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Local species diversity may be determined by processes operating locally, such as disturbance, predation and competition, or by regional processes, such as environmental structuring or history. Classical theory focusing on competition predicts that the species combining to form communities will be less similar to each other than they would be if they were assembled at random from a regional species pool. Theory focusing on environmental structuring predicts that species will be more similar to each other than expected by chance. A randomisation test that determines the extent to which local species lists represent random selections from a regional list, based on the average relatedness between species, was applied to data held in the MacroBen database. Little or no evidence was found for species lists of whole faunas at any scale being random subsets of species lists at larger scales. Species tend to be more closely related to each other than would be expected if they were assembled at random. Thus marine soft-sediment macrofauna are not locally assembled at random from regional species pools and it is likely that regional processes determine the assembly of communities. Focusing on the most abundant class within the macrofauna, a different pattern emerges, in that there is a much stronger tendency for local polychaete composition to be a random subset from regional pools at all scales. Thus it is not possible to determine whether local polychaete diversity is independent of both local and regional processes, or determined by a combination of both acting antagonistically.

First-time research of the pristine water area of Dvuyakornaya Bay (South-Eastern Crimea, Black Sea) revealed high taxonomic richness of benthic diatoms (Bacillariophyta). Altogether, 304 species, 78 genera, 37 families and 20 orders were identified. Among them 68 newly-found species for the Black Sea were marked. The largest species number was marked in the genera Navicula (41 species), Nitzschia (29), Amphora (25), Cocconeis (20), Diploneis (16), Lyrella, Fallacia and Planothidium (10 species respectively). Inter-regional comparative analysis of diatom species richness was carried out using Bray-Curtis similarity coefficient and Venn diagrams. Diatom taxocene of Dvuyakornaya Bay (DB) was compared with Bacillariophyta flora from several Crimean coastal sites under different level of anthropogenic impact, i.e. relatively pristine water area near Cape Fiolent (CF) and heavy polluted Sevastopol Bay (SB) and Balaklava Bay (BB). The highest similarity of species composition (58%) was registered between intact biotopes (DB vs CF) and between heavy polluted water areas (SB vs BB), despite the geographical remoteness of the compared areas, differences in hydrological-hydrochemical conditions and in bottom substrates patterns. The lowest species similarity of diatom taxocenes was observed between SB and CF (32.3%) and between SB and DB (36.5%). It was concluded that the content of technogenic pollutants (trace metals, PCBs, PAHs and pesticides) in the bottom sediments, as well as the heterogeneity of microbiotopes are represent major factors influencing on the species composition of benthic Bacillariophyta in the investigated coastal water areas.

Macroecology provides a novel conceptual framework for analysis of the distribution and abundance of organisms at very large scales. Its rapid development in recent years has been driven primarily by studies of terrestrial taxa; the vast potential of marine systems to contribute to the macroecological research effort remains largely untapped. International collaborative efforts such as MarBEF have provided fresh impetus to the collation of regional databases of species occurrences, such as the newly available MacroBen database of the European soft sediment benthic fauna. Here, we provide a first macroecological summary of this unique database. We show that in common with almost all previously analysed assemblages, the frequency distribution of regional site occupancies across species in the MacroBen database is strongly right-skewed. More unusually, this right skew remains under logarithmic transformation. There is little evidence for any major differences between higher taxa in this frequency distribution (based on the 8 animal classes for which we have sufficient data). Indeed, considerable variation in occupancy persisted across the taxonomic hierarchy, such that most variation occurred between species within genera. There was a weak positive relationship between local population density and regional occupancy across species, but this abundance-occupancy relationship varied considerably between higher taxa and between geographical areas. Our results highlight the potential of databases such as MacroBen to consolidate macroecological generalities and to test emerging theory.

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