Trawling Disturbance Research Articles

Complementarity and sensitivity of benthic state indicators to bottom-trawl fishing disturbance.

Many indicators have been developed to assess the state of benthic communities and identify seabed habitats most at risk from bottom trawling disturbance. However, the large variety of indicators and their development and application under specific geographic areas and management contexts has made it difficult to evaluate their wider utility. We compared the complementarity/uniqueness, sensitivity, and selectivity of 18 benthic indicators to pressure of bottom trawling. Seventeen common datasets with broad regional representation covering a range of pressure gradients from bottom trawling disturbance (n = 14), eutrophication (n = 1), marine pollution (n = 1), and oxygen depletion (n = 1) were used for the comparison. The outcomes of most indicators were correlated to a certain extent with response to bottom trawling disturbance, and two complementary groups of indicators were identified: diversity-based and biological trait-based indicators. Trait-based indicators that quantify the changes in relative abundance of sensitive taxa were most effective in identifying benthic community change in response to bottom trawling disturbance. None of the indicators responded to the trawling pressure gradient in all datasets, and some showed a response that were opposed to the theoretical expectation for some gradients. Indicators that showed clear responses to bottom trawling disturbance also showed clear responses in at least one other pressure gradient, suggesting those indicators are not pressure specific. These results emphasize the importance of selecting several indicators, at least one from each group (diversity and trait-based), to capture the broader signals of change in benthic communities due to bottom trawling activities. Our systematic approach offers the basis from which scientific advisors and/or managers can select suitable combinations of indicators to arrive at a sensitive and comprehensive benthic status assessment.

Physical and geochemical responses to bottom trawling on naturally disturbed sediments in the eastern Bering Sea

Abstract 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 over ∼12 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), δ13C, and δ15N isotope ratios and sediment size classes. Interannual changes observed in δ15N, 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 bottom-trawl effect 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.

Effects of sediment pulses on the deep-sea coral Goniocorella dumosa

ABSTRACT Seabed-contact activities operating in the deep sea can generate sediment plumes that pose varying levels of threat to benthic fauna. Corals are important components of deep-sea ecosystems and can be particularly sensitive to elevated suspended sediment concentrations. In this study, we exposed colony fragments of the New Zealand deep-sea scleractinian Goniocorella dumosa to four-day pulses of four target sediment concentrations: 0 mg l−1 (representing control conditions) and 45, 102 and 435 mg l−1 (targeting concentrations expected from mining and trawling disturbance). All coral fragments survived. Oxygen consumption rates were not affected by treatments and time. No visible detrimental effects on coral health were noted after the first pulse of sediment exposure. However, both a loss of coenosarc and instances of polyp mortality were observed on fragments exposed to suspended sediments during the following sediment pulses. This observed decline in coral health over time indicates that G. dumosa could cope with sediment disturbance from human activities that disturb the seafloor for periods of up to four days, but that repeated, or prolonged sediment exposure could cause a deterioration in the health condition of this species. This hypothesis should be further investigated in following studies.

Deepwater red shrimp fishery in the eastern–central Mediterranean Sea: AIS-observed monthly fishing effort and frequency over 4 years

Abstract. Deep-sea fishery in the Mediterranean Sea was historically driven by the commercial profitability of deepwater red shrimp (DWRS), and understanding spatiotemporal dynamics of fishing is key to comprehensively evaluate the status of these profitable resources and prevent stock collapse. A 4-year time series of observed monthly patterns and related frequency of trawling disturbance based on an automatic identification system (AIS) is provided with a resolution of 0.01∘×0.01∘, accounting for the spatial extent and temporal variability in deepwater (DW) bottom-contact fisheries during the period 2015–2018. The dataset was estimated from 370 fishing vessels that were found to perform trawling in deep water (400–800 m) during the study period, and they represent a significant part of the real fleet exploiting these fishing grounds in the study area. The reconstructed deepwater trawling-effort dataset is available at: https://doi.org/10.17882/89150 (Pulcinella et al., 2022). This large-scale and high-resolution dataset may help researchers of many scientific fields, as well as those involved in fishery management and in the update of existing management plans for deepwater red shrimp fisheries as foreseen in relevant recommendations of the General Fisheries Commission for the Mediterranean (GFCM).

Linking Species Functional Traits to Specific Biogeochemical Processes under Trawling Pressure.

