By K.L. Sterup, Victoria University of Wellington
Designing sustainable infrastructure requires consideration of a complex web of influences on overall ecosystem health, including light pollution in coastal environments, which can have a negative impact on marine life.
The modern world is a world of convenience, shaped by and for humans to make our lives easier, and allow us to prosper. Advances within the past three decades alone have propelled human society into a digital information age where all of our needs can be met without even leaving home.
As part of this societal advance, the ever-rising trend of coastal urbanisation has become a significant sustainable development issue. In a 2003 study, Christopher Small and Robert J Nicholls at Columbia and Middlesex universities found that global population density within 100 kilometres of a shoreline was three times higher than the global average population density. The possible consequences of coastal development for marine ecosystems are critical factors for planners and developers to consider, particularly in Aotearoa New Zealand, an island nation with a wealth of coastal resources with cultural and economic significance.
One such consequence of particular relevance to aquatic ecosystems is pollution. Pollution has become a daily reality in every environment on Earth, and its many forms can have different effects in these environments. It’s a complex web of interacting influences on overall ecosystem health to be considered when designing sustainable infrastructure.
We already know that coastal urban areas create pollution in the form of chemicals and heavy metals, plastics and sediment, all of which have well-documented effects on the health of humans and the surrounding environment, through direct and indirect mechanisms. Despite this, some pollutants have more subtle effects, which arise from the complex web of animal-plant-human-environment interactions in nature, and these pollutants also need to be considered when making infrastructural choices.
Light pollution is an unexpected but important influence on marine ecosystems, and is a direct result of the lighting choices that we make in our cities and harbours. DarkSky International defines light pollution as the alteration of outdoor (usually night-time) light levels from those that occur naturally as a result of human activity. Light pollution is created by unshielded outdoor light fixtures, such as street and dock lights, emitting light constantly throughout the night.
Light pollution has previously been criticised for the difficulty it creates for astronomers and stargazers, making the stars less visible to the human eye. Now, it is also beginning to attract the attention of biologists and ecologists as a significant factor affecting many species, even in relatively population-sparse countries like New Zealand.
While it may seem that light pollution would only affect the sky directly above the light fixtures, the spatial scale of the problem is exacerbated by sky glow, which occurs when clouds reflect upwelling light from artificial sources back to the Earth. In 2022, Ellery J McNaughton and colleagues at the University of Auckland observed that the sky was unnaturally bright throughout the year at sites more than 13 kilometres from the city centre. Furthermore, they predicted that the sky glow created by Auckland city would affect several nearby areas of ecological significance, both marine and terrestrial, such as the Waitākere Ranges and much of Hauraki Gulf/Tīkapa Moana.
My own research at Victoria University of Wellington, completed in 2023, used observations of sky glow at various points around the city to model sky glow across the nearshore coastal areas from Wellington Harbour to Kapiti Island. The results suggested that the skies over much of the Wellington coastline and locations up to 60 kilometres from Wellington city centre, including Taputeranga and Kāpiti marine reserves, are likely to be affected by sky glow. Further results of this research suggest that the sky glow created by Wellington city could be negatively affecting the growth of a small fish living in Wellington Harbour – for example, the common triplefin.
The connection between the brightness of the sky and the health of marine life may not be immediately obvious, but the answer lies in the moon. Many types of marine life, including fish, turtles, corals, seabirds, invertebrates and even some seaweeds, rely on the lunar cycle as a cue for important behaviours like reproduction, feeding, and resting. Sky glow confuses them, and disturbs these important behaviours.
Many animals are active during the night, either living fully nocturnally or experiencing increased periods of activity at dusk and dawn. Therefore, the amount of light available in surface waters at night determines foraging success for visually hunting species, as well as the likelihood of survival for the prey species of nocturnal predators. Taking these complex ecological interactions into account, the moon is a very important factor that determines the structure and composition of coastal ecosystems.
Light pollution interferes with coastal ecosystems by masking the lunar cycle. When the light emitted by cities is brighter than the moon, the ecological relationships between marine organisms change in ways that can manifest as consequences for individual animals and the entire community. For example, a 2017 paper published by Daniel Bolton and colleagues at the University of New South Wales, in Australia, found that the introduction of artificial light underneath the city wharf at night led to significant changes in the community assemblage of fish and invertebrates.
Furthermore, it is not just the brightness of the sky that can affect marine ecosystems, but also the wavelengths of light involved. Seawater absorbs certain wavelengths faster than others, such that the wavelengths that penetrate to the greatest depths play a more important role in coastal ecosystems. This point is especially relevant, since many cities in recent years have been investing in LED streetlights for their increased energy efficiency over traditional streetlights. Many LEDs, however, emit white light in the spectral range of 400–450 nanometres – short wavelengths that penetrate to great depths in seawater and are likely to be detectable by marine species.
In 2018, Wellington City Council installed more than 17,000 LED streetlights to improve energy efficiency, and the engineering design code for street lighting in Auckland also specifies that all new installations must be LEDs. It is true that LEDs emit less direct light pollution than the traditional light bulbs that were used previously, but the results of the sky glow research previously described in Auckland and Wellington make it clear that more still needs to be done to minimise harm to the surrounding coastal areas.
Aotearoa is already on a good track in minimising light pollution, with two internationally recognised Dark Sky Reserves already in place in Aoraki Mackenzie and Wairarapa. There is no reason that New Zealand’s urban areas can’t follow suit and invest in sustainable and ecologically friendly lighting infrastructure.
DarkSky International has useful guides to installing responsible lighting following five key principles: lights should be useful, targeted, low level, controlled, and warm-coloured. If these changes can be implemented in our coastal cities, then we will be making significant advances towards truly sustainable development. Modernity doesn’t have to come at the cost of the natural world. With consideration and effort from planners and developers, we can conserve the environment for the benefit of humans and all other members of our ecosystem.