LEICHTER, J.J.; HELMUTH, B.*; FISCHER, A.M.; Scripps Inst. Oceanography; Univ. South Carolina, Columbia; Cornell Univ., Ithaca: What lies beneath the surface: quantifying complex thermal environments on corals reefs

Understanding patterns of water temperature on coral reefs has become of prime importance in forecasting patterns of physiological stress due to changing environmental conditions. However, these patterns are often based on daily measurements of sea surface temperature, which by necessity neglect higher frequency temporal fluctuations in water temperature. A growing body of evidence suggests that corals are physiologically sensitive to rapid temperature changes on time scales of minutes to hours. We collected high frequency temperature data on six coral reefs in the Caribbean, Bahamas, and Florida Keys. Data were collected at 10 � 16 min intervals across depths from 10 � 36 m between 1997 and 2004, and analyzed along with concomitant records of sea surface temperature. Variability associated with high frequency internal waves and semi-diurnal (M2) internal tidal forcing was persistent at 5 out of the 6 sites and increased with increasing depth. Diurnal variability associated with daily heating and cooling of the water column was significant at all sites with greatest magnitude at shallowest depths. The maximum within-day temperature ranges of 2 � 8 �C were of equal magnitude to the seasonal range of daily mean temperatures at all sites. The amplitude of the seasonal variability showed a direct relationship with latitude among sites. By contrast, the variability at daily and faster frequencies showed a more complex relationship to site latitude and was greatest at the highest and lowest latitudes. Interactions of depth, site, and season across the study region are associated with distinct signals of thermal variability that may have significant implications for the physiology and ecology of corals and other reef organisms.