Expulsion of zooxanthellae (Symbiodinium) from several species of scleractinian corals: comparison under non-stress conditions and thermal stress conditions

Abstract

Corals expel zooxanthellae (Symbiodinium) not only under thermal stress conditions, but also under nonstress conditions. To better understand the significance of this, we compared cell numbers, morphologies and photosynthetic activities of the expelled Symbiodinium under different temperatures for six species of scleractinian corals; Acropora selago, Acropora muricata, Heliofungia actiniformis, Ctenactis echinata, Oxypora lacera and Pocil lopora eydouxi, kept in aquariua. During the eight day aquarium experiment, every coral expelled two types of Symbiodinium morphologies, normal and degraded form, and the ratios of these forms differed depending on the temperature. Under a non-stress, initial temperature condition of 27℃, mainly degraded cells were expelled. In contrast, when the water temperature was increased and reached to 32℃, the expulsion rates drastically increased,

Finding of 132, 173‐cyclopheophorbide a enol as a degradation product of chlorophyll in shrunk zooxanthellae of the coral Montipora digitata

“…Zooxanthellae with shrunken cytoplasm and reduced chloroplasts have been observed previously in corals under thermal stress (Fukabori 1998). Similar observations have been made for several coral species; e.g., M. digitata (Titlyanov et al 1996, Papina et al 2007, Stylophora pistillata (Titlyanov et al 1996, Kuroki and van Woesik 1999, Titlyanov et al 2001, Galaxea fascicularis (Bhagooli and Hidaka 2002), and Zoanthus sansibaricus (Reimer et al 2007), among others (Acropora selago, Acropora muricata, Heliofungia actiniformis, Ctenactis echinata, Oxypora lacera, and Pocillopora eydouxi ;Fujise et al 2013). Deformed zooxanthellae have also been observed in planulae of S. pistillata (Titlyanov et al 1998).…”

“…), among others ( Acropora selago , Acropora muricata , Heliofungia actiniformis , Ctenactis echinata , Oxypora lacera, and Pocillopora eydouxi ; Fujise et al. ). Deformed zooxanthellae have also been observed in planulae of S. pistillata (Titlyanov et al.…”

“…Moreover, some types of coral expel more normal zooxanthellae under thermal stress than under normal conditions (Fujise et al. ), and these species may possess other mechanisms to protect themselves when stressed. M. digitata , however, bleaches by degrading chl a to a non‐fluorescent pigment in a strategy to combat oxidative stress.…”

“…Coral bleaching is produced by reductions in the numbers of symbiotic zooxanthellae, but some corals under thermal stress generate bleached or pale zooxanthellae that do not have a shrunken form (Mise and Hidaka 2003). Moreover, some types of coral expel more normal zooxanthellae under thermal stress than under normal conditions (Fujise et al 2013), and these species may possess other mechanisms to protect themselves when stressed. M. digitata, however, bleaches by degrading chl a to a non-fluorescent pigment in a strategy to combat oxidative stress.…”

Biology of Symbiotic Dinoflagellates (Symbiodinium) in Corals

“…During this process, the expelled population is dominated by degraded and photosynthetically inactive cells. This phenomenon has been found in many scleractinian corals (Fujise et al 2014 ). Under stress, corals release more "healthy-looking" Symbiodinium , rather than the degraded form.…”