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Mapping benthic biocoenoses in the Malta offshore area

 

A good knowledge of benthic (sea floor) biotic assemblages is essential for successful management of activities, particularly those related to fisheries.  A basic requirement for any strategy or plan to manage and protect the seabed and its dependent fish stocks and other living resources, is a map showing the location, extent and character of the different benthic habitats. The compilation of such a map starts with the collection of samples from different stations within the area of interest, in this case, the Malta FMZ and adjacent waters within GFC Management Unit 15.

Since much of the area of interest is deep water (more than 100m and as deep as 1000m or more – see figure) samples are difficult to collect and it would be prohibitively expensive to organize a specific mapping study. Instead, samples from the Mediterranean Trawl Surveys (MEDITS) are used. These samples are actually the by-catch (non-target species) from MEDITS surveys and using these for research purposes therefore maximises the amount of information obtained from these surveys.  The by-catch biota in the samples are sorted, identified and counted, and the data are recorded as number of individuals of each species or higher taxon per station. Additionally, any sediment samples collected are analysed and the grain-size distribution and other physical parameters of the sediment are determined in order to characterize the sediments.

The biotic data are analysed using multivariate statistical techniques that group stations into clusters, based on the identity of the species present and their relative abundance; each major cluster therefore potentially represents a different biocoenosis. The location of stations belonging to each cluster/biocoenosis is then plotted on a map of the study area and the resulting maps are analysed to determine if there are any patterns of distribution of the assemblages of organisms, for example, if there are any correlations with depth of bottom type or some other feature. Additional information that may be obtained from a study of these biocoenotic maps includes the identification of habitats that are critical for a particular marine resource (for example, as feeding, breeding or nursery grounds for particular species of fish), those that might experience the largest changes in functionality as the environment changes, and those that are the most sensitive to anthropogenic or natural impacts.

BIOCENOSIS_1 

A map of the sea area surrounding the Maltese Islands, showing depth zones (coloured areas) and the stations from the 2009 MEDITS survey that were analysed for biocoenotic mapping (coloured circles). The stations are grouped according to the similarity of the benthic species and their abundance as resulting from cluster analysis.

Ongoing research involves extending and refining a first draft of the biocoenotic map compiled from the analysis of benthic fauna collected as by-catch during the 2009 MEDITS survey (shown in the figure), by incorporating the by-catch collected during the 2010 and 2011 MEDITS surveys in the analysis and by integration with data on the distribution and abundance of the MEDITS target species.

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Last Updated: 30 November 2011

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