First report of field sampling and identification of crown-of-thorns starfish larvae

Abstract

To date, field sampling and identification of the larvae of the coral-eating starfish Acanthaster planci have not been successfully performed (Birkeland 1990). We collected water samples (500 L) from 5 different depths (surface, 3 m, 7 m, 11 m, 15 m, and near the bottom) to find A. planci larvae on June 29, 2005, during the spawning period (Yasuda et al. 2010). The samples were obtained from Yabiji Reef, off Miyako Island, Okinawa, Japan (25°1′13.85″N, 125°14′49.20″E, Fig. 1A), where a population outbreak of A. planci was observed (Fig. 1B). We used a stereoscopic microscope to find and isolate 26 possible starfish larvae (gastrula and bipinnaria stages; Fig. 1C and D, respectively) from the samples, which were preserved in ethanol (＞70%). We extracted DNA using the DNeasy blood & tissue kit (Qiagen), and directly sequenced partial mitochondrial DNA fragments amplified by using a previously published COI primer pair (Vogler et al. 2008) and a putative control region primer pair (Timmers et al. 2011). The latter primer pair can discriminate A. planci from some common sea stars such as Protoreaster nodosus, Linckia laevigata, and Culcita novaeguineae. The following PCR conditions were used: denaturing step at 94℃ for 3 min, followed by 35 cycles of 94℃ for 20 s, 60℃ for 30 s, and 72℃ for 30 s with a final extension step at 72℃ for 5 min. The PCR cocktail contained 3.84 μL of ddH2O, 5 μL of KAPATaq TM Extra HotStart ReadyMix (Kapa Biosystems), 1 μL of template DNA, and 0.07 μL of 50 mM primers. Only 10 larvae were successfully analyzed, partly due to degradation of DNA, but all were identified as A. planci by BLAST search. Nine larvae at the gastrula stage were found in either the surface (2), 7 m (5), or near bottom (2) samples, while 1 larva at the bipinnaria stage was found in the surface sample. Salinity-Temperature-Depth (STD) data showed that the water temperature was 27.7-27.9℃ and chlorophyll a concentration was 0.3-0.4 μg/L at the sampling points from where we identified larvae of A. planci. Since the minimum threshold density of chlorophyll a for successful development is 0.4 μg/L (Fabricius et al. 2010), the larvae might have had access to limited food during the study period.

Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016): Scientific Advances and Emerging Opportunities

“…Moreover, genome sequencing of closely related species could provide a comparative genomic approach for population genomics and evolution within this group of animals. Other approaches such as eDNA could also serve as a tool to trace the distribution of early life stages of CoTS in the field [53,107,264]. These data will not only contribute to a better understating of CoTS genomics, but will also be required for effective conservation and management.…”

Detection of a High-Density Brachiolaria-Stage Larval Population of Crown-of-Thorns Sea Star (Acanthaster planci) in Sekisei Lagoon (Okinawa, Japan)

“…A flowmeter was calibrated during three replicate tows on an open frame (i.e., without a net). In a previous survey, more larvae were found at 7 m than at other depths, although there was a slight vertical distribution bias of A. planci larvae [19]. The volume of water filtered by the net was measured with a flowmeter (Rigo Co., Ltd., Tokyo, Japan) mounted at the net mouth.…”

“…These primers can discriminate A. planci from a few common coral reef sea stars, such as Protoreaster spp., Linckia spp., and Culcita spp. [19].…”

Integrated population genomic analysis and numerical simulation to estimate larval dispersal of Acanthaster cf. solaris between Ogasawara and other Japanese regions

“…These studies have indicated strong gene flow over a long distance along western boundary currents such as the Kuroshio Current region (genetic homogeneity from across the Ryukyu Islands to the temperate Pacific coast of mainland Japan, Yasuda et al, 2009) and the Eastern Australian Current region (the Great Barrier Reef, Nash et al, 1988; Benzie et al, 1999; Vogler et al, 2013; Harrison et al, 2017), while relatively limited gene flow and genetic differentiation were observed among distant Pacific islands (Yasuda et al, 2009; Timmers et al, 2012; Vogler et al, 2013). Overall, the studies found strong gene flow and genetic homogeneity in regions where strong currents are associated, although genetic data strongly reflect historical gene flow that was formed during past climate change, and the spatial extent of secondary outbreaks could be overestimated (Benzie 1999, Yasuda et al 2009, Yasuda et al 2015). Larval dispersal simulation studies in the Great Barrier Reef (GBR) have indicated southward larval dispersal along the Eastern Australian Current, which is consistent with historically observed patterns of secondary outbreaks of A. cf .…”

“…Miyake et al, 2009; Storlazzi et al, 2017), plankton-netting in the field (e.g. Yasuda et al, 2015; Suzuki et al, 2016), and drifting buoys (e.g. Fukuda and Hanamura, 1996), have been employed to estimate larval dispersal.…”