Light intensity, photoperiod duration, daily light flux and coral growth ofGalaxea fascicularisin an aquarium setting: a matter of photons?

Abstract

Light is one of the most important abiotic factors influencing the (skeletal) growth of scleractinian corals. Light stimulates coral growth by the process of light-enhanced calcification, which is mediated by zooxanthellar photosynthesis. However, the quantity of light that is available for daily coral growth is not only determined by light intensity (i.e. irradiance), but also by photoperiod (i.e. the light duration time). Understanding and optimizing conditions for coral growth is essential for sustainable coral aquaculture. Therefore, in this study, the question was explored whether more light (i.e. more photons), presented either as irradiance or as light duration, would result in more growth. A series of nine genetically identical coral colonies of Galaxea fascicularis L. were cultured for a period of 18 weeks at different light duration times (8 :0 hours dark) resulted in immediate bleaching and the corals died after 14 weeks. Hourly photosynthetic rates were significantly reduced in the 16 hour light treatment compared to the 8 hour light treatment. As a result, daily net photosynthetic rates were not significantly different, which may explain the observed specific growth rates. Acclimation to photoperiod duration appeared neither to be mediated by changes in chlorophyll-a concentration nor zooxanthellae density. Based on the results of this study, we can conclude that the enhancing effect of light on coral growth is not only a matter of photons. Obviously, the availability of light was not limiting growth in these experiments and was probably in excess (i.e. stressful amounts). Other factors are discussed that play a role in determining growth rates and might explain our results.

A dynamic bioenergetic model for coral-Symbiodiniumsymbioses and coral bleaching as an alternate stable state

“…The prediction of higher growth when light is reduced indicates that growth is not limited by low light in winter, but is actually reduced by excess light in summer 4 , consistent with the experimental findings of Schutter et al (2011). Seasonal summertime reductions in tissue biomass have also been well-documented in the field (Fitt et al 2000), along with reductions in net photosynthetic capacity (Muller-Parker 1987).…”

Measuring Photosynthesis in Symbiotic Invertebrates: A Review of Methodologies, Rates and Processes

“…A decrease in the maximum Fv/Fm over time implies that the rate of photodamage is exceeding the rate of repair of the damaged PSII. Photosynthetic Schutter et al (2011b) shows that corals are exposed to continuous light (i.e. 24 hours per day) bleached and died after 7 weeks.…”

Growth Rate Assessment of Alcyonacean <i>Sarcophyton glaucum</i> from Northern Hurghada, Red Sea, Egypt

“…Cultured corals are known to be highly prized for three main markets: a) the bioprospecting of natural products for the pharmacological and biomedical applications [16] [17]; b) the marine aquarium trade [18]; and c) coral reef restoration efforts [19] [20]. These cultured corals were influenced by numerous factors, such as water movement [21], temperature [13], and light [22] [23]. While the ex situ culture of corals involves higher production costs, it has the advantage of maximizing survival and growth rates through the optimization of culture conditions [24].…”