Effects of cyanide on coral photosynthesis: implications for identifying the cause of coral bleaching and for assessing the environmental effects of cyanide fishing
Rj. Jones et O. Hoegh-guldberg, Effects of cyanide on coral photosynthesis: implications for identifying the cause of coral bleaching and for assessing the environmental effects of cyanide fishing, MAR ECOL-PR, 177, 1999, pp. 83-91
Modulated chlorophyll fluorescence techniques were used to examine the effe
cts of cyanide (NaCN) from cyanide fishing on photosynthesis of the symbiot
ic algae (zooxanthellae) located within the tissues of the zooxanthellate h
ard coral Plesiastrea versipora. Incubating corals for 3 h in a cyanide con
centration of >10(-5) M NaCN under a saturating light intensity (photosynth
etically active radiation [PAR] intensity of 250 mu mol quanta m(-2) s(-1))
caused a long-term decrease in the ratio of variable to maximal fluorescen
ce (dark-adapted F-v/F-m). The effect of cyanide on dark-adapted F-v/F-m wa
s Light dependent; thus F-v/F-m only decreased in corals exposed to 10(-4)
M NaCN for 3 h under PAR of 250 mu mol quanta m(-2) s(-1). In corals where
dark-adapted F-v/F-m was significantly lowered by cyanide exposure, we obse
rved significant loss of zooxanthellae from the tissues. causing the corals
to discolour (bleach). To further examine the light-dependent effect of cy
anide and its relation to loss of zooxanthellae, corals were exposed to 10-
4 M NaCN or seawater only (control), either in darkness or under 250 mu mol
quanta m(-2) s(-1). ill significant decrease in dark-adapted F-v/F-m and l
oss of zooxanthellae only occurred in corals exposed to cyanide in the ligh
t. These results suggest cyanide causes the dissociation of the symbiosis (
bleaching) by affecting photosynthesis of the zooxanthellae. Quenching anal
ysis using the saturation-pulse technique revealed the development of high
levels of non-photochemical quenching in cyanide-exposed coral. This result
is consistent with the known property of cyanide as an inhibitor of the da
rk reactions of the Calvin cycle, specifically as an inhibitor of ribulose-
1,5-bisphosphate carboxylase/oxygenase (Rubisco). Therefore, chronic photoi
nhibition and an impairment of photosynthesis of zooxanthellae provides an
important 'signal' to examine the environmental effects of cyanide fishing
during controlled releases in situ.