Study the Twilight Zone before it is too late
The oceans’ twilight zone is the area just below 200m from the surface ocean down to 1000m. It plays a major role in removing and storing CO2 from the atmosphere, and is home to the largest and least exploited ocean fish stocks. It is also the zone through which the massive migration of fish and zooplankton move towards the surface to feed each night, before retreating back down at dawn. Yet despite its importance, the zone is physically, biogeochemically and ecologically poorly understood. It is a difficult region to study for a variety of substantial reasons, leaving many critics to suggest that coastal and near-shelf waters are more deserving of study, because of the significant environmental impacts there, and their importance to societies. Unfortunately, widespread environmental damage to these inshore regions can often not be avoided, so research efforts and local policies must aim to mitigate the worst effects. By contrast, the twilight zone is almost pristine, and as much of it lies beyond national jurisdiction, it is of common interest and responsibility, and global agreement is necessary to manage it.
This paper outlines the steps needed to ensure that enough is known about this complex global ecosystem to inform decisions about the impacts of climate change and potential future exploitation. We call on the international marine research community to focus its attention on the twilight zone during the upcoming United Nations Decade of the Ocean, and to seize the opportunity to establish a global policy that will protect this vast ecosystem for present and future generations.