The Geological Evidence: are CoTS plagues natural?
The 2017 Science Consensus Statement completely ignores the possibility that CoTS plagues are a natural phenomenon. It does not seek to dispute or refute this possibility – it simply does not examine it nor, indeed, mention it at all. A significant body of geological research is thus ignored, as also are opinions of many of the experts in CoTS research. For example, a major review of 30 years of CoTs research by 18 authors (Pratchett et al 2017)[1] comments that the question of
why outbreaks occur and whether they are natural or unnatural phenomena has . . . preoccupied much of the discussion around Acanthaster spp. (CoTS), but remains largely unresolved. [*]
The 2017 Consensus Statement should have addressed this uncertainty about such a basic question.
There is good reason to presume that CoTS outbreaks did not start in the 1960s, coincidentally at the same time as scientists started to study the GBR, but have instead been going on since time immemorial. The evidence has been gathered by geologists who have looked for the skeletal remains of CoTS.[2] It must be recalled that a coral reef is a roughly 50-100 metre high pile of calcium carbonate rubble and sand made largely from the remains of dead coral skeletons and any other organisms that have a skeleton or shell that have accumulated over time. A coral reef is literally growing on the remains of its dead ancestors. The sand and rubble near the surface was produced recently, but with further drilling deeper into the reef, the sediment becomes progressively older. Geologists (Walbran and Henderson,1989)[3] drilled into the reefs and, by searching for CoTS skeletal remains, have shown that CoTS outbreaks have occurred continuously during the last few thousand years and there is no evidence that they are more widespread today. Indeed, according to Walbran and Henderson, they may have been more common a few thousand years ago.
There was some critical commentary about this work (e.g. Fabricius and Fabricius, 1992)[4]. Henderson & Walbran (1992)[5] responded promptly but, curiously, their original work seems to have been almost forgotten, buried as deeply as the inconvenient ancient CoTS
[*] Emphasis was in the original work
[1] Pratchett, M.S., Caballes, C.F., Wilmes, J.C., Matthews, S., Mellin, C., Sweatman, H.P.A., Nadler, L.E., Brodie, J., Thompson, C.A., Hoey, J., Bos, A.R., Byrne, M., Messmer, V., Fortunato, S.A.V., Chen, C.C.M., Buck, A.C.E., Babcock, R.C. and Uthicke, S. (2017). Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016): Scientific Advances and Emerging Opportunities. Diversity, [online] 9(4), p.41. Available at: https://www.mdpi.com/1424-2818/9/4/41/htm
[2] Walbran, P.D., Henderson, R.A., Jull, A.J.T. and Head, M.J. (1989). Evidence from Sediments of Long-Term Acanthaster planci Predation on Corals of the Great Barrier Reef. Science, 245(4920), pp.847–850.
[3] See Endnote 7
[4] Fabricius, K.E. and Fabricius, F.H. (1992). Re-assessment of ossicle frequency patterns in sediment cores: rate of sedimentation related to Acanthaster planci. Coral Reefs, 11(2), pp.109–114.
[5] Henderson, R.A. and Walbran, P.D. (1992). Interpretation of the fossil record of Acanthaster planci from the Great Barrier Reef: a reply to criticism. Coral Reefs, 11(2), pp.95–101.
Great Barrier Reef Science Commentary 