Simple SummaryBottom trawls when fishing move over large areas with different parts of the gears physically impacting the sea bottom, including the trawling wires, doors, ground rope and net. In this way, the trawl nets remove animals from bottom waters, the sediment surface and shallow sub-surface. The animals that live in the sea bottom with their activities and lifestyle play an important role in major ecosystem processes such as nutrient cycling. In this study, we investigated the relationship between species functional characteristics and ecosystem functions under trawling pressure. Our results indicated that under trawling, more opportunistic lifestyles and deposit feeders were associated with the ecosystem processes while in the undisturbed areas these processes were connected with bioturbating and burrowing species. Finding these links helps scientists and policy makers to better predict the impact of fishing disturbance on marine environment and set appropriate thresholds for marine ecosystem impacts.The impact of otter trawling on the relationship between functional traits of benthic invertebrates and specific biogeochemical processes were investigated in the oligotrophic Cretan Sea. The fishery is managed through a seasonal closure during the summer. During two seasons (winter and summer) replicate samples were taken from the field from a commercial trawl ground and an adjacent control area. Environmental parameters related to sediment biogeochemistry were measured including particulate organic carbon, sedimentary organic carbon, bottom water and sedimentary chlorophyll a and phaeopigment concentrations as well as benthic oxygen consumption. A significant impact of trawling was recorded only for bottom water chlorophyll and sedimentary organic carbon. Furthermore, the links between species traits and specific ecosystem processes were affected by trawling, highlighting the importance of unique functional modalities on ecosystem functioning. The traits that mostly influenced benthic biogeochemistry in the control sites were related to bioturbation and burrowing activities. In contrast, in the trawled sites, the associated traits were related to more opportunistic lifestyles and deposit feeding species that do not act as bioturbators. Thus, under trawling disturbance, this shift can decouple the species-sediment relations and affect nutrient cycling.

Assessing the potential vulnerability of sedimentary carbon stores to bottom trawling disturbance within the UK EEZ

It is estimated that within the UK exclusive economic zone (UK EEZ), 524 Mt of organic carbon (OC) is stored within seabed sediment. However, the stability and potential vulnerability of OC in these sediments under anthropogenic stressors, such as bottom trawling activity, remains poorly quantified. To improve our understanding of the areas where sedimentary OC is likely to be at greatest risk from trawling events, we have developed a carbon vulnerability ranking (CVR) to identify areas of the seabed where preventative protection may be most beneficial to help maintain current OC stocks while further research continues to shed light on the fate of OC after trawling (e.g., remineralization, transport, and consumption). Predictive maps of currently available fishing intensity, OC and sediment distribution, and sediment OC lability have been generated within ArcGIS using fuzzy set theory. Our results show that the west coast of Scotland represents one of the key areas where sedimentary OC is potentially at greatest risk from bottom trawling activity. This is due mainly to the high reactivity of these OC rich sediments combined with the pressures of repetitive trawling activity within inshore waters. Our research shows that these OC hotspots are potentially at risk of disturbance from bottom trawling activity and should be prioritized for the consideration of future safeguarding (management) measures to ensure emissions are minimized and to provide greater protection of this natural carbon capital resource.

Effects of bottom trawling and hypoxia on benthic invertebrate communities

Marine benthic habitats in continental shelf regions are increasingly impacted by hypoxia caused by the combination of eutrophication and climate warming. Many regions that have the potential for hypoxic conditions are being fished by mobile bottom-contacting fishing gears. The combined effects of trawling and hypoxia may be synergistic and disproportionally impact benthic fauna, or they may act antagonistically, leading to smaller trawl impacts in hypoxic areas. Yet, few studies have quantified how bottom trawling and hypoxia interact to affect benthic communities. Here we examine these combined effects on benthic community biomass and abundance, the number of large organisms, the longevity distribution of the community and the vertical position of fauna in the sediment in the southern Baltic Sea. We find large declines in benthic biomass and abundance that co-occur with declines in near-bed oxygen concentrations from 5.8 to 0.8 ml O2 l-1. Conversely, no relationships and weak positive relationships are found between bottom trawl disturbance and benthic community biomass and abundance. No interacting effects between hypoxia and trawling are detected. Our findings therefore highlight a low likelihood of synergistic impacts of bottom trawling and hypoxia on the benthic communities studied. These results suggest that management may prioritize benthic protection from fishing in regions that are not in a state of oxygen stress.

