Abstract
Although marine caves are among the most species-diverse habitats in the Mediterranean Sea, most available studies have focused on their sessile fauna. This study provides the first quantitative assessment of motile fauna in 27 marine caves across four geographical subareas of the Aegean and Ionian Seas, using a rapid assessment visual census protocol, applied through 3 min time transects in each ecological cave zone. Multivariate analysis revealed that the motile community structure of the cave entrance was differentiated from that of the semidark and dark zones. Deeper caves were distinct from shallower ones while caves of the east Aegean differed from those around Crete Island. A total of 163 taxa were recorded, 27 of which are reported herein for the first time in marine caves of the eastern Mediterranean Sea, while three species (two native and one introduced) are recorded in Greek waters for the first time, enriching our knowledge on the permanent and occasional cave residents. Seventeen species were introduced, comprising more than half of the total fish abundance in the southeasternmost cave. Our limited knowledge of the motile fauna of Mediterranean marine caves coupled with the continued spread of introduced species highlights the urgent need for monitoring and conservation actions, especially within marine protected areas.