The impacts of artificial light at night on the ecology of temperate and tropical reefs

Abstract

Despite 22% of the world's coastal regions experiencing some degree of light pollution, and biologically important artificial light at night (ALAN) reaching large portions of the seafloor (greater than 75%) near coastal developments, the impacts of ALAN on temperate and tropical reefs are still relatively unknown. Because many reef species have evolved in response to low-light nocturnal environments, consistent daily, lunar, and seasonal light cycles, and distinct light spectra, these impacts are likely to be profound. Recent studies have found ALAN can decrease reproductive success of fishes, alter predation rates of invertebrates and fishes, and impact the physiology and biochemistry of reef-building corals. In this paper, we integrate knowledge of the role of natural light in temperate and tropical reefs with a synthesis of the current literature on the impacts of ALAN on reef organisms to explore potential changes at the system level in reef communities exposed to ALAN. Specifically, we identify the direct impacts of ALAN on individual organisms and flow on effects for reef communities, and present potential scenarios where ALAN could significantly alter system-level dynamics, possibly even creating novel ecosystems. Lastly, we highlight large knowledge gaps in our understanding of the overall impact of ALAN on reef systems. This article is part of the theme issue ‘Light pollution in complex ecological systems’.

The effects of artificial light at night (ALAN) on the circadian biology of marine animals

“…Outside of commercial fisheries, simulated ALAN exposure experiments have demonstrated the negative effects of ALAN on different offshore species. The majority of this research has focused on corals, which are highly photosensitive and have well-developed circadian behaviors (Rosenberg et al, 2019), and are thus intensely vulnerable to the effects of ALAN (Fobert et al, 2023). In coral species collected from oceanic environments, ALAN exposure reduced reproductive fitness by delaying gametogenesis and inhibiting synchronization of gamete release (Ayalon et al, 2021).…”

“…ALAN exposure has also been shown to negatively impact the physiology and overall fitness of reef fishes with significant effects on metabolism, embryo quality, growth, and survival (Fobert et al, 2023). In certain reef fishes, such as clownfish (Amphiprion ocellaris) and sergeant majors (Abudefduf saxatilis), the timing of embryo hatching is linked to specific intensities of light within the natural photoperiod.…”

Light pollution in complex ecological systems

“…Gaining a mechanistic and general understanding of the impacts of ALAN on different levels of ecological organization, as described in the preceding section, provides the basis to Parkinson & Tiegs [28] (m) Hölker et al [18] (n) Fobert et al [56] (o) Coetzee et al [61] (p) Evans [32] (a) (c, d, j, k) Figure 2. Effects of ALAN on complex ecological systems.…”

“…These findings, coupled with results demonstrating severe impacts on community composition, indicate profound implications for entire ecosystems and their functioning. For example, as emphasized in the review by Fobert et al [56], substantial changes at the system level are anticipated in both temperate and tropical coral reefs. Moreover, Hölker et al [51] discuss the possibility that responses to ALAN among or within taxonomic groups may create novel communities 'with no historical analogues'.…”

“…For example, as emphasized in the review by Fobert et al . [ 56 ], substantial changes at the system level are anticipated in both temperate and tropical coral reefs. Moreover, Hölker et al .…”