Fish and cephalopods monitoring on the Bay of Biscay and Celtic Sea continental shelves

The demersal fish and cephalopod communities of the continental shelves of the Bay of Biscay and the Celtic Sea have been monitored for more than 30 years by the EVHOE series of fisheries surveys. Since 1987, a total of 4247 stations have been sampled in the fall with a GOV bottom trawl in a depth range of 15 to 600 m. The main objective of these surveys is to monitor 22 benthic fish stocks and 10 cephalopods but also to provide a description of the distribution of a total of 250 fish and 50 commercial invertebrate taxa. The dataset (https://doi.org/10.17882/80041) provides abundance and biomass information by station for all observed taxa. Size distributions for a selection of species are also available. These data are part of a larger set of standardized European surveys that provide essential information for monitoring demersal communities in the Northeast Atlantic. We propose here a critical analysis of the dataset especially in terms of the evolution of the sampling effort and strategy as well as the taxonomic precision.

Exploring the role of temperature in observed inter-population differences of Atlantic cod (Gadus morhua) growth with a 4-dimensional modelling approach

Atlantic cod (Gadus morhua) is one of the most commercially important fish species in the North Atlantic. Environmental factors, such as water temperatures, influence growth of individuals over time, thus forming population-specific growth patterns across climatic regions. Here we develop an integrative approach to investigate the role of temperature in shaping geographic differences of cod growth in the Celtic Sea, North Sea, Iceland, and Barents Sea. We combine a physiology-based growth model and 50-years observational temperature data of 0.5 × 0.5° spatial resolution to simulate continuous growth of cod. The model generated weight-at-age data for the period 1959–2007 which we compared to observational data from fishery-independent scientific surveys. In the Celtic and the northern North Sea, simulated growth matches well observational data. We also show that relatively warm temperatures in the Celtic Sea facilitate maximum growth rates; future warming is likely to have a negative impact on growth of these cod stocks. Growth simulations in Icelandic waters and the Barents Sea are less consistent with local observational data. More complex growth patterns in these regions are probably shaped by ontogenetic shifts in temperature regimes, feeding conditions and physiological adaptations. These findings should stimulate further research on critical processes to be considered in population-specific projections of growth of cod and productivity.

The Provenance of Middle Jurassic to Cretaceous sediments in the Irish and Celtic Sea Basins: Tectonic and Environmental controls on sediment sourcing

The Jurassic and Cretaceous sedimentary infill of the Irish and Celtic Sea basins is intimately associated with the breakup of the supercontinent Pangea, and the opening of the Atlantic margin. Previous basin studies have constrained tectonism, basin uplift and sediment composition, but sediment provenance and routing have not received detailed consideration. Current hypotheses for basin infill suggest localised sediment sourcing throughout the Jurassic and Cretaceous, despite a dynamic tectonic and paleoenvironmental history spanning more than 100 million years. We present detrital zircon, white mica and apatite geochronology alongside heavy mineral data from five basins. Findings reveal that basin infill derived predominantly from distal sources with lesser periods of local sourcing. We deduce that tectonically induced marine transgression and regression events had a first-order control on distal versus proximal sedimentary sourcing. Additionally, tectonism which uplifted the Fastnet Basin region during the Middle–Late Jurassic recycled basin sediments into the connected Celtic and Irish Sea Basins. Detrital geochronology and heavy mineral evidence support three distinct provenance switches throughout the Jurassic and Cretaceous in these basins. Overall an integrated multi-proxy provenance approach provides novel insights to tectonic and environmental controls on basin infill as demonstrated in the Irish and Celtic Sea Basins.

The palaeoceanographic history of the Celtic Sea since the last deglaciation and its potential for carbon storage

