Acanthaster planci-IMPACT ON PACIFIC CORAL REEFS
A 1969 U.S. scientific study of Crown of Thorns Starfish in Micronesia has relevance for the current South Pacific COTs outbreaks from the Cook Islands across to the G.B.R.
Teams of scientists went to 16 islands within the U.S. Trust Territory under the direction of
Westinghouse Ocean Research Laboratory to assess the population structure of the starfish
Acanthaster planci and the impact of this species on Pacific coral reefs. In a companion effort, the
University of Hawaii. directed five teams that surveyed Hawaiian islands, Johnston Island, Majuro,
Arno, Kwajalein and Midway.
The findings of the study generally substantiated reports at recent increases in populations of
this starfish in the Pacific. The teams located considerable amounts of -coral `reef that had been killed
within the past five to ten years by Acanthaster planci and found substantial portions of coral reefs
currently being attacked, Wherever feeding was observed, the starfish Were eating either
scleractinian corals or sessile, colonial coelenterates. The infestations were judged to be of recent
occurrence, with the earliest reports dating back to World War II.
A "normal" population was considered to have fewer than 20 specimens per 20 minutes of
search. Yap, Ifalik, Woleai, Lamotrek, Kwajalein, Hawaii, Mokil, Midway, Kauai, Oahu, Maui and
French Frigate Shoals were found to have normal populations. Ten islands had sufficiently high
populations to be considered infested. These were: Saipan, Tinian, Truk, Ponape, Rota, Palau, Ant,
Guam, Majuro, and Arno. Johnston Island, Kapingamarangi, Nukuoro and Pingelap are questionable
areas, with high population levels of starfish that need to be examined at a later time to establish if an
increase or decrease of population is in progress.
Team leaders considered the problem significant and in need of considerable research. A
control program, which includes research into various aspects of Acanthaster planci, should be
instigated immediately. Such a control program should establish an active eradication effort on
infested reefs that have economic or scientific value as well as an educational program to inform
islanders of the nature of the problem and how they can contribute to research and control programs.
Definite causes of the infestation were not established by the study. Two hypothetical
mechanisms appear to offer the most promise for explaining the infestations. In one case a population
increase is presumed due to decrease of predation pressure on the larvae by corals in reef areas
freshly damaged by blasting and dredging. The other mechanism takes account of reduced predation
on adult starfish by tritons that are prized by shell collectors.