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1.
Shallow soft-bottom habitats including mangroves and mudflats provide important nursery functions for juvenile fishes, but little information exists concerning the relative nursery value of these habitats for juvenile fishes. We compared the potential of a mangrove and a mudflat in a semi-enclosed bay in Hong Kong to serve as fish nurseries by measuring species composition, dietary composition, gut fullness and diet breadth of juvenile fishes. Fish abundance was higher in mangrove than mudflat, but species richness was almost similar between the two habitats. After excluding Ambassis gymnocephalus, which was found mainly in the mangrove, difference in fish abundance between the two habitats was small. The gut fullness and diet breath of most species did not differ between mangrove and mudflat, suggesting that the two habitats were very similar in terms of providing feeding opportunity for juvenile fishes. While the importance of mangrove as nursery of fishes has been repeatedly emphasized, our data suggest that other soft-bottom habitats, such as mudflats, are also important and need to be protected.  相似文献   

2.
This study examined the diet of sympatric populations of migratory juvenile rainbow trout and landlocked koaro in the Waipehi and Omori Streams, Lake Taupo, New Zealand. In both species, diet was dominated, both numerically and by weight, by aquatic prey: Ephemeroptera, Trichoptera, and Diptera larvae were the most numerous prey items. Adult koaro and juvenile rainbow trout both fed on small koaro. Terrestrial prey items were present in low numbers in the diets of both koaro and juvenile rainbow trout, but were more important in terms of weight. Resource partitioning was weak although koaro consumed more small benthic invertebrates such as chironomid larvae, whereas the diet of rainbow trout contained more Ephemeroptera larvae and terrestrial insects. In the Waipehi Stream, koaro consumed both rainbow trout ova and koaro ova; in Omori Stream, trout ova were important in the diet of juvenile rainbow trout. Since the diets of koaro and juvenile rainbow trout in some Taupo tributaries are similar, populations may co‐exist by temporal and/or spatial partitioning of food resources, whereas trout predation on small koaro may be a limiting factor for koaro populations.  相似文献   

3.
Tropical shallow-water habitats such as mangroves and seagrass beds are widely acknowledged as important juvenile habitats for various coral reef fish species, most of which are commercially important to fisheries. Spatio-temporal variability in ontogenetic habitat use by fish among these tropical coastal ecosystems has rarely been investigated, yet there are sufficient reasons to believe that this plays an important role. In the present study, we test the spatio-temporal variability in patterns of ontogenetic habitat use by some mangrove/seagrass-associated coral reef fishes (Lethrinus harak, Lethrinus lentjan, Lutjanus fulviflamma and Siganus sutor). Abundances of these four species were investigated during two years in Tanzanian coastal waters, using underwater visual census in mangrove, seagrass, shallow and deep mudflat, and shallow and deep coral reef habitats. The study covered four distinct seasons of the year and was done at two spatially separated (>40 km) locations. Averaged across locations, seasons and years, juveniles (≤10 cm length) of the four study species had significantly higher relative densities in shallow-water (mangroves and seagrass beds) than in deep-water habitats (deep mudflats or coral reefs), whereas the opposite pattern was found for the adults (>15 cm). These findings suggest a strong and general pattern of ontogenetic habitat shifts from shallow- to deep-water habitats. However, specific habitat-use patterns of juveniles as well as adults differed significantly in time and space. Various species showed subtle to considerable flexibility in juvenile as well as adult habitat use across seasons, years, or at different locations. Furthermore, for some species the data suggest presence of ontogenetic habitat shifts at one location but lack thereof at the other location. In summary, ontogenetic habitat use needs to be considered at various spatial and temporal scales for the interpretation of habitat utilization by fish during different life stages. This is important for conservation and management of these habitats, as essential habitats or seasons may be ignored or over-emphasized with respect to their importance for fish during different parts of their life cycle.  相似文献   

