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1.
Seven meso- and bathy-pelagic fish species from the Mid-Atlantic Ridge (MAR) were firstly studied for fish parasites and feeding ecology. With a total of seven parasite species, the 247 meso- and bathy-pelagic deep-sea fish specimens belonging to the families Melamphaidae (3 spp.), Myctophidae (3 spp.) and Stomiidae (1 sp.) revealed low parasite diversity. The genetically identified nematodes Anisakis simplex (s.s.) and Anisakis pegreffii from the body cavity, liver and muscles of Myctophum punctatum were the most abundant parasites, reaching a prevalence of 91.4% and mean intensity of 3.1 (1–14). Anisakis sp. (unidentified) infected Chauliodus sloani and Poromitra crassiceps. Bothriocephalidean and tetraphyllidean cestode larvae infected Benthosema glaciale, the latter also occurring in C. sloani and Scopelogadus beanii, at low prevalences. Adult parasites at low infection rates included the digenean Lethadena sp. (2.9%), and the two copepod species Sarcotretes scopeli (5.7%) and Tautochondria dolichoura (5.3–11.4%). The myctophid Lampanyctus macdonaldi and the melamphaid Scopelogadus mizolepis mizolepis were free of parasites. Analyses of the stomach contents revealed crustaceans, especially copepods and euphausiids for the myctophids and also amphipods for the melamphaids as predominant prey items. While all stomachs showing distinct content comprising often unidentified ‘tissue’ (possibly gelatinous zooplankton), only C. sloani preyed upon fish. Though this feeding habit would enable transfer of a variety of crustacean-transmitted parasites into the fish, the parasite fauna in the meso- and bathy-pelagic fish was species poor. All observed parasites showed low host specificity, demonstrating no distinct pattern of host–parasite co-evolution. The MAR is no barrier for the parasite distribution in the North Atlantic meso- and bathy-pelagial.  相似文献   

2.
The northern Mid-Atlantic Ridge, from Iceland to the Azores (MAR), is the largest topographical feature in the Atlantic Ocean. Despite its size, few studies have described dietary patterns of pelagic fishes along the MAR. MAR-ECO, a Census of Marine Life field project, aimed to describe the food web structure of abundant fish species along the ridge through a series of research expeditions to the MAR. Among the midwater fishes sampled during the MAR-ECO project, Bathylagus euryops (Osmeriformes: Bathylagidae) was the biomass-dominant pelagic species and ranked third in total abundance. In this paper, we describe the dietary composition of B. euryops along the MAR. Overall, copepods represented the dominant prey group consumed by B. euryops. Multivariate analyses, including a cluster analysis and a canonical correspondence analysis, revealed that fish size significantly influenced the diet of B. euryops with ostracods representing the most important prey group at small sizes (<95 mm) and decapod shrimp and calanoid copepods becoming more important with increasing fish size. Due to the high abundance and biomass observed along the MAR combined with its role as a link for energy transfer between zooplankton and higher trophic level predators, B. euryops appears to be an ecologically important species in the oceanic food web of the North Atlantic Ocean.  相似文献   

3.
Metazoan parasites communities of marine fishes can include both adults and larval stages of several endoparasite groups that use fishes as intermediate or paratenic hosts. The richness and abundance of parasite species larvae that harbour a fish species can therefore be a good indicator of that species’ role as an intermediate host to endoparasite species.

The parasite communities of two small carangid fishes (Selar crumenophthalmus and Decapterus muroadsi) from Mexican Pacific coasts were quantified and analysed. Five hundred sixty-three carangids (S. crumenophthalmus, n?=?402; and D. muroadsi, n?=?161) were collected between April 2014 and April 2018 from three locations. Twenty-four metazoan parasite species were identified in both hosts: five species of Monogenea (adults), eight of Digenea (7 adults and 1 metacercaria), two of Cestoda (larvae), two of Nematoda (one adult and one larva), two of Acanthocephala (adults), and five of Copepoda. Larval helminths numerically dominated the endoparasite communities of both hosts, suggesting that these carangids are important intermediate hosts for several parasite species. Component parasite community richness and species composition differed between hosts, locations, and sampling years. Variations in host feeding behaviour, and body size were considered as important factors influencing these differences.  相似文献   


