Assessing evidence of phase shifts from coral to macroalgal dominance on coral reefs

Many marine scientists have concluded that coral reefs are moving toward or are locked into a seaweed-dominated state. However, because there have been no regional- or global-scale analyses of such coral reef "phase shifts," the magnitude of this phenomenon was unknown. We analyzed 3581 quantitative surveys of 1851 reefs performed between 1996 and 2006 to determine the frequency, geographical extent, and degree of macroalgal dominance of coral reefs and of coral to macroalgal phase shifts around the world. Our results indicate that the replacement of corals by macroalgae as the dominant benthic functional group is less common and less geographically extensive than assumed. Although we found evidence of moderate local increases in macroalgal cover, particularly in the Caribbean, only 4% of reefs were dominated by macroalgae (i.e.,>50% cover). Across the Indo-Pacific, where regional averages of macroalgal cover were 9-12%, macroalgae only dominated 1% of the surveyed reefs. Between 1996 and 2006, phase shift severity decreased in the Caribbean, did not change in the Florida Keys and Indo-Pacific, and increased slightly on the Great Barrier Reef due to moderate coral loss. Coral reef ecosystems appear to be more resistant to macroalgal blooms than assumed, which has important implications for reef management

Phase Behavior of Aqueous Na-K-Mg-Ca-CI-NO3 Mixtures: Isopiestic Measurements and Thermodynamic Modeling

A comprehensive model has been established for calculating thermodynamic properties of multicomponent aqueous systems containing the Na{sup +}, K{sup +}, Mg{sup 2+}, Ca{sup 2+}, Cl{sup -}, and NO{sub 3}{sup -} ions. The thermodynamic framework is based on a previously developed model for mixed-solvent electrolyte solutions. The framework has been designed to reproduce the properties of salt solutions at temperatures ranging from the freezing point to 300 C and concentrations ranging from infinite dilution to the fused salt limit. The model has been parameterized using a combination of an extensive literature database and new isopiestic measurements for thirteen salt mixtures at 140 C. The measurements have been performed using Oak Ridge National Laboratory's (ORNL) previously designed gravimetric isopiestic apparatus, which makes it possible to detect solid phase precipitation. Water activities are reported for mixtures with a fixed ratio of salts as a function of the total apparent salt mole fraction. The isopiestic measurements reported here simultaneously reflect two fundamental properties of the system, i.e., the activity of water as a function of solution concentration and the occurrence of solid-liquid transitions. The thermodynamic model accurately reproduces the new isopiestic data as well as literature data for binary, ternary and higher-order subsystems. Because of its high accuracy in calculating vapor-liquid and solid-liquid equilibria, the model is suitable for studying deliquescence behavior of multicomponent salt systems

Reef development at high-latitudes during multiple interglacial cycles: New evidence from Lord Howe Island, southwestern Pacific

Reef development during past Interglacial periods, when sea level and sea surface temperatures were higher than today, provide unique insights into how reef systems may respond to projected human-induced global warming. Lord Howe Island currently represents the southernmost limit of reef development in the Pacific. Reef growth of Pleistocene age has been inferred to have occurred around the island, and this paper provides the first detailed descriptions on the character of this development. Two phases of reef growth are identified, which occurred as isolated fringing reefs along the edge of the basaltic hills of the island. Uranium-series dating indicates that the upper part of the sequence is of Last Interglacial age, however extensive calcite recrystallisation meant the lower part of the sequence does not yield reliable ages. Calcite cements suggest that several phases of recrystallisation have occurred meaning the lower part of the sequence is most likely to represent reef of Penultimate Interglacial age. Component analysis of the sedimentary matrix within the reef indicates coralline algae dominated sands which are very similar to the modern reef environment. This suggests that the environment at Lord Howe Island has remained at or close to the environmental limits for reef growth during the past few interglacials, despite lithospheric plate motion moving this island further north into reef building seas