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1.
The present study investigates ecological patterns and relationships to environmental variables among a time-series of larval fish species abundance from late spring surveys (1981–2003) in the northwest Gulf of Alaska (GOA). Links between interannual variation in species abundance and the physical environment were explored using generalized additive modeling (GAM). Trends in larval abundance and connections with physical variables displayed patterns that indicate unique and complex responses among species to environmental forcing during the larval period. In particular, the observed patterns suggest that ontogenetic-specific responses, representing sub-intervals of early life, are important. In addition, a notable degree of synchrony in larval abundance trends, and similarity in links with physical variables, were observed among species with common early life history patterns. The deepwater spawners, northern lampfish, arrowtooth flounder, and Pacific halibut, were most abundant in the study area during the 1990s, in association with enhanced wind-driven onshore and alongshore transport. Years of high abundance for Pacific cod, walleye pollock, and northern rock sole were associated with cooler winters and enhanced alongshore winds during spring. High larval abundance for spring–summer spawning rockfish species and southern rock sole seemed to be favored by warmer spring temperatures later in the time-series. This apparent exposure–response coupling seems to be connected to both local-scale and basin-scale environmental signals, to varying degrees depending on specific early life history characteristics. Understanding such ecological connections contributes to the evaluation of vulnerability and resilience among GOA species’ early life history patterns to fluctuating climate and oceanographic conditions. This investigation also provides crucial information for the identification of “environmental indicators” that may have a broad-spectrum effect on multiple species early life history stages, as well as those that may be more species-specific in exerting control on early life history survival. Of particular interest was the emergence of the EP–NP (East Pacific–North Pacific) teleconnection index as the top-ranked variable in the GAM models exploring the connections between late spring larval abundance and the physical environment. The EP–NP index represents an important and often primary mode of spring–summer atmospheric variability in the northeast Pacific, with a strong expression in the GOA, and its connection with species in this study implies that it may be a climate mode of significant ecological importance.  相似文献   

2.
There have been no previous studies of the composition of nearshore larval fish assemblages along the coast of Portugal. We aimed to describe the composition and horizontal distribution patterns of larval fish assemblages and their temporal dynamics near a rocky reef at depths shallower than 13 m (inshore) and at two miles (3.70 km) from shore (offshore), as well as along transects perpendicular to the shoreline, from the reef to 10 miles offshore (18.52 km). Samples were taken using 5 min sub-surface trawls at the rocky shore of the Arrábida Marine Park (W Portugal). A total of 1021 larvae were collected, belonging to 61 taxa inshore and to 29 taxa offshore. Along transects, 626 larvae of 52 taxa were collected. Most larvae belonged to coastal species associated with rocky reefs. Total larval abundance and diversity were higher from May to July, which is consistent with the spawning activity of adults. Diversity and total larval abundance decreased significantly with increasing distance from shore, both in the inshore/offshore comparison and in the transects, where this decrease was evident at a very small spatial scale (within the first mile from the reef). Species assemblages differed in the pattern of distribution, with most species clearly associated to the extreme nearshore. The distribution patterns obtained were independent of the spawning mode of species. Results are discussed in the light of the possible physical mechanisms that can potentially act at the Arrábida Marine Park to facilitate larvae retention and the role of larval behaviour.  相似文献   