Transport of fine-grained sediment in oceanic currents: Holocene supply to sediment drifts around Flemish Cap by the Labrador Current

Hemipelagic sediment on the upper continental slope is commonly transported from the adjacent continental shelf, but along-slope transport of sediment by thermohaline currents may be an important source of sediment. One such case is Flemish Cap, a promontory of the eastern Canadian continental shelf protected from direct continental sediment supply by the deep-water Flemish Pass. Pleistocene sediment drifts around Flemish Cap accumulated glacially derived sediment from the north, transported by the Labrador Current. This study determines the changing sources and controls on the accumulation of bioturbated hemipelagic sediment through the Holocene. From a set of >150 box cores in water depths of 600–1200 m, some 30 push cores, up to 55 cm long, were studied in detail for stratigraphic variation in grain size, bulk geochemistry (XRF) and detrital petrology (granule petrology and qXRD). Criteria were developed to identify trawling disturbance. Two Holocene stratigraphic units, A) almost lacking ice-rafted detritus and B) with some coarse IRD and higher detrital carbonate, correlate with similar units farther north on the Labrador Shelf and Slope. Sedimentation rates based on 26 radiocarbon dates were ~ 0.02–0.03 m/ka over much of the region below the 800 m isobath, locally reaching 0.1 m/ka in some sediment drifts, but as low as 0.01 m/ka on southeastern Flemish Cap. Where sedimentation rate was >0.03 m/ka, the record of flow vigor from the sortable silt proxy since 6 ka shows three different zones of Labrador Current flow with different timing of changes in flow vigor. The mid to early Holocene record shows that the meltwater-driven inner Labrador Current extended across the entire study area. Where sedimentation rates are lower, periods of sediment bypassing are inferred and the sortable silt record varies little. Correlation with external drivers is hampered by century-scale core resolution and sparse dating control. The distinctive abundance of dolomite rock flour in hemipelagic sediments around Flemish Cap indicates important supply from Baffin Bay icebergs during the entire Holocene, diluted prior to 6 ka by sediment from Hudson Strait and some Labrador ice streams. Baffin Bay icebergs melt preferentially in the southern Labrador Sea, dropping their load, with the fine grained component transported to the south by the Labrador Current. Similar partitioning of coarse- from fine-grained components of IRD may take place on other high-latitude outer continental margins.

Ecosystem Functioning Under the Influence of Bottom-Trawling Disturbance: An Experimental Approach and Field Observations From a Continental Slope Area in the West Iberian Margin

Understanding the effects of bottom-trawling induced changes in benthic community structure, diversity and ecosystem functioning across different benthic-size components is imperative to determine the future sustainability of bottom-trawling fisheries in deep-sea regions. In this study, we combined field sampling observations with a pulse-chase experiment on sediments obtained from two stations of interest along the West Iberian Margin (WIM) distinguished by different trawling pressures. We compared these two stations in terms of meio- and macrofauna (infauna) standing stocks, biodiversity and several ecosystem function proxies. These proxies included: (i) 13C uptake by bacterial communities, (ii) infauna respiration rates, (iii) penetration of 13C in the sediment, and (iv) sediment pore-water nutrient concentrations. The pulse-chase experimental results were complemented with a larger biological dataset partially compiled from previous studies in the area, to investigate structural and functional diversity ecosystem functioning (respiration) patterns across the WIM. Our observations indicated that different regimes of trawling pressure influenced both macrofaunal respiration rates with disturbed sediments predominantly composed of deposit-/detritus-feeding smaller-sized macrofauna species. Moreover, sediment biogeochemical functioning (ammonium profiles) and 13C bacterial uptake showed differences among the two disturbance regimes. On the contrary, the biomass of small-sized biota, including bacteria and meiofauna, did not show marked differences between stations. The general depletion in macrofauna species richness across impacted areas of the study region was also correlated with a reduction in total biomass and respiration, suggesting that the long history of trawling disturbance at the WIM may affect regulatory ecosystem functions. These preliminary findings alert for the impacts of trawling on crucial functions of benthic ecosystems that may be imperceptible to the current tools used in monitoring programs.

