Nearshore energy subsidies support Lake Michigan fishes and invertebrates following major changes in food web structure

Benjamin A. Turschak, David Bunnell, Sergiusz Czesny, Tomas O. Höök, John Janssen, David Warner, Harvey A. Bootsma

Research output: Contribution to journalArticlepeer-review

Abstract

Aquatic food webs that incorporate multiple energy channels (e.g., nearshore benthic and pelagic) with varying productivity and turnover rates convey stability to biological communities by providing independent energy sources. Within the Lake Michigan food web, invasive dreissenid mussels have caused rapid changes to food web structure and potentially altered the channels through which consumers acquire energy. We used stable C and N isotopes to determine how Lake Michigan food web structure has changed in the past decade, coincident with the expansion of dreissenid mussels, decreased pelagic phytoplankton production, and increased nearshore benthic algal production. Fish and invertebrate samples collected from sites around Lake Michigan were analyzed to determine taxa-specific 13C:12C (δ13C) and 15C:14N (δ15C) ratios. Sampling took place during two distinct periods, 2002-2003 and 2010-2012, that spanned the period of dreissenid expansion, and included nearshore, pelagic and profundal fish and invertebrate taxa. The magnitude and direction of the δ13C shift indicated significantly greater reliance upon nearshore benthic energy sources among nearly all fish taxa as well as profundal invertebrates following dreissenid expansion. Although the mechanisms underlying this δ13C shift likely varied among species, possible causes include the transport of benthic algal production to offshore waters and increased feeding on nearshore prey items by pelagic and profundal species. δ15C shifts were more variable and of smaller magnitude across taxa, although declines in δ15C among some pelagic fishes suggest a shift to alternative prey resources. Lake Michigan fishes and invertebrates appear to have responded to dreissenid-induced changes in nutrient and energy pathways by switching from pelagic to alternative nearshore energy subsidies. Although large shifts in energy allocation (i.e., pelagic to nearshore benthic) resulting from invasive species appear to affect total production at upper trophic levels, changes in trophic structure and utilization of novel energy pathways may help to stabilize food webs following species invasions.

Original languageEnglish (US)
Pages (from-to)1243-1252
Number of pages10
JournalEcology
Volume95
Issue number5
DOIs
StatePublished - May 2014

Keywords

  • Dreissenid mussels
  • Food web
  • Invasive species
  • Lake Michigan
  • Omnivory
  • Stable isotopes

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

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