Natural vs. trawling-derived transport of sediment and particulate organic matter in a submarine canyon

Deep bottom trawling often occurs in the vicinities of submarine canyons since these morphological features act as nursery areas for commercial species. Previous studies in the submarine canyons incising the NW Mediterranean margin have highlighted that bottom trawling resuspends large volumes of sediment which are partly transported downcanyon as sediment gravity flows. To assess the contribution of downward particle fluxes in La Fonera Canyon (NW Mediterranean) linked to natural sediment transport events and bottom trawling, a near-bottom mooring equipped with a 24-cup sediment trap, a current meter, and a turbidimeter was deployed during 2017 in its axis (1200 m water depth), next to a trawling ground. Temporal variations in the quantity and composition of trapped particulate organic matter were assessed through the analysis of organic carbon (OC), total nitrogen (TN) and several biomarkers (lignins, cutin acids, p-hydroxybenzenes, benzoic acids, amino acid-derived products, dicarboxylic acids, and fatty acids).High downward particle fluxes (60-100 g&#183;m-2&#183;d-1) were registered in autumn and winter associated to torrential river discharges, seasonal storms and dense shelf water cascading. During these natural events, sediment transported downcanyon had high organic matter contents that were mostly terrigenous in origin. However, the highest downward particle flux (>140 g&#183;m-2&#183;d-1) was recorded in the onset of the bottom trawling season in March, after a 2-month seasonal trawling closure. During the following summer months no major natural sediment transport events occurred, but the high frequency of bottom trawling activities (10-26 hauls&#183;week-1) near the sediment trap caused considerably high downward particulate fluxes (80-125 g&#183;m-2&#183;d-1) during this season. Compared to autumn and winter months, sediment transferred downcanyon caused by trawling had lower organic matter contents, mostly consisting in refractory compounds (i.e. lignins, p-hydroxybenzenes and benzoic acids) with similar concentrations to those observed in the bottom sediments of the trawling grounds, confirming that this material originates from these areas. During periods with less trawling activity, lower sediment fluxes (30-50 g&#183;m-2&#183;d-1) with higher organic matter contents enriched in labile compounds (i.e. amino acid-derived products, di-carboxylic acids, and fatty acids) were recorded. These results highlight how bottom trawling activities on the flanks of submarine canyons modify the supply of sediment and organic matter downcanyon. The low-quality of organic matter transferred by bottom trawling activities may ultimately affect the fragile ecosystems dwelling in these deep environments.

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Organic biomarkers in deep-sea regions affected by bottom trawling: pigments, fatty acids, amino acids and carbohydrates in surface sediments from the La Fonera (Palamós) Canyon, NW Mediterranean Sea

Biogeosciences ◽

10.5194/bg-10-8093-2013 ◽

2013 ◽

Vol 10 (12) ◽

pp. 8093-8108 ◽

Cited By ~ 10

Author(s):

E. Sañé ◽

J. Martín ◽

P. Puig ◽

A. Palanques

Keyword(s):

Amino Acids ◽

Fatty Acids ◽

Organic Matter ◽

Mediterranean Sea ◽

Deep Sea ◽

Bottom Trawling ◽

Sediment Reworking ◽

Nw Mediterranean ◽

Nw Mediterranean Sea

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.

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Quantity and biochemical composition of particulate organic matter in a highly trawled area (Thermaikos Gulf, Eastern Mediterranean Sea)

Advances in Oceanography and Limnology ◽

10.4081/aiol.2015.5448 ◽

2015 ◽

Vol 6 (1/2) ◽

Cited By ~ 4

Author(s):

Antonio Pusceddu ◽

Silvia Bianchelli ◽

Roberto Danovaro

Keyword(s):

