Limnological
control of brine shrimp population dynamics and cyst production in the Great
Salt Lake, Utah
W.A. Wurtsbaugh, Z.M.
Gliwicz-2001
Hydrobiologia, 466(1-3): 119-132
Abstract:
In the Great Salt Lake of Utah, the brine shrimp Artemia
franciscana Kellogg is an important food resource for birds and they
produce dormant cysts that are harvested and used extensively in the
aquaculture industry. We analyzed the limnological factors controlling Artemia
growth and cyst production over 12 months in 1994 and 1995. Laboratory
experiments showed that inter-brood intervals were highly dependent on
temperature and slightly on food level. At optimal temperatures and
nutritious food, juveniles reached reproductive size within 7 d in the
laboratory. In winter when temperatures were less than 3 °C,
Artemia were absent from the lake, phytoplankton abundance was high
(≥13 Chl a μg
l-1), and the dominant grazers were ciliated protozoans. In the
spring, cysts hatched when phytoplankton was abundant (15–30
μg Chl a l-1), and
the Artemia grew and produced large clutches of ovoviviparous eggs.
Estimated naupliar production from these eggs was 80 l-1 from
April to May. Despite the high production of nauplii, Artemia
densities declined to 8 l-1by June and the growing shrimp
population grazed down the phytoplankton resource to <1 μg
Chl a l-1. With the depleted phytoplankton food resource
during the summer, Artemia growth slowed, lipid indices decreased,
clutch sizes declined, and females switched primarily to oviparous cyst
production. During the summer, there was limited production of ovoviviparous
eggs, and limited recruitment of juveniles, probably due to low food.
Although oviparous reproduction began in June, more than 90% of the cysts
were produced after July when female densities had declined to 1.5 l-1,
but nearly all of them were producing cysts. Estimated cyst production was
650 000 m-2, or 4.54 ×
106 kg dry weight for the entire lake. The reported commercial
harvest took 21% of the 1994 cyst production. That harvest had little impact
on the subsequent year's population, as Artemia densities were
ultimately controlled by algal production in the lake.
(Department of
Fisheries and Wildlife and Ecology Center, Utah State University, Logan, UT
84322-5210, U.S.A, E-mail: wurts@cc.usu.edu)