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.

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A practical strategy for analysing multispecies distribution patterns

Taphonomy and time-averaging of marine shelly faunas

Benthic macrofauna was sampled by grab at 16 stations in Hampton Roads and the adjacent Elizabeth River, Virginia, USA. Samples were taken in February, May and August. Sampling sites and species were grouped by a classification strategy which basically consisted of the Canberra metric dissimilarity-measure and flexible and group average clustering. Following reallocations, 8 site groups and 16 species groups instructively classified the 47 sites and 93 species considered in the analysis. The sites were grouped into “associations” on mud, muddy-sand and sand-bottom, and those in the Elizabeth River. Species groupings distinguished a few species most frequent at Elizabeth River or mud and muddy-sand sites, larger numbers of species restricted to muddy-sand and sand or solely to sand sites, ubiquitous species, epifaunal species which were microhabitat-restricted, and seasonal species. An analysis of numerically dominant species in the different associations indicated the relative importance of ubiquitous species and seasonally abundant species. Community-structure statistics (species diversity, species richness and evenness) showed definite spatial and temporal patterns. Diversity was high at sand and muddy-sand sites and low at mud and Elizabeth River sites. This spatial pattern was predominantly one of species richness. At Elizabeth River and mud stations, diversity increased from February to August because of increased evenness, while at sand and muddy-sand stations, diversity peaked in May in response to both high species richness and high evenness. The applicability of “community concepts”, the causes of substrate specificity, seasonality and species diversity, and the effects of pollution on community structure are discussed.

Classification and community structure of macrobenthos in the Hampton Roads area, Virginia

We examine global patterns of benthic macroinvertebrate biomass and its distribution among functional feeding guilds in marine intertidal cOnmlunities. Variation in ash-free dry biomass was related to physical variables (mean annual air and water temperatures, sediment grain size, inter- tidal slope, tide range and type, wave height and exposure) by least-squares regression analysis of data for 36 rocky shores and 245 sedimentary shores. Linear combinations of physical variables explain up to 44 % of the variance in total biomass on sedimentary shores and 40 % of the variance in the biomass on rocky shores. Grain size and wave exposure are the best single predictors of total biomass for sedi- mentary shores and rocky shores, respectively. Biomass estimates peak in temperate regions and are an order of magnitude higher on rocky shores than on sedimentary shores. In fact, macroinvertebrate biomass on temperate rocky shores attains levels 10 to 100 times higher than those documented for other benthic marine environments. Suspension feeders tend to dominate temperate intertidal commu- nities (they typically comprise> 30 to 60 % of the macroinvertebrate biomass), reflecting the importance of benthic-pelagic coupling in these ecosystems. Contrary to consumer stress models for rocky shores,. there is no compelling evidence for biomass limitation of grazers and carnivores at high wave exposure.

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Global patterns of macroinvertebrate biomass in marine intertidal communities

Benthic invertebrate data from thirty-nine lakes in south-central Ontario were analyzed to determine the effect of choosing particular data standardizations, resemblance measures, and ordination methods on the resultant multivariate summaries. Logarithmic-transformed, 0–1 scaled, and ranked data were used as standardized variables with resemblance measures of Bray-Curtis, Euclidean distance, cosine distance, correlation, covariance and chi-squared distance. Combinations of these measures and standardizations were used in principal components analysis, principal coordinates analysis, non-metric multidimensional scaling, correspondence analysis, and detrended correspondence analysis. Correspondence analysis and principal components analysis using a correlation coefficient provided the most consistent results irrespective of the choice in data standardization. Other approaches using detrended correspondence analysis, principal components analysis, principal coordinates analysis, and non-metric multidimensional scaling provided less consistent results. These latter three methods produced similar results when the abundance data were replaced with ranks or standardized to a 0–1 range. The log-transformed data produced the least consistent results, whereas ranked data were most consistent. Resemblance measures such as the Bray-Curtis and correlation coefficient provided more consistent solutions than measures such as Euclidean distance or the covariance matrix when different data standardizations were used. The cosine distance based on standardized data provided results comparable to the CA and DCA solutions. Overall, CA proved most robust as it demonstrated high consistency irrespective of the data standardizations. The strong influence of data standardization on the other ordination methods emphasizes the importance of this frequently neglected stage of data analysis.

Multivariate analysis of benthic invertebrate communities: the implication of choosing particular data standardizations, measures of association, and ordination methods

Martin L.H. Thomas

Papers

The classification and ordination of shallow-water benthic samples from Prince Edward Island, Canada

Influence of predation on shell morphology of Buccinum undatum L. on Atlantic coast of Canada