Fluorescent bands in massive corals record centuries of coastal rainfall

Abstract

Massive coral colonies on the Great Barrier Reef grow outwards at 5–25 mm yr⁻¹ (ref. 1). Skeletal density varies seasonally in all massive corals from the Great Barrier Reef and an exact temporal record of growth can be obtained by X-radiography of appropriately cut sections of the colony^2,3. Environmental influences on coral growth have been described from such analyses^4–6. This is the first report from the skeletons of massive corals of yellow green fluorescent bands which appear under long-wave UV light. Such fluorescence is confined to corals growing within 20 km of the shore and is not present in massive corals from mid- and outer shelf reefs of the central Great Barrier Reef region. The timing, width and intensity of the fluorescent bands correlate strongly with summer, monsoonal rainfall and coastal runoff. Large colonies, several centuries old, can provide long records of the strength and periodicity of terrestrial runoff to the tropical nearshore environment. Such records are potentially important to climatology, meteorology, agriculture, civil engineering and management of the Great Barrier Reef.