The influence of light conditions in natural habitats on autotrophic function and also effects of light intensities, ammonium additions and feeding with zooplankton on predation of the coral Stylophora pistillata in aquaria experiments were studied. Coral colonies were collected in the Gulf of Eilat (Israel) from depths 2 m, 20 m and 40 m. Some branches were maintained in aquaria during two weeks under different light regimes from 5% to 90% of PARO and with different feeding treatments: seawater; seawater enriched with (NH4)2S04; and seawater with the Artemia salina nauplii additions. It was shown that in exterior branches of the colonies zooxanthella population density and chlorophyll concentration (calculated as per polyp as per 106 zooxanthellae) increased with gradual reducing light intensity from 90% to 5% PARo, while the level of dividing zooxanthella frequency declined. With reducing light intensity from 20% to 5% PARo an average volume of zooxanthellae and the ratio of values of maximal gross photosynthesis and dark respiration of corals decreased. It was elucidated that ingestion rates as well as killing rates increased with reducing light intensity in the field and in the experimental aquaria. In most cases the value of the ratio of ingestion rate to killing rate was increased. Feeding of corals with inorganic nitrogen as well as with zooplankton stimulated the ingestion rate. When corals incubated under 90% and 20% PARo in all feeding treatments the highest daily rate of predation observed at morning hours and lesser - at evening hours. Under light intensity 5% PARo the rate of predation was high during the day in all feeding variants of the experiments. We conclude that with reducing light intensity in habitat the production capacities of autotrophic function of corals increased by accumulation of algal symbionts in exterior branches of corals and by increasing photosynthetic pigment concentration in the algae. In all probabilities, it depended on intensification of predation under shade. We assume that corals are capable of adapting to dim light not only by maximization of light absorption and its effective use, but also by intensification of heterotrophic function, at least predation.

Depth range
2- 40 m

Mesophotic “mentions”
0 x (total of 5060 words)

Classification
* Presents original data
* Focused on 'mesophotic' depth range
* Focused on 'mesophotic coral ecosystem'

Fields
Behavior
Physiology

Focusgroups
Scleractinia (Hard Corals)

Locations
Israel - Red Sea

Platforms
SCUBA (open-circuit or unspecified)