3.
We evaluated scale-dependent patterns of distribution of sandflat macroinfauna of a coastal lagoon, using different analytical approaches. The sampled area was divided into three sectors (outer, inner-north, inner-south) containing small promontories. At each side of the promontories we defined stations in a line transect across the sandflat. Thus, we evaluated sediment characteristics and macroinfaunal responses to sectors, orientations and intertidal levels; animal–sediment relationships were also studied. At a large scale, there was a clear pattern of sediment composition and macroinfaunal abundance. While the outer sector had medium to coarse sands, reflecting the high hydrodynamic conditions existing near the lagoon entrance, the inner sectors showed sandy and muddy sediments. Most species were in low abundances at the outer sector. At small scale, macroinfaunal abundance and species richness decreased sharply towards the upper sandflat level. Also at small scale, sediment composition limited the maximal densities reached by all species, with exception of the deposit-feeding polychaetes. Thus, the macroinfaunal community at muddy sediments was dominated by burrowing deposit-feeders, while all species peaked in sandy sediments. Our results suggest that physical factors shaping macroinfaunal communities operate at different scales and are better detected using several analytical approaches. Large scale patterns, associated with along-shore variations in disturbance by currents, were detected as changes in the mean abundance of macroinfauna. Small scale patterns, related to sediment characteristics, were observed as changes in maximal densities of macroinfauna. Small scale patterns, associated with the level of inundation of the sandflats, were detected through changes in the abundance and presence of macroinfauna. The evaluation of the role of the physical conditions on communities must involve the use of several sampling and analytical approaches.  相似文献   

4.
Studies on the early life history of fish in New Zealand started during the 1950s off the Northland coast. Since then taxonomy, seasonality in abundance, and vertical and horizontal distribution patterns have been described as well as aspects at the level of individuals, such as age, growth, and condition. I discuss the findings and issues that have developed from these studies and illustrate three undescribed presettlement reef fish. Results indicate that different taxonomic groups typically have different vertical and horizontal distribution patterns as well as different temporal patterns of abundance. This implies that general models of how “larval fish” behave are unrealistic. As a result, the importance of physical and biological processes that may influence the distribution and survival of ichthyoplankton will vary among categories of fish (such as pelagic and reef fish) and taxonomic groups within these. Based on knowledge of the distribution pattern of some species, there is considerable scope for focusing future research on specific groups offish in terms of ontogenetic changes in morphology, sensory abilities, growth, diet, condition, interrelationships with other plankters, and, in the case of reef fish, onshore transport.  相似文献   

5.
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   

6.
Whereas diel fish migration between mangrove and seagrass habitats has been recognized for decades, quantitative studies have focused mainly on diurnal patterns of fish distribution and abundance. In general, previous studies have shown that fish abundances decline with increasing distance from mangroves; however, evidence for such a pattern at night, when many fishes are actively feeding, is scarce. The present study is the first to report nocturnal fish abundances along a continuous distance gradient from mangroves across adjacent seagrass habitat (0–120 m). Here, we used nocturnal seine sampling to test the null hypothesis (based on diurnal studies and limited nocturnal work) that fish abundance would decrease with increasing distance from shoreline. We focused on species and life‐stage‐specific abundance patterns of Lutjanus griseus, Sphyraena barracuda, Archosargus rhomboidalis, and Haemulon sciurus. Results indicated that assemblage composition and structure differed significantly by season, likely influenced by temperature. However, within each season, the fish habitat use pattern at both the assemblage and species‐specific level generally failed to support our working null hypothesis. Species‐specific analyses revealed that, for most species and life‐stages examined, nocturnal abundance either did not change with distance or increased with distance from the mangrove‐seagrass ecotone. Our results suggest that analyses where taxa are grouped to report overall patterns may have the potential to overlook significant species‐ and stage‐specific variation. For fishes known to make nocturnal migrations, we recommend nocturnal sampling to determine habitat utilization patterns, especially when inferring nursery value of multiple habitats or when estimating fish production.  相似文献   

7.
In coastal marine ecosystems, spatial patterns of larval fish assemblages (LFAs) tend to exhibit geographic stability because of relatively stable spawning site selection and predictable oceanographic phenomena such as eddies. To evaluate the relationship between spatial heterogeneity and temporal variability of LFAs, we conducted a high spatiotemporal resolution ichthyoplankton survey from April to July in 2013 in the shallow waters (<20 m) of Haizhou Bay, China. Our analysis indicated three distinct assemblages, which were stable geographically but exhibited a gradual and directional change of species composition and abundance over our study period. Sea surface temperature was the most important environmental co‐variate for determining temporal variability of LFAs, likely owing to temperature effects of species composition and spawning period selection of adult fish, along with known temperature‐dependent survival rates of larval fish. Study of LFA spatiotemporal dynamics is essential for improved understanding of adult fish spawning behavior, and has potential to inform design and implementation of conservation and management measures (e.g. marine protected areas) in coastal systems.  相似文献   

