Assisted recovery of mediterranean native fish species by removal of two established invasive alien species, Pterois miles and Diadema setosum

The introduction of alien species is probably one of the most important factors affecting native biodiversity in various regions of the world. The Mediterranean is considered the most affected sea in the world. Although many efforts to control several invasive alien species (IAS) have been carried out in the Mediterranean, complete success has not been obtained so far. In the eastern Mediterranean (Levantine Sea), the island of Cyprus is among the first places where marine species migrating across the Suez Canal are reported and known to have been established. To test whether native species are able to recover in the absence of IAS, removal experiments of two established IAS, the common lionfish Pterois miles and the long-spined sea urchin Diadema setosum, were carried out at two submerged rocky reefs in Cyprus where human activities are limited. A baseline period of three months was dedicated to characterizing the fish communities by visual censuses, followed by a middle period of four months of monthly removals which ended with the second and final characterization period of three months of the fish communities. The removals of D. setosum were very effective suggesting that the recolonization rate of the species is considerably low. The removals of lionfish seem to help the populations remain small, although recolonization rates are higher than D. setosum. Moreover, our results suggest that the removal of these two species helps native fish recover while conversely affecting other alien fish in a negative manner. Despite the amount of enough data, it is possible to preliminarily estimate the rate of removals. Monitoring of the two IAS along with the native flora and fauna is suggested in these two sites to identify seasonality and trends.