Larkum, AWD 1988, 'High rates of nitrogen fixation on coral skeletons after predation by the crown of thorns starfish Acanthaster planci', Marine Biology, vol. 97, no. 4, pp. 503-506.
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At One Tree Reef, Great Barrier Reef, Australia, between 1983 and 1985, corals killed by the crown of thorns seastar Acanthaster planci L. gave rise to skeletons which were colonised rapidly by blue-green and other algae. For the next 3 to 9 mo these coral skeletons showed over three times more nitrogen fixation (acetylene reduction) than control substratum rates (9 to 32 nmol vs 3 to 10 nmol C2H2 cm-2 h-1, over all seasons). These values convert to relatively high annual fixation rates of 37 to 127 kg N ha-1 yr-1 but, at the low densities of A. planci on One Tree Reef (ca. 0.65 ha-1), this has little impact on the total nitrogen fixation rate and, as a result, on the level of organic nitrogen in the system. However, it is suggested that on reefs subjected to high aggregations of a. planci such an effect would enhance the level of organic nitrogen and lead to greater primary and secondary production throughout the reef system. © 1988 Springer-Verlag.
Larkum, AWD, Kennedy, IR & Muller, WJ 1988, 'Nitrogen fixation on a coral reef', Marine Biology, vol. 98, no. 1, pp. 143-155.
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Acetylene reduction was used to assess nitrogen fixation on all major substrates at all major areas over a period of 1 to 6 yr (1980-1986) at One Tree Reef (southern Great Barrier Reef). Experiments using 15N2 gave a ratio of 3.45:1.0 for C2H2 reduced:N2 fixed. Acetylene reduction was largely light-dependent, saturated at 0.15 ml C2H2 per ml seawater, and linear over 6 h. High fixation was associated with two emergent cyanophyte associations, Calothrix crustacea and Scytonema hofmannii, of limited distribution. Subtidally, the major contribution to nitrogen fixation came from well-grazed limestone substrates with an epilithic algal community in the reef flat and patch reefs (3 to 15 nmol C2H4 cm-2 h-1). Similar substrates from the outer reef slope showed lower rates. Nitrogen fixation on beach rock, intertidal coral rubble, reef crest and lagoon sand was relatively small (0.3 to 1.0 nmol C2H4 cm-2 h-1). Seasonal changes in light-saturated rates were small, with slight reduction only in winter. Rates are also reported for experimental coral blocks (13 to 39 nmol cm-2 h-1) and for branching coral inside and outside territories of gardening damselfish (3 to 28 nmol cm-2 h-1). This work supports the hypothesis that the high nitrogen fixation on the reef flat and patch reefs of the lagoon (34 to 68 kg N ha-1 yr-1) is because these subtidal areas support highly disturbed communities with the greatest abundance of nitrogen-fixing cyanophyte algae. It is calculated from a budget of all areas that One Tree Reef has an annual nitrogen fixation rate of 8 to 16 kg N ha-1 yr-1. © 1988 Springer-Verlag.
