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1.
Hydrological and hydrodynamic characteristics are important controls in all wetlands including coastal lagoons. Enhanced understanding of lagoon functioning can be obtained through the acquisition and interpretation of hydrological, meteorological and related data. The MELMARINA Project investigated links between hydrological and ecological conditions within North African coastal lagoons. It employed three primary sites: Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. Hydrological, meteorological and related data were acquired for these lagoons. Data included precipitation, evaporation, wind speed and direction, freshwater discharges into the lagoons, tides beyond the lagoons in the open sea, lagoon bathymetry and time series of lagoon water levels/depths. Data were acquired from secondary sources (including online archives) and targeted field survey and monitoring programmes. Interpretation of these data provides insights into the hydrological functioning of the lagoons and contributed to the modelling requirements of MELMARINA. The functioning of Merja Zerga is dominated by the exchange of water between the Atlantic and the lagoon. Large, tidally induced oscillations in water level are responsible for the inundation of extensive inter-tidal mudflats whilst the rapid replacement of water by exchanges with the sea diminishes the influence of freshwater inflows and winter rainfall. The smaller Mediterranean tides reduce the magnitude of lagoon–sea exchanges and result in much smaller water level oscillations within Ghar El Melh. As a result, this lagoon lacks the inter-tidal environments found within the Moroccan site and hydrodynamic conditions are more likely influenced by wind set up. Although freshwater inflows to Ghar El Melh are smaller than those in Merja Zerga, their effects, coupled with heavy winter rainfall, can persist due to longer residence times of water within the lagoon. Freshwater inflows are central to the functioning of Lake Manzala. Large discharges of relatively freshwater are provided by major drains which cross the Nile Delta. These influence lake water levels and are responsible for the freshwater conditions within large parts of the lake. The small tidal range of the eastern Mediterranean, coupled with constricted connections with the sea, reduces the influence of lake–sea exchanges and tidally induced water level oscillations within Lake Manzala. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons  相似文献   

2.
As part of a survey of the Mediterranean enchytraeids, large numbers of samples were collected from a wide range of habitats at 38 localities of Tunisia and Algeria in 1989. Twenty species were identified belonging to six genera. Five species are new records for Tunisia and 17 are new for Algeria. Most of the recorded species are widely distributed throughout Europe, or even cosmopolitan, but some have a more restricted range. Fridericia caprensis has a circummediterranean distribution, Fridericia sardorum seems to be endemic to the western Mediterranean and Fridericia berninii is known only from the Balearic Islands and Algeria. Enchytraeus minutus bisetosus n. ssp. is described. A critical revision of some species is also provided.  相似文献   

3.
Conservation status of the North American fish fauna in fresh water   总被引:1,自引:0,他引:1  
The status of the North American fish fauna includes 292 species of fishes in the categories of endangered, vulnerable, rare, indeterminate, and extinct. This constitutes 28% of the known fauna. The status of fishes and their habitats continues to decline, especially in the arid regions of western U.S.A. and northern Mexico. The Endangered Species Act is the most powerful tool currently available to protect rare fishes. While many fishes probably have been saved from extinction by this Act, surprisingly few have improved enough to be removed from under its protection.  相似文献   

