Can 3 starfish represent an outbreak? – It likely depends on where they were found.
Brood or Broadcast: Why not both?
Hubert Lyman Clark visited Torres Strait in 1913 with the Carnegie Institution of Washington. He found only 3 specimens of Acanthaster at Mer but examined many others from throughout the Indo-Pacific at the Museum of Comparative Zoology. This study in Torres Strait was published as H.L.Clark (1921) and was followed in 1938 and 1946 by books on the Echinoderm Fauna of Australia.
These 3 specimens at Mer were found “on the surface of the reef and not under rocks or coral slabs”. Clark suggests further that Acanthaster is often overlooked. Pratchett et al (2017) refer to Clark (1921), the Echinoderm Fauna of Torres Strait stating:
“On the GBR, it appears likely that outbreaks of A. cf. solaris were underway in 1913, given the relative ease with which Clark  collected CoTS in the Torres Strait.”
This was suggested by Pratchett et al (2017). Morgan S. Pratchett, Ciemon F. Caballes, Jennifer C. Wilmes, Samuel Matthews, Camille Mellin, Hugh P. A. Sweatman, Lauren E. Nadler, Jon Brodie, Cassandra A. Thompson, Jessica Hoey, Arthur R. Bos, Maria Byrne, Vanessa Messmer, Sofia A. V. Fortunato, Carla C. M. Chen, Alexander C. E. Buck, Russell C. Babcock and Sven Uthicke. Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016): Scientific Advances and Emerging Opportunities. Diversity 2017, 9, 41.
The evidentiary value of these 3 CoTS is unclear and it surely depends on what is meant by “likely” or “relative ease”. However, it also illustrates clearly our perception of the critical importance of population aggregation in fertilization success.
However, not all species of starfish are broadcast spawners and variation in gonopore position (oral v aboral) has been described by Hart et al. (2005) in a member of the Family Asterinidae. This variation indicates cryptic species in which “nonplanktonic offspring hatch and metamorphose without a dispersing planktonic larval phase”. Larval cloning was also identified in genera Luidia and Oreaster and another two members of the family Ophidiasteridae by Knott et al. (2003).
If either of these low-dispersal reproductive strategies ever occurred in the Family Acanthasteridae it would be of enormous ecological significance as it would greatly facilitate the establishment of small pre-outbreak local populations.
Can 3 starfish represent an outbreak? – Presently unclear.
Has such gonopore or larval variation ever been identified in CoTS? – I hope not.