Diversity of hard-bottom fauna relative to environmental gradients in Kongsfjorden, Svalbard

A baseline study of hard-bottom zoobenthos in relation to environmental gradients in Kongsfjorden, a glacial fjord in Svalbard, is presented, based on collections from 1996 to 1998. The total species richness in 62 samples from 0 to 30 m depth along five transects was 403 species. Because 32 taxa could not be identified to species level and because 11 species are probably new to science, the total number of identified species was 360. Of these, 47 species are new for Svalbard waters. Bryozoa was the most diverse group. Biogeographic composition revealed features of both Arctic and sub-Arctic properties of the fauna. Species richness, frequency of species occurrence, mean abundance and biomass generally decreased towards the tidal glaciers in inner Kongsfjorden. Among eight environmental factors, depth was most important for explaining variance in the composition of the zoobenthos. The diversity was consistently low at shallow depths, whereas the non-linear patterns of species composition of deeper samples indicated a transitional zone between surface and deeper water masses at 15–20 m depth. Groups of “colonial” and “non-colonial” species differed in diversity, biogeographic composition and distribution by location and depth as well as in relation to other environmental factors. “Non-colonial” species made a greater contribution than “colonial” species to total species richness, total occurrence and biomass in samples, and were more influenced by the depth gradient. Biogeographic composition was sensitive to variation of zoobenthic characteristics over the studied depth range. A list of recorded species and a description of sampling sites are presented

Study of the doubly charmed tetraquark T+cc

Quantum chromodynamics, the theory of the strong force, describes interactions of coloured quarks and gluons and the formation of hadronic matter. Conventional hadronic matter consists of baryons and mesons made of three quarks and quark-antiquark pairs, respectively. Particles with an alternative quark content are known as exotic states. Here a study is reported of an exotic narrow state in the D0D0π+ mass spectrum just below the D*+D0 mass threshold produced in proton-proton collisions collected with the LHCb detector at the Large Hadron Collider. The state is consistent with the ground isoscalar T+cc tetraquark with a quark content of ccu⎯⎯⎯d⎯⎯⎯ and spin-parity quantum numbers JP = 1+. Study of the DD mass spectra disfavours interpretation of the resonance as the isovector state. The decay structure via intermediate off-shell D*+ mesons is consistent with the observed D0π+ mass distribution. To analyse the mass of the resonance and its coupling to the D*D system, a dedicated model is developed under the assumption of an isoscalar axial-vector T+cc state decaying to the D*D channel. Using this model, resonance parameters including the pole position, scattering length, effective range and compositeness are determined to reveal important information about the nature of the T+cc state. In addition, an unexpected dependence of the production rate on track multiplicity is observed

A further biodiversity index applicable to species lists: variation in taxonomic distinctness

A further biodiversity index is proposed, based on taxonomic (or phylogenetic) relatedness of species, namely the Œvariation in taxonomic distinctness¹ (VarTD, Λ+) between every pair of species recorded in a study. It complements the previously defined Œaverage taxonomic distinctness¹ (AvTD, Δ+), which is the mean path length through the taxonomic tree connecting every pair of species in the list. VarTD is simply the variance of these pairwise path lengths and reflects the unevenness of the taxonomic tree. For example, a species list in which there are several different orders represented only by a single species, but also some genera which are very species-rich, would give a high Λ+ by comparison with a list (of equivalent Δ+) in which all species tended to be from different families but the same order. VarTD is shown to have the same desirable sampling properties as AvTD, primarily a lack of dependence of its mean value on the sample size (except for unrealistically small samples). Such unbiasedness is of crucial importance in making valid biodiversity comparisons between studies at different locations or times, with differing or uncontrolled degrees of sampling effort. This feature is emphatically not shared by indices related to species richness and also not by properties of the phylogeny adapted from proposals in other, conservation contexts, such as Œaverage phylogenetic diversity¹ (AvPD, Φ+). As with AvTD, the VarTD statistic for any local study can be tested for Œdeparture from expectation¹, based on a master taxonomy for that region, by constructing a simulation distribution from random subsets of the master list. The idea can be extended to summarising the joint distribution of AvTD and VarTD, so that values from real data sets are compared with a fitted simulation Œenvelope¹ in a 2 d (Δ+, Λ+) plot. The methodology is applied to 14 species lists of free-living marine nematodes, and related to a master list for UK waters. The combination of AvTD and VarTD picks out, in different ways, some degraded locations (low Δ+, low to normal Λ+) and the pristine island fauna of the Scillies (normal + , high Λ+). The 2 indices are also demonstrated to be measuring effectively independent features of the taxonomic tree, at least for this faunal group (although it is shown theoretically that this will not always be the case). The combination of Δ+ and Λ+ is therefore seen to provide a statistically robust summary of taxonomic (or phylogenetic) relatedness patterns within an assemblage, which has the potential to be applied to a wide range of historical data in the form of simple species lists

Multivariate measures of community stress and their application to marine pollution studies in the East Asian region

Three recently developed measures of stress on marine communities, which utilise species-dependent multivariate methods, are described. The first is a "meta-analysis" of benthic macrofaunal community data from NE Atlantic shelf stations with known community responses to pollution or disturbance at the phyletic level. These can be used as a training data set against which new data can be evaluated. The method has the advantages that it overcomes taxonomic difficulties (requiring phylum-level identification only) and offers the possibility of evaluating the severity of disturbance on a more globally comparative scale. Two other methods measure the increase in variability of multivariate community structure and the breakdown of zonation (or seriation) patterns as a result of disturbance. These latter methodologies are valuable because they can be used to assess environmental impacts on• those types of communities which are of primary conservation value in the East Asian region (notably coral communities and their associated biota) and which are therefore a major focus for environmental concern

