In situ underwater measurements of photosynthetic activity of coral zooxanthellae and other reef-dwelling dinoflagellate endosymbionts

Abstract

Chlorophyll fluorescence was used to assess the in situ photosynthesis of a range of reefdwelling endosymblonts. Such non-intrusive in situ measurements became possible after the recent development of a submersible pulse modulated fluorometer (DIVING-PAM, Walz, Germany). Several corals, a clam ( T~d a c n a maxima) and an anemone (Heteractis sp.) all showed strong chlorophyll a fluorescence signals originating from the dinoflagellate endosymbionts. Quenching analysis by the saturation pulse method revealed high quantum yields and light response curves characteristic of physiologically healthy sun plants. Rapid light curves (RLC) were applied to assess the light saturation behaviour of the different organisms in their rapidly changing natural environment. The 3 corals (Acropora aspera, Goniastrea sp. and Porites sp.), the clam i ? maxima, and the anemone Heteractis sp. all showed high photosynthetic activity. The corals had a maximum electron transport rate of 180 to 270 pm01 electrons m-2 S-', the Heteractis sp. displayed a maximum rate of approximately 120 pm01 electrons m-2 S-', whilst the T. maxima showed no saturation up to 1900 pm01 quanta m-* S-', where a rate of 325 pm01 electrons m-' S-' was observed. Three species of corals showed varying degrees of an apparent mid-day depression, occurring during the summer peak irradiance at low tide. Because quantum efficiency rapidly recovered during the afternoon period, when the irradiance levels decreased again, it is concluded from these preliminary investigations that the depression resulted mainly from down-regulation of photosystem 11. Depth did not appear to influence the RLCs of A. aspera growing at 2, 5 and 10 m. Coral morphology influenced the apparent electron transport rate at different locations within a single colony.

Photosynthesis and photoprotection in symbiotic corals

“…The second, chronic photoinhibition is associated with much more severe damage to PSII, recovers extremely slowly, and is interpreted as photon damage. Although dynamic photoinhibition occurs widely in phytoplankton , macroalgae (Hanelt et al 1993;Franklin et al 1996), and corals (Brown et al 1999;Hoegh-Guldberg and Jones 1999;Ralph et al 1999; this study), signs of chronic photodamage have previously been observed only in corals exposed to elevated temperatures (Jones et al 1998;Warner et al 1999) or intertidal corals under solar bleaching (Brown et al 2000). Our data on a number of shallow corals clearly suggest that the daily exposure to full sunlight leads to chronic photoinhibition, even at moderate temperatures (24-29ЊC).…”

Photoinhibition in shallow‐water colonies of the coral Stylophora pistillata as measured in situ

“…In addition, those studies were not performed in situ, but on corals held in aquariums, which might have been further stressed by the methods of dark adaptation used prior to the measurements. Using the last data point of rapid light curves performed in situ for several species at different times of the day, Ralph et al (1999) found similar midday depressions in maximum ETR and explained this also to be dynamic photoinhibition. In contrast to the above studies, the measurements in our study were performed in situ and under natural irradiances (without dark adaptations).…”

“…With the development of the Diving-PAM, measurements of chlorophyll fluorescence became applicable also for in situ research of coral photosynthesis (Beer et al 1998;Ralph et al 1999). However, those in situ works did not make use of the ambient irradiance during the measurements.…”

Photosynthetic responses of corals Mussismilia harttii (Verrill, 1867) from turbid waters to changes in temperature and presence/absence of light

“…) in the form of a rapid light curve (RALPH et al, 1999;GADEMANN, 2005). Light-adapted fluorescence yield (F s ) and maximum light-adapted fluorescence yield (F' m ) were determined at the end of a 10 sec period at each irradiance level, and the effective quantum yield of PSII as a function of irradiance was calculated from…”