4.
Habitat variability is one of the factors influencing species richness within estuarine systems, and a loss of habitat can result in a restructuring of the estuarine ichthyofaunal assemblage, particularly if these conditions persist over long time periods. The potential effects of the loss of extensive submerged macrophyte beds (Ruppia cirrhosa and Potamogeton pectinatus) on an estuarine fish assemblage were investigated through an analysis of a long-term seine net catch dataset from the temporarily open/closed East Kleinemonde Estuary, South Africa. Catch data for a 12-year period, encompassing six years of macrophyte presence and six years of macrophyte senescence, indicated that the loss of this habitat did not influence species richness but changes in the relative abundance of certain species were evident. A shift in dominance from vegetation-associated species to those associated with sandy environments (e.g. members of the family Mugilidae) was observed. However, species wholly dependent on macrophytes such as the critically endangered estuarine pipefish Syngnathus watermeyeri were only recorded during years when macrophyte beds were present, while vegetation-associated species such as the sparid Rhabdosargus holubi persisted at lower levels of relative abundance. The reduced abundance of all vegetation-associated fish species during years of macrophyte senescence was probably reflective of declining food resources resulting from the loss of macrophyte beds and/or increased vulnerability to predation. Submerged beds of aquatic plants are therefore important habitats within temporarily open/closed estuaries, South Africa’s dominant estuary type.  相似文献   

5.
Epibenthic fishes were collected with daytime beam trawl tows (n = 1713) in three shallow (<10 m) habitats of submerged aquatic vegetation (SAV), Zostera marina (eelgrass), Laminaria longicruris (kelp), Phyllophora sp. (algae), and unvegetated sandy/mud areas. We divided the Maine coast into three broad zones based upon geological features and sampled over five consecutive years; during April–November 2000 in the mid coast, in 2001 and 2002 along the south coast and in 2003 and 2004 along the eastern Maine coast. We quantified habitat use by eight economically important fish species (Gadus morhua, Microgadus tomcod, Pollachius virens, Urophycis chuss, Urophycis tenuis, Osmerus mordax, Tautogolabrus adspersus, and Pseudopleuronectes americanus) and 10 other common epibenthic species (n = 18 571). We identified the physical and biological variables most important in discriminating between habitats with and without individual fish species. Logistic regression models based on nearshore habitat characteristics were developed to predict the distribution of these species along the three zones representing broad geological regions of the Maine coast. Logistic regression models correctly classified individual fish species 58.7–97.1% of the time based on the temporal and physical habitat variables (month, temperature, salinity, and depth) and the presence–absence of submerged aquatic vegetation (Zostera, Laminaria, or Phyllophora). Overall fish presence and economically important fish presence were correctly classified 61.1–79.8% and 66.0–73.6% of the time, respectively. The Maine shallow water fish community was composed primarily of young-of-the-year and juvenile fishes with all habitats functioning as facultative nursery areas. Presence of most fish species was positively associated with Zostera, Laminaria, and to a lesser extent, Phyllophora. This study provides direct evidence of shallow waters of the Gulf of Maine as critical facultative nursery habitat for juvenile G. morhua, M. tomcod, P. virens, U. tenuis, U. chuss, T. adspersus, O. mordax and P. americanus, and many ecologically important species.  相似文献   

6.
This work aims to compile knowledge on ecologically rich habitats that deserve special protection in the Mediterranean high seas. Many marine ecosystems are currently threatened by fishing activities, such as bottom trawling, gillnets and demersal and pelagic long-lines. Especially vulnerable are areas described as either sensitive habitats or essential fish habitats. Among these we highlight the associations of sessile organisms, such as cold coral reefs, mostly detected on continental slopes, seamounts and on the walls of submarine canyons, and those areas considered as hot spots of diversity and habitat of vulnerable fauna, like cold seeps, hydrothermal vents and submarine canyons. Essential habitats for pelagic species are defined by oceanographic features like productive areas associated with upwelling, and in the Mediterranean the spawning areas and migratory routes of bluefin tuna, swordfish, and albacore are of high conservation interest. We propose that in a context of difficult fisheries management in Mediterranean international waters, or high seas, these vulnerable habitats should be protected through the establishment of a web of Marine Protected Areas coordinated by all the involved countries and controlled by strict surveillance.  相似文献   

7.
We documented the temporal occurrence patterns and habitat use of fish in the Mangyeong River estuary on the western coast of Korea from February to December 2003 based on monthly samples collected with a stow net. A total of 46 fish species were collected during the study period. Chelon haematocheilus, Konosirus punctatus, Neosalanx jordani, Sardinella zunasi, Synechogobius hasta, and Thryssa kammalensis were the predominate species, accounting for 84.4% of the collected fish. We classified the fish as brackish water (BF), coastal migratory (CMF), diadromous (DF), or freshwater (FF) fish. BF such as C. haematocheilus, S. hasta, and Coilia nasus were the most abundant and were collected almost year-round. As water temperatures increased in spring, adult CMF, such as K. punctatus, S. zunasi, T. kammalensis, T. adelae, Johnius grypotus, Miichthys miiuy, and Larimichthys polyactis, entered the estuary. In summer, large numbers of their juvenile offspring were caught, indicating a peak in fish abundance. The juveniles grew in the estuary before moving out to deeper waters for overwintering. Diadromous juveniles, such as those of Anguilla japonica (commonly known as glass eel), were collected in the spring during their upstream migration. FF, such as Carassius cuvieri and Acheilognathus rhombeus, were collected during the rainy season. In terms of the number of species, the number of individuals, and the biomass, the ratio of BF to all other fish type classifications in the Mangyeong Estuary (without a dam) was higher than that in the Geum River estuary (with a dam). The fish assemblage in the Mangyeong Estuary still maintained estuarine characteristics before dike enclosure, providing habitats for BF, nursery grounds for CMF, and migratory pathways for DF.  相似文献   

