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Aspects of the ecology and physiology of a tropical sponge and its macroalgal symbiont

Trautman, Donelle Ann (1996) Aspects of the ecology and physiology of a tropical sponge and its macroalgal symbiont. PhD thesis, Murdoch University.

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This study examined ecological and physiological aspects of the symbiotic relationship between the tropical sponge Haliclom cymiformis and the red macroalga Ceratodictyon spongiosum at One Tree Reef, Great Barrier Reef. Although Haliclona/Ceratodictyon occurs commonly in the shallow waters of coral reefs, the biology of this association, nor any other sponge-macroalgal association, has ever been studied in detail.

At One Tree Reef, I found that populations of the Haliclona/Ceratodictyon association were generally restricted to the rubble banks just inside the north eastern rim of the reef crest which surrounds One Tree Lagoon. Only one population of the association was found in the centre of the lagoon. At the rubble bank sites, large populations of the Haliclona/Ceratodictyon association appear to be maintained by asexual reproduction Strong wave turbulence often fragments larger sponges and the size-frequency distribution was strongly skewed toward smaller individuals. In the centre of the lagoon, individuals of the association grew to much larger sizes than those found at the rubble banks, even though this site has a sandy, rather than rubble, floor and was shown to have higher rates of sedimentation, lower irradiance and less turbulence than the rubble bank sites. It appears that the lack of suitable rocky substrata in the centre of the lagoon limits the recruitment of the association into new areas. Fusion experiments between intact individuals of Haliclona/Ceratodictyon collected from different sites. both on the edge and in the centre of One Tree Lagoon, showed sufficient histocompatibility to suggest that existing populations of Haliclona/Ceratodictyon may have originated from the same parent population.

Measurements of photosynthesis rates across a range of irradiances in the intact association were modelled using the hyperbolic tangent function, and me results showed that this association makes a significant contribution to the primary productivity of One Tree Lagoon. Haliclom/Ceratodictyon was shown to have a high rate of photosynthesis; during summer, maximum rates of photosynthesis produced approximately 434 µmol 02 mg chl a-1.h-1, at a saturating light intensity of 749 µmol photons.m-2.s-1 (i.e. the minimum irradiance required to reach the maximum rate of photosynthesis). Compensation irradiance (where the rate of photosynthesis is equal to the rate of respiration) was approximately 316 µmol photons.m-2.s-1, and the slope of the plot of photosynthesis versus irradiance at sub-saturating irradiances (a) was 0.77. The rate of respiration was also high, consuming 218 µmol O2 mg chl a-1.h-1. During winter the rate of maximum photosynthesis and the rate of respiration generally decreased as did the saturating irradiance, and the irradiances required to bring about maximum photosynthesis and compensation photosynthesis. The rates of photosynthesis at irradiances lower than the saturating light intensity generally increased at this time of year.

Photosynthesis and respiration in intact Haliclona/Ceratodictyon occurred at the same rate in the growing tips of the association and near the base. These rates were not affected by concentrations of oxygen up to 287.5 µmol O2.l-1, or by short-term nutrient enrichment with nitrogen, phosphorus, or a combination of the two, to ten times the ambient lagoon concentration. Differences were found in the rates of photosynthesis and respiration between day and night, when pieces of the association were exposed to the same levels of irradiance at different times over a 24 h period. Changes in temperature also affected the rates of photosynthesis and respiration in the intact association; the mean Q10 values for respiration and photosynthesis between 15°C and 30°C were 2.14 and 2.46 respectively. Photosynthetic rate and photosynthetic pigment concentrations were also increased when clumps of Haliclona/Ceratodictyon were subjected to prolonged reductions in irradiance. Similar results were obtained from pieces of the association which were collected from the site in the centre of One Tree Lagoon where the water held large volumes of suspended sediments.

Isolation of both the sponge and algal tissue was achieved in this study, but isolated sponge cells never survived for longer than 48 h. Isolated algal filaments could be maintained in culture for long periods but the photosynthetic rate was reduced following isolation and growth in culture, and they grew very slowly.

Active filter feeding by the sponge occurred at a constant rate during both day and night. The sponge could rapidly clear both particulate and dissolved organic matter from the water column. Despite high rates of photosynthesis and the presence of some ‘host release factor’ activity, relatively small quantities of photosynthetically fixed carbon appeared to be translocated from the isolated alga, when algal filaments were incubated in homogenized sponge tissue.

This association is therefore a significant primary producer, inhabiting areas in which not many large primary producers (algae or corals) can live. The success of Huliclona/Ceratodictyon in these environments is at least partly due to its ability to survive fragmentation, which is an important factor in the reproduction and dispersal of the association. The results presented here also suggest that the symbiosis is based on a structural rather than nutritional relationship between the partners. Thus the association is of unique physiological interest.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Biological and Environmental Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Borowitzka, Michael and Hinde, Rosalind
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