Cities are artificially lit to allow humans to make use of the night. This light pollution means that stars are often barely visible in urban skies.  Urban development in coastal areas is increasingly exposing marine ecosystems to artificial light.

This exposure is particularly acute in and near some of the world’s largest coastal cities and may carry physiological and behavioural consequences for the organisms that inhabit their coastal waters.

The Universities of Plymouth and Strathclyde quantified the magnitude of the natural and unnatural light reaching the marine ecosystems of a group of seven coastal cities with more than 10 million inhabitants: Tokyo, Shanghai, Mumbai, New York, Buenos Aires, Lagos and Los Angeles.

The research showed that for these cities, dosages of artificial light at night on the surface of the sea are up to six times greater than moonlight. Moonlight intensity only exceeded artificial lighting within a period of three days from the brightest full moons.

Impact on marine ecosystems

Natural sources of light at night have seasonal cycles. Night time light exposure has therefore historically been dependent on the moon and its cycle of waxing, waning and elevation in the sky. Artificial light sources, in contrast, have a fixed position irrespective of the season and shine with the same intensity throughout the night and all year round.

Scientific research has shown that light pollution can mask the natural cycle of the moon and can affect coastal organisms. Marine organisms, including coral reefs, rely on natural light cycles to regulate their physiological and biological processes. Several coral species simultaneously release their reproductive cells – called gametes – on cues from the lunar cycle.

Key maintenance processes in coral, such as symbiosis, can also be sensitive to artificial lighting. Symbiosis describes the close relationship between the two organisms that make up coral.

The spectral composition of artificial light at night (its red, green and blue light components) illuminating seafloor habitats may also disrupt visually guided ecological processes. Predators that usually feed in the day such as the herring gull may be able to see prey that would ordinarily be camouflaged at night, such as marine snails.

Resources:

The above is an extract and the full story can be read in Mongabay and The Conversation. The peer-reviewed paper – Disruption of marine habitats by artificial light at night from global coastal megacities – can be found here.