Metamorphosis of the invasive ascidianCiona savignyi: environmental variables and chemical exposure

Abstract

In this study, the effects of environmental variables on larval metamorphosis of the solitary ascidian Ciona savignyi were investigated in a laboratory setting. The progression of metamorphic changes were tracked under various temperature, photoperiod, substrate, larval density, and vessel size regimes. Metamorphosis was maximised at 18 °C, 12:12 h subdued light:dark, smooth polystyrene substrate, and 10 larvae mL−1 in a twelve-well tissue culture plate. Eliminating the air-water interface by filling culture vessels to capacity further increased the proportion of metamorphosed larvae; 87 ± 5% of larvae completed metamorphosis within 5 days compared to 45 ± 5% in control wells. The effects of the reference antifouling compounds polygodial, portimine, oroidin, chlorothalonil, and tolylfluanid on C. savignyi were subsequently determined, highlighting (1) the sensitivity of C. savignyi metamorphosis to chemical exposure and (2) the potential to use C. savignyi larvae to screen for bioactivity in an optimised laboratory setting. The compounds were bioactive in the low ng mL−1 to high µg mL−1 range. Polygodial was chosen for additional investigations, where it was shown that mean reductions in the proportions of larvae reaching stage E were highly repeatable both within (repeatability = 14 ± 9%) and between (intermediate precision = 17 ± 3%) independent experiments. An environmental extract had no effect on the larvae but exposing larvae to both the extract and polygodial reduced potency relative to polygodial alone. This change in potency stresses the need for caution when working with complex samples, as is routinely implemented when isolating natural compounds from their biological source. Overall, the outcomes of this study highlight the sensitivity of C. savignyi metamorphosis to environmental variations and chemical exposure.

Probing the Structure–Activity Relationship of the Natural Antifouling Agent Polygodial against both Micro- and Macrofoulers by Semisynthetic Modification

“…Against C. savignyi , some of the activity is lost upon structural alteration, implying both a specific target and a drimane-linked nonionic surfactant effect. It appears that the general “drimane effect” is sufficient to generate an antifouling effect similar to that recently reported for the commercial antifouling booster biocides chlorothalonil (EC 50 0.1 μg/mL) and tolylfluanid (EC 50 0.3 μg/mL) . These inhibitory values for the commercial biocides are almost identical to those reported by Bellas against C. intestinalis, implying a comparable sensitivity of these two related species despite diverging from a common ancestor more than 180 million years ago .…”

“…It appears that the general "drimane effect" is sufficient to generate an antifouling effect similar to that recently reported for the commercial antifouling booster biocides chlorothalonil (EC 50 0.1 μg/mL) and tolylfluanid (EC 50 0.3 μg/mL). 50 These inhibitory values for the commercial biocides are almost identical to those reported by Bellas 41 against C. intestinalis, implying a comparable sensitivity of these two related species despite diverging from a common ancestor more than 180 million years ago. 51 Bellas also reported an EC 50 for Sea-nine at 0.15 μg/mL against C. intestinalis.…”

“…The compounds were screened in a laboratory bioassay based on the model taxa C. savignyi. Adult C. savignyi were collected from Nelson Marina, Nelson, New Zealand, and were held in a 1000 L recirculating system at 18 ± 1 °C, 34 ± 1 psu, and 300 ± 50 mV ORP; constant full-spectrum fluorescent light prevented premature spawning. Daily feeds comprised 250 mL of an (8–9) × 10 6 cells mL –1 Isochrysis galbana Parke algal culture.…”

“…The compounds were screened in a laboratory bioassay based on the model taxa C. savignyi. 50 respectively. Each dish of eggs received eight drops of sperm suspension from each of the two other individuals.…”

Using Virtual AChE Homology Screening to Identify Small Molecules With the Ability to Inhibit Marine Biofouling

“…The ability of the rescreened leads to inhibit the settlement and metamorphosis of the Pacific transparent sea squirt Ciona savignyi larvae was investigated. Compounds were screened for effects following methods described in Cahill et al (2016). Adult brood stock were harvested from Nelson Marina, Nelson, New Zealand and held in a recirculating seawater system (18 ± 1 • C, 33 ± 1 PSU) and fed bulk-cultured Isochorysis glabana until ready to spawn (as indicated by full egg and sperm ducts).…”