Meeting Abstract
2.5 Saturday, Jan. 4 09:00 Quantification of symbiont fate in bleaching octocorals PARRIN, AP*; YAEGER, MA; BLACKSTONE, NW; Northern Illinois University; Northern Illinois University; Northern Illinois University apparrin@gmail.com
Octocorals form a major component of reef diversity and are often the dominant space occupiers. Many octocorals contain photosynthetic symbionts of Symbiodinium sp. As with other symbiont-containing cnidarians, octocorals are susceptible to bleaching in which symbionts die or exit the colony and the host becomes bleached. Recently, in three species of alcyonacean octocorals, Phenganax parrini, Sarcothelia sp., and Sympodium sp., we have shown that in addition to dying and exiting the colony, symbionts can migrate into the stolons. Symbiont fate may have implications for host fate, e.g. sequestered symbionts in the stolons may repopulate polyps after perturbation ceases. Consequently, quantification of symbiont fate is important. This is accomplished by using microscopy of thick sections from fixed specimens, colony morphometrics, and symbiont expulsion counts. For example, comparing thick sections of control and bleached colonies of Sarcothelia sp. shows a decrease in symbiont densities in the polyp tissue (mean ± SE, symbionts/ mm2, 3027.53 ± 536.20, 180.22 ± 72.54, control and bleached respectively) and an increase in the stolon lumen (21.79 ± 6.67, 4731.78 ± 1059.33, respectively). When these mean densities are combined with colony morphometrics the initial (I) and final (F) number of symbionts in a bleached colony can be determined. With counts of the number of symbionts expelled (E), the number that died (D) can also be calculated (I=F+D+E). Such calculations indicate that after perturbation, roughly 74% of the initial number of symbionts remained in the colony, 26% died, and a fraction of a percent were expelled. Results suggest that these three octocorals may sequester symbionts in the stolons during a bleaching episode.
