A community metabolism approach to examine the environmental regulation of coral growth

Lead Research Organisation: University of Essex
Department Name: Biological Sciences


Coral reef diversity and productivity are directly dependent on the ecological and biogeochemical dynamics (e.g. calcification, growth and recruitment) of corals, the key ecosystem architects. These corals can be stressed by relatively small modifications in temperature, light availability (turbidity and sedimentation) and storm damage, which in turn can lead to alterations of the physical and biological structure of the entire ecosystem. Further anthropogenic-induced stresses, such as over-fishing and coastal land use changes, compound this stress; however, it is now generally recognised that two of the greatest environmental threats to corals are thermal induced bleaching events and ocean acidification. Thermal bleaching refers to the dipigmentation of corals as they experience higher than average temperatures whist ocean acidification refers to the lowering of pH as elevated atmospheric CO2 slowly diffuses into seawater. Under these lower pH condiitons coral calcification rates are reduced. Research has now begun to focus on how these factors act in concert to affect coral growth; unfortunately, these studies are still technologically limited to enable full control over the complex carbon chemistry of seawater required for acidification studies. Furthermore, light availability has been ignored as a co-regulatory factor, which is surprising since light not only exacerbates coral bleaching but also enhances the rate of calcification. We have recently identified that corals with certain morphologies (Types, our terminology) exhibit alternative bleaching responses, which in turn are a function of calcification patterns and rates. Type 1 species have fast growth and calcification rates, but are extremely sensitive to environmental change. Type 2 species are more robust, slow growing and have reduced rates of calcification. Thus, the extent to which a species will be affected by climate change appears to be associated with, and potentially dependant upon, the primary growth processes. This relative susceptibility of coral Types has profound implications for both the biological and physical structure of coral reefs. Work proposed here builds on several successful studies from our laboratory examining the effect of environmental change on calcifying organisms. Existing 'pH stat' technology from these studies will be modified to provide full control of the inorganic carbon system of seawater. A series of experiments will be performed to examine, using this new technology, how coral Types respond to simultaneous changes in light, temperature and CO2, the primary factors regulating coral growth. Specifically, we focus on coral community metabolism since this represents the net activity of respiration, by the coral host and associated bacterial flora, and photosynthesis, by the coral's symbiotic microalgae, that ultimately contribute to growth (calcification). We will apply this community metabolism approach in the laboratory to obtain high levels of control upon gas exchange, thus allowing physical/chemical environmental conditions to be controlled with high precision and metabolic rates measured with high temporal resolution.


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Description In addressing our overall aim "To better understand how growth of reef building corals is moderated by light and CO2 and so gauge the likely growth of corals for future climate scenarios" we have produced substantial achievements and outcomes far beyond our originally proposed expectation:
1. Development, construction and application of a new pCO2-stat microcosm system: New hardware was custom built to measure and control seawater pCO2. Coupled to simultaneous measurements of pH (and O2/temprature) enables control of any inorganic carbon chemistry parameter and opens up new capabilities for monitoring (and controlling) seawater pH. Addressing all subsequent biological questions was critically dependent upon producing this hardware; an integral aspect was simultaneous development of novel software (program CCSI) that provided the monitoring and controlling capabilities and is now available to the wider research community.
2. Demonstrated that light availability regulates the metabolic response of corals to ocean acidification (OA): We experimentally observed for two model coral species that higher light intensities reduce the impact of OA upon calcification; these novel observations were further supported from a wider (meta) examination of previously published coral OA research from other coral species. Our work carries major implications: (i) low light reef environments will be the most heavily impacted by OA, and (ii) the outcome of future coral OA experiments will be critically dependant upon how light is controlled for.
3. Determined the influence of light-OA interactions upon corals' thermal stress susceptibility: A second set of experiments examined coral metabolism/calcification for various light-OA scenarios for (i) two different seasonal temperatures and (ii) an anomalous temperature stress experiment during the 'summer' treatment. Whilst we are still evaluating the coupled OA-light-seasonal temperature responses, it was clear that the OA treatments did not influence the outcome to anomalous stress; this is an exceptionally important observation and is contrary to what is currently widely accepted.
Exploitation Route We have made both major technical advances in experimentation and novel scientific advances for understanding how environmental change scenarios will impact key organisms (e.g. reef building corals). Our successes have (i) encouraged leading researchers to adopt our technological approaches through collaboration, (ii) highlighted to the international community the dangers of not controlling for a key variable (light) during OA experimentation, and (iii) demonstrated that current 'low light refuge' theory for coral bleaching will not apply to OA. Our advances have been extremely timely for international investment in directed OA programs and importantly our projects have enabled us to engage with NERC, EU, NSF and Brazilian Government funded consortia programs to extend the longevity of exploring our research aims. We have already begun engaging with biosensor industries (e.g. Chelsea Technologies Group and Qubit Systems) to explore marketing of the pCO2 control system and the aquarist industry (via the UK's Coral Aquarist Research Network) to optimize coral growth conditions to enhance market profitability.
Sectors Environment

Description Overall, our novel outcomes have so far been reported via peer reviewed journal publications (3), academic conference presentations (4), non-peer reviewed magazine articles (2), television/radio interviews (2) and public science talks (1). A further 3 papers are in preparation for peer review publication. Our substantial end-user engagement, despite our pathway to impact plan not being funded, and continued participation in parallel programs beyond the current lifetime of the project ensure significant longer-term and even wider impact of this research.
First Year Of Impact 2011
Sector Education,Environment
Impact Types Societal,Economic