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

Helminth parasites of fish in marine systems are often considered to be generalists, lacking host specificity for both intermediate and definitive hosts. In addition, many parasites in marine waters possess life cycles consisting of long-lived larval stages residing in intermediate and paratenic hosts. These properties are believed to be adaptations to the long food chains and the low densities of organisms distributed over broad spatial scales that are characteristic of open marine systems. Moreover, such properties are predicted to lead to the homogenization of parasite communities among fish species. Yet, these communities can be relatively distinct among marine fishes. For benthos, the heterogeneous horizontal distribution of invertebrates and fish with respect to sediment quality and water depth contributes to the formation of distinct parasite communities. Similarly, for the pelagic realm, vertical partitioning of animals with depth will lead to the segregation of parasites among fish hosts. Within each habitat, resource partitioning in terms of dietary preferences of fish further contributes to the establishment of distinct parasite assemblages. Parasite distributions are predicted to be superimposed on distributional patterns of free-living animals that participate as hosts in parasite life cycles. The purpose of this review is first, to summarize distribution patterns of invertebrates and fish in the marine environment and relate these patterns to helminth transmission. Second, patterns of transmission in marine systems are interpreted in the context of food web structure. Consideration of the structure and dynamics of food webs permits predictions about the distribution and abundance of parasites. Lastly, parasites that influence food web structure by regulating the abundance of dominant host species are briefly considered in addition to the effects of pollution and exploitation on food webs and parasite transmission.

Food webs and the transmission of parasites to marine fish

The present review provides a framework within which the impact of dredging on biological resources that live on the sea bed ("Benthic" communities) can be understood, and places in perspective some of the recent studies that have been carried out in relation to aggregates dredging in European coastal waters. The impact of dredging works on fisheries and fish themselves, and on their spawning grounds is outside the scope of this review. We have, however, shown that empirical models for shelf waters such as the North Sea indicate that as much as 30% of total fisheries yield to man is derived from benthic resources, and that these become an increasingly important component of the food web in near-shore waters where primary production by seaweeds (macrophytes) and seagrasses living on the sea bed largely replaces that by the phytoplankton in the water column. Because dredging works are mainly carried out in near-shore coastal deposits, and these are the ones where benthic production processes are of importance in supporting demersal fish production, our review concentrates on the nature of ben thic communities, their sensitivity to disturbance by dredging and land reclamation works, and on the recovery times that are likely to be required for the re-establishment of community structure following cessation of dredging or spoils disposal. Essentially, the impact of dredging activities mainly relates to the physical removal of substratum and associated organisms from the seabed along the path of the dredge head, and partly on the impact of subsequent deposition of material rejected by screening and overspill from the hopper. Because sediment disturbance by wave action is limited to depths of less than 30m, it follows that pits and furrows from dredging activities are likely to be persistent features of the sea bed except in shallow waters where sands are mobile. Recent studies using Acoustic Doppler Current Profiling (ADCP) techniques suggest that the initial sedimentation of material discharged during outwash from dredgers does not, as had been widely assumed, disperse according to the Gaussian diffusion principles used in most simulation models, but behaves more like a density current where particles are held together during the initial phase of the sedimentation process. As a result, the principal area likely to be affected by sediment deposition is mainly confined to a zone of a few hundred metres from the discharge chute. Our review suggests that marine communities conform to well-established principles of ecological succession, and that these allow some realistic predictions on the likely recovery of benthic communities following cessation of dredging. In general, communities living in fine mobile deposits, such as occur in estuaries, are characterized by large populations of a restricted variety of species that are well adapted to rapid recolonization of deposits that are subject to frequent disturbance. Recolonization of dredged deposits is initially by these "opportunistic" species and the community is subsequently supplemented by an increased species variety of long-lived and slow-growing "equilibrium" species that characterize stable undisturbed deposits such as coarse gravels and reefs. Rates of recovery reported in the literature suggest that a recovery time of 6-8 months is charactristic

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The impact of dredging works in coastal waters : A review of the sensitivity to disturbance and subsequent recovery of biological resources on the sea bed

Numerical classification encompasses a variety of techniques for the grouping of entities based on the resemblance of their attributes according to mathematically stated criteria. In ecology this usually involves classific~tion of collections, representing sites or sampling per1ods, or classification of species. Classification can thus simplify patterns of collection resemblance or species distribution patterns in an instructive and efficient manne r. Procedures of numerical classification are thoroughly reviewed, including data manipulations, computation ~f r e semblance measures and clustering methods. The 1mportance and e ffects of transformations and standardizations are di s cussed. It is particularly critical to choose an appropriate resemblance measure which best corresponds with the investigator's concept of ecological resemblance. Clus tering methods form groups on the basis of patter~s of inte r-entity similarity. Various types of clusterlng me thods e xist but currently the most useful and best de veloped are those which are exclusive, intrinsic, . hierarchical and agglomerative. Agglomerative clusterlng me thods which distort spatial relationships and intensely c luster are often most useful with ecological data. The value of post-clustering analyses in the interpretation of the results of numerical classifications is stressed. Thes e include reallocation of misclassified entities, comparison of classifications of collections with thos~ of species (nodal analysis), comparing alternate c~assl­ fi cations, testing differences among groups, relatlng clas sification to extrinsic environmental factors and i nterfacing classification with other multivariate analyses. The use f ulne ss of numerical classification is demonstrated f or obj ec tive analysis of the data sets resulting from field s urveys and monitoring studies conducted for the assessme nt of effe cts of pollution. However, to date few. pol l ution bio logists have applied the more powerful classlf i catory tec h nique s and post-clustering analyses.

Application of numerical classification in ecological investigations of water pollution

Sandy beaches dominate most temperate and tropical coastlines where they represent both important recreational assets and buffer zones against the sea In some areas they are very productive and are exploited commercially However, they have been regarded as marine deserts by many biologists and were largely neglected until Remane (1933) began studies on the coasts of Germany The work of Pearse et al (1942) was also pioneering and represented the first qualitative attempt to evaluate a whole beach system Since then sandy beach ecology has advanced considerably, though it has always lagged behind other aspects of coastal marine ecology in the attention it has enjoyed During this period biological research on beaches has spread from early taxonomic and qualitative studies through quantitative ecology and physiology of important species towards a more holistic systems approach today

Mary Potts Montgomery

Papers

The Use of Numerical Methods to Determine the Distribution of the Benthic Fauna Across the Continental Shelf of North Carolina