Comparison of univariate and multivariate aspects of estuarine meiobenthic community structure

In a survey of ten sites in the Tamar estuary in January 1984, spatial variability in the species composition and structure of nematode and copepod species assemblages was greater between sites over a range of 1–3 km than between replicates at the same site. Two aspects of meiofauna community structure were studied: (1) the multivariate information: the identities of the species or nematode feeding types are retained and used integrally with data on abundances during comparison of assemblages using multivariate analyses [multidimensional scaling ordination (MDS)] and (2) the univariate information: taxonomic identity is not retained during comparisons of assemblage structure; data analyzed includes numberical abundances, species counts and diversity. Multivariate aspects of species assemblage structure were closely correlated with salinity for both copepods and nematodes. For nematode assemblages sediment disturbance may also have been important and other unidentified factors have clear secondary effects on multivariate copepod assemblage structure. Univariate aspects of nematode assemblage structure did not appear to be correlated with the salinity gradient in the Tamar, sites at the mouth and head of the estuary had a more even nematode species distribution than those in the middle reaches. Nematode univariate assemblage structure may have been more strongly influenced by sediment disturbance caused by hydrographic processes, macrofauna, food resource availability or some combination of all three. Copepod abundances and species numbers were variable but assemblages became more dominated and less diverse with increasing distance away from the mouth of the estuary. Data from 1984 were compared with data from 1982 collected at three of the sites by Warwick and Gee (1984). Persistence of assemblage structure varied from site to site and according to the attribute of community structure under consideration

Meiobenthic and macrobenthic community structure along a putative pollution gradient in southern Portugal

Macro- and meiobenthos were sampled from Ria Formosa, Portugal along putative sewage pollution gradients in summer 1987 and winter 1988. The status of the benthos was assessed using multidimensional scaling ordination, ABC plots, and a variety of univariate indices of community structure. Meiobenthos in both seasons and macrobenthos in winter appeared to respond to sewage enrichment only in the immediate vicinity of the sewage outfalls and channels but ABC plots indicated that macrobenthic communities were moderately stressed throughout the area in summer. In the summer, human digging for shellfish results in considerable sediment turnover. Since meiofauna may be less affected by physical sediment disturbance than macrofauna this may explain why the macrofauna communities were apparently disturbed relative to the meiofauna even beyond the influence of the sewage. Sampling meiofauna with the macrofauna significantly increased our understanding of mans impact in this area. There was little correlation between macro- and meiobenthos in diversity, abundances, number of taxa and biomass and these indices gave no indication of an organic enrichment gradient

Bioturbation as a mechanism for setting and maintaining levels of diversity in subtidal macrobenthic communities

Over 2 years, experiments were conducted to compare the effects of sediment disturbance by different bioturbating, macrofaunal organisms on the diversity and structure of the associated infaunal community. The four species investigated were the bivalves Nuculoma tenuis (Montagu, 1808) and Abra alba (Wood, 1802), the heart urchin Brissopsis lyrifera (Forbes, 1841), and the burrowing decapod Calocaris macandreae (Bell, 1846). These organisms were chosen to allow assessment of the effects of contrasting feeding activities and body sizes of the bioturbating species on the diversity of the macrobenthic communities. Bioturbation by the sub-surface deposit feeders N. tenuis and B. lyrifera promoted higher levels of α and β diversity in treatments exposed to intermediate levels of disturbance. Whilst no such 'intermediate response' was demonstrated for A. alba or C. macandreae, it was evident that changes in the associated fauna were influenced by the feeding type of the bioturbating organism responsible. It was also shown that different elements of the associated community responded differently to biotic disturbance. The results indicate that the variability in density and distribution of such bioturbators are important factors in structuring infaunal communities, and in setting and maintaining levels of diversity in apparently homogeneous areas

Building on the concept of marine biological valuation with respect to translating it to a practical protocol: viewpoints derived from ajoint ENCORA-MARBEF initiative

Marine biological valuation provides a comprehensive concept for assessing the intrinsic value of subzones within a study area. This paper gives an update on the concept of marine biological valuation as described by Derous et al. (2007). This concept was based on a literature review of existing ecological valuation criteria and the consensus reached by a discussion group of experts during an international workshop in December 2004. The concept was discussed during an ENCORA-MARBEF workshop in December 2006, which resulted in the fine-tuning of the concept of marine biological valuation, especially with respect to its applicability to marine areas

Biodiversity links above and below the marine sediment-water interface that may influence community stability

Linkages across the sediment-water interface (SWI) between biodiversity and community stability appear to exist but are very poorly studied. Processes by which changes in biodiversity could affect stability on the other side of the SWI include carbon transfer during feeding, decomposition of organic matter, nutrient recycling, organism recruitment and structural stabilisation of sediments. The importance of these processes will clearly vary among habitats. Direct disturbance to communities on one side of the SWI, such as created by overfishing, habitat destruction, and species invasions, has the potential to impact communities on the other side of the SWI through the many functional links. Hypotheses are proposed to suggest further areas of research to fill the large gaps in our knowledge concerning the nature and intensity of such linkages. The linkage between benthic and pelagic diversity is likely to be tighter where there is a close energetic connection between the domains, such as polar and shallow coastal waters, and where communities are dominated by selective detritivores. The quantity of carbon reserves in the sediment and the predominant mode of larval development of sediment communities probably influence the stability of below SWI communities in the face of changes in above SWI diversity. The organisms, including hyperbenthos, that are found at the SWI may be of crucial importance to the linkage and stability of above and below SWI communities. [KEYWORDS: benthos, biodiversity, fish, links, pelagic, plankton, sediment-water interface, stability]

Denaturing gradient gel electrophoresis (DGGE) as a tool for identification of marine nematodes

Many phyla of marine invertebrates are difficult to identify using conventional morphological taxonomy. Larvae of a wider set of phyla are also difficult to identify as a result of conservation of morphology between species or because morphological characters are destroyed during sampling and preservation. DNA sequence analysis has the potential for identification of marine organisms to the species level. However, sequence analysis of specimens is time-consuming and impractical when species diversity is very high and densities of individuals huge, as they are in many marine habitats. The effectiveness of the 18S rRNA gene sequences for identification of one species-rich marine group, the Nematoda, is analysed. Following identification of variable regions of the 18S rRNA gene, primers were designed to amplify a small segment of sequences suitable for denaturing gradient gel electrophoresis (DGGE). The effectiveness of DGGE for identifying individual species is analysed. DGGE analysis of natural communities of nematodes detected less than ? of the species present. This fraction of the community probably represents the abundant species in the original samples. It is concluded that DGGE is not a useful tool for analysis of species richness in marine communities as it fails to detect rare species of which there are usually many in the marine benthic environment. However, DGGE may be a useful method for detecting changes in communities that influence the abundance of the most common taxa