Posts Tagged 'corals'

Diversity and stability of coral endolithic microbial communities at a naturally high pCO2 reef

The health and functioning of reef-building corals is dependent on a balanced association with prokaryotic and eukaryotic microbes. The coral skeleton harbours numerous endolithic microbes, but their diversity, ecological roles and responses to environmental stress, including ocean acidification (OA), are not well characterized. This study tests whether pH affects the diversity and structure of prokaryotic and eukaryotic algal communities associated with skeletons of Porites spp. using targeted amplicon (16S rRNA gene, UPA and tufA) sequencing. We found that the composition of endolithic communities in the massive coral Porites spp. inhabiting a naturally high pCO2 reef (avg. pCO2 811 μatm) is not significantly different from corals inhabiting reference sites (avg. pCO2 357 μatm), suggesting that these microbiomes are less disturbed by OA than previously thought. Possible explanations may be that the endolithic microhabitat is highly homeostatic or that the endolithic micro-organisms are well adapted to a wide pH range. Some of the microbial taxa identified include nitrogen-fixing bacteria (Rhizobiales and cyanobacteria), algicidal bacteria in the phylum Bacteroidetes, symbiotic bacteria in the family Endozoicomoniaceae, and endolithic green algae, considered the major microbial agent of reef bioerosion. Additionally, we test whether host species has an effect on the endolithic community structure. We show that the endolithic community of massive Porites spp. is substantially different and more diverse than that found in skeletons of the branching species Seriatopora hystrix and Pocillopora damicornis. This study reveals highly diverse and structured microbial communities in Porites spp. skeletons that are possibly resilient to OA.

Continue reading ‘Diversity and stability of coral endolithic microbial communities at a naturally high pCO2 reef’

The role of natural variability in shaping the response of coral reef organisms to climate change

Purpose of Review

We investigate whether regimes of greater daily variability in temperature or pH result in greater tolerance to ocean warming and acidification in key reef-building taxa (corals, coralline algae).

Recent Findings

Temperature and pH histories will likely influence responses to future warming and acidification. Past exposure of corals to increased temperature variability generally leads to greater thermotolerance. However, the effects of past pH variability are unclear. Variability in pH or temperature will likely modify responses during exposure to stressors, independent of environmental history. In the laboratory, pH variability often limited the effects of ocean acidification, but the effects of temperature variability on responses to warming were equivocal.

Summary

Environmental variability could alter responses of coral reef organisms to climate change. Determining how both environmental history as well as the direct impacts of environmental variability will interact with the effects of anthropogenic climate change should now be high priority.

Continue reading ‘The role of natural variability in shaping the response of coral reef organisms to climate change’

Natural ocean acidification at Papagayo upwelling system (North Pacific Costa Rica): implications for reef development

Numerous experiments have shown that ocean acidification impedes coral calcification, but knowledge about in situ reef ecosystem response to ocean acidification is still scarce. Bahía Culebra, situated at the northern Pacific coast of Costa Rica, is a location naturally exposed to acidic conditions due to the Papagayo seasonal upwelling. We measured pH and pCO2 in situ during two non-upwelling seasons (June 2012, May–June 2013), with a high temporal resolution of every 15 and 30 min, respectively, using two Submersible Autonomous Moored Instruments (SAMI-pH, SAMI-CO2). These results were compared with published data from the upwelling season 2009. Findings revealed that the carbonate system in Bahía Culebra shows a high temporal variability. Incoming offshore waters drive inter- and intra-seasonal changes. Lowest pH (7.8) and highest pCO2 (658.3 µatm) values measured during a cold-water intrusion event in the non-upwelling season were similar to those minimum values reported from upwelling season (pH = 7.8, pCO2 = 643.5 µatm), unveiling that natural acidification occurs sporadically also in non-upwelling season. This affects the interaction of photosynthesis, respiration, calcification, and carbonate dissolution and the resulting diel cycle of pH and pCO2 in the reefs of Bahía Culebra. During non-upwelling season, the aragonite saturation state (Ωa) rises to values of > 3.3 and enhances calcification. Aragonite saturation state values during upwelling season falls below 2.5, hampering calcification and coral growth. Low reef accretion in Bahía Culebra indicates high erosion rates and that these reefs grow on the verge of their ecological tolerance. The Ωa threshold values for coral growth, derived from the correlation between Ωa and coral linear extension rates, suggest that future ocean acidification will threaten reefs in Bahía Culebra. These data contribute to build a better understanding of the carbonate system dynamics and coral reefs key response (e.g. coral growth) to natural low-pH conditions, in upwelling areas in the Eastern Tropical Pacific and beyond.

Continue reading ‘Natural ocean acidification at Papagayo upwelling system (North Pacific Costa Rica): implications for reef development’

Environmental controls on modern scleractinian coral and reef-scale calcification

Modern reef-building corals sustain a wide range of ecosystem services because of their ability to build calcium carbonate reef systems. The influence of environmental variables on coral calcification rates has been extensively studied, but our understanding of their relative importance is limited by the absence of in situ observations and the ability to decouple the interactions between different properties. We show that temperature is the primary driver of coral colony (Porites astreoides and Diploria labyrinthiformis) and reef-scale calcification rates over a 2-year monitoring period from the Bermuda coral reef. On the basis of multimodel climate simulations (Coupled Model Intercomparison Project Phase 5) and assuming sufficient coral nutrition, our results suggest that P. astreoides and D. labyrinthiformis coral calcification rates in Bermuda could increase throughout the 21st century as a result of gradual warming predicted under a minimum CO2 emissions pathway [representative concentration pathway (RCP) 2.6] with positive 21st-century calcification rates potentially maintained under a reduced CO2 emissions pathway (RCP 4.5). These results highlight the potential benefits of rapid reductions in global anthropogenic CO2 emissions for 21st-century Bermuda coral reefs and the ecosystem services they provide.