8.
The Tam Giang – Cau Hai lagoon is a microcosm of the complex social-ecological challenges experienced in similar systems throughout Southeast Asia. Intensification and rapid change in livelihood strategies (production and gear type) have increased conflict and placed a significant strain on aquatic resources in the lagoon. Such changes are compounded by near-shore agricultural development and urbanization. In the long-term, resolving livelihood conflicts and sustaining ecosystems will require a shift in the planning and management model from one that is top-down and enforcement driven, to one involving greater decision making and management authority at the local level. Drawing on experiences with a long-term action research process in the lagoon, this paper examines the challenges and opportunities of implementing a co-management approach. Of particular focus is the growing recognition among authorities of the value of engaging local fishers and fish farmers in participatory process to resolve complex livelihood challenges, and the development of local management bodies (newly formed Fishing Associations) as a basis for emerging co-management of aquatic resources.  相似文献   

9.
The speculation that climate change may impact on sustainable fish production suggests a need to understand how these effects influence fish catch on a broad scale. With a gross annual value of A$ 2.2 billion, the fishing industry is a significant primary industry in Australia. Many commercially important fish species use estuarine habitats such as mangroves, tidal flats and seagrass beds as nurseries or breeding grounds and have lifecycles correlated to rainfall and temperature patterns. Correlation of catches of mullet (e.g. Mugil cephalus) and barramundi (Lates calcarifer) with rainfall suggests that fisheries may be sensitive to effects of climate change. This work reviews key commercial fish and crustacean species and their link to estuaries and climate parameters. A conceptual model demonstrates ecological and biophysical links of estuarine habitats that influences capture fisheries production. The difficulty involved in explaining the effect of climate change on fisheries arising from the lack of ecological knowledge may be overcome by relating climate parameters with long-term fish catch data. Catch per unit effort (CPUE), rainfall, the Southern Oscillation Index (SOI) and catch time series for specific combinations of climate seasons and regions have been explored and surplus production models applied to Queensland's commercial fish catch data with the program CLIMPROD. Results indicate that up to 30% of Queensland's total fish catch and up to 80% of the barramundi catch variation for specific regions can be explained by rainfall often with a lagged response to rainfall events. Our approach allows an evaluation of the economic consequences of climate parameters on estuarine fisheries, thus highlighting the need to develop forecast models and manage estuaries for future climate change impact by adjusting the quota for climate change sensitive species. Different modelling approaches are discussed with respect to their forecast ability.  相似文献   

10.
The concept of essential fish habitats (EFHs) is widely accepted for conservational and management purposes. EFHs are often considered as high quality habitats for fisheries species and subsequently of high values for society. In this study, fish and Substrate-Associated Prey (SAP) were sampled during the productive summer season 1998 (fish) and 2003 and 2004 (SAP) in shallow coastal rocky- and soft-bottom habitats on the Swedish west coast. The aim was to study the spatial and monthly variation of SAP as well as abundance and biomass of fish, and to examine if food items found in the diet of the fish assemblage were derived from SAP. We also examined if the diet of Ctenolabrus rupestris, a resident and abundant fish species in the shallow coastal habitats, and the diet of four seasonally abundant and commercially important fish species (Gadus morhua, Pleuronectes platessa, Salmo trutta and Scomber scombrus) were derived from SAP. There were significantly higher mean species number and abundance of the SAP assemblage on rocky compared to soft bottoms and the highest values were found on the rocky bottoms in August and in the shallowest (0–3 m) depth strata. There were no significant differences in number of fish species caught in the two habitats, although mean number of fish and mean biomass were significantly higher on rocky bottoms. Both habitats showed the same seasonal variation and the highest values of number of fish species, abundance and biomass were observed in June. On rocky bottoms, gastropods and amphipods were the most frequent food items in the diet of the entire fish assemblage and these items were also the most abundant SAP in this habitat. The dominant food items of the soft-bottom fish assemblage were decapods and fish, which were not common SAP. However, except for S. scombrus, the diet of the selected fish species showed a strong association to the SAP availability. Gadus morhua displayed the strongest association to SAP on rocky bottoms and P. platessa and C. rupestris to SAP on soft bottoms. Further, for C. rupestris, multivariate statistical analysis showed a significant association to the SAP assemblage on both rocky and soft bottoms. These results provide vital new information for the management and conservation of Essential Fish Habitats on the Swedish west coast.  相似文献   

