More on “What would eat a spiny sea urchin?”

Update:  just got two new comments on this:

Saw your post on coral list.  Toadfishes at San Blas also eat Diadema with little pre-processing of the meal.  The burrows of Sanopus barbatus on the reef can be localized by the long spines littering their ‘porch.’  Amphichthys cryptocentrus at San Blas are also known to eat Diadema but are also more of a generalist feeder (in an old Ross Robertson paper).
BTW, I recently saw an aggregation of ~500 Diadema spawn on Turneffe Atoll in Belize.

John Barimo, PhD
Field Coordinator and Coral Reef Biologist
Blackbird Oceanic Research Center
P.O. Box 207
Belize City, Belize
Telephone: +501 22 04256

Adjunct Professor
Peninsula College
1502 E. Lauridsen Blvd.
Port Angeles, WA 98362

Hi John:

I’d like to add to your list crabs which eat Diadema by chopping down their spines with their pincers as they move in for the kill, and all the small wrasses that attack small Diadema.  Back in the old days when you couldn’t turn over a piece of rubble without uncovering dozens of small Diadema, the juvenile wrasses and parrots (under 15 cm) would follow you around and pick them to pieces.  Back in early 2000s, Margaret Miller and I tried outplanting of juvenile hatchery raised Diadema in the 1-2 cm diameter and in one case, most of them were eaten within 30 minutes even though we tucked them into crevices.  There’s a reason they have all those big spines.  They have “food” written on a big sign on their foreheads.


Dr. Alina M. Szmant
Professor of Marine Biology
Coral Reef Research Program, Center for Marine Science
University of North Carolina Wilmington
5600 Marvin K. Moss Lane
Wilmington NC 28409
Tel:  (910)962-2362; fax: (910)962-2410;  cell:  (910)200-3913

Since making a post on the surprising variety of critters that eat the spiny urchin Diadema, a number of colleagues have sent their observations, videos, references, etc of other Diadema predators.  So I wanted to make a revised list for posterity.   When appropriate, ill include the source of the info.

In no particular order, predators of Diadema include: snapper, jacks, porcupinefishes, trunkfishes, grunts including black margate and white grunt, porgies, triggerfishes, pufferfish, large wrasses, parrotfish, octopuses, lobsters, several large gastropods, e.g., Triton’s trumpet snails and helmet shells (Cassis), small crabs (which eat juvenile Diadema), permit, saucereye porgy, southern stingray, hogfish, sea stars, e.g.,  Culcita and Oreaster, and zebra Moray.

Have we forgotten anyone?

We did some gut content analysis of fish in La Parguera Puerto Rico and
found these fish to have consumed Diadema:

saucereye porgy
southern stingray
white grunt

Randy Clark (NOAA)


Maybe I missed it but did not see  Hogfish mentioned as a Diadema
predator. I have watched them pick off all the spines one by one and
ten swallow the test in a single gulp. Back when I got through school
spearing Hogfish for restaurants (before the die-offf and when they
were called Hogsnapper) all  larger hogfish we took had at least a
dozen purple spots around the head. After the Diadema die-off hogfish
ceased to have those purple puncture spots. Apparently they switched
to other prey and are doing well.

Gene Shinn

Add the sea star Culcita to the list of possible Indo-Pacific suspects.
Some asteroids are known to eat urchins (Dayton et al., 1977; Rosenthal &
Chess, 1972; Schroeter et al., 1983) and I have witnessed Culcita eating
large numbers of Echinometra (Tonga)and Echinostrephus (Maldives – where it
could be collateral damage). It would not surprise me if they ate smaller
Diadema but I have not seen it in Maldives where I have made most of my
observations and Diadema are generally low density and adult thanks to a
diversity of predators (large Balistids especially).

Bill Allison

Dayton, P. K., R. J. Rosenthal, et al. (1977). “Population structure and
foraging biology of the predaceous Chilean asteroid Meyenaster gelatinosus
and the escape biology of its prey.” Marine Biology 39: 361-370.

Rosenthal, R. J. and J. R. Chess (1972). “A predator-prey relationship
between the leather star, Dermasterieas imbricata, and the purple urchin,
Strongylocentrotus purpuratus.” Fish. Bull. U.S. 70: 205-216.

