Osmoregulatory Functions in Invertebrate/Algal Symbiotic Systems and Their Potential Role in Catastrophic, Coral Bleaching Events

EPA Grant Number: FP916365
Title: Osmoregulatory Functions in Invertebrate/Algal Symbiotic Systems and Their Potential Role in Catastrophic, Coral Bleaching Events
Investigators: Shannon III, Thomas
Institution: University of Georgia
EPA Project Officer: Michaud, Jayne
Project Period: January 1, 2004 through December 31, 2007
Project Amount: $98,293
RFA: STAR Graduate Fellowships (2004) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Oceanography and Coastal Processes , Aquatic Ecosystems


The objective of this study is two-fold. The first objective (research already in progress) is to determine the cause of a novel basking behavior exhibited by a small marine flatworm, Convolutriloba retrogemma, a heterotrophic, acoelous turbellarian in obligate symbiosis with an intercellular, endosymbiotic alga. Based on current data, it appears the behavior is a method of photoregulation driven by osmotic changes in the worm tissues.

The second objective of this research is to determine the diel changes in photosynthate concentrations in stressed and unstressed anemone/alga symbiotic complexes. I hypothesize that diel cycles occur for both photosynthates and inorganic nitrogen; however, I feel that overall total body osmolarity will remain at equilibrium in unstressed anemones.

Further studies will be designed to research the effects of osmotic stress on cnidarian/alga complexes as a possible bioindicator of anthropogenic, environmental stress.


Objective 1. Currently, I am researching the effect of varying a light and food regimen on the C. retrogemma symbiotic complex. Focus is on light irradiance preference comparisons between fed and starved C. retrogemma to determine if the worms select specific irradiance levels based on their nutritional status. Given my observations of the worms’ basking behaviors, I hypothesize that holozoically fed worms will tend to seek out higher light levels (because their algal densities are higher than in starved worms) and that they are likely capable of metabolizing the photosynthate product(s) of the endosymbionts. Based on prior starvation tests, I expect that holozoic feeding by the worm will be necessary to obtain additional nutrients required to metabolize the algal photosynthate. When starved, I expect that the worm will need to consume the algae, not only for nutrition, but to control/minimize any build-up of unmetabolized algal product that will likely render the worm hyperosmotic to its surroundings. In a light gradient, if this holds true, the starved worm should exhibit photophobic behavior as a simple solution to minimizing photosynthesis. These results would substantiate a hypothesis that the observed basking behaviors of the worms are irradiance regulation methods utilized for optimizing metabolism depending on nutritional status and subsequent minimization of hyperosmotic stress.

Objective 2. I intend to measure osmolyte production over 24-hour periods in the common brown anemone Aiptasia and the giant anemone Condylactis gigantea. I am interested in how a sessile host with an intracellular endosymbiont (unlike the flatworm) deals with changes in its osmotic concentrations and how (or if) these concentrations vary over the course of a day. I will measure concentrations of photosynthates and inorganic nitrogen in stressed (elevated temperature and starvation) and unstressed anemones to determine the effect of these stresses on the ability of the host regulate its internal osmolarity.

This research is expected to further our understanding of the role that photosynthetic products play in invertebrate/alga symbioses, not only in host nutrition, but as molecules capable of altering the internal osmolarity of host cells and tissues. It is anticipated that environmental stress may result in the inability of the host to regulate photosynthate concentrations, thereby resulting in osmotic stress. In corals, this may further result in the dissolution of the algal symbioses (bleaching).

Supplemental Keywords:

fellowship, osmoregulation, osmotic changes, platyhelminthes, cnidaria, algae, symbiosis, photosynthesis, bleaching, coral bleaching,, RFA, Scientific Discipline, Water, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Oceanography, Aquatic Ecosystem, algal blooms, Ecological Risk Assessment, anthropogenic stress, nutrient dynamics, coral bleaching, flat worm, nutrient kinetics, bioindicator development, aquatic ecosystems, coral reef communities, algal bloom detection, ecosystem stress, ocean temperature

Progress and Final Reports:

  • 2004
  • 2005
  • 2006
  • Final