A new study looking into the reproduction of clown fish has found that artificial light at night can prevent any eggs from hatching. It’s just another in the long line of ways we are polluting our oceans and disrupting marine life.
When you think of pollution in our oceans there are plenty of things that jump to mind including plastics, oil spills and chemical dumping. But one you’ve probably never thought of is light pollution. Human populations are rapidly increasing around the globe and with that comes increased urbanisation, particularly along our coastlines. Therefore our oceans are brighter than ever at night and marine life seems to be struggling as a result. Because of this research into artificial light at night (ALAN) has become a major area of research for marine biologists. However the latest result by a team from Flinders University is possibly the most alarming to date. Their work into the reproduction of clown fish has shown that zero eggs hatched with the presence of artificial light, similar to that of a small seaside town. If other species of fish react in the same way it could mean population breakdowns, habitat displacement and knock-on effects to all marine life.
Artificial light at night (ALAN)
For all of evolutional history nature has been governed by predictable cycles of day and night, as well as their seasonal variations. This has underpinned crucial behaviours for plants and animals living both on land and in our oceans. However these predictable cycles of light and dark have been disrupted by our ability to produce our own artificial light. It is not just our ability to create artificial light that it is problematic, but how it is concentrated and located geographically. Urban areas like large towns and cities produce high levels of concentrated light that spill over into the natural world surrounding them. A large percentage of these areas are located along coastlines and on small islands, in total 22% of the earth’s coastlines are now believed to experience ALAN on a daily basis. Therefore large areas of varying marine habitats are being exposed to constant unnatural light pollution.
In a similar way to how noise pollution in the ocean has largely gone unnoticed in recent years, ALAN is an issue that has also slipped under the radar. But we are now starting to realise just how widespread and disruptive it can be to marine life. Sea turtles avoid well-lit beaches to lay their eggs on at night, the migration routes and foraging behaviour of several species of seabird have been altered and it also means marine plants and phytoplankton can bloom earlier resulting in reduced productivity in the oceans. Problems are also likely to increase moving forwards as the Earth is getting brighter by 2.2% every year. Therefore it is becoming increasingly important to study the effects of ALAN on marine life.
The latest and potentially most worrying finding has come from a team led by Emily Fobert from Flinders University in Australia. In their study they used pairs of clownfish in a lab to test for the effects of artificial light on different stages of their reproduction. Half the pairs were left in tanks or ‘love shacks’ to reproduce together under normal light cycles, 12 hours light followed by 12 hours dark. Whereas the other group were left in identical conditions but were also exposed to low level LED light overnight, mimicking the conditions in reefs near small seaside towns. Both groups successfully managed to mate and spawn eggs like in the wild. But to the surprise of the researchers none of the eggs under ALAN managed to hatch, whereas most of the control eggs successfully did. What was even more shocking was that once the unhatched eggs were returned to normal cycles of light and dark they eventually did hatch and at almost the same success rate as the control group.
In a press release Fobert says that “the presence of light is clearly interfering with an environmental cue that initiates hatching in clownfish”. But why do the eggs only hatch in the dark? The most likely reason is that if eggs hatch during the night there will be less predators around and it increases their chances of surviving their first few hours of life. There are obviously some serious concerns about eggs being unable to hatch. The most notable being that less individuals will make it into the next generation. But there are also compounding issues that make this a much more worrying issue.
The first is that reproduction is very costly for parents and continued failed attempts to mate could reduce their own chances of survival. Burke da Silva, a fellow researcher on the team, explains that “parents were awake longer at night and they were taking enormous care of these big beautiful embryos”. Another problem is that once clownfish have found an anemone to call home they are very unlikely to leave and find a new one meaning that they will struggle to adapt to ALAN in the future. Ecologist Thomas Davies from Bangor University, not involved in the study, believes that ALAN could even “cause an extinction in this species”.
Turn off the lights!
This study is just the latest to show that ALAN is a serious problem for certain marine life. Although not many fish species have undergone similar experiments, it is not unreasonable to suspect that others will be affected in a similar way. Obviously it’s not just the fish that suffer as a result of ALAN as a reduction in their population size will have major knock-on effects to the rest of their ecosystems. With each new species found to be in danger from ALAN and an increase in levels of pollution we need to start thinking about solutions now, before it’s too late. The obvious answer is to turn out the lights, or at least dim them. Rather than lighting up our cities and towns for the sake of it there should be more consideration of when and where light is needed and if it could be prevented. As with species like clownfish it should also be possible to turn out lights at certain times of the year to allow their reproduction to happen without interference.
Issues like ALAN and noise pollution may not be the most obvious or noticeable forms of pollution in our oceans. But due to the widespread disruption they can create we really should be a lot more worried about them than we currently are.