In the upper estuary of Yaquina Bay, Oregon, there is an annual
population explosion of Acartia tonsa, (Dana) a calanoid copepod,
during the months of July, August and September, followed by a rapid
decline to virtual extinction in November. The restricted estuarine
distribution affords an excellent opportunity to study the factors
governing the population dynamics of A. tonsa without the disadvantage
of potential mixing with other populations on different schedules
of development. Field densities of A. tonsa during the 1972 summer
were determined by twice weekly sampling with Clarke-Bumpus
plankton samplers. In addition, explanation of the production of A.
tonsa in the field was attempted by measuring the rates of egg production
and development in the laboratory under temperature (21°C) and
salinity (25‰) conditions comparable to those in the upper estuary.
Daily egg production was found to be 30.5 eggs*day⁻¹*female⁻¹.
The median rate of development from egg to adult required 11.5-11.6 days at 21°C in conditions of either laboratory cultured or wild
food organisms. Mortality rates were substantial during the experiments
as only 20-30% of the original populations survived to adulthood.
The cause of mortality is not known but may relate to the
molting process.
In the field, six successive generations of A. tonsa were
observed during the population explosion. The mean generation time
ranged from 16 days in August to 19 days in October. A maximum
density of 16,800 adults*m⁻³ in late August was followed by a crash
to 2,100 adults*m⁻³ 10 days later. Predation and over exploitation
of food resources are two possible causes of the crash. However
temperature appears to be the major factor for the subsequent decline
and disappearance of A. tonsa in the fall. This thesis presents
the first results of ongoing research into the population dynamics of
A. tonsa. / Graduation date: 1974
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28570 |
| Date | 22 April 1974 |
| Creators | Johnson, John Kenneth |
| Contributors | Miller, Charles B. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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