In the Northern Adriatic Sea the combination of hydrological processes and eutrophication causes periodical hypoxia and anoxia, sometimes followed by mass mortality of benthic organisms. We report the results of a 20-years (from 1990 to 2008) monitoring program carried out after the anoxic event of 1989 that caused benthic mass mortality over an area of about 1.200 km2. The recovery dynamics of the polychaete fauna was followed at 3 stations (including the one sampled 1 year before the event). Samples (0.1 m2 Van Veen grab, 2 mm sieve) were collected from 1989 to 1994 and from 2003 to 2008. All taxa were identified at species level. The analyses of univariate biodiversity indexes highlighted higher temporal variation of assemblage diversity in the period following the distrophic crisis, followed by a more stability in the next decade. Multivariate analyses suggested that the highest component of variation belonged to the factor year. Difference across years, however varied in magnitude, depending on station. The cluster analysis identified 4 main groups of years (1990-91, 1992-94, 2003-05, 2006-08), and the Canonical analysis of principal coordinates (CAP) showed species characterising each group. Univariate analyses on the distribution of these characteristic species confirmed the pattern derived from the whole assemblage, suggesting their possible role as indicator species. Our results highlight the importance of analyzing long-term dataset in order to well understand patterns of assemblage dynamics following strong events of disturbance. Assuming the 1989 anoxia as the event determining the biodiversity change, and considering our outcomes, which suggest the assemblages structure is still changing linearly, our data suggest that the polychaete fauna is still recovering without having reached a pattern of among-years stability. Focusing on the biology of the species characterizing the different periods might help in understanding the ecological processes that have determined the observed pattern.
Long term changes in soft-bottom polychaete assemblages following distrophic crises
Mikac B
;
2010
Abstract
In the Northern Adriatic Sea the combination of hydrological processes and eutrophication causes periodical hypoxia and anoxia, sometimes followed by mass mortality of benthic organisms. We report the results of a 20-years (from 1990 to 2008) monitoring program carried out after the anoxic event of 1989 that caused benthic mass mortality over an area of about 1.200 km2. The recovery dynamics of the polychaete fauna was followed at 3 stations (including the one sampled 1 year before the event). Samples (0.1 m2 Van Veen grab, 2 mm sieve) were collected from 1989 to 1994 and from 2003 to 2008. All taxa were identified at species level. The analyses of univariate biodiversity indexes highlighted higher temporal variation of assemblage diversity in the period following the distrophic crisis, followed by a more stability in the next decade. Multivariate analyses suggested that the highest component of variation belonged to the factor year. Difference across years, however varied in magnitude, depending on station. The cluster analysis identified 4 main groups of years (1990-91, 1992-94, 2003-05, 2006-08), and the Canonical analysis of principal coordinates (CAP) showed species characterising each group. Univariate analyses on the distribution of these characteristic species confirmed the pattern derived from the whole assemblage, suggesting their possible role as indicator species. Our results highlight the importance of analyzing long-term dataset in order to well understand patterns of assemblage dynamics following strong events of disturbance. Assuming the 1989 anoxia as the event determining the biodiversity change, and considering our outcomes, which suggest the assemblages structure is still changing linearly, our data suggest that the polychaete fauna is still recovering without having reached a pattern of among-years stability. Focusing on the biology of the species characterizing the different periods might help in understanding the ecological processes that have determined the observed pattern.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
