Craig Taylor and I get up around 6:30 A.M. to prepare for a stage-out at 8 with a dive around the habitat. As with all the previous days we have been living as saturated divers, our assignment is to locate fish that have been "tagged," either with an external marker fixed to its dorsal fin (these markers usually contain an identifying number) or with a surgically implanted "ultra high frequency sonic" tag, one that sends bursts of sounds back to a receiver which the aquanauts monitor. The VEMCO receiver Craig and I carry around with us is a hand-held device a foot or so long that looks like a big underwater flashlight. The closer we get to the tagged fish, the larger the display on a LCD screen bar graph, from zero to 100 percent. Over the past week and more, Boston University marine biologist Les Kaufman has attached or inserted nearly 40 different tags ranging from just over a centimeter to several centimeters in length.

Craig and I try to find as many tagged fish as possible in our two-hour dives to make sure they are swimming and behaving normally. This morning we found two parrotfish with internal tags made by LOTEK, one of the sponsors of our expedition along with National Geographic. One of the parrotfish displayed an external as well as internal tag, although the number written on its side was too small to observe easily. The Spanish hogfish Les had implanted the previous day swam past us under the habitat looking and acting exactly like you would expect it to behave.

After a brief stopover back at the habitat to warm up and sip a little coffee, Craig and I head out toward the northeast waystation one thousand feet away. We travel along one of the major expedition lines that help us keep our bearings and always return us to the Aquarius underwater laboratory. We are to meet Les Kaufman and his assistant Mike Burns at the waystation: a gazebo like structure that contains a huge bubble of air, enough for 4 divers to surface in, take their masks off, and talk about what they have seen and what they want to do next. Les and Mike are diving from a surface boat to help us locate and collect some small samples of mustard hill coral (Porites astreoides) for experiments back at the habitat. Les wants to test the effects of excess carbon dioxide on the health of his samples, an experiment to show the potential effects of global warming. Using a special permit to collect his samples, Les will detach small pieces of Porites and take them back to a workstation platform adjacent to Aquarius.

The coral will live inside acrylic domes to isolate them and allow Les to introduce carbon dioxide and monitor the results. Once Les, Craig, Mike and I have discussed our plan inside the gazebo we decide to first locate the red grouper Craig and I have been watching over the last four days to show the surgeon (Kaufman) his good work and to videotape the fish's behavior as part of our data collection. Sure enough, there it sits 325 feet from the gazebo just down the drop off it has chosen as its home base in a thicket of soft coral. It watches us warily, in full control, using its pectoral fins to float in place and when we get a little too close it swims up the sand channel to another hiding place, its movements betraying no discomfort or unusual behavior. Its lip bears a slight scar and we use that as one of our identifying features along with the strong pinger signal our VEMCO receiver picks up.

Satisfied that his surgery has been successful, Les leads the group back to the gazebo to collect the coral samples with a small chisel and hammer. Mustard hill coral is not Les's first choice for his experiment-yellow pencil coral (Madracis mirabilis) is because of its more rapid growth-but there aren't enough examples in the area so we settle for the Porites. Les selects three small clusters and puts them in a bucket which Craig and I will swim back to the habitat. Mike and Les, who are diving with a Nitrox mixture to allow them more bottom time, swim back to their boat waiting above, while Craig and I begin the ten minute trek back to Aquarius. I videotape the entire procedure.

On a platform adjacent to the moon pool, the three coral clusters are tied in place with colored string waiting for their small enclosing domes to be brought down the next day.