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As of 2004, this project is no longer current. Please see the Research Programs page for a list of current research projects.
Production of the Great Lakes Amphipod Diporeia spp. in Southeastern Lake Michigan
Mike Quigley
The Great Lakes amphipod Diporeia spp. is a highly prominent benthic invertebrate of the upper Great Lakes that comprises a large portion of resident macrofauna biomass, constitutes an important food base for fish, while representing a significant pathway for transfer of toxic contaminants to higher levels of the foodchain. A 6-year sampling effort at a 45-m site in southeastern Lake Michigan from 1984 to 1989 indicated that annual Diporeia production (grams dry-weight biomass produced per m2 per yr.) was higher than rates noted elsewhere in the Great Lakes and other North American lakes. Moreover, year-to-year production at the site varied more widely than noted elsewhere. Sampling in 1988 and 1989 at a 100-m site in southeastern Lake Michigan revealed a similar high level of Diporeia production, relative to depth.
The objective of this project is to estimate Diporeia production at three 45-m-deep Lake Michigan sites to determine how much the amphipod's production may vary spatially at a depth where its abundance is generally the highest in southeastern Lake Michigan. Additionally, sequentially-collecting sediment-traps deployed 15 m above the bottom will enable estimation of downward flux of carbon to sediments and provide for comparison of food availability on-site and associated Diporeia production.
(currently no active research on this project)
2000 Plans
Planned work during 2000 will focus on completing all size-frequency analysis and production calculations on remaining 1997 (Muskegon and Saugatuck) Ponar samples and 1998 collections (Muskegon and Grand Haven).
Results will be summarized within a manuscript and a scientific presentation outlining the relationship between Diporeia size and corresponding fish predation pressure.
1999 Plans
Project work will "piggyback" quantitative Ponar grab collections of Diporeia on fish collections that are part of the Lake Michigan Monitoring Project. Before or after fish collection off Muskegon (depths of 15-65 m), Ponar grabs will be taken and Diporeia size-frequency distributions determined. Subsequent comparison of numbers and size-frequencies of Diporeia in fish gut contents versus sediment-resident populations will provide insight on what amphipod size classes are most susceptible to fish predation and what portion of Diporeia production supports subsequent fish growth and production. Diporeia has been shown to be an important food item for slimy sculpin, bloater chubs, and whitefish.
A summer intern will carry out work on this project during June-August 1999. The intern will make Ponar collections during sampling cruises; process samples, and determine Diporeia size-frequency distributions in sediments, comparing these with size-frequency estimates from fish gut analysis.
1999 Accomplishments
Production Work
During 1999 included completion of size-frequency estimates of 1997 and 1998 Ponar grab collections of amphipods from a 45-m-deep site off Grand Haven, Michigan in southeastern Lake Michigan. The 1997 Diporeia production at the site was 13.3 gDWm-2y-1 and represented a decline of 62 percent compared with a previous 1989 P estimate of 35.1 gDWm-2y-1 at the site. During 1998, Diporeia production at the site fell lower to 3.4 gDWm-2y-1 , a 90 percent reduction from the 1989 production value. The decline resulted primarily from reduced amphipod abundance rather than major changes in length-weight relationships and causes of the population loss are not known.
Length-Weight Estimates
Because our production estimate method depends on population size-frequency changes to extrapolate resulting changes in biomass, reliable and accurate relationships between amphipod total length and dry weight were determined at the three sampling sites. Results indicated that length-weight relationships of Diporeia at the Muskegon and Grand Haven sites were similar, but that animal weight increased more rapidly with increasing total length for animals at the Saugatuck site. Given that the Saugatuck site had the consistently lowest overall animal abundance in 1997 and that all Diporeia had disappeared from the site by 1998, the trend toward heavier animals with increasing length is unexpected.
Feeding Studies
Given the recent widespread declines in Diporeia abundance and production in southeastern Lake Michigan, we initiated laboratory feeding studies during 1998 to assess Diporeia response to introduction of surficial sediments collected at Muskegon, Grand Haven, Saugatuck, and St. Joseph 45-m sites. Although more analysis will be required, preliminary results indicate that amphipod feeding rates (i.e. gut turnover) were highest for rations of surficial sediments from sites where amphipods were at lowest abundance or entirely absent. Such higher gut turnover rates may be due to the nutritionally poorer food quality of sediments at such sites, resulting in higher amphipod gut throughput as animals attempt to derive sufficient nutrition from such food.
1998 Accomplishments
Work during 1998 included continued size-frequency estimates of 1997 Ponar grab collections of amphipods from 45-m-deep sites off Muskegon, Grand Haven and Saugatuck, Michigan in southeastern Lake Michigan. At the Grand Haven site, 1997 Diporeia production was 13.3 gDWm-2y-1 and represented a decline from 1984 -1989 estimates that ranged from 17.9 to 35.1 gDWm-2y-1 . The decline resulted primarily from reduced amphipod abundance rather than major changes in length-weight relationships and may be associated with zebra mussel population increases over southern Lake Michigan. The mussel is a voracious filter feeder that may be responsible for an apparent decline in food quality and quantity available to Diporeia(see project under Aquatic Contaminants on Long-Term Trends in Benthic Populations). Moreover, preliminary analysis of Ponar collections during the 1998 field season indicate that the Diporeia population decline is continuing, and corresponding declines in production are likely at both Muskegon and Grand Haven sites.
Because our production estimate method depends on population size-frequency changes to extrapolate resulting changes in biomass, reliable and accurate relationships between amphipod total length and dry weight were determined at the three sampling sites. Results indicated that length-weight relationships of Diporeia at the Muskegon and Grand Haven sites were similar, but that animal weight increased more rapidly with increasing total length for animals at the Saugatuck site. Given that the Saugatuck site had the consistently lowest overall animal abundance in 1997 and that all Diporeia had disappeared from the site by 1998, the trend toward heavier animals with increasing length is unexpected.
Given the recent widespread declines in Diporeia abundance and production in southeastern Lake Michigan, we initiated laboratory feeding studies during 1998 to assess Diporeia response to introduction of surficial sediments collected at Muskegon, Grand Haven, Saugatuck, and St. Joseph 45-m sites. Although more analysis will be required, preliminary results indicate that amphipod feeding rates (i.e. gut turnover) were highest for rations of surficial sediments from sites where amphipods were at lowest abundance or entirely absent. Such higher gut turnover rates may be due to the nutritionally poorer food quality of sediments at such sites, resulting in higher amphipod gut throughput as animals attempt to derive sufficient nutrition from such food.
Last updated: 2004-04-23 mbl