Effects of chronic trawling disturbance on the production of infaunal communities

Trawling causes widespread physical disturbance in shallow shelf seas. While the impacts of trawling on the biomass and community structure of benthic fauna are well known, no existing studies have quantified the effects of trawling disturbance on the absolute production of small benthic infauna. We investigated the effects of beam trawling disturbance on the production of small benthic infauna (AFDM > 0.78 to 62.5 mg) at 9 sites that were subject to a 17.5-fold range in annual trawling disturbance, using a size-based approach that could be applied to other soft-bottom systems. We developed a generalised additive model to test for relationships between trawling disturbance and infaunal production and size structure, after accounting for differences in sediment characteristics and depth. The statistical power of our analyses to detect linear and non-linear relationships between production and disturbance, including increased production at intermediate levels of disturbance, was high (>90% probability of detecting a 50% change in production across the range of disturbance). The analyses showed that trawling frequencies of 0.35 to 6.14 times yr-1 did not have a significant effect on the production of small infauna or polychaetes. This result contrasts with order of magnitude decreases in the production of large infauna, and shows that small polychaetes with fast life histories are less vulnerable to trawling disturbance. Since small infaunal polychaetes are a key source of food for flatfishes, we conclude that beam trawling disturbance does not have a positive or negative effect on their food supply.

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