Bottom trawling reduces benthic denitrification and has the potential to influence the global nitrogen cycle

AbstractBottom trawling and eutrophication are large stressors that are critically coupled. Here we show, using a before‐after control‐effect design, the significant reduction in denitrification as a result of experimental bottom trawling in a shallow coastal system. Trawl disturbance destroys the complex three‐dimensional redox structures in surface sediments that maximize denitrification potential, resulting in up to a 50% reduction in net denitrification. The decrease in net denitrification also increased after each trawling event suggesting a declining resilience to trawling and eutrophication. Bottom trawling occurs at such a large scale that it could result in significant amounts of nitrogen being retained on the continental shelf. As such, impacts on the global ocean nitrogen cycle and associated eutrophication should be counted among the many negative consequences of extensive seafloor trawling.

Using large benthic macrofauna to refine and improve ecological indicators of bottom trawling disturbance

Abstract Bottom trawling alters the abundance, diversity, size-composition, and function of benthic communities. However, the ability to detect these impacts over large spatial scales can be obscured by various complicating factors, such as community adaptation to disturbance and co-varying environmental conditions. An ecosystem-based approach to fisheries management therefore requires ecological indicators which can ‘disentangle’ trawling effects from other natural and human drivers, and respond effectively to shifts in ecological quality. We collected benthic macrofaunal samples at 21 sites across a Norway lobster Nephrops norvegicus fishing ground in the Kattegat, and separated the benthic community into small (1–4 mm) and large (>4 mm) size fractions. Four taxonomic indicators (total density, species density, Shannon diversity, and biomass) and four functional indicators (functional diversity, functional richness, functional evenness, and functional dispersion) were calculated based on each size fraction, and the two fractions combined (pooled community). Here, we compare the ability of these indicators to detect trawling impacts across size categories. We show that indicators derived from large macrofauna were highly effective in this regard, and were less influenced by other environmental drivers, such as depth, sediment grain size, bottom current velocity, salinity, and temperature. This suggests that the taxonomic and functional characteristics of benthic communities display a size-dependent sensitivity to trawling disturbance, and therefore community metrics based on large benthic macrofauna may provide useful indicators. By contrast, indicators derived from the small fraction performed poorly, and those based on the pooled community demonstrated a varied ability to detect trawling. Small macrofauna are typically characterised by high density, diversity, and population growth rates, and their relative resilience to trawling may mask the response of the more sensitive macrofauna. This highlights an underlying issue with calculating indicators based on the whole benthic community. The approach outline here is easily applied, improves indicator performance, and has the potential to reduce laboratory workloads due to the fewer taxa and individuals required for analyses.

Evaluating impacts of bottom trawling and hypoxia on benthic communities at the local, habitat, and regional scale using a modelling approach

Abstract Bottom trawling disturbance and hypoxia are affecting marine benthic habitats worldwide. We present an approach to predict their effects on benthic communities, and use the approach to estimate the state, the biomass relative to carrying capacity, of the Baltic Sea at the local, habitat, and regional scale. Responses to both pressures are expected to depend on the longevity of fauna, which is predicted from benthic data from 1558 locations. We find that communities in low-salinity regions mostly consist of short-lived species, which are, in our model, more resilient than those of the saline areas. The model predicts that in 14% of the Baltic Sea region benthic biomass is reduced by at least 50%, whereas an additional 8% of the region has reductions of 10–50%. The effects of hypoxia occur over larger spatial scales and lead to a low state of especially deep habitats. The approach is based on a simple characterization of the benthic community, which comes with high uncertainty, but allows for the identification of benthic habitats that are at greatest risk and prioritization of management actions at the regional scale. This information supports the development of sustainable approaches to manage impact of human activities on benthic ecosystems.

Acute impacts of bottom trawl gears on benthic metabolism and nutrient cycling

Abstract Research on the environmental impacts of bottom fishing gears has focused mainly on structural characteristics of benthic habitats such as faunal composition and the physical features of the seafloor. This study focuses more on functional characteristics by addressing the biogeochemical consequences associated with tickler chain beam trawl and electric PulseWing trawl gears. In June 2017, professional fishermen trawled experimental transects with both types of gears in the Frisian Front area of the North Sea. Box core sediment samples and in situ landers were used to evaluate biogeochemical fluxes and sediment characteristics in untrawled and trawled areas (samples taken 3.5–70 h after fishing). A reduction of sedimentary chlorophyll a was observed, which was larger following tickler chain (83%) compared to PulseWing trawling (43%). This displacement of surface material caused significant decreases in the sediment oxygen consumption in tickler chain (41%) and PulseWing trawled samples (33%) along with a deeper penetration of oxygen in the sediment (tickler chain: 3.78 mm, PulseWing: 3.17 mm) compared to untrawled areas (2.27 mm). Our research implies that bottom trawl disturbance can lead to immediate declines in benthic community metabolism, with tickler chain trawling exhibiting more prominent alterations than PulseWing trawling on benthic biogeochemical processes.

