The invertebrate community of a coastal marsh on Saginaw Bay, Lake Huron, near Quanicassee, Michigan, was sampled from July through October of 1989, and April through December of 1990. Vegetation-water column, sediment core-water column and aquatic dip net samples were taken between 150 and 600 m from the shore in water depths averaging 30 to 60 cm. The emergent marsh was characterized by the emergent bulrush, Scirpus americanus Pers., growing on a substrate predominately composed of shifting sand, rather than the organic muck typical of many emergent marshes.
The macroinvertebrate community in the vegetation was represented by 54 species of insects and 11 other orders of macroinvertebrates. Macroinvertebrates in the marsh vegetation reached their greatest abundance and biomass on December 13, 1990, with 50,000 individuals m-2 and 1.5 g m-2 of biomass.
This community was dominated by Chironomidae, Oligochaeta, and the Ephemeroptera genus Caenis. Chironomid larvae were the most abundant insects, making up 80% of all insects collected on several dates. They reached mean densities of 12,000 m-2 on July 13, 1990, in the vegetation community. Chironomid larvae, along with oligochaetes and nematodes, were quite numerous in the cells of senescent S. Americanus vegetation.
In addition to the Chironomidae, the Ephemeroptera, Caenis Latipennis Banks and Caenis Amica Hagen, were among the more common and abundant insects present in the marsh. However, taxa that were more unique to this community included the Coleoptera, Hemiptera, Lepidoptera, and the Odonata, Ishnura verticalis Say, which are all associated with aquatic macrophytes. I. verticalis was less abundant in the marsh beyond 400 m from shore. This area of the marsh was in the highly-turbid offshore zone, with lower macrophyte density and increased wave action. The correlation between I. verticalis abundance and distance from shore needs further investigation.
The oligochaetes in the vegetation community were represented mainly by Naididae, with the genus Stylaria present only in the vegetation. Oligochaeta reached mean densities of 15,500 m-2 in the vegetation community on July 13, 1990.
The macroinvertebrate community in the marsh sediment was less diverse, probably because of the instability of the marsh sediment. Sixteen species of insects and 9 orders of macroinvertebrates were represented in the marsh sediment. The sediment community had its highest density and biomass during July, with 48,900 macroinvertebrates m-2 on July 13, 1989. The sediment macroinvertebrate community consisted mostly of Chironomidae, Oligochaeta, and Nematoda, with the chironomids and oligochaetes making up most of the community's biomass. Oligochaetes in the sediments reached a maximum mean biomass of 1,100 mg m-2 . and a density of 10,000 m-2, on June 8, 1990, with most of these being Tubificidae. The sediment macroinvertebrate community reached a mean weight 1.5 times greater than the maximum mean weight of the macroinvertebrates in the vegetation community.
The Quanicassee marsh supported 7.6 billion macroinvertebrates in every 0.5 km2 area of emergent vegetation, and every 0.5 km2 area of sediment supported 12.2 billion macroinvertebrates on July 13, 1990. The macroinvertebrate biomass in every half square kilometer of marsh sediment averaged 575 kg on July 13, 1989.
The most abundant crustacean zooplankton in the Quanicassee marsh were Acroperus harpae Baird, Alona quadrangularis (O. F. Muller), Camptocercus rectirostris Schodler, Ceriodaphnia, Chydorus sphaericus (O. F. Muller), Eurycercus lamellatus (O. F. Muller), Sida crystallina (O. F. Muller), Simocephalus, Acanthocyclops vernalis Fischer, Eucyclops agilis Koch, Harpactacoida, and Ostracoda. Cladocera dominated the abundance and biomass of the vegetation zooplankton community, but the sediment zooplankton community was dominated by the sediment.
C. sphaericus reached the highest abundances of any zooplankton in either the vegetation or sediment communities. S. crystallina dominated the vegetation community biomass, while Ostracoda dominated the sediment zooplankton biomass. S. crystallina abundance was positively correlated with water depths greater than 35 cm. E. lamellatus abundance, on the other hand, seemed to be related more to distance from shore than water depth, and was greatest between 250 and 400 m from shore. The abundance correlations of both of these Cladocera need further investigation.
The zooplankton in the Quanicassee marsh sediment reached a mean abundance of 356,700 m-3 on October 27, 1989, with a biomass of 5 g m-3. Zooplankton community abundance in the vegetation on this date was nearly 250,000 zooplankton m-3. Zooplankton biomass in the vegetation was greatest on August 10, 1990, with 15.1 g m-3. The macroinvertebrate and zooplankton communities in the vegetation and sediment of the Quanicassee marsh probably serve as an important food resource for fish inhabiting Saginaw Bay.
See Zebra Muscles in a Great Lakes Coastal Marsh for work on Zebra Muscles in Saginaw Bay.
Some photographs, other information on Dr. Brady can be found at the HSCW Speed Record page.
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