Organic Matter ◽

Mediterranean Sea ◽

Water Column ◽

Particulate Organic Matter ◽

Biochemical Composition ◽

Eastern Mediterranean ◽

Sediment Resuspension ◽

Natural Sediment ◽

Bottom Trawling ◽

Bioavailable Fraction

Bottom trawling represents nowadays one of the most severe anthropogenic disturbances at sea, and determines large impacts on benthic communities and processes. Bottom trawling determines also local sediment resuspension and the effects of the injection of large amounts of surface sediments into the water column have been repeatedly investigated. Few studies have assessed the consequences of sediment resuspension caused by bottom trawling on the quantity, biochemical composition and bioavailability of suspended organic particles and how these eventually rival those exerted by natural storms. To provide insights on this poorly addressed issue, we investigated concentrations and biochemical composition of total and enzymatically digestible pools of particulate organic matter (POM) in the Thermaikos Gulf (Mediterranean Sea) under calm sea conditions, during intensive trawling activities, and after a severe storm. We show here that sediment resuspension caused by trawling can cause large effects on POM quantity, biochemical composition and bioavailability. Both during trawling and after the storm, the relative importance of the carbohydrate pools increased (in the upper water column) and the total lipid concentrations decreased (in the intermediate and bottom layers) when compared to values measured during calm conditions. These results would suggest that bottom trawling could inject in the upper water column POM pools more refractory in nature (e.g., carbohydrates) than those present in calm or after-storm conditions. By contrast, we show also that the bioavailable fraction of biopolymeric C increased significantly during trawling in the upper water column of the shallowest stations and in the bottom water column layer of the deepest ones. These results provide evidence that bottom trawling can influence the overall trophic status of coastal waters, exerting effects similar or stronger than those caused by natural storms, though of variable amplitude depending on the water depth. Since bottom trawling is carried out worldwide and natural storms at sea can be frequent and intense, we claim for the need of assessing new adapting management strategies of bottom trawling in order to mitigate the synergistic impacts of anthropogenic and natural sediment resuspension on coastal biogeochemical cycles.

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Organic biomarkers in deep-sea regions affected by bottom trawling: pigments, fatty acids, amino acids and carbohydrates in surface sediments from the La Fonera (Palamós) Canyon, NW Mediterranean Sea

Biogeosciences Discussions ◽

10.5194/bgd-9-18601-2012 ◽

2012 ◽

Vol 9 (12) ◽

pp. 18601-18654

Author(s):

E. Sañé ◽

J. Martín ◽

P. Puig ◽

A. Palanques

Keyword(s):

Amino Acids ◽

Fatty Acids ◽

Organic Matter ◽

Mediterranean Sea ◽

Deep Sea ◽

Bottom Trawling ◽

Sediment Reworking ◽

Nw Mediterranean ◽

Nw Mediterranean Sea

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 analyzed 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 us to discriminate the long-term effects of trawled-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 mono-unsaturated 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.

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Composition and provenance of terrigenous organic matter transported along submarine canyons in the Gulf of Lion (NW Mediterranean Sea)

Progress In Oceanography ◽

10.1016/j.pocean.2013.07.013 ◽

2013 ◽

Vol 118 ◽

pp. 81-94 ◽

Cited By ~ 13

Author(s):

Catalina Pasqual ◽

Miguel A. Goñi ◽

Tommaso Tesi ◽

Anna Sanchez-Vidal ◽

Antoni Calafat ◽

...

Keyword(s):

Organic Matter ◽

Mediterranean Sea ◽

Submarine Canyons ◽

Terrigenous Organic Matter ◽

Gulf Of Lion ◽

Nw Mediterranean ◽

Nw Mediterranean Sea

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Biogeochemical characterization of the riverine particulate organic matter transferred to the NW Mediterranean Sea

Biogeosciences ◽

10.5194/bg-11-157-2014 ◽

2014 ◽

Vol 11 (1) ◽

pp. 157-172 ◽

Cited By ~ 21

Author(s):

M. Higueras ◽

P. Kerhervé ◽

A. Sanchez-Vidal ◽

A. Calafat ◽

W. Ludwig ◽

...

