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1.
南海北部上层鱼类浮游生物多样性和丰度的季节变化   总被引：1，自引：0，他引：1  
The objective of this study was to investigate the seasonal variations of ichthyoplankton diversity and abun-dance in the northern South China Sea based on the data collected during summer, winter and spring. In total, 95 taxa of larval fishes were identified. The greatest number of species was recorded in spring, followed by summer and winter. The number of species was distributed mainly in the coastal waters from the east of Leizhou Peninsula to the southeast of Hainan Island during the surveyed periods of summer and spring, but in the offshore waters during winter. The abundance of larval fish was lowest in winter, increased in spring, and reached the maximum in summer. High abundance of larval fish was generally restricted to coastal waters with the isobaths less than 50 m. Seasonal variations of larval fish richness, abundance and diversity index were significant （P〈0.001）. Carangidae was the most common and abundant taxon in summer and winter, whileSardinella sp.,Thrissa mystax andLeiognathus sp. were dominant in spring. High diversity and abundance of larval fish might be attributed to increased temperature and coastal upwelling in spring and summer.  相似文献   

2.
Monthly sampling for ichthyoplankton was conducted at three stations very near to the coast (near to shore shallow stations before the surf zone in direction to the shoreline) of Atlantic northwestern Portugal within contrasting localities: rocky shore, in front of a sandy beach receiving an estuary and a fishing port with heavy anthropogenic impact. Sampling was conducted from August 2002 to October 2003, always at full moon, at low tide and high tide in daylight hours, at the water column using a 48 cm diameter plankton net with 335 μm mesh. Analysis of the physico-chemical parameters pointed out the spatial (horizontal) homogeneity of the sampling area. Fish larvae from 41 taxa belonging to 17 families were identified; Blenniidae, Labridae, Ammodytidae, Clupeidae, Gobiidae, Soleidae and Gobiesocidae were the most representative during the study period. Parablennius gattorugine, Ammodytes tobianus, Symphodus melops, Sardina pilchardus, Lipophrys pholis and Coryphoblennius galerita were the most representative species (percentage contribution to total abundance). Peak abundance of fish eggs occurred during May, June and August 2003 and fish larvae occurred during May and July 2003 and August 2002 and 2003; there was a pronounced winter/early spring (March 2003) peak in larval abundance dominated by the small sandeel A. tobianus. This study identifies the occurrence of a conspicuous assemblage of larval fishes at very nearshore shallow environments of a variety of species with different adult habitats: the fish larvae assemblage was dominated by intertidal species. The present study has shown that temporal and spatial variations in the larval fish assemblage are related to environmental conditions and biological dynamics: the results suggest that abiotic conditions mediate biotic parameters, and that both abiotic and biotic characteristics regulated the larval fishes at very nearshore shallow environments.  相似文献   

3.
黄海中南部近岸海域春季鱼类浮游生物群落空间格局研究   总被引：6，自引：1，他引：5  
根据2015年春季在黄海中南部近岸海域进行的鱼类浮游生物大型浮游生物网水平拖网数据,采用生态多样性指数和多元统计分析等方法,研究了该海域鱼类浮游生物的种类组成和群落空间格局及其与环境因子的关系。结果表明,本次调查共采集到鱼类浮游生物35种,其中鱼卵21种,仔稚鱼23种。鱼类浮游生物隶属于8目18科34属,优势种为鳀（Engraulis japonicus）、鲬（Platycephalus indicus）、鱼衔属（Callionymus spp.）和小黄鱼（Pseudosciaena polyactis）。其中,鳀和鱼衔属主要分布于海州湾渔场海域,鲬主要分布于吕泗渔场海域,小黄鱼多分布于吕泗渔场北部海域。生态类型包括半咸水型、沿岸型和近海型种类。聚类分析表明,鱼类浮游生物群落可划分为以鱼衔属、鳀为优势种的站位组A（主要分布于海州湾海域）、以小黄鱼、黄鲫（Setipinna taty）等为优势种的站位组B（主要位于江苏沿岸海域）和以鲬为优势种的站位组C（主要位于江苏沿岸-近海海域）,以站位组B的群落物种多样性指数和均匀度指数最高。各站位组的鱼类浮游生物的生态类型和适温类型组成不同,这与其所处的海域生境有关。典范对应分析（CCA）表明,影响春季黄海中南部鱼类浮游生物群落空间结构的主要环境因子为水深和表层温度。同时也受洋流、底质类型等多种因素的综合影响。研究结果初步揭示了黄海中南部近岸海域鱼类浮游生物群落的空间格局,可为今后科学制定该海域水产种质资源保护区、资源量化管理等资源养护管理措施提供科学依据与技术支撑。  相似文献   

