Viability of Symbiodinium dispersed by the stoplight parrotfish Sparisoma viride Trigal Magala Velásquez-Rodríguez1, John Mario González2, Juan Armando Sánchez11 Abstract: Herbivorous fishes produce profound effects on the coral reef dynamics and represent a major role as resilience drivers. The finding of viable Symbiodinium cells in the stoplight parrotfish Sparisoma viride faeces supports the notion of these fishes as vectors of a free-living Symbiodinium (FLS) reservoir. However, the magnitude and potential effect of the zooxanthellae dispersed by S. viride was until now unknown. Thus, the purpose of this study was to estimate the FLS viable cells dispersal capacity by S. viride faeces through reefs. We aimed to quantify the number of viable vs. dead cells according to the size faeces pellets. Using a standardized protocol of flow cytometry, we found that to 23,12%±1,50 of the total zooxanthellae are viable in S. viride faeces. Moreover, there are resilience consequences related to S. viride FLS endozoochory evident with the constant input of viable symbiotic zooxanthellae in reefs. All fecal depositions analyzed contained a significant viable cells presence, suggesting a daily functional role that operates in every patch reef composed by S. viride biomass. This outstanding result, confers S. viride similar ecological attributes with herbivorous seeds dispersers in terrestrial ecosystems based on an analog endozoochorous strategy. We propose Symbiodinium icthyochorous dispersal as a new coral reef resilience driver. S. viride conservation efforts focus on overfishing regulation are a priority for the maintenance of its ecological functions and reefs` resilience feedbacks. Keywords: free-living Symbiodinium, ichthyochory, viability, parrotfishes, Sparisoma viride, reef resilience. Introduction: Coral reefs are among the most productive and diverse ecosystems in the world (Bonaldo, Hoey, & Bellwood, 2014). The contribution regarding economic, cultural, aesthetic and ecosystem services such as coastal protection, tourism and secure food sources for millions of people, confer coral reefs a unique value as research and conservation targets (Adam, Burkepile, Ruttenberg, & Paddack, 2015; Aswani et al., 2015; FAO, 2014). As a result of synergic natural and anthropogenic threats operating through hundreds of years, coral reefs face the Anthropocene era with high rates of degradation and increasing stress scenarios (Aronson & Precht, 2006; Mora, 2008; Pandolfi, 2015). Therefore, the current and future global challenge is to identify, understand and design strategies for the maintenance of coral reefs ecological functions that confers them resilience and sustainability (Bellwood, Hughes, Folke, & Nystrom, 2004). A major source of resilience capacity loss is the partial or total decrease of consumer functional groups (Bonaldo, Hoey, & Bellwood, 2014; Plass-Johnson, Ferse, Jompa, Wild, & Teichberg, 2015; Poore et al., 2012). Thus, fishes are considered the main consumers in coral reefs due to their roles in the transfer of energy between trophic groups, benthic algae communities composition, biomass and productivity shape 1 Laboratorio de Biología Molecular Marina, Departamento de Ciencias Biológicas, Universidad de los Andes. 2 Laboratorio de Ciencias Básicas Médicas, Departamento de Medicina, Universidad de los Andes. 1 effect, substrate availability for coral settlement, bioerosion, and sediment transport (Bellwood, Hughes, Folke, & Nystrom, 2004; Bonaldo et al., 2014; Mumby et al., 2006). In a global scale, overfishing constitutes the primary source of ecological functions decrease in reefs (MacNeil et al., 2015). Consequently, different size individuals and species are caught faster than others, generating a selection pressure which alters the base of trophic chains and biogeochemical processes carried by primary producers (Bellwood, Hoey, & Hughes, 2012; Poore et al., 2012). Massive herbivorous fishes extraction produce profound alterations in the reef dynamic and represent broad concern due to their role as resilience driver (Adam, Burkepile, Ruttenberg, & Paddack, 2015; Mora, 2015). In this sense, herbivorous large-bodied functional groups biomass contribute to control the benthic primary producers, promoting corals settlement, growth, and survivorship in the competitive relationship with algae (Bennett, Wernberg, Harvey, Santana-Garcon, & Saunders, 2015; Edwards et al., 2014). Parrotfishes (family Labridae, tribe Scarini) are considered the dominant herbivores in the Caribbean (Burkepile et al., 2013; Mumby et al., 2006). This monophyletic group of 10 genera and approximately 100 species with circumtropical distribution is the main contributor to consumer ecological functions in reefs (Bonaldo et al., 