What If Gone

Species → Hawksbill Turtle

Hawksbill Turtle

Eretmochelys imbricata

21,500 nesting females worldwide, median estimate
Extinction risk Critically Endangered
Coral reefMarine environmentCatastrophic declineOverfishing
Hawksbill Turtle (Eretmochelys imbricata)
Photo: Diego Delso, Wikimedia Commons (CC BY-SA 4.0)

What if it disappeared?

Impact High
Ongoing

The hawksbill turtle doesn't feed on sponges at random: a diet study shows it selects a handful of specific species, including Chondrilla nucula, a sponge otherwise known for its ability to rapidly invade available reef space at the expense of corals.

Documented
Detail

León, Y.M. & Bjorndal, K.A. (2002). Selective feeding in the hawksbill turtle, an important predator in coral reef ecosystems. Marine Ecology Progress Series, 245, 249-258.

The study documents the gut content and dietary preferences of hawksbill turtles in the Dominican Republic, confirming the species doesn't consume reef sponges in proportion to their abundance but preferentially targets certain fast-growing species.

Since 1998

A field experiment confirms the upstream mechanism: excluding sponge predators from a reef plot — using cages — lets sponges overgrow more coral than on control plots, proving that sponge predation does free up space for corals. But the experiment mainly involves angelfish, the main predators tested by exclusion, not the hawksbill turtle specifically.

Extrapolated
Detail

Hill, M.S. (1998). Spongivory on Caribbean reefs releases corals from competition with sponges. Oecologia, 117(1-2), 143-150.

Experiment conducted in Florida. The hawksbill turtle shares its main prey (Chondrilla nucula) with the spongivorous angelfish tested in this experiment, which makes a similar effect from its own grazing plausible — but no exclusion cage has isolated the turtle's specific effect, as it is too rare and too large for this kind of small-scale experimental setup.

What's missing to confirm it: A comparison of coral cover between reefs with and without hawksbill turtles present, at comparable angelfish density, to isolate the turtle's own effect.

For decades

A few regional hawksbill populations are increasing after decades of nesting-beach protection, but no study has yet measured whether this recovery translates into a measurable retreat of invasive sponges or a gain in coral cover on the reefs concerned.

Insufficient
Detail

Turtle population recovery is measured at nesting beaches, a direct and well-monitored indicator; the effect of that recovery on sponge-coral competition plays out underwater, at foraging sites often distinct from nesting sites, which makes the link far harder to establish and to fund.

Documentation

Last verified: August 10, 2026