Posts Tagged 'Porifera'

Climate change and tropical sponges: The effect of elevated pCO₂ and temperature on the sponge holobiont

As atmospheric CO₂ concentrations rise, associated ocean warming (OW) and ocean acidification (OA) are predicted to cause declines in reef-building corals globally, shifting reefs from coral-dominated systems to those dominated by less sensitive species. Sponges are important structural and functional components of coral reef ecosystems, but despite increasing field-based evidence that sponges may be ‘winners’ in response to environmental degradation, our understanding of how they respond to the combined effects of OW and OA is limited. This PhD thesis explores the response of four abundant Great Barrier Reef species – the phototrophic Carteriospongia foliascens and Cymbastela coralliophila and the heterotrophic Stylissa flabelliformis and Rhopaloeides odorabile to OW and OA levels predicted for 2100, under two CO₂ Representative Concentration Pathways (RCPs). The overall aim of this research is to bridge gaps in our understanding of how these important coral reef organisms will respond to projected climate change, to begin to explore whether a sponge dominated state is a possible future trajectory for coral reefs.

To determine the tolerance of adult sponges to climate change, these four species were exposed to OW and OA in the Australian Institute of Marine Science’s (AIMS) National Sea Simulator (SeaSim) in a 3-month experimental study. The first data chapter explores the physiological responses of these sponges to OW and OA to gain a broad understanding of sponge holobiont survival and functioning under these conditions. In this chapter I also address the hypothesis that phototrophic and heterotrophic sponges will exhibit differential responses to climate change. In the second and third data chapters I explore the cellular lipid and fatty acid composition of sponges, and how these biochemical constituents vary with OW and OA. Lipids and fatty acids are not only vital energy stores, they form the major components of cell membranes, and the structure and composition of these biochemical constituents ultimately determines the integrity and physiological competency of a cell. Therefore through these analyses I aimed to determine how OW and OA affects the metabolic balance of sponges, and to understand mechanisms underpinning observed systemic sponge responses. Finally, to provide greater insight into the population level impacts of climate change on tropical sponges, in the last data chapter I explore the response of the phototrophic species Carteriospongia foliascens to OW/OA throughout its developmental stages.

I found that while sponges can generally tolerate climate change scenarios predicted under the RCP6.0 conditions for 2100 (30ºC/ pH 7.8), environmental projections for the end of this century under the RCP8.5 (31.5ºC/ pH 7.6) will have significant implications for their survival. Temperature effects were much stronger than OA effects for all species; however, phototrophic and heterotrophic species responded differently to OA. Elevated pCO₂ exacerbated temperature stress in heterotrophic sponges but somewhat ameliorated thermal stress in phototrophic species. Furthermore, sponges with siliceous spiculated skeletons resisted the RCP 8.5 conditions for longer than the aspiculate species. Biochemical analysis revealed that spiculated species also have greater cell membrane support features, which is likely to contribute to the observed stress tolerance. I also found that the additional energy available to phototrophic sponges under OA conditions may be used for investment into cell membrane support, providing protection against thermal stress. Finally, larval survival and settlement success of C. foliascens was unaffected by OW and OA treatments, and juvenile sponges exhibited greater tolerance than their adult counterparts, again with evidence that OA reduces OW stress for some of these life stages.

Based on the species studied here, this thesis confirms that sponges are better able to deal with OW and OA levels predicted for 2100 under RCP6.0, compared to many corals for which survival in a high CO₂ world requires OW to remain below 1.5°C. This suggests sponges may be future ‘winners’ on coral reefs under global climate change. However, if CO₂ atm concentrations reach levels predicted under RCP8.5, the prognosis for sponge survival by the end of this century changes as inter-species sponge tolerances to OW and OA differ. Under this projection it is likely we will also start to see a shift in sponge populations to those dominated by phototrophic sponges with siliceous spiculated skeletons. Overall, this thesis gives a holistic view of OW and OA impacts on tropical sponges and provides the basis from which to explore the potential for a sponge-coral regime shift in a high CO₂ world.

Continue reading ‘Climate change and tropical sponges: The effect of elevated pCO₂ and temperature on the sponge holobiont’

Interactive effects of temperature and pCO2 on sponges: from the cradle to the grave

