Impacts of climate change on ocean productivity sustaining world fisheries are predominantly negative but vary greatly among regions. We assessed how 39 fisheries resources-ranging from data-poor to data-rich stocks-in the North East Atlantic are most likely affected under the intermediate climate emission scenario RCP4.5 towards 2050. This region is one of the most productive waters in the world but subjected to pronounced climate change, especially in the northernmost part. In this climate impact assessment, we applied a hybrid solution combining expert opinions (scorings)-supported by an extensive literature review-with mechanistic approaches, considering stocks in three different large marine ecosystems, the North, Norwegian and Barents Seas. This approach enabled calculation of the directional effect as a function of climate exposure and sensitivity attributes (life-history schedules), focusing on local stocks (conspecifics) across latitudes rather than the species in general. The resulting synopsis (50-82°N) contributes substantially to global assessments of major fisheries (FAO, The State of World Fisheries and Aquaculture, 2020), complementing related studies off northeast United States (35-45°N) (Hare et al.,

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Lynam, C. P., Halliday, N. C., Höffle, H., Wright, P. J., van Damme, C. J. G., Edwards, M., and Pitois, S. 2013. Spatial patterns and trends in abundance of larval sandeels in the North Sea: 1950–2005 – ICES Journal of Marine Science, 70: 540–553. Early recruitment indices based on larval fish data from the Continuous Plankton Recorder (CPR) have the potential to inform stock assessments of Ammodytes marinus in the North Sea. We evaluate whether the CPR data are reliable for sandeel larvae. Spatially, CPR larval data were comparable with catches by dedicated larval samplers (Gulf and bongo nets) during ICES coordinated surveys in 2004 and 2009. ICES data are also used to explore environmental influences on sandeel distributions. Temporally, CPR data correlate with larval data from plankton surveys off Stonehaven (1999–2005), with sandeel 0-group trawl data at the east Fair Isle ground (since 1984), and with recruitment data (since 1983) for the Dogger Banks stock assessment area. Therefore, CPR data may provide an early recruit index of relative abundance for the Dogger Banks assessment area, where the majority of the commercial catch of A. marinus is taken, and the Wee Bankie area that is particularly important for seabird foraging. While warm conditions may stimulate the production of sandeel larvae, their natural mortality is typically greater, in the Dogger Banks and Wadden Sea areas, when the larvae are hatched in warm years and/or with abundant 1-year-old sandeel that are likely to be cannibalistic.

Early life stages may on average gain a survival benefit from the regular return of parent fish to the same spawning grounds. Such areas may have a considerable spatial extent, occupation of which varies between spawning seasons. Northeast Arctic cod (Gadus morhua) is an ideal candidate to pinpoint the most influential biophysical factors in these respects due to its data richness and apparently strong “homing” behaviour. Their main spawning grounds, off northern Norway, are split in two by the Lofoten archipelago, and in the previous decade strong spawning activity was observed on the seaward continental shelf (Yttersida), while in recent years spawning activity in the wide fjord (Vestfjorden), that separates the islands from the Norwegian mainland, has again increased. Time-series of egg distribution were available from the 1980s, 1990s, and 2004–2012. We used several fixed and random factors to construct a statistical model for the distribution of recently spawned eggs, and hence, spawning adults in either area. We show that the most relevant covariates for the spatial distribution of eggs in Vestfjorden are local temperature and bathymetry, while at Yttersida influence affecting the whole stock, like regional ocean climate and age structure appear more important. Therefore, spawning inside the fjord may be constrained by suboptimal environmental conditions. Yttersida may be occupied by fish which have been displaced out of Vestfjorden when preferred conditions there are of limited extent.

Seagrasses are under pressure from multiple concurrent threats, including rising temperatures, invasive species and nutrient-driven algal accumulations. We quantified the abundance of drift algae and the invasive snail Batillaria australis in 3 Halophila ovalis seagrass beds in the Swan River Estuary (Perth, Western Australia), and tested in an aquarium experiment for interactive effects of temperature (21 vs. 27°C), cover of drift algae Chaetomorpha linum (0 vs. ). In the laboratory experiment, drift algae caused increased shoot mortality and leaf loss rate, and suppressed the formation of new nodes. Drift algae also decreased the depth of the sulphide horizon in the sediment and the oxygen concentration in the water column at night, suggesting increased risk of hypoxia. Invasive snails reduced the biomass of H. ovalis leaves and roots, increased leaf plastochrone interval and decreased the depth of the sulphide horizon. Finally, elevated temperature increased leaf loss and reduced leaf biomass, and, in the presence of drift algae, also reduced the length of the 2nd internode. We found relatively few significant higher-order interactions, suggesting a dominance of additive effects of stress. We conclude that temperature, drift algae and invasive snails are already affecting the ecological performance of H. ovalis in Swan River, and that these seagrass beds are likely to come under further pressure if these stressors increase in the future.