Heterotrophic feeding as a newly identified survival strategy of the dinoflagellate Symbiodinium.
Survival of free-living and symbiotic dinoflagellates (Symbiodinium spp.) in coral reefs is critical to the maintenance of a healthy coral community. Most coral reefs exist in oligotrophic waters, and their survival strategy in such nutrient-depleted waters remains largely unknown. In this study, we found that two strains of Symbiodinium spp. cultured from the environment and acquired from the tissues of the coral Alveopora japonica had the ability to feed heterotrophically. Symbiodinium spp. fed on heterotrophic bacteria, cyanobacteria (Synechococcus spp.), and small microalgae in both nutrient-replete and nutrient-depleted conditions. Cultured free-living Symbiodinium spp. displayed no autotrophic growth under nitrogen-depleted conditions, but grew when provided with prey. Our results indicate that Symbiodinium spp.'s mixotrophic activity greatly increases their chance of survival and their population growth under nitrogen-depleted conditions, which tend to prevail in coral habitats. In particular, free-living Symbiodinium cells acquired considerable nitrogen from algal prey, comparable to or greater than the direct uptake of ammonium, nitrate, nitrite, or urea. In addition, free-living Symbiodinium spp. can be a sink for planktonic cyanobacteria (Synechococcus spp.) and remove substantial portions of Synechococcus populations from coral reef waters. Our discovery of Symbiodinium's feeding alters our conventional views of the survival strategies of photosynthetic Symbiodinium and corals.
School of Earth and Environmental Sciences, Seoul National University, Seoul 151-747, Korea. hjjeong@snu.ac.kr
Hae Jin
HJ
Jeong
Yeong Du
YD
Yoo
Nam Seon
NS
Kang
An Suk
AS
Lim
Kyeong Ah
KA
Seong
Sung Yeon
SY
Lee
Moo Joon
MJ
Lee
Kyung Ha
KH
Lee
Hyung Seop
HS
Kim
Woongghi
W
Shin
Seung Won
SW
Nam
Wonho
W
Yih
Kitack
K
Lee
D001483:Base Sequence; D057894:Coral Reefs; D004141:Dinoflagellida / Q000166:cytology / Q000235:genetics* / Q000378:metabolism*; D017125:Genes, Protozoan; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism; D046940:Synechococcus / Q000378:metabolism; D014871:Water Microbiology
D009584:Nitrogen