Institut de recherche pour le développement (IRD), Frankreich
Info
The deep-water coral Leptoseris fragilis has been the object of many studies concerning its occurrence, water depth, and zooxanthellae use and activity.
In the summer of 1988, in the Gulf of Aqaba (Red Sea), Leptoseris fragilis corals, which normally live at depths around 110-120 meters, were collected from their substrate and "transplanted" at depths of 70 and 160 meters using an ROV.
At each depth, individuals were exposed in their natural growth position (oral side to the surface) or in a reverse growth position (oral side to the bottom).
After 1 year of exposure, corals were collected and zooxanthellae were isolated. As a function of light availability with depth and growth position, several algal parameters showed changes related to photoadaptations.
Zooxanthellae densities, already relatively low at a natural growing depth of 116 meters, decreased for specimens at 160 meters growing in a natural orientation.
Only degenerate algae were observed in corals with a downward facing mouth surface at the same depth (160 meters).
In terms of depth dependence, the volume of algae from at 160 meters depth decreased and the pigment content increased.
The concentrations of chlorophyll a and especially chlorophyll c 2 per cell were increased.
Compared to the natural amounts in 116 meters, the concentration of chlorophyll a in 160 meters was five times higher and that of chlorophyll c 2 eight times higher.
From this it could then be explained that the coral size decreases with the increase of water depth.
Leptoseris fragilis does not have tentacles to grasp prey, feeds on detritus by mucosal ingestion and on dissolved organic matter, but absolutely requires the energy of zooxanthellae for optimal development,
In the summer of 1988, in the Gulf of Aqaba (Red Sea), Leptoseris fragilis corals, which normally live at depths around 110-120 meters, were collected from their substrate and "transplanted" at depths of 70 and 160 meters using an ROV.
At each depth, individuals were exposed in their natural growth position (oral side to the surface) or in a reverse growth position (oral side to the bottom).
After 1 year of exposure, corals were collected and zooxanthellae were isolated. As a function of light availability with depth and growth position, several algal parameters showed changes related to photoadaptations.
Zooxanthellae densities, already relatively low at a natural growing depth of 116 meters, decreased for specimens at 160 meters growing in a natural orientation.
Only degenerate algae were observed in corals with a downward facing mouth surface at the same depth (160 meters).
In terms of depth dependence, the volume of algae from at 160 meters depth decreased and the pigment content increased.
The concentrations of chlorophyll a and especially chlorophyll c 2 per cell were increased.
Compared to the natural amounts in 116 meters, the concentration of chlorophyll a in 160 meters was five times higher and that of chlorophyll c 2 eight times higher.
From this it could then be explained that the coral size decreases with the increase of water depth.
Leptoseris fragilis does not have tentacles to grasp prey, feeds on detritus by mucosal ingestion and on dissolved organic matter, but absolutely requires the energy of zooxanthellae for optimal development,
