Temporal patterns in three-dimensional structure and activity of schools of the Atlantic silverside Menidia menidia

Temporal patterns in the structure and activity of schools of the Atlantic silverside Menidia menidia were investigated under laboratory conditions using a new computerized video technique for three-dimensional analysis. Fish were collected by seining at Middle Bridge, Pettaquamscutt River, South Kingstown, Rhode Island, USA. Approximately once a week from May to December, 1979, the behavior of a school was videotape-recorded in the laboratory at 30 min intervals from sunrise to sunset under a temperature and photoperiod regime simulating ambient field conditions. Four measurements of structure and activity were computed: (1) swimming speed (SPEED); (2) distance to nearest neighbor (NN); (3) mean direction of travel (DOT); (4) depth in the tank (DEPTH). Results demonstrated a strong seasonal rhythm in the behavior of schools, but were inconclusive in showing periodicities associated with daily, tidal or lunar cycles. NN and DEPTH were significantly different between spring, summer, fall and winter while SPEED changed significantly across 3 seasons (summer and winter were not significantly different). DOT was bimodally distributed, with peaks in spring and fall. Changes in these variables corresponded to shifts in the behavior of silversides from active, synchronized schools in spring and fall to inactive mills in summer and inactive non-schooling groups in winter. Changes in schooling behavior were only partly related to changes in temperature and photoperiod. Patterns of silverside schooling behavior correlated with their reproductive and migratory cycles and may represent an anti-predator strategy.     

Interaction between schools of fish and mysids

Summary A long-term daily census of 20 small patch reefs along the backreef of Tague Bay barrier reef, U.S. Virgin Islands, established that recently recruited postlarval French grunts, Haemulon flavolineatum, form mixed schools with at least two species of mysids (genus Mysidium). The formation of these taxonomically unrelated animals into socially interacting groups probably occurs because of the striking resemblance of postlarval grunts to mysids. Over a period of 5 d and as the postlarval grunts grow, these mixed associations break down, only to reform every 14–15 d as new postlarval grunts periodically recruit from the plankton. The fleeting but persistent formation of these mixedspecies schools is believed to initially provide protection to the grunts and, as the grunts grow, limited protection to the mysids. In additions, the grunts benefit trophically from the associations because they prey on the mysids.     

The three-dimensional structure of airborne bird flocks

Summary The three-dimensional structure of flocks of dunlin, Calidris alpina, and starlings, Sturnus vulgaris, was studied while birds were in transit between feeding, loafing and roosting sites. A technique was developed that uses standard photogrammetric methods to determine the three-coordinate position of birds in flocks from stereoscopic pairs of simultaneously exposed photographs. A comparison of nearest neighbour distances indicates that dunlin have a tighter, more compact flock structure than do starlings (Fig. 2; Table 2). Analysis of interbird angles in both the vertical and horizontal planes indicates that each dunlin's nearest neighbour is most likely to be behind and below it. This spatial structure results in areas in which few nearest neighbours occur (e.g., immediately in front and below) (Fig. 3). Flight speeds during transit flights are also presented (Table 4). The spatial structure and behaviour of dunlin and starling flocks appear to be very similar to the structure and behaviour of schools of fish.     

Molecular structure and composition of fish otoliths

Recent and fossil otoliths from 25 different fishes have been studied for their amino acid content and for their C¹³/C¹² and O¹⁸/O¹⁶ distribution in the carbonate fraction. The selection includes specimens from a wide phylogenetic range as well as from various freshwater and marine habitats. All otoliths are composed of aragonite, and their total organic matter ranges from 0.2 to 10%. The organic matter is a protein (MW>150,000), which is characterized by a high abundance of acidic amino acids. In comparison to molluscs that exhibit a wide variety of different mineralized tissues which are species specific, the proteinaceous matter of all otoliths is chemically rather uniform. The high abundance of oxygen-rich amino acids accounts for the ease of mineralization of the organic template. Namely, oxygen supplied by carboxyl grops is used for the coordination of Ca⁺⁺ ions, resulting in the formation of metal ion coordination polyhedra. Carbonate groups linked via hydrogen bridges to the template will exchange their oxygen with that of the metal polyhedra to stabilize the structure; Ca⁺⁺O₉ polyhedra are the consequence. Subsequent nucleation and crystal growth will lead to aragonite. Oxygen and carbon isotope data indicate that the aragonite is formed close to isotopic equilibrium with the sea. This is surprising, because seawater has no direct access to the inner ear where the otolith orginates. Isotope data may serve a threefold purpose: (1) to determine the mean water temperature where the fish lived, (2) to distinguish between fresh water and marine fish in ancient deposits, and (3) to reveal information on migrtory tendencies of fish.Contribution No. 2214 from the Woods Hole Oceanographic Institution.     

