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Title: Ecological studies of symbiosis in Convoluta roscoffensis
Author: Doonan, Shelagh A.
ISNI:       0000 0001 3429 2871
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1979
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1. Convoluta roscoffensis is an intertidel flatworm symbiotic with the green alga, Platymonas convolutae. Field studies of a population of Convoluta on Shell Beach, Herm, Channel Islands, involved the measurement of seasonal changes in numbers of Convoluta and in environmental conditions. Features of the habitat were measured, including the nutrient levels in the beach run-off water flowing over Convoluta colonies and the light energy available. 2. The position of the colonies on the beach meant that they received about 60% of available PAR (photosynthetically active radiation) i.e. 4883 E m-2 in 1977. The spacing of worms in the colonies (mean density 9.3 x 10 to the power 5 worms m-2) was such that they did not haye to shade each other. 3. Nutrient analyses revealed that the beach run-off water is rich in nutrients, and dominated by nitrate (mean concentration 6-16υg atoms N03-N 1to the power -1). Uptake of nutrients from the run-off water by Convoluta was not apparent. 4. The Convoluta population was most abundant in September and numbers were lowest in May and June. This pattern of fluctuation in numbers showed some relation to seasonal changes in light intensity but not to changes in nutrient levels. 5. Primary productivity measurements (using the 14C technique) of symbiotic and free-living Platymonas showed that both types of algae achieved assimilation numbers (mg carbon fixed (mg chlorophyll 'a')-1 h-1) which were in the range 1-3. Photosynthetic rate was higher in worms incubated in Herm run-off water than in offshore seawater. Comparisons between symbiotic and free-living Platymonas were made with respect to photoinhibiting light levels and the amounts of dark carbon fixation. 6. Extrapolation of primary productivity values to Convoluta in the field gave an estimated annual production of 872.9 g carbon m to the power -2 of colony for 1977. This is comparable with values for rich ocean waters and coral reefs. 7. Primary production measurements were also made on a tropical algal-invertebrate system, Zoanthus sociatus, at Discovery Bay, Jamaica. The oxygen technique was used, so the values of assimilation number were not directly comparable with those obtained for Convoluta, but the symbionts of Zoanthus (Gymnodinium microadriaticum) achieved assimilation numbers similar to those published for other free-living species of Gymnodinium. The symbionts isolated from Zoanthus were of similar size to and contained similar amounts of chlorophyll 'a' to the Platymonas symbionts of Convoluta. 8. Structural studies of the development of symbiosis in Convoluta showed that the host and symbiont are in very intimate contact. There was evidence for the controlled and integrated growth of host and symbiont in the distribution and orientation of the 20,000-70,000 algae inside Convoluta. The ratios of algal to host protein and cell volume were measured and compared with values for other algal-invertebrate systems to discover whether any general statements may be made regarding the proportions of algal to host tissue in established symbioses.
Supervisor: Not available Sponsor: Natural Environment Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Platyhelminthes ; Symbiosis ; Habitat (Ecology)