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GLIN==> GLERL seminar: Exotic Invertebrates and their impact on energy flow in the lower Great Lakes

Posted on behalf of Renda Williams <williams@glerl.noaa.gov>

GLERL Seminar Series Presents
Dr. Ora Johannsson
Canada Center for Inland Waters
Burlington, Ontario Canada

"Exotic Invertebrates and their impact on energy flow in the lower Great

Monday, October 2, 2000
1:00 - 2:00 p.m.
NOAA Great Lakes Environmental Research Laboratory
Main Conference Room (105)
2205 Commonwealth Blvd.
Ann Arbor, Mich.

Contact: Doran Mason, GLERL: 734-741-2148

Exotic invertebrates and their impact on energy flow in the lower Great

In the past 15 years a number of invertebrates have entered the lower Great
Lakes ecosystems.  Each has the potential to alter trophic relationships and
energy flow in these systems.  The most dramatic have been the zebra and
quagga mussels (Dreissena polymorpha and D. bugensis).  Their impacts have
been assessed primarily in Lake Erie, the Bay of Quinte and Saginaw Bay
because of the dramatic changes observed in these shallow, nutrient-rich
systems and in the case of the Bay of Quinte, the presence of a long-term
monitoring program.  No only has the water cleared, but seasonal areal
photosyntheis has declined in the presence of dreissenids translating into
less energy flow through the pelagic food-web.  Energy flow was tempered by
the level of planktivory.  Non-dreissenid benthic biomass did not decline
and energy flow through the benthos has increased due to the presence of
dreissenids.   Bythotrephes cederstroemi and Cercopagis pengoi are two
predatory cladocerans from the Ponto-Caspian region.  Bythotrephes arrived
in the early 1980s and is abundant in Lakes Erie, Michigan and Huron.
Cercopagis arrived in Lake Ontario in 1998.  These two species may not only
compete with the natural predatory cladocerans, Leptodora and Polyphemus but
also may alter the balance of trophic structure and zooplankton production
if they are not readily consumed by the native fish.  Bythotrephes in Lake
Erie can become very abundant even in planktivore dominated situations.  The
composition and vertical distribution of zooplankton suggests that they may
alter the seasonal pattern and extent of zooplankton production,
particularly of the cladocerans.  Cercopagis is smaller than Bythotrephes.
Initial studies suggest that it resides in the epilimnion and metalimnion
and likely consumes organisms in the size range of nauplii and Bosmina.  The
bulk of the zooplankton tend to reside lower in the water column than
Cercopagis.  Its consumption by fish and effect on energy flow are not yet
clear.  The net effect of these invertebrate invaders has been to decrease
the flow and efficiency of energy flow through the pelagic foodweb.

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