Between August and December, the peak of the olive ridley nesting season, the team surveyed a 21-kilometer stretch of beach on Guatemala’s southern coast, documenting more than 1,600 nesting events and measuring light levels at regular intervals along the sand. Using portable photometers, they recorded both skyglow and direct light sources, then compared nesting density against light intensity, day of the week, and other environmental variables such as sand temperature and beach width. The result was striking: nesting activity dropped measurably as artificial brightness increased, and the decline was steepest on Saturdays and Sundays, when beachfront hotels, homes, and visitors were most active.

The weekend pattern is particularly revealing. Because the same stretch of beach was sampled across both weekdays and weekends, factors like sand composition, slope, and vegetation remain essentially constant. What changes is the human footprint: more lights, more noise, more foot traffic, and more vehicles on the sand. The fact that turtles responded to this weekly rhythm suggests they are actively avoiding illuminated, disturbed sections of beach rather than simply being excluded by fixed habitat features. In effect, the researchers documented a behavioral response operating on a timescale of days, not years.

Olive ridleys are among the most abundant sea turtles in the world, but their populations have declined sharply over the past century due to egg harvesting, bycatch in fishing gear, and coastal development. Unlike some turtle species that nest in massive synchronized aggregations called arribadas, olive ridleys in this region nest solitarily at night, emerging from the surf to dig nests in the sand above the high-tide line. This nocturnal behavior makes them especially sensitive to light pollution, which can disorient hatchlings crawling toward the sea and deter adult females from coming ashore at all.

Artificial light at night is one of the fastest-growing forms of environmental change on the planet. Satellite imagery shows that artificially lit areas on Earth’s surface expand by roughly 2 percent each year, and coastal zones are among the most heavily affected. For sea turtles, whose nesting behavior evolved over millions of years on dark beaches, the consequences are direct and measurable. Studies elsewhere have shown that bright lights can cause hatchlings to wander inland and die from dehydration, exhaustion, or predation, while nesting females may abandon beaches they would otherwise use.

What makes the new Guatemalan study particularly valuable is its fine spatial and temporal resolution. Rather than comparing broadly different beaches, the researchers examined variation within a single coastline, isolating the effect of light from other confounding factors. They also measured light in a way that approximates what a turtle actually perceives from the beach, rather than relying solely on satellite data, which can miss low-level glow from individual homes and small businesses. This ground-truthing approach revealed that even modest illumination, well below the levels that would be obvious from orbit, was enough to suppress nesting.

The findings carry practical implications for coastal management across Central America and beyond. Guatemala’s Pacific coast has seen rapid growth in tourism and residential development in recent decades, and much of that growth has occurred with little consideration for wildlife. Simple interventions, such as shielded fixtures that direct light downward, motion-activated lighting, warm-spectrum bulbs that reduce the blue and green wavelengths turtles see most strongly, and seasonal curfews on beachfront illumination during nesting season, could substantially reduce the impact without requiring wholesale changes to coastal life.

Such measures have already proven effective elsewhere. In Florida, where loggerhead and green turtles nest on heavily developed beaches, lighting ordinances have been in place for decades, and studies show that compliant properties produce dramatically more successful hatchling emergences than non-compliant ones. Similar approaches have been adopted in parts of Australia, Oman, and the Caribbean. The Guatemalan study suggests that these lessons apply not only to large resorts but also to the small-scale, dispersed lighting that characterizes much of the developing-world coastline, which is often overlooked by both regulators and conservation programs.

The researchers also note that the weekend effect may compound other threats. If turtles are pushed away from illuminated beach sections on weekends, they may concentrate nesting in darker areas, increasing competition for space and raising the risk that nests are destroyed by later nesters digging into earlier clutches. Alternatively, females that cannot find suitable dark habitat may delay nesting or return to sea without laying, reducing overall reproductive output. Understanding these downstream consequences will require longer-term monitoring, ideally across multiple seasons and beaches with varying levels of development.