4.
The diet of at least 28 species of mesopelagic fish from the Pacific coast of Hokkaido was examined. The dominant family was the Gonostomatidae (42%) which was represented by five species. The most abundant species wasCyclothone atraria which together with the other species of this genus preyed predominantly on copepods. Euphausiids and copepods were dominant in the diet ofGonostoma gracile. The next most abundant family was the Myctophidae (32%) which was represented by seven species. The dominant species,Stenobrachius nannochir, preyed mainly on copepods. Copepods were also the dominant food item of the other myctophids except forLampanyctus jordani which fed mainly on euphausiids. The other important family was the Bathylagidae (21%).Leuroglossus schmidti was the dominant species and its diet was more diverse with ostracods, copepods, molluscs and larvaceans being the most important food items.Bathylagus ochotensis had a similar diet. Copepods were the most important food items for all but a few species and their occurrence in the fish stomachs was related to the known vertical distribution of both predators and prey. Ostracods and euphausiids were also important prey items, the latter especially in large fish species. Molluscs and larvaceans were restricted to the two species of the family Bathylagidae.  相似文献   

5.
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6.
The structure of the summer larval fish assemblage off the eastern coast of Tunisia and its relation to environmental conditions was studied, from ichthyoplankton samples taken during a survey conducted between 23rd June and 9th July 2008. A total of 68 larval fish taxa were identified, 52 to species level. The taxonomic composition and abundance of the larval fish assemblage showed high spatial heterogeneity. Mesoscale hydrographic features, such as eddies, seem to play an important role in the spatial distribution of fish larvae in the area, enhancing concentration and retention. The larval fish assemblage was dominated by the small pelagic species Sardinella aurita (26.6% of the total larval fish abundance), followed by Engraulis encrasicolus (22.6%), Spicara spp. (8.6%) and Mullus barbatus (6.8%). Shannon–Weaver index (H′) ranged between 0 and 2.62. The highest values were found offshore, at 95 miles east of Sousse, over depths around 250 m. The diversity was higher in this region as a result of transport by currents and retention by eddies. It has also been shown that the eastern coast of Tunisia is a spawning ground for the tuna species Auxis rochei, Thunnus thynnus and Thunnus alalunga. Larvae of mesopelagic fishes represented 5.46% of the total abundance, with Cyclothone braueri, Ceratoscopelus maderensis and Lampanyctus crocodilus being the most important species. Canonical correspondence analysis (CCA) indicated that depth was the most important environmental factor in explaining species distribution.  相似文献   

7.
Conventional laboratory studies of deep-sea fish metabolism are not possible as these fish are typically killed during recovery to the surface. As these species are important members of deep-sea communities, the lack of these data represents a significant limitation to our understanding of the functioning of this ecosystem. An autonomous fish respirometer vehicle was developed in order to measure the oxygen consumption of deep-sea fish in situ. This new lander allows measurements to be made without handling or stressing the animals and without the logistical problems and great cost of submersible operations. The design, operation, and measurement methodology are described and preliminary data for Coryphaenoides armatus at 4000 m are presented. These Atlantic data appear to confirm the low metabolic rate measured in this species when compared to other gadid species.  相似文献   

8.
Based on trawl surveys in the Bering Sea and Chukchi Sea during the 2010 Chinese National Arctic Research Expedition, fish biodiversity characteristics, such as fish composition, dominant species, biodiversity, and faunal characteristics were conducted. We also discussed the responses of fishes to the quick changes in Arctic climate. The results showed that a total of 41 species in 14 families were recorded in these waters. The dominant species were Hippoglossoides robustus, Boreogadus saida, Myoxocephalus scorpius, Lumpenus fabricii, and Artediellus scaber. There were 35 coldwater species, accounting for 85.37%, and six cold temperate species, occupying 14.63%. The habitat types of fish could be grouped as follows: 35 species of demersal fishes, five benthopelagic fishes, and one pelagic fish. The Shannon–Wiener diversity index(H)(range between 0 and 2.18, 1.21 on average) was not high, and descended from south to north. Climate change has caused some fishes to shift along their latitudinal and longitudinal distribution around the Arctic and Subarctic areas, and this could lead to the decline of Arctic fishery resources.  相似文献   

