title: Most Low-Abundance "Background" Symbiodinium spp. Are Transitory and Have Minimal Functional Significance for Symbiotic Corals.
abstract: Speculation surrounds the importance of ecologically cryptic Symbiodinium spp. (dinoflagellates) that occur at low abundances in reef-building corals and in the surrounding environment. Evidence acquired from extensive sampling, long-term monitoring, and experimental manipulation can allow us to deduce the ecology and functional significance of these populations and whether they might contribute to the response of coral-dinoflagellate mutualisms to climate change. Quantitative PCR was used here to diagnose the prevalence, seasonal variation, and abundances of Symbiodinium spp. within and between colonies of the coral, Alveopora japonica. Consistent with broader geographic sampling, only one species comprised 99.9 %, or greater, the population of symbionts in every sample. However, other Symbiodinium including the non-mutualistic species, Symbiodinium voratum, were often detected, but at estimated cell densities thousands-fold less than the dominant symbiont. The temporal variation in prevalence and abundances of these "background" Symbiodinium could not be definitively related to any particular environmental factor including seasonality and water chemistry. The prevalence (proportion detected among host samples), but not abundance, of S. voratum may weakly correspond to increases in environmental inorganic silica (SiO2) and possibly nitrogen (NO3). When multiple background Symbiodinium occurred within an individual polyp, the average cell densities were positively correlated, suggesting non-specific processes of cell sorting and retention by the animal. While these findings substantiate the existence of a broader, yet uncharacterized, diversity of Symbiodinium, we conclude that only those species which can occur in high abundance and are temporally stable are ultimately important to coral-dinoflagellate mutualisms. Many transient Symbiodinium spp., which occur only at trace abundances in the coral's microbiome, belong to different functional guilds and likely have little, if any, importance to a coral's physiology. The successful integration between host and symbiont into a stable functional unit should therefore be considered when defining host-symbiont specificity.
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea.
authors.forename: Moo Joon
authors.initials: MJ
authors.lastname: Lee
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea. hjjeong@snu.ac.kr.
authors.forename: Hae Jin
authors.initials: HJ
authors.lastname: Jeong
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea.
authors.forename: Se Hyeon
authors.initials: SH
authors.lastname: Jang
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea.
authors.forename: Sung Yeon
authors.initials: SY
authors.lastname: Lee
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea.
authors.forename: Nam Seon
authors.initials: NS
authors.lastname: Kang
authors.affiliation: School of Earth and Environmental Sciences, College of Natural Sciences, Seoul National University, Seoul, 151-747, Republic of Korea.
authors.forename: Kyung Ha
authors.initials: KH
authors.lastname: Lee
authors.affiliation: Department of Oceanography, Kunsan National University, Kunsan, 573-701, Republic of Korea.
authors.forename: Hyung Seop
authors.initials: HS
authors.lastname: Kim
authors.affiliation: Department of Biology, 208 Mueller Laboratory, Pennsylvania State University, University Park, PA, 16802, USA.
authors.forename: Drew C
authors.initials: DC
authors.lastname: Wham
authors.affiliation: Department of Biology, 208 Mueller Laboratory, Pennsylvania State University, University Park, PA, 16802, USA. tcl3@psu.edu.
authors.forename: Todd C
authors.initials: TC
authors.lastname: LaJeunesse
mesh_terms: D000818:Animals; D037421:Anthozoa / Q000469:parasitology*; D044822:Biodiversity; D004141:Dinoflagellida / Q000145:classification / Q000302:isolation & purification / Q000502:physiology*; D009584:Nitrogen / Q000378:metabolism; D010802:Phylogeny; D012621:Seasons; D013559:Symbiosis
chemical_list: D009584:Nitrogen
keywords: Coral microbiome; Dinoflagellates; Functional ecology; Host-symbiont specificity; Quantitative PCR