Abstract
On Conch Reef, Florida Keys, USA, we examine relationships between temperature variability measured with a unique, high-resolution sensor network, and the abundance of benthic reef organisms and carbon, nitrogen and oxygen stable isotopic composition of two abundant macroalgal species. Visualization of spatial temperature anomalies mapped onto measured reef bathymetry reveals episodic thermal patchiness and persistent thermal features likely indicating meter scale variability in nutrient supply. These patterns result from the relatively shallow depths of the offshore thermocline and an active internal wave field creating a hydrographic structure conducive to interactions of an offshore, subthermocline nutrient pool with reef topography. The distribution of major benthic reef organism taxa, as well as the stable isotopic composition of C, N and O, from the macroalgae Dictyota menstrualis and Halimeda tuna are all highly variable on scales of less than 10 m and are not necessarily depth-dependent. Covariability between spatial patterns of the temperature minima, depth and delta C-13 of D. menstrualis and H. tuna suggest a role of oceanographic forcing in inorganic carbon acquisition in these species. Comparisons of the measured temperature with the predicted temperature based on delta O-18 from H. tuna aragonite suggest a possible influence of low salinity water in the system and non-linear interactions between ambient conditions and calcification at fine temporal and spatial scales. These observations have implications for the interpretation of both contemporary and paleontologic reef environments where oceanographic forcing interacts with complex reef topography.