9.
Spatial and seasonal variations of fish assemblage composition were studied in three non-estuarine mangrove creeks of Zanzibar (Tanzania). Fish were collected monthly for one year at three sites (lower, intermediate and upper reaches) in each creek using a seine net (each haul covering 170 m2). Density, species number and diversity of fish were all higher at sites with dense cover of macrophytes (seagrass and macroalgae) than over unvegetated sandy sites. In general, fish assemblages mainly comprised juveniles of a few abundant taxa, e.g. Mugil cephalus, Mugilidae spp. and Leiognathus equulus at sites with mud substratum and Gerres oyena, Lethrinus harak and Sillago sihama at sites dominated by macrophytes. Multivariate analyses revealed significant separations in fish assemblage composition within the two creeks where the bottom substratum differed among sites. Overall, season seemed to have little effect on density, species number, diversity index (H′) and assemblage structure of fish. Water condition variables were also relatively stable across the season, although a short-term fluctuation primarily induced by decreased salinity, occurred during the heavy rains in April and May. Fish assemblage structure was not significantly affected by any of the abiotic factors tested. However, significant regressions were found between the other fish variables and environmental variables, but since these associations were mostly species-specific and generally inconsistent, we suggest that the overall distribution patterns of fish were mainly an effect of particular substrate preferences of fish species rather than contemporary water conditions.  相似文献   

10.
Long-term interannual changes in abundance, biomass, diversity and structure of littoral fish assemblages were examined between 1993 and 2009 by experimental trammel net fishing up to six times per year, within the warm period - May to September, at multiple areas along the eastern Adriatic coast with the aim of testing for the consistency of patterns of change across a large spatial scale (∼600 km). The results revealed spatially consistent increasing trends of total fish abundance and biomass growing at an average rate of 15 and 14% per year, respectively. Of the diversity indices analysed, the same pattern of variability was observed for Shannon diversity, while Pielou evenness and average taxonomic distinctness measures Δ∗ and Δ+ showed spatial variability with no obvious temporal trends. Multivariate fish assemblage structure underwent a directional change displaying a similar pattern through time for all the areas. The structural change in fish assemblages generally involved most of the species present in trammel net catches. A large pool of fish species responsible for producing the temporal pattern of assemblage change was relatively different in each of the areas reflecting a large geographic range covered by the study. An analysis of 4 fish species (Symphodus tinca, Pagellus erythrinus, Mullus surmuletus, Scorpaena porcus) common to each of the study areas as the ones driving the temporal change indicated that there were clear increasing trends of their mean catches across the years at all the study areas. A common pattern among time trajectories across the spatial scale studied implies that the factor affecting the littoral fish assemblages is not localised but regional in nature. As an underlying factor having the potential to induce such widespread and consistent improvements in littoral fish assemblages, a more restrictive artisanal fishery management that has progressively been put in place during the study period, is suggested and discussed.  相似文献   