As atmospheric CO2 concentrations rise, associated ocean warming (OW) and ocean acidification (OA) are predicted to cause declines in reef-building corals globally, shifting reefs from coral-dominated systems to those dominated by less sensitive species. Sponges are important structural and functional components of coral reef ecosystems, but despite increasing field based evidence that sponges may be ‘winners’ in response to environmental degradation, our understanding of how they respond to the combined effects of OW and OA is limited. To determine the tolerance of adult sponges to climate change, four abundant Great Barrier Reef species were experimentally exposed to OW and OA levels predicted for 2100, under two CO2 Representative Concentration Pathways (RCPs). The impact of OW and OA on early life history stages was also assessed for one of these species to provide a more holistic view of species impacts. All species were generally unaffected by conditions predicted under RCP6.0, although environmental conditions projected under RCP8.5 caused significant adverse effects; with elevated temperature decreasing the survival of all species, increasing levels of tissue necrosis and bleaching, elevating respiration rates and decreasing photosynthetic rates. OA alone had little adverse effect, even under RCP8.5 concentrations. Importantly, the interactive effect of OW and OA varied between species with different nutritional modes, with elevated pCO2 exacerbating temperature stress in heterotrophic species but mitigating temperature stress in phototrophic species. This antagonistic interaction was reflected by reduced mortality, necrosis and bleaching of phototrophic species in the highest OW/OA treatment. Survival and settlement success of C. foliascens larvae were unaffected by experimental treatments, and juvenile sponges exhibited greater tolerance to OW than their adult counterparts. With elevated pCO2 providing phototrophic species with protection from elevated temperature, across different life-stages, climate change may ultimately drive a shift in the composition of sponge assemblages towards a dominance of phototrophic species.

Continue reading ‘Interactive effects of temperature and pCO2 on sponges: from the cradle to the grave’

Restructuring of the sponge microbiome favors tolerance to ocean acidification

Ocean acidification is increasing and affects many marine organisms. However, certain sponge species can withstand low-pH conditions. This may be related to their complex association with microbes. We hypothesized that species with greater microbial diversity may develop functional redundancy that could enable the holobiont to survive even if particular microbes are lost at low-pH conditions. We evaluated the effects of acidification on the growth and associated microbes of three ubiquitous Mediterranean sponges by exposing them to the present pH level and that predicted for the year 2100. We found marked differences among the species in the acquisition of new microbes, being high in Dysidea avara, moderate in Agelas oroides and null in Chondrosia reniformis; however, we did not observe variation in the overall microbiome abundance, richness or diversity. The relative abilities to alter the microbiomes contributes to survivorship in an OA scenario as demonstrated by lowered pH severely affecting the growth of C. reniformis, halving that of A. oroides, and unaffecting D. avara. Our results indicate that functional stability of the sponge holobiont to withstand future OA is species-specific and is linked to the species’ ability to use horizontal transmission to modify the associated microbiome to adapt to environmental change.

Continue reading ‘Restructuring of the sponge microbiome favors tolerance to ocean acidification’

Effects of anthropogenic stressors on tropical sponge ecology

The impacts of coastal development, ocean acidification, and temperature increases on sponge ecology were investigated, with an emphasis on community-wide impacts. At three locations with varying degrees of coastal development and sediment supply, field surveys were used to assess existing sponge abundance, diversity, species richness and community composition in Jamaica. Sediment accumulation rate, total suspended solids and other water quality parameters were quantified. The community-wide consequences of coastal development and increased sediment supply were also investigated by monitoring the annual and seasonal recruitment, as well as community succession over 6 years and 30 months, respectively. Of the adult (existing) populations surveyed, the location with the lowest degree of coastal development and sediment supply had higher sponge abundance, diversity, species richness and a distinct community composition than the other two locations with higher coastal development. Sponge seasonal recruitment was similar in diversity and percent cover across all locations; however, the diversity and percent cover of sponges assessed annually was lowest at the location with the most coastal development and sediment supply, suggesting that post-settlement mortality was higher at this location. After 30 months, the location with the highest sediment supply had statistically more bare space, which is indicative of an overall lack of recruitment; this provides further evidence that post-settlement mortality is occurring and propagating community trajectory changes. Although the exact mechanism is unclear, this study provides correlative evidence that even moderate coastal development is influencing sponge communities on reefs along the northern coast of Jamaica

To determine the effects of industrialization and increasing atmospheric CO2 on sponges, two studies were performed to evaluate how 1) ocean acidification affects the interactions between a bioeroding sponge, Cliona varians , and a coral, Porites furcata and 2) how increasing temperature and decreasing pH affect sponge erosion of living and dead coral substrate. The results of the first study indicated that acidification had no negative physiological impacts on C. varians, and no significant impact on the survival of either coral or sponges. However, exposure to end-of-century levels of pH reduced calcification in P. furcata and led to a significant increase in sponge-mediated erosion. The second study provided a more comprehensive evaluation of the relevant interactions between sponges and living corals and evaluated the differential impacts of bioeroders on living and dead coral substrate under acidification and warming scenarios. The findings of this study suggest differential impacts of temperature, pH and sponge bioerosion for living and dead corals. Living coral calcification was significantly reduced by temperature and sponge treatments, with no significant effect of pH, while dead coral dissolution was primarily driven by pH, regardless of sponge presence or seawater temperature. The results of this study suggests that future acidification and warming studies should include ecologically relevant time scales, adequate acclimation periods, interactions, and multiple levels of community organization to better understand and predict ecosystem-level response to future environmental conditions. This dissertation represents an effort to understand how anthropogenic stressors are affecting sponge communities, and the subsequent implications for reef community structure and function.

