Article

Impact of bottom trawling on water turbidity and muddy sediment of an unfished continental shelf

Wiley
Limnology and Oceanography
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Abstract

Two experiments were carried out to study the effects of trawling in the muddy prodeltaic deposit of the LlobregatRiver in the northwestern Mediterranean. Trawling was conducted in two experimental lines, and bottom morphology, sediment texture, and water turbidity were analyzed before trawling and at different time intervals afterward. The tracks of the trawl gears were still observed in sonographs of the bottom 1 yr after the first experiment. The vertical grain size distribution of bottom deposits indicated that the thickness of the sediment removed by the net between the gears was about 2–3 cm on average, though the erosion produced by the gears was deeper. Resuspended aggregates with a high silt content settled during the first hour after trawling, generating a temporary increase in the silt content of the surface sediment. One day after trawling, the surface sediment was mixed and already had a similar grain size distribution to that before trawling. After the beginning of trawling, water turbidity increased first near the bottom for a few hours and later also at shallower levels of the water column within a period of 2–5 d after trawling. At the end of the experiment, about 10% of the sediment affected by trawling was diffused in the water column and the remaining 90% had settled on the bottom. Average turbidity in the water column increased by a factor of up to three for 4–5 d after trawling. This experiment shows that intense and continued trawling on continental shelves has a noticeable effect on water turbidity, which must be considered in addition to natural processes.

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... In addition, the ground rope and weights of the trawl gear can cause scouring and flattening of the seabed, particularly on muddy substrates (Churchill, 1989;Jones, 1992;Martıń et al., 2014). Bottom trawling also leads to sediment resuspension, contributing to the formation of turbid plumes and persistent nepheloid layers, principally when it is conducted over fine-grained sediments (Black and Parry, 1994;Pilskaln et al., 1998;Palanques et al., 2001;Durrieu de Madron et al., 2005;Palanques et al., 2014). Over larger spatial scales, high-resolution multibeam data on steep submarine canyon flanks revealed a general flattening and homogenization of the deep seafloor relief in heavily trawled areas, suggesting that recurrent trawling over the same fishing grounds would also result in a reduction in the morphological complexity . ...
... The penetration of the trawling gear into the seabed is higher in muddy sediments and the persistence of trawl marks is longer (Krost et al., 1990;Smith et al., 2007). Indeed, trawl marks can persist a few days in coastal sandy areas (Depestele et al., 2016) but up to a few years in rather deeper muddy environments (Palanques et al., 2001;Gilkinson et al., 2015). ...
... The patterns, persistence and degradation of trawl marks in coastal and shelf areas have been intensively studied during the last years because of their interest in estimating the fishing effort and assessing the physical impact of bottom trawling on the seabed (Palanques et al., 2001;Gilkinson et al., 2015;Depestele et al., 2016;Buhl-Mortensen and Buhl-Mortensen, 2018). However, evidence of the physical impact of bottom trawling over larger spatial and temporal scales on continental shelf environments remains poorly constrained (e.g., Oberle et al., 2016a;Oberle et al., 2016b). ...
Article
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Bottom trawling is a fishing method that involves towing of nets along the seafloor to catch demersal species. The dragging of trawling gears along the seafloor results in scraping and ploughing of the surficial sediments, leading to the formation of turbid plumes of resuspended sediments and causing measurable changes in the seabed morphology. High-resolution multibeam data, side scan sonar, sediment grain size and vessel tracking data have been used to investigate the impact of bottom trawling on the seafloor morphology and surficial sediments of the northern Catalan continental shelf (NW Mediterranean), providing new insights into the impact of this anthropogenic activity on the seafloor. Multibeam data evidenced the occurrence of large-scale erosive features as a consequence of repeated scouring by fishing gears in localized areas. They are characterized by elongated (70-300 m wide and up to 8 km long) channelized areas of high backscatter with variable incision (from 0.2 m to 1.2 m). The spatial distribution of these morphologies shows a similar pattern to that observed in the fishing intensity, with maximum values in the areas of increased trawling intensity, corresponding to the main fishing grounds. Side scan sonar data also shows higher densities of trawl marks in these areas than in the surroundings. Sediment cores collected on these features show an upward-coarsening trend in the first 4-5 cm of the core, suggesting that part of the finer fraction resuspended by trawling is winnowed, increasing the sand content of the surface sediment. The identification of such large erosive morphologies in the main fishing grounds evidences that repeated trawling over the same fishing ground during decades can result in deep excavation of the seafloor, leading to permanent large-scale morphological changes. Furthermore, the evolution of these erosive features over a 13-year interval points towards long recovery periods after the cessation of trawling activities.
... Dependent on the environmental setting, this may offset some of the losses from direct physical disturbance. However, counteracting this, sediment suspended by fishing can increase turbidity (Capuzzo et al., 2015;Palanques et al., 2001;Ruffin, 1998) which reduces light penetration and thus photosynthetic rates ( Figure 1a) . ...
... Depending on local hydrographic conditions, sediment may remain in suspension for extended periods of time, and can be transported across large vertical and lateral distances (de Madron et al., 2005;Ferré et al., 2008;Martín et al., 2006Martín et al., , 2008Oberle, Storlazzi, & Hanebuth, 2016;Palanques et al., 2006Palanques et al., , 2014Pusceddu et al., 2015). In the Northern Mediterranean, otter trawling resulted in average suspended sediment concentrations ranging between 6 and 50 mg/L, depending on the study site (de Madron et al., 2005;Palanques et al., 2001). Sediment within the water column was found to persist for up to 5 days (Palanques et al., 2001), while off-shelf transport was 1.4-9 times higher when compared to sediment volumes without trawling (Ferré et al., 2008;Palanques et al., 2014). ...
... In the Northern Mediterranean, otter trawling resulted in average suspended sediment concentrations ranging between 6 and 50 mg/L, depending on the study site (de Madron et al., 2005;Palanques et al., 2001). Sediment within the water column was found to persist for up to 5 days (Palanques et al., 2001), while off-shelf transport was 1.4-9 times higher when compared to sediment volumes without trawling (Ferré et al., 2008;Palanques et al., 2014). The loss of seabed topography, as discussed above (Martín, Puig, Palanques, & Giamportone, 2014;Oberle, Swarzenski, et al., 2016;Puig et al., 2012), may also alter local-scale hydrographic conditions, increasing sediment boundary water flows and the magnitude of sediment resuspension (Smith & McLean, 1977;Soulsby, 1997). ...
Article
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Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. By far the most widespread human activity occurring on the seabed is bottom trawling/dredging for fish and shellfish. A global first‐order estimate suggested mobile demersal fishing activities may cause 0.16–0.4 Gt of organic carbon (OC) to be remineralized annually from seabed sediment carbon stores (Sala et al., 2021). There are, however, many uncertainties in this calculation. Here, we discuss the potential drivers of change in seabed sediment OC stores due to mobile demersal fishing activities and conduct a literature review, synthesizing studies where this interaction has been directly investigated. Under certain environmental settings, we hypothesize that mobile demersal fishing would reduce OC in seabed stores due to lower production of flora and fauna, the loss of fine flocculent material, increased sediment resuspension, mixing and transport and increased oxygen exposure. Reductions would be offset to varying extents by reduced faunal bioturbation and community respiration, increased off‐shelf transport and increases in primary production from the resuspension of nutrients. Studies which directly investigated the impact of demersal fishing on OC stocks had mixed results. A finding of no significant effect was reported in 61% of 49 investigations; 29% reported lower OC due to fishing activities, with 10% reporting higher OC. In relation to remineralization rates within the seabed, four investigations reported that demersal fishing activities decreased remineralization, with three reporting higher remineralization rates. Patterns in the environmental and experimental characteristics between different outcomes were largely indistinct. More evidence is urgently needed to accurately quantify the impact of anthropogenic physical disturbance on seabed carbon in different environmental settings and to incorporate full evidence‐based carbon considerations into global seabed management. Subtidal marine sediments are one of the planet's primary carbon stores and strongly influence the oceanic sink for atmospheric CO2. Considering basic principles, we hypothesize that under certain environmental settings, trawling/dredging for fish and shellfish would reduce seabed sediment carbon storage; however, this may be offset by positive feedback mechanisms in some circumstances. A review of studies which directly investigated this impact in situ also highlighted mixed results. More evidence is urgently needed to accurately quantify this impact in different environmental settings, and incorporate full evidence‐based carbon considerations into global seabed management.
... Modification de la structure sédimentaire Le passage d'un chalut remet en suspension le sédiment superficiel (Palanques et al., 2001;De Madron et al., 2005;Ferré et al., 2008;Bradshaw et al., 2012;Mengual et al., 2016) ce qui augmenterait la turbidité locale et pourrait libérer des contaminants et de la matière organique enfouis dans le sédiment. Sous certaines conditions hydrologiques particulières, l'advection des particules fines remises en suspension par le chalutage augmenterait la granulométrie (dévasement) et réduirait la qualité du tri du sédiment à long-terme, sur les sites de pêche (Brown et al., 2005;Trimmer et al., 2005). ...
... For instance, it could remove the biogenic structures and homogenize the topography over large scales (Kaiser and Spence, 2002;Thrush et al., 2006Thrush et al., , 2001. By resuspending the superficial sediment, bottom-trawling could increase the local turbidity and release buried nutrients and pollutants (Bradshaw et al., 2012;Mengual et al., 2016;Palanques et al., 2001). ...
... It induces the bycatch, death or removal of non-target populations and promotes species that benefit from trawl pass (Bremner et al., 2003a;de Juan et al., 2007;Kenchington et al., 2007;Tillin et al., 2006) and fishing discards. Trawling also acts on the substrate through the resuspension of the superficial layer (Bradshaw et al., 2012;Mengual et al., 2016;Palanques et al., 2001) and the changes in the granulometry and the biogeochemical processes at the sedimentwater interface Trimmer et al., 2005). As a result, according to the intensity of these effects, benthic communities may be more or less affected. ...
Thesis
Cette thèse participe à accroitre les connaissances sur les facteurs régissant la structures des communautés benthiques de la Grande Vasière (GV) du Golfe de Gascogne. Une attention particulière a été portée au rôle du chalutage de fond, dont l’intensité a été estimée à l’aide des données VMS. A l’échelle de la GV, nos résultats suggèrent que le chalutage de fond serait le principal moteur de structuration du mégabenthos (> 10 mm). Cependant, cette hypothèse n’a pu être formellement démontrée en raison de la co-variation entre l’activité de pêche et certaines caractéristiques environnementales. Par conséquent, les travaux ont été poursuivis sur une zone restreinte de la GV, choisie de manière à minimiser les variations dans l’habitat, tout en conservant un large gradient d’intensité de chalutageNous avons ainsi observé des modifications saisonnières et temporaires de la structure des communautés méga et macro-benthiques (>1 mm) en lien avec le chalutage. Ils proviendraient essentiellement d’une disponibilité alimentaire accrue pour les prédateurs-charognards de la mégafaune et de modifications des caractéristiques sédimentaires pour la macrofaune. En revanche, l’étude de la diversité fonctionnelle montre que ces changements n’ont que des répercussions mineures sur le fonctionnement de l’écosystème. Nos conclusions suggèrent que l’écosystème benthique de la GV a probablement été façonné par plusieurs décennies de pêche intensive et qu’il est actuellement adapté à des perturbations anthropiques chroniques
... They can be found in DNV (Det Norske Veritas) (DNV, 2010a, b), or HSE (Health and Safety) recommendations (Spouge, 1999;HSE, 2006). Moreover, there have been scientific studies concerning the safety and risk assessment of underwater damage to cables (Palanques, Guillen & Puig, 2001;Dzikowski & Marcjan, 2016;Dzikowski, Marcjan & Bilewski, 2017). There have been many works devoted to the analysis of the causes of damage to underwater infrastructure. ...
