Investigation of light as a limiting factor in the distribution of benthic symbiont bearing foraminifera on the Great Barrier Reef (MTSRF Project 3.7.1)

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During August 2005, sediment was collected from four reefs in the Whitsunday Islands and two adjacent midshelf reefs, situated along a previously studied water quality gradient. The reefs at Repulse and Lindeman Islands are influenced by discharge generated by the Proserpine and O'Connell Rivers. In the outer Whitsunday Islands, Hook and Edward Islands reefs, are subject to terrestrial influence, which is largely derived from the islands themselves. The midshelf reefs, Barb Reef and Reef 19-138 are essentially unaffected by terrestrial discharge. Two sites were randomly chosen on the less exposed leeward side of each reef. At each site samples were collected from three depth zones along the reef slope: 2 to 5 m, 6 to 8 m and 9 to 13 m. For each depth zone at each site, three core samples were collected using cut-off 60 ml syringes. Each syringe was pressed vertically into the sand for at least half its length and all but the top 1cm of each core was discarded. Samples were combined to form a single sample per depth station and preserved in ethanol. Samples were later rinsed, dried and subsamples of symbiont bearing foraminifera identified. Amphistegina spp., Calcarina spp. and Heterostegina depressa, collected from the sediment sampling sites at Edward Island were cultured in tubes within a series of tanks in an outdoor aquarium system set up in mid September 2005 at AIMS. Specimens were subjected to three light regimes: open to sunlight, 30% sunlight and 10% sunlight.Over a two week period in November/December 2005, light measurements, temperature and salinity were recorded in each tank. Images of each individual foraminifera were taken before and at intervals during the experiment and the surface area of each individual determined. Pulse-amplitude-modulated (PAM) fluorometry was applied to assess the health of the symbiotic diatoms and their adaptation to various light levels. Additional specimens of the three taxa were collected from the Whitsunday Islands and the same process was applied within 2 hours of collection.
Field and experimental studies were undertaken to investigate the importance of light as an environmental factor influencing physiology and distribution of tropical benthic foraminifera.

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Maintenance and Update Frequency: notPlanned

Statement: Statement: Experimental Procedures:Light in each tank was measured every 10 minutes using Odyssey light loggers. The temperatures of each tank were recorded throughout the experiment using a hand-held thermometer.Images were taken of foraminifera using a Leica MZ16A microscope with a Leica DC100 digital camera attachment. The digital images were analysed with image analysis software (Optimas®) to determine the surface area of each individual. Prior to each image being taken, algal growth on the outside of the foraminiferal test was removed. Dead foraminifera, determined by loss of symbiont colouring and high external algal growth, were excluded from measurements.Pulse-amplitude-modulated (PAM) fluorometry was applied to assess the health of the symbiotic diatoms and their adaptation to various light levels. See: Schreiber U, Schliwa U, Bilger W (1986) Continuous recording of photochemical and non-photochemical chlorophyll fluorescence quenching with a new type of modulating fluorometer. Photosynth. Res. 10, 51-62.Ralph P, Schreiber U, Gademann R, Kuehl M, Larkum A (2005) Coral photobiology studied with a new imaging pulse amplitude modulated fluorometer. J. Phycol. 41, 335-342.Fluorescence measurements were taken with a WALZ Diving PAM fluorometer to measure the maximum quantum efficiency of photosystem II (Fv/Fm) after 15 minutes of dark adaptation. Prior to measurements, potential algal growth on the outside of the test was carefully removed by wiping. The foraminifera were placed individually under an 8 mm fiberoptic sensor with a piece of rubber tubing deployed on the end to ensure that all readings were taken at the same distance (6 mm), from the specimen. In cases where algal growth on the outside of the test was extensive and could not be removed, the specimen was not measured and presumed dead.Rapid light curves give a range of increasing light intensities, in this case from 0 to 760 µmol photon m-² s-¹. Effective quantum efficiency measurements (ØPSII), measured after exposing the foraminifera for 10 seconds to each light condition, were then used to calculate the relative electron transport rates (rETR) by multiplying the quantum efficiency (Y(PSII) and the Photosynthetic Active Radiation measurement (PAR):rETR= ØPSII x PAR Light curve parameters alpha (initial slope of the RLC), Ek (light intensity at onset of saturation), rETRmax (relative electron transport rate at light saturation) and beta (negative slope indicating photoinhibition) were calculated after fitting data to the model of Platt et al. (1980) using Sigmaplot statistical software.Platt T, Gallegos C, Harrison W (1980) Photoinhibition of photosynthesis in natural assemblages of marine phytoplankton. J. Mar. Res. 697-701.

Notes

Credit
Uthicke, Sven, Dr (Principal Investigator)