Diel activity of littoral and epipelagic teleost fishes in the Mediterranean Sea

Diel activity patterns are an important aspect of behavioural ecology, yet summarising works on diel activity patterns of fishes are lacking for several regions of the world, including the Mediterranean Sea. Based on a comprehensive review of literature, internet searches, citizen science and personal observations, we compile existing knowledge of diel activity of Mediterranean pelagic and demersal teleosts commonly occurring at depths shallower than 200 m as adults (393 native and 165 newcomer species, representing 124 families), using the categories strictly or mainly diurnal and nocturnal, crepuscular, cathemeral and diel vertical migration. Most of the available data refer to foraging activity patterns of adult fishes, while knowledge of time of reproduction, migratory movements, or territorial defence remains unknown for more than half of the species. Confamilial species often have the same activity pattern, although a high plasticity or diversity in diel activity patterns is seen in some families (Belonidae, Carangidae, Clupeidae, Gadidae, Gobiidae, Scombridae, Scorpaenidae, Sparidae, and Triglidae). We found correlations between adult feeding activity patterns and trophic level, habitat use and depth range: diurnal species have a lower trophic level, prefer shallower depths, and tend to occur over hard bottoms or have multi-habitat use, nocturnal species are mostly carnivorous and prefer soft bottoms in deeper waters, while cathemeral species are commonly carnivorous and pelagic. Our results do not support the hypothesis that nocturnal Indo-Pacific immigrants are more successful colonizers. The present work highlights the perils of over-generalizing activity patterns and shows that several gaps in knowledge of diel activity patterns of fishes remain despite that such knowledge can support conservation efforts.