Summer egg production rates of paracalanid copepods in subtropical waters adjacent to Australia’s North West Cape

Abstract

The biological oceanography of waters adjacent to Australia’s North West Cape (21° 49′S, 114° 14′E) was studied during the austral summers of 1997/98 and 1998/99. We measured egg production rate (EPR) by the small paracalanid copepods that dominated the calanoid community. Bottle incubation experiments were conducted at a shallow (∼20 m) station in the mouth of Exmouth Gulf, and at a shelf-break station (∼80 m). In 1997/98, we measured EPR by Paracalanus aculeatus, P. indicus, Acrocalanus gracilis and Bestiolina similis, but in 1998/99, we concentrated on P. indicus. Maximal observed EPRs by Paracalanus and Acrocalanus species were ∼ 30 eggs female−1 d−1, but B. similis attained only 17 eggs female−1 d−1. Sporadic measurements of EPR by P. aculeatus minor (maximum ∼ 4 eggs female female−1 d−1) and Parvocalanus crassirostris (∼ 9 eggs female−1 d−1) were also made. However, maximal EPRs were seldom achieved and were often less than 10 eggs female−1 d−1). There was no difference between EPR of either P. indicus or B. similis in 1997/98 and 1998/99, despite differences in temperature. Trophic resources severely limit copepod egg production in this area. We suggest that variability and skewness of egg production data derived from individual incubations may be used to judge the degree of food limitation of the population and the variability in feeding success between individuals. The dominance of small copepods and the invariance in their EPR suggest that pulses in physical forcing and subsequent primary production will be severely damped by trophodynamic processes before reaching larval fish.