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Keywords:

  • artificial lighting;
  • didson ;
  • predators;
  • schooling;
  • South Africa;
  • urbanization

Summary

  1. Urbanization has been identified as a global threat to biodiversity. Human population growth in coastal areas, including estuaries, is expected to increase considerably in coming decades, which will result in a proliferation of infrastructure such as jetties, wharfs and marinas. This infrastructure is often associated with artificial night lighting, yet the implications of these unnatural lighting regimes for the fish fauna in coastal ecosystems are unknown.
  2. We conducted novel, night-time surveys of the fish community directly adjacent to an artificial structure using an acoustic camera (didson). By manipulating the artificial lighting conditions (lighting either ‘on’ or ‘off’), we tested the effects of artificial light on fish abundance and behaviour.
  3. Clear differences in the abundance of fish were observed between the two light treatments. The occurrence of large-bodied predators (>500 mm TL) increased when the artificial lights were on. The behaviour of these fish also differed as they attempted to maintain their position within the illuminated area adjacent to the associated anthropogenic structure. The abundance of small shoaling fish also increased when the lights were on.
  4. It is possible that the conditions created by artificial lighting benefit piscivores through the concentration of prey and enhanced foraging capabilities in the case of visual predators. This has the potential to create unnatural top–down regulation of fish populations within urban estuarine and coastal waters.
  5. Synthesis and applications. As a consequence of a positive phototaxic response, the findings of this study suggest that artificial light often associated with man-made structures has the potential to alter fish communities within urban estuarine ecosystems by creating optimal conditions for predators. Future coastal developments should consider the ecological implications of lighting on aquatic communities. We recommend that lighting be minimized around coastal infrastructure and the use of red lights, which have limited penetration though water, be considered.