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June 05
             GLERL-CILER and GLSC Joint Seminar
             SPEAKER: Dr. Helene Limén, Department of Zoology, Stockholm
University, Sweden
            (Present address: GLIER, University of Windsor, Ontario,
             TIME: 10:30 a.m.
             WHERE: GLERL Main Conference Room #105

ABSTRACT: In deep soft-bottoms of the Baltic Sea, benthic invertebrates
rely to a
large extent on the input of organic material from the pelagic zone. A
large part of the spring diatom bloom settles to the bottom and previous
studies indicate that the settling material is of great importance for
both macro and meiobenthic species. During the late summer months, the
phytoplankton bloom is dominated by cyanobacteria, which may also settle
to the bottom             although not to the same extent as diatoms.
When the sedimentation rate is high and the breakdown of organic matter
intense, bottom sediments may become depleted of oxygen, which
subsequently affect the structure of benthic communities.

In a number of laboratory experiments and in one field study, the
responses of benthic invertebrates to settled organic material and
hypoxic conditions were investigated. Large interspecific differences in
the uptake of newly settled phytoplankton were found specifically within
amphipods, ostracods and nematodes. The amphipod, Monoporeia affinis,
assimilated significantly more of the labelled material compared to
Pontoporeia femorata. When the two
species were incubated together, M. affinis tended to suppress the food
uptake by P. femorata. Physical sediment disturbance generated by
amphipods also inhibited the uptake of settled phytoplankton by
ostracods, most likely through burial of the material. The species
specific uptake by ostracods was not caused by food competition over the
labelled material but most likely by food partitioning. The stable
carbon signature of ostracods from the field was
consistent with laboratory findings on ostracod food partitioning;
Candona neglecta seems to feed on newly settled material on surface
sediment layers whereas Paracyprideis fennica and Heterocyprideis
sorbyana seem to rely on organic material associated with deeper
sediment layers. Strong evidence for incorporation of settled pelagic
cyanobacteria by C. neglecta in the field was found, and this is the
first time that incorporation of such material into the
benthic food web has been demonstrated. Large unexpected differences in
assimilation of settled diatoms were found among nematode species from
the same trophic group. These results question the ecological validity
of placing nematodes into feeding groups based on the morphology of the
buccal cavity alone. Continuous and short term hypoxia resulted in
significant alterations in the benthic community structure.
Representatives from two important              meiobenthic groups,
nematodes and ostracods, seem to tolerate extended periods of hypoxia
while adaptations to hypoxic events interrupted by normoxia were shown
for both macrobenthic and meiobenthic organisms.

CONTACT: Dr. David Reid, NOAA/GLERL, 734-741-2019

Renda S. Williams
Executive Secretary to the Director
Phone: 734-741-2245
Fax: 734-741-2003
E-Mail: williams@glerl.noaa.gov

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