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

Ascidians (Chordata: Tunicata) from circalittoral and upper-bathyal soft bottoms of the Iberian Mediterranean. Bottom trawling impact

Responses of the infaunal peracarid Monokalliapseudes schubarti (Tanaidacea: Kalliapseudidae) to a bottom trawling disturbance and seasonality in an estuary of southern Brazil

ABSTRACTThe tanaid Monokalliapseudes schubarti is one of the dominant macrobenthic species in the shallow mudflats of southern Brazil. This species plays an important role in local trophic webs as a primary consumer and as a prey. This work investigated (1) the temporal variations in the population densities and structure of M. schubarti in the Patos Lagoon Estuary and (2) the potential impacts of shrimp trawling on the population densities, population structure and vertical stratification of the species in shallow areas of the estuary. The species exhibited significant temporal variability in its total densities and population structure, with a reproductive period observed during late summer and autumn, following an increase in salinity within the estuary. There were significant differences in M. schubarti densities, which appeared to be associated with variations in sediment texture and salinity. No well-defined pattern of trawling impact was identified; however, after high-impact trawling, decreases in the abundance of males and juveniles in the sediment superficial layer were recorded, and ovigerous females disappeared from the sampled area with relatively higher percentages of medium sand. Changes in the densities of different morphological categories observed after trawling were likely due to mortality, resuspension or rapid movement deeper into their tubes.

Response of soft-bottom macrobenthic assemblages to artisanal trawling fisheries in a subtropical estuary

Bottom trawling is one of the most harmful and widespread activities affecting benthic habitats and fauna. In this study, we analyzed the impact of shrimp trawling fisheries on the densities, assemblage structure and vertical stratification of the benthic macrofauna in shallow mudflats of the Patos Lagoon Estuary (Brazil). Experimental trawls of different intensities were performed during three shrimp fishing seasons (2015–2017), comparing macrofauna among before and after trawling, and a control zone. The changes in macrofaunal assemblages were more consistently related to natural variability than to trawling impact, being mostly influenced by sediment structure and salinity variation. The trawling impact was mainly detected in the area with higher percentages of fine sediments, with different macrofaunal responses in each month and stratum. Some non-significant decreases on total densities after trawling were observed, mainly on the superficial stratum, and signs of burial activities. The response to trawling disturbance of each species was different and it highly depended on their natural variability. Only five species showed significant variation to the trawling treatment (Erodona mactroides, Heleobia australis, H. charruana, Heteromastus similis and Laeonereis acuta), with temporally different responses. Decreasing densities were more related to the high impact treatment. In some seasons, decreases on the abundance of Monokalliapseudes schubarti after high impact trawls were up to 60% of the seasonal mean densities. Trawling fisheries may reduce macrobenthic densities but not their vertical stratification. The impact of trawling on key species may compromise the ecosystem function, as benthic macrofauna provide food sources for many aquatic resources. This study highlights trawling impacts in an estuarine nursery area, which should be fully considered since they may be reflected in the trophic webs.

Determining and mapping species sensitivity to trawling impacts: the BEnthos Sensitivity Index to Trawling Operations (BESITO)

