By Blair Witherington

Although lighting the way at night may seem like a harmless necessity, artificial lighting is one of the most profound ways humans alter the natural world. For animals that are active at night, such as nesting and hatching sea turtles, natural light fields provide important information that guides critical behaviors. Artificial lighting pollutes those light fields with dangerous misinformation. For example, artificial lights on sea turtle nesting beaches can deter female turtles from nesting and can disorient females and their hatchlings on their way to the sea. The disruption of hatchling movement has lethal consequences to hatchlings both on the beach and in nearshore waters. Artificial lighting on sea turtle nesting beaches is a severe threat to turtles and is a major conservation challenge on human-occupied beaches.

Hatchling sea turtles emerging from nests at night rely on the natural brightness contrast between seaward and landward directions—such as that presented by celestial light visible over an open seaward horizon and an opposing landward horizon silhouetted by a dune or coastal plants. In experimental light fields, hatchlings move toward the center of the brightest horizon with low light across a broad span. Over millennia, this orientation trait has consistently led hatchlings to the sea. Orienting toward a broadly bright horizon favors seaward movement, even when a celestial light such as the full moon shines above the land. The moon’s light may be bright, but it’s not as low as the seaward horizon, and its light passes through Earth’s atmosphere, lighting up competing directions and making the moon just one part of a brightened light field. Artificial light sources are different. Although proximity makes their light seem bright, the brightness is not sufficient to light other directions. As a result, artificial lighting on land produces a misleading light field directed toward the land. Misinformed sea turtle hatchlings that move in that direction often never make it to the sea.

Author affiliations

BLAIR WITHERINGTON, Inwater Research Group, Florida, U.S.A.

This article originally appeared in SWOT Report, vol. 17 (2022). Click here to download the complete article as a PDF.