4.
This article describes the use of satellite imagery for identifying key environmental characteristics within three North African coastal lagoons (Merja Zerga, Morocco; Ghar El Melh, Tunisia and Lake Manzala, Egypt) and for detecting the major environmental changes within these environments. A combination of Landsat MSS, Landsat TM, Landsat ETM+ and ASTER imagery was acquired for the three sites for a period covering the last three decades (1972–2004). Following geometric correction and enhancement, the interpretation of the most recent image acquired for each of the three lagoons provides important insights into their current conditions. For Merja Zerga, these include the distribution of the largest channels which drain extensive inter-tidal mudflats and the two major depositional features associated with sources of freshwater. The distribution of marginal aquatic vegetation is highlighted as is the intensive use of the surrounding landscape for agriculture. Intensive agriculture around Ghar El Melh is also indicated. The influence of the Mejerda River, which was diverted away from the lagoon over 100 years ago, is shown to persist as a residual area of deltaic deposits in shallow water that has been eroded over time. Coastal processes including the direction of the alongshore sediment transport and the influence of engineering work associated with port construction can also be recognised. Within Lake Manzala, vegetated islands divide the lake into a series of sub-basins which can be clearly distinguished. The large influence of human activities within this lake can be identified and include reclamation for agriculture and the conversion of parts of the lake bed for fish farms. The historical images available for the three lagoons provide important insights into decadal scale changes, which have been greatest at Lake Manzala. Since the early 1970s large parts of the lake, in particular in the southwest where the shoreline has migrated northwards, have been reclaimed. Major engineering works, such as the El Salam Canal and road embankments, are shown to have resulted in significant lake change. The distribution of emergent vegetation within the lake has also changed. Classification of images for this lake into open water, vegetation and land enables the quantification of these changes. Between 1973 and 2003, the lake declined in area by approximately 50%. Changes at Merja Zerga over the last three decades include reconfiguration of the marine outlet and the expansion of the internal delta at the end of the Nador Canal. The images of this site clearly demonstrate the intensification of agriculture around the lagoon. The most marked changes evident within the images of Ghar El Melh concern the sand bars that separate the lagoon from the sea. Geomorphological processes operating within the coastal zone have resulted in the straightening of the bars with central sections migrating out towards the sea. Remote sensing is established as a promising application for detecting the quantitative surface cover changes in coastal lagoons and their near landscapes. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons  相似文献   

5.
Surface sediments and sediment cores were collected from coastal lagoons and lakes located in the Southern Mediterranean Region (SMR) as part of the MELMARINA Project which involved integrated eco-hydrological monitoring and modelling. This study uses surface sediments and sediment cores to infer spatial characteristics and temporal changes at the MELMARINA primary sites, Merja Zerga in Morocco, Ghar El Melh in Tunisia and Lake Manzala in Egypt. In addition, surface sediment sampling was undertaken at Egyptian Lake Bardawil and sediment cores were collected from the Lagune de Nador (Morocco). Sediment distribution patterns are investigated using GIS with georeferenced sample locations to facilitate display and resurvey. Major variations in sedimentary organic matter and, particularly, carbonate content, occur within and between sites. Local landscapes combined with hydrological and biogeochemical processes influence the distributions of sediment bulk components (carbonates, organic material and clastic matter) and molluscan shells and shell debris are an important source of sedimentary carbonate at all three primary sites. Sediment cores were dated using natural (210Pb) and artificial (137Cs) radionuclides, and sediment accumulation rate changes indicate that sources of sediment supply varied markedly through the twentieth century but have generally diminished after the mid-1960s. Sedimentary siliceous microfossils (diatoms) were generally poorly preserved, but mollusc shell remains were well represented. Sediment chronologies and sediment bulk composition allow discussion of some recent changes in bulk, minerogenic and biogenic sediment accumulation patterns in the SMR lagoons. Sediment accumulation rates also varied between sites and multiple cores from Lake Manzala indicated that rates showed considerable spatial variability. Low-level sediment contamination by fossil fuel combustion particulates and trace metals was demonstrated for Ghar El Melh and Lagune de Nador where Pb and Zn accumulation rates were highest in twentieth century sediment. It is emphasized that sediment quality and quantity have strong influences on lagoon ecosystem function and sedimentation is relevant to hydromorphology and to concepts of ecological quality. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons  相似文献   

