生物集群相似性系数分析的适用性探讨

相似性系数的选择可能会影响生物集群间的β多样性分析。Bray-Curtis相似性系数是目前使用最广的系数之一,还有一些研究使用了欧氏距离等系数。通过非度量多维标度的结果直观对比了两个相似性系数在处理生物数据时的结果,以便了解两个系数的差异。分析结果表明,Bray-Curtis相似性系数比欧氏距离更适合处理包含很多零值的生物数据。生物数据中的零值与环境数据中的不同,不应该影响集群间相似性的计算。如果遇到完全没有生物的集群,可以选用零调整的Bray-Curtis系数,或者剔除此类集群后再计算Bray-Curtis相似性系数。一些研究忽略了相似性系数的差异,在比较和分析多元分析结果时应该慎重,以免在生态环境评价时被误导。     

Evidence that whales (Balaenoptera borealis) visit drifting fish aggregating devices: do their presence affect the processes underlying fish aggregation?

Evidence of the presence of a group of sei whales (Balaenoptera borealis) detected around drifting fish aggregating devices (FADs) was provided by omnidirectional multi‐beam sonar during a survey off the Seychelles (Indian Ocean). The short visit by the sei whales produced a significant change in the behaviour of the fish assemblage associated with the FAD. There was first a significant increase in fish density when the whales approached the FAD, then a marked decrease after the whales had moved away from the FAD. Furthermore, the fish density was still low, 3 h after the whales had left the FAD. We assume that the presence and behaviour of the sei whales led some of the fish initially associated with the FAD to move away from it. There has been a considerable increase in the use of drifting artificial FADs in the Indian Ocean in recent decades. The frequency of cetacean visits to drifting FADs in the Indian Ocean is unknown, but they may have a major impact on assemblages of pelagic fish species around FADs. The effect of marine mammals on FAD‐associated fish could be relevant to the ecological trap theory (FAD acting as a trap for their associated fish) because of their impact on the dynamics of fish aggregation processes, through commensalism and/or predator–prey interactions.     

Biodiversity and environmental characteristics of the bycatch assemblages from the tropical tuna purse seine fisheries in the eastern Atlantic Ocean

The impact of human activities such as fishing has been identified as a main factor in diversity loss in the open ocean. This paper studies the diversity patterns and environmental characteristics of the bycatch assemblages in Fish Aggregating Devices (FADs) and Free School sets (sets made on schools of tuna) from the tropical tuna purse seine fishery in the eastern Atlantic Ocean (35°W–15°E and 20°N–15°S). Data were collected from scientific observer programmes carried out between 2003 and 2011 on board Spanish and French fleets. The results showed different structure and diversity patterns of the bycatch assemblages depending on the fishing mode, with higher number of species and diversity found in FAD sets than in Free School sets. Bycatch assemblages showed preferences for specific oceanographic characteristics of the Atlantic Ocean, such as the equatorial and seasonal coastal upwelling systems, the Cape Lopez front system and the Guinea dome. The type of set and sea surface temperature play an important role to describe the diversity patterns of these species. These results confirm the importance of integrating different methods to study the marine ecosystem towards the correct implementation of the Ecosystem Approach to Fishery Management (EAFM).     

Enhancement of the benthic communities around an isolated island in the Antarctic Ocean

Insular marine biotas are often richer in faunal diversity than those from the open sea in the same geographical region. The existence of particular island effects were tested under polar conditions by comparing infaunal benthic assemblages on Peter I Island with those of similar latitudes in the open ocean at the Bellingshausen Sea and also from the coast of the Antarctic Peninsula. Sampling was carried out aboard the R/V Hespérides during the expedition named BENTART-2003 from 24 January to 3 March 2003. Benthic samples were collected at 18 stations ranging from 90 to 2 044 m depth, using an USNEL-type box corer (BC) dredge. Representatives of 32 higher taxa of invertebrates were found. Univariate and multivariate analyses revealed various patterns in the data. First, significant differences in polychaete abundance were detected between the stations located in the open sea and the remaining sites (island plus mainland sites). Bivalve abundances were also distinct between island and mainland sampling sites. Sediment columns taken from the island seafloor exhibited the highest rate of bioturbation by the infauna. These findings confirm the model that islands develop distinct assemblages characterized by the enhancement of the benthic communities even in cold waters. Several abiotic factors were measured simultaneously at the seafloor and along the water column to investigate faunal distribution patterns. Significant correlations were found between the benthic assemblages and a combination of two environmental variables: "island effect" (measured as a categorical variable) and the redox state of sediments. Richer and more complex benthic assemblages were found in Peter I Island’s sea bottom, whereas the more depauperate bottoms remained in the open sea.     

