Vertical Migration and Distribution of Primary Producers in Aquatic Ecosystems–The Effects of Enhanced Solar UVB

Häder, Donat‐P.

doi:10.1111/j.1751-1097.1997.tb08556.x

Cited by 4 publications

(1 citation statement)

References 5 publications

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“…UVR might affect organism's photosynthetic performances by inducing photoinhibition (Hoegh-Guldberg and Jones 1999). However, in the Mediterranean Sea, the penetration depth of UVR is of few metres (Häder 1997;Piazena and Häder 2009;Durrieu de Madron et al 2011), so that at 7-10 m depth, UVR are not a major component of the irradiance wavelengths. Inside the chamber, two pumps (Aussenpumpe Extra, Comet-Pumpen Systemtechnik, Kommanditgesellschaft) ensured continuous water mixing, with a constant flow of 12 L min -1 and the chamber was automatically and periodically flushed every 20 min and during the 20 min the incubation medium was renewed.…”

Section: Experimental Set Upmentioning

confidence: 98%

Photophysiology and daily primary production of a temperate symbiotic gorgonian

et al. 2014

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Gorgonians are one of the most important benthic components of tropical and temperate areas, and play a fundamental role as ecosystem engineers. Although global warming and pollution increasingly threaten them, the acquisition of nutrients, which is a key process in fitness and stress resistance, has been poorly investigated in such species. This study has thus used an advanced in situ incubation chamber for the first time with gorgonians, to assess the daily acquisition of nutrients and the photophysiology of the Mediterranean symbiotic species, Eunicella singularis. The xanthophyll cycle was assessed in parallel. This work has revealed that E. singularis presents a different functioning than the Mediterranean symbiotic corals. This gorgonian indeed relies on both autotrophy and heterotrophy in summer to optimize its energetic budget, while corals mainly shift to autotrophy for their respiratory needs and tissue growth. In addition, although E. singularis lives in the same depths/locations, and harbours the same symbiont genotype than the corals, the photosynthetic performances of their respective symbionts are significantly different. Indeed, E. singularis acquired 2-3 times less autotrophic carbon from its symbionts than corals, but maintained a positive carbon budget by reducing respiration rates, and by presenting maximal photosynthetic rates throughout the day, suggesting a very efficient light utilization. Almost no photoinhibition was observed under very high light levels, because of the induction of a xanthophyll photoprotection process. These results help understanding why gorgonians often dominate many benthic ecosystems.

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Section: Experimental Set Upmentioning

confidence: 98%

Photophysiology and daily primary production of a temperate symbiotic gorgonian

et al. 2014

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Gravitaxis in Euglena

Häder

Hemmersbach

2017

Advances in Experimental Medicine and Biology

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Motile microorganisms utilize a number of responses to external stimuli including light, temperature, chemicals as well as magnetic and electric fields. Gravity is a major clue to select a niche in their environment. Positive gravitaxis leads an organism down into the water column and negative gravitaxis brings it to the surface. In Euglena the precision of gravitaxis is regulated by an internal rhythm entrained by the daily light/dark cycle. This and the cooperation with phototaxis bring the cells into an optimal position in the water column. In the past a passive orientation based on a buoy mechanism has been proposed for Euglena gracilis, but now it has been proven that this flagellate possesses a physiological gravireceptor and an active orientation. Numerous experiments in space using satellites, rockets and shuttles as well as in parabolic flights have been conducted as well as in functional weightlessness (simulated microgravity) on ground-based facilities such as clinostats to characterize the gravitaxis of Euglena. The threshold for gravity perception was determined and physiological, biochemical and molecular components of the signal transduction chain have been identified. In contrast to higher plants, some algae and ciliates, Euglena does not possess sedimenting statoliths to detect the direction of the gravity vector of the Earth. The gravireceptors were found to be mechano-sensitive Ca-conducting ion channels thought to be located at the front end of the cell underneath the trailing flagellum. When activated by gravity-induced pressure due to sedimentation of the whole cell body, they allow a passive influx of calcium along a previously established ion gradient. The entering calcium binds to a specific calmodulin (CaM.2) which in turn activates an adenylyl cyclase producing cAMP from ATP. This cAMP is believed to activate a specific protein kinase A (PK.4), which is postulated to phosphorylate proteins inside the flagellum resulting in a bending and thus a course correction and reorientation with respect to the direction of the gravity vector. The elements of the signal transduction chain have been characterized by inhibitors and by RNAi to prove their involvement in gravitaxis.

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