Spatial and temporal photoacclimation of Stylophora pistillata: zooxanthella size, pigmentation, location and clade

Abstract

Photoacclimation of the symbiotic hermatypic coral Stylophora pistillata was studied both for colonies growing at different depths (1 to 20 m) sampled within the same season ('spatial photoacclimation') and for colonies growing at the same depth (5 m) but sampled throughout the year ('temporal photoacclimation'). Specimens were darker and had increased chlorophyll densities (chlorophyll per coral surface area) under low-light conditions caused both by increased depth and, in shallow-growing specimens, by the winter season. However, while increased depth involved increased zooxanthella chlorophyll content, acclimation to low irradiances by shallow-growing corals during the winter mostly involved an increase in algal density. In shallow-growing corals, both zooxanthella chlorophyll content and coral chlorophyll density fluctuated seasonally in correlation with light more than with nitrogen or temperature. This could be related to the fact that reefs in Eilat, Israel, are exposed to more solar radiation than many other reefs in the world. Histological analyses of high-light corals showed that zooxanthellae were located deeper inside the host tissue and were smaller in diameter compared to zooxanthellae from low-light corals. Additionally, while deep-water colonies hosted clade C zooxanthellae, colonies growing in shallow waters, both in high-and very low-light environments, hosted clade A. These clade differences were found to affect coral physiology, as examined in a short-term thermal stress experiment, with clade-A colonies having higher thermal resilience than clade-C colonies. Taken together, our results show evidence of different mechanisms that help adjust the light-capturing abilities of S. pistillata zooxanthellae to spatial and temporal changes in irradiance.

Shallow-water wave lensing in coral reefs: a physical and biological case study

“…Despite the fact that the area is a long way from the Equator, the corals in the Gulf of Eilat (Aqaba) receive, on average, 40% higher irradiance than lower-latitude tropical reefs elsewhere in the world (Winters et al, 2009). These high irradiances are a result of the unique environment of the northern Red Sea, where desert (with associated cloudless skies) surrounds a deep semi-enclosed gulf, with low nutrient input creating meso-oligotrophic water conditions similar to that of oceanic waters (Stambler, 2006).…”

“…Destructive coral physiology measurements were made only on the S. pistillata fragments as permits could not be obtained for destructive sampling of the F. abdita coral. Coral nubbins were airbrushed using filtered (0.45m) seawater, and the chlorophyll a (chl a) was extracted using methods outlined previously by Winters and colleagues (Winters et al, 2009). Total and host protein were determined using a Bradford Protein Analysis kit (Bio-Rad Laboratories, Hercules, CA, USA) following Bradford (Bradford, 1976).…”

“…High levels of solar irradiance have long been suspected to contribute to coral bleaching (Dunne and Brown, 1996;HoeghGuldberg, 1999;Winters et al, 2009). The increased frequency of bleaching events and impaired recovery of reefs post-bleaching require the development of management strategies to increase reef resilience and reduce climatic pressures on the reefs (Bruno and Selig, 2007;Hoegh-Guldberg et al, 2007).…”

Physiological and Biogeochemical Responses of Super-Corals to Thermal Stress from the Northern Gulf of Aqaba, Red Sea

“…All three species are common in this region. S. pistillata is a branching coral, a reproductive brooder, and is dominated by the endosymbiont Symbiodinium clade A (Shlesinger and Loya, 1985;Karako-Lampert et al, 2004;Winters et al, 2009;Byler et al, 2013;Ziegler et al, 2017). P. damicornis is also a branching coral, is a member of a genus that reproduces by both broadcasting and brooding (though spawning has never been documented for this species in the Red Sea), and is dominated by the endosymbiont Symbiodinium clade C (Shlesinger and Loya, 1985;KarakoLampert et al, 2004;Fine et al, 2013;Sawall et al, 2015;Ziegler et al, 2017).…”

Symbiodinium diversity in mesophotic coral communities on the Great Barrier Reef: a first assessment

“…Nonetheless, the finding that certain Symbiodinium types can occur across a broad range of light conditions ranging from near the surface to mesophotic depths, indicates that other environmental factors may be equally as important in driving the distribution of host-Symbiodinium associations. Although direct evidence is lacking, bathymetric differences in temperature regimes (Winters et al 2009, Cooper et al. 2011a), light spectra (Mass et al 2010, and/or increased availability of heterotrophic resources (Lesser et al 2010) are likely to be equally important in the distribution host-Symbiodinium associations and may explain some of the observed overlap between shallow and deep communities.…”