8.
In the northern Wadden Sea, the extent of intertidal seagrass beds, their plant biomass and shoot density highly depends on local current regimes. This study deals with the role of intertidal Zostera noltii beds as nursery for mobile epibenthic macrofauna and the impact of seagrass bed characteristics on their abundance and distribution patterns. According to their exposure to the main tidal gullies, sampling sites were separated into exposed, semi-exposed and sheltered. Dominant species of crustaceans and demersal fish were studied in respect of their abundances within seagrass beds and adjacent unvegetated areas. Quantitative sampling was performed at day and night high tide using a portable drop trap. In general, species composition varied little between seagrass beds and bare sand. However, the presence of vegetation had a quantitative effect increasing individual numbers of common epifaunal species. Abundances of 0-group shore crabs (Carcinus maenas), common gobies (Pomatoschistus microps) and brown shrimps (Crangon crangon) were highest within sheltered seagrass beds. With decreasing plant density habitat preference of epibenthos changed on species level. By regulating the habitat complexity the currents regime is profoundly influencing the nursery function of intertidal seagrass beds in the Wadden Sea.  相似文献   

9.
Environmental variables have been measured and sampling for ichthyoplankton has been conducted monthly, since April 2001, at three stations, located at the inner (1), middle (2) and outer (3) shelf of the central Cantabrian Sea. This paper presents the results of the study of the ichthyoplankton collected from July 2001 to June 2004. Fish larvae from 99 species, belonging to 37 families, were identified. Families with higher number of species were Gadidae, Sparidae and Labridae. The larval fish assemblage was dominated by pelagic fish species, with Sardina pilchardus, as the most abundant. There was a pronounced spring peak in larval abundance, dominated by S. pilchardus. A smaller peak, dominated by S. pilchardus and Micromesistius poutassou, was recorded in late winter at Stns 2 and 3. This pattern was evident for the three-year study. Results also indicate that this study was limited to the coastal larval fish assemblage inhabiting the central Cantabrian Sea shelf. This assemblage was temporally structured into other three assemblages: winter, late winter–spring and summer–autumn. Temperature was apparently a key factor in larval fish assemblage succession. In a scenario of global warming, this study constitutes a basis to evaluating the ongoing changes in the pelagic coastal ecosystem of the central Cantabrian Sea.  相似文献   

10.
One of the present concerns of fish biologists involves defining and identifying nursery habitats in the context of conservation and resource management strategies. Fish nursery studies usually report upon nursery occupation during the latter juvenile stages, despite the fact that recruitment to nurseries can start early in life, during the larval phase. Here we investigated the use of a temperate estuarine nursery area, the Lima estuary (NW Portugal), by initial development stages of flatfish species before and after metamorphosis, integrating the larval and juvenile phases. The Lima estuarine flatfish community comprised twelve taxa, seven of which were present as pelagic larvae, six as juveniles and three as adults. There was a general trend of increasing spring–summer abundance of both larvae and juveniles, followed by a sharp winter decrease, mainly of larval flatfishes. The Lima estuary was used by Solea senegalensis, Platichthys flesus and Solea solea as a nursery area, with direct settlement for the two first species. In contrast, indirect settlement was suggested for S. solea, with metamorphosis occurring outside the estuarine area. Estuarine recruitment of S. senegalensis varied between years, with young larvae occurring in the estuary throughout a prolonged period that lasted 6–9 months, corroborating the protracted spawning season. P. flesus, the second most abundant species, exhibited a typical spring estuarine recruitment, without inter-annual variations. Developed larvae arrived in the estuary during spring, whereas the 0-group juveniles emerged in the following summer period. The present study contributes new insight to our understanding of the economically important S. senegalensis, and highlights the importance of integrating the planktonic larval phase into traditional flatfish nursery studies.  相似文献   

