3.1 Sea urchin population monitoring
In February 2018, we detected another large mass mortality event
affecting the Eastern Atlantic archipelagos (Figure 2a). This time, the
mortality event was first detected on the eastern part of the
archipelago (Canary Islands), and a few weeks later it spread to
Lanzarote, Porto Santo and Madeira (Claudia Ribeiro and João Canning
Clode, personal communication) (see Figure 1 for dates), and extending
during spring and summer months (Gizzi et al. 2020). On Tenerife, there
was an overall average population reduction of 93.2% compared with
pre-mortality densities (before 2016 vs after 2018; F= 183.81,
p<0.01; Figure 2a). On La Palma island, there was an overall
population reduction of 93.1% (before 2016 vs after 2018;
F=55.30, p<0.01). It is important to note that populations on
La Palma never recovered after the first sea urchin mortality event;
densities after the event always remained lower than before the first
mortality event. For the Madeira archipelago, a rapid recovery after the
mortality have been described (Gizzi et al. 2020).