Allocentrotus fragilis (Jackson) was obtained from six stations
at depths of 100 to 1260 m on the continental shelf and upper slope off
Newport, Oregon.
Ages and growth rates of A. fragilis were determined by two
methods: 1) A procedure was developed to make growth zones of the
skeletal test plates visible. Alternating light and dark growth zones
were found to be formed semi-annually. The total number of growth
zones was used to indicate the urchin's age. 2) Age and growth rate
values were also determined from analyses of size-frequency distributions
of trawl collections from 200 m. Collections from other
depths were not adequate for size-frequency analyses.
Gonad indices of A. fragilis from 200 m were used to determine
spawning periodicity and frequency. A semi-annual frequency was
found, with spawning occurring in early spring and early autumn.
No A. fragilis specimens collected below 400 m were reproductively
mature.
The growth curve of A. fragilis from 200 m, which was plotted
from the mean test diameter of age groups defined by test plate
growth zones, shows a good least-squares fit with von Bertalanffy's
growth equation. Growth rates were similar for A. fragilis from
100-600 m, but decreased for specimens from 800 and 1260 m. The
maximum test diameter decreased with increasing depth below 200 m.
Variation of magnesium content of the calcareous skeletal
plates was due largely to variation with age. Little skeletal Mg variation
was found at different depths for specimens of the same age.
Greater Mg content differences occurred between young and old
specimens from the same depth, and between young and old test
plates of the same individual.
The effects of several environmental factors on the growth rate
and maximum size of A. fragi1is are discussed. Of these factors,
food availability, water temperature, and oxygen tension form
gradients with depth or distance offshore; and were considered to be
important in affecting the growth of A. fragilis. / Graduation date: 1971
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28896 |
| Date | 19 August 1970 |
| Creators | Sumich, James L. |
| Contributors | McCauley, James E. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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