Variation In Taxonomic Distinctness Research Articles

Thirty years of change: Assessing the dynamics of fish communities in Daya Bay, a semi-enclosed coastal ecosystem of the South China sea

Daya Bay is a semi-enclosed bay in the South China Sea which is a coastal ecosystem with significant ecological and economic value that is subjected to a variety of anthropogenic disturbances. However, long-term variation in fish community structure in this Bay remains uncertain. In this study, we aimed to explore the changing characteristics of fish species composition and community structure in Daya Bay during the past 30 years using data from 1989 to 2021 from bottom trawl surveys and historical literature data. As of now, a total of 544 species of fish have been identified in the Bay, belonging to 24 orders and 125 families. The structure of the fish community in the bay has changed over time. Firstly, there has been a clear decrease in the number of species and biomass of large fish. Secondly, the number of fish constituent orders and families has decreased. Moreover, both the average taxonomic distinctness and variation in taxonomic distinctness decreased from 1989 to 2021. Thirdly, there is low similarity among fishes at different time phases and distinct changes in the composition of dominant species. Present results indicate that the fish community structure in Daya Bay has tended to reflect a decline in diversity, shifts in composition, and shrinking of fish body size in the past 30 years. This study improves our understanding of fish species composition and its drivers over time in Daya Bay, providing important knowledge to support the protection and restoration of this ecosystem and the important ecosystem services it provides.

Continuous warming shifts the community pattern of periphytic protozoan fauna in marine environments

Protozoan fauna is playing an important role in the functioning of microbial food webs by transferring the flux of material and energy from low to high tropic levels in marine ecosystems. To assess effects of elevated temperature on the marine ecosystem, periphytic protozoan communities were used as the test microbial fauna, and were incubated in a temperature-controlled circulation system in a successive temperature gradient of 22 (control), 25, 28, 31 and 34 °C. The results showed that: (1) the test microbial fauna was shifted in both species composition and community structure; (2) the average taxonomic distinctness represented a clear decreasing trend, (3) while the variation in taxonomic distinctness significantly increased with increase of water temperature; and (4) the community pattern was significantly departed from an expectation when temperature increased by 12 °C. These results suggested that Protozoa may be used as a useful bioindicator of global warming in marine ecosystems.

Study on the taxonomic diversity of fish in the East China Sea hairtail national aquatic germplasm resources conservation zone

The species composition and taxonomic diversity of fish in the East China Sea hairtail national aquatic germplasm resources conservation zone (EHCZ) were analyzed by average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) based on the fishery resource survey from 2009 to 2022. It was found that there are 169 species of fish that are collected in the EHCZ, belonging to 26 orders, 73 families, and 131 genera. The Δ+ of EHCZ was about 65.5 and Λ+ was about 40.2. The Δ+ has exhibited a slightly down trend over the decade, which implies a slight decrease in fish diversity. The Δ+ was highest in spring, possibly due to fish migration for spawning. Most of the Δ+ of a year fall within the 95% confidence funnel for Δ+ values and all Λ+ of a year fall within the 95% confidence funnel for Λ+ values. The indices were relatively stable and close to the expected value. Moreover, we recommend optimizing the protection period, improving fishing gear and methods, reducing bycatch and decreasing the number of fishing vessels and vessel power to restore the fish diversity.

Taxonomic diversity of the macrobenthos and its relationship with environmental factors in the Huanghe River (Yellow River) estuary and adjacent seas, China

