Ciona intestinalis is a solitary tunicate with a translucent, cylindrical body that reaches 100–150 mm in height. Two siphons project from the top — one incurrent, one excurrent — filtering up to 15 litres of seawater per hour. The body is soft and gelatinous, attached at the base to any firm surface by a short stalk. Ciona occurs from the Mediterranean northward to central Norway, favouring sheltered harbours, fjords, and the relatively calm waters inside aquaculture arrays.
When water temperatures rise above 10–12 °C in late spring, Ciona populations can explode. A single individual produces thousands of eggs per spawning event, and larvae settle within 1–3 days. On mussel longlines and oyster bags, dense Ciona growth smothers stock, competes for planktonic food, and adds enough weight to sink poorly buoyed equipment. Inside salmon cages, colonies covering 60–80 % of the net surface reduce water throughflow to levels that measurably affect fish growth rates and feed conversion costs.
Ciona is soft-bodied and relatively easy to kill: air-drying for 6–12 hours or freshwater immersion for 2–4 hours destroys the tissue without harming cultured mussels or oysters. Wrasse deployed inside salmon pens graze on small individuals, slowing re-colonisation between mechanical cleans. Identifying the right treatment timing requires knowing when settlement peaks in your region. For a side-by-side look at tunicate control options, see the methods comparison, and browse related species like the club tunicate and star ascidian in our database.
Control Methods
Air-drying Freshwater treatment Manual removal Biological control (wrasse)