6.
Seasonal variations in phytoplankton species composition (frequencies) and densities (cell numbers) in nine North African coastal lakes selected in Morocco (Merja Sidi Bou Rhaba, Zerga and Bokka), Tunisia (Chitane, Ichkeul and Korba lakes) and Egypt (Edku, Burullus and Manzala lakes) were investigated during 1998. The main aim was to provide gase-line information about overall phytoplankton diversity and how phytoplanktoncharacteristics differ between these contrasting aquatic systems.Water samples were collected at approximately three monthly intervals and phytoplankton analysis revealed marked seasonal and spatial differences in the quantitative and qualitative composition of the communities at each site. The Egyptian lakes generally had larger crops (Manzala and Burullus had mean crop densities of more than 104 cells ml–1) but in the western North African sites only Korba and Sidi Bou Rhaba had closely comparable densities. Algae belonging to Bacillariophyceae, Chlorophyceae, Chrysophyceae, Cyanophyceae, Dinophyceae and Euglenophyceae were recorded. Taxa representative of all these algal groups occurred in two lakes (Korba and Manzala) but at the other seven sites only some of the groups were present.The Chlorophyceae was the most dominant group in lakes Burullus, Manzala, Korba and Sidi Bou Rhaba whereas Bacillariophyceae were dominant in lakes Zerga, Bokka and Edku. In Ichkeul and acidic Chitane the Dinophyceae and the Cyanophyceae were the dominant groups, respectively. The maximum percentage of Euglenophyceae occurred in Edku Lake but this group was absent in Sidi Bou Rhaba and Ichkeul. Cyanophyceans were present in significant numbers in all investigated lakes except in Ichkeul. A total of fifty-three genera were recorded, 17 of Chlorophyceae, 18 of Bacillariophyceae, 11 of Cyanophyceae, 3 of Chrysophyceae, 2 of Euglenophyceae and 2 of Dinophyceae. The maximum number of species (34) occurred in Burullus Lake and the minimum (6) in Ichkeul Lake. Only one lake (acidic Chitane) possessed species indicative of oligotrophic conditions. The Nile Delta lakes were the most species diverse sites.The phytoplankton communities of the nine North African lakes were composed entirely of cosmopolitan species but with one new species (Cyclotella choctawatcheeana) was recorded for the region. The data presented provide a contemporary account of the levels of algal diversity present in these sites at the end of the 20th century. The relevance of phytoplankton communities to assessment of lake status and future monitoring studies in the region is emphasised.  相似文献   

7.
The North African Middle Stone Age (NAMSA, ~300‐24 thousand years ago, or ka) features what may be the oldest fossils of our species as well as extremely early examples of technological regionalization and ‘symbolic’ material culture (d'Errico, Vanhaeren, Barton, Bouzouggar, Mienis, Richter, Hublin, McPherron, Louzouet, & Klein, 2009 ; Scerri, 2013a ; Richter, Grün, Joannes‐Boyau, Steele, Amani, Rué, Fernandes, Raynal, Geraads, Ben‐Ncer Hublin, McPherron, 2017 ). The geographic situation of North Africa and an increased understanding of the wet‐dry climatic pulses of the Sahara Desert also show that North Africa played a strategic role in continental‐scale evolutionary processes by modulating human dispersal and demographic structure (Drake, Blench, Armitage, Bristow, & White, 2011 ; Blome, Cohen, Tryon, Brooks, & Russell, 2012 ). However, current understanding of the NAMSA remains patchy and subject to a bewildering array of industrial nomenclatures that mask underlying variability. These issues are compounded by a geographic research bias skewed toward non‐desert regions. As a result, it has been difficult to test long‐established narratives of behavioral and evolutionary change in North Africa and to resolve debates on their wider significance. In order to evaluate existing data and identify future research directions, this paper provides a critical overview of the component elements of the NAMSA and shows that the timing of many key behaviors has close parallels with others in sub‐Saharan Africa and Southwest Asia.  相似文献   

8.
Exploitation of land and water resources has increased rapidly in North Africa during the 20th century, paralleling regional population growth. As part of the CASSARINA Project (see Flower, 2001), the environmental status of nine wetland lakes in Morocco, Tunisia, and Egypt was evaluated. All are conservationally important habitats and several are Ramsar Sites (internationally recognized bird reserves) and several support significant fisheries. All are shallow (<2 m in depth) but vary greatly in area.Where available, documentary information on relevant 20th century changes is given. Survey transects for aquatic vegetation were established and used to provide baseline ecological information on the aquatic plant communities during 1997–1999. Unusually, one site (Tunisian Megene Chitane) supported acidophilous vegetation (some taxa being nationally rare). Aquatic macrophytes declined catastrophically at two sites during the 1990s. Merja Bokka was drained in 1998 and, at Garaet El Ichkeul, fringing Phragmites and Scirpus spp. were lost, mainly as a result of salinity changes. Elsewhere, fringing macrophytes remain (extensively so in the Nile Delta lakes) common, despite major land reclamation and water quality problems, or are degraded by grazing (Merja Zerga). Marginal vegetation during 1997/98 changed markedly at Megene Chitane due to water level lowering.Documentary records indicated that throughout the 20th century, reclamation and hydrologic modifications, mainly for agricultural purposes, affected all nine sites. The loss of lake area by reclamation is substantial for the Nile Delta lakes (Edku, Burullus and Manzala). For the western sites, some data indicate increasing salinity in the most recent decade but the Delta lakes have become generally fresher during the 20th century, as supply of Nile water for irrigation increased.Despite intense human disturbance, many of the remaining CASSARINA sites still support regions of high aquatic diversity. Spatial scale monitoring of the larger sites for seasonal and inter-annual changes in open water area and in aquatic plant abundances is a key requirement for integrated environmental change assessment in the 21st century.  相似文献   

