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Vol. 54, 2015
High tolerance of
symbiotic larvae of Pocillopora damicornis to thermal stress
Dwi
Haryanti1*, Naoko Yasuda1
, Saki Harii2 and Michio
Hidaka1
1Department of Chemistry, Biology and Marine Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
2Sesoko Station, Tropical Biosphere Research Center, University of the Ryukyus, Motobu, Okinawa 905-0227, Japan
Abstract
Background: When
coral planulae, which use a horizontal mode of symbiont transmission,
are inoculated with Symbiodinium, they suffer greater oxidative stress
under strong light or high-temperature stress than non-symbiotic
counterparts. Thus, dinoflagellate symbionts may become a source of
reactive oxygen species (ROS) under stress. However, it remains unknown
whether vertically transmitted symbionts negatively affect coral larvae
under stress. We investigated the thermal tolerance of symbiotic
planulae of a vertical transmitter coral, Pocillopora damicornis.
Results: P. damicornis
larvae, which have a large number of symbionts, survived the
high-temperature treatment (32 °C) for 2 weeks. Significant reductions
in Symbiodinium cell density
were observed, but these did not lead to increased mortality of
planulae during the 2-week experimental period. Although no significant
difference was detected in the percentage of apoptotic cells between
temperature treatment groups, pre-bleaching larvae exposed to 31 °C
tended to exhibit higher percentages of apoptotic (TUNEL-positive)
cells in the gastrodermis than 32 °C-treated larvae, which contained
reduced numbers of Symbiodinium cells.
Conclusions: Symbiotic larvae of P. damicornis survived well under high-temperature conditions, although their Symbiodinium cell density decreased. This suggests that P. damicornis
larvae have the capacity to reduce the symbiont cell density without a
harmful effect on their survivorship under thermal stress. Further
studies on antioxidant systems and possible suppression of apoptotic
pathways are necessary to elucidate the mechanism underlying the high
thermal tolerance of symbiotic larvae of P. damicornis.
Key words: Apoptosis; Bleaching; Coral; Larvae; Survivorship; Symbiosis.
*Correspondence: E-mail: dwiharyanti@gmail.com
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