4.
The diverse pelagic fish assemblage of sub-tropical southern Queensland includes fishes with predominantly temperate distributions, such as tailor Pomatomus saltatrix, sardine Sardinops sagax, round herring Etrumeus teres, and Australian anchovy Engraulis australis. The peak spawning seasons of P. saltatrix, S. sagax and E. teres occur during late winter and early spring (June–October). Eggs and larvae of these three species are widely distributed in shelf waters and comprise >50% of the ichthyoplankton assemblage during this period. Mean monthly sea surface temperatures (SSTs) during late winter and early spring range from 21 to 23 °C, and are thus similar to those recorded in southern Australia during summer and autumn, which is the spawning season of these three species in those temperate waters. E. australis eggs occur mainly in inshore waters, and comprise >50% of fish eggs collected during summer and autumn when mean monthly SSTs in southern Queensland exceed 27 °C. E. australis also spawns mainly during summer and autumn in temperate Australia. Hence, water temperature may be less important as a determinant of the spawning season of E. australis than it is for the other three species. The suitability of southern Queensland for spawning by predominantly temperate species during late winter and early spring may contribute to the high diversity of the region's pelagic fish assemblage. Adult P. saltatrix, S. sagax and E. teres appear to migrate northwards into southern Queensland during early winter to spawn, and larvae may be transported southwards into temperate waters by the East Australian Current. This dispersal-migration pattern is similar to those observed for several species, including P. saltatrix, in the western boundary current systems off the east coasts of North America and Africa. Hence, pelagic fishes in ecosystems off the east coast of three continents migrate into sub-tropical waters to spawn, and larvae are transported back into temperate nursery areas by the prevailing current.  相似文献   

5.
This paper reports on the composition, abundance and distribution of the larval fish assemblage in the nearshore coastal waters off the St Lucia Estuary mouth, South Africa. Ichthyoplankton samples were collected over a 12 month period from five stations located along a transect up to 2·5 km offshore, and from two stations north and south of the estuary mouth, respectively. In all, 6126 fish larvae, representing 89 families and 186 species, were collected. Larvae in the families Myctophidae and Tripterygiidae comprised 21% and 16% of the total catch, respectively. The most abundant species were an unidentified triplefin, Tripterygiid 1 and the lanternfish Benthosema fibulatum, together which contributed nearly 18% of the total catch. Larvae of marine spawners independent of estuaries dominated the catch both in terms of density (90%) and in terms of number of taxa (89%). Some larvae of estuarine-associated species were present, in addition to a few specimens of estuarine resident species. Overall the dominant environmental variable affecting larval densities was temperature, particularly for Trypterygiid 1 where temperature contributed to 9% of the variance model. Densities of fish larvae peaked in November and December 1990 (late spring and early summer) and were lowest from January to June 1991 (summer, autumn an early winter). Different taxa dominated the catch each month with reef- and shelf-associated species accounting for the peak in August and September 1990, oceanic species in November 1990 and a mixture of the two groups in December. Overall larval densities were significantly higher in bottom samples with a trend of increasing densities offshore for reef and shelf taxa. The larvae of reef and shore taxa were predominantly preflexion larvae, whilst the few estuarine spawner species that were collected were mainly postflexion. Ontogenetic patterns related to depth and distance offshore were evident for the dominant species in each estuarine-association category.The present study has shown that temporal and spatial variations in the larval fish assemblage off St Lucia are related to environmental conditions and ontogenetic behavioural patterns of certain species. The origin of many of the larvae in the assemblages off the coast of St Lucia is probably from both local spawning populations in the shelf waters off KwaZulu-Natal and spawning populations farther north in shelf waters off Mozambique. Additional studies with more detailed oceanographic measurements will further our understanding of the physical processes that supply larvae to the St Lucia region.  相似文献   

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.
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   