11.
The purpose of this paper was to study the community structure, in terms of species composition, abundance and spatial distribution, of fish larvae in a wide coastal area of Sicily facing the Southeastern Tyrrhenian Sea, extending for 2300 km2 from Cape Cefalù to the west, to Cape Rasocolmo in the east. This study analyses how species are assembled in relation to an inshore–offshore gradient and also how environmental conditions, determined by surface circulation patterns occurring in the Central Mediterranean at the local scale, determine the distribution patterns. Samples from 39 stations were collected using a 60‐cm Bongo net during an ichthyoplanktonic survey carried out in June 2006. In all, 62 taxa, representing 32 families, were identified. Cyclothone braueri (59.6%), Engraulis encrasicolus (9.2%) Lampanyctus crocodilus (4.3%) and Lampanyctus pusillus (4.1%) were the most abundant species. The results showed that the highest abundance value (14830.6 fish larvae per 10 m2 sea surface) was observed in the western part of the study area. MDS, SIMPER and CCA analyses revealed well defined groups of stations and assemblages of larvae in accordance with an inshore–offshore gradient. The results of this study could have implications for the management of marine resources because the investigated area has already been identified as a nursery area for many pelagic and coastal fishes and a natural habitat for many species of high commercial interest.  相似文献   

12.
This paper synthesizes recent findings regarding microbial distributions and processes in the bathypelagic ocean (depth >1000 m). Abundance, production and respiration of prokaryotes reflect supplies of particulate and dissolved organic matter to the bathypelagic zone. Better resolution of carbon fluxes mediated by deep microbes requires further testing on the validity of conversion factors. Archaea, especially marine Crenarchaeota Group I, are abundant in deep waters where they can fix dissolved inorganic carbon. Viruses appear to be important in the microbial loop in deep waters, displaying remarkably high virus to prokaryote abundance ratios in some oceanic regions. Sequencing of 18S rRNA genes revealed a tremendous diversity of small-sized protists in bathypelagic waters. Abundances of heterotrophic nanoflagellates (HNF) and ciliates decrease with depth more steeply than prokaryotes; nonetheless, data indicated that HNF consumed half of prokaryote production in the bathypelagic zone. Aggregates are important habitats for deep-water microbes, which produce more extracellular enzymes (on a per-cell basis) than surface communities. The theory of marine gel formation provides a framework to unravel complex interactions between microbes and organic polymers. Recent data on the effects of hydrostatic pressure on microbial activities indicate that bathypelagic microbial activity is generally higher under in situ pressure conditions than at atmospheric pressures. High-throughput sequencing of 16S rRNA genes revealed a remarkable diversity of Bacteria in the bathypelagic ocean. Metagenomics and comparative genomics of piezophiles reveal not only the high diversity of deep sea microbes but also specific functional attributes of these piezophilic microbes, interpreted as an adaptation to the deep water environment. Taken together, the data compiled on bathypelagic microbes indicate that, despite high-pressure and low-temperature conditions, microbes in the bathypelagic ocean dynamically interact with complex mixtures of organic matter, responding to changes in the ocean’s biogeochemical state.  相似文献   

13.
Deep-sea or cold-water corals form substantial habitat along many continental slopes, including the southeastern United States (SEUS). Despite increasing research on deep coral systems and growing appreciation of their importance to fishes, quantitative data on fish communities occupying these ecosystems are relatively lacking. Our overall goals were to document the fish species and their relative abundances and to describe the degree of general habitat specificity of the fishes on and around deep coral habitats on the SEUS slope. From 2000 to 2006, we used the Johnson-Sea-Link (JSL) submersible (65 dives, 366–783 m), supplemented with otter trawls (33 tows, 365–910 m) to document fishes and habitats from off North Carolina to east-central Florida. Eight areas with high concentrations of deep-sea corals were surveyed repeatedly. Three general habitat types (prime reef, transition reef, and off reef) were defined to determine large-scale habitat use patterns. Throughout the area, at least 99 fish species were identified, many (19%) of which yielded new distributional data. Most species observed with the JSL were on prime reef (n=50) and transition reef (n=42) habitats, but the off reef habitat supported a well developed, but different fauna (n=25 species). Prime reef was characterized by Laemonema melanurum (21% of total), Nezumia sclerorhynchus (17% of total), Beryx decadactylus (14% of total), and Helicolenus dactylopterus (10% of total). The off reef areas were dominated by Fenestraja plutonia (19% of total), Laemonema barbatulum (18% of total), Myxine glutinosa (8% of total), and Chlorophthalmus agassizi (7% of total). Transition habitat exhibited a mixture of species that were also found on either prime reef or off reef habitats. Nezumia sclerorhynchus was the most abundant (25% of total) transition habitat species, followed by L. barbatulum (16% of total) and L. melanurum (14% of total). Several species (e.g., Anthias woodsi, B. decadactylus, Conger oceanicus, and Dysommina rugosa) demonstrated specificity to deep-reef habitats, while others (e.g., C. agassizi, Benthobatis marcida, F. plutonia, and Phycis chesteri) were always more common away from reefs. In addition to new distributional data, we provide behavioral and biological observations for dominant species.  相似文献   

