Global warming from anthropogenic greenhouse gas emissions causes temperature
increases in aquatic ecosystems. The rise in environmental temperatures places sensitive
organisms under thermal stress. Reef-building corals are a critically important group of
animals that provide many ecosystem services for coral reef ecology and the economy
and are at a high risk of loss from thermal stress. Thermal stress causes corals to lose
their colour, i.e. become bleached, resulting from the loss of symbiont zooxanthellae.
This diminishes the energetic benefits that zooxanthellae provide to corals leading to a
decline in coral health and high mortality rates. However, corals are also predators and
can thus draw nutrients from zooplankton prey to supplement their nutritional
requirements. This study investigated whether heterotrophic feeding can ameliorate the
effects of thermal stress on coral physiology by providing an alternative energy source
to zooxanthellar photosynthesis. Fragmented Pocillopora damicornis coral colonies
were exposed to daily maximum temperatures of up to 31°C while being either starved
or fed. During the experimental period coral nubbins were monitored for changes in
polyp extension, oxygen consumption rate, feeding rate, colour, chlorophyll a content,
zooxanthellae density, antioxidant potentials and DNA integrity during stress and after a
short recovery period. It was found that, as expected, coral polyp extension, oxygen
consumption rate, colour health, chlorophyll a content, zooxanthellae density and DNA
integrity were all adversely affected by thermal stress. This indicted that all these
measurements were viable biomarkers for assessing the negative effects of thermal
stress on coral health. Coral colour, oxygen consumption rate, chlorophyll a content,
lipid content, antioxidant potential and DNA integrity were all significantly improved
by feeding. These results indicate that feeding does play a role in improving overall
coral health and supports the physiological processes in coral tissue during and after
thermal stress. The conclusions from this study also have great significance for coral
reef ecology and management as predictions of reef resilience can be made from
zooplankton ecology and boosting zooplankton availability to corals may be considered
to mitigate the harmful effects of thermal stress and bleaching. / M.Sc. University of KwaZulu-Natal, Durban 2013.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/11212 |
| Date | January 2014 |
| Creators | Kisten, Yanasivan. |
| Contributors | Glassom, David., Vosloo, Dalene. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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