Impacts of chronic trawling disturbance on meiofaunal communities

Bottom trawling causes chronic and widespread disturbance to the seabed in shelf seas. Meiofauna may be impacted directly or indirectly by this disturbance, since the passage of trawls causes immediate mortality or displacement, changes sediment structure and geochemistry and affects the abundance of predators or competitors. Since meiofauna make a significantly greater contribution to benthic production than the larger macrofauna, there are compelling reasons to assess their response to chronic trawling disturbance. In this study, we determined the effects of trawling disturbance, season, sediment type and depth on the structure and diversity of nematode communities. Our analyses were based on comparisons between nematode communities in three beam-trawl fishing areas in the central North Sea. These areas were trawled with mean frequencies of I (low disturbance), 4 (medium) and 6 (high) times year 1 respectively. Our analyses showed that trawling had a significant impact on the composition of nematode assemblages. In two sampling seasons, the number of species, diversity and species richness of the community were significantly lower in the area subject to high levels of trawling disturbance than in the areas subject to low or medium levels of disturbance. However, levels of disturbance at the 'low' and 'medium' sites may have been insufficient to cause marked long-term changes in community structure. Many of the observed changes were consistent with responses to other forms of physical disturbance. The extent to which the observed changes in community structure reflect changes in the production of the nematode community remains unknown, although overall abundance was not significantly affected by trawling disturbance.