Applying an ecosystem approach requires a deep and holistic understanding of interactions between human activities and ecosystems. Bottom trawling is the most widespread physical human disturbance in the seabed and produces a wide range of direct and indirect impacts on benthic ecosystems. In this work, we develop a new index, the BEnthos Sensitivity Index to Trawling Operations (BESITO), using biological traits to classify species according to their sensitivity to bottom trawling. Seventy-nine different benthic taxa were classified according to their BESITO scores in three groups. The effect of trawling on the relative abundance of each group (measured as biomass proportion) was analysed using General Additive Models (GAMs) in a distribution model framework. The distribution of the relative biomass of each group was mapped and the impact of trawling was computed. Species with the lowest BESITO score (group I) showed a positive response to trawling disturbance (opportunistic response) whereas species with values higher than 2 (group III) showed a negative response (sensitive response). Species with a BESITO score of 2 did not show a significant response to the pressure (tolerant response). Trawling disturbance reduced relative biomass of sensitive species by 31% across the study area. This value increased to 46% when shelf-break was considered in isolation and reached values of 59.6% in the most impacted habitat (deep-sea muddy sands). The new index classified successfully the analysed species according to their sensitivity to trawling allowing modeling the impact of trawling disturbance on sensitive species, without the masking effect of opposed responses.

Benthic assemblages from a disturbed region by bottom-trawling fisheries off the SW Portuguese Margin

Event Abstract Back to Event Benthic assemblages from a disturbed region by bottom-trawling fisheries off the SW Portuguese Margin Sofia P. Ramalho1, 2*, Clara F. Rodrigues1, Mariana Almeida1, Patricia Esquete1, Luciana Génio1, Ascensão Ravara1, Nikolaos Lampadariou3, Ann Vanreusel2 and Marina R. Cunha1 1 University of Aveiro, Departamento de Biologia & CESAM, Portugal 2 Ghent University, Department of Biology, Marine Biology Research Group, Belgium 3 Hellenic Centre for Marine Research, Institute of Oceanography, Greece Bottom trawlers in operation off the SW Portuguese margin target predominantly deep-sea muddy-sediment areas bellow 200m water depth. To better understand the effects caused by this practice on the deep-sea benthic habitats biodiversity, three areas of interest along a continental slope area off the SW Portuguese margin were selected, using Vessel Monitoring Systems (VMS) data and in-situ observations obtained from Remotely Operated Vehicle (ROV) video surveys. These areas included a not trawled area, the main fishing ground and an area adjacent to the main fishing ground. In addition to video surveys, which allowed characterizing mega-epibenthic assemblages, replicate sediment samples across these areas were obtained for the study of macrobenthic assemblages, in terms of total standing stocks (abundance and biomass), total respiration, composition and both taxonomic and trophic diversity. Results showed that, in addition to the habitat heterogeneity associated with the study area, trawling pressure represents an important component of variation of the observed communities. Both fishing grounds that are recurrently impacted by trawling, and the adjacent areas that may be indirectly impacted by the re-suspended sediments and sporadically affected by trawl passages, showed a depletion of both mega-epibenthic and macro-infaunal abundances, lower taxonomic and trophic richness in comparison to undisturbed sites. Moreover, a lower functional redundancy resulting from the loss of species within most feeding guilds was observed in the macrofaunal core assemblage (i.e. characteristic, dominant or frequent taxa) of the areas under trawling disturbance. These results highlight the vulnerability of the deep-sea benthic ecosystems off the SW Portuguese margin to further increases in natural and anthropogenic disturbance or their synergistic effects. Acknowledgements This work was supported by CESAM (UID/AMB/50017) funds, granted by Fundação para a Ciência e a Tecnologia (FCT)/MEC through national funds, and co-funded by FEDER, within the PT2020 Partnership Agreement and Compete 2020. SPR work was funded through a MARES Grant, under Erasmus Mundus programme coordinated by Ghent University (FPA 2011-0016). CFR, PE, AR and LG were supported by the FCT grants SFRH/ BPD/107805/2015, SFRH/BPD/94985/2013, SFRH/BPD/112408/2015 and SFRH/BPD/96142/2013, respectively. Keywords: Mega-epifauna, macrofauna, Upper continental slope, trophic and structural biodiversity; disturbance, bottom-trawling fisheries, West Iberian Margin Conference: IMMR'18 | International Meeting on Marine Research 2018, Peniche, Portugal, 5 Jul - 6 Jul, 2018. Presentation Type: Oral Presentation Topic: Fisheries and Management Citation: Ramalho SP, Rodrigues CF, Almeida M, Esquete P, Génio L, Ravara A, Lampadariou N, Vanreusel A and Cunha MR (2019). Benthic assemblages from a disturbed region by bottom-trawling fisheries off the SW Portuguese Margin. Front. Mar. Sci. Conference Abstract: IMMR'18 | International Meeting on Marine Research 2018. doi: 10.3389/conf.FMARS.2018.06.00143 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 28 Apr 2018; Published Online: 07 Jan 2019. * Correspondence: PhD. Sofia P Ramalho, University of Aveiro, Departamento de Biologia & CESAM, Aveiro, Portugal, Portugal, sofia.pinto.ramalho@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Sofia P Ramalho Clara F Rodrigues Mariana Almeida Patricia Esquete Luciana Génio Ascensão Ravara Nikolaos Lampadariou Ann Vanreusel Marina R Cunha Google Sofia P Ramalho Clara F Rodrigues Mariana Almeida Patricia Esquete Luciana Génio Ascensão Ravara Nikolaos Lampadariou Ann Vanreusel Marina R Cunha Google Scholar Sofia P Ramalho Clara F Rodrigues Mariana Almeida Patricia Esquete Luciana Génio Ascensão Ravara Nikolaos Lampadariou Ann Vanreusel Marina R Cunha PubMed Sofia P Ramalho Clara F Rodrigues Mariana Almeida Patricia Esquete Luciana Génio Ascensão Ravara Nikolaos Lampadariou Ann Vanreusel Marina R Cunha Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Deep-Sea Mega-Epibenthic Assemblages from the SW Portuguese Margin (NE Atlantic) Subjected to Bottom-Trawling Fisheries

