Abstract
Coral reefs are in decline worldwide due to a combination of local and global causes. Over 40% of the recent coral loss on Australia’s Great Barrier Reef (GBR) has been attributed to outbreaks of the coral-eating Crown-of-Thorns Seastar (CoTS). Testing of the hypotheses explaining these outbreaks is hampered by an inability to investigate the spatio-temporal distribution of larvae because they resemble other planktotrophic echinoderm larvae. We developed a genetic marker and tested it on 48 plankton samples collected during the 2014 spawning season in the northern GBR, and verified the method by PCR amplification of single larva. Surprisingly, most samples collected contained CoTS larvae. Larvae were detected 100 km south of current outbreaks of adult seastars, highlighting the potential for rapid expansion of the outbreak. A minimum estimate suggested that larvae numbers in the outbreak area (>1010) are about 4 orders of magnitude higher than adults (~106) in the same area, implying that attempts to halt outbreaks by removing adults may be futile.
Highlights
Coral cover on Australia’s Great Barrier Reef (GBR) has declined by 50% over the past 30 years, and up to 42% of this decline has been attributed to the coral-eating Crown-of-Thorns Seastar (CoTS, Acanthaster planci)[1]
Two of seven samples collected on Ribbon Reef No 1 and none of the samples taken in stations up to 10 miles into the Coral Sea contained CoTS DNA
No CoTS DNA was detected in eight samples collected during three separate cruises outside the known spawning season, which confirmed that we detected embryos and larvae and not material of adult origin such as dislodged cells or free DNA
Summary
Coral cover on Australia’s Great Barrier Reef (GBR) has declined by 50% over the past 30 years, and up to 42% of this decline has been attributed to the coral-eating Crown-of-Thorns Seastar (CoTS, Acanthaster planci)[1]. CoTS produce indirectly developing and feeding (planktotrophic) larvae that contribute to their status as one of the ‘boom and bust’ species common in the Echinodermata[3]. Depending on factors such as food concentrations, temperature and salinity, larvae take 10 to > 40 d to reach settlement competency[4,5,6], giving the larvae considerable potential for broad dispersal. In the present study we developed a genetic method to identify CoTS larvae and apply this methodology to evaluate larval dispersal range in the outbreak area (~15 to 17° S) and southward toward the central GBR
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