Habitat biodiversity as a determinant of fish community structure on coral reefs

Increased habitat diversity is often predicted to promote the diversity of animal communities because a greater variety of habitats increases the opportunities for species to specialize on different resources and coexist. Although positive correlations between the diversities of habitat and associated animals are often observed, the underlying mechanisms are only now starting to emerge, and none have been tested specifically in the marine environment. Scleractinian corals constitute the primary habitat-forming organisms on coral reefs and, as such, play an important role in structuring associated reef fish communities. Using the same field experimental design in two geographic localities differing in regional fish species composition, we tested the effects of coral species richness and composition on the diversity, abundance, and structure of the local fish community. Richness of coral species overall had a positive effect on fish species richness but had no effect on total fish abundance or evenness. At both localities, certain individual coral species supported similar levels of fish diversity and abundance as the high coral richness treatments, suggesting that particular coral species are disproportionately important in promoting high local fish diversity. Furthermore, in both localities, different microhabitats (coral species) supported very different fish communities, indicating that most reef fish species distinguish habitat at the level of coral species. Fish communities colonizing treatments of higher coral species richness represented a combination of those inhabiting the constituent coral species. These findings suggest that mechanisms underlying habitat-animal interaction in the terrestrial environment also apply to marine systems and highlight the importance of coral diversity to local fish diversity. The loss of particular key coral species is likely to have a disproportionate impact on the biodiversity of associated fish communities.     

Influence of Benguela upwelling on the structure of demersal fish populations off Namibia

The effect of bottom-water dissolved oxygen on the structure of demersal fish communities off south Namibia was analized. Collections were made during two cruises of the zone in winter 1987 and summer 1988, i.e., before and after the intensive upwelling season. Multivariate analysis revealed four distinct associations, separated by latitude (ca 27°S) and depth (ca 300 m isobath), indicating that dissolved oxygen is an important factor affecting the distribution of demersal fish communities in the zone. Faunal diversity decreased in areas of low oxygen levels. The seasonal variation in upwelling reflected the extent of fish association, their composition, and the seasonal geographical displacement of their boundaries.     

Vertical structure of very nearshore larval fish assemblages in a temperate rocky coast

Small-scale vertical patterns of larval distribution were studied at a very nearshore larval fish assemblage, during the spring–summer period of several years, at two depth strata (surface and bottom) using sub-surface and bottom trawls. A total of 4,589 larvae (2,016 from surface samples and 2,573 from bottom samples) belonging to 62 taxa included in 22 families were collected. Most larvae belonged to coastal species. Although inter-annual variations in larval density and diversity could be found, total larval abundance was always higher near the bottom whereas diversity was higher at the surface. A marked distinction between the structure of surface and bottom assemblages was found. Sixteen taxa explained 95% of the similarity among surface samples. Larvae which contributed most to this similarity included species like clupeiformes, sparids and serranids, and also blenniids, tripterygiids and some labrids. In the bottom samples, fewer species were present, with only six taxa, almost exclusively from species which lay demersal eggs, contributing to 95% of the similarity between samples. Larvae present at the surface were significantly smaller than at the bottom. For some of the most abundant species found at the bottom, only small larvae occurred at the surface while the whole range of sizes was present at the bottom, indicating that larvae may be completing the entire pelagic phase near the adults’ habitat. These results indicate that larval retention near the reefs probably occurs for these species, although for others dispersal seems to be the prevailing mechanism.     

Seasonal changes in habitat structure underpin shifts in macroalgae-associated tropical fish communities

Habitat shifts play an important role in structuring faunal assemblages; however, research has focused on the influence of random disturbance events and information on how regular seasonal changes to habitat affect marine fauna remains largely unexplored, especially in the tropics. We recorded seasonal changes in the structure of tropical macroalgae fields within the Ningaloo lagoon (Western Australia) and related this to the density, biomass and species richness of fishes that represent key processes: juveniles, predators of juveniles and herbivores. The extent and direction of seasonal changes in macroalgae were inconsistent among sites, creating a highly dynamic habitat matrix across time and space. Species richness and density of fishes were largely maintained where density of holdfasts from canopy-forming macroalgae and/or cover was high across seasons, but shifted markedly in areas of macroalgae habitat loss: suggesting stable habitat structure is critical for the persistence of macroalgae-associated fishes. Our results demonstrate that macroalgae fields that maintain high structural complexity across different seasons are more likely to preserve key ecological processes and therefore warrant greater conservation attention within a spatial management framework.     

