Small-scale disturbances on soft bottom macrozoobenthos after mechanical cleaning operations in a central-western Mediterranean lagoon

Sardinia Island (Italy), even if relatively small, has over 100 lagoons totalling some 12,000 ha. Yet their
potential yield remain often unexpressed because they are subjected to environmental stress and
degradation. As far as benthic communities are concerned, one of the main disturbances is certainly the
accumulation of shell detritus, which progressively modifies the way benthic organisms interact with the
sediment.
2 - An experimental dredging study was therefore performed in the Calich lagoon (NW Sardinia), due to its
particular interest for fishing activities and potential semi-intensive mollusc culture. Changes in benthic
community structure were examined in two areas of the lagoon by analysing both the demographic profile
of several abundant species and the features of sedimentary matrix immediately after the cleaning
operations and seven months later. Data obtained were compared with those collected in undisturbed areas
of the lagoon. This allowed us to evaluate the effects of dredging operations on the benthic assemblages
unaffected by natural temporal shifts of the system.
3 - Univariate and multivariate analyses indicated a strong relationship between macrofaunal community
structure and intensity of the cleaning activities. At the dredged sites benthic fauna was not depleted but did
exhibit higher diversity and evenness indexes than at the undisturbed sites. This seemed to be a
consequence of decrease in the density of some abundant species at the dredged sites. Furthermore, a
general reduction of total organic content was observed in the upper sediment layer. Lastly, the cleaning
method employed is discussed in relation to its potential for impacting the benthos.