September 29th: Hot Lips, Sunken Ships
Written By Dan Suthers September 29-30, 2004
Today is our fourth day at this very special place. Following my writer's schedule again, I awoke after the morning boat departures and began the day with lunch for breakfast (chicken burritos: roll your own). As previously arranged with Kyle, HI-2 returned at 1300 to pick me up for an afternoon with the Mooring Team.
Hot Lips and Sharp Teeth at the STR Exchange
With the salvage ship Casitas in view, we motored across deep blue waters towards a dancing white line of breaking waves, beyond which lay a vast turquoise pool. Although an occasional storm was visible in the distance, the weather continued to be beautiful in our vicinity of this vast
of life. We worked our way into the reef and through the maze, dodging coral heads as we followed the GPS to the site of the a Surface Temperature Recorder (STR) device to be replaced. You can read more about STRs in this story.
The water was clear and gently rippled by a light wind, scrambling turquoise (sandy bottom), green (corals and algae) and purple (Montipora coral) into a tantalizing dance of colors. When we arrived at the site, our cox'n Merlyn Gordon directed that the anchor be thrown into a sandy region to avoid damaging coral. Then we snorkeled over to the STR, which lay just before the waves breaking on the outer reef. As at Laysan, I alternated between photographing the work and the reef. When we were done we took a brief look around.
Shortly, a whitetip reef shark swam by. Just as I began following and photographing it, I suddenly felt a severe sharp stinging across both of my lips. I could not see the organism responsible. I surfaced and told Danny, who suggested that they take me back to the boat. Not wanting to miss the shark, I told him I was OK and began to follow the young hunter again. Later when we returned to the boat I learned that Stephani had been stung on her leg shortly thereafter, and that the responsible creature was a Portuguese Man-Of-War. My lips stung for perhaps 10 minutes, then merely felt hot, and before long I had forgotten the incident.
On the return to HI-2 I noticed a large coral structure (pictured left) with many fissures in it, creating homes for algae, fish, and other invertebrates. In some small caves nearby, fish darted into safety at my approach and cautiously peeked out. Coral is more than just another animal in this rich ecosystem: it creates as well as inhabits the ecosystem's habitat, so is fundamental to most of the marine life in the NWHI.
Probing a Thermocline
We spent the rest of the afternoon traversing the southern edge of Pearl and Hermes, performing Conductivity, Temperature and Depth (CTD) drops from the HI-2. You can learn more about how these measurements are taken in this article. Originally the plan for the day was to traverse up the northwest edge. However, Kyle had been emailing his supervisor in Honolulu, Kevin Wong, and colleage Ron Hoeke, who does computer models for oceanography. They were interested in the thermocline (change in temperature with depth) along the southern edge of the reef. The readings reported by the Mooring Team showed a sudden change in temperature. These readings were taken in the morning: Ron and Kevin wanted to know whether the same effect is seen in the afternoon: is it due to time of day, or is another physical explanation needed?
The bottom slopes off gently until reaching about 80 feet in depth, when it drops off suddenly and steeply. This being the leeward side of the atoll, the wind is blowing surface water away from the atoll, so cold water is drawn up from below to replace it (because "nature abhors a vacuum"). Kyle and Danny both told me that when diving the boundary between the warmer upper water and the cold water coming from below was actually visible like a shimmering layer. They stopped right at the boundary and could feel the water change temperature as they went up and down with the wave action. They could put one hand above the boundary and one hand below and feel the difference.
There is a lot we don't know about currents and basic physical parameters of the ocean in this region, yet these have implications for reef life. For example, an up-welling of cold water from the deep could also bring nutrients with it. These nutrients could enable a growth in the phytoplankton (microscopic plant) population, which themselves are eaten by zooplankton (microscopic animals), which are eaten by larger animals in turn, on up the food chain and ultimately affecting the food supply for large predators.
Recall that Pearl and Hermes Atoll is named for two whaling vessels that wrecked here nearly simultaneously, and that yesterday our Fish Team had investigated the site of two potential shipwrecks discovered by the crew of the M/V Casitas, a marine salvage vessel up here to remove marine debris from the reefs. Everyone who went came back excited about the possibility (not yet confirmed) that these wrecks could be the Pearl and the Hermes.
This evening, Randy Kosaki radioed the Casitas to discuss the marine archeological find. A press release is being prepared in Honolulu, and Randy wants to be sure that the Casitas crew get proper credit for the discovery. I listened as he interviewed them like a true reporter. Later, Randy and Darla gave me photographs of the shipwreck and asked that I mail them to specialists in Honolulu. You can read more about the discovery in this feature story.