L'approccio morfo-funzionale come descrittore alternativo per lo studio delle comunità malacologiche di fondo mobile
Author(s)
Biddittu, Andrea
Date Issued
March 15, 2010
Type
Doctoral Thesis
Abstract
The macrozoobenthic communities have such particular dynamics so as to permit an integrated
valuation of the space – temporal alteration of the ecosystem. Soft bottom macrobenthic animals,
are in fact relatively sedentary, have long life-spans and are represented by a great number of species with different tolerance to stress and, at last, they play an important role in recycling nutrients.
Taking into consideration this heterogeneity and complexity, ecologists have the necessity to
identify the emerging properties in order to simplify the structures and the processes of the system.
In this framework the “community structure” is much more efficient than the “species” as indicator of the status of the ecosystem as it represents the historical memory of the system.
Identical species listed in different time and space are equivalent to equal state of the system
and each shift in the list-vector corresponds to a significant change of the state of the system.
Although the taxonomical approach has several point of weakness it might be difficult to
compare taxonomical identifications made by different experts; the skills and the knowledge of
taxonomists may vary due to many different factors such as experience and practice. Moreover the link between the species and their functional role couldn’t be directly evaluated.
The contribution of the benthic assemblages to ecosystem functioning will be dependent on the
biological characteristics, or traits, exhibited by constituent species, as these determine how the
species influence ecological processes. For example, burrowing activities of benthic invertebrates may alter sediment conditions through the resuspension of fine particles into overlying waters, may change the distribution of different-sized particles within sediments and may produce increases in the oxygen and water contents. These activities also transport buried organic matter and nutrients to
the sediment–water interface, stimulating benthic microflora and microfauna communities and
hence decomposition processes.
The present research provides a comparison between the taxonomical and non taxonomical
approach in the study of the soft bottom benthic assemblages using a multitraits approach, stressing the role of the Mollusc syntaxon to the ecosystem functioning.
This phylum is, among the macrozoobenthic animals, a group of extreme heterogeneity in
terms of feeding behaviour, habitus, reproduction and morphology. It is considered as efficient
descriptor of benthic communities, meaning that they are excellent environmental indicators and the analysis of the marine malacofauna is often enough to provide valuable information about the state of health of an ecosystem.
The characterizing element of the Mollusc syntaxon is the shell, a calcareous exoskeleton
produced always in the first life stages and following almost ever the body growth of the animal.
For this reason, the shell is the interface through which the animal acquaints itself with its external environment, and its morphology must allow the typical primary functions of the animal (feeding, reproduction, locomotion, etc.).
The morphological analysis of the shell and its variation among taxa may represent a useful
tool to identify variations in the environmental conditions and to evaluate the ecological status of an ecosystem. The research of this Thesis is based upon this approach, defining an alternative
procedure for the evaluation of the structure of the soft bottom benthic communities and the
recognition of recurrent typologies through the utilization of alternative descriptors to the
taxonomic one.
The data set object of the study is made of 60 sample surveys that came from all over the
Italian peninsula and collected at several depths. By comparing the shell shape of each species and by using geometrical models available in literature, it is possible to identify morphological categories (morphotaxa) transversal to the traditional taxonomical ones (species) with the aim to represent different aspects of the ecological functions in benthic communities and ecosystems.
The comparison between the traditional synecological approach (species or structural analysis)and the morpho-functional one has allowed the valuation of the coherence between shape and habitat.
Furthermore, the bathymetric and sedimentological analysis has allowed to recognize
preferential ranges for each morphotaxon, while the biocoenotic analysis of the structural elements of each morphotaxon and the study of obtained result of each sample survey obtained by
Multivariate Analysis (Correspondence Analysis - CA; Indicator Species Analysis, ISA) has
allowed to recognize recurrent typologies along the depth gradient.
The collection and organization of morphological information has been useful to realize a
preliminary data set relative to the morpho-functional traits of soft bottom marine Molluscs, and therefore, to valuate and create analytical tools based upon alternative descriptors to the
taxonomical ones, useful in the biological monitoring and in the valuation of the ecological status of the marine ecosystems.
Additional information
Dottorato di ricerca in Ecologia e gestione delle risorse biologiche
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