8.
白令海特征区域的表层沉积硅藻分布及其古海洋学意义   总被引：1，自引：1，他引：0  
对白令海表层沉积物样品进行硅藻分析,共鉴定硅藻30属56种(含变种),并确定17种硅藻新记录,其中包括Kisseieviella carina等3种化石种。白令海表层沉积物中的硅藻优势种为Neodenticula seminae,Fragilariopsis cylindrus和Fragilariopsis oceanica,在白令海北部陆坡深水区附近以Neodenticula seminae为主,而在白令海北部陆架以Fragilariopsis cylindrus和Fragilariopsis oceanica为主。对硅藻结果进行聚类分析,可以划分出3个硅藻组合,硅藻组合Ⅰ代表海冰种硅藻组合,组合Ⅱ代表受阿拉斯加流影响的大洋浮游硅藻组合,组合Ⅲ代表上述两个硅藻组合之间的过渡组合。Fossula arctica是17种硅藻新记录之一,首次记录于白令海表层沉积物中,其百分含量分布趋势与Fragilariopsis cylindrus和Fragilariopsis oceanica的相近,在白令海北部陆架为11.7%~17.1%,而在陆坡深水区附近明显减少,是继Fragilariopsis cylindrus和Fragilariopsis oceanica之后白令海又一海冰指示种,并有望成为一种有效的海冰变化替代物运用于晚第四纪以来白令海海冰进退历史研究。  相似文献   

9.
The continental shelf off Namibia is influenced by the Benguela Current with variable intensity year-round, and upwelling there has an important effect on the spawning habits of fish. During three cruises to northern Namibia, carried out in intensive and weak upwelling seasons, there were notable differences in the ichthyoplankton fauna. General features of the hydrography and plankton and an index of larval diversity calculated for all ichthyoplankton stations occupied during the three cruises are presented. Low larval diversity seemed to be related to centres of upwelling and, conversely, high larval diversity to hydrological stability. Principal components analysis was used to study the ichthyoplankton association patterns and their relation to external factors. In cruises carried out in upwelling periods (winter and spring) the main factors were identified as depth and latitude. A good relationship was found between species in the north of the survey area and warmer Angolan water during the autumn cruise. Hierarchical classification methods were also used, the points coefficient of correlation being used as a similarity index and the U PGM A as algorithm. Results obtained by this method of classification coincided with those obtained from principal components analysis.  相似文献   

10.
Autumn ichthyoplankton assemblage structure in the Gulf of Alaska (GOA) region has not previously been characterized. Ichthyoplankton data from September 2000 and 2001 survey collections were analyzed to describe assemblages in the western GOA, to examine interannual variation in assemblages, and to relate observations to oceanographic conditions. Taxa with the highest frequency of occurrence (2000/2001) included Osmeridae (94/87%), Hexagrammos lagocephalus (57/45%), Sebastes spp. (35/47%) and Bathymaster spp. (27/57%). Through the use of clustering techniques and ordination, three identifiable larval assemblages common to both years were identified. Slope assemblages appeared well defined in both years, while nearshore and mid-shelf assemblages tended to be more loosely associated and variable between years. Analyses of environmental variables (temperature, salinity, water depth, distance from shore, and water transport) suggest ichthyoplankton assemblage structure is affected primarily by bathymetry and circulation. We demonstrate that early autumn ichthyoplankton assemblage structure in the GOA is fundamentally linked to variations in macro- (slope vs. shelf) and meso-scale topography (on-shelf proximity to land masses), and suggest that these intrinsic associations may be modified by spatial and temporal variations in local hydrographic conditions.  相似文献   

11.
《Journal of Sea Research》2007,57(2-3):198-208
Dover sole (Microstomus pacificus) and rex sole (Glyptocephalus zachirus) are both commercially valuable, long-lived pleuronectids that are distributed widely throughout the North Pacific. While their ecology and life cycle have been described for southern stocks, few investigations have focused on these species at higher latitudes. We synthesized historical research survey data among critical developmental stages to determine the distribution of life cycle stages for both species in the northern Gulf of Alaska (GOA). Bottom trawl survey data from 1953 to 2004 (25 519 trawls) were used to characterize adult distribution during the non-spawning and spawning seasons, ichthyoplankton data from 1972 to 2003 (10 776 tows) were used to determine the spatial and vertical distribution of eggs and larvae, and small-meshed shrimp trawl survey data from 1972 to 2004 (6536 trawls) were used to characterize areas utilized by immature stages. During the non-spawning season, adult Dover sole and rex sole were widely distributed from the inner shelf to outer slope. While both species concentrated on the continental slope to spawn, Dover sole spawning areas were more geographically specific than rex sole. Although spawned in deep water, eggs of both species were found in surface waters near spawning areas. Dover sole larvae did not appear to have an organized migration from offshore spawning grounds toward coastal nursery areas, and our data indicated facultative settling to their juvenile habitat in winter. Rex sole larvae progressively moved cross-shelf toward shore as they grew from April to September, and larvae presumably settled in coastal nursery areas in the autumn. In contrast with studies in the southern end of their range, we found no evidence in the GOA that Dover or rex sole have pelagic larval stages longer than nine months; however, more sampling for large larvae is needed in winter offshore of the continental shelf as well as sampling for newly settled larvae over the shelf to verify an abbreviated pelagic larval stage for both species at the northern end of their range.  相似文献   