<p>Shelf seas account for around 10-30% of ocean productivity, 30-50% of inorganic carbon burial and up to 80% of organic carbon storage (Sharples et al., 2019); as such, shelf-sea sediments are a potential store of carbon and could play an important role in the ‘blue’ carbon cycle, and thus global climate. UK shelf-sea hydrography is dominated by seasonal stratification which drives productivity; however, stratification evolved with sea-level and tidal dynamic changes over the Holocene epoch on the UK shelf, and thus carbon stores will have changed over time. These shallow marine environments are typically seen as erosional environments and have therefore been somewhat overlooked in terms of palaeoenvironments with only a few studies from the UK continental shelf (e.g. Austin and Scourse, 1997). Here we use a core collected from the Celtic Deep, on the UK shelf, to explore environmental change, and the evolution of stratification in this setting and the potential role it plays in the global carbon cycle.</p><p>JC106-052PC, a 7.5m long marine sediment core, was recovered in 2018 at a water-depth of 116 m from the Celtic Deep (a relatively deep trough in the Celtic Sea between Britain and Ireland) as part of the BRITICE project. A radiocarbon date of 10,435 ±127 years cal BP at 4.1m suggests the core covers the Holocene epoch and preceding deglacial period. Preliminary multiproxy data from this expanded archive (ITRAX XRF, organic content, benthic foraminifera assemblages) points to changing environmental conditions and productivity potentially reflecting the evolution of seasonal stratification in the Celtic Sea over the Holocene. Work currently focuses on increasing the resolution of the benthic foraminifera record of JC106-052PC, extending the record into the deglacial period, and applying a benthic foraminifera transfer function approach to estimate sea-surface temperature of the Celtic Sea during the Holocene and deglacial period.  </p><p>This study aims to increase our understanding of the shelf-sea dynamics and productivity of the Celtic Sea over the last deglacial to Holocene period. By elucidating the response of the Celtic Sea to changing sea level and oceanographic conditions, and its capacity to act as a carbon store, we can better understand the role of other shelf environments, potentially benefiting global studies of palaeoclimate and future climate change. </p>

Using biological traits to get insights into the bentho-demersal community sensitivity to trawling in the Celtic Sea

Coastal marine ecosystems are under many pressures, including bottom trawling, which is the most widespread human activity that directly affects seabed habitats. Therefore, it is of great importance to characterize the impacts of bottom trawling on bentho-demersal communities, which can be done through the study of indicators sensitive to trawling pressure. Using a functional indicator applied to 54 underwater video transects, we mapped the sensitivity to trawling of epibenthic invertebrates and fish communities in the Celtic Sea. We determined the relative influence of environmental and fishing variables on sensitivity and traits distribution. Our results suggest that community sensitivity to trawling is mainly driven by a spatial gradient of depth and primary productivity that separates the area into two main regions: a shallow, productive area, with low sensitivity and a higher abundance of swimming and crawling organisms, and a deeper, less productive area, with higher sensitivity due to a higher abundance of fixed, filter-feeding organisms. Fishing intensity also drives the sensitivity of communities confirming that they have already been shaped by a long history of mixed fisheries. The methodology used here provides a valuable monitoring tool and could be used to predict communities’ response to changes in fishing intensity and climate change.

The Celtic Sea Through Time and Space: Ecosystem Modeling to Unravel Fishing and Climate Change Impacts on Food-Web Structure and Dynamics

Both trophic structure and biomass flow within marine food webs are influenced by the abiotic environment and anthropogenic stressors such as fishing. The abiotic environment has a large effect on species spatial distribution patterns and productivity and, consequently, spatial co-occurrence between predators and prey, while fishing alters species abundances and food-web structure. In order to disentangle the impacts of the abiotic environment and fishing in the Celtic Sea ecosystem, we developed a spatio-temporal trophic model, specifically an Ecopath with Ecosim with Ecospace model, for the period 1985–2016. In this model, particular attention was paid to the parameterization of the responses of all trophic levels to abiotic environmental changes. Satellite remote sensing data were employed to determine the spatial distribution and annual fluctuations of primary production (PP). Spatial and temporal changes in the habitat favorable for zooplankton were predicted with a novel ecological-niche approach using daily detection of productivity fronts from satellite ocean color. Finally, functional responses characterizing the effect of several abiotic environmental variables (including, among others, temperature, salinity and dissolved oxygen concentration, both at the surface and at the bottom) on fish species groups’ habitat suitability were produced from the predictions of statistical habitat models fitted to presence-absence data collected by multiple fisheries-independent surveys. The dynamic component of our model (Ecosim) was driven by time-series of fishing effort, PP, zooplankton habitat suitability and abiotic environmental variables, and was fitted to abundance and fisheries catch data. The spatial component of our model (Ecospace) was constructed, for specific years of the period 1985–2016 with contrasted abiotic environmental conditions, to predict the variable distribution of the biomass of all functional groups. We found that fishing was the main driver of observed ecosystem changes in the Celtic Sea over the period 1985–2016. However, the integration of the environmental variability into the model and the subsequent improvement of the fit of the dynamic Ecosim component highlighted (i) the control of the overall pelagic production by PP and (ii) the influence of temperature on the productivity of several trophic levels in the Celtic Sea, especially on trophic groups with warm and cold water affinities. In addition, Ecospace predictions indicated that the spatial distributions of commercial fish species may have substantially changed over the studied period. These spatial changes mainly appeared to be driven by temperature and may, therefore, largely impact future fisheries given the continuity of climatic changes.