A Comparison of some methods for analysing changes in benthic community structure

Statistical methods for analysing changes in community structure fall under the three general headings of univariate, graphical/distributional and multivariate. These methods are applied to a variety of benthic community data (macrobenthos, meiobenthos, corals, demersal fish), from a variety of localities (intertidal/subtidal, temperate/tropical) and over both spatial and temporal scales. Four general conclusions emerge from this comparative study: (1) The similarity between sites or times based on their univariate or graphical/distributional properties is usually different from their clustering in multivariate analyses. (2) Species dependent (multivariate) methods are much more sensitive than species independent (univariate and graphical/distributional) methods in discriminating between sites or times. (3) In examples where more than one component of the fauna has been studied, univariate and graphical/distributional methods may give different results for different components, whereas multivariate methods tend to give the same results. (4) By matching multivariate ordinations from subsets of environmental data to an ordination of faunistic data, the key environmental variables responsible for community change may be identified

A practical strategy for analysing multispecies distribution patterns

A strategy is presented for analysing marine biological survey data and relating the biotic patterns to environmental data. To avoid circular argument, biotic and environmental data are kept separate. The strategy is illustrated by a worked example using data on the distribution of 182 nematode species in 107 samples in the River Exe estuary. Nineteen stations are grouped Into 4 main clusters using complementary classification and multi-dimensional scaling (MDS) ordination techniques. These are both based on root-root transformed abundance data with the Bray-Curtis measure of similarity. Indicator species characterising each group are extracted using information statistics. Inverse analyses give clusters of co-occurring species which are strongly related to the station groups. Relationships of station groups to environmental variables are revealed by superimposing data for one variable at a time on the MDS plot, showing that some station groups differ in sediment granulometry and others in salinity, for example. Some of the other factors plotted show no difference between station groups. Similarly, physiognomic characteristics of the species are superimposed on the MDS plots of the inverse analysis of species groups, revealing differences in setal length and trophic status between the species groups. Finally, the 4 major station groups and species groups are related to one another in terms of morphological adaptation to the habitat

Increased variability as a symptom of stress in marine communities

An increase in variability between samples collected from impacted vs. control areas is described for four different types of marine communities: meiobcnthos subjected to organic enrichment, macrobenthos in the vicinity of the Ekofisk oil-field, reef-corals following the 1982-3 El Niño and fish on coral reefs which are subjected to mining. In each case there is a clear log-log relationship between the variance and the mean abundance for all species in a particular treatment group. The standard deviation for a given mean increases with increased perturbation in all cases, but is most marked for the meiobenthos and macrobenthos examples. Variability in species diversity (H') tends to increase with increasing levels of perturbation, but this increase is only significant for the macrobenthos. In all cases a pronounced increase in variability among replicate samples from perturbed treatments was revealed by multivariate analysis (non-metric Multi-Dimensional Scaling ordination). A comparative Index of Multivariate Dispersion (IMD) is suggested as a measure of this increased variability

Practical measures of marine biodiversity based on relatedness of species

In contrast to terrestrial biodiversity, marine biodiversity has a number of distinctive features that suggest that a broader strategy for its conservation might be more appropriate than a local reserve-based one. Traditional diversity measures based on species richness and evenness often have disadvantages in the assessment of biodiversity change on wide spatial scales and long timescales. Alternative measures based on the degree of relatedness of species overcome these problems to varying degrees. They fall into two categories. Taxonomic distinctiveness measures are used as a means of preferentially selecting species from an inventory for conservation purposes: species that diverge close to the base of a phylogenetic or taxonomic tree and have few close relatives will preserve more evolutionary history than those that diverge further up and have more congeners. Complementary subsets of species can also be selected to provide representativeness of the widest range of evolutionary characters. Taxonomic distinctness measures, on the other hand, are a means of comparing patterns of relatedness in community samples in the field, and monitoring changes in these patterns over space or time. They measure either the average distance apart of all pairs of individuals or species in a sample, traced through a taxonomic tree, or the variability in structure across the tree. These measures are beginning to find application in broad scale geographical comparisons of biodiversity, in environmental impact assessment and in evaluation of surrogates for biodiversity estimatio

Species size distributions in marine benthic communities

Species body size distributions from eight temperate benthic communities show a highly conservative pattern with two separate lognormal distributions, corresponding to the traditional categories of meiofauna and macrofauna. The meiofaunal mode occurs at a dry body weight of 0.64 μg and the macrofaunal mode at 3.2 mg, with a trough between them at 45 μg. It is suggested that there is a particular body size at which meiofaunal life-history and feeding traits can be optimised, and another for macrofaunal traits. As size departs in either direction (larger or smaller) from these optima, fewer species of the same size are able to co-exist. The split occurs at 45 μg because many life history and feeding characteristics switch more or less abruptly at about this body size, compromise traits being either non-viable or disadvantageous. Meiofauna and macrofauna therefore comprise two separate evolutionary units each with an internally coherent set of biological characteristics. The expression of this conservative pattern is modified by water depth: the proportion of macrofauna species increases from intertidal situations to deeper water, and it is suggested that mechanisms of resource partitioning and diversity maintainence in the meiofauna and macrofauna are affected differentially by sediment disturbance. Salinity does not affect this proportionality, and so does not differentially affect mechanisms for maintaining species diversity in any particular size category of animals. Meiofauna species size distributions may be modified in sandy sediments because of physical impositions on interstitial or burrowing lifestyles. Brief discussion of some implications of these observations includes speculations on the larval ecology of macrofauna, on gigantism in Antarctic invertebrates, and on the benthic Sheldon spectrum