ASSOCIATION OF LOW-FREQUENCY CURRENTS AND CROWN-OF-THORNS STARFISH OUTBREAKS

Analyses of 25 yr of coastal currents have revealed slow periods and long-term cycles in longshore current intensity and direction during the annual spawning season of crown-of-thorns starfish. Extraordinary natal larval recruitment during periods of slow, low-frequency longshore currents may be a critical factor associated with primary outbreaks of the starfish on the Great Barrier Reef (GBR). Slow currents result in high local retention of larvae within the eddy-induced well-mixed zone around a reef, with a corresponding potential for abnormally high recruitment back to the natal reef or region. Numerical simulations show that after a crown-of-thorns starfish outbreak is established, large latitudinal sectors of the GBR may be inundated by larvae. Observed southerly progressions of secondary starfish outbreaks were significantly correlated with predicted larval excursions, transmitted by low-frequency currents during spawning seasons. Secondary infestation of reefs, however, could not explain primary events or the noteworthy exceptions in inter-annual outbreak advance along the GBR, suggesting that an outbreak during 1978 at 18 to 19' S may have been primary and independent of the earlier events further north.