BullBULLETIN Mar Sci. OF 93(4):1009–1010.MARINE SCIENCE. 2017 00(0):000–000. 0000 https://doi.org/10.5343/bms.2017.1032doi:10.5343/

Diet of Acanthaster brevispinus, sibling species of the coral-eating crown-of-thorns startfish, Acanthaster planci sensu lato

Hideaki Yuasa 1, Yukihiro Higashimura 1, Keiichi Nomura 2, Nina Yasuda 3 *

1 Graduate School of Agriculture, University of Miyazaki, Gakuen-kibanadai-nishi-1-1, Miyazaki 889-2192, Japan. 2 Kushimoto Marine Park Center, Arita Kushimoto, Wakayama, 649-35, Japan. 3 Organization for Promotion of Tenure Track, University of Miyazaki, Gakuen-kibanadai-nishi-1-1, Miyazaki 889-2192, Japan. * Corresponding author email: .

Acanthaster planci sensu lato (Linnaeus, 1758) (crown-of-thorns starfish) is notorious for predating on hard corals the in the Indo-Pacific reefs; however, the natural diet of its sibling species, Acanthaster brevispinus brevispinus Fisher, 1917, is unknown. Only a few reports on A. brevispinus occurrence are available, indicating that A. brevispinus is a rare species. This species occurs in the Philippines (Fisher 1919), the Great Barrier Reef, Australia (Birkeland and Lucas 1990), and off the town of Kushimoto, south of the Japanese mainland (Saba et al. 2002). Although population outbreaks of A. planci sensu lato have been well documented, there have been no reports of outbreaks of A. brevispinus. According to Lucas and Jones (1976), A. planci sensu lato and A. brevispinus differ in preferred habitat and morphology, but they are genetically compatible, indicating recent speciation. Lucas and Jones (1976) suggested that A. planci sensu lato evolved from an A. brevispinus-like ancestor that inhabited

Bulletin ofof MarineMarine Science Science 1009 © 2017 2011 Rosenstiel Rosenstiel School School of of MarineMarine &and Atmospheric Atmospheric Science Science of theof the University University of of Miami Miami Portraits of Marine Science 1010 BULLETINBulletin OF of MARINEMarine Science. SCIENCE. Vol VOL 93, 00, No NO 4. 0.2017 0000 deep, sandy areas and infrequently fed on reef-building corals. To our knowledge, ours is the first report on the diet ofA. brevispinus from a temperate coral reef region off Japan. All A. brevispinus individuals found around Kushimoto (33.2835°N, 135.3955°E) between 2003 and 2016 were observed feeding exclusively on soft corals, especially Dendronephthya species (e.g., Dendronephthya nipponica Utinomi, 1952 and Dendronephthya (Morchellana) habereri Kükenthal, 1905), even when the preferred prey of A. planci sensu lato (Acropora corals such as Acropora solitaryensis Veron and Wallace, 1984) were more abundant (A: March 19, 2003, at a depth of 20 m; B: August 31, 2006, at a depth of 20 m; C: January 31, 2007, at a depth of 18 m. All photographs were taken by the Kushimoto Marine Park Center.). An aggregation of approximately 20 A. brevispinus individuals and 10 A. planci sensu lato individuals was observed in 2003 within a 100-m2 area of a rocky reef off the coast of Kushimoto at a depth of 20 m. In 2003, the warm Kuroshio Current was nearby Kushimoto, suggesting that higher temperature and/or larval transport from the southern region were associated with this aggregation. Following this event, outbreaks of A. planci sensu lato, occurring at 11.1 starfish per 15 min (approximately 2000 m2), were reported in Kushimoto waters in 2004 (in total, more than 10,000 A. planci sensu lato per year were removed), and this abundance was maintained until 2008 (Nomura 2009). In contrast, very few A. brevispinus were found after Dendronephthya soft corals had been mostly depleted in 2004. Off Kushimoto, hard corals (such as Acropora spp.) are much more abundant than soft corals, including Dendronephthya spp. A decrease in the amount of available food for A. brevispinus after 2004 may be associated with a lower survival rate and/or reproductive output than A. planci sensu lato, and consequently could have resulted in a lower population density. Our observation also provides new insight into the mechanism of reproductive isolation between A. brevispinus and A. planci sensu lato. Unlike on the Great Barrier Reef, where A. brevispinus and A. planci sensu lato inhabit different areas (Lucas and Jones 1976), we found these two species to be sympatric off Kushimoto, indicative of some biological mechanisms to avoid natural hybridization, such as variation in spawning time. Given that adult size and fecundity of the two species are comparable (Lucas and Jones 1976) and that A. brevispinus have never exhibited population outbreaks, the evolutionary divergence of a coral-specialist such as A. planci sensu lato from an A. brevispinus-like ancestor may have changed the fate of Indo- Pacific reef ecosystems. Further understanding of the ecological differences between sibling species will provide important clues with regard to the population outbreaks exhibited by A. planci sensu lato (Yasuda 2017).

Acknowledgments

This research was funded by the Environment Research and Technology Development Fund of the Ministry of the Environment, Japan (4RF-1501), JSPS KAKENHI Grant Numbers 17H04996 Grant-in- Aid for Young Scientists and the Program to Disseminate Tenure Tracking System from the Ministry of Education, Culture, Sports, Science and Technology (MEXT).

Literature Cited

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