Cj. Hall et Cw. Burns, Effects of salinity and temperature on survival and reproduction of Boeckella hamata (Copepoda : Calanoida) from a periodically brackish lake, J PLANK RES, 23(1), 2001, pp. 97-103
The freshwater calanoid copepod Boeckella hamata Brehm, occurs periodically
in Lake Waihola, New Zealand, a shallow, tidally-influenced lake that expe
riences daily and seasonal fluctuations in salinity, and seasonal changes i
n temperature, To determine whether these environmental changes might contr
ibute to the copepod's disappearance from the lake in summer, we tested the
survival and egg production of B. hamata at a range of salinities (20-3000
mg l(-1) Cl) and two temperatures (10 degreesC, 20 degreesC). Adults survi
ved for 20 days or more only at salinities less than or equal to 1000 mg l(
-1) Cl; survival was higher at 10 degreesC than at 20 degreesC, and higher
for females (86% at 10 degreesC, 14% at 20 degreesC) than males (43% at 10
degreesC, 0% at 20 degreesC). The mean total eggs produced per female in th
ree successive clutches decreased with temperature from 20 eggs at 10 degre
esC to 15 at 20 degreesC; egg production rates increased however, as clutch
es were produced more frequently. Staged increases in salinity did not incr
ease copepod survival, indicating that B. hamata adults cannot tolerate the
magnitude, or rate, of seasonal fluctuations in salinity to which they are
exposed in the lake. We conclude that the ability of B. hamata to tolerate
warm, saline conditions influences its presence and role in brackish ecosy
stems.