Snail grazing effects on the composition and metabolism of benthic diatom communities and subsequent effects on fish growth
Snail grazing effects on the composition and metabolism of benthic diatom communities and subsequent effects on fish growth
Date
1980-06
Authors
Connor, Michael Stewart
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DOI
10.1575/1912/1613
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Keywords
Marine ecology
Fishes
Ecology
Growth
Diatoms
Benthos
Fishes
Ecology
Growth
Diatoms
Benthos
Abstract
Eastern mud snails (Ilyanassa obsoleta) in densities of zero, six or
twelve snails were placed in flow-through-laboratory microcosms (765
cm2) and incubated for five weeks. Other tanks were raked daily to a
depth of 10 mm. Grazing by low densities of snails significantly
increased chlorophyll standing stock, respiration and gross
photosynthesis as measured by light and dark exchange of oxygen and
carbon dioxide compared to untreated tanks. The standing stocks of algal
pigments, respiration and photosynthesis were depressed in the microcosms
which received the 12-snail or the raking treatments. Simulating snail
excretion by fertilization with ammonium increased chlorophyll standing
stock by a similar magnitude, but this effect could be inhibited by
raking the sediments daily. At low densities Ilyanassa's acceleration of
nutrient cycling stimulates algal growth, but this effect is overwhelmed
at higher densities by overgrazing and stirring inhibition.
The dominant benthic algal group in the containers were pennate
diatoms. Grazed containers contained a larger percentage of the
non-motile classes of diatoms, as compared to the motile forms which
predominated in the untreated microcosms. The snails are able to
selectively graze these mobile species. Their gut contents are enriched
in carbon. nitrogen and algal pigment content by 20-40 times over the
surface sediments.
A small, non-significant, growth effect can be seen in the snails'
response to density changes, but another marsh consumer, Fundulus
heteroclitus, grows faster at low snail densities when snails are absent.
Description
Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June, 1980
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Citation
Connor, M. S. (1980). Snail grazing effects on the composition and metabolism of benthic diatom communities and subsequent effects on fish growth [Doctoral thesis, Massachusetts Institute of Technology and Woods Hole Oceanographic Institution]. Woods Hole Open Access Server. https://doi.org/10.1575/1912/1613