9.
All nine wetland lakes in the CASSARINA North African suite of sample sites have been disturbed strongly by human activity during the 20th century. Dated lake sediment core were used to provide evidence of the extent of recent environmental change at each site. Sedimentary diatoms at seven sites were useful for inferring salinity change trends during the last century. At two sites preservation problems severely degraded the sedimentary diatom record. Sediment core integrity was otherwise established.Lithostratigraphic measurements indicated some site specific changes in soil erosion and sediment composition but, for the Egyptian Delta lakes, no physical signal synchronous with Aswan High Dam construction was found. Sedimentary diatom assemblages were generally site characteristic and halophilous taxa were common. At two sites planktonic diatoms indicated some recent eutrophication but generally the assemblages were more indicative of salinity changes. Diatom-inferred salinity trends for the seven sites typically indicated that reductions in water salinity occurred sometime during the early or mid 20th century.Rather than climate, hydrological modification of water resources is implicated as the primary driver of salinity changes during most of the 20th century. In the western North African region these modifications were mainly local land drainage and water diversion programmes to alleviate winter flooding and/or promote summer water availability. In the Delta region, the Nile has been intensively exploited since antiquity and intensively so from the late 19th century to release more fresh water for agriculture. Here, diatom records indicate that freshening began well before the Aswan High Dam but salinity fluctuations have tended to diminish during the latter part of the 20th century. A small reversal in the water freshening trend in the 1980/90s was possibly a response to land subsidence/sea-level change or to reduced freshwater supply.Freshwater supply to the sites is generally diminishing as former freshwater surpluses switch to deficit. One site (Merja Bokka, Morocco) became completely dry in 1998 as agriculture encroached and Megene Chitane, the only acid lake in Tunisia, is currently affected by excessive inflow abstraction. At the beginning of the 21st century, eight of the nine CASSARINA sites persist as viable but modified aquatic ecosystems. They nevertheless continue to support valuable aquatic biodiversity, especially in the Delta sites and in Chitane. The modern diatom communities are clearly tolerant of considerable environmental change but the remaining sites are increasingly threatened by major hydrological disturbance. Base-line floristic data for the late 20th century are given but continuous biomonitoring combined with effective management is needed urgently to help conserve North Africa's diminishing natural wetland lake resources.  相似文献   

10.
The fish community of the small (17·5 ha) intermittently open East Kleinemonde estuary was sampled between 1994 and 1997 to estimate population size, standing stock, growth and productivity. The estuarine-spawning species were numerically more abundant ( n c . 750 000) but due to their small size contributed only 11·7% to the total biomass. The total annual productivity of all fishes in the estuary ( n c . 890 000), with a standing stock of 28·44 g m −2, was calculated at 55·89 g m−2 year−1. The small sparid Rhabdosargus holubi with a production estimate of 41·35 g m−2 year−1 accounted for <74% of the total fish production in this estuary.  相似文献   