... The estimated and observed values for seabed penetration of bottom trawls in sand and mud are typically in the range of 5-20 cm but under unusual conditions such as very soft mud, an uneven seabed or a rigging failure, a trawl door may dive 50 cm or more into the sediment for a short period. Fishermen try to avoid deep seabed penetration because it increases fuel costs and gear damage without increasing catches, rising fuel prices and pressure from the environmental community (Palanques, Guillen & Puig, 2001). When a trawl passes over a submarine cable, a number of different outcomes are possible. ...
... There may be no apparent contact at all. Trawls are designed to pass over seabed obstacles; therefore more than 90 per cent of such crossings do not result in cable damage (Palanques, Guillen & Puig, 2001). Modern cables are often buried more than 60 cm into the sediment from the shore down to water depths of up to 1,500 m, therefore contact with normal fishing gear is highly unlikely. ...
Article
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Accidental damage to underwater cables caused by ship traffic seems to be a current problem. According to the statistics more than 44 percent of such damage is caused by fishing vessels. The reason for the next 14 percent is damage from ships' anchors. The construction of the underwater installation risk model was based on the determination of the density of the traffic in the area where the installation is located. There are several models used to assess the risk of underwater cable damage requiring the implementation of data on the density of traffic of fishing vessels. For this purpose, they usually use AIS (Automatic Identification System) data or statistical data on traffic density in the areas called fishing squares. The aim of this article was to compare traffic data that was based on two independent systems AIS and VMS (Vessel Monitoring System) and verify the reliability of them. The research was carried out in the area of the Slupsk Bank where an underwater cable has been damaged several times. The authors have demonstrated the need to verify the data from both systems in order to obtain reliable information about fishing vessels.
... The scraping and ploughing of the seabed produced by bottom trawling causes increases in near-bottom turbidity due to sediment resuspension (Jones, 1992;Pilskaln et al., 1998;Palanques et al., 2001;Durrieu de Madron et al., 2005;Karageorgis et al., 2005;Dellapenna et al., 2006;O'Neill and Summerbell, 2011) and upward siltation of the underlying seabed sediment because of a preferential redeposition of the coarser silt fraction and advection of the finer silt and clay fractions by currents, following their resuspension (Martín et al., 2014a;Palanques et al., 2014;Paradis et al., 2021b). ...
... In many shelf areas, where natural processes such as storms, riverine sediment discharges and tides can be very energetic, natural sediment dynamics can be more prominent than trawling disturbance, masking its effect on bottom sediments (Bhagirathan et al., 2010;Mengual et al., 2016;Oberle et al., 2016a). On the Mediterranean continental shelves, dynamic processes are usually less energetic than in more open oceanic settings, and sediment resuspension by trawling can be more similar to that induced by natural processes and have a clear impact on the bottom sediment (Palanques et al., 2001;Ferré et al., 2008;Palanques et al., 2014). In deeper slope environments, the trawling effects become even more dominant and persist over larger spatial and temporal scales, as natural sedimentary disturbances are more infrequent . ...
Article
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Submarine canyons are preferential pathways for transport of particulate matter and contaminants from the shelf to the deep sea. The Gulf of Palermo continental margin has a very narrow shelf (about 2–3 km wide on average) and is incised by several submarine canyons that favour shelf-slope sediment transfer. A sediment core collected on the outer shelf and six sediment cores taken at different depths along the Oreto, Eleuterio and Anerella submarine canyons were analysed to study the transfer and historical record of trace metal contamination in the Gulf of Palermo continental margin. Trace metals, major elements, organic carbon and sediment grain size were analysed in these cores, which were dated with ²¹⁰Pb to assess their historical compositional evolution since the late 19th century. Hg, Pb, Cu, Zn and Cd content increased until the 1970s and 1980s, associated with the increase in urbanization and industrial activities in the Palermo area, and Hg was the contaminant that reached the highest enrichments. However, the increasing trend of these metals contamination was reversed in the 1970s and 1980s, coinciding with drastic changes in the terrigenous content and grain size of sediments in the canyon axes. These changes occurred when bottom trawling fleets expanded to deeper fishing grounds equipped with powerful trawlers around the Gulf of Palermo canyon heads and flanks and along the Oreto canyon axis. Bottom trawlers have resuspended large amounts of sediment, which have been transferred into the canyons since the 1970s and 1980s and have thus increased sediment accumulation rates. This resuspended sediment has been mixing with the sediment transferred and accumulated along the canyons, diluting and reducing its trace metal contamination levels since the expansion of the bottom trawling fleets.
... Generally, the impacts of bottom trawling activities have been studied in shallow water environments, and mostly include the scraping and ploughing of the seabed by the use of heavy trawl doors that leave big furrows behind (Krost et al. 1990;Smith et al. 2003). The design of these heavy trawls also causes increases in near-bottom turbidity due to the sediment resuspension (O'Neill and Summerbell 2011), which contributes to the formation of turbid plumes and persistent nepheloid layers that are afterwards advected by local currents, waves and tides (Churchill 1989;Durrieu de Madron et al. 2005b;Palanques et al. 2001Palanques et al. , 2014. However, shallow water environments on the continental shelf (< 120 m depth) are periodically impacted by natural sediment resuspension processes, masking the consequences of this anthropogenic activity. ...
... The higher values calculated for the trawling season indicate that trawling can more than double the suspended sediment load in the water column, which is in agreement with suspended sediment inventories previously documented in other trawling grounds, both in shallow and deep-water environments (Palanques et al. 2001Arjona-Camas et al. 2019). Suspended sediment concentrations in the water column did not vary significantly when the trawling fleet was not operating on weekends and holidays at the flanks of the canyon. ...
Article
Full-text available
Increases of water turbidity and suspended sediment transport in submarine canyons have been associated with high-energy events such as storms, river floods and dense shelf water cascading (DSWC), and occasionally with bottom trawling along canyon flanks and rims. To assess the variations on the water column turbidity and sediment transport in the Palamós Canyon linked to both natural and trawling-induced processes, an autonomous hydrographic profiler, as well as a near-bottom current meter and a turbidimeter were deployed in the canyon axis (929 m depth) from February to June 2017, covering a trawling closure (February) and trawling activities (March-June). Periods of enhanced water turbidity during the trawling closure were mostly associated with storms and DSWC events, transporting turbid dense waters into the canyon. In absence of such events, the water column displayed low suspended sediment concentrations (~ 0.3 mg L− 1) until the trawling season began, when particulate matter detachments, ranging between > 1 mg L− 1 and 3.8 mg L− 1, were observed at the water depths where the trawling grounds are found. During the trawling closure, high near-bottom suspended sediment fluxes (35–44 g m− 2 s− 1) were sporadically registered at ~ 920 m depth associated with a major storm and DSWC event. Smaller but more frequent increases of near-bottom suspended sediment fluxes (0.1–1.4 g m− 2 s− 1) were recorded during trawling activities. Despite these smaller trawling-induced suspended sediment fluxes, 30 days of continuous bottom trawling activity transported a total amount of 40 kg m− 2, of similar magnitude to that generated by a major DSWC event (50 kg m− 2). Since bottom trawling in Palamós Canyon is practiced on a daily basis throughout the year, a much larger contribution of anthropogenically derived water turbidity and suspended sediment transport can be expected.
... However, Bradshaw et al. (2012) and Linders et al. (2017) showed that a plume of fine sediment was still clearly detectable several days after trawling, just as we found in this study. Those authors, as well as Schubel et al. (1979), Churchill (1989), Schoellhamer (1996), Palanques et al. (2001Palanques et al. ( , 2014, and Mengual et al. (2016) concluded that trawling likely contributed substantially to overall suspension and turbidity in the bottom water in the frequently trawled areas where those studies were performed. The relative contribution can also be higher during seasons where fishing is most intensive and natural suspension and sedimentation processes are low (Churchill, 1989;Palanques et al., 2014;Mengual et al., 2016). ...
... The relative contribution can also be higher during seasons where fishing is most intensive and natural suspension and sedimentation processes are low (Churchill, 1989;Palanques et al., 2014;Mengual et al., 2016). When suspended sediment is transported away from trawled areas, it can cause large-scale export of sediment to other areas, for example off-shelf (Churchill, 1989;Palanques et al., 2001;Ferré et al., 2008;Oberle et al., 2016bOberle et al., , 2018Paradis et al., 2018), thus potentially affecting areas that are not themselves trawled. ...
Article
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Bottom trawling is known to affect benthic faunal communities but its effects on sediment suspension and seabed biogeochemistry are less well described. In addition, few studies have been carried out in the Baltic Sea, despite decades of trawling in this unique brackish environment and the frequent occurrence of trawling in areas where hypoxia and low and variable salinity already act as ecosystem stressors. We measured the physical and biogeochemical impacts of an otter trawl on a muddy Baltic seabed. Multibeam bathymetry revealed a 36 m-wide trawl track, comprising parallel furrows and sediment piles caused by the trawl doors and shallower grooves from the groundgear, that displaced 1,000 m³ (500 t) sediment and suspended 9.5 t sediment per km of track. The trawl doors had less effect than the rest of the gear in terms of total sediment mass but per m² the doors had 5× the displacement and 2× the suspension effect, due to their greater penetration and hydrodynamic drag. The suspended sediment spread >1 km away over the following 3–4 days, creating a 5–10 m thick layer of turbid bottom water. Turbidity reached 4.3 NTU (7 mgDW L–1), 550 m from the track, 20 h post-trawling. Particulate Al, Ti, Fe, P, and Mn were correlated with the spatio-temporal pattern of suspension. There was a pulse of dissolved N, P, and Mn to a height of 10 m above the seabed within a few hundred meters of the track, 2 h post-trawling. Dissolved methane concentrations were elevated in the water for at least 20 h. Sediment biogeochemistry in the door track was still perturbed after 48 h, with a decreased oxygen penetration depth and nutrient and oxygen fluxes across the sediment-water interface. These results clearly show the physical effects of bottom trawling, both on seabed topography (on the scale of km and years) and on sediment and particle suspension (on the scale of km and days-weeks). Alterations to biogeochemical processes suggest that, where bottom trawling is frequent, sediment biogeochemistry may not have time to recover between disturbance events and elevated turbidity may persist, even outside the trawled area.
... In Europe, bottom trawling is estimated to disturb 79% of the coastal seabed (European Commission, 2020). The effects are diverse, reaching from increased resuspension and near-bottom turbidity caused by the scraping of the seafloor (Jones, 1992;Palanques et al., 2001;de Madron et al., 2005;Dellapenna et al., 2006;O'Neill and Summerbell, 2011;Bradshaw et al., 2012;Martín et al., 2014a;Mengual et al., 2016) to the alteration of the benthic habitat and damage, removal or changes of benthos (Craeymeersch et al., 1997;Jennings and Kaiser, 1998;Koslow et al., 2001;Kaiser et al., 2006;Queirós et al., 2006;Trimmer et al., 2005;Muthuvelu et al., 2013;van Denderen et al., 2015;Howarth et al., 2018;Sciberras et al., 2018;Sköld et al., 2018) to distinct changes in ecosystem functioning (Larsen et al., 2005;Tillin et al., 2006;Pusceddu et al., 2014;Rijnsdorp et al., 2018). The magnitude of disturbance is context-dependent (e.g. ...
