Artificial light at night and apparent predation on juvenile Neohelice granulata during two deployment periods at Mar Chiquita, Argentina

Over the past decade, artificial light at night (ALAN) has become one of the most spatially extensive anthropogenic disturbances along coastlines worldwide, yet whether its capacity to alter predation is a fixed property of illumination intensity or depends on the ecological context in which it occurs has received little attention. Here we evaluate this question using replicated tethering experiments at the microtidal lagoon of Mar Chiquita (south-western Atlantic coast of Argentina) in two deployment periods (spring and summer), quantifying apparent predation on juvenile Neohelice granulata under ALAN (cold-white LED, ≈ 38 lux) and natural-darkness controls. A Generalised Linear Mixed Model with experimental night as a random intercept revealed a significant interaction between light condition and season. In spring, ALAN significantly increased the probability of juvenile predation relative to natural darkness, whereas no detectable effect was found in summer. Placed alongside the published effect at a macrotidal, structurally simpler site, ALAN sensitivity follows an ordered gradient consistent with an amplifying-effect hypothesis, whereby ALAN would amplify predation in proportion to the underlying susceptibility state of predators and prey (adult nutritional condition, juvenile developmental vulnerability and habitat structural complexity) rather than being a fixed property of light intensity alone, although adult nutritional condition was not measured directly and is inferred from published seasonal values for this population. These results indicate that the same habitat may shift between high- and low-sensitivity states across seasons, that single-season assessments may systematically underestimate cumulative predation exposure, and that targeted light management during juvenile settlement is, in principle, a more efficient conservation approach than year-round restrictions, although we did not evaluate its costs or feasibility.