Unhatched truths: Why are sensitive turtles nesting on popular beaches?

Across the Mediterranean, a surprising trend is emerging—loggerhead sea turtles are increasingly choosing to lay their eggs on beaches heavily used by humans.

But while beachgoers might consider these events as a sign of environmental recovery, new research suggests the reality beneath the sand is far more complex.

In their study, Using Embryonic Morphometrics To Diagnose Developmental Stress And Target Sustainable Management Of Sea Turtle Nesting In Malta, published in Frontiers in Ocean Sustainability, authors Isaak Koroma and Adriana Vella explore why these turtles are expanding into new territories and what the fate of their offspring reveals about the health of coastal environments.

The primary driver behind this “secondary colonisation” of the central and western Mediterranean is climate change. As sea surface temperatures rise in traditional nesting strongholds, loggerhead turtles (Caretta caretta) are being pushed northward and westward toward higher latitudes. In the Maltese islands, this creates what researchers describe as a “coastal squeeze.”

With sandy beaches making up just 2.4% of Malta’s coastline, turtles have little option but to nest in high-traffic areas shared with tourists, cafes, and boats.

A recurring question is why a sensitive species would choose such noisy, brightly lit environments. The study suggests that while climate-driven instincts are pushing turtles into these habitats, the “anthropogenic silence” experienced during the COVID-19 lockdowns offered anecdotal evidence of their sensitivity to human presence. When activity dropped, nesting success became more observable, highlighting noise and light as significant deterrents that turtles are now forced to navigate.

The ‘biological ledger’

The research introduces a different way of interpreting nest failure. Rather than treating a nest as simply successful or unsuccessful, the authors frame unhatched embryos as a “biological ledger”. In other words, a physical record of the stresses experienced during incubation.

By examining 122 unhatched embryos over six years (2020–2025), the study found that most developmental failures occurred during the final third of incubation. This is a critical phase when oxygen demand peaks.

The authors hypothesise that chronic noise pollution, particularly low-frequency vibrations from marine vessels, may travel through sand and disrupt the cues embryos rely on to synchronise hatching. Human activities such as trampling and mechanical beach cleaning are also identified as factors that compact sand, potentially reducing gas exchange and effectively suffocating developing embryos.

Returning to natal beaches

The study warns of a “protection gap,” where even legally conserved beaches may fail to produce hatchlings if environmental conditions remain too stressful. One emerging concern is a “geomagnetic mismatch.”

Sea turtles navigate back to their natal beaches using the earth’s magnetic field. However, coastal development involving sea walls and steel reinforcement may be producing “evolutionary traps,” where turtles return to artificial structures instead of natural sandy shores.

To address these challenges, Koroma and Vella call for greater “science integration” across biology, coastal physics, and policy. They propose “sensory corridors” with strict controls on light and noise during the 50-day incubation period.

By treating unhatched embryos as diagnostic data rather than simple failure, the researchers argue that these increasingly used nesting sites could be transformed into more resilient long-term sanctuaries.