The pattern of resource partitioning versus depth for corals collected
in February, 1983, from Jamaica was investigated by analyzing their
stable nitrogen isotope composition. Observations were made on isolated zooxanthellae
and corresponding algae-free animal tissue from nine species of symbiotic
corals at four depths over a 50-m bathymetric range, and from a nonsymbiotic
coral at 1 m. 5 15N values versus depth ranged from +3.54 to -2.15 %0
for zooxanthellae and from +4.71 to +0.23 %0 for animal tissue. In those
species that occurred over a 30- to 50-m depth range, both animal tissue and
zooxanthellae tended to be depleted in 15N as depth increased to 30 m. In a few
species animal tissue was enriched in 15N from 30 to 50 m. Depletion of 15N in
zooxanthellae with increasing depth may be the result of depth-dependent differences
in their nitrogen-specific growth rates. Animal tissue was consistently
more depleted in 15N than for the nonsymbiotic coral Tubastrea coccinea (Ellis)
at the same depth, but it was still slightly more enriched in 15N than corresponding
zooxanthellae in 16 of 25 paired samples. The latter trend was not
correlated with depth. A comparison of 5 13C and 5 15
N for zooxanthellae and
animal tissue over 50 m revealed a tendency toward depletion of heavy isotopes
as depth increases. Increased carbon fixation appears to be accompanied by
decreased nitrogen fractionation
