Fear of the light may help tiny ocean creatures survive a brighter future

An aversion to light has long been a survival tactic used by the smallest creatures in our ocean, but research co-led by the University of Strathclyde has discovered this photophobia may already be protecting them against impacts of environmental changes in the Arctic.

Known as zooplankton, these microscopic creatures swim hundreds of meters every day, up and down the water column in response to the changing light. By staying deep below the surface during the daytime, they can avoid predators. Only during the relative safety of night can they come nearer the surface to feed on phytoplankton.

The underwater light in the Arctic is changing in various ways. As sea ice in the Arctic melts at an increasing rate because of climate change, more light penetrates the water. Added to an increase in light from infrastructure and shipping, these changes are potentially making zooplankton—a crucial part of the ocean food web—more vulnerable to predators.

But an international group of Arctic scientists, led by Strathclyde and the Scottish Association for Marine Science (SAMS) has discovered that zooplankton have an established threshold of light tolerance, regardless of the time of day, season or year, suggesting they are capable of adapting to dramatic changes in light.

As the depth at which this light level is found moves up and down the water column between day and night, and across seasons, zooplankton are seen to remain below it, avoiding the shallow depths where it is light.

The findings have been published in Biology Letters.