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1.
Environmental influences on the qualitative and quantitative composition of phytoplankton and zooplankton in North African coastal lagoons 总被引:9,自引:8,他引:1
M. Ramdani N. Elkhiati R. J. Flower J. R. Thompson L. Chouba M. M. Kraiem F. Ayache M. H. Ahmed 《Hydrobiologia》2009,622(1):113-131
Within the framework of the international research project MELMARINA, seasonal dynamics of plankton communities in three North
African coastal lagoons (Merja Zerga, Ghar El Melh, and Lake Manzala) were investigated. The sampling period extended from
July 2003 to September 2004 with the aim of evaluating hydrological and other influences on the structure, composition and
space-time development of these communities in each lagoon. Phytoplankton in Merja Zerga showed a quasi-permanent predominance
of marine diatoms in the open sea station and in the marine inlet channel. Dinoflagellates were abundant in summer and early
autumn in the marine inlet and extended into the central lagoon station. In Ghar El Melh, marine species (especially diatoms
and dinoflagellates) dominated despite occasional winter inflows of freshwater. In Lake Manzala, freshwater species generally
predominated and the planktonic communities were comparatively very diverse. Chlorophyceae contributed 39% of the total species
recorded and diatoms and cyanophyceans were also common; the Dinophyceae, Euglenophyceae, Chrysophyceae and Cryptophyceae
less so. Zooplankton communities in both Ghar El Melh and Merja Zerga were dominated by marine copepods. Rotifera, Copepoda,
Ostracoda, and Cladocera were recorded in both lagoons as were meroplanktonic larvae of Polychaeta, Cirripedia, Mysidacea
and Gastropoda and free living nematodes. Ghar El Melh was the more productive of these two lagoons with spring and early
summer being the productive seasons. Zooplankton communities in Lake Manzala were generally dominated by rotifers and highest
zooplankton abundances occurred in April (2003). Sampling stations near the marine inlets showed the highest diversity and
the zooplankton communities showed considerable spatial variation within this large lagoon. The three lagoons represent very
different water bodies contrasted strongly in terms of tidal effects and freshwater availability. Yet, there are some similarities
in ecosystem structure. Space-time development of the plankton communities was similar especially in Merja Zerga and Ghar
El Melh. Species abundances and specific diversities indicated that seasonal changes in salinity and nutrient concentrations
were the main influential factors. Lake Manzala was the most productive lagoon and all the three sites supported toxic algal
species. Relatively low plankton biomass in Merja Zerga and Ghar El Melh probably resulted from a combination of factors including
highly episodic nutrient inputs, light suppression (by turbidity) and nutrient competition with benthic algae. Water quality
variables were largely driven by the hydrological regime specific to each lagoon. Nutrient enrichment and, particularly for
Lake Manzala, sea level rise threaten the sustainability of the planktonic ecosystems in all three lagoons.
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
2.
F. Ayache J. R. Thompson R. J. Flower A. Boujarra F. Rouatbi H. Makina 《Hydrobiologia》2009,622(1):15-43
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
3.
Hydrological characteristics of three North African coastal lagoons: insights from the MELMARINA project 总被引:11,自引:9,他引:2
J. R. Thompson R. J. Flower M. Ramdani F. Ayache M. H. Ahmed E. K. Rasmussen O. S. Petersen 《Hydrobiologia》2009,622(1):45-84
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
4.
Application of remote sensing to site characterisation and environmental change analysis of North African coastal lagoons 总被引:8,自引:6,他引:2
M. H. Ahmed B. M. El Leithy J. R. Thompson R. J. Flower M. Ramdani F. Ayache S. M. Hassan 《Hydrobiologia》2009,622(1):147-171
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.
R. J. Flower P. G. Appleby J. R. Thompson M. H. Ahmed M. Ramdani L. Chouba N. Rose R. Rochester F. Ayache M. M. Kraiem N. Elkhiati S. El Kafrawy H. Yang E. K. Rasmussen 《Hydrobiologia》2009,622(1):85-112
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.
