Abstract
Abstract. Deep-sea ecosystems are in general adapted to a limited variability of physical conditions, resulting in high vulnerability and slow recovery rates from anthropogenic perturbations such as bottom trawling. Commercial trawling is the most recurrent and pervasive of human impacts on the deep-sea floor, but studies on its consequences on the biogeochemistry of deep-sea sediments are still scarce. Pigments, fatty acids, amino acids and carbohydrates were analysed in sediments from the flanks of the La Fonera (Palamós) submarine canyon (NW Mediterranean Sea), where a commercial bottom trawling fishery has been active for more than 70 yr. More specifically, we investigated how trawling-induced sediment reworking affects the quality of sedimentary organic matter which reaches the seafloor and accumulates in the sediment column, which is fundamental for the development of benthic communities. Sediment samples were collected during two oceanographic cruises in spring and autumn 2011. The sampled sites included trawl fishing grounds as well as pristine (control) areas. We report that bottom trawling in the flanks of the La Fonera Canyon has caused an alteration of the quality of the organic matter accumulated in the upper 5 cm of the seafloor. The use of a wide pool of biochemical tracers characterized by different reactivity to degradation allowed for us to discriminate the long-term effects of trawl-induced sediment reworking from the natural variability caused by the seasonal cycle of production and sinking of biogenic particles. Differences between untrawled and trawled areas were evidenced by labile amino acids, while differences between spring and autumn samples were detected only by the more labile indicators chlorophyll a and monounsaturated fatty acids. These results suggest that changes in the biochemical composition of the sedimentary organic matter caused by bottom trawling can be more relevant than those associated with natural seasonality and pose serious concerns about the ecological sustainability of deep-sea trawling activities.
Highlights
Commercial bottom trawling is a fishing activity that consists in pulling heavy fishing gear over the seafloor, with negative effects on the sedentary macrofauna and on fish stocks (Jones, 1992; McConnaughey et al, 2000; Thrush and Dayton, 2002; Morato et al, 2006; Thrush and Dayton, 2010)
We report that bottom trawling in the flanks of the La Fonera Canyon has caused an alteration of the quality of the organic matter accumulated in the upper 5 cm of the seafloor
These results suggest that changes in the biochemical composition of the sedimentary organic matter caused by bottom trawling can be more relevant than those associated with natural seasonality and pose serious concerns about the ecological sustainability of deep-sea trawling activities
Summary
Commercial bottom trawling is a fishing activity that consists in pulling heavy fishing gear over the seafloor, with negative effects on the sedentary macrofauna and on fish stocks (Jones, 1992; McConnaughey et al, 2000; Thrush and Dayton, 2002; Morato et al, 2006; Thrush and Dayton, 2010). It has been recently estimated that the overall oceans’ area (including continental shelf regions and seamounts) used as trawling grounds accounts for 20 million km (World Resources Institute, 2000), of which about one-fourth is located on the continental slope regions (Puig et al, 2012). Due to their low resilience, deepwater areas (> 200 m) are more vulnerable to anthropogenic disturbance than shallow, high-energy environments (McConnaughey et al, 2000), and for this reason, the effects of bottom trawling on the deep benthic communities and their habitats need to be studied carefully. Sañé et al.: Organic biomarkers in deep-sea regions affected by bottom trawling
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