Impact of UVR and temperature on symbiotic dinoflagellates from tropical coral reef ecosystems

BANASZAK, A. T.; VILLAFAÑE, V. E.; GUENDULAIN GARCIA, S. D.; LOMBARDO, L.; HELBLING, E. W.

Mar del Plata

Congreso; The Changing Coastal and Estuarine Environment: A Comparative Approach; 2012

Coastal and Estuarine Research Federation

Coral-reef ecosystems are characterized by exposure to high UVR levels due to the low solar zenith angles typical of tropical regions as well as the naturally low ozone concentrations in combination with the high transparency of the overlying water column. Over geological time, UVR has been a strong selective pressure for coral-reef dwelling organisms to adapt photoprotective and repair mechanisms to cope with this stressor. Over the last few decades, a new stressor, rising sea surface temperature, has been increasingly documented in coral reef environments and implicated in coral bleaching events. Coral bleaching is defined as the breakdown of the relationship between the coral host and its photosynthetic dinoflagellate symbionts belonging to the genus Symbiodinium such that the coral tissue becomes pale. In extreme cases, bleaching events can lead to widespread mass mortality of corals. The combination of high UVR levels and increased temperature may have important effects on corals and their symbionts. Here we describe a series of experiments that were undertaken with various genetic types (clades) of Symbiodinium using both artificial and natural solar radiation where UVR and PAR (photosynthetically active radiation) were varied in combination with ambient and increased temperatures. Our results suggest that the various Symbiodinium clades that were tested have widely different responses to UVR and temperature in terms of the quantum yield of photosystem II (PSII) fluorescence as well as their inhibition and recovery rates. Our data demonstrate that the variety of responses is due to differences in the photoprotective and non-photochemical quenching mechanisms characteristic of each clade