... The passage of trawling gear displaces and resuspends surface sediment with high water content (Palanques et al., 2001;Simpson and Watling, 2006), exposing deeper-buried sediment with lower water content at the sediment-water interface . This was confirmed by our experiment as indicated by the reduction of surface water content inside the track. ...
Article
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Experimental benthic dredging was conducted in an unfished area in the Baltic Proper to mimic the impact of trawling, with a focus on benthic biogeochemical processes. Sediment cores were taken on the track where the surface sediment had been scraped away and compared to undisturbed controls. Benthic fluxes were immediately affected and pore water DIC profiles were truncated. The time needed for the sediment to readjust to a new steady state seemed to be nutrient-specific. Sediment properties (profiles of chlorophyll, organic carbon and water content) were found to change significantly. Macrofauna was removed completely by the dredge pointing out the potential loss of highly valuable functions that are associated with them. In the Baltic Sea, in areas which were previously the most heavily fished, the frequency of trawling may have left little time for recovery and potentially kept the seabed in a permanent state of transient biogeochemical cycling.
... sediment, or a reduction in energy that finally penetrates the seabed which also contributes to a lower volume backscatter along the tracks (Fig. 8D). Before and after otter trawl experiments (sediment cores) carried out by Palanques et al. (2001) detect only minor changes in sediment grain size inside the tracks one day after trawl. Schwinghamer et al. (1998) came to a similar conclusion that otter trawling is not influencing the grain size (detected by RoxAnn). ...
... Therefore, the actual conservation potential could be much longer. Studies document that seafloor alterations and trawl marks can have varying longevity depending on the substrate (because penetration is lower in sandy sediments due to the high mechanical resistance of the sediment) (DeAlteris et al., 1999) and natural remediating factors like bioturbation, wave action and currents (Jones, 1992;Polet and Depestele, 2010;Palanques et al., 2001). Another factor which was not further examined in this study is the impact of bacteria. ...
Article
The physical impact of demersal fishing was studied in three different areas of the German North Sea sector by use of a multibeam echosounder. The areas represent typical shallow seas siliciclastic habitats in variable distance to the coastline. Their seabed substrate is dominated by coarse silt close to the shore and by fine sand in the most distal area on the Dogger Bank. The study documents the utility of the multibeam as a suitable tool to map large seafloor areas, as well as to quantify and qualify the footprints of the fishing groundgear. Besides the depth and amplitude information, the multibeam data allows the analysis of the incidence angle-dependent variation of the backscatter signal that provides additional information on the seabed impedance, roughness, volume scatter and substrate type. Two main types of destructive seafloor pattern were observed in the three areas. The dominant type are pairs of parallel furrows exhibiting widths of 6-9 m and depths of 2-6 cm and is related to beam trawling. Separation distance of the pair furrows is 16-23 m. The second type are pairs of narrow furrows (3-4 m) with much larger separation distance of 110-120 m. They are attributed to otter board trawling. A comparison of their mechanical ramification shows that the fishing gear incises the seafloor and modifies seafloor structures and properties. Our investigation documents that beam trawling has the greatest physical impact and exhibits the highest furrow density in the three study areas. The created furrows can persist for at least 4 months in a substrate of very fine sand. Depending on the hydrodynamic regime, the furrows can be later refilled by finer sediments, or levelled out by storm wave-induced turbulence reaching the seafloor. The hy-drofoils used in otter trawl to spread the net likewise incise the seafloor, but the furrows are much narrower. However, the ground rope of the net towed between the boards scratches the seafloor and levels the microscale topography along track widths of ca. 100 m.
... This would result in lower backscatter (smoother surface) compared to the surrounding sediment. Depending on the local hydrodynamics, bottom currents can instead transport the material away and settle it down elsewhere, which was described by Palanques et al. [58] and Mengual et al. [59]. As a result, they observed a coarsening of the sediments along the trawled tracks, due to the removal of the fine-grained fraction (silt to clay). ...
... Palanques [58] observed OTB marks in muddy sediments on the Ebro Shelf (20-70 m water depth): these TM did not show any changes after a few days but after a year they appeared with lower backscatter values. They related the relative longevity to the cohesive properties of the muddy sediment (mud content >60%). ...
Article
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The anthropogenic impact in the German Exclusive Economic Zone (EEZ) is high due to the presence of manifold industries (e.g., wind farms, shipping, and fishery). Therefore, it is of great importance to evaluate the different impacts of such industries, in order to enable reasonable and sustainable decisions on environmental issues (e.g., nature conservation). Bottom trawling has a significant impact on benthic habitats worldwide. Fishing gear penetrates the seabed and the resulting furrows temporarily remain in the sediment known as trawl marks (TM), which can be recognized in the acoustic signal of side-scan sonars (SSS) and multibeam echo sounders (MBES). However, extensive mapping and precise descriptions of TM from commercial fisheries at far offshore fishing grounds in the German EEZ are not available. To get an insight into the spatial patterns and characteristics of TM, approximately 4800 km 2 of high-resolution (1 m) SSS data from three different study sites in the German EEZ were analyzed for changes in TM density as well as for the geometry of individual TM. TM were manually digitalized and their density per square kilometer was calculated. In general, TM density was highest in August and October. Moreover, different gear types could be identified from investigating individual TM in SSS data. Beam trawl marks were observed to have widths of up to 22 m whereas otter board marks showed widths up to 6 m. The persistence of TM was estimated to 2-7 days minimum for all three sites based on the SSS data from 2015-2019. A maximum persistence could be defined at one site (Dogger Bank) and it was five months for the investigation period 2016-2017. Besides the main factors driving TM degradation (wave-base impact, sediment-type), different methods for TM detection (SSS, MBES, underwater video) are discussed. The study provides valuable information on the physical impact of bottom trawling on the seabed and can support existing monitoring strategies.
... Trawling is also responsible for seabed changes. They can concern sediment lithology and composition, for instance through a fine fraction winnowing within surficial sediment (Palanques et al., 2001Brown et al., 2005;Simpson and Watling, 2006;Oberle et al., 2015b). Impacts on micro-topography are abundantly noticed in literature with typical tracks let on the seabed, whose remanence becomes higher in low energetic environments with muddy seabed (Linnane et al., 2000;Palanques et al., 2001;Gilkinson et al., 2015). ...
... They can concern sediment lithology and composition, for instance through a fine fraction winnowing within surficial sediment (Palanques et al., 2001Brown et al., 2005;Simpson and Watling, 2006;Oberle et al., 2015b). Impacts on micro-topography are abundantly noticed in literature with typical tracks let on the seabed, whose remanence becomes higher in low energetic environments with muddy seabed (Linnane et al., 2000;Palanques et al., 2001;Gilkinson et al., 2015). Lastly, many studies from literature underlined consequences on exchanges at the water/ sediment interface and especially on nutrients fluxes, on sediment biogeochemistry (e.g. ...
Article
Based on experiments, a trawling-induced erosion dynamics was included in a 3D realistic and pre-validated hydro-sedimentary model so as to assess its contribution to the overall regional sediment dynamics in the specific case of the Bay of Biscay continental shelf. The effect of trawling was investigated throughout a 5-year period in terms of horizontal/vertical fluxes and changes in seabed mud content, and compared to the natural variability of sediment fluxes at different spatio-temporal scales. Trawling is shown in the model to significantly contribute to sediment re-suspension, and changes in the seabed at the scale of the shelf. The contribution of trawling to re-suspension is >80% during the high fishing season at many locations on the outer shelf and over the Grande-Vasière area (a large and intensively trawled muddy zone located in the middle of the shelf). The contribution of trawling is significantly weaker in winter and at annual scale, particularly over zones with (muddy-) sand facies (between 1‰ and 1%), but remains high, and reaches 20% of the annual erosion over muddy areas (e.g. northern part of the Grande-Vasière). This significant trawling-induced erosion dynamics results in high sediment fluxes which increase natural poleward dynamics from a few percent up to 40%, and contributes to the natural offshore export of sediment on the outer shelf (e.g. +35% of mud fluxes along the 130 m isobath). It is noteworthy that trawling-induced fluxes are larger in winter although the corresponding re-suspension is lower than in summer: this is due to stronger near-bottom flows occurring at this period (largely influenced by energetic wind conditions). In contrast, on the inner shelf, trawling-induced sediment fluxes are rather oriented towards the coast. Finally, simulation results reveal a trawling signature on changes in the seabed. A significant decrease (between 10% and >50%) in mud content is simulated over trawling hotspots, especially over the internal part of the Grande-Vasière and on mud patches located in front of the Gironde estuary. Conversely, trawling causes or intensifies mud deposition on both sides of these preferentially trawled areas.
... The analysis of data collected in areas subjected to variable effort matched our predictions on the response of benthic communities to trawling activities (Stage 4): higher densities of sessile and emergent suspension feeders in the less trawled areas, compared to higher densities of small, burrowing, deposit feeders in the heavily trawled sites (de Juan and Demestre, 2012). Also, environmental modifications were observed in the most heavily trawled sites, with a homogenised muddy bottom and increased near-bottom turbidity (Palanques et al., 2001). ...
Preprint
It is crucial that societies are informed on the risks of impoverished ecosystem health for their well-being. For this purpose, Ecological Integrity (EI) is a useful concept that seeks to capture the complex nature of ecosystems and their interaction with social welfare. But the challenge remains to measure EI and translate scientific terminology into operational language to inform society. We propose an approach that simplifies marine ecosystem complexity by applying scientific knowledge to identify which components reflect the state or state change of ecosystems. It follows a bottom-up structure that identifies, based on expert knowledge, biological components related with past and present changing conditions. It is structured in 5 stages that interact in an adaptive way: stage 1, in situ observations suggest changes could be happening; stage 2 explores available data that represent EI; stage 3, experts' workshops target the identification of the minimum set of variables needed to define EI, or the risk of losing EI; an optative stage 4, where deviance from EI, or risk of deviance, is statistically assessed; stage 5, findings are communicated to society. We demonstrate the framework effectiveness in three case studies, including a data poor situation, an area where lack of reference sites hampers the identification of historical changes, and an area where diffuse sources of stress make it difficult to identify simple relationships with of ecological responses. The future challenge is to operationalize the approach and trigger desirable society actions to strengthen a social-nature link.
... The Chatham Rise supports a productive deep-sea fishery, mainly focused on hoki (Macruronus novaezelandiae), hake (Merluccius australis), ling (Genypterus blacodes), orange roughy (Hoplostethus atlanticus) and oreo (Family Oreosomatidae) species (Fisheries New Zealand 2023). Bottom trawling is the main method used in several of these fisheries and can cause sedimentation (Linders et al. 2018;Paradis et al. 2018), which recent studies have demonstrated can significantly alter environmental conditions (Palanques et al. 2001;Bradshaw et al. 2021;Epstein et al. 2021;Paradis et al. 2021;Arjona-Camas et al. 2022). However, our understanding of the effects of sedimentation from trawling on benthic communities is limited (Hinchen et al. 2021), and no in situ studies of its potential effects have been carried out in the deep sea around New Zealand. ...