Fish assemblages across the marine to low salinity transition zone of a temperate estuary

This 3-year study provides a large-scale perspective of fish assemblage structure across an ocean–estuarine ecotone, given range of salinity encountered (0.1–32) based on sampling at 12 stations along 40 km from the Mullica River (river), Great Bay (bay), and the adjacent inner continental shelf (ocean) in southern New Jersey. Otter trawl (4.9 m, 6 mm mesh) collections were dominated by young-of-the-year of most of the 49 species encountered. Species richness and abundance appeared greatest in the ocean, decreased (with an increase in inter-station variability) in the bay, and appeared to increase again towards the uppermost river stations. The same areas contained three non-discrete, but identifiable, fish assemblages based on Detrended Correspondence Analysis. Members of the Triglidae and Stromateidae characterized the ocean and bay, whereas representatives of the Percichthyidae and Ictaluridae characterized the river. Several species, including Anchoa mitchilli and Cynoscion regalis, exhibited a ubiquitous distribution across the sampling area. Further analyses with Canonical Correspondence Analysis identified salinity and geographic distance, among the variables examined, as the most important determinants in shaping the assemblages. Other contributors included habitat heterogeneity and water depth. In summary, these observations indicate that large-scale patterns in the structure of this estuarine fish assemblage are primarily a result of individual species' responses to dominate environmental gradients, as well as ontogenetic migrations, whereas smaller-scale patterns appear to be the result of habitat associations that are most likely driven by foraging, competition, and/or predator avoidance.     

To what extent are the fish compositions at nearshore sites along a heterogeneous coast related to habitat type?

This study has tested the following main hypotheses. (1) The composition of fish assemblages in nearshore waters along the lower west coast of Australia will differ significantly among four habitat types (1–4), which could be distinguished quantitatively from each other by differences in the values for a statistically selected suite of enduring environmental variables. (2) The extents of the differences in ichthyofaunal composition among the four habitat types will statistically match those in the suite of environmental variables that distinguish those habitat types. A 60.5 m long seine net, with 9 mm mesh in the bunt, was used seasonally for 2 years to sample fish from sites representing each of the four nearshore habitat types, which differed broadly in their exposure to wave activity and the extent and location of seagrass beds. The compositions of the fish faunas in each habitat type were significantly different from each other in all but one case. Ichthyofaunal composition did not differ significantly between years in any habitat type and differed significantly among seasons in only one habitat type. The arrangement of the rank orders of similarity in matrices constructed from the abundances of the fish species at each site also did not differ between years but did differ among seasons. Moreover, the arrangement of the ranks in the similarity matrices produced from the ichthyofaunal data recorded at the various sites in each season were significantly correlated with that in the distance matrix constructed from the environmental data for those sites, with the correlation (ρ) ranging from 0.476 in winter to 0.696 in autumn. These results thus demonstrate that the extents of the differences in the fish compositions among the various habitat types parallel those in the environmental data for the corresponding habitat types. The subset of species that provided the best correlation with the environmental distance matrix, and which was thus most responsible for distinguishing among the fish compositions at the four habitat types, was also determined for each season.     

Zonation and spatial distribution of littoral fish communities from the southwestern Finnish coast (Archipelago and Bothnian Sea,Northern Baltic Sea)

The aim of our study was to test whether the distribution of littoral fish assemblages would reflect both their immediate environment with reference to local underwater vegetation, including larger scale geographic archipelagial zonation. A total of 62 locations were sampled using beach seine and underwater video along the southwestern Finnish coastline in summer 2001. At all locations, water temperature, water transparency and benthic vegetation patterns (depth ranges of plant species or taxa) were recorded. Using correspondence analysis, our results showed a clear division of the Archipelago Sea into three separate zones based on littoral fish species assemblages. Overall, fish assemblages formed three distinct site groups, being dominated by pike and cyprinids, by percids and gobies, or by gasterosteids, and showed clear inner, middle and outer archipelago zones respectively, within the study area. Our results suggest that while vegetation in the study sites was diverse, it failed to express the zonation reflected by the littoral fish assemblages, which showed a definite zonation pattern which broadly reflected previous reports using both physical and biological parameters. We interpret our results to show that littoral vegetation is better in expressing small-scale differences between study sites, while littoral fish communities are more robust in detecting changes over a larger geographical scale.     

