Ocean News

Hawksbill turtles: sculpting the reef and keeping the peace.

21st January 2010

Over the past four years Rainer von Brandis has familiarised himself with a population of the usually timid hawksbill turtle in the Amirante Islands, Seychelles. This has allowed him to observe the turtles behaving naturally in their aquatic environment, revealing just how important they are for the maintenance of biodiversity on coral reefs.

The remote nature of Rainer’s study site, combined with a sound conservation policy in the Seychelles, means it supports relatively healthy turtle numbers. Consequently it has been possible to monitor how the hawksbill turtles function within a coral reef ecosystem outside of the relentless over-exploitation that has left them classified as Critically Endangered by the IUCN. Gradually, Rainer has been able to determine their prey preferences, how much they eat, their habitat requirements and even social interactions.

Due to the naturally high levels of hawksbill foraging pressure at the study site, the sponges they normally feed upon are restricted to secluded locations within the reef substrate. Using their flippers or beaks, the turtles then have to break the substrate apart to remove parts that would otherwise shelter the sought after sponges. By doing this not only are the turtles sculpting the reef topographically whilst foraging, but also exposing otherwise inaccessible food for reef fish and creating sheltered micro-habitats for other reef dwellers such as moray eels and shrimp.

Perhaps more important is the role they play in mediating the competition for space between sponges and hard corals. Seeing as sponges would normally out-compete hard corals for space, the consumption of a quarter of a tonne of sponges by a single turtle each year helps settling hard corals to establish and get a head start. In this way the local hawksbill turtle population has been pivotal to the recovery of the study reefs after approximately 90% of the hard coral community died in 1998 due to unusually high sea water temperatures. Without a healthy population of foraging hawksbills, sponges could have rapidly dominated the reef landscape and subsequently supported a far less diverse ecosystem.

In all likelihood, it could well be that the majority of the world’s reefs were considerably more abundant and spectacular in the days prior to the mass slaughter of turtles for their shells and meat.

Undoubtedly hawksbill, as well as other, turtles have an important role to play in the balanced functionality of marine ecosystems, but they face an alarming number of threats worldwide that has decimated turtle populations to the point of their classification as Critically Endangered by the IUCN.

Be sure to check back soon to learn more on what threats these turtles face and what we as individuals can do to help.