Karl D. Castillo

Bio: Karl D. Castillo is an academic researcher from University of North Carolina at Chapel Hill. The author has contributed to research in topics: Coral & Coral reef. The author has an hindex of 17, co-authored 46 publications receiving 971 citations. Previous affiliations of Karl D. Castillo include University of South Carolina.

Influence of thermal history on the response of Montastraea annularis to short-term temperature exposure

Abstract: Acclimation of reef corals to environmental conditions has been related to metabolic response at large geographic scales, but regional relationships have rarely been described. Physiological responses to temperature increases of Montastraea annularis (Ellis and Solander 1786) from an inner lagoon and an outer barrier reef in the Gulf of Honduras, southern Belize, were compared in May 2003. The hypothesis that inferred differences in thermal history would result in contrasting responses to elevated temperature was tested. Ambient seawater temperatures adjacent to corals at 4–5 m depth were measured every 15 min at inner lagoon and outer barrier reef collection sites for 1 year (June 2002–May 2003). Monthly averages and 3-day running averages (warmest period, July–October 2002) of daily maximum seawater temperatures were significantly higher (by ∼0.5°C) at inner lagoon reef compared to outer barrier reef sites. M. annularis photosynthesis (P) and respiration (R) rates were measured in respirometers at six temperatures between 29°C and 35°C approximately every hour, with repeated measurements over 3 h. P and R were significantly lower across most temperature treatments for samples collected from the inner lagoon compared to outer barrier reef. Both inner and outer reef M. annularis displayed an increase in P and R with increasing temperature between 29°C and 32°C, but above 32°C P and R sharply declined. P/R ratio versus temperature showed a significant difference between the elevations of the regression lines suggesting that M. annularis from the outer barrier reefs may have been more physiologically stressed than those from the inner lagoon reefs when exposed to acute temperature changes. These results emphasize that thermal stress must be considered within the context of acclimation temperature, and that short-term exposures may have physiologically important effects on this species.

The reef-building coral Siderastrea siderea exhibits parabolic responses to ocean acidification and warming

Abstract: Anthropogenic increases in atmospheric CO 2 over this century are predicted to cause global average surface ocean pH to decline by 0.1–0.3 pH units and sea surface temperature to increase by 1–4°C. We conducted controlled laboratory experiments to investigate the impacts of CO 2 -induced ocean acidification ( p CO 2 = 324, 477, 604, 2553 µatm) and warming (25, 28, 32°C) on the calcification rate of the zooxanthellate scleractinian coral Siderastrea siderea , a widespread, abundant and keystone reef-builder in the Caribbean Sea. We show that both acidification and warming cause a parabolic response in the calcification rate within this coral species. Moderate increases in p CO 2 and warming, relative to near-present-day values, enhanced coral calcification, with calcification rates declining under the highest p CO 2 and thermal conditions. Equivalent responses to acidification and warming were exhibited by colonies across reef zones and the parabolic nature of the corals9 response to these stressors was evident across all three of the experiment9s 30-day observational intervals. Furthermore, the warming projected by the Intergovernmental Panel on Climate Change for the end of the twenty-first century caused a fivefold decrease in the rate of coral calcification, while the acidification projected for the same interval had no statistically significant impact on the calcification rate—suggesting that ocean warming poses a more immediate threat than acidification for this important coral species.

Decline of forereef corals in response to recent warming linked to history of thermal exposure

Abstract: Porites lutea in the Andaman Sea 17 and Diploastrea heliopora in the central Red Sea 2 , is negatively correlated with regional SST. However, these studies also show that the calcification response of corals to ocean warming is highly variable, both taxonomically and geographically. It is this variability in corals’ response to warming that has compelled investigations of the ability of corals to acclimatize and/or adapt to recent and predicted future ocean warming 3 , and whether their unique acclimatization and/or adaptive capacities can be used to improve coral reef management in the face of rapid global climate change 18 .

Thermal and pCO2 Stress Elicit Divergent Transcriptomic Responses in a Resilient Coral

Abstract: The oceans are becoming warmer and more acidic as a result of rising atmospheric pCO2. Transcriptome plasticity may facilitate marine organisms’ acclimation to thermal and acidification stress by tailoring gene expression to mitigate the impacts of these stressors. Here, we produce the first transcriptome of the abundant, ubiquitous, and resilient Caribbean reef-building coral Siderastrea siderea, and investigate this corals’ transcriptomic response to 95 days of thermal (T = 25, 28, 32°C) and CO2-induced acidification (324, 477, 604, 2553 µatm) stress. The S. siderea transcriptome was assembled using RNAseq and then Weighted Gene Correlation Network Analysis was employed to obtain systems-level insights into the coral’s stress response. Exposure of the coral to both elevated temperature and acidification elicited strong but divergent transcriptomic responses. Gene Ontology analysis suggests that long-term thermal stress disrupts homeostasis by increasing transcription of protein-coding genes associated with protein catabolism and suppressing transcription of genes involved in responding to environmental stimuli. Both next century (604 µatm) and extreme-high (2553 µatm) pCO2 stress increased transcription of genes associated with respiration, highlighting the potentially greater energetic requirements of maintaining calcification under high-pCO2 conditions. Under extreme-high-pCO2, increased transcription of H+-transporter genes was observed, consistent with the proposed role of proton transport in facilitating coral calcification under elevated pCO2. These results suggest that 95 days of exposure to 32°C seawater elicits a more adverse transcriptomic response (i.e., broad scale reductions in gene expression) than exposure to extreme-high acidification (2553 µatm; i.e., increased expression of genes associated with ion transport) within S. siderea—with the response to extreme warming suggesting cellular shutdown and the response to extreme acidification indicating capacity for acclimation. These results are consistent with the observation that rates of net calcification for the investigated corals were more negatively affected by the prescribed thermal stress than by the prescribed acidification stress. This study demonstrates how transcriptome plasticity may promote coral acclimation to these global change stressors, but that there are limits to the efficacy of this plasticity.

Comparison of in situ and satellite-derived (MODIS-Aqua/Terra) methods for assessing temperatures on coral reefs

Abstract: 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, recent findings have suggested that subsurface temperatures may differ considerably from those at the surface We compared concomitant in situ and satellite-derived SST measurements on two different coral reefs off southern Belize Seawater temperatures adjacent to corals at 3 to 5 m depth were measured every 10 to 30 min, from June 2002 to December 2007 An accompanying data set of seawater temperatures was collected every 10 min at 1, 3, 6, 9 and 15 m depth, from October 2006 to December 2007 Concurrent nighttime and daytime SST measurements from MODIS Aqua and Terra platforms with a spatial resolution of 4 km were obtained for comparative purposes Results indicate a negative (cool) bias for remotely sensed SSTs when compared with in situ measurements for both satellites across these two locations Compared with daytime values, nighttime satellite-derived SST measurements yielded larger negative biases and were less correlated with in situ 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 the importance of “sea-truthing” and complementing satellite-derived SST readings with in situ data when measuring temperatures on coral reefs

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

Abstract: The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Three decades of high-resolution coastal sea surface temperatures reveal more than warming

Abstract: A detailed assessment of near-shore temperature changes is needed for improved forecasts of the consequences of coastal warming. Here, changes in coastal sea surface temperature are estimated, showing that although 71% of the world's coastlines are warming, the rates of change have varied spatially.