11.
The spatial size distribution of grunts and snappers have previously indicated the separation of juveniles in nursery habitats from the adults on the coral reef. This implies life cycle migrations from nursery habitats (such as seagrass beds and mangroves) to the coral reef. If diet shifts are related to such migrations, then the diets of these fish must change before or around the fish size at which such migrations take place. A wide size range of juveniles of two grunt species (Haemulon sciurus and Haemulon flavolineatum) and of two snapper species (Lutjanus apodus and Ocyurus chrysurus) were caught in seagrass beds and mangroves, and their gut contents identified and quantified. Regression analysis between fish size and dietary importance of small crustaceans showed a negative relationship in all four species. Positive relations were found for H. sciurus, L. apodus and O. chrysurus between fish length and the dietary importance of decapods, and for L. apodusand O. chrysurus between fish length and prey fish importance. Critical changes in the fish diets with fish size were examined by application of a Canonical Correspondence Analysis (CCA). The CCA yielded three clusters of size-classes of fishes with similar diets, and application of a Mantel test showed that each of these clusters had significantly different diets, and that each cluster diet was significantly specialised. The size at which a fish species ‘switched’ from one cluster to another was compared with size-at-maturity data and with the typical size at which these species migrate from the nursery habitats to the coral reef. H. sciurus and H. flavolineatum may be prompted to migrate from the nursery habitats to coral reef habitats because of dietary changes, or because of the development of the gonads. For L. apodus and O. chrysurus, a dietary changeover forms a more likely explanation for nursery-to-reef migrations than does sexual maturation because these species reach maturity at sizes much larger than the maximum size of individuals found in nursery habitats. Although other factors may theoretically initiate or promote the migration patterns, the results of this study indicate that ontogenetic dietary changes may crucially influence the nursery-to-coral reef migrations of these reef fish species.  相似文献   

12.
Well-developed aerial roots of mangroves make it difficult to study how fish utilize the mangrove forest as a habitat. In the present study, we compared the differences in fish assemblages in three major types of habitats of mangrove estuary (vegetated area, treeless mudflat, and creek) of a mangrove bay in Hainan Island, China, at different seasons during two consecutive years. Three types of gears, centipede net, gill net and cast net, were used in the different habitats of mangrove estuary and sampling efficiencies among gears were evaluated. Centipede nets were used in all the three types of habitats and cast nets and gill nets in treeless mudflats and creeks. Fish assemblages were dependent on gears used. Centipede net could efficiently catch fish occurring both inside and outside of vegetated areas efficiently. A total of 115 fish species in 51 families were collected. In terms of numbers of species per family, Gobiidae was the most diverse (17 species), followed by Mugilidae (5 species). Almost all of the fish were juvenile or small fish and few predators were recorded, implying low predation pressure in the bay. ANOVA analysis showed that significant seasonal and spatial variation existed in species richness, abundance, and biomass, which were less in the vegetated areas than those of treeless mudflats and creeks. The attraction of vegetated areas to fish was less than that of creeks and mudflats. Many species were specific to a particular habitat type, 4 species occurring exclusively in the creeks, 45 species occurring exclusively in the treeless mudflats, and 5 species occurring exclusively in the vegetated areas. The results indicated that mangrove estuaries were potentially attractive habitats for juvenile and small fish, but this attraction was accomplished by a connection of vegetated areas, treeless mudflats and creeks, not only by vegetated areas.  相似文献   

