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Long-Term Trends in Benthic Populations
Collaborators:
Monitoring of the 40 sites in the southern basin is a joint effort with EPA-GLNPO, who provides the R/V Lake Guardian as a sampling platform.
This is a long term monitoring project
that documents changes in the benthic macroinvertebrate community in the
southern basin of Lake Michigan. The project was designed so that samples
are collected at 40 sites for two consecutive years every 5 years. Samples
were collected in the spring, summer, and fall in 1980-81, 1986-87, 1992-93,
and 1998-99. The 40 sites were originally sampled in the 1960s by other
researchers.
Papers have been published on trends in the benthic community through 1993. The recent completion of taxa identification and data entry for samples collected in 1998-99 allowed us to compare the community in these two years to the community in all previous years and to assess recent trends. Data analysis was limited to the taxa that were historically dominant in the southern basin: Diporeia, Oligochaeta, and Sphaeriidae. The 40 sites were divided into four depth intervals (16-30 m =11 sites; 31-50 m = 12 sites; 51-90 m = 11 sites; > 90 m = 6 sites) and a mean density for each of the three dominant taxa was determined for each depth category. Between 1992-93 and 1998-99, Diporeia continued to decline at depths less than 50 m (Figure 1). The decline was most dramatic at sites in the 31-50 m depth interval. Oligochaetes have apparently stabilized at sites in the 16-30 m interval after declining at this interval between 1980-81 and 1992-93 (Figure 2). However, sphaeriids have continued to decline in both the 16-30 m and 31-50 m intervals (Figure 3).
The decline of Diporeia is a unique event. While other taxonomic groups declined, Diporeia completely disappeared from large areas. Because of the rapid decline of Diporeia, samples were collected at the 40 sites every year since 1999. Based on our most recent data collected in 2002, Diporeia densities continued to decline in the 31-50 m interval and are now entirely gone to depths of 50 m in the southeast portion of the lake.
Figure 1. Density trends in the amphipod Diporeia in the southern basin of Lake Michigan between the mid-1960s and 1998-99.
Figure 2. Density trends in Oligochaeta in the southern basin of Lake Michigan between the mid- 1960s and 1998-99.
Figure 3. Density trends in the Sphaeriidae in the southern basin of Lake Michigan between the mid-1960s and 1998-99.
2005 Plans
In keeping with the original sampling design, we plan to sample again in spring, summer, and fall 2005 at the same 40 sites in the southern basin. Also, we plan to begin processing all the samples collected in 2004.
2004 Progress
This project began in 1980 to determine responses of the benthic community to phosphorus control measures. The 40 sites sampled this year were originally sampled in the 1960s by other researchers. The project was designed so that samples are collected at these 40 sites for two consecutive years every 5 years. Thus, samples have been collected in the spring, summer, and fall in 1980-1981, 1986-87, 1992-93, and 1998-99. Recent emphasis has been on assessing changes in the benthic community resulting from the spread of zebra mussels and quagga mussels (Dreissena polymorpha and Dreissena bugensis).
Beginning in 2000, samples were collected every year (fall only), and only abundances of Diporeia and dreissenids were documented. This was a result of the dramatic and rapid decline in populations of the former organism and the increase in the latter organisms. In 2004, we returned to sampling in spring, summer, and fall, and also documenting abundances of the entire benthic community. The sorting and counting of organisms collected in 2004 is continuing.
Papers have been published that provide a detailed analysis of benthic changes through 1993. These papers give species-specific summaries of trends and discussions of probable causes. A paper completed this past year provided a summary of trends for just the major groups through 1999. The long term plan is to sample again in spring, summer, and fall 2005 and then complete a species-specific analysis of trends for the period between 1992-1993 and 2004-2005. This analysis will include data from 1998-1999.
Past Accomplishments
In 2003, we completed counting Diporeia and Dreissena in the 2002 samples (120 total samples) and completed preliminary assessment of 1998-99 data. Also, samples were again collected at all 40 sites in September 2003.
In 2002 we collected samples in the fall at the same 40 sites in the southern basin of Lake Michigan and count all Diporeia and zebra/quagga mussels. All data collected in 1999 was placed into a spreadsheet.
In 2001 samples were collected at the 40 sites and all Diporeia and zebra/quagga mussels were sorted and counted. All organisms in the 1998-99 samples were identified to the lowest practical taxonomic level and the 1998 data was placed into a spreadsheet. A report was written and submitted to GLNPO-EPA that documents densities of the major benthic groups in 1998 and discusses any changes compared to prior years.
Benthic samples were collected at 159 sites throughout Lake Michigan in August 2000. This is an expansion of the long-term monitoring program in the southern basin which consists of 55 sites. The additional sites were located in the central and northern portions of the lake. The objective was to document lakewide distributions of Diporeia and determine long-term trends in abundances.
All organisms collected at the 55 sites in the southern basin in 1998 have been counted and identified. All organisms collected in 1999 have been picked and sorted but have yet to be identified.
Benthic samples were collected at up to 55 sites in southern Lake Michigan in May, July, and September of 1999. This is a continuation of the long-term monitoring program that was initiated in 1980. All macroinvertebrates collected in the May samples have been picked and sorted. Based on these May values, the density of Diporeia continues to decline throughout the southern basin. Taxonomic identification of individuals collected in 1998 continued. Oligochaetes and chironomids were cleared and mounted on slides, and all amphipods were identified to genus.
