DAILY JOURNAL

Monday | August 8, 2005

When the fishes go to sleep

Most reef creatures have working hours and sleeping hours. This means that, like cities, reefs at day and at night are completely different worlds. Tonight we dived to observe the night owls and learn about life in the dark.

Some of us left the White Holly on two small boats after a delicious Mexican dinner of chicken tacos and guacamole. The sky was packed with stars, and the sea was warm and inviting. When the crescent moon dived in the black velvet sea, we jumped into the darkness. The goal of this dive was two-fold: to collect water near the corals for an analysis of the microbial world, and to set up a video camera with powerful underwater lights to film the nocturnal life.

Setting up the video system implies loading a 1500 W electric generator, a heavy tripod, a digital video camera, underwater lights mounted onto an aluminum bar, 100 meters of cable, two dive tanks, and the dive gear of two people on a small boat tied to the side of the White Holly. A little breeze and small wavesmoved both boats and made the transfer of gear in the dark only more cumbersome.

James Neihouse and I went down while Christian McDonald helped us lower the camera system from the boat and coordinated the diving safety. Once in the bottom, at about 10 meters depth, we placed the camera system on a sandy patch within the reef. It took us less than five minutes to install it, but this was enough time for the lights to attract an amazing variety of living beings.

At first the reef, lit by our hand-held diving lights, appeared desert. Most fishes rest at night, and all we could see was a few sea urchins moving about. As soon as the camera lights were on, however, a myriad of little creatures appeared from the dark. The first to come were long, hairy worms the size of spaghetti. They were followed by fish larvae, which look like narrow ribbons of transparent jell-o, and by minuscule shrimp and crab larvae. Viewed from afar, these swarms of marine animals concentrating around the lights looked like huge clouds of mosquitos. Then silvery fishes the size of small anchovies appeared, swimming like lightning towards the lights in kamikaze trajectories, to swim away as fast as they came. They were eating the underwater mosquitos.

We came back to the surface and waited for 30 minutes. After that time we pulled the camera system into the boat and came back to the White Holly, to unload everything once again. The work was far from completed, since we still had to fill the tanks, rinse the camera housing and the lights, and watch the videotape to learn what other animals were attracted to the lights after we left. It was 11 pm, and we decided to watch the videotape tomorrow.

Like reef creatures, we also have habits, and they include sleeping at night. In this expedition we work strenuous 16-hour days, and there is no room for night owls.

—Enric Sala
Scripps Line Islands Expedition 05