Dominant features in three-dimensional turbulence structure: comparison of non-uniform accelerating and decelerating flows

The results are presented from an experimental study to investigate three-dimensional turbulence structure profiles, including turbulence intensity and Reynolds stress, of different non-uniform open channel flows over smooth bed in subcritical flow regime. In the analysis, the uniform flow profiles have been used to compare with those of the non-uniform flows to investigate their time-averaged spatial flow turbulence structure characteristics. The measured non-uniform velocity profiles are used to verify the von Karman constant κ and to estimate sets of log-law integration constant B_r and wake parameter П, where their findings are also compared with values from previous studies. From κ, B_r and П findings, it has been found that the log-wake law can sufficiently represent the non-uniform flow in its non-modified form, and all κ, B_r and П follow universal rules for different bed roughness conditions. The non-uniform flow experiments also show that both the turbulence intensity and Reynolds stress are governed well by exponential pressure gradient parameter β equations. Their exponential constants are described by quadratic functions in the investigated β range. Through this experimental study, it has been observed that the decelerating flow shows higher empirical constants, in both the turbulence intensity and Reynolds stress compared to the accelerating flow. The decelerating flow also has stronger dominance to determine the flow non-uniformity, because it presents higher Reynolds stress profile than uniform flow, whereas the accelerating flow does not.     

Stability and structure of a fish community on a coral patch reef in Hawaii

Two complete collections of the fishes residing on an isolated coral patch reef ( 1500 m²) at Oahu, Hawaii, were made 11 years apart. Of the 112 species of fishes in both collections combined, only 40% were in common, but these made up more than 85% of the wet biomass in each collection. The two assemblages of fishes were similar in trophic structure and standing crop. Many coral reef fish communities are dominated by carnivorous forms. In the present study, planktivorous fishes were the most important trophic group in the community; this was related to abundant zooplankton resources. Following the second collection in 1977, recolonization by fishes was followed for 1 year. Recolonization proceeded rapidly and was primarily by juvenile fishes well beyond larval metamorphosis. Within 6 months of the second collection, the trophic structure had been re-established. The MacArthur-Wilson model of insular colonization described the recolonization process and predicted an equilibrium situation in less than 2 years. The recolonization data suggested that chance factors may explain the colonization process on a small scale, but a relatively deterministic pattern emerged when considering the entire reef. Thus, at the community level the fishes are a persistent and predictable entity.     

Tropical coastal habitats as surrogates of fish community structure, grazing, and fisheries value

Habitat maps are frequently invoked as surrogates of biodiversity to aid the design of networks of marine reserves. Maps are used to maximize habitat heterogeneity in reserves because this is likely to maximize the number of species protected. However, the technique's efficacy is limited by intra-habitat variability in the species present and their abundances. Although communities are expected to vary among patches of the same habitat, this variability is poorly documented and rarely incorporated into reserve planning. To examine intra-habitat variability in coral-reef fishes, we generated a data set from eight tropical coastal habitats and six islands in the Bahamian archipelago using underwater visual censuses. Firstly, we provide further support for habitat heterogeneity as a surrogate of biodiversity as each predefined habitat type supported a distinct assemblage of fishes. Intra-habitat variability in fish community structure at scales of hundreds of kilometers (among islands) was significant in at least 75% of the habitats studied, depending on whether presence/absence, density, or biomass data were used. Intra-habitat variability was positively correlated with the mean number of species in that habitat when density and biomass data were used. Such relationships provide a proxy for the assessment of intra-habitat variability when detailed quantitative data are scarce. Intra-habitat variability was examined in more detail for one habitat (forereefs visually dominated by Montastraea corals). Variability in community structure among islands was driven by small, demersal families (e.g., territorial pomacentrid and labrid fishes). Finally, we examined the ecological and economic significance of intra-habitat variability in fish assemblages on Montastraea reefs by identifying how this variability affects the composition and abundances of fishes in different functional groups, the key ecosystem process of parrotfish grazing, and the ecosystem service of value of commercially important finfish. There were significant differences in a range of functional groups and grazing, but not fisheries value. Variability at the scale of tens of kilometers (among reefs around an island) was less than that among islands. Caribbean marine reserves should be replicated at scales of hundreds of kilometers, particularly for species-rich habitats, to capture important intra-habitat variability in community structure, function, and an ecosystem process.     