In 1998, data collected in 1986-87 and 1992-93 was analyzed and a paper published that documents changes between 1980-81 and 1992-93. Overall, densities of the three major groups, Diporeia (Amphipoda), worms (Oligochaeta), and fingernail clams (Sphaeriidae), declined 58 % at sites less than 50 m in water depth. For the former two groups, the decline occurred over the entire southern basin and was likely a result of phosphorus abatement programs and declines in pelagic productivity. The decline in Diporeia occurred mostly in the south/southeastern portion of the lake and was attributed to food competition (diatoms) with the zebra mussel. The average decline in Diporeia was 82% at sites in this portion of the lake. At some sites, Diporeia declined from 10,000 per square meter to less than 100 per square meter. Since the monitoring scheme is to sample for two consecutive years every five years, we again sampled at the 40 sites in spring, summer, and fall 1998.
Products
Publications
+ brochure with general information on decline in Lake Michigan bottom life
Nalepa, T. F., Fanslow, D. L., Lang, G. A., and Ruberg, S. A. Recent trends in benthic macroinvertebrate populations in Lake Michigan. Chapter in book on Lake Michigan, M. Munawar and T. Edsall (eds) (accepted).
Barbiero, R. P., Nalepa, T. F., and Tuchman, M. L. Status of phytoplankton, zooplankton, and benthos. 2003. In The State of Lake Huron in 1999. Edited by M. P. Ebener. Great Lakes Fish Comm. Spec. Pub. 03-XX. (accepted)
Nalepa, T. F. 2003. Indicator #93: the benthic amphipod Diporeia spp. In State of the Lakes Report. Great Lakes National Program Office, EPA.
Neilson, M. A., Painter, D. S., Warren, G., Hites, R. A., Basu, I., Weseloh, D. V., Whittle, D. M., Christie, G., Barberio, R., Tuchman, M., Johannsson, O. E., Nalepa, T. F., Edsall, T. A., Fleischer, G., Bronte, C., Smith, S. J., and Bauman, P. C. 2003. Ecological monitoring for assessing the state of the nearshore and open waters of the Great Lakes. Environ. Monit. Assess. 88: 103-118.
Madenjian, C. P., Fahnenstiel, G. L., Johengen, T. H., Nalepa, T. F., Vanderploeg, H. A., Fleischer, G. W., Schneeberger, P. H., Benjamin, D. M., Smith, E. B., Bence, J. R., Rutherford, E. S., Lavis, d. S., Robertson, D. M., Jude, D. J., and Ebener, M. P. Dynamics of the Lake Michigan food web, 1970-2000. 2002. Can. J. Fish. Aquat. Sci. 59:736-753.
Nalepa, T. F., Schloesser, D. W., Pothoven, S. A., Hondorp, S. A., Fanslow, D. L., Tuchman, M. L., and Fleischer, G. W. 2001. First finding of the amphipod Echinogammarus ischnusand the mussel Dreissena bugensis in Lake Michigan. J. Great Lakes Res. 384-391.
Nalepa, T. F., Hartson, D. J., Buchannan, J., Cavaletto, J.F., Lang, G. A., and Lozano, S. J. 2000. Spatial variation in density, mean size, and physiological condition of the holarctic amphipod Diporeia spp. in Lake Michigan. Freshwat. Biol. 43:107-119.
Nalepa, T. F., Lang, G. A., and Fanslow, D. L. 2000. Trends in macroinvertebrate populations in southern Lake Michigan over the past several decades. Verh. Internat. Verein. Limnol. 27:2540-2545.
Nalepa, T. F. 1999. Dramatic changes in benthic macroinvertebrate populations in southern Lake Michigan. Aquatic Nuisance Species Update, 4 (30).
Nalepa, T. F., Hartson, D. J., Fanslow, D. L., Lang, G. A., and Lozano, S. J. 1998. Decline in benthic macroinvertebrate populations in southern Lake Michigan, 1980-1993. Can. J. Fish. Aquat. Sci. 55: 2401-2413.
Landrum, P. F., and Nalepa, T. F. 1998. A review of factors affecting the ecotoxicology of Diporeia spp. J. Great Lakes Res. 24: 889-904.
Nalepa, T. F., Hartson, D. J., Fanslow, D. L.., Lang, G. A., and Lozano, S. J. 1998. Declines in benthic macroinvertebrate populations in southern Lake Michigan, 1980-1993. Can. J. Fish. Aquat. Sci. 55: 2402-2413.
Presentations
Nalepa, T. F., Fanslow, D. L., and Ruberg, S. A. 2003. Current trends in benthic macroinvertebrate populations in Lake Michigan with emphasis on Diporeia spp. and Dreissena (zebra mussel and quagga mussel). Lake Michigan: State of the Lake 03’ Conference, Muskegon, MI, October, 2003.
Milestone Reports
Milestone-00-4-2: Determine the role of zebra mussels on the decline of the amphipod Diporeia spp.
Last updated: 2005-08-16 ahc