Welcome arrivals? The ecology and distribution of range-shifting gilthead seabream Sparus aurata in UK inshore waters
Date: 29 June 2020
University of Exeter
PhD in Biological Sciences
This thesis brings together information from three different techniques to provide novel information on the ecology of range-shifting gilthead seabream Sparus aurata in the Northeast Atlantic. My chapters take a systematic look at the ecology of S. aurata around the UK, to help explain the drivers that are facilitating the northwards ...
This thesis brings together information from three different techniques to provide novel information on the ecology of range-shifting gilthead seabream Sparus aurata in the Northeast Atlantic. My chapters take a systematic look at the ecology of S. aurata around the UK, to help explain the drivers that are facilitating the northwards range-shift. First, I use species distribution modelling to investigate the relative importance of temperature on the current distribution of S. aurata, and how it is likely to affect the species range in the future. I find that northern populations of S. aurata appear to be occupying a very different thermal niche to those in the native range, indicating that either a niche shift has occurred, or that northern populations consist primarily of non-reproducing adults. Although this distinction has important implications for successful management of the species, I also find that climate change is likely to result in a further northward shift by 2050. This climate-driven shift is likely to facilitate reproducing populations in the English Channel and the Celtic Sea, assuming that suitable nursery areas are available. Second, I use otolith microchemistry to identify whether multiple sources are contributing to S. aurata populations in the English Channel. Using a multi-element approach, I find evidence for three sources contributing to S. aurata populations in the Channel that have shared otolith chemistry, and that these are temporally stable. These sources could relate to environments that are either spatially or temporally-discrete. I also find that, although there appears to be some mixing after spawning, the three different sources do not contribute equally to populations in the Channel. This mixing could occur during larval dispersal or subsequent adult movement. The multi-element approach allows speculation as to where these sources could be and provides a basis for future research into identifying specific spawning locations. Finally, I use stable isotopes to investigate the potential consequences of increasing S. aurata populations on European seabass Dicentrarchus labrax, by examining the potential for resource competition between juveniles. I find that although both species appear to be feeding on similar prey, they also appear to have different realised niches within the study system. This apparent resource partitioning could indicate a negative competitive effect or a positive indirect effect through indirect mutualism. To my knowledge, this is the first in-depth study of S. aurata in UK waters. Therefore, this thesis provides useful information that can help inform future management measures and conservation of this target species.
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