Influence of environmental conditions on the distribution of Amphipoda,Talitridae, in the lagoon complex of Ghar El Melh (north‐east of Tunisia) 下载免费PDF全文
Raja Jelassi Hajer Khemaissia Martin Zimmer Dieter Garbe‐Schönberg Karima Nasri‐Ammar 《African Journal of Ecology》2017,55(4):451-464
The study of the spatiotemporal distribution of talitrid amphipods was carried out along a transect in three stations belonging to the lagoon complex of Ghar El Melh, namely the supralittoral zones of the old harbour of Ghar El Melh, the opposite to Boughaz and Sidi Ali Mekki lagoon. Four species belonging to Talitridae family with two different genera were identified at all stations. These species are Orchestia gammarellus, Orchestia mediterranea, Orchestia stephenseni and Platorchestia platensis. The first two species were collected during the four seasons. The study of the density showed that the most important global mean density in talitrid was found in the supralittoral zone of opposite to Boughaz. In addition, statistical analysis showed a significant difference in the seasonal distribution of amphipods based on plant associations. Furthermore, the highest diversity of talitrid was observed in the winter in the supralittoral zone of opposite to Boughaz and in summer in the supralittoral zones of Sidi Ali Mekki lagoon and the old harbour of Ghar El Melh. Results showed that at all stations, a highly significant correlation of amphipod community with Cymodocea banquette was observed. Moreover, principal component analysis showed that the distribution of the different species depends on climatic and edaphic factors. 相似文献
7.
A.A. Fathi H.M.A. Abdelzaher R.J. Flower M. Ramdani M.M. Kraïem 《Aquatic Ecology》2001,35(3-4):303-318
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
8.
North African wetland lakes: characterization of nine sites included in the CASSARINA Project 总被引:1,自引:0,他引:1
Mohammed Ramdani Roger J. Flower Najat Elkhiati Mohammed M. Kraïem Adel A. Fathi Hilary H. Birks Simon T. Patrick 《Aquatic Ecology》2001,35(3-4):281-302
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.
John S. Balirwa 《African Journal of Ecology》2007,45(2):120-129
Inland fishery ecosystems in Africa are characterized by patterns of overexploitation, environmental degradation and exotic species introductions. Ecological complexity and diversity of aquatic habitats dictate that fishes in general are not evenly distributed in a water body. However, fisheries management regimes tend to ignore this basic principle, assume generalized conditions in a water body, and focus more on ‘desired’ objectives such as maximizing catch. The result is to disregard fish habitat boundaries and anthropogenic influences from the catchment that influence fish production. Overexploitation and environmental degradation disrupt sustainable socioeconomic benefits from the fisheries, create uncertainty among investors, but leave some managers calling for more information with the expectation that the fisheries will recover with time. Open access to the fisheries and full control of fishing effort remain challenges for managers. Exotic species introductions and fish farming can increase production, but such interventions require firm commitment to sound ecological principles and strict enforcement of recommended conservation and co‐management measures in capture fisheries. The general tendency to downplay fishing effort issues, other ecosystem values and functions or rely on temperate fisheries models until a new cycle of overexploitation emerges, characterizes many management patterns in inland fisheries. Aquaculture is not an option to challenges in capture fisheries management. Aquaculture should be developed to increase fish production but even this practice may have negative environmental impacts depending on practice and scale. Decades of information on Lake Victoria fisheries trends and aquaculture development did not stop the collapse of native fisheries. The successfully introduced Nile perch (Lates niloticus) has shown signs of overexploitation and aquaculture has again been considered as the option. By reviewing significant trends associated with Nile perch and its feasibility in aquaculture this paper uses Lake Victoria to illustrate ‘special interest management’ targeting selected species of fish rather than the fisheries. 相似文献
10.