... However, the coralligenous still lacks effective habitat-and species-based conservation and management measures (Bevilacqua et al. 2021), as well as a shared approach to assess its environmental status (Di Camillo et al. 2023). As a matter of fact, these habitats face multiple threats, including thermal anomalies linked to climate change (Cerrano et al. 2000;Garrabou et al. 2001Garrabou et al. , 2009Garrabou et al. , 2022Huete-Stauffer et al. 2011), mechanical damage from fishing activities and scuba diving (Luna, Pérez, and Sánchez-Lizaso 2009;Markantonatou et al. 2014;Betti et al. 2023), increased turbidity and sedimentation (Palanques, Guillén, and Puig 2001;Balata et al. 2005;Ponti et al. 2014) and invasive species Balata 2008, 2009;Ponti et al. 2018). Fishing impacts are increasingly of concern due to their severe effects on the health status of marine communities, especially on erect species (Valisano et al. 2019;Betti, Bavestrello, Bo, Ravanetti et al. 2020;Pulido Mantas et al. 2022), and have been identified as major contributors to the degradation of coralligenous communities at basin scale (Deudero and Alomar 2015;Consoli et al. 2018Consoli et al. , 2019de Carvalho-Souza et al. 2018), being omnipresent in the north-western Mediterranean Sea (Angiolillo and Fortibuoni 2020). ...
Article
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Coralligenous, a typical Mediterranean mesophotic habitat, is a highly diverse assemblage, severely threatened by several stressors, including fishing litter. To characterise the coralligenous of the upper mesophotic of the Portofino Promontory (Ligurian Sea, Italy), video transects at 35 and 50 m depth were performed at four sites. Benthic assemblages and lost fishing gears were recorded, and the two depths compared. A higher coverage of taxa with complex 3D structures was found at 50 m, mainly due to the gorgonian Paramuricea clavata . However, the overall low density of this species (0.4–6.6 colonies/m ² ), together with the impact caused by 120 fishing lines found along the transects, highlights the need for tailored conservation measures. With climate change moving further down the water column and fishing impacts being a major cause of degradation, the design of marine protected areas needs to be extended to include mesophotic depths, contributing to the 30 × 30 targets agreed upon at the COP15.
... Ad-ditionally, the initial trawl disturbance can cause a disproportionately large impact on the seafloor, whereas previously disturbed areas can be relatively insensitive (NRC 2002 ). These material differences can cause substantially different OC and N remineralization rates in otherwise similar physical regimes (Palanques et al. 2001, Burdige 2007. ...
Article
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Recent concerns that commercial bottom trawling can contribute to a significant release of sequestered marine carbon have highlighted a need for research in this area. Here, a Before-After Control-Impact (BACI) experimental design was utilized in a previously untrawled area of the eastern Bering Sea. Six pairs of experimental and control corridors were sampled before, after, and 1 year after a trawl disturbance. Each experimental corridor was fished four consecutive times o ver ∼1 2 h with a commercial otter trawl. Results were contextualized with minimum detectable effects (MDE), and showed no evidence of a trawl effect on total organic carbon (P = .999, MDE ± 0.05% TOC), total nitrogen (P = .999, MDE ± 0.02% TN), δ 13 C, and δ 15 N isotope ratios and sediment size classes. Interannual changes observed in δ 15 N, sand, silt, and clay are attributed to natural variation. The study suggests that the characteristics of the study site, such as storm disturbances, high sand content, and low carbon content, limited the bot tom-trawl ef fect on sediment composition following this initial trawl disturbance. The findings highlight the importance of site-specific studies that account for local conditions to support best management practices for commercial bottom trawling.
... It appears from this study that some tracks may be at least 8 years old, and our repeated survey in 2023 showed no signs of track degradation since our initial survey in 2019. This observation is consistent with the findings of our previous study in the southern Stockholm Archipelago, where trawl tracks created for the study remained recognizable by MBES 18 months after formation, albeit with a slightly weaker backscatter signal (Bradshaw et al., 2021) and with other studies on soft seabeds (Krost et al., 1990;Palanques et al., 2001). In addition, in areas with very heavy trawling pressure, tracks may overlap to such an extent that it may be difficult to separate them in images and newer tracks may obliterate older tracks that would otherwise have persisted for a much longer time (Bruns et al., 2020;Lüdmann et al., 2021). ...
... The drag force exerted by trawling gears can scrape off, resuspend, and mix sediments (e.g., Palanques et al., 2001;O'Neill and Summerbell, 2011;Oberle et al., 2016). Sediment resuspension may lead to sediment coarsening and loss of organic carbon associated with fine-grained materials (Pusceddu et al., 2014;Paradis et al., 2019). ...
Article
Trawl-fishing is broadly considered to be one of the most destructive anthropogenic activities toward benthic ecosystems. In this study, we examine the effects of bottom-contact fishing by otter trawls on the geochemistry and macrofauna in sandy silt sediment in an area of the Baltic Sea where clear spatial patterns in trawling activity were previously identified by acoustic mapping. We calibrated an early diagenetic model to biogeochemical data from various coring locations. Fitting measured mercury profiles allowed for the determination of the sediment mixing and burial velocity. For all sites, independent of the trawl mark density, good fits were obtained by applying the model with the same organic matter loading and parameter values, while iron fluxes scaled linearly with the burial velocity. A sensitivity analysis revealed that the fitted sulfate reduction rate, solid sulfur contents, ammonium concentration, and both the isotopic composition and concentration of dissolved inorganic carbon provided reliable constraints for the total mineralization rate, which exhibited a narrow range of variability (around ±20 % from the mean) across the sites. Also, the trawling intensity did not significantly correlate with total organic carbon contents in surficial sediment, indicating limited loss of organic matter due to trawling. The fits to the reactive iron, acid volatile sulfur, chromium(II) reducible sulfur contents, and porewater composition demonstrate that sediment burial and mixing primarily determine the redox stratification. The mixing depth did not correlate with trawling intensity and is more likely the result of bioturbation, as the analyzed macrofaunal taxonomy and density showed a high potential for sediment reworking. The extraordinarily long-lived Arctica islandica bivalve dominated the infaunal biomass, despite the expectation that trawling leads to the succession from longer-lived to shorter-lived and bigger to smaller macrofauna. Our results further suggest that a clear geochemical footprint of bottom-trawling may not develop in sediments actively reworked by tenacious macrofauna.
... The deep sea (<200 m depth) is considered as one of the most diverse and largest ecosystems on Earth (Robison, 2009;Ramirez-Llodra et al., 2010;Clark et al., 2016b), hosting unique and fragile communities and playing a key role in the ocean services used by humans (Jobstvogt et al., 2014;Thurber et al., 2014;Levin and Bris, 2015). The deep-sea benthos is impacted by direct and indirect fisheries disturbances (Clark and Rowden, 2009;Moore and Squires, 2016;Clark et al., 2016a), such as the killing of non-target benthic animals, ploughing of the seabed and the resuspension of sediments, which can smother fauna (Palanques et al., 2001;Mangi et al., 2016;Clark et al., 2016a). Recognizing the growing threat to deep-sea ecosystems, the United Nations General Assembly (UNGA) called upon member states and regional fisheries management organizations and arrangements (RFMO/As) to identify areas beyond national jurisdiction (ABJN) where benthic vulnerable marine ecosystems (VMEs) occur or are likely to occur, in order to prevent significant adverse impacts from fishing practices (UNGA, 2006). ...
Article
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A significant proportion of Southern Ocean seafloor biodiversity is thought to be associated with fragile, slow growing, long-lived, and habitat-forming taxa. Minimizing adverse impact to these so-called vulnerable marine ecosystems (VMEs) is a conservation priority that is often managed by relying on fisheries bycatch data, combined with threshold-based conservation rules in which all “indicator” taxa are considered equal. However, VME indicator taxa have different vulnerabilities to fishing disturbance and more consideration needs to be given to how these taxa may combine to form components of ecosystems with high conservation value. Here, we propose a multi-criteria approach to VME identification that explicitly considers multiple taxa identified from imagery as VME indicator morpho-taxa. Each VME indicator morpho-taxon is weighted differently, based on its vulnerability to fishing. Using the “Antarctic Seafloor Annotated Imagery Database”, where 53 VME indicator morpho-taxa were manually annotated generating >40000 annotations, we computed an index of cumulative abundance and overall richness and assigned it to spatial grid cells. Our analysis quantifies the assemblage-level vulnerability to fishing, and allows assemblages to be characterized, e.g. as highly diverse or highly abundant. The implementation of this quantitative method is intended to enhance VME identification and contextualize the bycatch events.
... Physical disturbances generated by bottom trawl are known to induce changes such as reduced benthic habitat complexity (Watling and Norse 1998), increased local turbidity and enhanced release of the organic matter normally buried in the sediments (Palanques et al., 2001). Trawling also leads to mortality in benthic invertebrates and thus affect the structure and the functioning of benthic invertebrate communities (Collie et al., 2000;Rijnsdorp et al., 2018). ...
Article
Various environmental parameters such as temperature, depth and currents influence the composition and distribution of benthic assemblages. However, the impact of trawling on benthic communities depends on their species composition since not all benthic species are equally sensitive to trawling. Moreover, trawling can have effects on benthic species similar to some natural disturbances, such as a local increase in turbidity. Thus, species adapted to these natural disturbances may be resistant to a certain level of trawling. This study evaluates the joint influence of environmental parameters and trawling pressure on four functional sensitivity indices in three environmentally contrasted areas: the English Channel, the Gulf of Lion and the eastern coast of Corsica, the two latter being located in the Mediterranean Sea. The different environmental parameters influencing the behaviour of these indices were identified in each of the study areas. These parameters were divided into two groups according to the type of influence they have on the benthic community. The first group of variables, used for modeling “Scope for Growth” (SfG), relates to the resilience of species, while the second, “Disturbance” (Dist), concerns their resistance to physical impacts. This work highlighted that the distribution of benthic species in the English Channel is mainly linked to physical disturbances and therefore to their resistance, whereas it is mainly parameters linked to the resilience of communities that influence the distribution of benthic fauna in the Mediterranean. The effect of abrasion could be distinguished from the natural environmental disturbances in the English Channel and Gulf of Lion where trawling was found to have a significant effect on functional sensitivity indices. The composition and distribution of benthic communities in Corsica, did not seem to be influenced by trawling pressure.
... Several studies have demonstrated that resuspension caused by bottom trawling can create turbid clouds and persistent nepheloid layers with high suspended sediment concentration, which have been observed mainly on continental shelves (Churchill, 1989;Schoellhamer, 1996;Palanques et al., 2001Palanques et al., , 2014Ferré et al., 2008). In contrast, the occurrence of turbidity increases caused by trawling activities in slope environments has been less investigated. ...
Article
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Continental margins are transitional areas between the land and the deep ocean where large amounts of particulate matter are supplied, transported, and ultimately deposited in the deep sea. High-energy hydrodynamic processes such as storms, ocean currents, or internal waves and tides, as well as bottom trawling activities contribute to the resuspension and remobilization of these particles. These mechanisms favor their transference from the continental shelf to the continental slope and maintain high concentrations of particulate matter in the water column forming nepheloid layers. The temporal evolution of the hydrographic and nepheloid structure in the upper slope off Vancouver Island (British Columbia, Canada, NE Pacific) was assessed by analyzing 4 months (from mid-August to late-November 2018) of sensor data from Ocean Networks Canada (ONC) NEPTUNE cabled seafloor observatory. The distribution of particulate matter during the study period illustrated a well-defined turbidity structure consisting of surface nepheloid layers (SNLs) at <100 m depth associated to primary and secondary productivity, intermediate nepheloid layers (INLs) between 150 and 300 m depth at the shelf-break and upper slope domain, and bottom nepheloid layers (BNLs) developed at >400 m depth. Moderate storm events occurred during fall when the more intense INLs were recorded at shelf-break depths. However, not all the INLs recorded during this period occurred in coincidence with these storms, indicating that these INL detachments were modulated by a different sediment resuspension mechanism. Analyses of fishing vessel activity during the study period revealed that trawlers operated over the same depth range as these INLs. Our results suggest that, in combination with the regional currents, the presence of continuous fishing along the continental slope off Vancouver Island contributes to the advection of suspended sediment particles, playing a major role in their transfer as nepheloid layers.
