Development, growth, and reproduction of the cyclopoid copepod Limnoithona tetraspina in the upper San Francisco Estuary

Abstract

Limnoithona tetraspina is a small cyclopoid copepod that was introduced to the San Francisco Estuary (SFE), USA, in 1993 and became the most abundant copepod species in the low- salinity zone (LSZ). Two previous studies have shown that it feeds only on motile prey, predominantly ciliates. Little is otherwise known of its biology or its role in the estuarine foodweb. We determined development times, growth rates, and fecundity of L. tetraspina from March to August of 2006 and 2007. The mean growth rate of copepodites in both years was 0.03 d -1 , which is low relative to values reported for related Oithona spp. Development times were longer in the field than in the laboratory at food saturation, indicating food limitation in the SFE. Mean weight-specific fecundity rate in 2007 was 0.10 d -1 , which is twice that of 2006, but within the range of reported values for Oithona spp. Low growth and fecundity rates indicate that the population success of L. tetraspina is due to low mortal- ity. L. tetraspina may avoid certain mortality agents (e.g. visual predation) to which larger copepods are susceptible.