harbour light

It is estimated that, with Antarctica excluded, just under a quarter of the world’s coastal regions experience artificial lighting at night.

Much of this is seen as a necessity for operational and safety reasons, not to mention the economics of transporting goods. When night falls, these areas are brightly lit with artificial lights, ensuring that not even darkness can halt their production. But, according to a new study, this can affect the surrounding marine community.

In a study published in the Royal Society journal Biology Letters, scientists have conducted a small experiment that has quite literally shone a light on how the behaviour of organisms is being altered by this phenomenon.

Researchers from Bangor University and the University of Exeter used rafts and three LED light intensity treatments in the Menai Strait, looking at how this affects the choice of habitat for marine invertebrates, which use light to find the best place spend their adult years.

“I knew that the larvae of sessile invertebrate – small animals that live in sediment or attach to hard surfaces – used the spectral identity and intensity of light to identify optimal habitats to settle in,” says Tom Davies an ecologist from the University of Exeter.

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“If you live in a shaded habitat you tend to seek out somewhere that is not in direct light, whereas if you are not living in a shaded habitat – say for example colonising the algae – you might look for somewhere that is brightly lit. I thought there was potential for artificial light to influence this process in marine systems.”

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Davies and his colleagues discovered that this was, indeed, true in practice; species were encouraged or deterred by light. Keel worms, for example, move toward the light, attaching themselves to vessels and marine structures, while other species were seen to move to darker waters.

An ecosystem under threat?

The effect of altered behaviour can be damaging to the ecosystem, with creatures using light to regulate when and where biological processes take place.

One example is creatures using variations of lunar light intensity to time their broadcast spawning events.

“A number of coral species do this. This is all about maximising the chance,” adds Davies.

“If you imagine [the] corals all along the Great Barrier Reef, [they] all want to spawn at the same time to reproduce. If they all do it at the same time they maximise the chance that male and female will come into reproductive contact with each other, so they time that using variations of lunar light intensity to a very specific time period.

“The thing about artificial light is that – in high abundance around cities – it can completely and totally destroy the signal of lunar light intensity, as a result of things like artificial sky glow, which is light that is scattered in the atmosphere and reflected back to the ground, [and] can be greater in intensity than the brightness of a full moon.”

“The thing about artificial light is that – in high abundance around cities – it can completely and totally destroy the signal of lunar light intensity.”

Another area of concern is diel (or diurnal) vertical migration of sea plankton, which use the intensity of light to regulate their depth. So, as the sun goes down they come up to the surface waters, and if the sun comes up they back down to the depths.

Sea turtle hatchings are also disorientated by artificial light, says Davies, as they use light clues to navigate to the sea, while some adult green turtles avoid nesting in artificially lit areas.

And it’s not only creatures dwelling in the water that are affected. “There are a whole range of bird species that collide with artificially lit ships,” Davies adds “This is particularly problematic in Polar Regions where they use bright lights to find icebergs. They are really quite far-reaching effects.”

Damage to vessels

Such effects are not just limited to the ecosystem, however. The study also found that the light could increase the prevalence of fouling species – organisms that attach and settle on structures like ship hulls and oil rigs.

These species can damage vessels and are costly to remove, and some of the consequences include increased drag, higher fuel consumption, damage to the structure, and a loss of manoeuvrability.

Those most at risk are vessels and structures operating in tropical conditions and shallow coastal waters because of increased light, heat and nutrients.

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“Things like keel worms [and] sea squirts attach themselves to vessels and hard structures anyway,” says Davies. “But, because larvae biology can be influenced by natural light cues, it seems reasonable to suggest that they might be affected by artificial light in terms of where they would settle.”

One remedy is anti-fouling coatings to protect hulls from corrosion, and the market for such products is growing with the expansion of sea trade.

These coatings can improve performance, but other solutions have also been introduced – including anti-fouling film applied below the water line and a risk assessment tool in Australia which enables operators to check their vessel for biofouling risk.

So what can be done?

Looking at the issue of lighting, however, the solutions are harder to pinpoint. Davies and his team believe more research is necessary – involving “a longer-term study that looks at the impacts of the settlement for ecosystem services, that is focused both on the direct implications of the effects of artificial light for maritime industries as well as the impact of light on marine ecosystems” – although much of this depends on gathering the required funds.

One area that could provide some joy is through spectral manipulation.

Davies explains: “LEDs offer the potential of manipulating the spectral outputs – the amount of light given out at different wavelengths.

“In terrestrial systems – an ecosystem found only on landforms – there is the classic case of moths being attracted to light. There is now a body of evidence that supports the notion it is the shorter wavelength of light that is attractive to moths.”

“LEDs offer the potential of manipulating the spectral outputs – the amount of light given out at different wavelengths.”

Based on this knowledge, Davies suggests that LEDs might be developed to avoid using the shorter wavelength to prevent the moth attraction – and the same approach could be used for mitigation solutions in marine systems.

“The one caveat to manipulating the spectral identity of the light is that different biological responses are evolved to utilise different wavelengths of the light spectrum,” he says.

“While you might say we will avoid using short wavelengths, [but] if coral used short wavelengths to regulate their broadcast spawning, wouldn’t you then have to put more light into longer wavelengths in order to achieve the same visual brightness to humans to make the light useful in the first place?

“[Also], using longer wavelengths might affect some other biological process.”

Davies also believes that shielding, where the output is controlled to minimise glare and light that travels straight up, is a possibility.

“Another potential is to actually look at when we use light and why we use light – is it important and strictly necessary?” he adds.

“A lot of marine light pollution is being caused by industries that need to use light for safety reasons, [such as] on oil rigs, ships, [but] maybe [we could be] looking around that and thinking about what is strictly necessary and what isn’t.”

However, what is needed now is deeper investigation to determine the extent to which marine life is both drawn and deterred by the light, and how the light pollution question can be answered.