BIODIVERSITY INDEX EVOLUTION IN SHALLOW WATER AREAS

Biol. Mar. Mediterr. (2010), 17 (1): 72-73
I. Locci, M. Espa, F. Palmas, A.A. Pendugiu, P. Pesci, A. Sabatini
Department of Animal Biology and Ecology, University of Cagliari,
Via T. Fiorelli, 1 - 09126 Cagliari, Italy.
[email protected]
BIODIVERSITY INDEX EVOLUTION
IN SHALLOW WATER AREAS OF SARDINIAN SEAS (10-100 M)
EVOLUZIONE DEGLI INDICI DI BIODIVERSITÀ
NELLA FASCIA COSTIERA DEI MARI SARDI (10-100 M)
Abstract – Biological diversity is considered an important factor for ecosystem stability. The aim
of this study is to examine the temporal evolution of classical biodiversity indexes for shallow waters
(10-100 m) demersal assemblages in specific locations of the Sardinian seas, which have been subject to
different fishing pressure over the past 14 years (1994-2007). Our results indicate that fishing pressure
appeared to affect the diversity of shallow waters species, showing different biodiversity index reactions on
different levels of fishing effort. The validity and reliability of this index as a measure of environmental
stress and its potential use for the monitoring of demersal ecosystem is then discussed.
Key-words: demersal assemblages, Sardinia, biodiversity.
Introduction - The high concentration of human population near coasts and
the oceans’ productive coastal margins, strongly affects marine ecosystems and its
resources (Halpern et al., 2008). Industrial fishing in particular can have both direct
and indirect consequences on marine systems (Fogarty et al., 1998; Greenstreet and
Hall, 1996), including effects on species diversity. Several studies have underlined the
role of biodiversity in ecosystem functioning (Worm et al., 2006; Hector and Bagchi,
2007). In the light of the above, come out the importance of biological diversity,
and the development of further tools for monitoring its status should be considered
imperative. The aim of this study is to examine the answer of biodiversity indexes in
consequence of fleet evolution, on shallow waters demersal assemblages.
Materials and methods – Data were collected over 1994-2007 period, within the
framework of the international MEDITS research programme. The year 2002 was
excluded due to a sensible delay in starting the survey. Only the 10-100 m depth range
were considered. Species abundances data were used to calculate Shannon’s index
(H’), species richness (lnS) and Pielou’s evenness (J’). Fishing effort were evaluated
by means of Regione Autonoma della Sardegna fleet archives. These data regarded
the number of trawlers (<30 GT) involved in shallow water fishing, considering 7
separated zones.
Results – Investigated areas, due to fleet renewal which involved the replacement
of the old low-tonnage wooden boats with large deep sea iron boats, have been
subjected to a decreasing fishing pressure over the past 14 years, resulting in a
general decrease of about 24% in fishing boats but different for each zone (Tab. 1).
We found sensible changes in biodiversity, with an increase for areas SE, N, and S
and a decrease for area W. These results are in agreement with the diverse behavior
of fishing effort, which usually display opposite trends than biodiversity indexes do.
Conclusions – The use of biodiversity indexes as an instrument for assessing
marine resources is a subject of continued debate (Ungaro et al., 1998).
Our analysis on biodiversity, based on data from 14 annual trawl surveys,
showed different temporal trends in the 8 areas considered. The varying intensity of
Biodiversity index evolution in shallow water areas of Sardinian seas
Fig. 1 - Location of the investigated areas.
Localizzazione delle aree investigate.
73
Tab. 1 - Shannon’s index trends.
Trends dell’indice di Shannon.
exploitation described, enabled us to identify the effects that such disturbance has
had on biodiversity, both positively correlated with fishery yield (Ungaro et al., 1998;
Worm et al., 2006).
According to our results evaluation of biodiversity trend evolution, allow us to
detect environmental modifications that otherwise would pass unnoticed. Although
further investigations are necessary, biodiversity indexes could be an important
support to classical stock assessment methodologies.
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