Zooplankton migrate under influence of moonlight in dark Arctic winter

New research performed by biologists from different universities has shown that zooplankton migrate vertically through the waters of the Arctic Ocean by using moonlight during dark winter nights. By studying acoustic data recorded by moored instruments, the scientists found that the vertical migration patterns of zooplankton in winter are driven by lunar illumination across the entire Arctic, in fjord, shelf, slope and open sea environments. During the Arctic winter, zooplankton shift their known diel vertical migration (DVM) periods from a solar day (24 hours) to a lunar day (24.8 hours) when the moon rises above the horizon. In addition, mass sinking of zooplankton from the surface waters to a depth of approximately 50 meters occurs during periods of full moon (every 29.5 days). The scientists suggest that lunar vertical migration (LVM) may enable zooplankton to avoid visual predators, such as carnivorous zooplankters, fish and birds, which use moonlight to hunt during the polar night. The discovery of LVM in the Arctic indicates that light-mediated patterns of biological migration may occur even without the presence of sunlight and has important implications for the exchange of carbon between the surface waters and deeper waters during the Arctic winter.

Journal reference: Last, K. S., Hobbs, L., Berge, J., Brierley, A. S. & Cottier, F. (2016). Moonlight Drives Ocean-Scale Mass Vertical Migration of Zooplankton during the Arctic Winter. Current Biology, 26, 1-8.

Image: Icebergs in the Arctic near Cape York, Greenland. Credit: Brocken Inaglory, Wikimedia Commons.

Corals actively supply nutrients to their environment

In a new study published in PNAS, corals have been shown to actively manipulate their environment by stirring up currents to supply nutrients to reef ecosystems. The scientists studied six different species of growing reef corals in a laboratory tank and observed their movements with microscopes and video cameras. They found that through small epidermal appendages called cilia, polyps are able to create vortical currents that greatly enhance their exchange of dissolved oxygen and nutrients such as nitrogen and phosphorus with the surrounding water. Coral reefs were previously assumed to be dependent entirely on ambient flow and turbulence for their nourishment, but these results show that they have the ability to actively affect mass transport. This mechanism may be critical to the survival of corals and is likely part of their evolutionary succes.

Click here to watch the accompanying video for a fascinating look at how corals stir up water currents and control nutrient transport.

Journal reference: Shapiro, O. H., Fernandez, V. I., Garren, M., Guasto, J. S., Debaillon-Vesque, F. P., Kramarsky-Winter, E., … & Stocker, R. (2014). Vortical ciliary flows actively enhance mass transport in reef corals. Proceedings of the National Academy of Sciences111(37), 13391-13396.

Image: Corals in the Red Sea, Egypt. Source: Mahmoud Habeeb, Wikimedia Commons.