Oxygen production in the hydrozoan, Millepora on the Great Barrier Reef

Samples of gas from freshly broken branches of the hydrozoan, Millepora tenella were collected from Britomart Reef. The gas was collected underwater by breaking branches under an inverted glass funnel connected to a separatory funnel. The gas was then transferred underwater to pre-rinsed 5 ml Teflon septum glass vials with only minute amounts of seawater included in the sample. Samples were refrigerated immediately after extraction.

Analyses were carried out at the Queensland Government Chemical Laboratories in Brisbane using a Hewlett-Packard 5840 gas chromatograph fitted with a thermal-conductivity detector. The gas analysed contained oxygen, nitrogen, carbon monoxide, carbon dioxide and methane.

Millepora fronds covering a vertical projection area of about 50 cm² were broken out of larger colonies and placed inside plastic bags. At the same depth, the bagged corals were placed on a plywood board and hammered to break up the coral and release trapped gases. Gas was extracted from the bags with a hypodermic syringe and gas volumes read underwater.

Thin sections of Millepora tenella skeleton were produced to examine the internal structure of the coral. Scanning electron micrographs were also taken to examine the extent and location of algal borings within the skeleton of Millepora tenella. Data on algal boring were compared with data for Stylophora pistillata, a scleractinian coral with a similar branching habit.