity to the known M. edulis × M. galloprovincialis hybrid zone in Europe. Mytilus trossulus was first found in Scotland at aquaculture sites, where it was associated with significant losses in production and reductions in profitability. Mytilus trossulus and its hybrids have been identified at higher frequencies in farm stock than in natural intertidal populations, raising concerns about the potential wider impact of M. trossulus genotypes at mussel aquaculture sites in Scotland. The present study clarifies the composition of Mytilus species in cultivation at Scottish mussel aquaculture farms, by screening samples from 41 mussel aquaculture sites using a high-throughput real-time PCR methodology. Mytilus edulis alleles were detected at all sites. Mytilus galloprovincialis alleles were detected from samples collected at 39 sites, and M. trossulus alleles were found at five sites. Overall, M. trossulus genotypes were restricted in their geographical distribution. It is suggested that, in order to support the sustainability of the Scottish shellfish cultivation industry, the economic impact arising from the presence of M. trossulus could be limited through good management practice.  相似文献   

6.
The effects of crab aquaculture on the water and sediment quality and the pelagic and macrobenthic community of the adjacent reclamation area of Guchenghu Lake, Jiangsu Province were evaluated over two consecutive crop cycles from April 2010 to November 2011. The results indicated that most of the nutrient concentrations in both the water column and the sediment varied temporally and showed significant spatial differences. The peak values of most of the physico-chemical parameters measured were obtained during the summer or autumn, whereas the opposite result was observed for suspended solids. A higher zooplankton density and lower phytoplankton biomass were observed in ponds than in other sampling sites, whereas Cyanophyta (80 %), with Planktothrix rubescens as the dominant taxon, was predominant in the canal closest to the ponds. The benthic community was dominated by Bellamya aeruginosa in the ponds. Limnodrilus hoffmeisteri was the predominant species in the canal. Comparative analysis of the impact of crab culture showed that it produced a relatively low level of disturbance but introduced large quantities of nutrients and organic matter into the canal around the farming ponds. The introduction of these substances increased the risk that Guchenghu Lake would be affected by pollution.  相似文献   

7.
本研究针对渤海中部某船舶碰撞溢油事故,基于欧拉-拉格朗日方法,对事故发生后的油膜漂移扩散和油膜消失后的溶解态分布趋势,分别进行了数值模拟。在此基础上,界定事故溢油对渤海天然渔业资源的影响范围,进而估算天然渔业资源损失。结果显示:溢油量按13 m3计算,油膜存在期约为72 h,累加油膜扫海面积约为69.19 km2;油膜消失后,事故溢油仍会以溶解态、乳化态或悬浮颗粒态在海水中扩散,水体中的石油烃含量符合渔业水质标准,溢油在第11天中午即可抵岸;油膜会造成渔业资源损失,油膜消失后,悬浮颗粒态和乳化态石油在岸滩等因素影响下会形成凝聚态石油,并对潮间带生物造成影响。其影响面积结合溶解态抵岸区域内自然岸线长度予以估算,经评估,在油膜扫海区域及受影响潮间带范围内,事故经济损失额合计为631.9万元。本研究对数值模型方法在溢油事故天然渔业资源损失评估中的应用方面做了有益尝试,为无现场观测数据支撑的海洋溢油事故天然渔业资源损失评估提供了一个可行的方法。  相似文献   