A three-dimensional experimental investigation of the structure of the spanwise vortex generated by a shallow vortex dipole

The three-dimensional dynamics of shallow vortex dipoles is investigated by means of an innovative three-dimensional, three-component (3D-3C) scanning PIV technique. In particular, the three-dimensional structure of a frontal spanwise vortex is characterized. The technique allows the computation of the three-dimensional pressure field and the planar (x, y) distribution of the wall shear stress, which are not available using standard 2D PIV measurements. The influence of such a complex vortex structure on mass transport is discussed in the context of the available pressure and wall shear stress fields.     

The behavior of heterotypic resting schools of juvenile grunts (Pomadasyidae)

Resting schools of juvenile grunts (less than 12 cm length), composed primarily of Haemulon flavolineatum and H. plumieri, were studied from 1972 to 1976 on a series of patch reefs surrounded by seagrass beds on the northeast coast of St. Croix, U.S. Virgin Islands. Juvenile grunts form large inactive multispecies schools in reef areas by day. Repeated censuses over several years reveal that certain parts of the reef, particularly those with large formations of the corals Porites porites and Acropora palmata, are traditional schooling areas. When the fishes reach a size of about 15 cm, the H. plumieri form homotypic schools which roam the patch reefs but are no longer associated with particular formations of coral. In contrast, larger H. flavolineatum are uncommon on the patch reefs and they may move offshore to deeper water. The schools of juvenile grunts migrate some distance away (often 100 to 300 m) into seagrass-covered areas to feed on invertebrates at dusk each day. The routes which are followed into the seagrass beds are precise and persist over years. At dawn the grunts return to the reef on the same routes. Mass marking and release experiments show that juvenile grunts will move over long distances (approximately 3 km) to reach a home reef.     

Wave exposure,swimming performance,and the structure of tropical and temperate reef fish assemblages

We examined the relationship between swimming performance, wave exposure, and the distribution patterns of labrids on temperate rocky reefs, in comparison with previous functional analyses of a tropical assemblage. Visual censuses of the distribution and abundance of labrids across two major gradients of wave exposure (depth and aspect to prevailing winds) were made at two offshore islands near Port Stephens, New South Wales, Australia. Distinct shifts in species composition and abundance were evident between high and low wave exposure habitats on temperate rocky reefs, particularly between deep and shallow habitats on exposed reef fronts. The swimming performances of temperate labrids were assessed through examination of pectoral fin shape (aspect ratio) and in situ swimming speeds. A diversity of pectoral fin morphologies was exhibited within this temperate assemblage, ranging from rounded to tapered fins (aspect ratios of 0.52 and 1.43, respectively). Fin shape was strongly correlated (Pearsons correlation 0.884, P<0.001) with swimming speed (ranging from 1.05 and 3.06 body lengths s^–1), in a relationship comparable to that observed in tropical labrids. Inter-specific differences in swimming ability provided some explanation for differences in the distribution and abundance of temperate labrids in relation to wave exposure. However, our findings suggest that although coral reef labrids appear to predominantly use high aspect-ratio fins to successfully occupy wave-exposed habitats, temperate labrids appear to be using an enhanced swimming ability through increased body size.Communicated by G.F. Humphrey, Sydney     

Understanding origins of present-day genetic structure in marine fish: biologically or historically driven patterns?

Determining the origin of genetic structure is of wide interest because of its use in stock discrimination in marine organisms. Schematically, genetic differentiation can result from historical patterns maintained over geological time or from present-day isolation attributable to biological characteristics of the species. We used a comparative approach to population genetic analysis based on allozyme polymorphism to determine the impact of reproductive strategy (i.e. biological origin) and habitat (i.e. historical origin) on the genetic structure of individuals sampled from five isolated islands in French Polynesia. Eight species of coral reef fishes from two families (Chaetodontidae and Pomacentridae) were selected to test the impact of sea-level change (historical origin) and reproductive strategy (biological origin) on genetic structure. Seven of the eight study species showed significant divergence in allelic frequencies computed over all sites. For these seven species, multilocus F_stvalues ranged from 0.0114 to 0.0287. None of the eight species showed a significant relationship between genetic divergence and geographical distance between sites. Significant divergence (difference in allozyme frequencies) between some pairs of sites occurred but was unrelated to distances between them. These results suggest that the genetic structure of coral reef fish in French Polynesia is likely to be driven according to an island model in which migrations between populations are rare and random in space and time. Overall, none of the species showed congruent genetic structures between sites sampled. Genetic structure of the eight species did not appear significantly related either to reproductive strategy or habitat preference. Genetic diversity (heterozygosity) was significantly correlated with these two factors, with species laying benthic eggs and/or inhabiting lagoons showing significantly higher multilocus heterozygosity than species laying pelagic eggs and/or living on the outer reef slope. Overall, the absence of differences according to habitat and/or reproductive strategy did not provide any conclusive pattern regarding the origin of the genetic structure, but the limited divergence in allelic frequencies suggests recent differentiations.     

