Expedition journal. Nerina Holden 16 August 1999 11:30pm

More work on the coral in the lab today; we have nearly finished. Coral is an interaction between an animal host and an algal symbiont. The algae contain the chlorophyll that converts light energy to chemical energy to feed the host. Using this photosynthesis, we have been running a series of measurements to assess the coral's health.

We measure how healthy the coral is by taking the "quantum yield of photosynthesis," using fluorescence, a by-product of photosynthesis, as the indicator. A bleached coral will produce little or no fluorescence. We have taken "light" measurements and "dark" measurements. During light measurements (typically taken underwater) coral is exposed to normal daylight, which is variable, so we also take dark readings, flashing a standardized light at the coral after it has been kept in the dark. The growing tip of a coral can often appear whitish and may be mistakenly identified as bleached or dead. However these tips are actually healthy and will produce a fluorescence signal indicating that they are photosynthesizing. This fluorescence is different to that shown in Justin's pictures. The host tissue produces the fluorescence in Justin's pictures; the algae produces fluorescence in ours.

The signal from a coral varies according to the amount of chlorophyll it contains, so we measure chlorophyll concentrations too, and take samples for DNA analysis to ensure accurate identification of the host and algae. Bleached corals have little or no algae so we have also been measuring the number of algal cells in the host. My job in the lab is to extract the algal cells from the coral and preserve them ready for counting. I extract them by blasting them out of the tiny piece of coral with a "Water Pik" which you may have in your bathrooms for cleaning your teeth. A Water Pik sprays your teeth clean with a fine, high powered, jet of water and is perfect for extracting algae from coral. Lastly, we look at the reflectance spectra of the coral, and compare these measurements to the others.

Reading all that may make you think that we take large samples in order to get our data, but all of the above can be completed with a few square centimeters of coral.

The Aquanauts sorely miss ice cream; they have little freezing capability in the Habitat so we thought we would take them down a tub of vanilla when we went this morning to collect and deliver equipment.

Whilst CC and I finished up in the lab, Ania, Uli and Otto headed out to Conch reef, the ice-cream secretly stashed in a bucket of ice that the Aquanauts needed to keep samples fresh. On the way down to the Habitat the bucket lid popped off. Uli did a mad underwater scramble to save ice, lid and ice cream, and nearly succeeded. The science stuff was saved, but the ice cream merrily floated to the surface. On arrival at the Habitat the loss of our surprise delivery was confessed and mayhem ensued when the Aquanauts realized it was ice cream. Meanwhile, the ice cream had been rescued by Otto, who had leaped into the brine thinking a piece of important scientific equipment was floating past our boat.. He radioed to the Habitat to ask if the 'sample' had to get to the Habitat. A great cry rose from the depths and the ice cream was duly brought down by Otto. Phew.