8.
  1. An extensive area of seagrass covering the shore of part of the South African estuary ranked highest in overall national conservation and biodiversity importance (the Knysna estuarine bay) was killed by a series of seasonal green‐tidal blankets of Ulva starting in the late austral summer of 2015, leaving bare muddy sediment. An earlier (2011) survey of then seagrass macrobenthic assemblages at 27 stations along over 1 km of that shore was exactly repeated in 2018 after this event.
  2. After loss of seagrass, intertidal macrofauna became significantly less speciose (1:0.61), spatially and systematically more uniform (1:1.30 and 1:1.63), but more (not the usual less) abundant (0.62:1). Assemblage composition also changed, with polychaete numbers (small nereidids, spionids, fabriciids and an endemic paraonid) increasing from <50% of total macrofaunal individuals to >90% (although cirratulids decreased), whereas small malacostracan crustaceans (except the amphipod Grandidierella sp.) and microgastropods diminished to insignificant levels—microgastropods for reasons possibly unconnected with the green tide.
  3. Comparison with areas not vegetated in 2014, however, indicated that although macrofaunal abundance was greater in the 2018 Ulva‐induced bare areas, levels of per unit area biodiversity (number of species, species and taxonomic diversity per station) were comparable. This suggests that the effect of local loss of seagrass cover is context dependent, particularly with regard to pre‐existing local seagrass versus adjacent bare‐sediment differentials, and does not necessarily lead to any “degraded” state.
  4. Decreased local importance of small malacostracans may severely impact the region's usage by the adult and juvenile fish for which it is an important nursery and feeding ground.
  相似文献   

9.
  • 1. Extensive diamond mining occurs on land and in the sea on the west coasts of South Africa and Namibia, raising fears that diamond‐mining activities may impact commercial rock‐lobster fisheries and benthic communities. To explore this possibility, the effects of the diamond‐mining fines‐discharge on intertidal and subtidal rocky‐shore communities and on the population structure of the rock lobster Jasus lalandii were assessed at Elizabeth Bay.
  • 2. Sampling over six years at sites covering a range of wave exposures compared impacted sites with comparable reference sites never exposed to the fines. Percentage cover and densities of benthic organisms were recorded on both intertidal and subtidal reefs. Rock‐lobster abundance was estimated from counts and catch‐per‐unit‐effort, and their length frequencies and sex ratios compared in impacted and reference areas.
  • 3. The deposition of fines had no effect at wave‐exposed sites, but did impact intertidal and subtidal communities at sheltered localities where fines accumulated because wave action was insufficient to disperse them. Reductions of grazers, proliferation of algae and increased dominance by filter‐feeders were recorded at the impacted sites and persisted throughout the monitoring programme. Differences in community structure associated with different levels of wave exposure were, however, greater than those produced by depositing fines. The detected effects of fines‐deposits on the benthos were local and likely to be reversible after cessation of mining.
  • 4. The fines‐deposit had no detectable effects on the sex‐ratio, size or abundance of rock lobsters, indicating that there is no conflict between the deposition of fines and the fishery for rock lobsters, although substantial inter‐site variability makes it difficult to regard the results as definitive.
Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

10.
为了解海域微生物的群落结构和空间差异,探究其与环境的潜在联系,选择大型石化基地浙江舟山市鱼山岛海域,以期为我国海洋工程建设的环境管理提供技术支撑。在基地建设围填海时期,设置10个海域生态监测站,按《海洋监测规范》和《海洋调查规范》对海域沉积物进行取样调查。结果显示,海域环境明显受到长江、钱塘江等入海河流的影响,有机碳(TOC)、石油类(Oil)、砷(As)、镉(Cd)、铜(Cu)和铅(Pb)均在海域西北形成高值区,并逐步向东部海域递减。应用Illumina MiSeq宏基因组高通量测序技术,在海域沉积物中鉴定得到古菌和细菌共39门、260科、431属。从门水平上看,变形菌门(Proteobacteria)在各站位均表现出明显优势,其相对丰度占总数的39%;其它较为丰富的门类包括放线菌门(Actinobacteria)、酸杆菌门(Acidobacteria)、绿弯菌(Chloroflexi)、拟杆菌门(Bacteroidetes)和泉古菌(Crenarchaeota)。从属水平上看,Gamma变形菌是最主要的优势菌,其它主要种类还有Deltar变形菌、拟杆菌、放线菌、酸杆菌、浮霉菌(Planctomyces)、Beta变形菌和黏球菌(Myxococcus),Delta变形菌成为微生物群落的主要种类之一,显示海域环境一定程度地受到了沿岸人类活动的影响。微生物与环境因子的相关性分析表明,有机碳、砷和底栖生物对微生物门水平的群落分布具有显著性影响,奇古菌、黏胶球形菌和P-SR1与石油类、砷、铅、镉等重金属呈显著负相关。  相似文献   

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