For now, the message from Guatemala’s dark beaches is clear: the glow of a single weekend can leave a measurable mark on one of the ocean’s oldest reproductive rituals. As coastal development accelerates across the tropics, the study offers both a warning and a practical template. Protecting nesting beaches from light does not require halting development; it requires designing it with the biology of the animals that share the shoreline in mind. For the olive ridleys of the eastern Pacific, that difference could determine whether future generations of hatchlings emerge into moonlight or into the glow of a beachfront bar.

Subject of Research: Effects of artificial light at night on olive ridley sea turtle nesting behavior on Guatemalan beaches

Article Title: Into the light: the adverse effects of artificial light at night on nest density of olive ridley sea turtles (Lepidochelys olivacea)

Article References: Carbonell Ellgutter, J. A., Rosell, F., Renssen, H., Hawkes, L. A., & Reinhardt, S. (2026). Into the light: the adverse effects of artificial light at night on nest density of olive ridley sea turtles (Lepidochelys olivacea). Frontiers in Marine Science, 13, Article 1746438. https://doi.org/10.3389/fmars.2026.1746438

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1746438

Keywords: olive ridley sea turtle, light pollution, sea turtle nesting, Guatemala, coastal development, weekend effect, hatchling disorientation, wildlife conservation, Central America, nocturnal behavior, tourism impact, lighting ordinances

The study, published in the journal Discover Conservation, monitored seven olive ridley nests during the 2020–2021 nesting season, which runs from September through January in Ghana. Researchers led by Baidoo Abigail, Addo Samuel, and Agyekumhene Andrews deployed miniature HOBO U22 temperature data loggers directly into egg clutches as females were laying, positioning the devices near the center of the clutch where metabolic heat accumulates most. A second logger was buried roughly two meters from each nest at identical depth, acting as a control that recorded the background temperature of the surrounding beach sand. Both loggers recorded measurements every fifteen minutes for the entire incubation period, generating an unusually high-resolution record of the thermal environment experienced by developing embryos.

The most striking result concerns the moment when nest and sand temperatures part ways. For the first nineteen days of incubation, temperatures inside the eggs and in the adjacent sand tracked each other closely, with no statistically significant difference between them. But from day twenty onward—the period that coincides with the thermosensitive window during which hatchling sex is determined—nest temperatures rose consistently above sand temperatures and stayed elevated until the hatchlings emerged. The researchers attribute this divergence to metabolic heating: as embryos grow, their collective metabolic activity generates heat that warms the clutch from within, a phenomenon well documented in sea turtles but never before quantified at this West African site.

The numbers reveal how warm this rookery already runs. Mean nest temperatures across the seven nests ranged from 30.7 to 33.3 degrees Celsius, averaging 32.4 degrees, while adjacent sand temperatures averaged a cooler 31.7 degrees. When nest and sand temperatures diverged, the difference typically spanned 0.3 to 1.7 degrees Celsius, averaging about 0.9 degrees. These figures matter enormously because olive ridley turtles exhibit temperature-dependent sex determination: pivotal temperatures that produce equal numbers of males and females have been reported near 30.0 to 30.5 degrees Celsius, with anything warmer producing females. Since mean nest temperatures during the middle third of incubation—the critical sex-determining window—ranged from 31.5 to 32.9 degrees, the researchers conclude that the monitored nests exceeded pivotal thresholds for a substantial portion of development, strongly implying a female-biased hatchling output. Although sex ratios were not measured directly, the thermal signature alone is telling.

Temperature exerted its clearest influence on the pace of development. Incubation duration ranged from 45 to 57 days across the seven nests, averaging about 48 days, and was strongly and negatively correlated with mean nest temperature, with a correlation coefficient of minus 0.88. Warmer nests hatched markedly sooner, and mean nest temperature explained roughly 78 percent of the variation in incubation duration among nests. This relationship is among the most robust in reptilian developmental biology, but its confirmation in Ghanaian sands underscores how powerfully thermal conditions govern the timeline from egg to emergence, even across a modest sample of nests.