Data on the macrobenthos, bottom seawater, and sediment from 26 sampling stations in the Huanghe River estuary and adjacent seas in China, were collected in June 2020. Community structure, species diversity, taxonomic diversity of the macrobenthos, and the relationships of these variables with environmental factors were analyzed. The funnels and contours of average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) were used to indicate the disturbance status of the estuary seas. These findings revealed differences in macrobenthic community structure and biodiversity between the estuary and the adjacent seas. A total of 88 macrobenthic species were collected in the Huanghe River estuary and its adjacent seas. Abundances in the estuary, Section C, and Section D were 60 ind. m−2, 183 ind. m−2, and 320 ind. m−2, respectively, The biomass in the estuary, Section C, and Section D was 6.74 g·m−2, 15.72 g·m−2, and 9.07 g·m−2, respectively. There were significant differences in the number of species and their abundances between the estuary and adjacent seas (p < 0.01). Glycinde bonhourei, Sternaspis scutata, Moerella hilaris, Liljeborgia serrata, Iphinoe tenera, and Lineus sp. were the dominant species. The community dissimilarity of the estuary and adjacent seas reached >79.66% (p = 0.001). The results of k-means clustering analysis showed that the macrobenthic community could be divided into three types. High Margalef richness index (d) and Shannon–Wiener diversity index (H′) values were observed in the northern portion of the estuary and the seas in Laizhou Bay. The theoretical mean values of Δ+ and Λ+ were 90.8 and 267.7, respectively. High values of Δ+ were observed in Section A2-B2-C2-D2 where the communities were distantly related. Low values were observed in Laizhou Bay. The distribution of Λ+ was the complete opposite of that of Δ+. Deviations in the 95% confidence interval were observed at five stations (A2, A3, B1, B2, and D2). The northern sea of the Huanghe River estuary was disturbed. Spearman correlation analysis showed that ∆ was positively correlated with total organic carbon, heavy metals, fine silt, and clay. Heavy metal and TOC in the Huanghe River estuary and adjacent seas may be positively correlated with the reproduction of opportunistic species.

Preliminary studies of the tardigrada communities from a polymetallic nodule area of the deep South China Sea

Knowledge about marine tardigrades from the South China Sea is very scarce, with only four species from shallow waters recorded to date. The present study investigated the structure and diversity of tardigrade communities from the deep sea (1517-1725 m) at 8 stations in a polymetallic nodule area of the northern South China Sea. A total of 151 arthrotardigrades were collected belonging to 11 genera (Angursa, Batillipes, Coronarctus, Euclavarctus, Exoclavarctus, Halechiniscus, Moebjergarctus, Raiarctus, Rhomboarctus, Tanarctus and Tholoarctus), representing 17 species. Two Angursa species (Angursa sp. 4 and Angursa sp. 3) were the most abundant (25.2% and 14.6%, respectively), followed by Moebjergarctus sp. (13.9%). Specimens were mostly (90.7%) distributed in the upper layer of the sandy-mud sediment (0-1 cm). The SIMPROF test showed that the composition of tardigrade communities at all stations was not significantly different. At different stations, the number of species, Shannon-Wiener diversity index and Pielou’s evenness index ranged from 4 to 10, 1.94 to 2.87, and 0.75 to 1.00, respectively. The average taxonomic distinctness (Δ+) ranged from 72.50 to 90.00, and the variation in taxonomic distinctness (Λ+) ranged from 316.67 to 1181.25. This study provides some basic information about the biodiversity of the marine tardigrade community in the South China Sea.

Relationship between species richness, taxonomic distinctness, functional diversity, and local contribution to β diversity and effects of habitat disturbance in the riparian spider community of the Ganga River, India

BackgroundIn the riverine riparian ecosystem, particularly in India, the knowledge of the effects of habitat disturbance on taxonomic distinctness, functional diversity, and local contribution to β diversity (LCBD) of spider community is elusive. The present study examined the relationships between the index of taxonomic distinctness (Δ+), index of variation in taxonomic distinctness (λ+), functional evenness (FEve), functional divergence (FDiv), functional dispersion (FDis), and LCBD of spider community of the Ganga River and the effects of habitat disturbance on these indices. A total of 27 sampling sites were selected along the bank of the Ganga River. Based on the rating of the disturbance scores, the sites were classified into lowly, moderately, and highly disturbed sites. To understand the relationships between species richness, Δ+, λ+, FDis, FDiv, FEve, LCBD, and habitat disturbance score, Pearson’s correlation was calculated, followed by the linear regression model. The one-way multivariate analysis of variance was used to find differences in taxonomic distinctness and functional diversity in the different disturbed sites.ResultsSignificant relationships were found between λ+ and Δ+, FDis and Δ+, FDis and λ+, FDiv and species richness, FEve and species richness, FEve and λ+, FEve and habitat disturbance, LCBD and FEve, and LCBD and habitat disturbance. A significant difference was present in the indices of functional diversity between the lowly, moderately, and highly disturbed sites. Agriculture, garbage dump, human settlement, and created embankment influenced the spider community's λ+, FEve, and LCBD.ConclusionUnrestrained anthropogenic activities exacerbate habitat disturbance by affecting ecological processes. Thus, understanding linkages between ecosystem disturbance, taxonomic, functional, and β diversity can be fundamental to managing and conserving natural resources. This work highlights the importance of including taxonomic and functional diversity to comprehend the impact of habitat disturbance on riverine riparian spiders beyond just the number of species. An integrated taxonomic and functional diversity approach coupled with β diversity can be used to support environmental assessment, restoration, and conservation planning of the biological resources of the Ganges River.