12.
European sardine (Sardina pilchardus) and European anchovy (Engraulis encrasicolus) are two species of economical and ecological significance in the Bay of Biscay (north-east Atlantic). However, the trophic ecology of both species is still poorly known in the area, and more generally, few studies have considered the potential trophic overlap between sardines and anchovies worldwide. This study aims to highlight the trophic links between the mesozooplankton and adults of these two pelagic fish in the Bay of Biscay, through carbon and nitrogen stable isotope analysis (SIA). Mesozooplankton and individuals of sardines and anchovies were collected during one season (spring 2010), over spatially contrasted stations within the study area. First, the potential effect of preservation (ethanol vs. freezing) and of delipidation (by cyclohexane) on mesozooplankton δ13C and δ15N values was assessed. Results demonstrated the necessity to correct for the preservation effect and for lipid contents in mesozooplankton for further analyses of sardines' and anchovies' diet through SIA. Next, this study highlighted the interest of working on identified mesozooplanktonic organisms instead of undetermined assemblages when unravelling food sources of planktivorous fish using stable isotopes. The inter-specific variability of isotope values within a planktonic assemblage was effectively high, probably depending on the various feeding behaviours that can occur among mesozooplankton species. Intra-specific variability was also significant and related to the spatial variations of baseline signatures in the area. To investigate the foraging areas and potential diet overlap of S. pilchardus and E. encrasicolus, mixing models (SIAR) were applied. Both fish species appeared to feed mainly in the neritic waters of the Bay of Biscay in spring and to select mainly small- to medium-sized copepods (e.g. Acartia sp., Temora sp.). However, E. encrasicolus showed a greater trophic plasticity by foraging more offshore and on a wider range of prey sizes, while S. pilchardus seemed more limited to coastal areas and the mesozooplanktonic species of these waters for feeding.  相似文献   

13.
The study focuses on ichthyoplankton populations in the southern Angola Current, the Angola-Benguela Front and the coastal upwelling area of the northern and central Benguela Current. The horizontal and vertical distributions of eggs and larvae of sardine Sardinops sagax, anchovy Engraulis encrasicolus and horse mackerel Trachurus trachurus capensis were examined in relation to distribution patterns of temperature, salinity and dissolved oxygen. Samples were collected during February–March 2002 using a Bongo net and a multiple opening/closing net in five depth layers (0–30m, 30–60m, 60–100m, 100–140m and 140–220m). Eggs and larvae were restricted mainly to the shelf areas in the Angola-Benguela Font and southern Angola Current waters. Their vertical distributions in the Angola-Benguela Front and northern Benguela upwelling region showed a sharp decline in abundance at about 60m depth. This decline appeared to be correlated to the distribution of dissolved oxygen in the water column It is hypothesised that low oxygen concentrations have a strong impact on the development and survival of the early life-cycle stages of fish, and that recruitment of sardine and other pelagic species relies more on the upward extension of the oxygen minimum layer than was previously thought.  相似文献   