13.
In 2004, we surveyed demersal fishes and habitats on the continental shelf off central California (65–110 m depth) using the occupied submersible Delta. Our objectives were to estimate the relative abundance of habitats and to examine demersal fish species composition, diversity, density, and sizes relative to these habitats. A total of 112 transects were completed covering 32 km of seafloor. A higher density of fishes was estimated in boulder and cobble habitats than in mud and brachiopod beds. More than 80% of the fishes were small, measuring 20 cm or less in total length. Species with small maximum size (primarily pygmy rockfish, Sebastes wilsoni, and blackeye gobies, Rhinogobiops nicholsii) accounted for nearly half (49%) of the total number of 12,441 fishes. Most fishes were immature, with only 4 of 20 harvested species having more than 50% of the individuals larger than the size at first maturity. Our study area on the continental shelf may be an ontogenetic transition zone for immature fishes before they move to their adult habitat on the slope. Alternatively, historical fishing pressure may have contributed to the lack of large, mature fishes in the survey area. Understanding the importance of these habitats to fishes at various life stages will improve our ability to assess these deepwater fish stocks and effectively manage these living resources on an ecosystem basis.  相似文献   

14.
Diadromous fish species dominate the New Zealand freshwater fish fauna and make up 15 of the 17 native fish species found on the Taranaki Ring Plain. Trajectories of occurrence in relation to elevation and distance from the sea are described for 11 diadromous and 2 non‐diadromous species using data from the New Zealand Freshwater Fish Database and data collected over the summer of 1997/ 98. Distinctive distributions were found for most of the species related to their differing migratory strategies and abilities. The species were ranked based on components of these trajectories to compare their penetrative ability. Comparison of the ranking methods used revealed they produced similar results. The ranking of the 11 diadromous species in Taranaki relative to each other revealed similar rankings to those for the same species from the West Coast of the South Island. The non‐migratory native fish, Cran's bully (Gobiomorphus basalis), was not found on the western side of the mountain. This distribution is thought to be the result of the local extinction of non‐migratory species in high gradient or unstable streams.  相似文献   

15.
The protection of imperilled fish species is increasingly urgent given ongoing fisheries declines and the degradation of aquatic habitats. In Canada, threatened aquatic species were less likely than terrestrial species to be listed under the Species at Risk Act (SARA), the main legal instrument for bestowing protection, in the early years of the Act's implementation. In this paper, the existence of economic thresholds that might have hampered the protection of Canadian marine and freshwater fishes is examined. The analysis of the socio-economic data used to inform listing decisions about threatened fish taxa over the past decade reveals that the likelihood of being listed declines non-linearly with increasing estimated costs of protection but does not vary with proposed threat status. The estimated threshold cost (i.e., the point at which the likelihood of not being listed=0.5) was ∼$5,000,000 (∼$1,400,000 to ∼$31,400,000, 95% CI) per decade for freshwater species but only ∼$90,000 ($∼50,000 to ∼$140,000, 95% CI) per decade for marine fish taxa. In fact, no marine fish species with an anticipated cost of listing greater than zero was listed for protection. The presence of existing management legislation and qualitative statements about negative impacts of listing on exploitation generally led to denying protection to marine but not to freshwater species. These findings highlight both a large and inconsistent emphasis on costs of protection in SARA listing decisions, to the detriment of marine fish species.  相似文献   

16.
Management of fish populations is often focused on the exploitation of adult fish. Maintaining the habitat requirements of all life stages may also be an important consideration. We investigated the value of structured habitat to juvenile fishes within a northeastern New Zealand harbour using artificial seagrass units (ASUs). Specifically, we deployed ASUs across treatments with high vs. low habitat manipulations. We hypothesised that if the abundance of recruiting juvenile fishes was greater on the high habitat availability treatments this would suggest that the availability of habitat was limiting juvenile fish abundance. Our analyses were focused on the four most abundant fishes that settled on our ASUs: snapper (Pagrus auratus); spotty (Notolabrus celidotus); trevally (Pseudocaranx dentex); and an assemblage of pipefish species. For snapper, spotty and pipefish, abundance was greater on the high habitat availability treatments. This result would be unlikely to occur if the availability of juvenile fishes was limiting, suggesting that juvenile fish abundance is more likely to be limited by habitat. In terms of spatial gradients, spotty abundance and size increased with distance into the harbour. The spatial gradient present for spotty indicates the importance of placing the habitat dependency of juvenile fish into a landscape context. Overall, these results demonstrate that maintaining structured habitats may be an important consideration for some valuable inshore fish populations in northeastern New Zealand.  相似文献   