Taxonomic diversity of fishes from two coral-reef waters of the South China Sea

Context Conservation of coral-reef fishes requires an understanding of their spatial and temporal responses to climate change and anthropogenic disturbance, which also requires an understanding of patterns in their taxonomic diversity. Aims To describe the species composition, taxonomic diversity and G-F diversity-measurement index of Qilianyu Island and Meiji Reef, South China Sea, coral-reef fish assemblages. Methods Coral reef-dwelling fish were sampled in 2018 and 2019 at Meiji Reef and Qilianyu Island by using various fishing gears, identified to the lowest taxonomic category, and their taxonomic relatedness was compared at levels of class, order, family, genus and species. Key results The reef-dwelling fish fauna of this region comprises 123 species in 5 orders (dominated by Perciformes, at 78%), 22 families and 46 genera. The average taxonomic distinctness (Δ+) of Qilianyu Island fish assemblages is 55.52, and variation in taxonomic distinctness (Λ+) is 138.18; for Meiji Reef, values for Δ+ and Λ+ are 53.02 and 135.33 respectively. Conclusions High species diversity and low taxonomic diversity are important features of coral-reef fish assemblages in the South China Sea. Implications The high species diversity of reef fish in the South China Sea, along with a well-distributed assemblage of families and genera, is crucial for preserving the region’s fish biodiversity. Consequently, timely prioritisation of reef fish conservation is essential.

Variation in bird taxonomic distinctness, but not body mass or niche overlap, explains the robustness of Neotropical seed dispersal networks

Abstract Frugivory and seed dispersal are fundamental ecological processes for the maintenance and conservation of tropical forest areas and ecosystem resilience. Here we investigated factors that could affect the relationship between frugivorous birds and fruit consumption, such as body mass, niche relationships, and species taxonomic groups, and the effects of such factors on the robustness of mutualistic bird-plant interaction networks. More specifically, we used Horn-Morisita niche overlap, the body mass coefficient of variation, and the variation in taxonomic distinctness index (varTD) as explanatory variables, and we applied multiple linear regression to test the that increased robustness in bird-plant frugivory networks occurs where birds have larger trophic niche overlaps and lower body mass variations and decreased robustness where they are more taxonomically diverse, in response to less functional redundancy. The analysis was based on literature data and fecal samples of birds collected after mist netting procedures. Bird body mass and niche overlap did not explain the variation in robustness in seed dispersal networks. However, different from expected, the results showed an effect of variations in taxonomic distinctness, suggesting that the larger the taxonomic distinctness of birds in a frugivore assemblage, the larger the robustness of the networks. Some hypotheses were suggested to explain this effect. Regardless of the factors that lead varTD to favor the robustness of mutualistic bird-plant networks, the results demonstrated that conserving diversity above the species level, and not just species limited to a few taxonomic groups, can be an important strategy for ecosystem conservation over time.

Effects of river-lake disconnection and eutrophication on freshwater mollusc assemblages in floodplain lakes: Loss of congeneric species leads to changes in both assemblage composition and taxonomic relatedness

River floodplain ecosystems host one of the highest freshwater molluscan biodiversity on Earth. However, multiple human disturbances, such as loss of hydrological connectivity and deterioration of water quality, are seriously threatening most floodplain lakes throughout the world. Given the high imperilment rate of freshwater molluscs but the scarcity of studies examining the anthropogenic effects on this fauna, we test the response of mollusc assemblages to river-lake disconnection and eutrophication in 30 lakes in the Yangtze River floodplain, China. The species richness of entire Mollusca, Gastropoda and Bivalvia and 6 dominant families were all much lower at disconnected lakes than that in connected lakes, and decreased with increasing water eutrophication. The assemblage structure differed significantly among four lake groups for datasets based on entire Mollusca, Gastropoda and Bivalvia, indicating the serious impacts of hydrological disconnection and eutrophication. Moreover, the connected lakes showed significantly lower values of average taxonomic distinctness (Δ+) but higher values of variation in taxonomic distinctness (Λ+) than disconnected lakes. Such variations were triggered by the extirpation of congeneric and endemic species (mainly from families Unionidae and Viviparidae), which giving a waring of the loss of mollusc endemism in this region. In general, the present study showed that river-lake disconnection and deterioration of water quality resulted in serious biodiversity declines of both gastropods and bivalves in the Yangtze River floodplain lakes. A systematic approach including restoration of river-lake connectivity and habitats and improvement of water quality should be implemented in the conservation planning in this large river floodplain.