The past,present and future use of drifting fish aggregating devices (FADs) in the Indian Ocean

The use of drifting fish aggregating devices (FADs) has become the dominant practice in tropical tuna purse seine fishing. However, just as FADs can increase fishing efficiency, their use has been associated with several negative ecosystem impacts, and moves are being made to manage the use of FADs. In the evaluation of potential management options it is important to consider how fishers will respond to the introduction of control measures, which first requires an understanding of fishery and fleet dynamics. This paper addresses this need by characterising the past and present use of FADs in the Indian Ocean tropical tuna purse seine fishery. The paper describes historical trends in fishing practices, summarises spatiotemporal patterns in the use of FADs and establishes and attributes variation in FAD fishing strategies within the fleet. It also provides an overview of current FAD management policies in the Indian Ocean and examines the observed effects of existing measures on the behaviour of the purse seine fleet. Using this comprehensive understanding, the potential impact on the purse seine fleet of a number of plausible FAD management options are discussed and inferences are drawn for the future sustainability of tropical tuna purse seine fishing in the Indian Ocean.     

Effects of management strategies on the landscape ecology of a Marine Protected Area

Marine Protected Areas (MPAs) are important tools for the conservation of coral reefs and associated habitats. We utilized a Geographic Information System (GIS) to evaluate the effect of marine park management in one of Mexico's most important MPAs by comparing benthic habitat structure between the MPA and an adjacent unmanaged region. Characters compared included measure of habitat β-diversity, total area and fragmentation of 15 different habitat classes, and size distributions of the patches of each of those classes. Habitat fragmentation distribution was similar between regions, but significantly higher β-diversity was seen in the managed area, and differences also occurred in the area and fragmentation of several substrate classes. The results suggest that management strategies which limit physical impact on benthic habitats are having a positive effect on the integrity of several important habitats in the MPA.     

Spatial patterns in meiobenthic assemblages in intermittently open/closed coastal lakes in New South Wales, Australia

Intermittently closed and open lakes and lagoons (ICOLLs) are important features of the Australian coastline. Local authorities frequently open lakes by bulldozing or dredging the mouths, in an effort to improve water-quality and to reduce the risk of flooding and these interventions provided an opportunity to examine large-scale patterns in meiobenthos in relation to isolation from the sea. Even at a coarse level of taxonomic resolution (phylum, class and order), consistent differences between assemblages of meiobenthos in different reaches of the lakes and between open and closed lakes were revealed. The abundance of meiobenthos generally decreased with increasing distance from the sea. Multivariate analyses showed that nematodes, copepods and turbellarians were characteristic of assemblages near the mouths of lakes while polychaetes and oligochaetes characterised those in more isolated areas. Furthermore, assemblages in the inner reaches of open lakes also differed from those in closed lakes. Isolated localities were less diverse and more spatially variable. Differences in meiobenthos between natural lakes and those that are artificially opened became apparent when open and closed were analysed separately. Lakes that are kept open artificially are similar to naturally open lakes despite other impacts associated with human activities. These results are considered in the context of isolation and the implications of proposed changes in the way mouths are manipulated are discussed.     

Spatial discordance in fish,coral, and sponge assemblages across a Caribbean atoll reef gradient

Certain biodiversity patterns on coral reefs are generally consistent but we still lack fundamental insight into how assemblages vary across spatially heterogeneous reef systems. We compared fish, coral, and sponge assemblages across a symmetrical physiographical gradient (windward forereef, lagoon patch reef, leeward forereef) of the Glover's Reef atoll, Belize. Species richness of fishes and corals was highest in the deep habitat (15 m) on the windward forereef. Sponges were diverse and abundant on both deep windward and leeward forereefs but not on the exposed shallow (5 m) windward forereef. Fish and benthic assemblages were relatively distinct in each reef zone, with the lagoon patch reef communities consisting of a combination of leeward and windward species. Nevertheless, there were no clear patterns in community similarity matrices of fish and benthic assemblages, suggesting that overall coral and sponge assemblages had weak or no direct association with patterns in fish assemblages. A closer examination of fish trophic groups indicated that planktivores and predators were predictably associated with depth, whereas herbivores were associated with shallow protected reefs. None was specifically associated with spatial location along the atoll gradient. These patterns of diversity distribution are important for identifying spatial conservation priorities. A Marine Protected Area (MPA) at Glover's Reef encompasses substantial windward forereef and patch reef habitats. A much lesser extent of protection is afforded the leeward forereef that supports faunal assemblages that are unique and productive, if not as diverse as the windward forereef. Isolated coral atolls can serve as ideal systems to study spatial heterogeneity and biodiversity patterns, but more experimental studies are needed to reveal the mechanistic processes underlying these patterns.     