Hydrodynamic-ecological model analyses of the water quality of Lake Manzala (Nile Delta, Northern Egypt) 总被引:9,自引:8,他引:1
E. Kock Rasmussen O. Svenstrup Petersen J. R. Thompson R. J. Flower M. H. Ahmed 《Hydrobiologia》2009,622(1):195-220
Lake Manzala remains the largest of the Nile Delta lakes and has undergone substantial recent changes particularly over the
last 30 years due to regulation of freshwater inflows, land reclamation and increasing loads of BOD and nutrients. The latter
are particularly associated with polluted drains flowing into the lake. An increasing fraction of the N load may also come
from the expanding fish farming industry within and around the lake. Over the past 20–25 years, the N load from the drains
has increased three times whilst the P load has remained approximately constant. This is despite a 40% reduction in freshwater
inflows due to diversion of water towards the Sinai for land development. As a result of these changes, the concentration
of total N in the drains has increased 4.5 times while the total P concentration has increased by 50% over the same period.
Increases in nutrient concentrations can be attributed to increase in the use of fertilizer combined with an expanding population
served by sewers, improved living standards and increased industrial production. Nutrient enrichment has resulted in declining
water quality and eutrophication, especially in the southern parts of Lake Manzala. A combined hydrodynamic-ecological model
has been set up for the lake and is used to analyse the development of water quality as a function of the load of organic
material and nutrients. Model results show that 86% of the N load and 59% of the P load are retained within the lake. Despite
the efficient treatment of wastewater by the lake ecosystem, approximately 6,000 tonnes of N and 1,300 tonnes of P are exported
to the Mediterranean through the two main lake–sea connections. This nutrient export has important implications for coastal
fisheries production. The present investigation suggests that the current anthropogenic nutrient load to the coastal zone
exceeds that of pre-Aswan High Dam conditions despite large reductions in the annual pulse of water and nutrients brought
about by the dam. A series of model simulations with reduced nutrient load are investigated in order to identify the conditions
required to enable the propagation of vegetation throughout the lake. Submerged rooted vegetation is used as an indicator
for water quality as it needs light for growth and in polluted, eutrophicated waters turbidity increases hampering vegetation
growth. Simulation results indicate that the nutrient load has to be reduced to approximately 25% of the present loads if
submerged rooted vegetation is to become re-established in the more polluted south eastern parts of the lake.
Guest editors: J. R. Thompson & R. J. Flower
Hydro-ecological Monitoring and Modelling of North African Coastal Lagoons 相似文献
11.
Nutrient enrichment and fisheries exploitation: interactive effects on estuarine living resources and their management 总被引:3,自引:1,他引:2
D. L. Breitburg J. K. Craig R. S. Fulford K. A. Rose W. R. Boynton D. C. Brady B. J. Ciotti R. J. Diaz K. D. Friedland J. D. Hagy III D. R. Hart A. H. Hines E. D. Houde S. E. Kolesar S. W. Nixon J. A. Rice D. H. Secor T. E. Targett 《Hydrobiologia》2009,629(1):31-47
Both fisheries exploitation and increased nutrient loadings strongly affect fish and shellfish abundance and production in
estuaries. These stressors do not act independently; instead, they jointly influence food webs, and each affects the sensitivity
of species and ecosystems to the other. Nutrient enrichment and the habitat degradation it sometimes causes can affect sustainable
yields of fisheries, and fisheries exploitation can affect the ability of estuarine systems to process nutrients. The total
biomass of fisheries landings in estuaries and semi-enclosed seas tends to increase with nitrogen loadings in spite of hypoxia,
but hypoxia and other negative effects of nutrient over-enrichment cause declines in individual species and in parts of systems
most severely affected. More thoroughly integrated management of nutrients and fisheries will permit more effective management
responses to systems affected by both stressors, including the application of fisheries regulations to rebuild stocks negatively
affected by eutrophication. Reducing fishing mortality may lead to the recovery of depressed populations even when eutrophication
contributes to population declines if actions are taken while the population retains sufficient reproductive potential. New
advances in modeling, statistics, and technology promise to provide the information needed to improve the understanding and
management of systems subject to both nutrient enrichment and fisheries exploitation.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
Guest editors: J. H. Andersen & D. J. Conley
Eutrophication in Coastal Ecosystems: Selected papers from the Second International Symposium on Research and Management of
Eutrophication in Coastal Ecosystems, 20–23 June 2006, Nyborg, Denmark 相似文献
12.