11.
春季东海有害藻华高发区仔稚鱼时空分布   总被引：1，自引：0，他引：1  
根据2011年春季(3月29日—5月27日)海洋综合调查,对东海有害藻华高发水域(28°15′36″~30°30′16″N、121°52′36″~123°15′6″E)的仔稚鱼种类组成、时空分布以及主要优势种与环境因子的相关性进行了探讨。调查共采集到仔稚鱼27种,前几位优势种分别为日本鳀Engraulis japonicus、鰕虎科sp.(Gobiidae sp.)、六丝钝尾鰕虎Amblychaeturichthys hexanema、小黄鱼Larimichthys polyactis,该4种占据了总丰度的91.23%。优势种丰度和发育阶段组成的时空变化显示,日本鳀在调查期间有两次产卵小高峰,其仔鱼孵化后向岸漂流;小黄鱼和六丝钝尾鰕虎在此期间只有一次产卵高峰,其仔鱼在舟山群岛邻近水域进行保育。可以看出,调查水域及邻近水域是部分鱼类产卵,仔稚鱼保育、向岸漂流的场所或途径,是鱼类早期生活史中重要生境,一旦暴发有害藻华,补充群体将受到不良影响。多元分析结果显示,所选环境因子对几位优势种仔稚鱼的分布影响不大,推测产卵场位置和保育方式可能是更重要的原因。  相似文献   

12.
This study focuses on the composition, abundance and distribution of ichthyoplankton in the inner shelf area off Bahía Blanca Estuary on the SW Atlantic Ocean during late spring. Eggs and larvae of Brevoortia aurea, Engraulis anchoita, Parona signata, Sciaenidae spp. – such as Cynoscion guatucupa and Micropogonias furnieri –, and Odontesthes argentinensis were found. Species richness was low probably as a result of season and shallow depths. Ichthyoplankton abundance reached values close to 10 000 per 10 m−3 (eggs) and 4000 per 10 m−3 (larvae) and displayed a spatial distribution pattern with maximum abundance values restricted to a band parallel to the coast. Differences between egg and larval patterns, probably derived from a different displacement and hydrodynamic behavior, were observed. Egg and larvae distribution patterns were found related with spawning areas and to directly depend on salinity and mesozooplankton. The larvae distribution pattern, in particular, was found to inversely depend on particulate organic carbon. In addition, the geographic location of egg and larvae maxima strongly coincided with a saline front reported for this area in springtime, thus suggesting a direct relationship with it.  相似文献   

13.
This study focuses on body size–abundance distributions of nano- and micro-phytoplankton guilds in coastal marine areas of the Southern Adriatic–Ionian region. The aim of the study was to evaluate the occurrence of common patterns of body size–abundance distributions in relation to physical, chemical and biological environmental forcing factors and to taxonomic composition of phytoplankton guilds. This paper is based on data collected during four oceanographic cruises carried out seasonally along the Southern Apulian coast (Adriatic and Ionian Seas, SE Italy) as a part of the INTERREG II Italy–Greece Program. The study was performed at 21 stations located on 7 transects perpendicular to the coastline, with 3 stations per transect at a distance of 3, 9 and 15 NM from the coastline. At each station, profiles of the major physical features of the water were determined and water samples were collected for phytoplankton and nutrient analysis. Overall, 320 nano- and micro-phytoplankton taxa were identified, 76% of which at species level, with phytoplankton cells ranging in size from 0.008 to 4697.54 ng. Body size–abundance distributions showed some common features: they were relatively invariant (average similarity 65%) with respect to taxonomic composition (average similarity 32%), right skewed (90%), leptokurtic (77%) and log normal (76%). Moreover, abiotic, biotic and spatial ecosystem components accounted for up to 75% of body size–abundance distribution variation. The results of this study suggest that body size–abundance distributions are an intrinsic property of marine phytoplankton communities, emphasising functional dependence on ecological constraints related to trophic factors and intra-guild coexistence relationships.  相似文献   