Keyword(s):

Organic Matter ◽

Particulate Organic Matter ◽

High Water ◽

Terrestrial Organic Matter ◽

Rhône River ◽

Δ13c And Δ15n ◽

Coastal Rivers ◽

Rhone River ◽

Nw Mediterranean ◽

Nw Mediterranean Sea

Abstract. A large amount of terrestrial organic matter is annually delivered by rivers to the continental shelf, where this material is either degraded, buried or transferred to the deep sea by hydrodynamic processes such as storms. The relative amount of terrestrial organic matter in the marine sediments is often determined by analysing the stable isotopes (δ13C and δ15N) and the C / N ratio of organic matter because the various particulate organic matter (POM) sources have distinct isotopic compositions. With the objective to refine and better interpret POM sources in the marine environment, we have characterized monthly terrestrial POM delivered by eight rivers discharging to the NW Mediterranean Sea: the Rhône, Hérault, Orb, Aude, Têt, Fluvià, Ter and Tordera rivers. These rivers were simultaneously sampled from November 2008 to December 2009 and the concentrations of total suspended matter (TSM), particulate organic carbon (POC) and nitrogen (PN), as well as their stable isotopic ratios (δ13C and δ15N) were determined. During the survey, three rainstorm events with winds coming from the E–NE and the S–SE impacted the NW Mediterranean. Depending on the direction of incoming winds, the fluvial response (amount of water discharge and TSM) was different. Rivers draining the Alps (Rhône River) and Central Massif (Hérault, Orb, and Aude rivers) were mostly impacted by rainstorms associated with winds coming from the S–SE, while rivers draining the Pyrenees (Têt, Fluvià, and Ter rivers) and the Montseny Massif (Tordera River) were impacted by rainstorms associated with winds coming from the E–NE. In addition, the spatial evolution of water discharges shows a different hydrological regime of the Rhône River, with relatively constant and high water stages and TSM concentrations when compared to coastal rivers, characterized by long periods of low water stages. TSM concentrations are positively correlated to water discharges (high water flows resuspended riverbed sediments) but show an inverse relationship with POC and PN relative contents (mostly due to dilution and by low availability of light in river waters during flood events). TSM in most of the coastal rivers have on average 2.5–3 times higher POC and PN mean contents than the Rhône River (8.5 and 1.5%, respectively, for coastal rivers compared to 3.6 and 0.5%, respectively, for the Rhône River). This discrepancy may be caused by the long drought periods in small coastal Mediterranean watersheds that enhance the eutrophication in studied coastal rivers. The δ13C ratios of organic matter also reflect this discrepancy between high and low water stages with values ranging from −33.2 to −24.5‰. The enriched 13C values (−26.3 ± 0.4‰ for the Rhône River and −26.9 ± 1.2‰ for coastal rivers), measured during high water stages, express mostly a mixture of terrestrial source (plant remains and soils) whereas depleted 13C values (∼ −30‰) associated with low water stages exhibit a source with predominant freshwater algae. The high δ15N mean values (>8‰) found in Têt, Ter and Tordera rivers may underline the importance of denitrification processes as a consequence of the eutrophication and anthropogenic impact.

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Diets of Juvenile Atlantic Menhaden (Brevoortia tyrannus) in Three Estuarine Habitats as Determined from Fatty Acid Composition of Gut Contents

Journal of the Fisheries Research Board of Canada ◽

10.1139/f75-075 ◽

1975 ◽

Vol 32 (5) ◽

pp. 587-592 ◽

Cited By ~ 15

Author(s):

H. Perry Jeffries

Keyword(s):

Fatty Acids ◽

Organic Matter ◽

Fatty Acid Composition ◽

Fatty Acid ◽

Particulate Organic Matter ◽

Alimentary Canal ◽

Atlantic Menhaden ◽

Gut Contents ◽

Brevoortia Tyrannus ◽

Fatty Acid Compositions

Juvenile Atlantic menhaden (Brevoortia tyrannus) feed on zooplankton and particulate organic matter, but the importance of each material in the diet cannot be visually determined, because food is ground to an amorphous paste in the fish’s gizzard-like stomach. During early digestion in the anterior alimentary canal, fatty acids do not appear to change significantly, at least with respect to relative concentrations of saturated and unsaturated groups. Because zooplankton and particulate organic matter have markedly different fatty acid compositions, a hypothetical mixture of the two components can be calculated that best accounts for the observed fatty acid distributions of gut contents. Decreasing reliance on zooplankton, from bay through river to marsh, probably reflects resource abundances in three habitats and demonstrates adaptability of juvenile menhaden to different food supplies.

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