14.
The coastal regions of the northeast Pacific support large, economically valuable fishery resources and provide nursery areas for many fish species. Over the last few decades, there have been dramatic shifts in species abundance and composition in this area. In this paper, we examine the springtime spatial patterns in the ichthyoplankton of three oceanographically different regions, the Southeast Bering Sea, the Gulf of Alaska and the U.S. West Coast. The data examined are a subset of a larger database (comprising data from cruises conducted from 1972 to 1997) that is being used to investigate spatial, seasonal and interannual patterns in ichthyoplankton of the northeast Pacific in relation to environmental conditions. Ichthyoplankton were collected during seven cruises using 60-cm bongo nets. Spatial patterns of ichthyoplankton were examined using both classification and ordination techniques. Relative Bray-Curtis dissimilarity coefficients calculated from the log10 (n+1) of abundance data were used as input to the numerical classification of species and stations. Nonmetric multidimensional scaling was also applied to the abundance data to examine geometric patterns in the data. The numerical analyses of the species abundance data sets for each cruise revealed spatial patterns in the ichthyoplankton that suggest the occurrence of geographically distinct assemblages of fish larvae in each region. For all three sampling regions, the assemblage structure is primarily related to bathymetry, and Shelf, Slope, and Deep-Water assemblages are described. This shallow to deep-water gradient in species occurrence and abundance reflects the habitat preference and spawning location of the adult fish. Another degree of complexity is superimposed on this primary assemblage structure in each region and seems to be related to local topography and the prevailing current patterns. The patterns in ichthyoplankton assemblages of the three regions in the northeast Pacific Ocean described here form the basis for future investigations of spatial and temporal patterns in the ichthyoplankton of the subarctic Pacific.Regional Index Terms: Northeast Pacific Ocean, Southeast Bering Sea, Gulf of Alaska, U.S. West Coast.  相似文献   

15.
Two oceanographic surveys were conducted across the salinity gradient of the Río de la Plata Estuary during austral late spring and summer. Ichthyoplankton was dominated by families Sciaenidae, Clupeidae, Engraulidae, Cynoglossidae and Carangidae. The distribution of larval fish assemblages was strongly associated to the salinity structure. Oceanographic conditions were characterized by a large salt wedge (180 km long and a vertical salinity gradient up to 10 units per meter). During both sampling periods each ichthyoplankton assemblage was related to the same region of the salt wedge: the fresh water environment, the bottom salinity front, the mixohaline zone and the outer portion (surface salinity front) of the estuary. Larval assemblages were not related to the thermal structure. Reproductive activity of fishes inside the Río de la Plata Estuary is relatively common (60% of the teleosts sampled use this estuary as a nursery ground). Moreover, the high incidence of pelagic eggs spawners (75% of the species present in the ichthyoplankton) in the Río de la Plata contrasts to the vast majority of estuaries, where this reproductive strategy is poorly represented. Estuarine dynamics plays a dominant role in allowing this reproductive style in this estuary. Spring–summer wind pattern should generate a retentive environment which could minimize advective losses of eggs and larvae to the adjacent ocean.  相似文献   

16.
Temporal changes of a macrobenthic assemblage in harsh lagoon sediments   总被引：1，自引：0，他引：1  
An opportunistic macrobenthic assemblage was studied from 2001 to 2003 in a central area of the Cabras lagoon (western Sardinia, Italy), known to be affected by environmental disturbances (i.e. organic over-enrichment of sediments, and episodic events of hypoxia/anoxia and sulphide development). We identified recurrent seasonal changes in this macrobenthic assemblage, with a general impoverishment in summer and a recovery in winter/spring. The nereids Neanthes succinea and Hediste diversicolor were found to replace the spionid Polydora ciliata as the most dominant species in the summer for 3 consecutive years. Occasional, unsynchronized appearances of small-sized deposit feeders, such as Tubificidae, Capitella cf. capitata, chironomid larvae and Hydrobia spp., were observed in winter/spring. We suggest that these changes are driven by the interplay of environmental conditions (worse in summer) with numerous biotic factors. This includes different tolerance levels of taxa to low oxygen concentrations and sulphides, variability in larval supply and post-larval transport, as well as competition for space and food between and within different functional groups, and facilitation through animal bioturbation and sediment reoxidation. A conceptual model is proposed to demonstrate how environmental conditions and biotic interactions may control the benthic assemblage in such a harsh lagoon environment.  相似文献   

17.
Twice monthly sampling over two 16 month periods at a shallow site on Newfoundland's east coast showed the fish assemblage to be dominated by four taxa (Gasterosteus aculeatus, G. wheatlandi, Osmerus mordax, Gadus spp.) that accounted for 96% of the individuals collected. Of the 16 479 fish measured, 65% were adults based on the estimated size of first spawning. The fish assemblage was dominated (86%) by species with demersal eggs, several of which spawn at the same shallow sites used by juveniles as nursery sites. Coastal spawning and demersal eggs maintain offspring in coastal nursery areas where survival is thought to be increased. Number of species and number of fish were both correlated with water temperature being highest from mid-summer to early autumn and lowest in winter. Temperature, time of spawning, and movements of juveniles and adults facilitated grouping species into five assemblages based on seasonal abundance: seasonal periodic species (summer and winter), regular species, regular species collected in all seasons except winter, and occasional (rare) species. At the diel scale, two consistent species groupings were observed: species that showed no significant difference between day and night and species caught primarily at night. Number of night species exceeded day species by a factor of two. No seine-caught species in shallow water exhibited significantly higher catches during the day. Observations by SCUBA divers indicated some species were more abundant during day time at slightly deeper depths. This observation in conjunction with day and night seining in shallower water, suggests these species aggregate in deeper water during day and move to shallow waters at night.  相似文献   

