Phytotoxicity of Photosystem II (PSII) herbicides to coral

Abstract

Recent reports of contamination of the Great Barrier Reef Marine Park by herbicides used in antifouling paints and in agriculture have caused concern over the possible effects on corals in nearshore areas. Pulse-Amplitude Modulated (PAM) chlorophyll fluorescence techniques were used to examine changes in the maximum effective quantum yield (F /F m ') of symbiotic dinoflagellates within the host tissues (in hospite) of the coral Seriatopora hystrix exposed to a number of Photosystem II (PSII) inhibiting herbicides in short-term toxicity tests. The concentration of herbicide required to reduce F /F m ' by 50% (median effective concentration [EC 50 ]) differed by over 2 orders of magnitude: Irgarol 1051 (0.7 g l -1 ) > ametryn (1.7 g l -1 ) > diuron (2.3 g l -1 ) > hexazinone (8.8 g l -1 ) > atrazine (45 g l -1 ) > simazine (150 g l -1 ) > tebuthiuron (175 g l -1 ) > ionynil (>1 mg l -1 ). Similar absolute and relative toxicities were observed with colonies of the coral Acropora formosa (Irgarol 1051 EC 50 : 1.3 g l -1 , diuron EC 50 : 2.8 g l -1 ). Time-course experiments indicated that F /F m ' was rapidly reduced (i.e. within minutes) in S. hystrix exposed to Irgarol 1051 and diuron. On return to fresh running seawater, F /F m ' recovered quickly in diuron-exposed corals (i.e. in minutes to hours), but slowly in corals exposed to Irgarol 1051 (i.e. hours to days). Time-course experiments indicated that the effects of diuron (3 g l -1 ) on S. hystrix were inversely related to temperature over the range 20 to 30C, although initially the effects were less at the lower temperatures. Repeated exposure to pulses of Irgarol 1051 (daily 2 h exposure to 30 g l -1 over 4 d) resulted in a 30% decrease in the density of symbiotic dinoflagellates in the tissues of S. hystrix.