Objectives

Determine changes in density and biomassof dreissenid population since 1991-1996.

Determine changes in density, biomass, and species composition of the benthicmacroinvertebrate community since 1987-1996.

Dive Sites

Ponar Sites

2008 (F)2009 (F)2010 (F)

2006 (F)2007 (S,S,F)2008 (S,S,F)2009 (F)

Site-D

Site-P

Inner Bay (5 sites) Outer Bay (1 site) Year Density Biomass Density Biomass 1991 9,305 ± 6,389 12.3 ± 7.6 3,408 ± 2,772 0.7 1992 31,334 ± 15,627 58.6 ± 28.1 4,695 ± 2,542 19.5 1993 3,803 ± 1,592 4.5 ± 2.1 5,813 ± 2,384 15.3 1994 5,633 ± 1,945 9.2 ± 2.4 9,925 ± 1,590 32.6 1995 2,562 ± 1,126 4.9 ± 1.6 3,824 ± 525 27.1 1996 5,261 ± 3,2242 14.7 ± 6.4 6,981 ± 1,670 57.5 Mean 4,314 8.3 6,636 33.1 2008 538 ± 103 2.0 ± 0.4 596 ± 54 3.9 2009 421 ± 90 1.5 ± 0.6 411 ± 55 2.0 2010 1,808 ± 996 1.4 ± 1.0

Mean (± SE) Density (no./m2) and AFDW Biomass (g/m2) of Dreissena in Saginaw Bay

Site-D: 7,693 ± 414Site-P: 1,511

Year %Quagga %< 5 mm 2008 76.1 13.3 2009 74.9 38.0 2010 80.3 93.1

Mean of All Inner Bay Dive Sites (n=5)

Site-D: 87.7 92.4Site-P: 99.3 3.3

Year St. 4 St. 7 St.10

1991 7 0 10

1992 0 12 10

1993 7 55 0

1994 5 60 14

1995 0 2 2

1996 0 11 0

2006 0 21 0

2007 10 60 33

2008 0 377 0

2009 0 300 0

Dreissenid Density (No./m2) at Sites with Soft Bottom (Silt)

Site Density

% < 5mm

St. 5 6,144 97.4

St. 6 223 48.8

St. 13 442 85.9

St. 14 3,510 97.0

St. 15 500 85.9

St. 16 391 53.3

St.- D 7,277 90.9

St.- P 1,511 3.3

Density (No./m2) of Dreissenids and Percentage of Small Individuals (< 5 mm) at all Dive Sites

Why is the dreissenid population lower in 2008-2010 compared to 1991-1996?

1) Goby predation

2) Near-bottom conditions unsuitable

Credit: N. Hawley

Credit: D. Kashian

St. 5 - Inner Saginaw Bay

Future Work

Determine length-weight regression fordreissenids collected in 2010

Complete analysis of benthic macroinvertebratesand write manuscript