... These studies should also consider the direct impact of trawling gears on the seafloor, because bottom trawling has also been reported as an important driver of sediment resuspension, caused by the passage of the fishing gear through bottoms, becoming an important seafloor micro-morphology disturbing process in muddy and moderate-energy continental shelves [88] and a driver of deep seascape evolution [89,90]. Sediment resuspended, as a result of trawl fishing, also has a wide variety of additional effects including the smothering of feeding and respiratory organs [91], which can affect the settlement and feeding of the biota. ...
Article
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The scientific exploration of Mallorca Channel seamounts (western Mediterranean) is improving the knowledge of the Ses Olives (SO), Ausias March (AM), and Emile Baudot (EB) seamounts for their inclusion in the Natura 2000 network. The aims are to map and characterize benthic species and habitats by means of a geological and biological multidisciplinary approach: high-resolution acoustics, sediment and rock dredges, beam trawl, bottom trawl, and underwater imagery. Among the seamounts, 15 different morphological features were differentiated, highlighting the presence of 4000 pockmarks, which are seafloor rounded depressions indicators of focused fluid flow escapes, usually gas and/or water, from beneath the seabed sediments. So far, a total of 547 species or taxa have been inventoried, with sponges, fishes, mollusks, and crustaceans the most diverse groups including new taxa and new geographical records. Up to 29 categories of benthic habitats have been found, highlighting those included in the Habitats Directive: maërl beds on the summits of AM and EB, pockmarks around the seamounts and coral reefs in their rocky escarpments as well as fields of Isidella elongata on sedimentary bathyal bottoms. Trawling is the main demersal fishery developed around SO and AM, which are targeted to deep water crustaceans: Parapenaeus longirostris, Nephrops norvegicus, and Aristeus antennatus. This study provides scientific information for the proposal of the Mallorca Channel seamounts as a Site of Community Importance and for its final declaration as a Special Area of Conservation.
... Trawling using bottom fishing gear has been shown as an anthropogenic activity which can cause significant seabed sediment disturbance and remobilisation (e.g. O'Neill and Summerbell, 2011;Palanques et al., 2001). Trawling intensity is most heavily concentrated in the WISMB for the Dublin Bay Prawn (Nephrops norvegicus) (Kaiser et al., 1996;O'Higgins et al., 2019). ...
Article
The seafloor is increasingly being used for siting renewable energy and telecommunication infrastructure as well as supporting key fisheries and biodiversity. Understanding seabed stability and sediment dynamics is, therefore, a fundamental need for offshore engineering and geoscience and biological studies. In this study we aim to quantify the levels of sediment mobility in the Irish Sea: an area of increasing socio-economic interest and subsequent seabed pressures. The temporal and spatial interaction between bathymetry, hydrodynamics and seabed sediments leads to a complex pattern of erosion, bedload transport and deposition which can affect seabed infrastructure and modify habitats. Information on current and wave conditions were obtained from numerical modelling to assess their role in generating seabed hydrodynamic conditions. These outputs were coupled with observed seabed grain-size data to predict the exceedance of sediment mobility thresholds by bed shear stress values for a period of one year according to empirical formulae. Exceedance frequency values were used to calculate a number of sediment disturbance and mobility indexes to allow for a robust assessment of sediment dynamics. Sediment in the Irish sea, on average, is being mobilised 35% of the time during the year, with 35% of the spatial area studied being mobilised over 50% of the time. Even in areas of low sediment mobilisation frequency (<5%), there are implications for bedform dynamics. The spatial patterns of the calculated sediment mobility are discussed in the context of current seabed geomorphology and the implications for both engineering and environmental considerations.
... If these estimated numbers are at least in the right ballpark, it turns out that the investigated Cadiz MDCs are a major component in the regional source-to-sink carbon cycle (Thomas et al., 2004). This situation requires a better understanding of offshore carbon recycling mechanisms and retention times due to high-energy impacts to the seabed, such as storm events (Gutiérrez-Mas et al., 2009;Ruiz et al., 2013) and bottom trawling (Palanques et al., 2001;Oberle et al., 2016). ...
Article
Mud depocenters (MDCs) are common elements on modern continental shelves and act as a major shallow-marine sink for fluviogenic material. These most proximal depocenters, thus, play a major role in material cycling and carbon availability on global and regional scales, though individual formation history, dependence on external forcing mechanisms, and material composition makes each of them a unique case. This study establishes a chronostratigraphic framework and deciphers the depositional dynamics for the two main MDCs on the continental shelf in the eastern Gulf of Cadiz, as a prime example, with the goal to calculate a regional sediment and carbon budget. Based on the analysis of 2040 km of subbottom profiles and 18 sediment cores, the fine-grained depocenters began to grow during maximum flooding around 6.5 cal ka BP. Sedimentation rates ranged between 2 and 35 cm/ka until 2.7 cal ka BP and increased significantly around the Roman Warm Period (30–200 cm/ka), caused by regional humidification as well as mining and agricultural activities. After 1.0 cal ka BP, sedimentation rates rose further (20–3000 cm/ka), due to land clearing in coincidence with erosion-favoring aridity during the Islamic period and the Medieval Climate Anomaly. Unprecedented sediment accumulation started with the Industrial Era. The total sediment volume of the two MDCs is 5.80 km³ with a dry mass of 12,971 Mt. 85 Mt. of organic matter and 3637 Mt. of carbonate make this depocenter an important shallow-marine sink, with a total of 521 Mt. carbon as a significant player in the regional terrestrial-marine carbon cycle.
... Natural sediment samples were collected with a multicorer from the Chatham Rise. The top 5 cm of the sediment column were used for this experiment, as this surface layer is most likely to be disturbed and resuspended in the water column by bottom-contact fisheries and mining (Palanques et al., 2001). Sediments were frozen at − 20 • C to kill any living fauna. ...
Article
The generation of sediment plumes by human activities, such as bottom fishing and potential deep-sea mining, poses threats to deep-sea benthic fauna. Sponges are important components of deep-sea ecosystems and can be particularly sensitive to elevated suspended sediment concentrations. In this study, we exposed the deep-sea New Zealand sponge Ecionemia novaezealandiae (Dendy, 1924) (Demospongiae: Ancorinidae) to a range of suspended sediment concentrations (SSC) (32, 78 and 475 mg l⁻¹) and control conditions (no added sediment) continuously for two weeks. Survival was high (97%), with only one death (at the highest SSC). Half of the sponges in the 475 mg l⁻¹ treatment showed partial necrosis by the end of the two-week exposure. Respiration rates of sponges in the sediment addition treatments decreased relative to control sponges by 27, 37 and 60%, respectively, after day 1; and by 7, 17, and 27%, respectively, after 14 days of suspended sediment exposure. At the end of the experiment, sectioning of the sponges revealed sediments deep in the tissue of all specimens, including controls, indicating previous incorporation of sediment occurred in their natural environment. Despite the high survival, the decreased respiration rates and partial necrosis with increasing SSC indicated a decline in sponge condition that could affect this species beyond the disturbance period.
... This includes both increased resuspension of available sediments and input of new particulate material by glacial melting and increased erosion on land (Walling, 2009). Besides these climate change-related impacts, there are also direct human activities like trawling, sand extraction, and coastal engineering measures that can contribute to reduced light availability (Palanques et al., 2001). However, other effects of altered light climate on higher trophic levels occur besides those indirectly mediated via phytoplankton. ...
... The average speed of the trawler was maintained at 2 knots so that direction and trawl efficiency could be kept. This type of trawl gear can easily disturb the top 2-3 cm of the bottom sediment between the panels and eventually reaching the top 10 cm below the trawl panels (Palanques et al. 2001;Durrieu de Madron et al. 2005). Each resuspension operation had to cope with the closeness to the coastline, the shallow water depths of the area and the distance amongst the two vessels while in operation to keep safety issues within acceptable limits. ...
Article
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Portmán Bay in Southern Spain is one of the most extreme cases in Europe of anthropogenic impact on the marine ecosystem by the disposal of mine tailings resulting from the processing of sulphide ores. First, the composition and extent of the surficial deposit were investigated from geochemical and metal analysis on high spatial density of sediment samples. Then, a disturbance experiment was conducted in the coastal area off Portmán Bay in order to investigate the potential impact of mining activities on marine ecosystems. Two research vessels were used for that experiment, one performing as a trawler resuspending bottom sediments while the other monitor the behaviour of turbid plumes thus generated and the evolution of their characteristics through time by using a range of acoustic and optical tools together with water and bottom sediment sampling for biogeochemical and metal analyses. The surficial part of the submarine extension of the mine tailings deposit is highly concentrated in As, Cd, Pb, Fe and Zn with peak concentrations adjacent to the present coastline, from where they decrease seawards before reaching average values for the Mediterranean Sea around 50-m water depth. The artificially triggered resuspension of the surface layer of the deposit led to the formation of resuspension plume about 100 m in width and up to 6 m in height. Resuspended plume was composed of fine particles which rapidly aggregated into flocs of 100 μm. While the biggest particles settled rapidly, the finest fraction remained in suspension during at least 3 h. Resuspended sediment and metal concentrations in particles remained at relatively high levels throughout the experiments following triggering. Fe, Pb, and As concentrations in resuspended particles showed a continuous increase while trawling before decreasing in parallel with the settling down of the resuspended sediments. Those metals have higher affinity with fine particles than with coarse ones, so that while the coarsest fraction from sediment plumes settled first, the finest fraction remained in suspension thus increasing the metals/sediments concentration ratio. On the other hand, Cd and Zn concentrations in suspended particles did not change significantly over time, which is thought to be caused by the fast dissolution of such metals in seawater. Beyond waste dumping itself, the observed increase in some metals in marine particulate material could have a significant impact on the adjacent coastal ecosystems due to their toxicity above certain thresholds. The consequences of the resuspension experiment here presented can be extrapolated to the impact of seafloor mining activities leading to the resuspension of metal-rich particle plumes into the water column. The experimental set-up presented here may be further explored for investigating metal behaviour during seafloor mining activities.
... As a result, the area-weighted average sediment penetration depth across all gear types corresponds to 2.44 cm. The fraction of carbon in each cell that resettles in that same cell after trawling (p crd i ) was assumed constant at 0.87, and was estimated using the average from studies that quantified the amount of sediment load lost following trawling or mining [77][78][79][80][81] . For this study we focused only on the proportion of carbon that is labile (p lab i ), and thus more prone to remineralization after a disturbance. ...
Article
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The ocean contains unique biodiversity, provides valuable food resources and is a major sink for anthropogenic carbon. Marine protected areas (MPAs) are an effective tool for restoring ocean biodiversity and ecosystem services1,2, but at present only 2.7% of the ocean is highly protected³. This low level of ocean protection is due largely to conflicts with fisheries and other extractive uses. To address this issue, here we developed a conservation planning framework to prioritize highly protected MPAs in places that would result in multiple benefits today and in the future. We find that a substantial increase in ocean protection could have triple benefits, by protecting biodiversity, boosting the yield of fisheries and securing marine carbon stocks that are at risk from human activities. Our results show that most coastal nations contain priority areas that can contribute substantially to achieving these three objectives of biodiversity protection, food provision and carbon storage. A globally coordinated effort could be nearly twice as efficient as uncoordinated, national-level conservation planning. Our flexible prioritization framework could help to inform both national marine spatial plans⁴ and global targets for marine conservation, food security and climate action.