11.
Abstract: The revision of the radiolitid rudist bivalve Praeradiolites biskraensis (Coquand), including shell morphology and structure, taxonomical status, and palaeogeographical and stratigraphical distribution, was undertaken. We studied Coquand’s collection, other specimens from the type locality, Col de Sfa, and other Algerian fossil localities, as well as recently collected material from the Gafsa region in Tunisia. A neotype from Col de Sfa is proposed. The stratigraphical distribution of the species is bracketed in the Upper Cenomanian, using the distribution of co‐occurring ammonites in Tunisia and microfossils in Algeria. The palaeogeographical distribution is verified for Algeria and Tunisia based on all records in North Africa. Survey of the taxonomical status and problems of related radiolitid genera has resulted in revised diagnoses of Praeradiolites Douvillé, Eoradiolites Douvillé, Sphaerulites Lamarck and Radiolites Lamarck and revealed problems with Radiolites fleuriaui d’Orbigny, which is being the type species of Praeradiolites. Maghrebites gen. nov. is proposed for the North African radiolitid rudist Praeradiolites biskraensis (Coquand).  相似文献   

12.
13.
Horizontal starch gel electrophoresis was used to score mobilities of seven different enzymes in species of Bulinus from North and West Africa. An account of the intra- and inter-population variation observed was given. Based on the data obtained it was suggested that enzymic data should be used as taxonomic characters in parallel with morphological and anatomical characters. It is suggested that enzymic characters could be used to place taxa into synonymy if the data are collected in such a way that one can write up an enzyme profile for the single individual. The nine taxa of Bulinus known to occur in North and West Africa were revised, the taxon B. jousseaumei was synonymized with B. globosus , and the two taxa B. guernei and B. rohlfsi were synonymized with B. truncatus. As a result of the revision only six species could be recognized as valid from the area, these being B. forskalii, B. globosus, B. senegalensis, B. truncatus, B. ugandae and B. umbilicatus. Finally, some enzymic characters are suggested that may be used for a reliable identification of these morphologically very difficult taxa.  相似文献   

14.
15.
The systematic features of a small West African marine gobiid fish, Gobius nigricinctus Delais 1951, are redescribed from the holotype with special emphasis on the head lateral-line canal and sensory papillae (tree neuromast) systems. A junior synonym is found to be Gobius lepidogenys Robins 1970. The status of G. nigricinctus is best expressed in a new monotypic genus, Gorogobius , with closest affinity to the Atlantic-Mediterranean Corcyrogobius and Odondebuenia , Similarities in head sensory papillae arrangement exist between Gorogobius and certain 'seven-spined' genera of the New World tropical insular fauna, but G. nigricinctus is shown not to be a recent transatlantic immigrant. The validity of the tribe Gobiosomini as a natural grouping endemic to the Americas is questioned. Close resemblance in striped coloration between Gorogobius and small Indo-West Pacific gobies, especially Quisquilius eugenius , is shown to be the result of convergent evolution.  相似文献   

16.
The biogeographical analysis of Arctic and North Atlantic waters north of 30°N is based upon the distribution of 150 Mysidacea (Crustacea) species. The reasons for biogeographical divisions conducted independently by faunae of pelagic and benthopelagic mysids are adduced. The original schemes of the Arctic and North Atlantic division are proposed. Using the fauna of pelagic mysids, one biogeographical realm, one province and one transitional zone are designated in cold and temperate waters. Using the fauna of benthopelagic mysids, one biogeographical realm and four provinces are designated in those waters.  相似文献   

17.
Tropical Africa is home to an astonishing biodiversity occurring in a variety of ecosystems. Past climatic change and geological events have impacted the evolution and diversification of this biodiversity. During the last two decades, around 90 dated molecular phylogenies of different clades across animals and plants have been published leading to an increased understanding of the diversification and speciation processes generating tropical African biodiversity. In parallel, extended geological and palaeoclimatic records together with detailed numerical simulations have refined our understanding of past geological and climatic changes in Africa. To date, these important advances have not been reviewed within a common framework. Here, we critically review and synthesize African climate, tectonics and terrestrial biodiversity evolution throughout the Cenozoic to the mid-Pleistocene, drawing on recent advances in Earth and life sciences. We first review six major geo-climatic periods defining tropical African biodiversity diversification by synthesizing 89 dated molecular phylogeny studies. Two major geo-climatic factors impacting the diversification of the sub-Saharan biota are highlighted. First, Africa underwent numerous climatic fluctuations at ancient and more recent timescales, with tectonic, greenhouse gas, and orbital forcing stimulating diversification. Second, increased aridification since the Late Eocene led to important extinction events, but also provided unique diversification opportunities shaping the current tropical African biodiversity landscape. We then review diversification studies of tropical terrestrial animal and plant clades and discuss three major models of speciation: (i) geographic speciation via vicariance (allopatry); (ii) ecological speciation impacted by climate and geological changes, and (iii) genomic speciation via genome duplication. Geographic speciation has been the most widely documented to date and is a common speciation model across tropical Africa. We conclude with four important challenges faced by tropical African biodiversity research: (i) to increase knowledge by gathering basic and fundamental biodiversity information; (ii) to improve modelling of African geophysical evolution throughout the Cenozoic via better constraints and downscaling approaches; (iii) to increase the precision of phylogenetic reconstruction and molecular dating of tropical African clades by using next generation sequencing approaches together with better fossil calibrations; (iv) finally, as done here, to integrate data better from Earth and life sciences by focusing on the interdisciplinary study of the evolution of tropical African biodiversity in a wider geodiversity context.  相似文献   

