Kelp are large brown macroalgae living mostly in shallow subtidal rocky habitats of temperate and arctic coastal regions. There, they are important foundation species due to their complex tri-dimensional structure and high productivity, which support a large diversity of associated organisms and provide a variety of ecosystem services of ecological and economic value.

Kelp forests are naturally resilient systems. Nevertheless, they are increasingly threatened by human and natural perturbations, including climate change, coastal anthropogenic development and herbivory. In general, shifts in patterns of distribution and abundance of kelp populations can be driven by a range of top-down and bottom up processes operating at multiple scales in space and time. Populations at their distributional range edges are expected to be firstly affected. Understanding patterns of distribution of kelps and their multiple drivers acting at local and global scales is crucial for predicting their responses under scenarios of current and expected environmental variation. This scientific information is essential for effective protection and management actions of these habitat formers and of the variety of associated biodiversity and ecosystem goods and services that rely on them.

This thesis aimed at assessing, by means of surveys, field and laboratory experiments conducted from 2011 to 2016, the patterns of distribution, abundance and diversity of kelp populations in the Iberian Peninsula, and understanding how abiotic and biological factors, acting separately or in complex interactions, shape their ecological and physiological responses.