How are the Mediterranean islands polluted by artificial light at night?

Highlights

• The light pollution level is extremely high on the biggest Mediterranean islands.

• The light pollution level correlates with human population density of these islands.

• There are 49 islands or their parts with “pristine” skies in the Mediterranean.

• Four dark sky refugia are highlighted within the territory of the Mediterranean Sea.

• Recommendations for changing of the current ALAN-related situation are given.

Abstract

The Mediterranean is considered as a World Biodiversity Hotspot because of the significant reservoir of endemics, which are threatened with destruction. Island ecosystems have special importance for biodiversity conservation in this region. However, most of them are under strong anthropogenic influences: recreational pressures, infrastructure development, fires etc. At the same time, new types of anthropogenic pressures have developed, one of which is the preponderance of artificial light at night (ALAN) and sky glow. This factor has not been perceived as dangerous for people and biodiversity until recently. However, the latest researches show the opposite conclusion: ALAN has a significant influence on reproduction, navigation, behavior, foraging, habitat selection, communication, and social interactions of all living organisms. Therefore, we have estimated the level of light pollution on the fifteen biggest islands of the Mediterranean using tools available from Google Earth Pro, and the New World Atlas of Artificial Sky Brightness in the form of a kmz layer created by Falchi et al. (2016). In addition, islands or their parts without ecological light pollution have been selected. The obtained results argue that light pollution is extremely high on these larger islands; there are no areas with zero-level of ecological light pollution. As well it has been found that the level of light pollution of these islands correlates with their human population density. Nevertheless, there are 49 small islands or their parts with “pristine” skies, and their total area is 118.67 km². Also, four dark sky refugia (Western (313,593 km²), Adriatic (331 km²), Aegean (12,448 km²), and Eastern (841,195 km²)) were highlighted within the territory of the Mediterranean Sea. That is 46,61% of its total area. Special attention has been paid to protected areas of the region in the context of combating light pollution, as well as the potential for astro-tourism development. Recommendations for changing of the current ALAN-related situation are given.

Introduction

The Mediterranean is considered a World Biodiversity Hotspot because of the significant reservoir of endemics and the fact that many are threatened with extinction (Myers et al., 2000). Its local flora is rich containing about 24000–25000 species with a high degree of endemism, up to 63.5% (Greuter, 1991; Heywood, 2002). The local fauna is also characterized by its richness and its high level of endemism. There are 298 species (of which 38 are endemic) of mammals (Temple and Cuttelod, 2009), 534 species of birds including 63 endemics (Blondel et al., 2010), 299 species (117 endemics) of reptiles (Cox et al., 2006), 109 species (54 endemics) of amphibians (Cox et al., 2006), 622 species (280 endemics) of freshwater fish (The Critical Ecosystem Partnership Fund, 2017), and 600 species of marine fish with approximately 74 endemic species (Abdul Malak et al., 2011). Invertebrates are highly diverse in the Mediterranean region: anthozoans are represented by 151 species (Coll et al., 2010) with approximately 26 endemic species amongst them (del Mar Otero et al., 2017); freshwater mollusks account for 629 species, including 384 endemic species (The Critical Ecosystem Partnership Fund, 2017); there are 61 species of damselflies and 104 species of dragonflies, 23 of them are endemic (Riservato et al., 2009); 463 species of butterflies (98 endemic species) (Numa et al., 2016); about 580 species of dung beetles occur in the region, of which approximately 150 are endemic; at least 576 species of saproxylic beetles represented here with approximately 338 endemic species (The Critical Ecosystem Partnership Fund, 2017). This rich and unique biodiversity has been formed to a large extent due to island isolation over a long period of time in the Mediterranean (Blondel et al., 2010; Greuter, 2001; Thompson, 2005). As a result, the flora of Sicily has 305 species of vascular plants, with 11.3% being endemic, the flora of Crete – 165 species or 10.1% being endemic, the flora of Sardinia – 61 species of which 5.4% are endemic, and the flora of Corsica – 131 species with 4.5% being endemic (Junikka et al., 2006). Therefore, the islands have special value to this region; many of them belonging to the ten Mediterranean Basin hotspots based on plant endemism and richness (Medail and Quezel, 1999). However, there is a very strong anthropogenic influence on natural ecosystems, which is causing biodiversity loss in the Mediterranean (Coll et al., 2010; Greuter, 1991). Though the human impact on the Mediterranean islands, from early prehistoric settlements through antiquity to the Middle Ages, has been profound, the situation has been changing for the worse in the last few decades; the speed of deterioration of natural habitats has increased exponentially (Greuter, 2001). Moreover, new threats are appearing. One of these is ecological light pollution which is increasing rapidly on a global scale (Kyba et al., 2017). This has already been documented for the Mediterranean (Bennie et al., 2015b; Caruana et al., 2020; Peregrym et al., 2020a).

While the impact of artificial light at night (ALAN) is being ignored by decision-makers at local and national levels, as well as by related organizations and even by some scientists, the problem becomes more dangerous for ecosystems, species, and human health (Abraham et al., 2019; Dominoni et al., 2020; Falchi, 2018; Schroer and Hölker, 2017). However, the fact that 80% of the world and more than 99% of U.S. and European populations live under light-polluted skies shocks (Falchi et al., 2016). In addition, its consequences are deep and serious, because they have a significant influence on reproduction, navigation, behavior, foraging, habitat selection, communication, and social interactions of all living organisms. There is, already, a lot of published data about the ALAN and sky glow affecting plants (Bennie et al., 2018; Brelsford and Robson, 2018; ffrench-Constant et al., 2016; Giavi et al., 2020; Knop et al., 2017; and others), invertebrates (Ayalon et al., 2019; Davies et al., 2012; Grubisic et al., 2018; Macgregor et al., 2017; Owens et al., 2019; Underwood et al., 2017; van Grunsven et al., 2018; and others), and vertebrates (Grubisic et al., 2019; Schroer and Hölker, 2017; Touzot et al., 2020; and others), including humans (Cho et al., 2015; Dominoni et al., 2016; Johnson and Munshi-South, 2017; and others). Consequently, cascading effects with unpredictable results appear in terrestrial and water ecosystems (Bennie et al., 2015a; Bolton et al., 2017; Davies et al., 2020; Depledge et al., 2010; Garratt et al., 2019; Hölker et al., 2015; Maggi et al., 2020; Navarro-Barranco and Hughes, 2015; Perkin et al., 2011; Russo et al., 2019; Sanders et al., 2015; Sanders and Gaston, 2018; Spoelstra et al., 2015). Besides, ALAN can be a driver of evolution across urban-rural landscapes (Hopkins et al., 2018).

In considering the described situation where the Mediterranean islands are natural habitats for many unique species, and the ALAN impact increase on them, it was decided to estimate the strength of the impact of artificial light at night in these territories.