Recognition and Selection of Settlement Substrata Determine Post-Settlement Survival in Corals

Abstract

Abstract. Habitat recognition and selective settlement by dispersive propagules greatly increases the post-settlement survival chances of sessile organisms. To better understand the key role some species can play in the structure of highly complex coral reef ecosystems, we compare the role of two independent, but sequential, processes: settlement choice and post-settlement survival. This study describes the chemical and physical recognition and ranking of specific settlement substrata by coral larvae. Several species of crustose coralline algae (CCA) are known to induce coral settlement; however they also employ physical and biological anti-settlement defense strategies that vary greatly in effectiveness. We examine the interactions between settling larvae of two common reef building coral species (Acropora tenuis and A. millepora) and five species of CCA (Neogoniolithon fosliei, Porolithon onkodes, Hydrolithon reinboldii, Titanoderma prototypum, and Lithoporella melobesioides) that co-occur on reef crests and slopes of the Great Barrier Reef, Australia. Distinct settlement patterns were observed when coral larvae were provided with a choice of settlement substrata. Settlement on the most preferred substratum, the CCA species T. prototypum, was 15 times higher than on N. fosliei, the least preferred substratum. The rates of postsettlement survival of the corals also varied between CCA species in response to their antisettlement strategies (shedding of surface cell layers, overgrowth, and potential chemical deterrents). Rates of larval settlement, post-settlement survival, and the sensitivity of larvae to chemical extracts of CCA were all positively correlated across the five species of CCA. Nonliving settlement substrata on coral reefs is sparse; consequently the fact that only a few CCA species (notably T. prototypum) facilitate coral recruitment, has important implications for structuring the reef ecosystem.

Elevated seawater temperature causes a microbial shift on crustose coralline algae with implications for the recruitment of coral larvae

“…fosliei is a key reef-building primary producer on the GBR and other coral reefs (Harrington et al, 2004). The low-thermal tolerance of this species is of concern as CCA are especially vulnerable to increases in ocean acidification (pCO 2 ), which is projected to intensify under continued conditions of climate change (Kuffner et al, 2008).…”

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

“…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.…”

Effects of monsoon-driven wave action on coral reefs of Guam and implications for coral recruitment

“…If blooms of macroalgae, turf algae, or cyanobacteria dominate the benthos, coral larvae may not find appropriate space to settle or may be overgrown by the algae if they do find a place to settle (Birkeland 1977;Hughes 1989). On the other hand, larvae from Acropora, Agaricia, and other genera of corals have been shown to metamorphose in response to chemical cues found in certain species of crustose coralline algae (CCA) Hey ward and Negri 1999;Harrington et al 2004). Thus, reef areas with high CCA cover and low cover of other algae may facilitate coral recruitment if larvae are present.…”