Anguillicola crassus, parasite nematode of the European eel Anguilla anguilla, was recorded for the first time in Tunisia (1999) in the Ichkeul lagoon. Its distribution has since spread toward Bizerte and Ghar El Melh lagoons. The monthly epidemiological survey reveals that A. crassus exists throughout the year in the Ichkeul lagoon. In this lagoon, its prevalence is low in winter (12% in December), with a marked increases in the spring reaching a maximum in March (35%), before it starts to decrease in summer with a minimum in July (4.35%), which in turn is followed by a pronounced new rise in autumn (30% in November). However, mean intensity values do not show such a marked variation. The majority of the values are between 1 and 1.5 parasites per host. In the Bizerte and Ghar El Melh lagoons, the presence of this nematode is limited only to one to three months. Investigations in the Tunis lagoon did not reveal until now the presence of A. crassus. It has been observed that the length of the eel influences the prevalence values: A. crassus becomes less common if the length of the eel increases. Comparatively with the global epidemiological values of A. crassus signalled subsequently (1999) in the Ichkeul lagoon, we note that the present values record a clean increase. 相似文献
13.
M.M. Kraïem C. Ben Hamza M. Ramdani A.A. Fathi H.M.A. Abdelzaher R.J. Flower 《Aquatic Ecology》2001,35(3-4):335-345
Age and growth characteristics of the thin-lipped Grey Mullet (Liza ramada) were investigated in three North African wetland lakes: Merja Zerga (Morocco), Garâat Ichkeul (Tunisia) and Edku Lake (Egypt). Age structure of the mullet populations was very similar in all three study lakes. Small differences in growth were indicated, especially for the Moroccan population, where growth tended to be slower than for the other two populations. The fastest growth was observed in the Edku population while the best condition was observed in the Ichkeul population. Compared with some European populations, the sampled North African populations have faster growth and better condition factors. 相似文献
14.
Hajer Khemaissia Raja Jelassi Catherine Souty‐Grosset Karima Nasri‐Ammar 《African Journal of Ecology》2013,51(2):348-357
In Tunisia, while wetlands are considered as remarkable habitats for their faunal and floral diversity, few studies on the species diversity of terrestrial isopods were performed. To fill this gap, the spatio‐temporal distribution of Oniscidea at Ghar El Melh lagoon (north‐east of Tunisia) was analysed. Sampling was carried out with 50 × 50 cm quadrats along a perpendicular transect to the shoreline. Nine species of terrestrial isopods belonging to seven genera were identified. Chaetophiloscia elongata Dollfus, 1884 was the most abundant species in all seasons except for summer; its relative abundance ranged from 38.9% to 77% in summer and autumn, respectively. Hill diversity indices ranged from 0.86 to 0.94 and equitability indices from 0.33 and 0.68. The statistical analysis showed a significant difference of isopod species and plant associations among seasons. 相似文献
15.
巢湖渔业资源现状及其对水体富营养化的响应研究 总被引:15,自引:0,他引:15
2002年至2004年期间,对巢湖鱼类资源进行调查,共发现鱼类54种,隶属16科、9目,主要以鲤科鱼类为主(35种),占64.8%,与20世纪80年代相比,鱼类种类数减少了40种,主要表现在洄游性种类急剧减少,甚至消失。渔业资源结构(渔获物)表现为以湖鲚、太湖新银鱼等小型鱼类为优势种类,在渔产量的比例不断上升,而大型鱼类(如翘嘴、鲤等)的种群结构趋于低龄化,产量呈下降趋势。结合已有的历史资料,分析巢湖渔业资源变化的影响因素,结果表明造成巢湖渔业资源结构变化受人为活动的影响主要表现在水利工程修建、过度捕捞和水体富营养化等方面。同时探讨近20年巢湖渔业捕捞产量与水体氮磷含量变化的相互关系发现,水体磷的含量变化显著影响巢湖渔业的捕捞产量。因此,合理利用巢湖渔业资源,需要减轻水体富营养化,控制捕捞强度和人为调整渔业结构使得巢湖渔业可持续发展。 相似文献
16.
