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The role of Sagitta enflata in the southern Kaneohe Bay ecosystem

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Title:The role of Sagitta enflata in the southern Kaneohe Bay ecosystem
Authors:Szyper, James P.
LC Subject Headings:Sagitta enflata.
Marine ecology--Hawaii--Kaneohe Bay.
Kaneohe Bay (Hawaii)
Date Issued:Dec 1976
Publisher:University of Hawaii, Honolulu
Citation:Szyper, James P. The role of Sagitta enflata in the southern Kaneohe Bay ecosystem. Honolulu:University of Hawaii, 1976.
Abstract:The chaetognath Sagitta enflata dominates the standing stock of
macrozooplankton,and of planktonic carnivores, in the southern basin
of Kaneohe Bay. During 1973-74, sampling with vertical net hauls showed
no horizontal patchiness in the population. The abundance varied
temporally, mainly over periods of months; shorter-term variations were
similar to those expected between replicate hauls. Between 1968-69 and
1973-74, both the stock and the dominance of Sagitta in the community
increased; both may be related to enrichment of the basin with sewage.

Individual Sagitta eat an average of seven prey items per animal
per day. The ration in terms of nitrogen or other weight measures
varies with animal length, larger Sagitta ingesting more material each
day, but smaller Sagitta ingesting a larger fraction of their own body
weight daily. Sagitta's predation has little impact on the prey
populations, other than Oikopleura, which is the main food of larger Sagitta.

Sagitta excretes ammonium and phosphate at rates roughly similar to
other zooplankton of similar size. When feeding is prevented during
excretion experiments, the specific excretion rates decrease rapidly
with time, approaching those observed in laboratory-starved animals.
Like other zooplankton, Sagitta has higher N/P ratios in its body tissue
than its prey; its soluble excreta thus have a still lower ratio.
Despite its abundance and dominance of macroplankton stock, Sagitta is
only a minor contributor to nutrient regeneration in the southern basin,
which is to be expected, based on its trophic position.

The population's rates of growth and mortality were considerably
higher than the net change in the stock during most periods analyzed.
The instantaneous rates of birth and death are strongly correlated,
suggesting a feedback mechanism regulating the population.

The population incorporates carbon at about 1% of the rate of
primary production in the basin. This is consistent with ecological
efficiencies of 10% at each of the two steps froln producers to
herbivores to Sagitta's position as the dominant primary carnivore
among the plankton. Most of Sagitta's production is probably consumed
by predators in the southern basin. The major predator may be nehu, a
fish taken for tuna bait from this and other nearby environments.

With the planned diversion of sewage from the basin, it is likely
that both the stock and the dominance of Sagitta in the southern basin
will decrease.
Description:Thesis for the degree of Master of Science (University of Hawaii at Manoa). Typescript. Bibliography: leaves 140-147.
Pages/Duration:154 pages
Rights:All UHM dissertations and theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission from the copyright owner.
Appears in Collections: Ph.D. - Oceanography

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