Bottom trawling fisheries are a common threat to the health of continental margins worldwide. Together with numerous environmental and biological processes, physical disturbance induced by trawlers can largely shape the benthic habitats and their associated assemblages. At the SW Portuguese Margin, crustacean bottom trawlers have exploited deep-sea habitats for a few decades, but its effects on the benthic biodiversity are practically unknown. During the spring-summer of 2013 and 2014, several Remotely Operated Vehicle (ROV) video transects were used to investigate mega-epibenthic abundance, composition and diversity in soft-sediment areas subjected to varying trawling pressures off Sines and Setubal (200-800 m). Differences in mega-epibenthic assemblages were linked with environmental changes (depth, grain size, primary productivity) and trawling disturbance. The effect of trawling was assessed between segments with similar habitat characteristics, i.e. muddy-sand bottoms between 300–500 m. Areas subjected to intensive trawling pressure showed a generally flattened seabed, with abundant recent trawl marks (up to 3 scars/100 m), indicating that the seabed physical integrity was compromised. Significant negative correlations were detected between various mega-epibenthic diversity indices (S, H’ and ET(20)) and trawling pressure (h.cell-1.y-1). Furthermore, the distinct mega-epibenthic assemblages and absence of several sessile erect morphospecies at both low and highly disturbed locations by trawling off Sines, namely all seapen morphospecies found in non-trawled areas, demonstrates the negative influence of trawling fisheries on the benthic component of the study area. Also, low dissimilarity between assemblages from the main fishing grounds and the adjacent low-disturbance locations, suggests that the potentially negative influence of trawling can extend beyond the targeted areas (e.g. by the plumes of re-suspended sediments). The observed deleterious effects of trawling on mega-epibenthic fauna together with the intensification of trawling pressure in the study area, stress the need for adequate monitoring programs and regulatory measures to halt the long-term loss of biodiversity and allow the sustainability of fisheries at the SW Portuguese Margin.

Using underwater video to assess megabenthic community vulnerability to trawling in the Grande Vasière (Bay of Biscay)

SUMMARYTrawling activities are considered to be one of the main sources of disturbance to the seabed worldwide. We aimed to disentangle the dominance of environmental variations and trawling intensity in order to explain the distribution of diversity patterns over 152 sampling sites in the French trawl fishing-ground, the Grande Vasière. Using a towed underwater video device, we identified 39 taxa to the finest taxonomic level possible, which were clustered according to their vulnerability to trawling disturbance based on functional traits. Using generalized linear models, we investigated whether the density distribution of each vulnerability group was sensitive to trawling intensity and habitat characteristics. Our analyses revealed a structuring effect of depth and substratum on community structure. The distribution of the more vulnerable group was a negative function of trawling intensity, while the distributions of the less vulnerable groups were independent of trawling intensity. Video monitoring coupled with trait-based vulnerability assessment of macro-epibenthic communities might be more relevant than the traditional taxonomic approach to identifying the areas that are most vulnerable to fishing activities in conservation planning.