Can microscale habitat-related differences influence the abundance of ectoparasites ? Multiple evidences from two juvenile coastal fish (Perciformes: Sparidae)

The ectoparasite communities of two juvenile Diplodus species, D. sargus and D. puntazzo, were studied in a rocky coast of the Central Tyrrhenian sea (Mediterranean Sea) where three neighbouring nursery areas showed a differential availability of microhabitats due to a gradual protection gradient capable of influencing local hydrodynamic conditions. Five parasite forms were detected on juvenile hosts: Peniculus fistula, the two larval forms of gnathiids (praniza and zuphea stages), Caligus sp. and Anilocra physodes. Among these species an increasing rates of infestation (up to 57%), from the less protected to the most sheltered site, was detected. The largest infestation rate occurred in the most enclosed site, where P. fistula was the most infective species, also capable of affecting the body condition of juvenile fishes. In addition, to investigate behavioural processes among infected fish, both gut content analyses and in situ HD video sequences were used. Our results demonstrate that ectoparasites cannot be considered as accidental food items, implying an active removal of parasites among conspecifics. The highest frequencies of cleaning interactions were recorded during high ambient light conditions, suggesting the role of visual displays as an important factor in stimulating cleaning interactions.