Palaeoecological patterns of change in marine invertebrate faunas across the End-Triassic mass extinction event: Evidence from Larne, Northern Ireland

The End-Triassic mass extinction event [ETE] (201.5 Ma) marks a drastic turnover and loss of >50% of marine biodiversity. Suggested environmental factors include extreme climate change and global carbon-cycle perturbations linked to Central Atlantic Magmatic Province (CAMP) volcanism. Considerable attention has been paid to disentangling the causes and selectivity of the ETE, whilst downplaying the patterns of change in the structure and functioning of marine paleofauna. Here we provide detailed quantitative information from across the Triassic-Jurassic boundary at Waterloo Bay, Larne, Northern Ireland, to describe patterns of changes in different palaeoecological parameters across the ETE. The analysis was based on abundance data of species sampled from approximately 1 m intervals through the sequence. Dominance and richness were estimated using rarefaction techniques and β-diversity index, and distinctness diversity indices were calculated. Changes in species composition were evaluated by multivariate analysis (nMDS, ANOMSIM and SIMPER). Rank abundance models were fitted, and functional diversity were estimated based on an ecospace model, applied to each sampled unit to detect changes in structure and ecological complexity. Across the ETE three distinctive states were identified: the pre-extinction state (Westbury Formation), characterised by an assemblage with high species richness and ecological redundancy, and with low taxonomic variation and functional diversity. The extinction state (Cotham and Langport members) represents a shift of the marine ecosystem, where >70% marine species disappears decreasing the ecosystems functioning the marine ecosystem around 80%. The recovery state (Lias Group), commencing some ~150 ky after the extinction, with ecologically complex assemblages as new taxa colonised, increasing variation in taxonomic distinctness and new contributing ecological traits and functional richness through the Hettangian. The palaeoecological patterns described here are robust enough to discount possible facies effects, but more important, is consistent with other studies reported globally, and demonstrates that the ecological signals detected in this study are real.

Ecological Quality Status (EcoQs) of Chabahar sub-tropical bay based on multimetric macrobenthos-indexes approach: Response of bio-indexes to sediment structural/pollutant variables

The present study aims to test the applicability of the macrobenthos indexes (AMBI, M-AMBI, BENTIX, BOPA; Shannon (H′);average taxonomic distinctness (Δ+), variation in taxonomic distinctness (Λ+) and total taxonomic distinctness (sΔ+) to assess the EcoQs of Chabahar Bay. Sampling was performed in the pre-monsoon period of 2017 from 19 stations. Five sediment texture/pollutant variables include grain size, total organic matter (TOM), PAH, heavy metal Pollution Load Index (PLI) and depth were also measured. Distribution pattern of macrobenthos as well as inter/intra relationship of the biotic and abiotic variables was investigated through multivariate statistical approaches. The Pearson and Rosenberg model was used to determine critical limit of TOC to reduce species richness, and as a criterion to select under-stressed stations. PCA analysis of all of indexes was used to evaluate the EcoQs of the polluted, suspected polluted or healthy stations. DistLM analysis showed that the sediment grain size followed by depth and TOM were main variables that significantly determined the distribution pattern of macrobenthos. Sensitive/tolerant indexes showed 84% full agreement as “acceptable” on most stations (including low-high TOC), while H′ values assessed all stations as “unacceptable”. The funnel plot of Λ+ could identify disturbed (high TOC) muddy stations, but was not a strong indicator of TOC disturbance for non-muddy stations. Among all indexes used in this study only the Λ+ showed significant correlation with PAH, TOM and sediment grain size. We believe that the Λ+ index works well in muddy substrates if the stress type is TOM overloading or PAH pollution. However this index alone does not make good judgment on the EcoQs of the studied area, so we recommend multimetric use of different indexes. The findings of the present study suggest that the physicochemical composition of sediment plays a key role in the distribution of macrobenthos and subsequently EcoQs assessment of Chabahar Bay, therefore, any anthropogenic activity affecting sediment could cause dramatic changes in macrobenthos assemblages.

