Metamorphosis of broadcast spawning corals in response to bacteria isolated from crustose algae

Abstract

External chemical signals provide a mechanism for broadcast-spawning scleractinian corals to recognise suitable substrata for larval settlement and metamorphosis. These morphogens can be extracted from crustose coralline algae (CCA) and the skeletons of some coral species, however the precise origin of the chemical inducers has not yet been conclusively demonstrated. Microorganisms have been reported to induce metamorphosis in various species of echinoderms, molluscs, polychaetes and cnidarians. We report that Strain A3, a species of Pseudoalteromonas isolated from the CCA Hydrolithon onkodes (Heydrich), was able to induce significant levels (up to 51.5% ± 5.8 SE) of metamorphosis of Acropora willisae Veron & Wallace, 1984 and A. millepora (Ehrenberg, 1834) larvae in laboratory assays. This experiment was repeated daily over 4 d, and the spat developed normally into juvenile polyps in flow-through aquaria. Approximately the same number of larvae underwent partial metamorphosis, forming flattened discs that were not attached to the substrata. Larvae underwent full settlement, attachment and metamorphosis only in the presence of Pseudoalteromonas A3 plus inert chips of the coral skeleton Porites sp., indicating that the calcareous matrix may play a role in the synthesis of inducers from Pseudoalteromonas Strain A3. This discovery provides evidence for a widening range of morphogenic sources and demonstrates the role that microorganisms may play in fine-scale coral recruitment. In addition, the synthesis of chemical inducers by Pseudoalteromonas Strain A3 may have biotechnological applications for reef re-seeding. KEY WORDS: Coral · Metamorphosis · Settlement · BacteriaResale or republication not permitted without written consent of the publisher

Larvae of Pocillopora damicornis (Anthozoa) settle and metamorphose in response to surface-biofilm bacteria

“…Furthermore, this and other studies have demonstrated some connection between metamorphosis of marine invertebrate larvae and bacterial species of the genus Pseudoalteromonas (Hadfield 2011). Species belonging to this genus have been shown to induce settlement of the larvae of the hydrozoan Hydractinia echinata (Müller 1973, Seipp et al 2007) and the corals Acropora willisae and A. millepora (Negri et al 2001). The species Pseudoalteromonas luteoviolacea also induces metamorphosis in the larvae of the polychaete Hydroides elegans (Huang & Hadfield 2003) and the sea urchin Heliocidaris erythrogramma (Huggett et al 2006).…”

“…Calcareous substrata, such as coral skeleton or rubble without CCA may also induce settlement (Heyward & Negri 1999). In addition to the CCA-generated morphogens, bacteria associated with CCA have been found to produce cues for the settlement of some coral species, specifically 2 species of Acropora, for which bacteria were inductive both in biofilms and in suspension (Negri et al 2001). Golbuu & Richmond (2007) who studied settlement stimuli for corals in Guam found one coral species (Goniastrea retiformis) that preferred CCA and another (Stylaraea punctata) that preferred biofilm.…”

“…Many studies testing the settlement of various coral species have led to the conclusion that CCA play a major role in settlement, with different coral species preferring a different species of CCA. Negri et al (2001) found that although a sterilized CCA (Hydrolithon onkodes) could induce settlement in the 2 species of Acropora they studied (A. willisae and A. millepora), a particular bacterial strain isolated from this CCA also induced settlement in the absence of CCA. Thus, the authors concluded that CCA might not be the sole inducer of coral settlement in these species.…”

“…Anthozoans, particularly corals, utilize a diverse range of cues. Cues can be associated with crustose coralline algae (CCA) (Morse et al 1988, 1996, Baird et al 2003, Baird & Morse 2004, Harrington et al 2004, Golbuu & Richmond 2007, Kitamura et al 2007, Ritson-Williams et al 2010, Price 2010 or marine bacteria and biofilms (Negri et al 2001, Webster et al 2004. Four species of Acropora (A. tenuis, A. millepora, A. palmata, and A. cervicornis) have been shown to preferentially settle on a particular species of CCA, Titanoderma prototypum (Harrington et al 2004, Ritson-Williams et al 2010, which is also preferred by other hard corals (Pocillopora spp.…”

Aboral localization of responsiveness to a metamorphic neuropeptide in the planula larva of Acropora tenuis

“…Microorganisms on the substrates trigger a sequence of metamorphosis and settlement, and calcareous algae (Morse et al 1996) and a bacterium (Negri et al 2001) have been identified as environmental inducers for meta morphosis of acroporids' larvae. Following reception of external cues, internal signal cascades are supposed to perform metamorphic reactions, including cell differenti ation, in larvae.…”