Adult sea urchins and their embryos are ideal targets to investigate the medium- and long-term effects of various toxic agents, such as organic and inorganic pollutants, to forecast and mitigate their environmental effects. Similarly, small colonial tunicates such as Botryllid ascidians may reveal acute toxicity processes and permit quick responses for the management of contaminants impacting coastal waters, to preserve the functional integrity of marine ecosystems. This investigation compares the functional responses of two model invertebrates, the sea urchin Paracentrotus lividus and the sea squirt Botryllus schlosseri, to chronic and acute exposures to organic and inorganic toxic agents. Such heavy metals as copper produce both acute and chronic effects on marine biota, while polycyclic aromatic hydrocarbons (PAHs) mainly produce chronic effects at the concentrations ordinarily measured in marine coastal waters. Both models were tested over a range of concentrations of copper and PAHs. Copper triggered a clear effect in both species, producing a delay in the embryo development of P. lividus and a rapid death of sea squirts. B. schlosseri was less sensitive to PAHs than P. lividus. The results on both species may synergistically contribute to assess the toxicity of organic and inorganic compounds at various concentrations and different physiologic levels.

Violet sea squirts are noteworthy model organisms, because they provide insights into various physiologic processes, including cell senescence, ageing, apoptosis and allorecognition. Consequently, their culture is critical to permit experimental studies. Most papers refer to short periods of rearing using various feeds, both living and conserved, missing a formal justification for their use or indications of their actual nutritional value. Here, we use two behavioural responses—the percentage of open siphons and the frequency of zooid contractions—as compared to the abundance of suspended microparticles during feeding tests, to identify feeds able to promote filter-feeding. The results will enable to formulate compound diets that maximise positive physiological responses. Our tests demonstrated that plant items, such as dry microalgae and cyanobacteria (Arthrospira platensis, commercially known as Spirulina), along with living planktonic Haptophyta (Isochrysis galbana), trigger clear positive reactions, represented by a higher frequency of zooid contractions and larger proportions of open siphons. These responses correspond to decreases in the concentrations of suspended microparticles during the experiment and indicate higher filter-feeding activity. In contrast, feeds commonly administered to colonies, such as milk powder, dried eggs and artificial plankton, triggered negative behavioural responses, and their intake was lower during the feeding trials.