2014; Comeros-Raynal et al., 2012). Their beak-like oral jaws (oral teeth fused) and pharyngeal jaw apparatus, constitute functional innovations that conferred specialized feeding morphology making parrotfishes unique within reef fishes. As a result, they effectively grind calcareous material and feed on multiple substrata (algal turfs on dead coral, macroalgae, seagrass and live corals) depending on their three functional groups (Bonaldo et al., 2014; Price et al., 2010). In this sense, browsers consume macroalgae without leaving scars on the substratum and contribute to prevent coral-macroalgae phase shifts. In contrast, scrapers bite slightly into the substrate leaving a scrape signal of the removal material, while excavators make prominent scars as a result of deep bites during feeding (Francini-filho, Moura, Ferreira, & Coni, 2008; Sánchez, Gil, Chasqui, & Alvarado, 2004). Among parrotfishes ecological functions, corallivory represents a highly specialized one related with excavators feeding mode (Bonaldo et al., 2014). The stoplight parrotfish Sparisoma viride (up to 510mm fork length terminal phase) is the primary excavator at the Colombian Caribbean (Francini-filho et al., 2008; Reyes-Nivia, Garzón-Ferreira, & Rodríguez-Ramírez, 2004; Sánchez et al., 2004). For S. viride, live coral represents near 1% of the total diet, being its primary feeding substratum the Epilithic Algal Matrix (EAM) on dead coral surfaces (McAfee & Morgan, 1996), which is a complex aggregation of short filamentous algae growing in turf, mixed with microalgae, macroalgae propagules, sediment, detritus and fauna associated (Bonaldo et al., 2014). Regarding coral species preference, S. viride forages mainly on Orbicella annularis, Montastrea cavernosa, O. faveolata, O. franksi, Agaricia agaricites, Porites porites, P. astreoides, Pseudodiploria strigosa and Colpophyllia natans (Bonaldo et al., 2014; Castro-Sanguino, 2010; Reyes-Nivia et al., 2004; Rotjan & Lewis, 2005; Sánchez et al., 2004). During corallivory, S. viride ingests coral fragments that pass through the digestive tract and are released as fine sediment in subsequent defecation (Perry, Kench, O’Leary, Morgan, & Januchowski-Hartley, 2015). One functional ecology key finding made by Porto et al. (2008) and Castro-sanguino & Sánchez (2012) is the ability of unicellular dinoflagellate endosymbionts cells, referred as zooxanthellae (Symbiodinium), to survive S. viride gut passage and maintain viable in faeces. Symbiodinium studies are 2 numerous due to their role as cnidarian symbionts in the holobiont coevolution processes, specifically in scleractinian corals (Levin, Suggett, Nitschke, van Oppen, & Steinberg, 2017). The mutualistic relationship Symbiodinium-coral is based on the exchange of algal photosynthetic products and animal nitrogen compounds discarded. In detail, Symbiodinium translocates photosynthetically-fixed carbon to host as energy demand supplement promoting its calcification rates; and complementary, host confers to symbionts the inorganic nutrients required for photosynthesis and offers protection from predators (Muller-Parker, D’Elia, & Cook, 2015; Stambler, 2011). The occurrence of viable Symbiodinium cells in S. viride faeces means this parrotfish acts as a key dispersal agent (endozoochory) and supports the maintenance of zooxanthellae environmental reservoirs in reefs (Castro-sanguino & Sánchez, 2012; Porto et al., 2008). Free-living Symbiodinium (FLS) are ubiquitous in environmental reservoirs and refers to cells living outside a cnidarian host that conserve the capacity of establishing symbioses (Thornhill, Howells, Wham, Steury, & Santos, 2017). Particularly, FLS possess a motile stage with two flagella (dinomastigote). This swimming stage often alternates with the zooxanthellae coccoid one according to a diurnal pattern registered in cultures (Muller-Parker et al., 2015). The links between FLS and zooxanthellae in symbiosis are: firstly, FLS were symbiotic zooxanthellae before a host expelled it; secondly, FLS are dispersed by host larvae or corallivorous fishes; and thirdly, FLS are available for juveniles or adult hosts uptake (Cunning, Yost, Guarinello, Putnam, & Gates, 2015). Understanding FLS physiology, reproduction, distribution, dispersion and population genetics is currently limited and a priority as part of Symbiodinium life cycle comprehension (M. R. Nitschke et al., 2016; Porto et al., 2008). Research efforts developed in order to identify environmental reservoirs confirmed Symbiodinium presence in the water column (Granados-Cifuentes, Neigel, Leberg, & Rodriguez-Lanetty, 2015; Littman, van Oppen, & Willis, 2008; Takabayashi, Adams, Pochon, & Gates, 2012); benthic macroalgae beds (Porto et al., 2008; Venera-Ponton, Diaz-Pulido, Rodriguez-Lanetty,