Preliminary data on the occurrence of alien macroalgae in the vermetid reef along the coasts of Favignana Island (Southern Tyrrhenian Sea)

Intertidal vermetid reefs are highly diverse systems that provide numerous habitats for animal and vegetal species, leading to an increase of intertidal biodiversity. These habitats, particularly vulnerable to environmental changes and human activities, are now experiencing high mortality in several areas of the Mediterranean Sea. Since alien macroalgae are nowadays considered one of the most serious threats to biodiversity and natural ecosystem functioning, we provide a first baseline assessment of the occurrence of alien species in the vermetid reef along the coasts of the Island of Favignana (Egadi Islands Marine Protected Area). Surveyes carried out in 2015 revealed the only presence of Caulerpa cylindracea Sonder (Bryopsidales, Caulerpaceae). The alga, exclusively recorded within the cuvettes, showed low values of abundance (class 1: cover <10%) except for San Giuseppe and Punta Longa localities where the values of abundance fell within the class 3 (cover <40% and >20%). No significant correlations were highlighted between the abundance values of C. cylindracea and those of the dominant macroalgae inhabiting the cuvettes.