Continue reading ‘Environmental controls on modern scleractinian coral and reef-scale calcification’

Bioeroding sponges and the future of coral reefs

Bioeroding sponges play a central role in carbonate cycling on corals reefs. They may respond differently to habitat deterioration than many other benthic invertebrates, because at some locations, their abundances increased after disturbance. We reviewed literature on these sponges in context of environmental change and provide meta-analyses at global level. A difficult taxonomy and scarce scientific expertise leave them inadequately studied, even though they are the best-known internal bioeroders. They are sheltered within the substrate they erode, appear to be comparatively resilient against environmental change and can have heat-resistant photosymbionts and ‘weedy’ traits, including multiple pathways to reproduce or disperse and fast growth and healing abilities. Especially temperature stress appears to disable calcifiers stronger than bioeroding sponges. Moreover, increases in bioeroding sponge abundances have been related to eutrophication and disturbances that led to coral mortality. Chemical sponge bioerosion is forecast to double with doubled partial pressure of carbon dioxide, but reduced substrate density may counteract this effect, as dominant sponges erode more in denser substrates. Case examples portray shifting impacts of bioeroding sponges with environmental change, with some reefs already being erosional. Most available data and the largest known species record are from the Caribbean. Data from the Coral Triangle and India are largely restricted to faunistic records. Red Sea, Japanese and cold-water reef bioeroding sponges are the least studied. We need more quality research on functions and interaction effects, about which we are still insufficiently informed. With many calcifiers increasingly failing and bioeroding sponges still doing well, at least at intermediate levels of local and global change, these sponges may continue to significantly affect coral reef carbonate budgets. This may transform them from valuable and necessary recyclers of calcium carbonate to problem organisms.

Continue reading ‘Bioeroding sponges and the future of coral reefs’

Sponge reefs of the British Columbia, Canada Coast: impacts of climate change and ocean acidification

Sponge reefs living in deeper shelf waters on the western margin of North America are somewhat insulated from surface water effects of localized ocean warming but are susceptible to increasing hypoxia associated with ocean stratification and increasing upwelling. The largest reef complexes are projected to experience increasing upwelling and low-oxygen events in the future as part of the observed and projected changes in ocean ventilation accompanying increased atmospheric carbon dioxide concentrations. Inshore and shallow reefs are subjected to surface water warming in fiords. Surface water productivity is anticipated to change slightly likely having limited negative impact on the sponge reefs which are adapted to relatively low-nutrient situations. It is unknown the extent to which glass sponges might be resilient to lower oxygen conditions. While filtration is an energetically costly method of feeding, glass sponges appear to be adapted to reduce their energetic needs by using ambient flow to assist filtration. Populations that experience extreme hypoxia in some fiords may be extirpated by extreme anoxic events. Ocean acidification will not have as large an effect on the siliceous skeleton sponges as it will on corals and other carbonate-dependent organisms though it is possible changing pH will affect tissue functioning and homeostasis by compromising membrane pumps. Hexactinellid sponges and sponge reefs have been resilient to changing climate and ocean environments in the geologic past.

Continue reading ‘Sponge reefs of the British Columbia, Canada Coast: impacts of climate change and ocean acidification’

Active modulation of the calcifying fluid carbonate chemistry (δ11B, B/Ca) and seasonally invariant coral calcification at sub-tropical limits

Coral calcification is dependent on both the supply of dissolved inorganic carbon (DIC) and the up-regulation of pH in the calcifying fluid (cf). Using geochemical proxies (δ11B, B/Ca, Sr/Ca, Li/Mg), we show seasonal changes in the pHcf and DICcf for Acropora yongei and Pocillopora damicornis growing in-situ at Rottnest Island (32°S) in Western Australia. Changes in pHcf range from 8.38 in summer to 8.60 in winter, while DICcf is 25 to 30% higher during summer compared to winter (×1.5 to ×2 seawater). Thus, both variables are up-regulated well above seawater values and are seasonally out of phase with one another. The net effect of this counter-cyclical behaviour between DICcf and pHcf is that the aragonite saturation state of the calcifying fluid (Ωcf) is elevated ~4 times above seawater values and is ~25 to 40% higher during winter compared to summer. Thus, these corals control the chemical composition of the calcifying fluid to help sustain near-constant year-round calcification rates, despite a seasonal seawater temperature range from just ~19° to 24 °C. The ability of corals to up-regulate Ωcf is a key mechanism to optimise biomineralization, and is thus critical for the future of coral calcification under high CO2 conditions.

Continue reading ‘Active modulation of the calcifying fluid carbonate chemistry (δ11B, B/Ca) and seasonally invariant coral calcification at sub-tropical limits’


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Ocean acidification in the IPCC AR5 WG II

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