Toxicity and palatability of some British ascidians

Bioassays were conducted to test crude extracts of nine temperate-water ascidians for bioactivity against a range of marine organisms. The extracts generally produced moderate to weak effects, with the exception of those from the ascidian Clavelina lepadiformis, which consistently produced high mortalities against invertebrates. Some of these were then tested in simple palatability assays for feeding-deterrent effects. In general, no strong effects were detected for assays with shore crabs (Carcinus maenas) and fishes (the goby Pomatoschistus minutus and the grey mullet Chelon labrosus). Feeding-deterrent effects were observed with Carcinus maenas for the extracts of Aplidium proliferum, Botryllus schlosseri and Dendrodoa grossularia. It is postulated that these ascidians are unpalatable, but no toxic effects are evident.