MEPS 385:51-64 (2009)  -  DOI: https://doi.org/10.3354/meps08056

ABSTRACT: A field experiment was conducted to examine the short- and long-term effects of otter trawling on a macrobenthic infaunal community in shallow subtidal waters of Faxaflói Bay (SW Iceland) that had never been trawled before. The experimental design consisted of 4 sites trawled 10 times and 4 areas left undisturbed (controls). Sampling of fauna and sediments was carried out in June 1997, immediately after trawling, and subsequently 2 and 7 mo later, in order to investigate longer term impacts of trawling. No significant treatment effects could be detected on total abundance or on multivariate structure, and tests for individual species revealed only a single short-term effect (for the bivalve Thyasira flexuosa). However, trawling affected several aspects of diversity with significant short-term reduction in species richness and persistent effects on the Shannon-Wiener index. Power analysis revealed that larger changes were needed to detect changes in abundance compared to measures of diversity. Analyses of qualitative changes revealed a decreasing trend in abundance of the majority of taxa (especially the rarer ones) immediately after trawling. This was the most likely cause for the reduced diversity and the augmented small-scale variability in species richness. The size of initial impacts and the persistence of effects were largely consistent with those of previous studies in similar environments. Similar to other types of environmental impacts in aquatic environments, our analyses reveal that impacts of trawling on measures of diversity can be detected at a high statistical power and that larger effects are necessary to detect impacts on abundances.

KEY WORDS: Otter trawl · Experimental fishing · Infauna · Variability · Analysis of variance · Iceland · Diversity · Power analysis