14.
Vertical and horizontal distribution patterns of larval and juvenile fishes were described from five offshore petroleum platforms in the north-central Gulf of Mexico. Light traps and passively-fished plankton nets were used nocturnally between 1995–2000 to collect fishes in surface and deep (15–23 m depth) waters within the platform structure, and light traps were also used in surface waters directly down-current of the platforms. Light traps fished at the surface, as opposed to at-depth, collected greater CPUEs and greater diversity of larval and juvenile fishes. Of the dominant taxa collected by light traps, clupeids, engraulids, synodontids, and presettlement blenniids were most common in surface waters within the platform, while postflexion scombrids and settlement-size blenniids and pomacentrids were most common in surface waters down-current of the platforms. Deep plankton nets collected greater densities of non-clupeiform larval fishes, although surface plankton nets collected greater numbers of taxa. The vertical distribution patterns described for dominant larval fish collected by plankton nets were generally consistent with those from other studies, i.e. clupeid, carangid, sciaenid and scombrid larvae more abundant in surface waters at platforms, and synodontid, bregmacerotid, gobiid and bothid larvae more abundant in deeper waters. Oil and gas platforms likely impact larval and juvenile fish populations, particularly considering their proliferation in the Gulf (i.e., over 4000 platforms). The results from this study provide valuable baseline information for future research investigating how platforms impact the life history stages of fish populations.  相似文献   

15.
Abstract. Fish assemblages of three shallow marine caves from the Salento Peninsula (Apulia, SE Italy) were investigated in July 2000. Data were collected in situ by using visual census. A total of nineteen fish species were recorded inside the caves. The species richness generally displayed a similar pattern in all three caves, decreasing from the entrance towards the innermost sections, whereas the patterns of total fish abundance differed among caves. Apogon imberbis (mainly represented by juveniles) was the most important species in terms of number of individuals (accounting for more than 85% of the censused fish) and showed a fairly even distribution inside the investigated caves. Without the numerical contribution of A. imberbis , fish abundance decreased from the entrance to the inner sections and this pattern was common to all three caves. Juvenile fishes of economic interest ( e. g., Diplodus vulgaris and Epinephelus marginatus ) were also recorded inside. The present study suggests that: (1) environmental constraints could affect distribution patterns in fish species richness and in the abundance of several fish along the axis of "blind caves" (with a single entrance), as already observed for sessile benthos and plankton assemblages; (2) shallow marine caves of the Salento Peninsula could exert the role of refuge and/or nursery for some littoral fish species during the adult and/or juvenile stages of their life histories.  相似文献   

16.
Fluctuations in various attributes of a surf-zone fish community were examined by beach seining at a series of sites spanning a wave-exposure gradient in the Saldanha Bay–Langebaan Lagoon system, on the South African west coast. During April 1994, 24 species, totalling 25 676 individuals and 434 kg, were captured. Three teleosts,Atherina breviceps, Liza richardsoniiandPsammogobius knysnaensis, dominated numerically, while three elasmobranchs,Rhinobatos annulatus, Mustelus mustelusandMyliobatis aquila, dominated the biomass. Elasmobranchs displayed no discernible distribution patterns. Two important trends were, however, evident in the teleost catches: overall teleost abundance (mean density) increased markedly as wave exposure decreased; and highest species richness and diversity, and lowest dominance were both recorded at intermediate levels of exposure. A positive relationship between fish size and exposure was also evident for at least two of the species. These trends were attributed primarily to the availability and abundance of suitable food resources, and to physical disturbance introduced by breaking waves.  相似文献   