东海中南部鱼类群聚结构的空间特征

依据1997～2000年东海中南部(25°30'～29°00'N,120°30'～127°00'E)四个季节的底拖网调查资料,运用聚类分析和非度量多维标度(NMDS)的方法分析了东海中南部鱼类群聚结构的空间特征,结果显示,东海中南部鱼类群聚大致可分为近海群聚和外海群聚.在不同季节两个群聚的种类组成保持了相对的稳定,并且具有一定的持续性.近海群聚的特征种类为带鱼、发光鲷等.外海群聚的特征种类主要为黄鳍马面鲀、短尾大眼鲷、黄鲷等.鱼类群聚与环境因子水深有较好的相关关系.     

Spatial pattern of coastal fish assemblages in different habitats in North‐western Mediterranean

Variability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type.     

Consistency of temporal and habitat-related differences among assemblages of fish in coastal lagoons

The consistency of habitat-related differences in coastal lagoon fish assemblages was assessed across different spatial and temporal scales. Multimesh gillnets were used to sample assemblages of fish on a monthly basis for 1-year in three habitats (shallow seagrass, shallow bare and deep substrata) at two locations (>1 km apart), in each of two coastal lagoons (approximately 500 km apart), in southeastern Australia. A total of 48 species was sampled with 34 species occurring in both lagoons and in all three habitats; species caught in only one lagoon or habitat occurred in low numbers. Ten species dominated assemblages and accounted for more than 83% of all individuals sampled. In both lagoons, assemblages in the deep habitat consistently differed to those in the shallow strata (regardless of habitat). Several species were caught more frequently or in larger numbers in the deep habitat. Assemblages in the two shallow habitats did not differ consistently and were dominated by the same species and sizes of fish, possibly due to habitat heterogeneity and the scale and method of sampling. Within each lagoon, very few between location differences in assemblages within each habitat were observed. Consistent differences in assemblages were detected between lagoons for the shallow bare and deep habitats, indicating there were some intrinsic differences in ichthyofauna between lagoons. Assemblages in spring differed to those in summer, which differed to those in winter for the shallow bare habitat in both lagoons, and the deep habitat in only one lagoon. Fish-habitat relationships are complex and differences in the fish fauna between habitats were often temporally inconsistent. This study highlights the need for greater testing of habitat relationships in space and time to assess the generality of observations and to identify the processes responsible for structuring assemblages.     

Taxonomic diversity of fish assemblages in the Changjiang Estuary and its adjacent waters

Taxonomic diversity of fish assemblages in the Changjiang Estuary(Yangtze River Estuary) and its adjacent waters was analyzed based on bottom trawl surveys carried out by R/V Beidou in June,August and October 2006.Four groups of fishes were identified for each survey by the twoway indicator species analysis(TWIA).Taxonomic distinctness,species richness and phylogenetic diversity were used to detect changes in taxonomic structure of fish assemblages.Most dominant fish species mainly belonged to Perciformes,Pleuronectiformes,Clupeiformes,Scorpaeniformes and Tetraodontiformes.Species richness in offshore waters of the survey area was higher than that in the other area.The average taxonomic distinctness value(AvTD,△+ ) of each fish assemblage was close to the average taxonomic distinctness of master list in the Changjiang Estuary(79.9),and had a positive correlation with species richness and Shannon diversity index(H ).A negative correlation was found between variations in taxonomic distinctness(VarTD,Λ + ) and traditional diversity indices,which were caused by fish species component that led to longer average path lengths among species.Taxonomic diversity index(△) had the similar results with species richness,H ,Simpson diversity index(D) and Pielou's evenness index(J ).VarTD also kept stable,which further certificated that fish assemblages and ecological environment were in equilibrium.Taxonomic distinctness index(△* ) was relatively stable in most of fish assemblages,and had higher values in some fish assemblages for a few absolutely dominant species.The present study showed that fish community formed new equilibrium stability in 2006 in the Changjiang Estuary when compared with those in the corresponding months of annual survey from 1985 to 1986.And AvTD in each sampling station was lower than AvTD of master list in the Changjiang Estuary,so some ecological niches were absent in each sampling stations from taxonomic or phylogenetic relationships,these would be helpful to stock natural resource and maintain ecological equilibruim of fish assemblages.     