... Together with the bottom shear stress induced by both waves and bottom currents, bottom trawling is contributing to control sediment resuspension in coastal areas [13][14][15][16][17][18][19][20]. As such, it can deeply affect surface sediments, benthic macrofauna and bioturbation [13,[21][22][23][24]. RiOMar mud fields are organically enriched as compared to surrounding sediments and often constitute preferential fishing areas [19,20]. ...
Article
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The spatial distributions of (1) surface sediment characteristics (D0.5, Sediment Surface Area (SSA), Particulate Organic Carbon (POC), Chlorophyll-a (Chl-a), Phaeophytin-a (Phaeo-a), Total and Enzymatically Hydrolyzable Amino Acids (THAA, EHAA), δ13C) and (2) sediment profile image (apparent Redox Potential Discontinuity (aRPD), numbers and depths of biological traces) characteristics were quantified based on the sampling of 32 stations located within the West Gironde Mud Patch (Bay of Biscay, NE Atlantic) in view of (1) assessing the spatial structuration of a temperate river-dominated ocean margin located in a high-energy area, (2) disentangling the impacts of hydrodynamics and bottom trawling on this structuration, and (3) comparing the West Gironde Mud Patch with the Rhône River Prodelta (located in a low-energy area). Results support the subdivision of the West Gironde Mud Patch in a proximal and a distal part and show (1) the existence of depth gradients in surface sedimentary organics characteristics and bioturbation within the distal part; (2) no evidence for a significant effect of bottom trawling, as opposed to Bottom Shear Stress, on the West Gironde Mud Patch spatial structuration; and (3) major discrepancies between spatial structuration in the West Gironde Mud Patch and the Rhône River Prodelta, which were attributed to differences in tidal regimes, sedimentation processes, and local hydrodynamics, which is in agreement with current river-dominated ocean margin typologies.
... It impacts benthic ecosystems in two ways. First, fishing gear disrupts epibenthic sediments, resulting in the loss of habitat complexity and resuspension of sediments into the water column [6][7][8] , reducing the sedimentary organic-matter content 9,10 , and increasing turbidity and biochemical oxygen demand in the water column 11,12 . Second, trawling disrupts benthic community structure, selectively removing large-bodied target and non-target species, which are usually K-selected, resulting in a community dominated by relatively small r-selected species 13,14 . ...
Article
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Bottom trawling, which is highly detrimental to seabed habitats, has been banned in some jurisdictions to mitigate the problems of habitat destruction and overfishing. However, most reports of ecosystem responses to trawling impacts originate from temperate latitudes, focusing on commercial species, and recovery of invertebrate macrobenthos from trawl ban has hardly ever been studied in the tropics. In Hong Kong (lat. 22.4°N), a history of intensive trawling with various types of gears has long degraded coastal ecosystems. To facilitate the recovery of fisheries resources and associated benthic ecosystems, the Government of the Hong Kong Special Administrative Region implemented a territory-wide trawl ban on December 31, 2012. Comparison of surveys conducted in June 2012 (before the trawl ban) and June 2015 (2.5 years after the ban) revealed higher organic contents in sediment and lower suspended-solid loads in water column, as well as a significant increase in site-based abundance, species richness, functional diversity and among-site similarity of macrobenthos after the trawl ban. Our results suggest that the imposition of a trawl ban can be an effective measure for biodiversity conservation in tropical coastal waters.
... En raison d'un accès plus hâtif aux eaux arctiques (Melia et al., 2016), les prédictions de captures de ces espèces montrent une augmentation importante d'ici 2100 pouvant atteindre 6.95 (± 5.07) millions de tonnes sous un scénario RCP8.5 (+ 4.9°C d'ici 2100) dans l'Archipel Canadien (Tai et al., 2019). Le déploiement des engins de pêche comme les chaluts hauturiers et de fond induirait, entre autres, des perturbations au sein des écosystèmes benthiques telles que la remise en suspension de la matière organique et la destruction d'habitats vulnérables, comme les structures biogéniques (Mayer et al., 1991;Palanques et al., 2001;Thrush et Dayton, 2002). Ces changements pourraient induire un changement dans la composition des communautés benthiques et réduire considérablement leur diversité ainsi que modifier le fonctionnement de l'écosystème benthique (Thrush et Dayton, 2002). ...
Thesis
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The Arctic Ocean is emerging as one of the regions that is most affected by climate change. A significant increase in precipitation and sea surface water temperatures are expected and will undeniably lead to a significant loss of sea ice cover. Because of their effects on physicochemical parameters, these changes are expected to directly impact the surface primary producers (sea ice algae and phytoplankton), thereby limiting organic matter input towards the seafloor. It is thus commonly accepted that climate change will affect the distribution, diversity and abundance of benthic communities, due to its impact on environmental parameters (pelagic-benthic coupling and physicochemical parameters), and on ecosystem services and functions (e.g., benthic remineralization). As a consequence, the decrease in sea ice cover, the desalination of the surface layer or the increase in shipping traffic in the Hudson Bay Complex and in the eastern Canadian Arctic will likely lead to major changes in benthic community structure and biogenic structural habitats. In this context and since the impacts of climate change on benthic arctic ecosystems were still poorly understood, the objectives of this thesis were to i) describe the diversity and distribution of epibenthic communities in the Hudson Bay Complex and ii) understand the effects of climate change on biodiversity and benthic ecosystem functioning. The outcomes of this thesis allowed us to i) provide the most recent survey on epibenthic organisms in the Hudson Bay Complex and their relationships with environmental variables; ii) identify diversity hotspots sensitive to climate change; and iii) document and compare benthic biodiversity and fluxes within biogenic structures and adjacent bare sediments in the Canadian Arctic. A total of 380 taxa have been identified from 46 stations sampled across the Hudson Bay Complex. Despite the relatively low spatial coverage of our sampling, we estimated that our survey represented 71% of the taxa present in the Hudson Bay Complex. We showed that biomass, abundance, diversity and spatial distribution of epibenthic communities were strongly influenced by substrate, salinity, food supply and sea ice cover. We also showed that freshwater inputs were responsible for the lowest biomass, abundance and diversity observed along the coasts. In contrast, data collected from polynyas, further offshore, showed strong pelagic-benthic coupling resulting in high productivity in terms of biomass, abundance and diversity. Moreover, hierarchical modeling of species communities highlighted the influence of sea ice and indirectly of sea ice algae on the epibenthic communities occupying the central Hudson Bay. Projections of the structure of epibenthic communities under a RCP4.5 climate scenario revealed that the central Hudson Bay emerges as the most vulnerable area to climate change with a future diversity loss related to the decrease of sea ice. On the contrary, it would appear that coastal areas will serve as refuges and increase the diversity. In addition, our study showed that the presence of biogenic structures in deep habitats improved the trapping of organic matter, leading to a higher density of infauna in these environments compared to bare sediments. Their presence has also been found to enhance sediment nutrient release in the form of nitrates and ammonium. However, our study could not demonstrate these effects in a shallower sponge habitat. By providing new knowledge on the current and future distribution of epibenthic communities in the Hudson Bay Complex and the benthic ecosystem functioning in habitats with biogenic structures, results obtained during this thesis will contribute to the designation of Ecologically and Biologically Significant Areas, as well as to the establishment of Marine Protected Areas and conservation strategies in the Arctic Ocean.
... A decrease in benthic density occurs immediately after a bottom trawling passage due to mortality resulting from damage caused by the fishing gear (Tuck et al. 1998). Fishing may also indirectly affect benthic communities by disturbing the surface sediment of the sea floor, causing sediment homogenization and reductions in habitat complexity (Palanques et al. 2001;van Denderen et al. 2015). However, the extent of the ecological impacts of fishing is mainly determined by how coastal populations behave (fishing patterns and seafood consumption) (Kuster et al. 2005). ...
Article
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Spatio-temporal patterns of macrobenthic epifaunal communities with fishing disturbances indicate that the fishing process directly leads to a decrease in diversity and substratum sediment homogenization. However, it has not yet been explored exclusively at the community reconstruction dynamic level with fishing changes over time. This study monitored the macrobenthic epifaunal communities during the implementation of a fishing moratorium policy in order to elucidate the fishing-driven variations in the macrobenthic epifaunal communities. Bottom trawl surveys were conducted before (BEF), during (DUR), and after (AFT) a summer fishing moratorium. During each survey, macrobenthic species and surface sediment samples were collected from two transects located at two different depths. The results showed that the communities in the DUR phase were undisturbed, while the communities were disturbed in both the BEF and AFT phases. Compared with the BEF and AFT phases, there was an abundance of peak spawning species as well as the impact on macrobenthic communities in relation to the lightened fishing disturbance, significant increases in species richness, abundance, and biomass were observed in the DUR phase. Prohibition of fishing during summer facilitates the resilience of macrobenthic communities by maximizing spawning and reducing bottom disturbance to larval, thereby enhancing overall fishery resources.
... Repeated dredging can lead to long-term modification of local sediment properties and particle and solute transport rates at the dredged site (Moon et al., 1994;Pilskaln et al., 1998;Mikkelsen and Pejrup, 2000), and the use of trawls and similar types of mobile fishing gear can have comparable effects (e.g. Palanques et al., 2001;. The removal of fine-grained particles from continental shelves through anthropogenic resuspension on a global scale is estimated to be up to six times as large as it would be through purely natural causes of resuspension, closely matching the input of fine-grained material from riverine sources (Oberle et al., 2016). ...
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factors, which are identified in this review and may be moderated by others, such as currents, granulometry, nutrient and matter inputs, as well as living organisms. In turn, the occurrence of exchanges can influence adjacent environments and organisms. Major gaps in the present knowledge include the temporal and spatial variation in many of the processes driving benthic/pelagic exchange processes and the variability in the relative importance of individual processes caused by this variation. Furthermore the accurate assessment of some anthropogenic impacts is deemed questionable due to a lack of baseline data, and long-term effects of anthropogenic actions are often unknown. It is suggested that future research should be transdisciplinary and at ecosystem level wherever possible, and that baseline surveys should be implemented and long-term observatories established in order to fill the current knowledge gaps.
... Palanques et al. (2001) showed evidence of how sediment re-suspension from trawlers working at 600-800 m depth reached a depth of 1200 m. ...
... Beside the functional role, benthic organisms are key factors for the sediment stability, water column turbidity, nutrients and carbon cycles, and contaminant sequestering processes (see Thrush and Dayton, 2002). Many fishing gears (trawls and dredges) are dragged over the sea bottom and their physical impact depends on their mass, the degree of contact with the seafloor and the speed of trawling, influencing particle size, resuspensions regimes, and biogeochemical fluxes (Palanques et al., 2001;Lucchetti and Sala, 2012), as well as the microbial activity (Watling et al., 2001). Moreover, the sediment quality is intimately linked to the presence of fisheries target species and to the benthic community supporting it. ...
