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Pelagic-Benthic Coupling in Nearshore Lake Michigan: Linking Pelagic Inputs to Benthic Productivity
This project closely examines the population dynamics and physiological condition of Diporeia at selected sites in the southeastern portion of Lake Michigan to determine potential causes for the decline and total loss of Diporeia in this region. In 2005, most effort in this project was focused on completing a manuscript that examines data collected since 1997.
Collaborators
Eugene Stoermer, University of Michigan, and John
Robbins, GLERL -- collaboration on a project to examine temporal
changes in the diatom record in sediments from southeastern Lake Michigan.
The purpose is to determine if changes in diatom abundance and composition
can be linked to the loss of Diporeia.
Gretchen Messick, NOS-Cooperative Oxford Laboratory --
collaboration to examine pathogens and parasites in dreissenids.
Project Accomplishments
This project was
initiated in 1997 to examine reasons for the decline of Diporeia
in Lake Michigan. Physiological characteristics and population dynamics
of animals from various sites were examined relative to selected physical
and chemical variables. The hypothesis was that the decline of Diporeia
was related to a decline in available food because of the filtering activity
of dreissenid mussels (zebra and quagga mussels). In 1997 and 1998, samples
were collected monthly (April to November) at four sites along the 45-m
contour (off St. Joseph, Saugatuck, Grand Haven, and Muskegon). These
sites initially had varying densities of Diporeia ranging from
0 m-2 at St. Joseph, to 10,000 m-2 at Grand Haven and Muskegon. By 1998,
densities declined to 0 m-2 at Saugatuck and Grand Haven, and to 4,000
m-2 at Muskegon. In 1999 and 2000, monthly samples were collected at Grand
Haven and Muskegon only. By fall 2000, population densities at Muskegon
had declined to < 500 m-2, and the population disappeared entirely by
2002. In addition to density estimates, individuals at each site were
collected for analysis of lipid content in 1997-2002. As densities declined,
lipid content of both juveniles and adults increased. If food was limiting,
it might be expected that lipid content would have declined. An examination
of abundances of young-of-year (0-3 mm), juveniles (3-5 mm), and adults
(> 5 mm) before and after the establishment of dreissenids (in 1989) indicated
that recruitment was still occurring bu the juveniles were not surviving
to become adults (Fig. 1).
Pelagic
inputs, as an indicator of potential food, were measured with sediment
traps deployed from late March to mid October/November. Traps were deployed
at all four sites in 1997 and 1998, but only at Grand Haven and Muskegon
in 1999. Material collected was analyzed for total carbon and biogenic
silica. Beginning in 1998 we also collected surficial sediment samples
for carbon content, biogenic silica, and chlorophyll.
In 2001, we continued to collect monthly samples at the Muskegon site, and also added monthly collections at two other sites, a 45-m site off Little Sable Point, and a 95-m site off Muskegon. Diporeia were still abundant at both these sites. Sedimentation traps were not placed at these sites, but surficial sediment samples were collected for carbon, silica and chlorophyll. In addition to the previously mentioned biological variables, we also measured ETS, gut-fullness, and C:N. The sampling program in 2002 was similar to the program in 2001.
As mentioned, densities at the 45-m site off Muskegon declined to zero in 2002, and densities at the 45-m site off Little Sable Point declined to zero in 2003. Thus, X-2 was the only site where animals were available to measure physiological variables in 2003. In addition to collecting animals on a monthly basis at X-2, laboratory experiments were conducted to determine if reduced food supplies were a potential cause of the decline. Juveniles and adults from X-2 were placed into sediments from X-2 and M-45 at various densities for a 90-day period. Mortality and various physiological variables were monitored. Samples were analyzed in 2004.
In 2005 a workshop was held to further explore reasons for the decline in Diporeia and to discuss more recent density trends. The workshop was jointly sponsored by GLERL and EPA.
A manuscript was completed and tentatively accepted that summarizes density trends, lipid content, length-weight, and size-frequency of Diporeia populations at the various sites, and also presents trends in chemical variables from the sedimentation traps and the sediments.
Figure 1. Densities of young-of-year (0-3 mm), juveniles (3-5 mm), and adults (>5 mm) at several 45-m sites before (1986-1989) and after (1997-2001) establishment of Dreissena.
Publications
Brochure: general information on decline in Lake Michigan bottom life
Nalepa, T. F., Fanslow, D. L., Messick, G. Characteristics and potential causes of declining Diporeia populations in southern Lake Michigan and Saginaw Bay, Lake Huron. Proceedings of Whitefish-Diporeia Workshop, Gt. Lakes Fish. Comm. Tech. Rep. 66, Ann Arbor, MI, 157-188 (2005).
Dermott, R., Munawar, M., Bonnell, R., Carou, S., Niblock, H., Nalepa, T. F., and Messick, G. Preliminary investigations into causes of the disappearance of Diporeia from Lake Ontario. Proceedings of Whitefish-Diporeia Workshop, Gt. Lakes Fish. Comm. Tech. Rep. 66, Ann Arbor, MI, 203-232 (2005).
Messick, G.A., R.M. Overstreet, T.F. NALEPA, and S. Tyler. Prevalence of parasites in amphipods, Diporeia spp. from Lakes Michigan and Huron, USA. Diseases of Aquatic Organisms 59:159-170 (2004).
2005 Presentations
Nalepa, T. F. 2005. Aquatic invasive species and food web disruptions in the Great Lakes. Invaders of the Great Lakes: Options for Prevention and Management. Conference, Michigan State University, East Lansing, MI. March, 2005.
Nalepa, T. F. 2005. Food web disruptions in the context of invasive species and other stressors. Aquatic Invasive Species Symposium, National Wildlife Foundation, Chicago, IL. May, 2005.
Foley, A. J., Nalepa, T. F., and Walker, G. K. 2005. Associated epibiont populations and the decline of Diporeia spp. (Amphipoda) from Lake Michigan. 48th Conference on Great Lakes Research, International Association for Great Lakes Research, Ann Arbor, MI. June, 2005.
Nalepa, T. F., Fanslow, D. L., and Foley, A. J. 2005. Declines in the benthic amphipod Diporeia spp. in the Great Lakes: is there evidence for food limitation? ASLO 2005 Summer Meeting, American Society of Limnology and Oceanography, Santiago, Spain. June, 2005.
Nalepa, T. F. 2005. The disappearance of Diporeia in the Great Lakes: in search of a cause. NOAA Great Lakes Seminar Series, Ann Arbor, MI. September, 2005
Last updated: 2005-11-17 mbl