Open Access. Powered by Scholars. Published by Universities.®
- Discipline
Articles 1 - 2 of 2
Full-Text Articles in Aquaculture and Fisheries
A Hemimysis Driven Novel Ecosystem At A Modified Boulder Breakwall, Eric John Geisthardt
A Hemimysis Driven Novel Ecosystem At A Modified Boulder Breakwall, Eric John Geisthardt
Theses and Dissertations
The US Army Corps of Engineers (USACE) is mandated to maintain and repair aging breakwall structures in all commercial ports on the Great Lakes. In May of 2014, the construction of Milwaukee Harbor USACE “green” breakwall (GBW) reconciliation created complex rocky aquatic habitat by depositing cobble-sized stone as a veneer over standard 6-10 ton boulders, thus creating “control” (boulder) and “treatment” (cobble) habitats. The breakwall is home to a prolific population of Hemimysis anomala, the introduced Ponto-Caspian mysid, which is significantly more abundant on cobble versus boulders (p<0.05, using a novel trap for Hemimysis). Fish and forage communities were sampled in 2015 and 2016 using a combination of experimental and micromesh gill nets, night scuba diving surveys, and a novel Hemimysis trap. This nearshore lithophilic mysid appears to provide a significant new seasonal food resource in the Milwaukee Harbor for pelagic prey fishes during inshore spawning migrations and upwelling events. Alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) fed heavily on Hemimysis with some individuals consuming hundreds of mysids. Night scuba diving surveys and gill netting confirmed that rainbow smelt preferred to forage on the cobble section (p<0.05), and also consumed more Hemimysis there than they did at the control breakwall site (p<0.05). Hemimysis were also the primary food item consumed by nearshore game fishes such as YOY yellow perch (Perca flavescens), YOY largemouth bass (Micropterus salmoides), and juvenile rock bass (Ambloplites rupestris) caught at the breakwall. This study provides the first documented evidence that where abundant in the Laurentian Great Lakes, Hemimysis do have the ability to significantly impact local food webs and drive the feeding ecology of both pelagic transient and nearshore resident fishes.
Changes In The Lake Michigan Trophic Structure: As Revealed By Stable C And N Isotopes, Benjamin Turschak
Changes In The Lake Michigan Trophic Structure: As Revealed By Stable C And N Isotopes, Benjamin Turschak
Theses and Dissertations
Food web structures which incorporate both slow (nearshore or detrital) and fast (pelagic) energy channels convey stability upon food web biota through asynchrony and multichannel trophic omnivory. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and energy flows. I used stable C and N isotopes and gut content analysis to determine how Lake Michigan food web structure and stability has changed in the past decade, coincident with the expansion of dreissenid mussels and a decrease in pelagic phytoplankton production. Fish and invertebrate samples collected near the port of Milwaukee, WI were …