14.
Specimens of Mora moro were collected in two seasons and three localities of the Balearic Sea (NW Mediterranean Sea) and parasitological, dietary (to prey-species level), enzymatic and histological data were obtained, alongside with environmental information (T, S, O2). The relationships among fish parasite load, condition indices, diet, enzymatic activity of muscular acetylcholinesterase (AChE) and lactate dehydrogenase (LDH), intensity of splenic melano-macrophage centres (MMC) and hepatic granulomas were tested. M. moro showed a rich and abundant parasite fauna, and was a new host record for 17 out of the 18 different endoparasite taxa found. Significant differences were detected among locality-season groups, in turn related to different environmental variables, for Anisakidae gen. sp., Anisakis Type II and Tetraphyllidea fam. gen. sp.; thus, they are proposed as potentially useful as biological tags for geographical discrimination of M. moro in the NW Mediterranean Sea. Detailed relationships were found between parasite taxa and prey ingested (e.g. Anisakidae gen. sp. related with meso-bathypelagic crustaceans; Anisakis Type I with benthopelagic squids). Most parasites were linked to samples with highest levels of near-bottom O2, which is consistent with direct relationships found between near-bottom O2 and zooplankton biomass in the Balearic Basin. Total parasite abundance and the abundance of Tetraphyllidea fam. gen. sp. showed a significant relationship with the activity of AChE and the abundance of Anisakis Type II with LDH. AChE was associated with hepatosomatic index (HSI) and condition factor (K); LDH with gonadosomatic index (GSI), K and fish total length (TL). LDH activity showed differences among sampling groups. Splenic MMC and hepatic granulomas were not associated with fish parasite load. A positive relationship was found between MMC area and fish TL and LDH activity.  相似文献   

15.
The Mondego estuary fish assemblage was studied for the accumulation of PCBs. Three sampling stations were visited along an estuarine salinity gradient, and, in total, 15 species were collected. Analysis of PCBs revealed no significant differences among the sampling stations, although differences were observed among the fish assemblages. Fish assemblages could be divided into three groups. The first group comprised those with higher concentration (more than 10 ng g− 1, dw), included the species Gobius niger, Sardina pilchardus, Anguilla anguilla, Pomatoschistus microps, Chelidonichthys lucerna and Liza ramada; the second group with medium concentration (5–10 ng g− 1, dw), included the species Pomatoschistus minutus, Dicentrarchus labrax, Atherina presbyter, Chelon labrosus, Diplodus vulgaris, Platichthys flesus and Cilata mustela; and a third group with low concentration (less than 5 ng g− 1, dw), included the species Solea solea and Callionymus lyra. A positive correlation was found between lipid content and PCB concentrations. To evaluate the influence of the residence time of species on the accumulation of PCBs, species were divided into two groups: species that spend more than 3 years in the estuary, and species that spend less than 3 years in the estuary. Species that spend more than 3 years in the estuary presented higher concentrations than species that spend less than 3 years in the estuary. CBs 138 and 153 had higher concentration, and tended to increase with time spent in the estuary.  相似文献   