Perhaps surprisingly, temperature told a much weaker story about reproductive success itself. Hatching success ranged widely, from 53.4 to 95.5 percent, with a mean of 81 percent, and emergence success ranged from 44.3 to 92.9 percent, averaging 75.2 percent. Yet neither measure showed a meaningful correlation with mean nest temperature, and incubation duration likewise bore no relationship to success rates. The authors interpret this variability as evidence that factors beyond temperature—sand moisture, gas exchange within the nest chamber, beach compaction, and disturbance—interact in complex ways to determine whether embryos survive. The finding is a caution against attributing nest outcomes to temperature alone, particularly in natural environments where multiple stressors overlap.

The hatchlings themselves offered additional clues about thermal stress. Morphological abnormalities, most frequently non-uniform carapace development, were observed in hatchlings from nests with mean temperatures ranging from 32.6 to 33.2 degrees Celsius, and the two hottest nests, averaging 33.0 and 33.2 degrees, produced the greatest number of anomalies. Locomotor performance, assessed through a self-righting test in which hatchlings were placed upside down on moist sand and timed as they flipped themselves upright, showed a moderate association with nest temperature, though the relationship did not reach statistical significance in the small sample. Such performance traits are closely linked to post-emergence survival, since hatchlings that cannot right themselves or crawl quickly are more vulnerable to predators on their frantic dash to the sea.

The study also carries practical implications for how scientists model the future of sea turtle populations under climate change. Many recent studies estimate nest temperatures from sand temperature data by adding a correction—typically 0.5 to 1.0 degrees Celsius—to account for metabolic heating. The Ghanaian measurements, showing an average nest-to-sand difference of about 0.9 degrees during divergence, provide direct empirical support for the magnitude of such corrections at a tropical site where incubation temperatures already press against pivotal thresholds. The researchers note that the beach at Songor was artificially nourished in 2010 as part of coastal erosion mitigation, a process known elsewhere to alter sand thermal properties, though sediment characteristics were beyond the scope of this study. With global climate change projected to raise sand temperatures further, and with local coastal development reshaping nesting microclimates, accurate in-nest measurements will become ever more critical for forecasting sex ratios and hatchling survival.

The work is not without limitations. Seven nests constitute a small sample, spanning a single nesting season, and the statistical power to detect subtle relationships was correspondingly limited; tendencies toward cooler deeper nests and warmer larger clutches matched published patterns but did not reach significance. Fine-scale thermal gradients within clutches were not assessed, and hatchling sex was never directly determined. Still, as the authors emphasize, this study delivers the first baseline characterization of olive ridley nest thermal dynamics anywhere in West Africa, filling a conspicuous geographic gap in global sea turtle science. As temperatures continue to climb at nesting beaches worldwide, understanding precisely what developing embryos experience inside their eggs—not just what the surrounding sand feels like—may prove decisive for conserving one of the ocean’s most vulnerable travelers, and for ensuring that Ghana’s beaches keep producing hatchlings capable of completing their ancient journey back to the sea.

Subject of Research: Effects of incubation temperature on olive ridley sea turtle nest success and hatchling development at the Songor Ramsar Site, Ghana

Article Title: Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana

Article References: Abigail, B., Samuel, A., & Andrews, A. (2026). Effects of incubation temperature on olive ridley sea turtle nest success at the Songor Ramsar Site, Ghana. Discover Conservation, 3(1), Article 40. https://doi.org/10.1007/s44353-026-00109-8

Image Credits: AI Generated

DOI: 10.1007/s44353-026-00109-8

Keywords: olive ridley sea turtle, incubation temperature, metabolic heating, temperature-dependent sex determination, hatching success, Songor Ramsar Site, Ghana, climate change, nest temperature, hatchling performance, West Africa, conservation