Interspecific differences in fouling of two congeneric ascidians (Eudistoma olivaceum and E. capsulatum): is surface acidity an effective defense?

Abstract

Ascidian specimens were collected from the Indian River Lagoon, Florida, USA, in November 1987. Eudistoma olivaceum (Van Name) was fouled by only two species of epifaunal invertebrates and the percent cover of epibionts was negligible. Colonies of E. capsulatum (Van Name) were fouled by up to 17 species of epifaunal invertebrates, epibionts covered an average of 12.5% of the surface area of these colonies. Extracts of E. olivaceum exhibited potent cytotoxic, antimicrobial and antiviral activity in laboratory bioassays, while the activity of extracts of E. capsulatum was insignificant. The toxicity of extracts of each ascidian was negatively related to the percent cover of fouling organisms. Surface acidity of each ascidian was positively related to the percent cover of epibionts: E. olivaceum was nearly neutral (pH = 6), while E. capsulatum was highly acidic (pH = 1 to 2). Larval settlement and growth of ancestrulae of the cheilostome bryozoan Bugula neritina (Linnaeus) were inhibited at very low concentrations of crude extract of E. olivaceum. Crude extracts of E. capsulaturn inhibited settlement and growth of B. neritina only at concentrations of approximately an order of magnitude greater than those of E. olivaceum. Differences in the degree to which these congeneric ascidians are fouled is related to differences in the chemical defenses they possess. Acidity is not an effective inhibitor of settlement by epifaunal invertebrates.

Palatability and chemical anti-predatory defenses in common ascidians from the Antarctic Peninsula

“…In contrast, the literature on tropical and temperate ascidians suggests secondary metabolite feeding deterrents are more common (Young & Bingham 1987, Lindquist & Fenical 1991, Lindquist et al 1992, Pisut & Pawlik 2002, López-Legentil et al 2006). The present study provides additional information relevant to the long-standing debate about the role of inorganic acids in the provision of defenses against predation in ascidians (Parry 1984, Davis & Wright 1989, Pawlik 1993, Pisut & Pawlik 2002. Stoecker (1978Stoecker ( , 1980 concluded that sulfuric acid in the tunics of Aplousobranch and Phlebobranch ascidians deterred potential predators and inhibited fouling.…”

“…signifera that caused feeding deterrence in a suite of sympatric coral reef fish. Alkaloids (eudistomins) were also isolated from the tunic of the tropical colonial ascidian Eudistoma olivaceum (Davis & Wright 1989); these alkaloids did not deter fish feeding, but were effective as antifoulants (Davis 1991). Larvae of the Caribbean ascidian Trididemnum solidum contain a variety of secondary metabolites which deter feeding in the pinfish L. rhomboides, as well as in the sea urchin Arbacia punctulata and the sea anemone Aiptasia pallida.…”

“…In addition to organic secondary metabolites, inorganic acids have also been shown to provide chemical defenses in ascidians (Parry 1984, Davis & Wright 1989, Pawlik 1993, Pisut & Pawlik 2002. A number of species sequester sulfuric acid on their tunic surfaces or in special acid-filled surface bladder cells.…”

“…A number of species sequester sulfuric acid on their tunic surfaces or in special acid-filled surface bladder cells. These acids have been implicated both in the provision of antifoulant activity (Davis & Wright 1989) as well as serving as antifeedants (Pisut & Pawlik 2002). While there has been some suggestion that acids would be rapidly neutralized in seawater (Parry 1984), recent studies have demonstrated that their deterrent properties are retained for a period of time sufficient to deter ecologically relevant predators (Pisut & Pawlik 2002, McClintock et al 2004).…”

Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?

“…These assays, however, did not decouple the possible defenses of acids from secondary metabolites that may decrease palatability. Heavy metals, such as vanadium, have also been proposed to provide ascidians with anti-predatory and anti-fouling defenses (Stoecker, 1978(Stoecker, , 1980a, but the validity of this hypothesis was subsequently disputed (Parry, 1984;Davis and Wright, 1989;reviewed in Pawlik, 1993;however, see Discussion).…”