Abyssal nematode assemblages in physically disturbed and adjacent sites of the eastern equatorial Pacific

The nematode assemblages of experimentally impacted and adjacent sediments in abyssal depths of the eastern equatorial Pacific were investigated 7 years after a physical disturbance. A total of 3048 nematodes belonging to 68 genera and 26 families were identified. The nematode fauna at both disturbed and control sites was dominated by specimens belonging to the genera Acantholaimus, Chromadorita, Thalassomonhystera, Desinoscolex, Halalaimus and Diplopeltula. These genera contribute to about 55% and 50% of total nematode fauna in the disturbed and control sites, respectively. The mean relative abundance of the dominant genus Acantholaimus amounted to about 20%. Generic diversity, evenness and richness at the undisturbed sites do not significantly differ from the corresponding median values at the disturbed sites. Mean k-dominance curves show differences in community structure between treatments. Ordination of square- and fourth-root-transformed family abundances revealed groupings of the disturbed and undisturbed samples (significant at the 5% level), whereas ordination of genus abundances did not. Sample variability was investigated by inspection of the relationship between variance and mean abundance of genera and families in each sample group and by calculating the comparative index of multivariate dispersion (IMD). There is a clear increase in the standard deviation for a given mean of genus or family abundances at the disturbed sites. A higher variability among the disturbed samples, however, does not appear to be true in the multivariate sense. (C) 2001 Elsevier Science Ltd. All rights reserved.