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The Seasonal Development of a Population of Diaptomus ashlandi Marsh, and Related Phytoplankton Cycles in Lake Washington
Author(s) -
COMITA G. W.,
ANDERSON G. C.
Publication year - 1959
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.1959.4.1.0037
Subject(s) - hypolimnion , epilimnion , phytoplankton , population , thermocline , oceanography , chlorophyll a , environmental science , ecology , biology , zoology , geology , nutrient , eutrophication , botany , demography , sociology
The development of a Diaptomus ashlandi population and the simultaneous phytoplankton cycles in Lake Washington, Seattle, were studied in samples taken from October 1949 to October 1950. The lake is 8762 ha in area and 65.2 m deep in its deepest part. Temperature measurements showed that stratification began late in March, and the surface maximum of 22.2° C occurred late in August. Typically the epilimnion was 10 m deep, the thermocline 10 m, and hypolimnion 40 m. Chemical determinations showed the lake to be slightly alkaline usually, but during the summer months the pH was above 8.0. Alkalinity ranged from 0.246 to 0.524 millequivalents/liter. Phosphate determinations showed a winter maximum and summer minimum in the surface and 15 m water, with an accumulation in the bottom waters as summer progressed. Dissolved oxygen was abundant, but in the hypolimnion was depleted at the rate of 2.0 mg/cm 2 /month during the summer. Cell volume and chlorophyll measurements showed that a phytoplankton bloom occurred in spring and another in late August. The taxonomic composition of these is presented. The Diaptomus ashlandi population was found to be monocyclic. The period of greatest sexual activity was noted by counting the number of females carrying spermatophores. By this measure transfer of spermatophores lasted for approximately six months starting in January and continuing through July with the peak occurring in April, but egg production occurred from October to the following August, with the largest pulse occurring from mid‐January to mid‐March. These eggs developed into the nauplius stages which lasted until mid‐June. Development through the copepodid stages was traced to October 28 at which time the single annual cycle was complete. Six nauplius and six copepodid stages were noted in the life cycle. The approximate time required for all the nauplii to undergo their development was 75 days. For the copepodids, I and II together required 65 days; III, 40 days; IV, 84 days; V, 90 days; and VI, 5 to 6 months. Study of separate hauls from the epilimnion and hypolimnion showed that the epilimnion was the site of most of the activity of D. ashlandi during the period of growth and metamorphosis in the summer. A coefficient of correlation was computed for chlorophyll concentration and mean number of eggs/sac in the epilimnion. This was 0.598, which was significantly different from zero at the 1 per cent level. Metasome measurements were made on all the copepodids. These showed that the period of maximal size for the adult females occurred from June to September 1950. This increase in size began just as the peak of phytoplankton had passed. The summer females were found to be significantly larger than the winter females at the 1 per cent level. Study of the sex ratios showed that females were in excess for much of the year, although males were in excess for as long as 3 months (April, May, June).