Planktivory in the changing Lake Huron zooplankton community: Bythotrephes consumption exceeds that of Mysis and fish

Abstract

1. Oligotrophic lakes are generally dominated by calanoid copepods because of their competitive advantage over cladocerans at low prey densities. Planktivory also can alter zooplankton community structure. We sought to understand the role of planktivory in driving recent changes to the zooplankton community of Lake Huron, a large oligotrophic lake on the border of Canada and the United States. We tested the hypothesis that excessive predation by fish (rainbow smelt Osmerus mordax, bloater Coregonus hoyi) and invertebrates (Mysis relicta, Bythotrephes longimanus) had driven observed declines in cladoceran and cyclopoid copepod biomass between 2002 and 2007. 2. We used a field sampling and bioenergetics modelling approach to generate estimates of daily consumption by planktivores at two 91-m depth sites in northern Lake Huron, U.S.A., for each month, May-October 2007. Daily consumption was compared to daily zooplankton production. 3. Bythotrephes was the dominant planktivore and estimated to have eaten 78% of all zooplankton consumed. Bythotrephes consumption exceeded total zooplankton production between July and October. Mysis consumed 19% of all the zooplankton consumed and exceeded zooplankton production in October. Consumption by fish was relatively unimportant -eating only 3% of all zooplankton consumed. 4. Because Bythotrephes was so important, we explored other consumption estimation methods that predict lower Bythotrephes consumption. Under this scenario, Mysis was the most important planktivore, and Bythotrephes consumption exceeded zooplankton production only in August. 5. Our results provide no support for the hypothesis that excessive fish consumption directly contributed to the decline of cladocerans and cyclopoid copepods in Lake Huron. Rather, they highlight the importance of invertebrate planktivores in structuring zooplankton communities, especially for those foods webs that have both Bythotrephes and Mysis. Together, these species occupy the epi-, meta-and hypolimnion, leaving limited refuge for zooplankton prey.

Invasive species triggers a massive loss of ecosystem services through a trophic cascade

“…These findings show a cascading impact of Bythotrephes that has not been previously documented in other lakes (21) and that is unusually large for an invertebrate predator (28). Possibly, this effect is related to the feeding mode of Bythotrephes vs. other invertebrate predators (18,29,30), and this topic could be addressed by additional research.…”

“…The spiny water flea, Bythotrephes longimanus (hereafter Bythotrephes), which is nonnative in North America, is a voracious zooplanktivore that has the capacity to consume more zooplankton than fish and other invertebrate planktivores combined (18). Despite this planktivory and large documented ecological impacts on zooplankton communities (19,20), Bythotrephes has not been found to have cascading effects on lake primary production and water clarity (21).…”

Changes in zooplankton community structure associated with the disappearance of invasive alewife in Saginaw Bay, Lake Huron

“…These filter feeders contributed to dramatic reductions in water column light attenuation, phosphorous levels, and chlorophyll concentrations in Saginaw Bay . Further, heightened planktivory by the invasive invertebrate Bythotrephes longimanus may exert a structuring influence on zooplankton communities in Lake Huron (Bunnell et al 2011).…”

Effects of Bythotrephes longimanus (Crustacea, Cladocera) on the abundance, morphology, and prey community of Leptodora kindtii (Crustacea, Cladocera)

“…Recent studies have suggested that Bythotrephes can consume large portions of zooplankton productivity (Strecker & Arnott, 2008;Bunnell et al, 2011), yet a number of planktivorous fish may avoid consuming Bythotrephes (Barnhisel & Kerfoot, 2004) or experience lower net growth because Bythotrephes spines occupy gut space but have no nutritional value (Parker Stetter et al, 2005), resulting in an overall loss of food available to planktivores. This reduced availability of energy may drive planktivores to forage on other resources, such as large-bodied Leptodora.…”