Shining the light on marine infrastructure: The use of artificial light to manipulate benthic marine communities

Abstract In urbanised areas, marine infrastructure alters natural light regimes, creating habitats that are permanently shaded, affecting the community structure of settling and resident biota. While applications of artificial lights have been suggested to minimise impacts of shading or manipulate community composition for specific aims (e.g. carbon capture, biosecurity), their use has not been evaluated. We used two field experiments to test the effect of artificial light of low (1 × 20,000 lumen light) and high (3 × 20,000 lumen light or 1 × 66,000 lumen light) intensities (7 AM–7 PM on–off cycle) on benthic communities on marine infrastructure. Specifically, we assessed whether artificial lights (i) led to the development of communities similar to those under natural light conditions, (ii) enhanced the abundance of algae and discouraged invertebrates (functional groups that are inversely impacted by shade) and whether (iii) the extent to which artificial lights impact marine communities varies across environmental settings (high and low turbidity) where natural light availability differs. Impacts were assessed on new (two sites) and established communities (one site). We also assessed the effect of artificial light on predation/herbivory pressure using a caging experiment at the low turbidity site. For new communities developing on bare substrate in low turbidity conditions, low intensity artificial light resulted in similar communities to bare substrate exposed to natural light levels. High intensity artificial light increased algal cover beyond communities developing in natural light. Caging increased the cover of algae and invertebrates across all treatments. In turbid locations, artificial light (high and low) increased algal abundance, though to a lesser extent. The addition of artificial light had limited effects on established benthic communities. Synthesis and applications . Our experiments indicate that artificial lights can be effective in reversing effects of shading, but that targeted outcomes (e.g. increased algal or reduced invertebrate cover) are limited to bare substrates and low turbidity environments where more light is available, and algae are naturally abundant.