17.
As part of an investigation into the role of East African mangrove creeks as fish spawning and nursery areas, nocturnal ichthyoplankton sampling was carried out at five stations in Tudor Creek, Mombasa, Kenya, from September to November 1985. Throughout the creek, the salinity was close to that of seawater at about 35‰, but from the mouth to the upper creek there were gradients of increasing temperature and turbidity, and decreasing depth and dissolved oxygen concentration. Pelagic eggs and larvae of fish considered to be creek residents and creek non-residents were distinguished. Gradients of decreasing egg and larval abundance (particularly of non-residents), and of decreasing diversity of recognized types, were apparent from the mouth towards the upper creek. Such a distribution suggests that the mangrove system is not an important spawning or development area for the earliest life-history stages of non-resident species. The existence of the gradients also has implications both for sampling at fixed stations in tidal waters, and for investigating the existence of circatidal and semilunar spawning cycles in fish.  相似文献   

18.
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   

19.
On intertidal sandflats spatial patterns of benthic communities are influenced by biogenic habitat structures such as mussel beds or seagrass meadows. These structures represent ecological islands hosting a different and often more diverse and abundant community than surrounding sandflats. However, few studies have been carried out on tube aggregations of the polychaete Lanice conchilega, although its tube tops are conspicuous habitat features on European intertidal coasts with densities reaching several thousand per m2.The aim of this study was to determine differences between benthic communities associated with tube aggregations and tube-free areas, and to investigate the longevity of community patterns around L. conchilega tubes. From 1995 to 2000, the L. conchilega population of an intertidal sandflat off the Eastern Friesian coast was sampled annually. Multivariate analysis showed significant differences between the L. conchilega and reference communities. Species diversity and abundance were higher among tube aggregations. This pattern developed rapidly after L. conchilega colonisation but was also readily destroyed, mainly due to dynamic changes of the L. conchilega population.Five species of benthic macrofauna were exclusively found among L. conchilega tubes, and four species were more abundant in tube aggregations than in reference areas. Only one species, the polychaete Aphelochaeta marioni, was found in lower numbers in dense L. conchilega aggregations.Hence, it is concluded that L. conchilega is a habitat engineer, which alters the composition of the benthic community and contributes to its patchy distribution pattern. However, this pattern is dynamic and ephemeral. Effects of tube aggregations depend on the population dynamic of L. conchilega itself and the species composition in the surrounding sands.  相似文献   

20.
Partitioning of temperature resources amongst an estuarine fish assemblage   总被引：1，自引：0，他引：1  
Temperature (i.e. habitat at any given temperature) is an ecological resource for which organisms compete to maximise growth and other fitness measures, but the temperature (thermal habitat)-resource concept has not been widely applied to the study of estuarine fish. Temperature–abundance relationships for 16 fish and four invertebrate species from the Thames estuary were analysed to test hypotheses regarding temperature resource partitioning. Significant temperature–abundance models were apparent, explaining >65% of the variability in 13 fish species and 50% of variability in three invertebrate species. Fish demonstrated differential responses to temperature across the range. Invertebrates generally preferred warmer conditions than fish. Calculated thermal niche breadths indicated species preferenda spread across the recorded temperature range and some separation along the thermal niche axis within the same functional guild or taxonomic group. Calculated overlap coefficients and resource separation ratios provided some evidence for resource separation and demonstrated that species closely aligned on other niche axes (e.g. physical habitat use, feeding type) were most likely to be separated in terms of their use of thermal habitat resources, suggesting where other niche axes variables are not separating species, division of the temperature resources may be preventing competition between fish species. Few fish species demonstrated significant overlap with potential invertebrate prey, suggesting facultative use of the estuary to exploit optimal thermal habitat rather than food supply. The temporal migration pattern of fish in estuaries is therefore interpreted as a response to resource separation along the temperature axis which limits potential competition between functionally or taxonomically similar species. Thermal resource partitioning in estuaries has temporal rather than spatial dimensions and provides an example of the niche compression/expansion hypothesis.  相似文献   

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