Vertical variability in taxonomic breadth of biofilm-dwelling ciliates in marine bioassessment surveys

To determine the effects of water depths on taxonomic breadth of biofilm-dwelling ciliates in marine ecosystems, (1-month) baseline survey was conducted in coastal waters of the Yellow Sea, northern China. Utilizing glass slides as artificial substrates, samples were collected at four depths of 1, 2, 3.5 and 5 m after a 14-day exposure period. Taxonomic patterns and taxonomic distinctness measures showed a significant difference among four water depths. Ellipse tests on the pairs of average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) demonstrated a vertical variability in taxonomic structure of the ciliate communities from 1 m to 5 m, with high levels at 1 and 2 m compared to those at the other two depths. These results suggest that water depth may significantly shape the taxonomic breadth of biofilm-dwelling ciliates, and that an optimal sampling strategy should be determined before monitoring surveys in marine ecosystems.

Climate Change and Species Invasion Drive Decadal Variation in Fish Fauna in the Min River, China

Freshwater fishes are threatened by increasing environmental changes and human disturbances. The Min River, the largest river in Southeastern China, contains unique fish fauna for the Oriental realm. Due to environmental changes brought by forty years of economic growth, fish numbers have dramatically declined. The average taxonomic distinctness in the 1970s was significantly higher than that in 2015, while no significant differences were found in the variation in taxonomic distinctness between the two periods. Due to the river network and habitat diversity, fish fauna composition showed significant spatial differences but lower variation than the decadal variation. Precipitation was determined to be the most influential factor in determining the spatial pattern of fish fauna, followed by temperature. Species introduced for aquaculture have invaded the endemic fish community after escape and should be reconsidered in the trade-offs between economic development and ecological protection.

Response of traditional and taxonomic distinctness diversity indices of benthic macroinvertebrates to environmental degradation gradient in a large Chinese shallow lake.

A variety of biodiversity metrics are available to assess the quality of aquatic ecosystems. However, different types of metrics perform with considerable variation and provide various information involved in ecosystem conditions. Taxonomic distinctness (TD) indices have been recommended as desirable measures for assessing environmental degradation, but their utility based on lake macroinvertebrates is still largely unknown. Here, we evaluated the response of traditional and taxonomic distinctness diversity indices (the average taxonomic distinctness, Δ+, and variation in taxonomic distinctness, Λ+) of benthic macroinvertebrates to environmental degradation gradient in Lake Taihu, the third largest freshwater lake in China. Benthic assemblages responded markedly to human disturbances, with significance among-region differences in community composition throughout four seasons. The traditional biodiversity indices (Shannon-Wiener diversity and Pielou's evenness) showed high sensitivity in discriminating anthropogenic impacts, with highest values in macrophytic region but lowest values in eutrophic region. In contrast, Δ+ and Λ+ did not perform well in distinguishing sites subjected to different disturbance levels. The Pearson correlation and multiple regression analysis both indicated that traditional biodiversity metrics (Shannon-Wiener diversity, taxon richness, and Pielou's evenness) responded more readily to water quality variables (Secchi depth, electrical conductivity, and comprehensive trophic level index) than Δ+ and Λ+. Despite the weak correlations between TD indices of benthic macroinvertebrates and water quality in the present study, we suggest that the TD indices should still be considered in bioassessment programs because they provide useful complementary information on traditional diversity indices.

