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The ecology and energetics of Aplysia juliana (Quoy and Qaimard, 1832)

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Title:The ecology and energetics of Aplysia juliana (Quoy and Qaimard, 1832)
Authors:Sarver, Dale Jere
Keywords:Aplysia juliana
Opisthobranchia -- Hawaii
Date Issued:1978
Abstract:The objectives of this study were: 1) to estimate recruitment rates for Aplysia juliana on a weekly basis throughout the year at two field locations on Oahu, Hawaii; 2) to examine the interrelationships between food intake, growth rate, maximum size and fecundity; 3) to establish an energy budget; and 4) to determine the interactions between recruitment, adult density, food density and season. Recruitment occurred year-round although rates were higher in winter than in summer. Recruitment occurred in pulses which lasted from one to three days and the intensity of settlement varied between locations. Aplysia juliana larvae settle on available species of the green alga Ulva and spend about three weeks feeding on the alga and growing before migrating to the adult habitat under rocks. Mortality while on the algae is very high and fewer than 2% survive to move to the adult habitat. Maximum sizes of A. juliana attained under laboratory conditions were nearly five times larger than those seen in the field. Animals caged in the field grew rapidly until they reached sexual maturity when growth stopped. Animals raised in the laboratory continued to grow for several weeks after the onset of egg laying. This difference in growth pattern is attributed to limited access to food in the field imposed by their nocturnal habits and the activity-repressive response to heavy wave action. Maximum sizes of animals in the field varied both between locations and within the same location at different times of the year. These differences were attributed to variation in alga density, temperature, and possibly variations in nutritional quality of the algae. Caloric content of U. lactuca from the Sand Island study site varied from 1850 to 3150 calories per dry gram. Figured on a caloric basis, adult A. juliana, under ad libitum feeding conditions, allocated 10.69% of its nutritional energy into reproduction, 5.45% into somatic growth, 10.65% into respiration and 27.28% into feces over a 3½ month period. About 46% of the ingested calories were unaccounted for and were apparently lost to mucus production, excretion, and activity costs. Caloric assimilation efficiency was 72.7%, caloric net growth efficiency 22.2%, caloric gross growth efficiency 16.4% wet weight gross growth efficiency 23.6% and dry weight gross growth efficiency 10.95%. The relative allocation to reproduction decreased when animals were raised on reduced food rations unless rationing was sufficiently low to prevent growth, in which case all energy above maintenance costs went to egg production. Caloric gross growth efficiency did not significantly change with lower rations. At various field sites investigated, population numbers fluctuated greatly and frequent extinctions occurred. Aplysia juliana persists under such highly variable conditions by reaching sexual maturity early, and by producing millions of eggs over an extended reproductive life.
Bibliography: leaves 133-140.
xi, 140 leaves ill
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Appears in Collections: Ph.D. - Zoology

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