Marine demosponge responses to a changing ocean; effects of sedimentation and temperature increases on Tethya burtoni metabolism
Beets, F. L. (2017). Marine demosponge responses to a changing ocean; effects of sedimentation and temperature increases on Tethya burtoni metabolism (Thesis, Master of Science (Research) (MSc(Research))). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/11535
Permanent Research Commons link: https://hdl.handle.net/10289/11535
As atmospheric CO₂ levels currently increase at an unprecedented rate, the effects of climate change are increasingly recognized as a significant threat. Changes to climate are predicted to influence natural systems, including increased storm events, that for an erosion prone country like New Zealand means exacerbated sedimentation in coastal habitats. Additionally, climate change is increasing sea surface temperatures globally and will continue to do so in coming decades. More studies investigating the effects of climate related pressures on marine sponge physiology are needed. These unique invertebrates are a diverse, ubiquitous and functionally important group. Studies examining climate change effects on sponges tend to investigate tropical species and in this regard, limited work has been done in New Zealand. This research investigates how the pressures of increasing sea surface temperature and sedimentation affects the metabolism of the temperate demosponge, Tethya burtoni. Aquaria based experiments were conducted while ancillary in situ data investigated current day temperature and sedimentation in various T. burtoni habitats. Experiments addressed the immediate respiration response of T. burtoni under four sediment concentration treatments (ambient loads; 20 and 100 mg l⁻¹, storm proxy loads; 500 and 1000 mg l⁻¹) and four sediment grain size classes (<500-250 µm, <250-125 µm, <125-63 µm, <63 µm) at 500 mg l⁻¹. An additional experiment investigated the effects of long-term exposure (20-days) to fine sediments (<63 µm) at a storm proxy load (500 mg l⁻¹). Finally, the effects of IPCC projected sea surface temperature increase of low change; 2°C and high change; 4°C were investigated. Temperature treatments were based on the Tauranga mean annual sea surface temperature; 18°C and summer maximum; 23°, while IPCC projections were added to the latter giving treatments of 25°C and 27°C. High sediment loads at storm proxy concentrations significantly reduced the respiration rate of T. burtoni, while ambient concentrations had no significant effect. The two finest sediment grain size classes also reduced respiration rates significantly. These results suggest a protective response to reduce further clogging of the aquiferous system. The long-term experiment did not indicate any differences in respiration in the treatment group. Supplementary observations indicate that this may have been due to an issue with aquaria conditions. Sedimentation results in situ found that T. burtoni habitats experience varying amounts of sedimentation, though grain size compositions show similarity across sites. The temperature experiment indicated that 25°C and 27°C had significant impacts on T. burtoni survival with significant disease prevalence and morphological changes. The 18°C and 23°C had no significant effect on survival despite some signs of physiological stress present in the latter. Temperature data collected in situ confirms experimental ranges used, though with greater variability. These results suggest that a temperature threshold between 23°C and 25°C may exist and that in the absence of adaptation or acclimation, T. burtoni may be compromised under future conditions. The loss of sponge populations and even increased reductions in metabolic processes, as they relate to important ecosystem services such as benthic carbon flux, could have a significant effect on coastal trophic dynamics.
University of Waikato
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