Article
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Bivalve molluscs fishery is of great importance along the Italian coasts, both in economic and landing terms, and different edible bivalve species are harvested both in Adriatic and Tyrrhenian Seas. A medium-term assessment of the impact of the hydraulic dredges targeting razor clam Ensis minor on macro-benthic community was made during two surveys carried out in winter 2017 and late spring – summer 2018 in central Tyrrhenian Sea, which represents the main fishing ground for this species. The study area was located between 1 and 4 m depth, within 0.3 nautical miles from the coast. A net sampler (40 cm width, 18 cm height, and 14 mm mesh size) was mounted on a commercial dredge (3 m width) and enabled to collect specimens of the smallest sizes for the entire community present in the areas. A control area was identified where fishing does not occur, in order to compare exploited and not exploited sea bottoms. The results show that benthic assemblages found in dredged areas are characterized by species living in high-energy habitat, due to the closeness to the shore, and thus showing a high resilience at medium-term disturbs. Differences in species richness were not clearly evident both for the entire community and for the mollusc assemblages evaluated over the two surveys, among the control and the impacted areas, with few exceptions mainly depending on local conditions and anthropic pressure. Thus, even if the benthic community is typical of a moderately disturbed environment, the effects of fishing on the community structure are still discernible over and above the natural variation.
... Detailed knowledge of water turbidity is fundamentally important to improve understanding of marine ecosystem and many biogeochemical processes, such as productivity of planktonic and benthic algae, heat transfer in the upper water layer, and sediment transport and resuspension (Platt et al. 1988; Morel and Antoine 1994;Chen, Hu, and Muller-Karger 2007;Wu et al. 2007;Shi and Wang 2008). Water turbidity undergoes large variations as a response to changes in water components because of the dynamic hydrographic environments in oceanic waters and coastal regions (Palanques, Guillén, and Puig 2001;Doxaran et al. 2009). In general, water turbidity is mainly modulated by water constituent concentrations, such as phytoplankton, suspended solids, etc. (Kosten et al. 2012;Mao et al. 2018). ...
Article
Water turbidity plays an important role in marine biogeochemical processes and ecosystem. Remote sensing of water turbidity in the Eastern China Seas is still a challenging task due to its large variations spanning more than three orders from coastal highly turbid waters to offshore clear waters. Thus, this study developed a new blended remote sensing algorithm for accurately estimating water turbidity in the whole Eastern China Seas from Geostationary Ocean Colour Imager (GOCI). The general idea of the new blended algorithm is to combine the band forms with the best abilities for deriving water turbidity in turbid waters and relatively clear waters, respectively. Evaluations based on field data showed a good performance of the new blended algorithm with values of the determination coefficient (R²), root-mean-square error (RMSE), mean absolute error (MAE), and mean relative error (MRE) of 0.884, 47.96 NTU, 29.59 and 48.13%, respectively. The proposed algorithm was applied to the GOCI data of 2015; and large spatiotemporal variations of water turbidity in the Eastern China Seas were observed. High values of water turbidity were observed in winter for both coastal and offshore waters, whereas the lowest values were observed in summer. Sediment resuspension drove by wind and tidal forcing, and sediment transportation related to current might be responsible for spatiotemporal variations of water turbidity, while the detailed study is required for further investigations. Overall, this study provides a technological basis which can be used to understand the variation patterns of water turbidity in the Eastern China Seas from GOCI satellite measurements.
... It has already been hypothesized that the importance of sponges (Geodia spp.), through organic matter trapping and filtration, lies in the reduction of the detrital input to the adjacent soft-sediment communities, impacting the local biodiversity and carbon cycling 14 . It has also been hypothesized that the removal of the sponges will remove the structuring and functional effect of sponges, and that the increase in organic matter in the sediment if not immediately consumed by the infauna 38 , can create a local oxygen depletion. The oxygen depletion will diminish the potential of colonization due to avoidance by larvae 39 , and the habitat will take a long time to recover. ...
Article
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Deep-sea sponge grounds are vulnerable marine ecosystems, which through their benthic-pelagic coupling of nutrients, are of functional relevance to the deep-sea realm. The impact of fishing bycatch is here evaluated for the first time at a bathyal, sponge-dominated ecosystem in the high seas managed by the Northwest Atlantic Fisheries Organization. Sponge biomass surfaces created from research survey data using both random forest modeling and a gridded surface revealed 231,140 t of sponges in the area. About 65% of that biomass was protected by current fisheries closures. However, projections of trawling tracks estimated that the sponge biomass within them would be wiped out in just 1 year by the current level of fishing activity if directed on the sponges. Because these sponges filter 56,143 ± 15,047 million litres of seawater daily, consume 63.11 ± 11.83 t of organic carbon through respiration, and affect the turnover of several nitrogen nutrients, their removal would likely affect the delicate ecological equilibrium of the deep-sea benthic ecosystem. We estimated that, on Flemish Cap, the economic value associated with seawater filtration by the sponges is nearly double the market value of the fish catch. Hence, fishery closures are essential to reach sponge conservation goals as economic drivers cannot be relied upon.
... In particular, the large-size epifaunal invertebrates, such as arborescent sponges and gorgonians, can clearly be mechanically affected and show the injuries also for years after the damage (Bavestrello et al., 1998). Moreover, the documented general increase of turbidity and sedimentation along coastal areas (Mateos-Molina et al., 2015), can compromise the survival mainly of suspension feeders (Boudouresque, 1990;Palanques et al., 2001). Pollution and waste-waters affect richness and density of the biggest epifaunal species and increase the abundance of most tolerant ones and bioeroders (Hong, 1980). ...
Article
Thanks to several European directives and conventions there is a general increase of awareness regarding the key ecological role of coralligenous habitats in the Mediterranean Sea, addressing several research projects to standardize protocols for the description of its integrity. Here we surveyed 13 stations along the Italian coasts of the Western Mediterranean Sea, using video-transects technique, comparing the biological structure of coralligenous assemblages and testing the importance of their three-dimensional complexity as a proxy to define their health conditions. We considered the diversity of taxa, fishing impacts and the entity of damage on gorgonian's choenenchyme due to thermal stress, to evidence a gradient in the coralligenous health conditions. Here we developed a method to evaluate coralligenous complexity, selecting categories of taxa particularly sensitive to multiple stressors, named Structural Descriptors to describe the three-dimensional structure of the bioconcretions and to assess a unique Index of 3D - Structural Complexity.
... Trawling activities may affect the sediment community function, carbon mineralization and bio-geochemical fluxes because the physical effects of trawling are equivalent to those of an extreme bioturbator 2 . The impact of physical contact of bottom trawl fishing gear on the seabed produces a significant aftermath: It releases clouds of suspended sediment 3 ; re-suspend and bury biologically recyclable organic material 4 ; and for releases nutrients to the overlying water column 5 . Most studies of the physical processes related to towed fishing gears have focused on the hydrodynamic forces acting on the gears and the related netting/gear deformation 6 , while studies of this kind are very limited. ...
Article
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The present study was carried out to understand the impact of bottom trawling on the hydrographic, nutrient and sediment characteristics of Cuddalore and Parangipettai coastal waters during April 2014-March 2015. The present study addressed the impact of trawling on the sediment re-suspension, biochemical composition and bioavailability of organic matter in two coastal waters off Bay of Bengal. Sampling was carried out in four depth stations at 10, 20, 30, 40 m. Water and sediment samples were collected before and after trawling. The variations in total organic carbon and sediment nutrients were prominent in relation to stations and seasons. Pronounced changes were observed in water nutrients before and after trawling, while there was a minor effect on dissolved oxygen, total organic carbon and sediment nutrients. Conforming to the results, the PCA plot drawn for both the regions also revealed similar trend by the fact that the water nutrients had positive correlation with samples collected after trawling in all the stations, while dissolved oxygen, soil nutrients and total organic carbon showed negative correlation with the samples collected before trawling in all the stations.
... The effects of trawling on sediment properties are more pronounced as depth increases. Palanques et al. (2001) demonstrated that trawl-related resuspension of fine muddy sediments under stratified waters led to the production of a fine nepheloid layer at the sediment-water interface that was subject to resuspension on several successive tides. This indicates that the fine sediments within trawl tracks become unconsolidated and are themselves more prone to erosion by natural physical processes in the immediate period following initial disturbance. ...
Article
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Bottom trawling accounts for nearly a quarter of wild-capture seafood production, but it is associated with physical disturbance of the seabed leading to changes in benthic abundance, habitat structure, and biogeochemical processes. Understanding the processes of benthic depletion and recovery in relation to different types of fishing gears, and in different seabed types, is an important pre-requisite to inform appropriate management measures to limit or reduce the effects of trawling on the seabed. The combined approaches of meta-analysis and modelling that link fishing-gear penetration of the seabed to benthic depletion, and recovery to taxon longevity, have enabled the development of a modelling framework to estimate relative benthic status in areas subject to trawling. Such estimations are highly sensitive to the spatial resolution at which fishing footprint (trawl track) data are aggregated, and this leads to overinflated estimates of fishing impacts on benthos when coarse-level aggregation is applied. These approaches present a framework into which other “sustainability” criteria can be added, e.g., the consideration of carbon footprints of fishing activities.
... SSS permits the sonification of wide areas of the seafloor in relatively short periods of time [24], and it is the most approved system for underwater sound imaging of anthropogenic and natural features, and textures of the seafloor [25,26]. The locations of trawl door scars are visualized accurately by SSS sonograms [27,28] that contributed to many studies to investigate the importance of seafloor disturbances [10,[27][28][29][30][31][32][33][34][35][36][37][38][39][40]. The manual interpretation of SSS images is a laborious task that takes considerable time and there is important necessity to design computer aided image-processing systems that could automatically detect and quantify TMs. ...
Article
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Bottom trawl footprints are a prominent environmental impact of deep-sea fishery that was revealed through the evolution of underwater remote sensing technologies. Image processing techniques have been widely applied in acoustic remote sensing, but accurate trawl-mark (TM) detection is underdeveloped. The paper presents a new algorithm for the automatic detection and spatial quantification of TMs that is implemented on sidescan sonar (SSS) images of a fishing ground from the Gulf of Patras in the Eastern Mediterranean Sea. This method inspects any structure of the local seafloor in an environmentally adaptive procedure, in order to overcome the predicament of analyzing noisy and complex SSS images of the seafloor. The initial preprocessing stage deals with radiometric inconsistencies. Then, multiplex filters in the spatial domain are performed with multiscale rotated Haar-like features through integral images that locate the TM-like forms and additionally discriminate the textural characteristics of the seafloor. The final TMs are selected according to their geometric and background environment features, and the algorithm successfully produces a set of trawling-ground quantification values that could be established as a baseline measure for the status assessment of a fishing ground.
... Slope reworking may occur during periods of enhanced bottom current activity, and open continental slopes are often sites of large drift mounds. Dense water cascades from the shelf, due to trawling and seafloor mining activity, are also common (Palanques et al., 2001;Shapiro et al., 2003). Submarine landslides and debris flow deposits are not restricted to active margins, they can also be common in passive margin settings, for example Eastern United States, NW African, and Norwegian margins (e.g., Masson et al., 2010;Hodgson et al., 2018b). ...