Structure and dynamics of distinct fish assemblages in three reaches (upper,middle and lower) of an open tropical estuary in Brazil

We collected fishes and environmental variables in three zones (upper, middle and lower) of a small open tropical estuary during flood tide. The aim was to test for differences in fish assemblages along a gradient from freshwater to marine waters and to detect any seasonal variation in fishes and environmental variables across these zones. A total of 111 species (18 in the upper, 50 in the middle and 66 in the lower estuary) were recorded, forming three distinct fish assemblages, with the family Eleotridae dominating in the upper, Gerreidae in the middle, and Sciaenidae in the lower estuary. Only two species (Geophagus brasiliensis in the upper and the middle zones, and Eucinostomus argenteus in the middle and the lower zones) composed more than 1% of the total number of individuals in more than a single zone. Short‐term (tidal) changes in salinity in the middle estuary were associated with different assemblages in the three estuarine zones, even in winter, when the differences in salinity are lowest between the middle and the lower zones. Seasonal variation in salinity was irrelevant, except in a protected sidewater lagoon in the middle estuary. Low salinity seasonal change may be related to the lack of seasonal variation in the structure of fish assemblages in all estuarine zones.     

Reef fish structure assemblages in oceanic islands of the eastern tropical Pacific: Revillagigedo Archipelago and Clipperton atoll

Revillagigedo Archipelago and Clipperton atoll are oceanic islands located in the eastern tropical Pacific. The composition and trophic structure of their fish assemblages have never been characterized in detail, and the aim of this study was therefore to analyse the community structure and assess the similarity of fish assemblages between these two areas. Underwater visual fish censuses were conducted using band transects at two depth levels in three islands of the Revillagigedo Archipelago (Socorro, San Benedicto, and Roca Partida) and at Clipperton atoll. We calculated ecological indices (density, richness, Shannon diversity, Pielou evenness, and taxonomic distinctiveness) for each transect. These were compared in order to determine quantitative differences among the islands and bathymetric levels. Qualitative analyses (ANOSIM, nMDS, and SIMPER) were also performed. Finally, we analysed the trophic structure of the assemblages and the functional diversity of the four studied sites. The results showed significant differences for all indices, except diversity (H′). Roca Partida was the site with greatest abundance and richness due to the presence of pelagic species in large numbers. No significant differences were found in functional diversity, suggesting a high degree of ecological redundancy. Lower‐level carnivores with mean trophic level values of between 3.3 and 3.8 dominated both areas. The ordination analysis did not show a clear difference in fish composition among the islands, although Clipperton atoll has a particular fauna characterized by endemic species (Thalassoma robertsoni and Stegastes baldwini). In conclusion, the fish communities of the studied areas seem quite similar, but their assemblage structure differs. In particular, Clipperton is differentiated by the influence of endemic species.     

Assemblages of Southeast-South Brazilian Coastal Systems Based on the Distribution of Fishes

Multivariate principal components analysis and cluster analysis were performed on data representing presence or absence of 498 species of juvenile and adult fish species in twenty-four coastal marine systems (bays, coastal lagoons, estuaries and coastal zones) distributed from southeast to southern Brazil. Five groups of coastal systems were identified based on fish assemblage similarity: estuaries and bays of the southeast area; an estuary of the southern area; coastal lagoons; rocky coastal zones; and the continental platform. Species assemblages for each zone were identified and used as surrogate habitat indicators to compare and contrast the groups. Stepwise multiple regression of environmental and physical variables as predictors of the number of species indicated that only ‘ area ’ was included in the model as the most important variable explaining the variation of the number of species in these data sets. The total number of fish species increased as surface area increased.     

Economic impact of climate change and climate change adaptation strategies for fisheries sector in Solomon Islands: Implication for food security

Fisheries resources play a major role in the national economy and to food security in Solomon Islands. Climate change is likely to have a substantial impact on fish production that can lead to a fragile food security condition in the country. This paper assesses the potential economic impact of three important climate change adaptation strategies – natural resource management (NRM), fish aggregating devices (FAD) and aquaculture – in Solomon Islands. The study used a country-specific partial equilibrium economic model with six fish sub-sectors and analyzed potential impact of alternate climate change adaptation strategies for 2035 and 2050. The modeling and scenario analyses show that total fish demand is likely to surpass domestic fish production in 2050. Without appropriate climate adaptation strategy, per capita consumption of domestically produced fish will decline, which has serious negative food security implications for the country. The economic (welfare) analysis conducted based on modeling results show that the national level net economic gains due to climate change adaptation strategies are substantial. If cost and topographic conditions permit, low-cost inshore FADs are expected to be a good mechanism for augmenting domestic supplies of tuna and similar species in Solomon Islands.