Modeling the physical environment on coral reefs

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

(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.

Experimental investigation of the impact of seawater temperature and CO₂-induced ocean acidification on coral reefs

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

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

Long-term field comparison of coral physiological performance among reef zones

Quantify and compare a variety of physiological response parameters of corals by conducting reciprocal transplant experiments among reef zones
(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 two of this project.

Climate change impacts on coral reefs

Investigating variations in coral skeletal extension over approximately the last century

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

Investigating the effects of thermal history including temperature variability on coral skeletal extension

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

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.

(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 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