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, A^＋） 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, Ht, 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.

Taxonomic, functional, and phylogenetic diversity patterns reveal different processes shaping river fish assemblages in the Eastern Huai River Basin, China

Understanding contributions of different environmental drivers to the structure and function of river biota is critical for biodiversity and environmental conservation.Yet,there is no consensus on which drivers have the greatest impact on fish diversity,especially in watersheds disturbed by multiple human activities.Fish taxonomic,phylogenetic,and functional diversity at both alpha and beta dimensions and their environmental drivers were studied in a total of 84 river sites from three watersheds,Huai River watershed(HRW),Sui River watershed(SRW),and Yishusi River watershed(YRW)in the Eastern Huai River Basin of China.Results showed that rivers in the three watersheds had no significant difference in both taxonomic and functional alpha diversity.Rivers in the HRW had significantly higher phylogenetic alpha diversity.For taxonomic and phylogenetic beta diversity,the overall beta diversity and turnover component were significant higher in the HRW.For functional beta diversity,the overall beta diversity was significantly lower in the HRW.Multiple linear regression(MLR)and redundancy analysis(RDA)showed that local(e.g.,nutrients,dissolved oxygen,river width,transparency),regional(e.g.,wetland),climate(e.g.,temperature),and spatial variables structured alpha and beta fish diversity.Variation partitioning analysis indicated that the pure contributions of local and spatial variables were more important than that of climate and regional variables,which suggested that spatial effects and local environmental filtering were the main factors driving the beta diversity of fish assemblages in these rivers.The current study highlights the importance of considering multidimensional diversity and multiple environmental factors for conserving river fishes.

Temporal and spatial variation of fish community and their nursery in a tropical seagrass meadow

Fish species composition and spatio-temporal variability of the community were studied in a tropical seagrass meadow located in a lagoon in the eastern part of North Sulawesi. The diversity of fish community in the seagrass meadows was relatively high, with the Shannon-Wiener index ranging from 1.57 to 3.69. The family Apogonidae was the most dominant in abundance(8.27 ind./(100 m2)) and biomass(28.49 g/(100 m2)). At the species level,Apogon lateralis and Sphaeramia orbicularis were the most dominant species in abundance and biomass,respectively. For spatial distribution on species, the end, middle and mouth of the lagoon clustered together as a whole, which may be due to the substrate types found in those zones. The fish species, fish abundance and fish biomass were greater in the dry and wet seasons than in the transition season, which is explained by the strong monsoon, which provides a more suitable environment and food for the fish. The maximum length of 93.10% of the captured species was less than their length at maturity, indicating that seagrass meadows are nursery habitats for many fishes. Therefore, protection of the seagrass meadows is essential for fisheries and sustainable resource utilization.

Spatial and temporal characteristics of trophic structure of the southern Huanghai Sea fish communities

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 ） .

Influences of diel and tidal cycles on fish assemblage in eelgrass(Zostera marina) bed of southern Korea during autumn

Short-term tidal and diel variations of autumn fish assemblage in a Zostera marina bed were investigated using 3 h interval samplings for 24 h in both spring and neap tide using a small beam trawl.A total of 1 346 fishes belonging to 19 species were collected at spring tide,whereas 1 115 fishes belonging to 17 species were at neap tide.The common fish species were Nuchequula nuchalis,Acanthogobius flavimanus,Takifugu niphobles,Acentrogobius pflaumii,and Pholis nebulosa with the former three species dominating at spring tide,while the latter two species being abundant at neap tide.Diel variation in abundance was significant with higher abundance at night than day,but there were no significant differences between spring and neap tides,and between ebb and flood tides（three-way ANOVAs）.Diel variation in the abundance of fishes may be influenced by tidal range and cycle,and day-night differences of food availability and behaviors of fishes indirectly.Non-metric multidimensional scaling（n MDS） ordination and analysis of similarity（ANOSIM） results revealed significant differences in species compositions both between day and night,and between spring and neap tide.Eelgrass beds are highly productive marine ecosystem,and thus,our results will contribute to conservation of seagrass ecosystem in the study area.

The First Vertebrate Assemblage Dominated by Fishes and Turtles of the Jehol Biota in Jilin Province, NE China

Objective The Early Cretaceous sediments are well-exposed in southern Jilin Province,and yield abundant invertebrate and plant fossils,including the typical EosestheriaEphemeropsis trisetalis-Lycoptera（E-E-L）assemblage of the Jehol Biota（Shao Tiequan et al.,2017）.However,vertebrate fossils,especially tetrapods,are extremely rare and there is no formal documents on these fossils.Recently,a new fossil site dominated by fishes and turtles has been discovered in the middle part of the

Long-Term Persistence of Propeller and Anchor Damage to Seagrass Canopy and Demersal Biodiversity in Puerto Rico

Seagrass ecosystems support high biodiversity and productivity and constitute critical links to adjacent ecosystems. However, there is a growing concern that increasing recreational navigation may affect its ecological processes and functions, which may affect its recreational and tourism values, compromising local economies and livelihoods. The long-term impacts (1996-2011) of recreational navigation on seagrass benthic community structure were assessed by addressing the question of whether long-term effects of recreational navigation had a significant impact on seagrass community structure and on its benthic faunal assemblages. Findings evidenced: 1) a consistent spatio-temporal gradient in the ecological conditions of seagrasses across the scoured areas, with increased percent seagrass cover, density and canopy height, and seagrass benthic biodiversity with increasing distance from disturbed areas;2) a decline in percent seagrass cover, and an increased macroalgal and cyanobacterial percent cover through time around the disturbed areas;3) a significant shift in seagrass assemblage biodiversity as a response to boating that followed the intermediate disturbance hypothesis;4) an adverse effect on the spatial distribution and survival of multiple benthic invertebrate taxa;and 5) a significant decline in cnidarians, echinoids, ophiuroids, holothurians, and gastropods, and an increase in polychaetes, platyhelminths, and hermit crabs, particularly in areas exposed to boating. Spatio-temporal variation in seagrass community structure explained the observed variation in benthic faunal assemblages. The long-term consequences on ecosystem functions and management needs are discussed to foster the conservation of seagrasses.

Spatiotemporal variability of fish assemblage in the Shatt Al-Arab River,Iraq

Objective:To study spatial and temporal variability of fish assemblage in the Shatt Al-Arab River.Methods:This study was conducted from December 2011 to November 2012.Water temperature,salinity,dissolved oxygen and transparency were measured from three sites in the river.Several fishing methods were adopted to collect fish including gill nets,cast net,electro-fishing and hook and lines.Associations between the distribution of fish species and the environmental variables were quantified by using canonical correspondence analysis.Results:The results showed that the fish assemblage consisted of 58 species representing 46 genera and 27 families belong to Osteichthyes except one(Carcharhinus leucas)relate to Chondrichthyes.Number of species increased in summer and autumn months and sharply decreased in winter.Tenualosa ilisha was the most abundant species comprising 27.4%of the catch,followed by Carassius auratus(23.7%)and Liza klunzingeri(10.6%).The dominance(D_(3))value for the main three abundant species was 61.7%.Nine species were caught for the first times from the river include eight marine.The overall values of diversity index ranged from 0.67 in March to 2.57 in October,richness index from 2.64 in January to 3.71 in September and evenness index from 0.22 in March to 0.73 in August.Conclusions:Spatially,the fish assemblages of Shatt Al-Arab River can be divided into three ecological fish guilds,namely,common species,seasonal species and occasional species.