Responses of the macroinvertebrate taxonomic distinctness indices of lake fauna to human disturbances in the middle and lower reaches of the Yangtze river

Abstract In recent decades, floodplain lakes have been among the most endangered ecosystems in the world due to human activities, and they are experiencing severe degradation in ecological function and declines in biodiversity. Previous studies have mostly concentrated on the effects of human disturbances on the traditional taxonomic structure of aquatic communities, but little is known about the responses of other facets of biodiversity measures (e.g., phylogenetic relatedness) to anthropogenic impacts. Here, we examined the effectiveness of species richness and taxonomic distinctness (TD) indices (the average taxonomic distinctness, Δ+, and variation in taxonomic distinctness, Λ+) in determining anthropogenic effects based on four datasets of macroinvertebrate communities in 31 shallow lakes in the Yangtze floodplain. The species composition and number of entire taxa and three subsets (mollusk-, insect- and oligochaete-only taxa) were all significantly different among the five lake groups, with the highest species richness in the river-connected lakes, followed by the oxbow, macrophytic, macrophytic-algal transition and algal lakes. For the TD indices, only the Λ+ of entire taxa showed clear differences among lake groups, with the highest values in the algal lakes and the lowest values in the river-connected lakes. However, the TD indices based on the other three datasets showed no differences and did not clearly reveal the degree of anthropogenic disturbances as we expected. However, the spatial pattern of species richness was largely influenced by lake area rather than by water quality. In contrast, the TD indices were insensitive to lake area and responded more readily to water quality than species richness. We proposed that the TD indices provided a useful complement to traditional diversity indices (e.g., species richness) and could be considered as a potential bioassessment metric for detecting the environmental degradation level of freshwater lakes.

Application of taxonomic distinctness indices of fish assemblages for assessing effects of river-lake disconnection and eutrophication in floodplain lakes

Abstract The taxonomic distinctness (TD) indices have been recommended as robust measures for detecting human disturbances, due to their appealing properties such as independence of sampling settings and statistical framework for discriminating disturbed habitats by randomization test. Here we test the application of two widely-used TD indices, namely average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+), for assessing the effects of anthropogenic impacts (loss of river-lake connectivity and deterioration of water quality) based on the presence/absence data of fish assemblages from the floodplain lakes in the Yangtze River Basin, China. The river-disconnected lakes showed significantly lower Δ+ values than connected lakes, and the Δ+ values slightly decreased with increasing water eutrophication. Whereas no significant difference was detected for Λ+ values of fish assemblages among lake groups. The Δ+ funnel plot can relatively well discriminate anthropogenically disturbed lakes, identifying about half of the disconnected lakes as disturbed, and the percentage of lakes identified as disturbed increased with increasing deterioration of water quality. Furthermore, we found species richness was highly related to lake area but not to nutrient levels. On the contrary, the Δ+ was independent of lake area and responded significantly to water quality gradients, implying that the index is comparable among lakes with different surface area. In summary, the Δ+ index of fish assemblages showed advantages over species richness for assessing anthropogenic effects in the Yangtze floodplain lakes. Therefore, the Δ+ of fish assemblages could be considered as a potential metric for lake bioassessment and management in the studied region in particular and for other river floodplains in general.

Assessment of benthic diatoms taxonomic diversity at coastal biotopes with different anthropogenic impact (Crimea, the Black Sea)

An analysis of the taxonomic diversity of benthic diatoms was carried out for near-shore biotopes of Crimea with different content of trace metals and organic pollutants (PCBs, PAHs, DDTs). Taxonomic distinctness indices such as average taxonomic distinctness, AvTD (Δ+) and variation in taxonomic distinctness, VarTD (Λ+) were used for evaluation of the hierarchical structure of diatom taxocenes of two intact sites (Dvuyakornaya Bay and Cape Fiolent) and two heavily polluted water areas (Sevastopol Bay and Balaklava Bay). The highest similarity of species was revealed between healthy biotopes, in spite of their differences in hydrological and hydrochemical conditions. AvTD values for Dvuyakornaya Bay and Cape Fiolent (Δ+ = 79.0 and 76.7, respectively) were lower in comparison with expected average levels (Δ+ = 82.2) evaluated for the flora of benthic Bacillariophyta (1094 species) registered for the Northern part of the Black Sea (NPBS). As established, the taxonomic trees of the diatom taxocenes at pristine water areas are characterized by a moderate degree of vertical evenness and high variability of distances between neighboring clusters of species; they are mainly formed by polyspecific branches close on the genus level. The AvTD values for diatom taxocenes of the heavily polluted Sevastopol Bay (Δ+ = 83.6) and Balaklava Bay (Δ+ = 84.1) were significantly higher than the corresponding indices for undisturbed biotopes and exceeded the expected average level for the entire list of Bacillariophyta for NPBS. The upward trend of AvTD along the increasing technogenic impact can be caused by the disappearance of taxonomically close species with low tolerance from the same genus and prevalence of oligo- and monospecies branches in architectonics of the hierarchical tree. The present study shows that the application of TaxD indices can be considered an additional appropriate indicator tool for quantifying changes in the hierarchical structure of diatom taxocenes under persistent anthropogenic stress.