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An estimated 8.3 billion tons of non-biodegradable plastic has been produced over the last 65 years. Much of this is not recycled and is disposed into the natural environment, has a long environmental residence time and accumulates in sedimentary systems worldwide, posing a threat to important ecosystems and potentially human health. We synthesize existing knowledge of seafloor microplastic distribution, and integrate this with process-based sedimentological models of particle transport, to provide new insights, and critically, to identify future research challenges. Compilation of published data shows that microplastics pervade the global seafloor, from abyssal plains to submarine canyons and deep-sea trenches (where they are most concentrated). However, few studies relate microplastic accumulation to sediment transport and deposition. Microplastics may enter directly into the sea as marine litter from shipping and fishing, or indirectly via fluvial and aeolian systems from terrestrial environments. The nature of the entry-point is critical to how terrestrially sourced microplastics are transferred to offshore sedimentary systems. We present models for physiographic shelf connection types related to the tectono-sedimentary regime of the margin. Beyond the shelf, the principal agents for microplastic transport are: (i) gravity-driven transport in sediment-laden flows; (ii) settling, or conveyance through biological processes, of material that was formerly floating on the surface or suspended in the water column; (iii) transport by thermohaline currents, either during settling or by reworking of deposited microplastics. We compare microplastic settling velocities to natural sediments to understand how appropriate existing sediment transport models are for explaining microplastic dispersal. Based on this analysis, and the relatively well-known behavior of deep-marine flow types, we explore the expected distribution of microplastic particles, both in individual sedimentary event deposits and within deep-marine depositional systems. Residence time within certain deposit types and depositional environments is anticipated to be variable, which has implications for the likelihood of ingestion and incorporation into the food chain, further transport, or deeper burial. We conclude that the integration of process-based sedimentological and stratigraphic knowledge with insights from modern sedimentary systems, and biological activity within them, will provide essential constraints on the transfer of microplastics to deep-marine environments, their distribution and ultimate fate, and the implications that these have for benthic ecosystems. The dispersal of anthropogenic across the sedimentary systems that cover Earth’s surface has important societal and economic implications. Sedimentologists have a key, but as-yet underplayed, role in addressing, and mitigating this globally significant issue.
... Bottom trawls were found to have severely damaged 30-50% of cold-water coral reef structures in some regions (Fosså et al., 2002), and have also been shown to considerably reduce the richness, diversity, and abundance of deep-sea soft sediment communities (Cryer et al., 2002). In addition to direct physical damage, bottom trawling resuspends sediments that can smother benthic filter feeding organisms even outside of the trawled area (Palanques et al., 2001). ...
Article
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Resolutions of the United Nations General Assembly (UNGA) require states and competent authorities to protect vulnerable marine ecosystems (VMEs), ecologically important habitats in the deep sea that are considered to be especially at risk from anthropogenic disturbances such as fishing. The lack of data concerning the location and extent of VMEs poses a significant obstacle to their protection. Habitat suitability modeling is increasingly used in spatial management planning due to its ability to predict the distribution and niche of marine organisms based on limited input data. We generated broad-scale, medium-resolution (1 km²) ensemble models for ten VME indicator taxa within the New Zealand Exclusive Economic Zone and a portion of the South Pacific Regional Fishery Management Organisation (SPRFMO) convention area. Ensemble models were constructed using a weighted average of three habitat suitability model types: Boosted Regression Trees, Maximum Entropy, and Random Forest. All models performed well, with area under the curve scores above 0.9, and ensemble models marginally outperformed any of the individual modeling approaches. Highly suitable habitat for each VME indicator taxa was predicted to occur in relatively small areas throughout the region, typically associated with elevated seafloor features with steep slopes. Determining the spatial distribution of VME indicator taxa is critical for assessing the current and historical extent of bottom trawling impacts on benthic communities, and for supporting the improved spatial management of fisheries in the South Pacific Ocean. Given the additional threats of climate change and ocean acidification to VME indicator taxa throughout the deep sea, habitat suitability modeling is likely to play an increasing role in designing effective, long-term protection measures for cumulative impacts on VMEs.
... With regard to sediment grain size, T fine sediments exhibit lower porosity than coarse sediments. Human activities such as bottom trawling can affect the natural distribution of fine and coarse sediments by removing the finest sediment fraction (Palanques et al., 2001). Hydrodynamics can also alter the distribution of fine and coarse sediments. ...
Article
In this study we tested the validity of sedimentary pigments and phytoplankton as biomarkers of upwelling events. Based on the evidence from satellite and reanalysisdatasets that unusually intense upwelling conditions occurred in summer 2014 off the SE coast of Algarve (Portugal), we looked at pigments and phytoplanktonbefore and after summer 2014 in order to test their use as biomarkers of upwelling conditions. From the analysis of summer anomalies with respect to the 2003–2014average, we show that summer 2014 was characterized by exceptional westerly winds, colder waters and higher chlorophyll, pointing to unusual upwelling con-ditions. In order to confirm or not the intense upwelling in summer 2014 suggested by satellite data, the concentration of sedimentary pigments has been quantified.Sediments were sampled offthe SE Algarve coast in spring and in summer-autumn 2014, above 60 m depth. Labile sedimentary pigments have been used asindicators of recently produced and non-degraded organic matter available as good quality food for consumers. We tested if the particular oceanographic conditionsobserved in summer 2014 were registered by sedimentary pigments by comparing their concentration and vertical distribution in spring and in summer-autumn.Based on the data on sedimentary pigments, also the phytoplankton composition has been studied. CHEMTAX software has been used to quantify the taxonomiccomposition of the phytoplankton community and it has been found that the relative contribution of dinoflagellates and diatoms to Chl-awas highest both in springand in summer-autumn. Based on the SIMPER test, the contribution of dinoflagellates and diatoms to the average square distance between seasons was low,suggesting weaker stratification of the water column also in summer-autumn, maybe related to the intense upwelling conditions of summer 2014. Oceanographicdata, together with the distribution of sedimentary pigments and phytoplankton taxa in spring and in summer-autumn, suggest that exceptional upwelling eventsoccurred in summer 2014 offthe SE coast of Algarve. 50 days' free access: https://authors.elsevier.com/c/1YUSh4wy0KatvU
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Havsbaserad vindkraft kan påverka fisk på olika sätt under anläggnings- drifts- och avvecklingsfasen. Under anläggningsfasen är lokalt ökade ljudvolymer och spridning av sediment faktorer att beakta. Under driftsfasen tillför havsbaserade vindkraftverk en hårdbottenmiljö som kan fungera som artificiellt rev där fisk ansamlas. Viktigt med en lokal bedömning av hur fisk påverkas när vindparker ska anläggas, eftersom det råder olika förutsättningar i de havsområden som omger Sverige. Mycket talar för att vindkraftverk till havs inte utgör ett hot för fiskarter eller fiskpopulationer.
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Astonishing species richness and high number of endemics make the Mediterranean Sea a biodiversity hotspot. Unfortunately, the Mediterranean Sea is also a hotspot of human pressure, because of the high population density along its coasts, the intensity of tourism, the huge volume of maritime traffic, and a rate of marine invasion with few equals in the world. Being a semi-closed basin, the Mediterranean Sea is also particularly exposed to the consequence of sea water warming. Conserving the Mediterranean marine biodiversity has therefore become a priority. A major step towards this goal has been the Barcelona Convention, adopted in 1976 and signed by all Mediterranean countries and the European Union, with the aim of protecting the marine environment and the coastal region of the Mediterranean. The aim of this Special Issue is to collate papers reporting on the results of these conservation initiatives: present status of protected habitats and species, trajectory of change in marine ecosystems, activities of marine protected areas, biodiversity monitoring and management plans.
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Industrial seabed mining is expected to cause significant impacts on marine ecosystems, including physical disturbance and the generation of plumes of toxin-laden water. Portmán Bay (NW Mediterranean Sea), where an estimated amount of 60 Mt of mine tailings from sulphide ores were dumped from 1957 to 1990, is one of the most metal-polluted marine areas in Europe and worldwide. This bay can be used to assess the impact on marine ecosystems of particle settling from sediment plumes resulting from mine tailings resuspension. With this purpose in mind, we conducted a field experiment there to investigate subsequent effects of deposition of (artificially resuspended) contaminated sediments on (i) prokaryotic abundance and meiofaunal assemblages (in terms of abundance and diversity), (ii) the availability of trophic resources (in terms of organic matter biochemical composition), and (iii) a set of ecosystem functions including meiofaunal biomass, heterotrophic C production and C degradation rates. The results of this study show that mine tailings resuspension and plume deposition led to the decline of prokaryotic abundance and nematode's biodiversity. The later decreased because of species removal and transfer along with particle resuspension and plume deposition. Such changes were also associated to a decrease of the proteins content in the sediment organic matter, faster C degradation rates and higher prokaryotic C production. Overall, this study highlights that mine tailing resuspension and ensuing particle deposition can have deleterious effects on both prokaryotes and nematode diversity, alter biogeochemical cycles and accelerate C degradation rates. These results should be considered for the assessment of the potential effects of seabed mineral exploitation on marine ecosystems at large.
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Tracks of bottom trawling gear, in particular of otter boards, have been mapped from side—scan sonar records. The extent of disturbance per unit area was quantified by relating the area covered by trawl to the total area. Frequency classes were defined and related to sediment type and water depth. The density of trawl tracks is highest below 20 m and in mud areas. Taking into account fishing effort data, it can be concluded that some areas are ploughed at least once a year by the boards alone.
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The effects of trawling disturbance on a benthic community were investigated with a manipulative field experiment in a fine muddy habitat that has been closed to fishing for over 25 yr. We examined the effects of extensive and repeated experimental trawl disturbance over an 18 mo period on benthic community structure and also followed the subsequent patterns of recovery over a further 18 mo. During the period of trawl disturbance the number of species and individuals increased and measures of diversity (Shannon's exponential H' and Simpson's reciprocal D) and evenness decreased in the trawled area relative to the reference site. The cirratulid polychaetes Chaetozone setosa and Caulleriella zetlandica were found to be most resistant to disturbance, whilst the bivalve Nucula nitidosa and polychaetes Scolopolos armiger and Nephtys cirrosa were identified as sensitive species. Multivariate analysis and abundance biomass comparison plots confirmed that community changes occurred following disturbance, with some differences between treatment and reference sites still apparent after 18 mo of recovery. Physical effects, examined with Side-scan and RoxAnn, were identifiable immediately after disturbance, but were almost indistinguishable after 18 mo of recovery. Such long recovery times suggest that even fishing during a restricted period of the year may be sufficient to maintain communities occupying fine muddy sediment habitats in an altered state.
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The passage of a beam trawl across the seabed leads to the direct mortality, or indirect mortality through subsequent predation, of some benthic species. In addition, animals retained in, or those that pass through, the cod end may also die as a result of the fishing process. The extent of this additional mortality needs to be quantified to calculate total mortality of non-target species associated with this type of fishery. Hence, we investigated the survival of animals caught by a 4 m beam trawl, in order to identify those species most sensitive to capture. Starfishes, hermit crabs and molluscs were highly resistent to the effects of capture (>60% survived in all cases). Fishes (except dogfish), sea urchins and swimming crabs suffered higher mortality after capture. Generally, the majority of the animals that passed through the meshes of the cod end survived. Experimental investigation of the cause of damage to certain species concluded that the chain matrix fitted to the gear was largely responsible for the injuries sustained. The types of injuries and their extent were species-specific, and were related to the fragility and physical characteristics of each species. Our experiments revealed that while some species are highly sensitive to capture, others are capable of surviving the effects of capture.
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This paper reviews the impact of bottom trawling — beam- or groundtrawl — on animals of the sea bed. The area of study is restricted to the North Sea, however, the final conclusions have a far wider application. Protests against the use of trawls date back to the period of their introduction; for northwest Europe this was the thirteenth century, and it still evokes protests up to the present day. Trawling does affect benthic life, the trawl penetrates up to 30 mm into the soil, depending on the substrate. All types of trawls are basically similar in their action on the bed. Beam trawls with tickler chains catch much more benthos than do ground trawls without tickler chains. Some groups of animals suffer far more damage than others, e.g. echinoderms. It is not unlikely that in the long-term a shift in species and numbers may occur along the same lines such as has been found in the German Wadden Sea where polychaetes are on the incline and molluscs and crustaceans on the decline.
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Un proceso a diferentes escalas de tiempo y espacio
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