According to the Centro de Investigacións Mariñas of Galicia barnacle captures are likely to be favoured by alterations due to climate change, though clam and cockle farming will be hit.
Clams and cockles will be negatively affected by torrential rains as their principal beds lie at the mouth of rivers. Heavy rains will bring a large influx of fresh water harmful to shellfish. High water temperatures will lead to proliferation of pathogenic agents which attack clams and cockles.
On the plus side, the production of barnacles has increased in recent years coinciding with a fall in algal blooms, though the article does not explain why. More soon when I understand this.
More on barnacles from Iberianature