Renewal time and the impact of harmful algal blooms on the extensive mussel raft culture of the Iberian coastal upwelling system (SW Europe)

The extension and intensity of the upwelling season in the NW Iberian Peninsula (42°N–43°N) have decreased by 30 and 45% over the last 40 years, respectively. Accordingly, the renewal time (τ) of the Rías Baixas, four large coastal inlets where 15% of the World extraction of blue mussels occurs, has increased by 240%. We indirectly demonstrate here that the growing τ has caused the increasing occurrence of harmful microalgae in these embayments, dramatically affecting mussel raft cultivation. The equation D = 365(1 − exp(−τ/c1)) explains 80% of the variability of the number of days per year that mussels cannot be extracted from the hanging ropes because of the occurrence of harmful microalgae (D). The coefficient c1 = 37 ± 2 days indicates that an average τ over the upwelling season of >25 ± 1 or 50 ± 3 days reduce mussel extraction to only 50 or 25% of the year, respectively.