During this year’s Plymouth Ocean Science Voyage aboard Pelican of London 25 youngsters from Devon and Cornwall sailed to the Channel Islands. As we spent a day of research in a beautiful bay enclosed by the islands of Sark and Brecqhou, one project group explored the underwater world using an ROV.
We used my blueye Pioneer ROV to observe fish and the seabed, recording video for 10 minutes each, near the surface, at mid-depth (8.5 m) and near the bottom (19 m) by day and night.
It was mid-September and the water was laden with marine snow. This is the term marine scientists use for dead organic matter slowly drifting in the water column. It’s made up from dead algae, animal parts and faeces. Anything from the small gelatinous blobs and strings of dead cells held together by bacteria we see in the video to a whale carcass is considered marine snow.
By day, we saw little evidence of larger organisms in the bay, and soon it became apparent why: the vast expanse of rippled sand at the sea bed offered little shelter and food for juvenile fish or crustaceans. Perhaps larger fish may have avoided the bay because there is little reason to come here and also to avoid being easily spotted by potential predators?
A lone flat fish highlights that this environment is dominated by benthic life, organisms that shelter, live and feed in the sediment.
During the night, fish were plentiful in the bay, with shoals of mackerel milling around the ship. The ROV dive confirmed that fish of different sizes and species had arrived in the bay, dashing in front of the camera, attracted by its light. Perhaps the fish came into the bay under the cover of darkness to feed? Smaller fish may feast on microscopic plankton or marine snow and bigger fish on smaller ones.
At the bottom, another flatfish hunts by night…and we wonder: When do fish sleep?
Featured Image: still from the video taken with the blueye Pioneer ROV. (c) C Braungardt 2024.
Challenging Habitat 