| dc.description.abstract | Marine climate change is having an impact on individual species and fish communities at local and global scales. Under continuing climate change, marine species and communities are predicted to change their distribution to follow preferred thermal conditions. However, availability of suitable habitats and depths will limit opportunities for many species, especially those with physiological and ecological dependence on benthic habitats and demersal communities. This thesis begins in Chapter 1 by exploring existing research recording how climate change has affected marine species, especially those in the Northeast Atlantic, followed by a summary of how future marine warming is predicted to change species distributions, abundances and associated harvesting opportunities. In Chapter 2, the influence of relatively fine-scale environmental variation on European plaice (Pleuronectes platessa) growth in the North Sea is analysed. Detailed analysis of spatially segregated plaice sub-groups shows that accepted growth responses to temperature variation are not always seen in heavily exploited fish that don’t reach their full age and size potential. Chapter 3 presents current, and predicts future, distribution of key commercial fish species in the North Sea. Standardised survey data are used to develop, test and predict species abundances using generalised additive models (GAMs) coupled with climate projections to 2050. The models predict that future distributions of demersal (bottom-dwelling) fish will be strongly constrained by availability of preferred habitat at suitable depth, unless species are able to acclimate or adapt to tolerate warmer conditions or move to previously uninhabitable locations. Chapter 4 presents analysis on a newly compiled fisheries survey dataset, spanning from the southern end of Spain to the northern coast of Norway, and standardises the data using least square mean estimates of abundance. Principal coordinate analysis suggests that surface temperature is the main driver of fish assemblages, alongside salinity, depth and nitrate. Under future warming scenarios, we predict that whole fish assemblages will shift northwards and eastwards by 2050 and increasingly by 2100. Chapter 5 reports on an analysis spanning the past century of marine global warming showing that abundance increases have been more prominent in marine species studied towards the poleward extent of their ranges, with abundance declines more prominent at the equatorward extent of ranges. This evidence of omnipresent large-scale changes in abundance of marine species is consistent with warming over the last century, suggesting that adaptation has not provided a buffer against the negative effects of warmer conditions at the equatorward extent of species ranges. Together this body of research shows restrictions on distributions for many species over recent decades. However, species studied at their extreme range margins and predictions for the future show species tracking their preferred thermal range. Therefore, projected sea temperature increases of up to 1.5°C over pre-industrial levels to 2050 and 2100 will likely drive latitudinal abundance shifts in marine species. Not all species are predicted to shift at the same rate likely resulting in mismatches between more mobile species that are able to track thermal preferences and those that rely on suitable benthic and demersal habitats and communities to thrive. This has repercussions for both wider ecological functioning and commercial opportunities, especially across the heavily exploited Northeast Atlantic and for species already showing adaptive responses to fishing pressure. | en_GB |