18.
The seasonal variation in the larval fish community related to the hydrography in the East China Sea (ECS) off northern Taiwan was studied from February to November 2004. Hydrographic conditions in the southern ECS are strongly influenced by the different water masses due to the seasonal monsoon system. A total of 173 taxa of larval fish belonging to 68 families and 105 genera were identified during the study period. The highest abundance of larval fish was recorded in winter, a moderate abundance was seen in late spring and summer, and the lowest abundance in autumn. Significantly higher abundances were usually found in the mixing zone than in ECS and the Kuroshio Current, and the number of species of larval fish was greater during the warm period than during the cold period. The larval fish fauna in the southern ECS is a mixture of endemic and exotic species; the latter come from the coastal waters of mainland China when the northeasterly monsoon prevails, from the South China Sea during the southwesterly monsoon, and from the Kuroshio waters year-round. The succession of water masses induced by the monsoon systems and the high nutrient levels caused by frontal turbulence and topographic upwelling may determine the distributions of larval fish in terms of abundance and composition.  相似文献   

19.
Larval fish community structure was studied in the northeastern Aegean Sea (NEA) over an area influenced by the advection of Black Sea water (BSW). Sampling was carried out in early summer during a period of 4 years (2003–2006). Taxonomic composition and abundance presented high variability in space that remained relatively constant among years. Tow depth and indicators of trophic conditions in the upper water column (i.e., zooplankton displacement volume, fluorescence) explained significantly the structure of larval assemblages during all surveys. The northern continental shelf (Thracian and Strymonikos shelf), where a large amount of enriched, low salinity BSW is retained, was dominated by larvae of epipelagic species, mainly anchovy (Engraulis encrasicolus). Interannual changes in horizontal extension of the BSW seemed to match closely observed changes in the distribution of anchovy larvae. Mesopelagic fish larvae were particularly abundant beyond the continental shelf (over the North Aegean Trough) where a strong frontal structure is created between the low salinity waters of BSW origin and the high salinity waters of the Aegean Sea. Larvae of certain mesopelagic species (e.g., Ceratoscopelus maderensis) may occasionally be transported inshore when the prevailing current meanders towards the coast or feeds anticyclonic gyres over the continental shelf.  相似文献   

20.
The spatial and temporal characteristics of trophic structure of fish communities in the southern Huanghai Sea were examined based on the data sampled from bottom trawl surveys conducted during the autumn of 2000 and the spring of 2001. Hierarchical agglomerative cluster method and bootstrap randomization were used to identify significant trophic groups for each fish assemblage in the southern Huanghai Sea. A total of six major trophic groups were identified within this system, which classified predators based upon location in the water column or prey size （ i. e. , benthic to pelagic predators or fish to small invertebrate prey predators）. The similarity level used to identify significant trophic groups in each assemblage ranged from 24% to 34%. Although planktivores were the dominant trophic group in each assemblage （60% - 79% ）, there were spatial and temporal variations in the trophic structure, which reflected the differences in the abundance and availability of dominant preys. Simplified food webs were constructed to evaluate the most important trophic relationships between the dominant prey taxa and the fishes in each assemblage within this system. Although there were some differences in the key prey species among different food webs, pelagic prey items （mainly euphausiids and copepods） represent the most important energetic link between primary producers and higher trophic level predators. The trophic level for most fishes was between 3 and d, and the weighted mean trophic level for each assemblage ranged from 3.3 to 3.4. Compared with previous study in the mid-1980s, there was an obvious downward trend in the trophic level for most fish species, which resulted mainly from the fluctuation in key prey species in the Huanghai Sea. The decrease in the importance of Japanese anchovy seems to be offset by other abundant prey species such as Euphausia pacifica and copepods （ mainly Calanus sinicus ） .  相似文献   

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