Crow White 《Theoretical Ecology》2009,2(3):127-138
Predictions on the efficacy of marine reserves for benefiting fisheries differ in large part due to considerations of models
of either intra- or inter-cohort population density regulating fish recruitment. Here, I consider both processes acting on
recruitment and show using a bioeconomic model how for many fisheries density dependent recruitment dynamics interact with
harvest costs to influence fishery profit with reserves. Reserves consolidate fishing effort, favoring fisheries that can
profitably harvest low-density stocks of species where adult density mediates recruitment. Conversely, proportion coastline
in reserves that maximizes profit, and relative improvement in profit from reserves over conventional management, decline
with increasing harvest costs and the relative importance of intra-cohort density dependence. Reserves never increase profit
when harvest cost is high, regardless of density dependent recruitment dynamics. I quantitatively synthesize diverse results
in the literature, show disproportionate effects on the economic performance of reserves from considering only inter- or intra-cohort
density dependence, and highlight fish population and fishery dynamics predicted to be complementary to reserve management.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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Indicators have been recognised as a useful tool aiding the implementation of an ecosystem approach to fisheries in marine ecosystems. Studies, such as the IndiSeas project (www.indiseas.org), use a suite of indicators as a method of assessing the state and trends of several of the world's marine ecosystems. While it is well known that both fishing and climatic variability influence marine fisheries in the southern Benguela ecosystem there are currently few studies in support of fisheries management that make use of environmental indicators in order to include climatic impacts on marine fish populations. Trends in ecological, fishing and environmental indicators can be utilised in a way that allows an overall ecosystem trend to be determined, and can therefore be used to aid decision support within southern Benguela fisheries. In this study trends in indicators were determined using linear regressions across three time periods, Period 1: 1978–1993, Period 2: 1994–2003 and Period 3: 2004–2010. These time periods were selected based on the timing of regime shifts within the southern Benguela, including changes in upwelling, wind stress and temperature. Each ecological indicator received a score based on the direction and significance of the observed trend with respect to fishing. To account for the impacts of fishing and environmental drivers on ecological indicators, scores were adjusted by predetermined factors, depending on the extent and direction of trends in these indicators. Weightings were applied to correlated ecological indicators to account for their redundancy, and lessen their impact on overall ecosystem score. Mean weighted scores were then used to establish an overall ecosystem score for each time period. Ecosystem classification was determined as follows: 1–1.49 = improving, 1.5–2.49 = possibly improving, 2.5–3.49 = no improvement or deterioration, 3.5–4.49 = possible deterioration, 4.5–5 = deteriorating. The ecosystem was observed to neither deteriorate nor improve across Period 1 or 2 (mean weighted scores: 2.75 and 2.56 respectively), however, during Period 3 a possible improvement was observed (mean weighted score: 1.99). This study shows that the sequential analysis of suites of ecological, fishing and environmental indicators can be used in order to determine ecosystem trends, accounting for both the impacts of fishing and the environment on ecosystem components. 相似文献
20.
Sibylle Riedmiller 《Environmental Biology of Fishes》1994,39(4):329-338
Synopsis The introduction of the Nile perch into Lake Victoria has dramatically altered the fishery in that lake and contributed to the decline of the fishery for indigenous tilapias. One sector of the fishery in Lake Victoria has benefitted from the Nile perch introduction, although catches have declined in recent years. Inefficient enforcement of fisheries regulations has had a detrimental effect on indigenous species but may also have contributed to the recent decline in Nile perch catches. Fisheries development plans have tended to favour capital-intensive fisheries and to ignore small scale subsistence fisheries. A case study at Wichlum Beach on the Kenyan shores of Lake Victoria has revealed the efficiency of traditional fishing and fish drying methods as well as the high ecological costs of the practice of kiln-drying Nile perch. Forty-five tons of firewood are used per month at Wichlum Beach alone for kiln-drying perch. The increased economic viability of the fishery has attracted professionals into the industry and resulted in the development of an export-oriented trade. The Yala Swamp adjacent to Lake Victoria has been extensively drained as part of a large land reclamation scheme and more draining is planned. Increased environmental awareness in Kenya, and Kenya's membership in the Convention on Wetlands of International Importance, has resulted in a critical review of these plans. 相似文献