Illuminated seascapes

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Key Points:

  • The many known negative impacts of light pollution begs the question of whether illuminated seascapes in urban areas are exerting selective pressure on marine organisms.
  • Thus far, studies addressing this question have been limited.

Figure from Davies et al. (2014): Known and potential impacts of artificial light pollution on marine ecosystems. (a) Suppression of zooplankton diel vertical migration by artificial skyglow. (b) Bird strikes on lit ships at night. (c) Extension of visual foraging behavior in coastal wading birds into the night. (d) Disruption of settlement site selection in sessile invertebrate larvae. (e) Aggregation of fish under pier lights leads to intensified predation. (f) De‐synchronization of broadcast spawning from lunar phase (corals releasing gametes). (g) Displacement of nesting sea turtles from artificially lit nesting areas. (h) Disorientation of seaward migration in sea turtle hatchlings by street lights.

Light pollution affects a whole suite of marine organisms beyond turtles, as detailed in an excellent review by Thomas Davies and colleagues at the University of Exeter.

A conceptual figure from their paper summarizes known impacts, which relate to navigation, reproduction, larval settlement, relationships between predators and their prey, and communication:

Populations of marine organisms appear to persist in illuminated seascapes, despite numerous ways in which artificial light is thought to threaten their survivorship may be threatened by artificial light.

Could artificial light be acting as a selective force in urban areas?

It’s unclear at this stage.

We might expect evolutionary responses to light pollution, particularly in the tropics, as noted by Travis Longcore and Catherine Rich in a 2004 paper: light pollution “is more likely to affect tropical species adapted to diel patterns with minimal seasonal variation than extratropical species adapted to substantial seasonal variation.”

However, adaptations to light pollution among marine organisms have yet to be thoroughly studied, and empirical evidence is lacking. Hopefully this will be explored further soon.