Seasonal patterns in the abundance of Ectopleura crocea (Cnidaria: Hydrozoa) on a shipwreck in the Northern Adriatic

Ectopleura crocea is an Anthomedusan hydroid, frequently recorded and abundant on artificial substrates. Here we examine whether the abundance of this species varies seasonally on a shipwreck in the Northern Adriatic at a depth of 10–12 m. Individuals were first found in late autumn when temperatures had dropped below 15 °C, forming scattered colonies composed of a few, small hydranths bearing immature gonophores. Substratum cover and density increased throughout late winter and spring, reaching a peak in April. At temperatures of about 19 °C, colonies were no longer present in June and remained absent throughout the summer. The polyp gut contents comprised mostly crustaceans.