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Nearshore energy subsidies support Lake Michigan fishes and invertebrates following major changes in food web structure
Author(s) -
Turschak Benjamin A.,
Bunnell David,
Czesny Sergiusz,
Höök Tomas O.,
Janssen John,
Warner David,
Bootsma Harvey A.
Publication year - 2014
Publication title -
ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.144
H-Index - 294
eISSN - 1939-9170
pISSN - 0012-9658
DOI - 10.1890/13-0329.1
Subject(s) - pelagic zone , benthic zone , food web , profundal zone , invertebrate , ecology , fishery , predation , benthos , biology , environmental science , oceanography , geology
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 13 C: 12 C (δ 13 C) and 15 N: 14 N (δ 15 N) 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 δ 13 C 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 δ 13 C 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. δ 15 N shifts were more variable and of smaller magnitude across taxa, although declines in δ 15 N 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.