US EPA

7880716 

Journal Article 

Zooxanthellae population density and physiological state of the coral Stylophora pistillata during starvation and osmotic shock 

Titlyanov, EA; Tsukahara, J; Titlyanova, TV; Leletkin, VA; Van Woesik, R; Yamazato, K 

2000 

1 

Symbiosis
ISSN: 0334-5114 

28 

4 

303-322 

WOS:000087765800003 

Regulation of symbiotic zooxanthellae populations in hermatypic corals may include growth limitation by the host, release of healthy-looking zooxanthellae, and degradation of zooxanthellae. Here we experimentally change the zooxanthellae densities in branches of Stylophora pistillata corals through starvation and osmotic shock. We follow the subsequent changes of the zooxanthellae population dynamics. Prolonged starvation (40 days) caused a 50% loss of zooxanthellae, a 70% decrease in photosynthesis (P calculated per polyp), a 3-fold decrease in proliferating zooxanthellae frequency (PZF) and two-three-fold increase in degrading zooxanthellae frequency (DZF). The increase of the numbers of zooxanthellae in various stages of degradation was closely coupled to an increase in the release of degraded zooxanthellae particles (dzp). At the same time, zooxanthellae volume increased by 80% but chlorophyll content and the photosynthetic capacity of the zooxanthellae did not change. Polyps subjected to osmotic shock (17 parts per thousand) expelled about one third of their zooxanthellae along with elements of animal cells. PZF and DZF levels varied slightly. We assume that zooxanthellae densities in corals are a consequence of differential rates of zooxanthellae division and degradation regulated by the coral host. Only under extreme conditions are zooxanthellae population densities regulated by expulsion of healthy zooxanthellae. 

Stylophora pistillata; corals; zooxanthellae; starvation; osmotic shock; feeding; photosynthesis; respiration; chlorophyll