Data collected and used for the completion of a PhD in Marine Biology. Chapter 2 contains data on count, length, weight, and condition of juvenile sea bass in different estuarine habitats, chapter 3 contains data on stomach fullness and dietary differences between habitats using dDNA metabarcoding, Chapter 4 contains data on density and length of larval sea bass over different depths on flood and ebb tides, and chapter 5 contains data on winter temperatures for multiple Essex habitats, as well as the Bay of Biscay (France) and the Tagus (Portugal), and also data on juvenile sea bass temperature dependent growth rates.