Ascidian Larvae Prefer Hydrophobic Substrates for Settlement.

Area of Science:

• Marine Biology
• Ecology
• Materials Science

Background:

• Larval settlement site selection is critical for sessile marine invertebrates.
• Understanding substrate preferences is key to controlling biofouling, a significant issue caused by species like *Ascidia sydneiensis* and *Ciona robusta*.
• Hydrophilicity and hydrophobicity of substrates influence larval settlement behavior.

Purpose of the Study:

• To investigate the substrate wettability preferences of ascidian larvae during settlement.
• To determine if ascidian larvae show a preference for hydrophilic or hydrophobic surfaces.
• To explore potential applications of these preferences in biofouling mitigation strategies.

Main Methods:

• A four-choice assay was used to test larval settlement preferences.
• Substrates with varying water wettability (contact angles: 115°, 80°, 31°, 14°) were employed.
• Three ascidian species (*Phallusia philipinennsis*, *Ascidia sydneiensis*, *Ciona robusta*) were studied.

Main Results:

• Larvae of all three ascidian species significantly preferred more hydrophobic substrates.
• No larvae settled on the most hydrophilic substrate (SH2CLHF, contact angle 14°).
• A clear preference gradient was observed, with settlement decreasing as substrate hydrophilicity increased.

Conclusions:

• Ascidian larvae exhibit a consistent preference for hydrophobic substrates.
• This preference is contrary to the use of hydrophobic materials in some antifouling applications.
• The observed substrate preference offers a novel avenue for developing effective biofouling control measures.