A temperature-dependent relationship between benthic invertebrate biomass and trawling pressure

Bottom trawling can cause acute depletion of benthic invertebrate biomass, thus reducing competition among surviving organisms and increasing food availability by generating carrion. As ectotherms are generally smaller and grow faster with increasing temperature, they may be less vulnerable to trawling and quicker to replenish biomass in warmer waters. Therefore, the chronic effect of bottom trawling on benthic invertebrate biomass may depend on local sea temperature and, hence, be under the influence of climate change. We tested this hypothesis using benthic grab samples from 200 sites spanning the North Sea and data on trawling pressure in the areas where samples were collected. The relationship between benthic community biomass and swept area ratio (the average number of times the seabed is trawled per year) was negative where annual bottom water temperature was low (8°C), positive in relatively warm water (11°C) and approximately neutral at intermediate temperature (9.5°C). These relationships were attributed to changes in mean body mass, not community abundance. Our results are consistent with theoretical expectations and suggest that climate modulates the chronic effect of bottom trawling on benthic invertebrate biomass. Confirming causality and determining the broader consequences for community structure and ecosystem functioning should be priorities of future research.