The spectral and spatial distribution of light pollution in the waters of the northern Gulf of Aqaba (Eilat)

Abstract

The urbanization of the shores of the Gulf of Aqaba has exposed the marine environment there, including unique fringing coral reefs, to strong anthropogenic light sources. Here we present the first in situ measurements of artificial nighttime light under water in such an ecosystem, with irradiance measured in 12 wavelength bands, at 19 measurement stations spread over 44 square km, and at 30 depths down to 30-m depth. At 1-m depth, we find downwelling irradiance values that vary from 4.6 × 10−4 μW cm−2 nm−1 500 m from the city to 1 × 10−6 μW cm−2 nm−1 in the center of the gulf (9.5 km from the city) in the yellow channel (589-nm wavelength) and from 1.3 × 10−4 μW cm−2 nm−1 to 4.3 × 10−5 μW cm−2 nm−1 in the blue channel (443-nm wavelength). Down to 10-m depth, we find downwelling irradiance values that vary from 1 × 10−6 μW cm−2 nm−1 to 4.6 × 10−4 μW cm−2 nm−1 in the yellow channel and from 2.6 × 10−5 μW cm−2 nm−1 to 1.3 × 10−4 μW cm−2 nm−1 in the blue channel, and we even detected a signal at 30-m depth. This irradiance could influence such biological processes as the tuning of circadian clocks, the synchronization of coral spawning, recruitment and competition, vertical migration of demersal plankton, feeding patterns, and prey/predator visual interactions.

Combined salinity and acidity stressors alterDaphnia magnapopulation growth and structure under severe absence of photoperiod

“…The fourth is an under-examined side effect of constant light exposure on the onset of increased Daphnia reproduction under certain levels of salinity and/or acidity stress that are considered otherwise unfavourable for exponential reproduction. Light pollution effects, in terms of artificial light, sky glow and interference with daylight-night-time patterns, which increasingly affect aquatic ecosystems and ecological interactions [34,106], are becoming a serious concern associated with urbanisation and industrialised zones with increasing human population around the globe [30,34,107–110]. The far-reaching effects of extended light exposure [34] may not only lead to changes in vital phototactic behaviours with disruptive impacts on the aquatic system [30,34], but may also extend to how zooplankton respond to a cocktail of stressors [77,111].…”

How dark is a river? Artificial light at night in aquatic systems and the need for comprehensive night‐time light measurements

“…Tamir, Lerner, Haspel, Dubinsky, and Iluz () measured underwater spectra at 19 locations at different depths in the coastal waters of the Gulf of Eilat, Israel with a profiling multispectral radiometer with 12 spectral channels between 300 and 900 nm and mapped the extend of ALAN for these waters. They showed that wavelengths at 589 and 443 nm can still be detected in depths greater than 10 m at a great distance from the shore.…”

“…They used a commercial DSLR camera with a fisheye lens to acquire all‐sky and vertical plane hemispherical images and a small single‐channel SQM photometer for long‐term measurements. Jechow, Kolláth, Lerner, et al () later showed that the DSLR method can also be used from a moving boat, taking measurements in the Gulf of Eilat near some measurement spots of Tamir et al ().…”

“…They used a commercial DSLR camera with a fisheye lens to acquire all-sky and vertical plane hemispherical images and a small single-channel SQM photometer for long-term measurements. Jechow, Kolláth, Lerner, et al (2017a) later showed that the DSLR method can also be used from a moving boat, taking measurements in the Gulf of Eilat near some measurement spots of Tamir et al (2017). Ges, Bará, García-Gil, Zamorano, and Masana (2018) compared the predictions of the skyglow model by Falchi et al (2016) to SQM observations made during a transect with a boat from Barcelona, Spain, out to sea.…”

“…Thus, a measurement in the horizontal plane appears most straightforward. For larger water bodies and especially rivers, transects or multipoint measurements are recommended (Ges et al, 2018;Jechow, Kolláth, Lerner, et al, 2017a;Ludvigsen et al, 2018;Tamir et al, 2017). Single-point measurements on multiple water bodies like performed by Secondi et al (2017) are also reasonable especially in their context of small water bodies like ponds.…”