Carbonate Dehydratase in Marine Organisms of the Great Barrier Reef

Abstract

Carbonate dehydratase (EC 4.2.1.1, other name 'carbonic anhydrase') activity was found in 28 of 29 species of marine algae and angiosperms and in a mixed culture of phytoplankton collected in the vicinity of Lizard Island on the Great Barrier Reef of Australia. The species included 13 member- of the Chlorophyta, 4 of the Phaeophyta, 7 of the Rhodophyta, 2 of the Cyanophyta and 3 subs merged marine angiosperms. One of the two blue-green algae showed no detectable enzymic activity. The levels of activity ranged from 100 to 4800 units per milligram chlorophyll and were generally comparable with those of terrestrial angiosperms based on chlorophyll content, but were only a small fraction when compared on the basis of fresh weight.

Culture of the green alga Chlorodesmis fastigiata in 'CO₂-free' sea water (1.4 mg CO₂ per litre) for 4 h did not lead to an induction of carbonate dehydratase activity.

Some of the species of algae producing calcium carbonate contained the highest activities recorded but others had low activities. A correlation between high carbonate dehydratase activity and calcium carbonate deposition could not be adduced.

Symbiotic zooxanthellae (Gymnodinium microadriaticum) of the hard coral Pocillopora damicornis and the clam Tridacna maxima also contained carbonate dehydratase (940 and 340 units per milligram chlorophyll, respectively). The host tissues contained about five times the activity of their respective zooxanthellae.