Management of crown-of-thorns sea star (Acanthaster planci L.) outbreaks: Removal success depends on reef topography and timing within the reproduction cycle

Ocean & Coastal Management (Impact Factor: 1.77). 02/2013; 71:116-122. DOI: 10.1016/j.ocecoaman.2012.09.011

ABSTRACT Removals of crown-of-thorns sea stars (Acanthaster planci L.) are crucial initiatives limiting the damage to coral reefs during outbreaks, but have often been unable to control the populations. We hypothesized that reef topography and exact timing of removals (before reproduction) determine their success and studied these in reefs along the western shore of Samal Island in the Philippines. To accurately compare results of various studies, relationships between crown-of-thorns weight, underwater diameter and surface diameter were established. An outbreak of A. planci was removed from an isolated reef (surrounding water column >40 m) during 42 dive hours. In August 2009, 14 specimens h-1 were removed, but this sharply decreased to <4 h-1 after the third dive and no specimens were found in May and December 2011. All specimens were found at depths ≤18 m, which confirmed that migration to isolated reefs is very unlikely. Mean gonado-somatic index (GSI) ranged from 6–15 in April–May 2010 and March–April 2011. During the rest of the year, mean GSI was between 0–4. Maximum GSI of 22.0 was found for one female specimen in April 2010. Diameter frequency distributions showed a new cohort (7 ≤ diameter ≤ 10 cm) between November 2009 and February 2010 and maturation occurred at a diameter of 13–16 cm. Removals are recommended to be performed in isolated reefs where migration from adjacent areas is limited and before reproduction in April reducing the chance of future outbreaks.

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