Many coastal processes are regulated by day/night cycles and are expected to be altered by Artificial Light at Night (ALAN). The goal of this study was to assess the influence of ALAN on the settlement rates of intertidal barnacles. A newly designed settlement plate equipped with a small central LED light source was used to quantify settlement rates in presence/absence of ALAN conditions. “ALAN plates” as well as regular settlement plates were deployed in the mid rocky intertidal zone. Both ALAN and control plates collected early and late settlers of the barnacles Notochthamalus scabrosus and Jehlius cirratus. Early settlers (pre-metamorphosis cyprids) were not affected by ALAN. By contrast, the density of late settlers (post-metamorphosis spats) was significantly lower in ALAN than in control plates for both species, suggesting detrimental ALAN impacts on the settlement process. The new ALAN plates represent an attractive and alternative methodology to study ALAN effects.

A large-scale oil spill has reached over 3000 km of the NE Brazilian coast since August 2019. The cause and origin of this spill remain mysterious, and the impacts on coastal ecosystems have not been clearly understood so far. Despite the efforts to remove the oil (mainly from local communities), oil stains are still present in beaches, mangroves, and beachrocks. In this short report, we describe the occurrence of the barnacle Chthamalus bisinuatus Pilsbry, 1916 colonizing oil spill stains on intertidal surfaces of beachrocks one year after the first oil records. We quickly assessed oil stains across three different reefs located at the Conde municipality, Bahia (NE Brazil), where the species was identified and its density on oil stains calculated. The occurrence of barnacles in oil stains was restricted to zones in the wake of the reefs. Their densities varied from 0 to 238 ind./dm², with an average of 34 ± 68 ind./dm². If we account for dead individuals (empty barnacle plates), they correspond to 25.9% of the sampled population. The presence of oil possibly affected barnacle survival rates but did not seem to prevent barnacle individuals from reaching adult sizes. We also found individuals of the snail Echinolittorina lineolata (d'Orbigny, 1840) crawling on these barnacles, indicating that the barnacle assemblages on oil stains are stable enough to provide refuge for these snails. It is not clear if the presence of barnacles on oil reflects the resistance of these crustaceans to the oil toxicity or is just a result of a low substrate selectivity by the cypris larvae.