Coastal Crabs Are Silent Killers of Baby Sea Turtles todayheadline

A new study sheds light on a grim reality for newly hatched loggerhead sea turtles along Australia’s west coast: a feeding frenzy orchestrated by golden ghost crabs.

These swift, nocturnal predators are proving to be a surprisingly deadly threat to the endangered hatchlings, challenging previous assumptions about how often and in what manner these vulnerable creatures fall prey. Researchers from Edith Cowan University (ECU) and the Department of Biodiversity, Conservation and Attractions (DBCA) used infrared videography to observe these attacks, uncovering details of predation that were previously hidden by darkness and remote locations.

The findings, published in the journal Food Webs, indicate that ghost crabs, while known omnivores, are far more effective predators of sea turtle eggs and hatchlings than once fully understood. This new insight raises concerns for the long-term survival of loggerhead turtle populations, which are already classified as endangered.

Unmasking the Nighttime Attack

Studying how sea turtle hatchlings are preyed upon is difficult, especially at night and in distant areas, without disturbing natural behaviors. To overcome this, the researchers employed infrared videography along the Ningaloo Coast at Bungelup Beach and Gnaraloo Bay. This allowed them to observe the golden ghost crabs’ feeding habits in their natural habitat and in a controlled aquarium setting at the Minderoo Exmouth Research Laboratory.

Previous research often relied on indirect evidence, such as disturbances to turtle nests or counts of predated eggs. “Previous studies are mostly limited to evidence of loggerhead turtle nest disturbances and egg counts. While even fewer studies have investigated the mechanics of hatchling predation once they have emerged from the nest,” said Dr. Casper Avenant, an Adjunct Lecturer at ECU and lead researcher on the study.

A Methodical and Brutal Approach

The golden ghost crab’s hunting methods are systematic. When encountering a turtle egg, crabs often create a distinctive slit in the shell, consuming the contents through this opening. For hatchlings, the attack is even more direct. Ghost crabs typically restrain the baby turtles by gripping them around the neck with a large claw.

The smaller claw then goes to work, cutting through the soft skin around the neck to partially or fully sever the head. The crab then feeds from the cavity created. This behavior was consistently observed in both field and laboratory settings. “In terms of predator behaviour, it was interesting to note that ghost crabs display similar approaches for breaching eggshells when subduing and feeding on hatchlings,” Dr. Avenant noted.

What’s more, the research shows that these crabs appear to anticipate when hatchlings will emerge. They often gather near nests just before the turtles begin to surface. This anticipation highlights a sophisticated predatory strategy. Aquarium-based feeding experiments also confirmed the crabs’ strong preference for animal flesh, including turtle eggs and hatchlings, over their usual diet of brown algae, solidifying their role as efficient predators of early-life sea turtles.

Key Research Observations:

• Infrared video revealed detailed prey handling of eggs and hatchlings.
• Ghost crabs often decapitate hatchlings by gripping the neck and cutting with a smaller claw.
• Crabs congregate near nests, seemingly anticipating hatchling emergence.
• Laboratory tests confirmed ghost crabs prefer animal flesh over algae.
• High densities of ghost crabs can lead to widespread destruction of turtle clutches.

Impact on Turtle Survival

The findings are stark: on beaches with high ghost crab populations, multiple crabs can attack hatchlings emerging from nests over several nights. This often leads to partial destruction of turtle clutches, or even complete failure for nests to hatch. “As an endangered species, a high level of predation of eggs and hatchlings could be an issue for the long-term survival of loggerhead turtle populations,” explained Professor Glenn Hyndes, ECU Professor in Coastal Ecology.

Indeed, earlier research by Dr. Avenant showed that more than 35% of loggerhead eggs within nests at Ningaloo were consumed by predators, with some individual rookeries experiencing an 80% loss. Of the hatchlings that successfully emerged, nearly half (45%) were subsequently predated.

A Global Challenge for Sea Turtles?

Ghost crabs are found on sandy beaches worldwide, wherever sea turtles are known to nest. While this study focused on the golden ghost crab in Australia, other ghost crab species have been implicated in similar predation globally. This research provides a detailed look at specific feeding behaviors, including how crabs rupture eggshells and subdue hatchlings, adding to observations made for other ghost crab species elsewhere. The consistency in these predatory approaches across different species suggests a broader pattern of effective predation by ghost crabs on the vulnerable early life stages of sea turtles.

Understanding these specific predatory behaviors is crucial for conservation efforts. How can conservationists better protect these tiny, vulnerable creatures from such an ever-present, yet often unseen, threat?

The use of infrared videography in this new study has proven to be a powerful

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