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Effects of Differential Fish Grazing on the Community Structure of an Intertidal Reef Flat at Enewetak Atoll, Marshall Islands

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Title: Effects of Differential Fish Grazing on the Community Structure of an Intertidal Reef Flat at Enewetak Atoll, Marshall Islands
Authors: Miller, Alan C.
Issue Date: Oct 1982
Publisher: University of Hawai'i Press
Citation: Miller AC.1982. Effects of differential fish grazing on the community structure of an intertidal reef flat at Enewetak Atoll, Marshall Islands. Pac Sci 36(4): 467-482.
Abstract: Miller AC.1982. Effects of differential fish grazing on the community structure of an intertidal reef flat at Enewetak Atoll, Marshall Islands. Pac Sci 36(4): 467-482.
The high and middle intertidal zones of the northeastern portion
("barren") of the limestone bench on the windward side of Enewetak Island,
Enewetak Atoll, Marshall Islands, have a significantly higher number of herbivorous
fishes grazing at high tide than the same intertidal zones of the reef flat
300 m to the southwest ("algae-covered"). This portion of the reef flat in the
barren, heavily grazed area has a significantly lower coverage by erect, macroscopic
algae and a lower algal biomass than the same portion of the reef flat in the
algae-covered area. The removal of part of the limestone substratum by the
grazing fishes as they feed and the reduced coverage by erect, macroscopic algae
result in a lower topographic relief in the barren area than found in the algaecovered
area. The heavily grazed area has a significantly lower number of
mobile epifaunal invertebrate species and individuals per square meter than the
lightly grazed area. Differences in infauna (sipunculans, polychaete worms, and
tanaid crustaceans) are not so clear.
When portions of the barren area were excluded from fish grazing activity for
three months, the substratum under the exclosures had 100%coverage by an
algal mat; the density of mobile invertebrate epifauna was an order of magnitude
higher than in quadrats outside the exclosures.
Although the high and middle intertidal community is subjected to apparently
severe physical stresses (desiccation, insolation, wave shock, ultraviolet radiation,
and osmotic stress from evaporation in the tide pools and rainfall), it
appears to be principally structured by the grazing activities of herbivorous
fishes. The high level of grazing in the barren area results in coverage by
filamentous blue-green algae and a diatom-bacterial film, which may be a
nutritionally more important food source to the fishes than the coralline algae in
the algae-covered area.
URI/DOI: http://hdl.handle.net/10125/481
ISSN: 0030-8870
Appears in Collections:Pacific Science Volume 36, Number 4, 1982



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