18.
Three North African coastal lagoons were selected as primary sites for integrated ecological and hydrological monitoring and modelling as part of the MELMARINA Project (see Flower & Thompson, 2009). The three sites, Merja Zerga (13.2 km2, Morocco), Ghar El Melh (35.6 km2, Tunisia) and Lake Manzala (c. 700 km2, Egypt), are permanent water bodies with at least one well-defined connection with the sea. This article provides an account of each lagoon’s physical characteristics and recent development including the impacts of human activities. The two sites on the Mediterranean (Ghar El Melh and Lake Manzala) are characterised by small tidally driven variations in water level whilst Merga Zerga, on the Atlantic coast, experiences large tidally induced water level variations and so contains large inter-tidal environments. All the three lagoons receive freshwater inflows from their landward margins, varying in magnitude, seasonality and ecological significance. Freshwater inflows from drains strongly influence ecological conditions within Lake Manzala. All the three lagoons have significant biodiversity interest, especially for resident and migratory birds as well as fish, and support local human populations. Each lagoon experienced significant changes during the twentieth century possibly affecting declines in biodiversity value. These largely resulted from agricultural expansion and intensification and include reclamation and hydrological modifications which have both decreased freshwater inflows due to upstream diversions (Merja Zerga and Ghar El Melh) and increased the influx of freshwater through the return of irrigation drainage (Merja Zerga and Lake Manzala). All three sites experienced nutrient enrichment due to agricultural runoff and discharge of domestic wastewater. Industrial waste discharge is a particular, but not exclusive, problem for Lake Manzala. Problems of water quantity and quality will increase through the twenty-first century with increasing demands for water while effects of climate change will enhance freshwater scarcity. Conflicts between human and environmental uses of water will increase and unless improvements in water use efficiency and wastewater treatment can be brought about wetlands including coastal lagoons are likely to suffer further loss and degradation. These problems will be compounded by sea level rise. Guest editors: J. R. Thompson & R. J. Flower Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons  相似文献   

19.
Eighteen species of Limoniidae and two species of Pediciidae are recorded for the first time in Morocco, of which 15 species are new to North Africa. An updated checklist of Moroccan short-palped craneflies (Limoniidae and Pediciidae) is appended, containing 73 species in 25 genera.  相似文献   

20.
The heart ventricles of farmed gilthead seabream (Sparus aurata), European seabass (Dicentrarchus labrax) and Senegalese sole (Solea senegalensis) have been examined and we compared them to the corresponding fish from wild populations. These results can help to understand the differences in farmed fish hearts and in the myocardial structure that this condition of growth can produce. Several parameters were measured in the two groups. Numerical comparisons included heart mass, cardiac and ventricular index, ventricle height:width ratio, width and alignment of bulbus arteriosus, ventricular angles and compacta thickness. We confirm that the normal shape of wild fish hearts can be modified as a result from the adaptation to different environments. These changes can modify the structure of myocardium and compromise the cardiac function in farmed species. The ventricle of farmed fish present differences in shape, were misaligned, rounder, with a wider bulbus and thinner compact layer. Further studies are necessary to reveal functional significance and possible causes of these abnormal hearts and improve the cardiac welfare of Mediterranean species in culture as a way of ensuring a level of production compatible with economic benefits.  相似文献   

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