Chemically mediated interactions between macroalgae Dictyota spp. and multiple life-history stages of the coral Porites astreoides

Abstract

Competition between corals and macroalgae is often assumed to occur on reefs, especially those that have undergone shifts from coral to algal dominance; however, data examining these competitive interactions, especially during the early life-history stages of corals, are scarce. We conducted a series of field and outdoor seawater-table experiments to test the hypothesis that allelopathy (chemical inhibition) mediates interactions between 2 common brown macroalgae, Dictyota pulchella and D. pinnatifida, and the coral Porites astreoides at different life-history stages of the coral. D. pinnatifida significantly reduced larval survival and larval recruitment. The extracts of both D. pinnatifida and D. pulchella significantly reduced larval survival, and the extract of D. pulchella also negatively influenced larval recruitment. There was no measurable effect of the crude extracts from Dictyota spp. on the photophysiology of adult corals. Our results provide evidence that these Dictyota species chemically compete with P. astreoides by negatively affecting larval settlement and recruitment as well as the survival of larvae and new recruits. Macroalgae may perpetuate their dominance on degraded reefs by chemically inhibiting the process of coral recruitment.KEY WORDS: Allelopathy · Coral-algal interactions · Dictyota · Chemical defense · Phase shift Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 426: [161][162][163][164][165][166][167][168][169][170] 2011 Thacker et al. 1998). Habitat selection, differential growth rates and physical or chemical defenses may be important in mediating competitive interactions among species (Jackson & Buss 1975, Connell et al. 1997, Thacker et al. 1998, Knowlton & Jackson 2001, Ritson-Williams et al. 2009, Rasher & Hay 2010.Macroalgae are known to negatively influence the settlement and recruitment of coral larvae (Kuffner & Paul 2004, Birrell et al. 2005, Kuffner et al. 2006, Birrell et al. 2008a,b, Diaz-Pulido et al. 2010) and the survival and growth of juvenile corals (Birkeland 1977, Van Moorsel 1985, Box & Mumby 2007, Ritson-Williams et al. 2009). Dictyota spp., brown macroalgae common on reefs in the Florida Keys and throughout the Caribbean, caused recruitment inhibition and avoidance behavior in larvae of the coral Porites astreoides and increased the mortality rates of recruits (Kuffner et al. 2006). Dictyota spp. inhibited larval recruitment through unknown competitive mechanisms that exceeded the effects of space occupation alone. Allelochemical effects could account for this, because Dictyota spp. are known to chemically inhibit the settlement of invertebrate larvae (Schmitt et al. 1995, Walters et al. 1996 and can cause bleaching and death of adult corals in direct contact with the algae (Rasher & Hay 2010). Dictyota spp. are known to be rich in terpenoid natural products that can function as chemical defenses against generalist herbivores (Hay 1996, Paul et al. 2001, Vallim et al. 2005. To better determine the me...

Competition induces allelopathy but suppresses growth and anti-herbivore defence in a chemically rich seaweed

“…Seaweeds in the genera Dictyota, Lobophora and Halimeda have together become the spatial dominants on many degraded fore-reefs (e.g. [27,28,34]), and several species in these genera produce allelochemicals that reduce coral survival, reproduction and recruitment [28,31,33]. Whether these Caribbean seaweeds induce allelopathy in response to competition remains unknown, but our findings reveal that some chemically rich seaweeds can increase their damage to corals by inducing allelopathy.…”

“…As these seaweeds become abundant, they reduce the growth, survival and reproduction of corals [24][25][26]. Among those that proliferate, seaweeds in the genera Dictyota, Lobophora and Halimeda are chemically rich and some may use chemical warfare against coral competitors (allelopathy) to maintain dominance [28,[31][32][33]. However, it remains unknown whether coral-seaweed competition affects the concentration of allelochemicals or herbivore deterrents in seaweeds, and the effects of competition on seaweed growth remain inadequately described.…”

Natural history of coral−algae competition across a gradient of human activity in the Line Islands

“…Many macroalgae produce secondary metabolites (i.e. allelochemicals) that cause some of these negative effects on different coral life stages (Gross 2003, Rasher & Hay 2010, Paul et al 2011, Rasher et al 2011. Turf algae, a diverse assemblage of filamentous algae, also have a variety of effects on corals.…”

Spatial and temporal limits of coral-macroalgal competition: the negative impacts of macroalgal density, proximity, and history of contact

“…As competitive interactions between corals and macroalgae increase, macroalgae are expected to hasten coral decline, limit coral recovery (Burkepile & Hay 2008, Mumby & Steneck 2008, Hughes et al 2010), and enhance macroalgal resilience via positive feedbacks (Hoey & Bellwood 2011, Dell et al 2016, van de Leemput 2016). Macroalgae can harm corals via physical mechanisms such as shading, abrasion, and overgrowth (McCook et al 2001), chemical mechanisms such as allelopathy (Rasher et al 2011, Vieira et al 2016), suppression of coral settlement (Kuffner et al 2006, Paul et al 2011, Dixson et al 2014), or disruption of coral microbiomes that protect against coral pathogens (Nugues et al 2004, Smith et al 2006, Barott et al 2012, Zaneveld et al 2016). Macroalgae also alter coral interactions with corallivores (Wolf & Nugues 2013, Clements & Hay 2015, Brooker et al 2016).…”