16.
Our understanding of the significance of sound production to the ecology of deep-sea fish communities has improved little since anatomical surveys in the 1950s first suggested that sound production is widespread among slope-water fishes. The recent implementation of cabled ocean observatory networks around the world that include passive acoustic recording instruments provides scientists an opportunity to search for evidence of deep-sea fish sounds. We examined deep-sea acoustic recordings made at the NEPTUNE Canada Barkley Canyon Axis Pod (985 m) located off the west coast of Vancouver Island in the Northeast Pacific between June 2010 and May 2011 to determine the presence of fish sounds. A subset of over 300 5-min files was examined by selecting one day each month and analyzing one file for each hour over the 24 h day. Despite the frequent occurrence of marine mammal sounds, no examples of fish sounds were identified. However, we report examples of isolated unknown sounds that might be produced by fish, invertebrates, or more likely marine mammals. This finding is in direct contrast to recent smaller studies in the Atlantic where potential fish sounds appear to be more common. A review of the literature indicates 32 species found off British Columbia that potentially produce sound could occur in depths greater than 700 m but of these only Anoplopoma fimbria and Coryphaenoides spp. have been previously reported at the site. The lack of fish sounds observed here may be directly related to the low diversity and abundance of fishes present at the Barkley Canyon site. Other contributing factors include possible masking of low amplitude biological signals by self-generated noise from the platform instrumentation and ship noise. We suggest that examination of data both from noise-reduced ocean observatories around the world and from dedicated instrument surveys designed to search for deep-sea fish sounds to provide a larger-scale, more conclusive investigation into the role, or potential lack thereof, of sound production.  相似文献   

17.
Seagrass grazing by fish was measured in a large seagrass-dominated temperate bay (Geographe Bay, Western Australia) to examine whether: (1) seagrass herbivory occurs; (2) the level of herbivory is influenced by nitrogen in seagrass leaves; and (3) how herbivory and herbivorous fish communities vary with water depth and seagrass species. Species and abundance of fish and herbivore bite marks on seagrass leaves were recorded from diver surveys of 23 sites of varying depth ranging from 1 m to 18 m. Posidonia sinuosa, Posidonia coriacea, Amphibolis griffithii, and Amphibolis antarctica seagrass leaves were collected, dried and analysed for total nitrogen. Evidence for low levels of seagrass grazing was found at over half the sites surveyed, though high levels of grazing were recorded at only one site. An east–west pattern was observed in the location of grazed sites and of herbivorous fish species that corresponded with the general prevalence of patch reefs, indicating that reef associated fish assemblages may be responsible for the observed grazing. Total nitrogen was elevated in seagrass leaves associated with drains, although increased nitrogen was not associated with increased grazing. While grazing was recorded in this temperate seagrass meadow, the abundance of herbivorous fish was low and the amount of biomass removed by them was small compared to the balance of the meadow remaining, and to seagrass grazing studies elsewhere.  相似文献   

18.
This study examines the parasite fauna of Bathypterois mediterraneus, the most common fish below 1500 m in Western Mediterranean waters. Samples were obtained during July 2010 from the continental slope of two different areas (off Catalonia and Balearic Islands) in three different bathymetric strata at depths between 1000 and 2200 m. The parasite fauna of B. mediterraneus included a narrow range of species: Steringophorus cf. dorsolineatum, Scolex pleuronectis, Hysterothylacium aduncum, Anisakis sp. larva 3 type II and Sarcotretes sp. Steringophorus cf. dorsolineatum and H. aduncum were the most predominant parasites. H. aduncum showed significant differences in abundance between depths of 2000–2200 m with 1000–1400 m and 1400–2000 m, irrespective of locality, whereas S. cf. dorsolineatum showed significant differences between the two localities at all depths except for 2000–2200 m. We suggest the possible usefulness of these two parasites as geographical indicators for discriminating discrete stocks of B. mediterraneus in Western Mediterranean waters.  相似文献   

