Artificial light at night (ALAN) mediates transient spatial aggregation of an ecosystem engineer, the crab Neohelice granulata (Dana, 1851) (Decapoda: Brachyura: Varunidae), under different ecological contexts

Abstract

Artificial light at night (ALAN) alters natural light regimes in much of the world. The effect of ALAN has been studied in several organisms, although not so much in crustaceans, especially in adult stages. We evaluated the relationship between different intensities of ALAN and the abundance of burrows, and surface activity of the crab Neohelice granulata (Dana, 1851). The study was conducted in 2016 and 2017, in two salt marshes, San Antonio Oeste and Mar Chiquita, Argentina, both having different ecological contexts. During new-moon nights we counted the number of burrows and crabs on the surface and along a gradient of artificial light caused by street lighting with high-pressure sodium lamps. We found that the number of crabs on the surface increased with light intensity and that crabs were almost exclusively males. In contrast, we found that the number of burrows was not related to light intensity, suggesting that the increase of crabs on the surface was mainly due to an increase in their activity. We considered two main mechanisms causing the increase on surface activity of crabs: 1) an increase in the frequency of emergence and short-distance excursions around their burrow and 2) an increase of mobility with long-distance directional displacement from dark to lit areas. Overall, our observations suggest that the presence of ALAN can modify individual crab behavior (i.e., aggregation) and consequently effects on ecosystem functioning.