An approach to determining homogeneity in taxonomic breadth of periphytic ciliate communities in colonization surveys for bioassessment

Abstract Taxonomic distinctness is powerful tool to test the departure of a community from an expected pattern of taxonomic structure in response to environmental change. To determine the homogeneity in taxonomic breadth of periphytic ciliates, a 1-month baseline colonization survey was conducted in Jiaozhou Bay, near Qingdao, northern China, using glass slides as artificial substrates. A total of 240 slides were collected at depths of 1, 2, 3.5 and 5 m after colonization periods of 3, 7, 10, 14, 21 and 28 days. The taxonomic composition and structure of the periphytic ciliate communities differed among the four water depths. The temporal variations in all four taxonomic diversity/distinctness measures had different patterns of variability at each depth. Ellipse test on the pairs of average taxonomic distinctness (Δ+) and variation in taxonomic distinctness (Λ+) demonstrated a spatial variability in homogeneity in taxonomic structure of the ciliate communities from 1 m to 5 m, with high levels at 1 and 2 m compared to those at the other two depths. These results suggest that taxonomic distinctness is a useful indicator to identify the homogeneity in taxonomic breadth of periphytic ciliate communities during the colonization process in marine ecosystems.

Diversity of reef associated fishes in hook and line fishery at Mandapam, Gulf of Mannar, south-east coast of India

Reef associated fishes landed by hooks and lines at Mandapam landing centre in Ramanathapuram District, Tamil Nadu for a period of four years from October 2008 to May 2012 were studied based on fortnightly samplings. The hook and line fishing is seasonal in Gulf of Mannar and lasts for six months annually from October - November to April - May, as this area remains rough during the rest of the year. The average annual landing of fish during the study period was 171 t with a peak of 295 t in 2008-09 and showed a decline since then. A total of 32 species of reef associated fishes belonging to 14 families were landed. Among them, Sphyraena barracuda contributed the maximum with a share of 42% followed by Caranx heberi (15%). Family-wise landings indicated the dominance of Sphyraenidae (46%). The diversity index (H’) was the highest during 2008-09 and the evenness of distribution of individuals among different species did not show significant variation in different years. Funnel plots of average taxonomic distinctness (∆+ ) and variation in taxonomic distinctness (λ+ ) indicated that the values in most of the years are within the normal limits.

Redundant or complementary? Evaluation of different metrics as surrogates of macrophyte biodiversity patterns in Mediterranean ponds

Ecological metrics constitute one of the mainstream tools in modern ecology to assess varying information about processes and patterns of regional biodiversity. However, the performance of different metrics on Mediterranean pond macrophyte assemblages is still largely unknown, thus hampering the selection of suitable indices for biomonitoring purposes. In an attempt to fill this gap of knowledge, we compared the response of six ecological metrics (i.e. species richness, Shannon diversity, beta diversity, functional diversity, and average and variation in taxonomic distinctness) to determine which ones are redundant and constructed Generalized Additive Models (GAM) to assess their utility for macrophyte biodiversity evaluation. The study was performed at assemblage level in a vast area of approximately 94,000 km2 in northwestern Spain. Several environmental filters related to habitat conditions revealed themselves to have considerable impact on biodiversity measures. Physical factors exhibited the highest drop in deviance values for species richness, Shannon diversity and functional diversity, whereas beta diversity and taxonomic distinctness metrics were more sensitive to water chemistry changes. Our results, based on correlations among indices and partial response curves to primary environmental drivers, showed complementarity in at least three different biodiversity measures (i.e. functional diversity, beta diversity and taxonomic distinctness). Ultimately, the use of a combination of these three metrics should provide a complete picture of macrophyte biodiversity patterns and their response to major environmental forces, including the variation in the identities of species among communities and the functional and phylogenetic status of species. These findings underline the importance of considering different biodiversity measures for conservation planning at regional scale and should assist in the selection of suitable indices for future pond management initiatives in Mediterranean landscapes.