Spatio-temporal structure of pelagic larval and juvenile fish assemblages in coastal areas of New Caledonia,southwest Pacific

This study aims at describing the diversity and composition of larval and juvenile fish assemblages in coastal areas of New Caledonia, southwest Pacific, and identifying the environmental factors that influence the seasonal and spatial patterns of these assemblages. A total of 97 taxa belonging to 7 orders and 26 familis were captured in three bays near Nouméa by light trapping every month between January 2002 and June 2003. The assemblages were dominated by Clupeiform larvae and juveniles (96.4% of total abundance) and followed by Perciform larvae (3%). The number of taxa per sample varied from less than five in July–August to more than ten in October–November and abundances followed the same seasonal pattern. Analyses of similarity showed significant differences in the assemblages caught in the three bays and analyses of contribution to the dissimilarity revealed that these differences were due to the most abundant families. The constant part of the relationship between environmental variables and the composition of assemblages was assessed by the partial triadic analysis STATICO, a statistical approach that takes into account the strong seasonality of the data. Rainfall, wind direction and thermal stratification of the water column were found to play a major role in the structure of the assemblages, although tidal amplitude and wind speed became important when Clupeidae and Engraulididae were excluded from the analyses. The richness, relative abundances and seasonal variations of the assemblages caught in three bays under study are close to what has been observed elsewhere in the tropics. This study shows the efficiency of the STATICO analysis for identifying the environmental factors that have a permanent effect on assemblages and sorting them out from those which act temporally or on specific locations. The high abundances and diversity of coral-reef fish larvae observed in coastal zones of New Caledonia suggest that further studies are needed to fully explore the role of the coastal zones of New Caledonia as nurseries.     

高职院校职业资格证书制度的研究与探索

为深化高等教育改革，适应社会发展和市场变化对人才培养的客观要求与需要，国家有关部门率先在上海等地高校大学生中进行职业资格鉴定的首批试点，并针对2003届高职毕业生就业实际情况，着重实施毕业生职业资格培训工程，取得了部分成果与有益经验．但在实践中存在诸多问题和矛盾，需要进一步加以完善和规范．     

The imperiled fish fauna in the Nicaragua Canal zone

Large‐scale infrastructure projects commonly have large effects on the environment. The planned construction of the Nicaragua Canal will irreversibly alter the aquatic environment of Nicaragua in many ways. Two distinct drainage basins (San Juan and Punta Gorda) will be connected and numerous ecosystems will be altered. Considering the project's far‐reaching environmental effects, too few studies on biodiversity have been performed to date. This limits provision of robust environmental impact assessments. We explored the geographic distribution of taxonomic and genetic diversity of freshwater fish species (Poecilia spp., Amatitlania siquia, Hypsophrys nematopus, Brycon guatemalensis, and Roeboides bouchellei) across the Nicaragua Canal zone. We collected population samples in affected areas (San Juan, Punta Gorda, and Escondido drainage basins), investigated species composition of 2 drainage basins and performed genetic analyses (genetic diversity, analysis of molecular variance) based on mitochondrial cytb. Freshwater fish faunas differed substantially between drainage basins (Jaccard similarity = 0.33). Most populations from distinct drainage basins were genetically differentiated. Removing the geographic barrier between these basins will promote biotic homogenization and the loss of unique genetic diversity. We found species in areas where they were not known to exist, including an undescribed, highly distinct clade of live bearing fish (Poecilia). Our results indicate that the Nicaragua Canal likely will have strong impacts on Nicaragua's freshwater biodiversity. However, knowledge about the extent of these impacts is lacking, which highlights the need for more thorough investigations before the environment is altered irreversibly.