Schroeter, S. C., J. Dixon, et al. (1983). “Effects of the Starfish Patiria
miniata on the Distribution of the Sea Urchin Lytechinus anamesus in a
Southern Californian Kelp Forest.” Oecologia 56(2/3): 141-147.


Hi John,

I remember seeing on a few occassions, at night, Triton’s trumpet snails apparently eating urchins, including Diadema. West Indian sea stars, Oreaster, eat them as well.

Lonnie Kaczmarsky


Eight years ago, I filmed a Zebra Moray feeding on a Diadema.  See the low
res version attached to this email.  You can see the Eightline Wrasse and
Saddle Wrasse opportunistically jumping in as well.


Bryce Groark
Living Ocean Productions

click here to watch Byrce’s awesome video!


Hi John,

I will confirm pufferfishes (porcupine) for D. antillarum (by patiently breaking tips further and further until able to be upturned and eaten) and brutal octopus/triggerfish battle of D. savignyi in Easter Island (dense Diadema populations). The triggerfish split the urchin with a strike from above (and took a few spines in the face (long and not deep), and each would periodically drop their half to fish over the other half. An amazing battle.

Eric Borneman
Dept. of Biology and Biochemistry
University of Houston

I also wanted to highlight the comments made by Alastair Harborne regarding my mention of his new paper and appologize for the long delay in responding to and acknowledging his clarification.  I just moved (temporarily) from North America to Brisbane, Oz, with three kids, two surfboards and one wife.  The last few weeks have been a tad busy.  I spent at least a few days deciphering Aussie cell phone plans.  (I finally have a plan, an unlocked iphone and a number, but no idea how long it will last or when/how I am meant to “top up”.)

Hi there,

I wanted to add to this thread because my paper was cited at the start as an example of how there is a common misconception that Diadema only have a few predators. Within my paper I draw heavily on the Randall paper that lists the range of fishes that predate on urchins, and also discuss the effects of invertebrate predators in the Discussion. Indeed I use Randall’s data (on the percentage of fish of each species that contained urchins spines within their stomachs) to weight the biomass of predators inside and outside the marine reserve in order to reflect the fact that some species feed more heavily on Diadema than others. I think the Randall data are interesting because in only 6 species did more than 20% of individuals contain urchin spines (at a time when urchins were much more abundant than they are now). This suggests a hypothesis that while a range of species may feed on Diadema, potentially only a few species feed on them at a sufficient rate to regulate their populations. There is also an interesting question of the number of species that can feed on urchins of different sizes – I suspect that most of the species listed by Randall can take juvenile urchins, but perhaps only a subset can feed on large adults.

The comment about the few specialist predators in my paper (which incidentally, as the rest of the paragraph shows, was not a statement by me but a cited statement from Pinnegar et al, 2000) was a reflection on the potentially different effect of Caribbean marine reserves on urchins compared to in the Indian Ocean. In the Indian Ocean, Tim McClanahan and others have demonstrated that reserves can increase the abundance of urchin predators, and reduce damaging urchin plagues. Obviously urchin plagues have not been an issue in the Caribbean since the mass mortality in the 1980s, although the Sammarco data from Jamaica suggest that this may have been a problem before that time (at least in some habitats). The issue in the Caribbean is rebuilding Diadema abundances while simultaneously trying to rebuild fish communities that include urchin predators. Urchin population dynamics are complex, poorly understood, and influenced by a range of variables, but it seems likely that the abundance of a few key predators (few possibly being relative compared to the number of predators of, say, a larval fish recruiting to a reef) may be an important top-down control of Diadema densities.


Pinnegar JK, Polunin NVC, Francour P, Badalamenti F, Chemello R,
Harmelin-Vivien ML, Hereu B, Milazzo M, Zabala M, D’Anna
G, Pipitone C (2000) Trophic cascades in benthic marine
ecosystems: lessons for fisheries and protected-area management.
Environ Conserv 27:179–200

1 thought on “More on “What would eat a spiny sea urchin?”

  1. Hi John,
    This is a very interesting piece; Jarrett Byrne pointed it out to me. Interactions definitely tend to be underestimated, and generally underreported. But there is a lot of information in the distributed literature if one has the time and access. In my (unpublished) compilation of Greater Antillean reefs, I estimate nine invertebrate consumers and 30 “fish” consumers of Diadema.

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