|Title||Substrate relations of the burrowing amphipod Pontoporeia affinis Lindstrom|
|Year of Publication||1962|
|Degree||Doctor of Philosophy|
|Number of Pages||92 pp.|
|University||University of Michigan|
|City||Ann Arbor, MI|
|Thesis Type||Doctor of Philosophy|
1. Pontoporeia affinis, a burrowing amphipod and the predominant macrobenthic invertebrate in the upper Great Lakes, was studied with regard for its association with the bottom sediments. The primary requirement of the sampling method was to obtain a sediment sample which was undisturbed in order that precise data of its nature could be obtained through laboratory analsysis. A corer was used to achieve this end. 2. The particle size distribution of the sediments in the study area graded from coarse well-sorted sands in the shallow water at the mouth of the bay to fine less well-sorted sediments in the deep water of Lake Michigan. 3. Loss on ignition was utilized to estimate the organic material in the sediments. Over the sandy sediments the organic matter was largely restricted to a thin detrital layer. The amount of organic material in the silty deep-water sediments was several times that of the sandy sediments. 4. Bacteria were counted directly. Their numbers were found to correlate with the estimates of organic content. The numbers of bacteria per gram of dry sediment ranged from 126000000 to 860000000. 5. The distribution of P. affinis in the study area showed no correlation with depth or particle size of the seidments, but was correlated with the numbers of bacteria per gram of sediment. The numbers of P. affinis collected from several of the sampling stations exceeded the maximum reported from the literature. 6. In the laboratory P. affinis selected sediment particle sizes smaller than 0.50 mm. There was no apparent resolution of size differences in experiments utilizing sediments finer than 0.50 mm. 7. In the laboratory P. affinis selected substrates whose surface layers had been enriched with organic materials. When the experimental substrates were allowed to condition, probably by the growth of bacteria on the surfaces of the particles, they were selected over the washed control substrates. 8. Size frequency distribution in quasi-quantitative field samples indicates that the newly hatched individuals are released from the brood pouch in the late spring or early summer. Laboratory rearing is suggested for the precise delineation of the developmental sequence, but it appears that the development is direct through seven or eight instars to sexual maturity. 9. Relationships of P. affinis to the substrate have been shown to be strongly influenced by the presence of bacteria and organic matter. This organism has been shown to ingest this material but the energy transfer has yet to be ascertained. The predominance of P. affinis in the benthic community and its high population densities indicate that when this information becomes available a large portion of the benthic trophic system may be more understandable.