17.
Distribution, abundance, and habitat preferences of native fish were investigated down the length of a relatively pristine, medium‐sized, fourth‐order stream on Stewart Island, New Zealand. A limited fish fauna was recorded (six species), including three threatened large galaxiid species (Galaxias argenteus, Galaxias fasciatus, and Galaxias brevipinnis), which have restricted distributions on mainland New Zealand. Results indicated that these large galaxiids occupy diverse habitats including pools and backwaters within the mainstems of this stream. Their extensive distributions and wide habitat usage were attributed to factors such as the intact catchment vegetation, unmodified stream channel, and the absence of introduced fishes, particularly salmonids. Results suggest that some native species have been excluded from mainstem habitats elsewhere in New Zealand. It was also evident that interactions among the native species influenced habitat use; G. brevipinnis avoided backwaters, runs, and pools in reaches occupied by G. fasciatus and Anguilla dieffenbachii; whereas G. fasciatus appeared to avoid habitats occupied by G. argenteus and A dieffenbachii. Maximum densities and biomass of galaxiids and eels occurred in deepwater habitats (>0.75 m). Furthermore the fish inhabiting these deeper waters were larger and more likely to be female. These findings have significant implications for the design and application of sampling protocols for native New Zealand fishes and for the protection of their habitats. If deeper waters are not sampled then species, sex, and size biased data may result.  相似文献   

18.
Mesopelagic fish,the most important daily vertically migrating community in the oceans,are characterized by high lipid content which may obscure the interpretation of stable isotopes analysis.Demersal fish,which are important consumers in the food web dominated by mesopelagic fish,also have a high lipid content.Here we collected 127 fish samples from the South China Sea and evaluated the effect of lipid contents on δ13C of mesopelagic and demersal fish.In lipid-extracted mesopelagic f...  相似文献   

19.
The construction of an estuary barrage, an instream structure in the lower reaches of a river, causes significant physical changes in water flow patterns and river morphology, and results in altered environmental conditions. Here, we examined the impact of the Geum River estuary barrage, completed in 1990, on fish assemblages by using a literature search and fresh surveys of fishways in the barrage. We found that fish assemblages upstream and downstream of the barrage were altered following its completion. After construction, more species were found in the freshwater area, with a particularly great increase in freshwater species. Conversely, estuarine and marine species were only consistently caught in the downstream salt-water area, although the number of species increased. In total, 15,829 fish from 47 species and 20 families were identified at the three types (pool and weir, rubble type, and boat passage) of fishways in the barrage. The dominant species were Chelon haematocheilus, an estuarine species, Coilia nasus, a diadromous species, and Erythroculter erythropterus, a freshwater species. The mean total length of fish (101.9 ± 76.0 mm) in the boat passage fishway was approximately 100 mm lesser than those in the pool and weir (207.2 ± 112.8 mm) and rubble type (205.8 ± 112.7 mm) fishways. The boat passage fishway was the most efficient for fish movements. The current fishway system is not sufficient for fish migration, and thus additional ways are required to improve the system such as the boat passage. Few estuarine or diadromous species were found in both freshwater and salt-water areas, but freshwater fishes that accidently moved to salt-water area actively used fishways. Therefore, fishway management in the Geum River estuary barrage has to focus on freshwater fish; however, this may need to change to a focus on migratory fishes depending on ecological life cycles of migratory fish.  相似文献   

20.
Stable carbon and nitrogen isotopes (δ13C, δ1?N) were used to analyse food web dynamics of two of the main estuaries of the Portuguese coast: Tejo and Mira. The ultimate sources of organic matter supporting production of some of the most abundant and commercially important fish species were determined; and seasonal, inter- and intra- estuarine differences in the trophic relations among producers and consumers were identified. Stable isotope analysis was performed in different producers, primary consumers (main prey items for fish) and fish species (Solea solea, Solea senegalensis, Pomatoschistus microps, Dicentrarchus labrax, Liza ramada, Diplodus vulgaris and Atherina presbyter) of two areas in each estuary, in July and October 2009. Model calculations showed that the main prey for the fish species in the Tejo estuary used mostly salt marsh-derived organic matter as nutritional sources, with no marked differences between the sampled months. Trophic levels of fish species from the same estuary differed at multiple scales: inter-species, seasonally and spatially (both between and within estuaries). Significant differences in isotopic composition of fish species were more pronounced spatially (between the two sampled areas in the estuary) than seasonally (between sampled months). Trophic relationships in both estuaries demonstrated that organic matter is transferred to higher trophic positions mainly through benthic pathways. This shows the flexibility of these species to share resources and to exploit temporary peaks in prey populations. The present results showed that extensive disturbance in intertidal habitats from both estuaries may potentially change the balance of organic matter in the base of these complex food webs.  相似文献   

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