Ammonia and Inorganic phosphate excretion by zooplankton from inshore waters of the Great Barrier Reef, Queensland. I. Relationship between excretion rates and body size

Abstract

Ammonia and phosphate excretion rates were measured on various copepods and some ctenophores, siphonophores, decapod larvae, mollusc larvae, polychaete larvae, chaetognaths and appendicularians from inshore waters of the Great Barrier Reef during warm and cold seasons.

Regression analyses showed high correlations between the excretion rate and body weight of zooplankton:

in the warm season,

log y_n = 0.518 + 0.525 log x (n = 348. r = 0.612)

log y_p = -0.174 + 0.429 log x (n=117, r=0.570),

and in the cold season,

log y_n = 0.186 + 0.518 log x (n = 268, r = 0,777)

log y_p = -1.002 + 0.740 log x (n = 255, r = 0.694),

where y_n is ammonia excretion (nanograms N per animal per hour), y_p is phosphate excretion (nanograms P per animal per hour), x is body dry weight (micrograms per animal); n is the number of measurements, and r is the correlation coefficient.

Since the two regression lines for ammonia excretion were parallel a Q₁₀ value of 2.53 was calculated from the results of warm and cold seasons. This calculation was not possible for the phosphate excretion because the regression lines between the seasons were not parallel. The mean ratio of ammonia excretion to phosphate excretion (N:P ratio, by atoms) was 28.56 in the warm season and 24.48 in the cold season.

The present results were compared with those of other workers who used zooplankton from different seas, and the effects of experimental conditions, such as injury of specimens, container size, incubation time and feeding on the excretion rates are discussed.