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Harbor dredging and benthic infauna : a case study

This study of the immediate, localized effects of a small dredging
operation on the benthic invertebrate community in the shipping
channel of Coos Bay, Oregon, was designed: 1) to measure the extent
of the physical removal of benthic macro- and meiofauna by hopper
dredging; 2) to record the subsequent benthic effects of mid-channel
spoiling; and 3) to monitor the rate and pattern of biological readjustment
in the affected areas. Replicate Shipek grab samples
before and after dredge operations were restricted spatially and
temporally to delineate rapid and localized biological responses.
Faunal abundance, taxa composition, species diversity and qualitative
sediment characteristics were studied.
Immediate declines in faunal abundance at the dredge and spoil
sites were temporary and re-adjusted to pre-dredging abundance
levels within 28 days. Temporary increases in diversity reflected
changes in the relative abundance of taxa arising from siltation and
burial of organisms.
Following re-adjustment, populations increased in all areas
except the dredge channel. Localized population declines are hypothesized
to result from the unsuitability of newly exposed sediment for
settlement of pelagic larvae.
Although most taxa were adversely affected by dredging activity,
Capitella ovincola was relatively unaffected and increased dramatically
within the dredge channel within 18 days after dredging.
Qualitative sediment characteristics were generally the same
before and after dredge operations except for localized increases in
wood debris at both dredge and spoil sites.
The effects of dredging activity are thought to be dependent on:
1) the size and duration of the dredge operation, 2) pre-dredging
history and frequency of dredging, 3) the type of benthic community,
4) depth of water and sediment type, 5) draft and size of the dredging
vessel and 6) shipping and related harbor activities. The direct,
benthic effects of this dredging operation were short term. The
temporary nature of these changes was linked to the small scope of
the dredging operation and the adaptability of the benthic community.
It is hypothesized that periodic disruption of the sediment surface by
small scale maintenance operations may have less effect on the benthic
community than the daily presence of heavy shipping and industrial
and domestic pollution. / Graduation date: 1974
Date12 September 1973
CreatorsParr, Robert Alexander
ContributorsMcCauley, James E.
Source SetsOregon State University
Detected LanguageEnglish

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