19.
Seamounts are thought to support special biological communities, and often maintain high standing stocks of demersal and benthopelagic fishes. Seamount fish fauna have been described in several studies but few works have included species taken below 600 m. The demersal fish assemblages of the Seine and Sedlo seamounts (northeast Atlantic) from the summits to 2000 m depth were investigated based on longline survey catch data, conducted as part of the OASIS project. A total of 41 fish species from 24 families were caught at Seine near Madeira, and 30 species from 19 families were caught at Sedlo north of the Azores. Both fish faunas have high affinities with the neighbouring areas of the Azores, Madeira and with the eastern North Atlantic and the Mediterranean Sea. Overall abundances and mean body weights were slightly higher at Sedlo seamount, appearing in conformity with the latitudinal effect of increasing species abundance and productivity from south to north. The differential influence of the Mediterranean Water at each seamount may contribute to explain (a) the differences found in vertical distribution of common species, which tend to distribute deeper at Seine, and (b) the observed changes in the species composition and dominance in deeper waters. Multivariate analysis revealed a vertical structure that is approximately coincident with the expected zonation of water masses at each seamount. Physiological tolerance to the prevailing vertical hydrological conditions may explain the species distribution and the large-scale vertical assemblage structure found. However, further ecological factors like productivity patterns affecting the amount and quality of the available food appear to shape the abundance, diversity or dominance patterns of functional groups within those main assemblages. At Seine, the species Trachurus picturatus dominated the catches, mainly at the shallower edge of the plateau, appearing consistent with the sound-scattering layer interception hypothesis [Isaacs, J.D., Schwartzlose, R.A., 1965. Migrant sound scatterers: interaction with the sea floor. Science 150, 1810–1813]. At both seamounts mesopelagic feeders (e.g., Beryx splendens) dominate the upper-slope assemblages (<800 m), while the mid-slope assemblages (800–1200/1300 m) and the lower-slope assemblages (>1300 m) were dominated by squaliform species (e.g., Centrophorus squamosus, Centroscymnus coelolepis, Etmopterus princeps) along with Mora moro or the Antimora rostrata. The lower abundance of C. squamosus observed at Seine may be a result of the fishing activities in the area, since the species is an important by-catch of the black-scabbard fish fishery in the Madeira archipelago. The slightly higher predominance of scavenger species at Seine in deeper assemblages may be the result of an ecological response favouring this functional group in lower productivity regimes. Especially relevant was the record of large reproductive aggregations of B. splendens and Epigonus telescopus found at the edge of the Sedlo plateau.  相似文献   

20.
The Lima estuary (NW Portugal) is at the end of an international watershed, whose potential role as a spawning and nursery habitat for local fish populations has not been previously examined. To address this knowledge gap, fortnightly plankton surveys were conducted between April 2002 and April 2004. A total of 12,903 larvae, belonging to 20 families and 50 taxa were collected, with a mean abundance of 8 individuals per 100 m3. Gobiidae was the most abundant family comprising 71% of the total catch, followed by Clupeidae with 12% of the total. The top six abundant taxa (Pomatoschistus spp., Sardina pilchardus, Ammodytes tobianus, unidentified Clupeidae, Symphodus melops and Solea senegalensis) represented 91% of the total catch. Fish larvae showed a seasonal trend with abundances increasing during spring and summer. Diversity was generally low (H′ = 0.65) with high dominance of very few taxa. Near the ocean, the larval fish assemblage was more diverse due to the presence of marine species. In the lower estuary Channel zone, abundance was lower than in the two upstream salt marsh zones (North and South zones) and no statistical differences in abundance or diversity values were found within the latter zones. ANOSIM results demonstrated seasonal differences in the species composition, mainly during the second winter period which was typified by a pelagic species A. tobianus. The community in the Channel zone was more diverse in comparison with the other zones, which were highly dominated by the most abundant species. The spatial and temporal trends of the most abundant species were typical for Iberian estuaries, with the exception of the low abundance of anchovy larvae and the unusually high numbers and frequency of S. pilchardus, usually mentioned as accidental in estuarine systems. Overall results suggest that the Lima estuary larval fish assemblage has a strong seasonality and affinity to the salt marsh zones. It seems that spawning seasonality controlled the presence of temporary estuarine residents, while environmental aspects controlled the general abundance trend of the resident species.  相似文献   

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