Abundance patterns at the invasion front: The case of Siganus luridus in Linosa (Strait of Sicily, Central Mediterranean Sea)

Abstract

The dusky spinefoot (Siganus luridus) has spread through much of the eastern Mediterranean since its introduction in 1920. In the present study, we monitored the abundance of this invader around the island of Linosa (Strait of Sicily), where the species was first recorded in 2003. Data were periodically collected along two temporal windows, 2005-06 and 2012-15, by both underwater visual census and surface snorkelling. Local ecological knowledge was investigated to gain complementary information. Both approaches highlighted significant proliferation of this tropical invader, with an average abundance of 0.36 individuals per 250m2 across the 0-30-m depth range. Dense aggregations of more than 100 adult individuals were observed in September 2015, and a coherent spatial structure at the small scale (<1km) was demonstrated. Considering the biogeographical relevance of this population, located at the western edge of its exotic distribution, these findings can be taken as a valuable case study for understanding invasion processes in the marine environment.