In 2009, the Wadden Sea was inscribed into the UNESCO World Heritage List in recognition of the ‘Outstanding Universal Value’ especially related to the characteristic biodiversity and the ongoing geological, ecological and biological processes. The UNESCO World Heritage status is the highest possible award for a natural site and recognition and acknowledgement of its outstanding global importance. In 2018, the Ministers of Denmark, Germany and the Netherlands recognized the importance of nocturnal darkness for the ecosystem and the humankind as well as the potential effects of light pollution on the conservation of the Wadden Sea World Heritage.
To better understand the relationship between light emissions and the Outstanding Universal Value of our World Heritage, PRW commissioned, within the Trilateral Dark Sky Initiative, in collaboration with the Common Wadden Sea Secretariat and the Partnership Hub, a scientific literature review of the known effect of Artificial Light at Night on organisms and ecosystems in the Wadden Sea or similar habitats. This document collects the most important existing literature, highlights existing knowledge gaps and provides brief recommendations to mitigate these effects.
The dark side of Light
While light is generally seen as positive, there is mounting evidence that ALAN changes behaviour, space use, migration, physiology, development, and reproduction in almost all organism groups, including plants and microorganisms. Moreover, Artificial light at night (ALAN) is a growing factor in the anthropogenic environment.
Proven effects for birds and insects
Special focus of research so far has been on birds and insects. The Wadden Sea World Heritage area is an important part of the East Atlantic migration route. Yearly, almost 10 to 12 million birds use this area. ALAN has shown to change flight paths by attracting birds, thus posing a high risk of fatal bird strikes to millions of birds worldwide each year. Insects are also attracted to light sources and ALAN changes reproductive behaviour, which results in local reduction of insect populations. In all terrestrial ecosystems, insects play a vital role, and individual consequences have been shown to translate through cascade-effects into food webs and entire ecosystems. We also expect that the effects of ALAN on the barrier islands and coastal areas will translate to the intertidal habitats.
Sufficient indications of more far-reaching effects
Less is known about the impacts of ALAN on marine ecosystems, but freshwater habitats have been shown to be especially sensitive to ALAN. Even low light levels are enough to interfere with fish hormone production, suppress plankton movements, and influence algal growths. In regard of marine and intertidal habitats, many questions still need to be answered, however, it is clear even now that ALAN is a serious environmental stressor. It most likely weakens the resilience of individuals and ecosystems to other stressor like climate change or chemical pollutants, exponentiating this damage.
Towards responsible lighting
Based on current evidence, ALAN needs to be used with care, especially in areas with mostly unchanged biological processes. Generally, the use of ALAN needs to be justified by balancing benefit and harm. Where ALAN is needed, it is necessary to follow light planning criteria and to apply the best available knowledge in terms of technology and design, in order to create illumination that reduces harmful effects to the environment.
S. (Sonja) van der Graaf. E-mail: firstname.lastname@example.org. Tel: +31 (0)6 1148 7120.