Continue reading ‘Effects of anthropogenic stressors on tropical sponge ecology’

Impact of high pCO2 and warmer temperatures on the process of silica biomineralization in the sponge Mycale grandis

Siliceous sponges have survived pre-historical mass extinction events caused by ocean acidification and recent studies suggest that siliceous sponges will continue to resist predicted increases in ocean acidity. In this study, we monitored silica biomineralization in the Hawaiian sponge Mycale grandis under predicted pCO2 and sea surface temperature scenarios for 2100. Our goal was to determine if spicule biomineralization was enhanced or repressed by ocean acidification and thermal stress by monitoring silica uptake rates during short-term (48 h) experiments and comparing biomineralized tissue ratios before and after a long-term (26 d) experiment. In the short-term experiment, we found that silica uptake rates were not impacted by high pCO2 (1050 µatm), warmer temperatures (27°C), or combined high pCO2 with warmer temperature (1119 µatm; 27°C) treatments. The long-term exposure experiments revealed no effect on survival or growth rates of M. grandis to high pCO2 (1198 µatm), warmer temperatures (25.6°C), or combined high pCO2 with warmer temperature (1225 µatm, 25.7°C) treatments, indicating that M. grandis will continue to prosper under predicted increases in pCO2 and sea surface temperature. However, ash-free dry weight to dry weight ratios, subtylostyle lengths, and silicified weight to dry weight ratios decreased under conditions of high pCO2 and combined pCO2 warmer temperature treatments. Our results show that rising ocean acidity and temperature have marginal negative effects on spicule biomineralization and will not affect sponge survival rates of M. grandis.

Continue reading ‘Impact of high pCO2 and warmer temperatures on the process of silica biomineralization in the sponge Mycale grandis’

Climate change stressors destabilize the microbiome of the Caribbean barrel sponge, Xestospongia muta

The effect of climate change, both thermal stress and ocean acidification, on coral reefs is of increasing concern with the effects on calcification at the organismal level, and changes in the ratio of accretion to erosion on larger spatial scales of particular interest. But far fewer studies have been done on non-calcifying organisms, such as sponges, that have important ecological roles on coral reefs. Here we report the results of a combined thermal stress and ocean acidification experiment on the ecologically dominant barrel sponge, Xestospongia muta, found on coral reefs throughout the Caribbean basin. The results show that ocean acidification alone, as well as its interaction with elevated seawater temperature, has significant effects on the sponge microbiome. Specifically, the significant interactive effects of thermal stress and ocean acidification led to a decline in the productivity potential of the symbiotic cyanobacteria in these sponges with a subsequent impact on nutrient transfer, as carbohydrate, between symbiont and host. Additionally, while neither environmental stressor predictably changed sponge microbiome community composition, ocean acidification alone reduced the stability of sponge microbiomes and their predicted functions. Future changes in ocean acidification and thermal stress predicted by current climate models could negatively impact the microbiomes of coral reef organisms and therefore also affect their organismal performance and fitness in the future.

Continue reading ‘Climate change stressors destabilize the microbiome of the Caribbean barrel sponge, Xestospongia muta’

Sponge erosion under acidification and warming scenarios: differential impacts on living and dead coral

Ocean acidification will disproportionately impact the growth of calcifying organisms in coral reef ecosystems. Simultaneously, sponge bioerosion rates have been shown to increase as seawater pH decreases. We conducted a 20-week experiment that included a 4-week acclimation period with a high number of replicate tanks and a fully orthogonal design with two levels of temperature (ambient and +1 °C), three levels of pH (8.1, 7.8 and 7.6) and two levels of boring sponge (Cliona varians, present and absent) to account for differences in sponge attachment and carbonate change for both living and dead coral substrate (Porites furcata). Net coral calcification, net dissolution/bioerosion, coral and sponge survival, sponge attachment, and sponge symbiont health were evaluated. Additionally, we used the empirical data from the experiment to develop a stochastic simulation of carbonate change for small coral clusters (i.e., simulated reefs). Our findings suggest differential impacts of temperature, pH and sponge presence for living and dead corals. Net coral calcification (mg CaCO3 cm−2 d−1) was significantly reduced in treatments with increased temperature (+1 °C) and when sponges were present; acidification had no significant effect on coral calcification. Net dissolution of dead coral was primarily driven by pH, regardless of sponge presence or seawater temperature. A reevaluation of the current paradigm of coral carbonate change under future acidification and warming scenarios should include ecologically relevant time scales, species interactions, and community organization to more accurately predict ecosystem-level response to future conditions.

Continue reading ‘Sponge erosion under acidification and warming scenarios: differential impacts on living and dead coral’


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