Effects of the herbicide diuron on the early life history stages of coral

The effects of the herbicide diuron on the early life history stages of broadcast spawning and brooding corals were examined in laboratory experiments. Fertilisation of Acropora millepora and Montipora aequituberculata oocytes were not inhibited at diuron concentrations of up to 1000 μg l−1. Metamorphosis of symbiont-free A. millepora larvae was only significantly inhibited at 300 μg l−1 diuron. Pocillopora damicornis larvae, which contain symbiotic dinoflagellates, were able to undergo metamorphosis after 24 h exposure to diuron at 1000 μg l−1. Two-week old P. damicornis recruits on the other hand were as susceptible to diuron as adult colonies, with expulsion of symbiotic dinoflagellates (bleaching) evident at 10 μg l−1 diuron after 96 h exposure. Reversible metamorphosis was observed at high diuron concentrations, with fully bleached polyps escaping from their skeletons. Pulse amplitude modulation (PAM) chlorophyll fluorescence techniques demonstrated a reduction in photosynthetic efficiency (ΔF/Fm′) in illuminated P. damicornis recruits after a 2 h exposure to 1 μg l−1 diuron. The dark-adapted quantum yields (Fv/Fm) also declined, indicating chronic photoinhibition and damage to photosystem II.