|Fertilized Eggs||Antarctic Sea Urchin|
|Tracy is looking to collect urchins in a shallow area. The distance between the sea ice and the bottom is only five feet here.|
|Seals like to hang out around the dive holes to use them for breathing. The primary reason for drilling several safety holes while diving is so in case a seal decides to take up residence in the dive hole while you're underwater, you still have a way to get out.|
|In a deep ravine a large solitary sponge glows in the lights. McMurdo Sound has many beautiful sponges.|
|This time, Tracy will spawn the urchins inside of a cage in order to prevent the starfish from getting at them.|
|24 hours after the spawning urchins have been put inside the cage, the starfish have been attracted to the site and cover the downstream side of the cage. Although the cage has wroked in terms of keeping the starfish out, there are just too many starfish on it for the divers to observe what is going on. We need a bigger cage next time.|
|At the end of a dive Tracy exits out through the dive hole.|
|Common bottom inhabitants near Tent Island: the sea urchin Sterechinus neumayeri , the starfish Odontaster validus , and a small fish at top center, Trematomus beranchii|
|This is the start of a spawning experiment. Tracy has collected urchins and injected them with Kcl, which stimulates them to release their gametes. We want to know if the eggs will float off the bottom or sink in between the rocks.|
|24 hours after the spawning above, Tracy returns to find that the spawning area has now been overun by starfish. In fact, there are too many starfish for her to see where the eggs have gone. Maybe the starfish are eating the eggs? We've got to do more experiments to figure out what's going on.|
|The starfish Odontasteris very common along the coast of Ross Island and can aggregate in dense assemblages. They have very sensitive chemoreceptors that allow them to detect potential food items over large distances. Perhaps some chemical released by the spawning urchins attracts the starfish, as they move in for an easy meal of urchin eggs.|
|The ice sheet of McMurdo sound grinds into Tent Island as it slowly creeps seaward. The resulting pressure produces many cracks and ice crevices that sculpt the overhead ice layer into a 'cavernous' appearance.|
|One of the interesting things about the marine invertebrate community in McMurdo Sound is the high prevalence of large sponge species.|
|As the divers ascend the safety line, they approach the 'tube' that has been bored through the 8' ice; the dive tenders in the hut are watching for them to surface.|
Tracy Hamilton is the diver in our group and here she is out collecting urchins at Little Razor Back Island. The Delbridge Islands are essentially the remains of an old caldera rim from an ancient volcano. They are due west of Mt. Erebeus, which is an active volcano here that has probably developed from the same geothermal activity that produced the Delbridge caldera rim.
Underwater, the upper layer of the ice sheet forms a cloud-like layer which when combined with the 800+ ft visibility makes the underwater realm look like another atmoshopere. Bottom contour has a steep slope as the sides drop quickly off into the deep caldera. As the divers start to head back, you can see two bright circles in the ice sheet above: those are the outer safety ice holes. The primary ice hole through which the divers enetered the water is in between these two, but darkened because there is a dive-hut over it that obstructs the direct sunlight.