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Current Projects


Modeling and developing new methodologies to document the thermal regime on coral reefs

sattemp

(Published:  Castillo and Lima, Limnology and Oceanography: Methods (2010) 8:107-117)

Thermal stress has been regarded as one of the most important parameters monitored on reefs to assess coral health, and therefore, it is important to have accurate temperature data for reef environments. Whereas most studies of thermal stress on reefs have relied on sea surface temperature (SST) data, our preliminary assessments suggests that subsurface temperatures may differ considerably from those at the surface. To investigate this issue, we compared concomitant field temperature measurements and satellite-derived SST records on two different coral reefs on the Mesoamerican Barrier Reef System, the second largest barrier reef system in the world. Our results indicate a negative (cool) bias for satellite-derived SSTs records when compared with subsurface field measurements on coral reefs. Compared with daytime values, nighttime satellite-derived SST measurements yielded larger negative biases and were less correlated with field measurements. Understanding these biases will not only provide a better evaluation of the thermal regime on individual reefs, but will also create opportunities for more precise temperature comparisons among coral reef environments. We stress here the importance of “sea-truthing” and complementing satellite-derived SST records with field based data when measuring temperatures on coral reefs. These results are now available to coral reef biologists, ecologists, physiologists, and conservationists as they use readily accessible satellite-derived SST records to assess how their individual reef systems are responding to climate change.





Investigating the effects of warming and CO2-induced ocean acidification on corals

Ocean Acidification

(In preparation: collaborative project with the Ries and Bruno Labs)

Atmospheric carbon dioxide-induced ocean acidification and rising seawater temperature are identified as two of the greatest threats to modern coral reefs. Within this century, surface seawater pH is expected to decrease by at least 0.3 units, and sea surface temperature is predicted to rise by 1 to 3 degree Celsius. However, uncertainty remains as to whether ocean acidification or ocean warming will have the more deleterious impact on coral reefs over the next century. In this experiment we  employed 90-day laboratory experiments to investigate the impact of CO2-induced ocean acidification and temperature on calcification of the Caribbean reef-building coral Siderastrea siderea. Corals were exposed to four pCO2 experimental seawater treatments (280, 477, 604, and 2553 ppm) and three temperature treatments ( 25, 28, and 32 degree Celsius). Results are currently in preparation.



Quantify  coral physiological response using reciprocal transplant experiments among reef zones


coral

(This is an ongoing experiment)

Eighteen source coral colonies were transplanted from each reef zone (forereef, backreef, nearshore). Six colonies were transplanted within the source reef zone and six colonies each were transplanted to the other two reef zones. Individual source coral colonies within each reef zone were collected from a  distance 3-5 m apart to minimize confounding factors associated with microhabitat differences. Colony size were similar across colonies ranging between 15 and 25 cm in diameter. Transplanted colonies were glued to ceramic tiles and were randomly placed at their transplanted location. Physiological parameters are measured annually. We are currently into year three of this project.



Investigating variations in coral skeletal extension over approximately the last century


Xradio

Extend

(Published: Castillo et al., PLoS ONE (2011) 6: e14615)

In this project we investigated century-scale variations in skeletal extension for the slow-growing massive scleractinian coral Siderastrea siderea inhabiting the forereef, backreef, and nearshore reefs of the Mesoamerican Barrier Reef System in the western Caribbean Sea. Coral cores were extracted, slabbed, and X-rayed. Annual skeletal extension was estimated from adjacent low- and high-density growth bands. Since the early 1900s, forereef coral colonies have shifted from exhibiting the fastest to the slowest skeletal growth, while growth rates for backreef and nearshore colonies have remained relatively stable. These results suggest that forereef S. siderea colonies are more susceptible to environmental stress than backreef and nearshore counterparts, which may have historically been exposed to higher natural baseline stressors. Our findings should improve our ability to predict and potentially mitigate the effects of future environmental stressors on coral reef ecosystems.




Investigating the effects of thermal history on coral skeletal extension

TempExt


(Published: Castillo et al. 2012, Nature Climate Change)

We further reconstructed the thermal history including the history of thermal variability for the Mesoamerican Barrier reef System to constrain the cause(s) of the observed reductions in coral skeletal growth for forereef corals. Our results indicate that over the last three decades in the western Caribbean Sea, forereef coral skeletal extension declined with increasing seawater temperature and associated thermal stress, while skeletal growth for backreef and nearshore corals were not impacted. Our results suggest that natural diurnal and seasonal thermal fluctuations that, over geological timescales, have characterized backreef and nearshore environments to a greater extent than forereef environments, may have promoted acclimatization and/or adaptation to more recent anthropogenic thermal stress. Collectively, these findings reveal how corals have responded to recent anthropogenic warming, offer insights into how they are likely to respond to future warming, and highlight the importance of understanding cross-reef differences in coral thermal tolerance for managing coral reef ecosystems in an era of rapid regional and global climate change.





An examination of the effects of climate change on corals across a latitudinal gradient on the Mesoamerican Barrier Reef System
 

NS



(Ongoing Experiment: collaborative project with the Ries Lab)

This study is designed to examine Siderastrea siderea growth trends along a north-south gradient on the Belize Barrier Reef System. We are investigating and comparing calcification response for corals from the more southern portions of the forereef environment with those for corals from the more northern portions of the the MBRS. This is a very interesting question because in our previous study published in Nature Climate Change a pattern emerged within the forereef zone (southern MBRS), where colonies from the more thermally stable northern portions of the forereef environment―more proximal to the open ocean―exhibited a more negative calcification response to recent seawater warming than colonies from the more thermally variable southern portions of the forereef environment―located more distal from the open ocean. These observations of corals’ responses to thermal stress within the forereef zone, support the assertion that corals that have historically been exposed to more stable baseline seawater temperatures may ultimately be more vulnerable to recent and future warming resulting from the anthropogenic emission of greenhouse gases.

Stay tuned! Several other projects are currently in development!

We are also collaborating on a variety of different projects with the Ries Lab, Bruno Lab, and the Marchetti Lab.
                                           




© 2013 University of North Carolina at Chapel Hill   
Maintained by K. D. Castillo, Pualani Armstrong, and Ashley D. Foguel
   Last Updated - November, 2013