Response of Benthic Macroinvertebrates to Whole-Lake, Non-Native fish Treatments in Mid-Elevation Lakes of the Trinity Alps, California
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Hydrobiologia (2013) 714:201–215 DOI 10.1007/s10750-013-1537-2 PRIMARY RESEARCH PAPER Response of benthic macroinvertebrates to whole-lake, non-native fish treatments in mid-elevation lakes of the Trinity Alps, California Karen L. Pope • Erin C. Hannelly Received: 20 February 2013 / Revised: 18 April 2013 / Accepted: 28 April 2013 / Published online: 15 May 2013 Ó Springer Science+Business Media Dordrecht (outside the USA) 2013 Abstract Introduced fish reduce the abundance and were not affected by treatment. Taxon richness of diversity of native aquatic fauna, but the effect can be macroinvertebrates was about 40% greater in the reduced in complex habitats. We manipulated fish control lakes compared to the treatment lakes but did populations in forested mountain lakes to determine not differ among treatments. Our results suggest that whether or not fish affected benthic macroinvertebrate fish reduce susceptible macroinvertebrate richness and composition across lakes with differing habitat abundances, but that changes associated with altera- complexity. We compared abundance, biomass, body- tions of fish composition are confounded by other length, and community structure of benthic macroin- factors in complex lake habitats. vertebrates from 16 lakes with three treatments (fish stocked, suspended stocking, fish removed) and Keywords Aquatic insects Á Introduced trout Á unstocked fishless ‘‘controls’’. Over 4 years, we Habitat complexity Á Libellula Á Chironomidae Á assessed the relative importance of fish and environ- Klamath Mountains mental variables influencing the composition of ben- thic macroinvertebrates. Control lakes had the greatest overall abundance of macroinvertebrates when chi- Introduction ronomid midges were excluded. Abundances of insects in the clinger/swimmer functional group and Macroinvertebrate assemblages in lakes are deter- caddisflies were greatest in the control lakes but were mined by both abiotic and biotic factors and the primarily influenced by habitat variables including the regional pool of colonizing species. Abiotic conditions availability of aquatic vegetation and wood. Total such as temperature and pH set habitat parameters that biomass and mean body length of macroinvertebrates limit the potential macroinvertebrate assemblage, and then biological interactions such as competition and predation determine the composition of a given Handling editor: Katya E. Kovalenko community (Wellborn et al., 1996; de Mendoza et al., 2012). The constantly changing interactions K. L. Pope (&) USDA Forest Service, Pacific Southwest Research between abiotic and biotic factors within lakes create Station, 1700 Bayview Dr., Arcata, CA 95521, USA distinct macroinvertebrate assemblages (McPeek, e-mail: [email protected] 1998; Blumenshine et al., 2000). While each lake supports a unique biota, lakes are E. C. Hannelly Department of Biological Sciences, Humboldt State susceptible to widespread influences that may be University, 1 Harpst St., Arcata, CA 95521, USA strong enough to cause similar responses in community 123 202 Hydrobiologia (2013) 714:201–215 structure across landscapes. For instance, large-scale macrophytes provided refugia for benthic macroin- introductions of predatory fishes into naturally fishless vertebrates so that fish were unable to effectively prey lakes have had some significant and characteristic upon them. effects on aquatic invertebrate populations over wide Most field studies assessing the impacts of nonna- geographic areas (Carlisle & Hawkins, 1998;McNaught tive trout on invertebrates have focused on alpine et al., 1999; Knapp et al., 2001; Nystrom et al., 2001; habitats and have not used lake-scale experimental Resetarits, 2001; Angelon & Petranka 2002;Knapp manipulations. We implemented a 4-year, whole-lake et al., 2005). Fish are visual predators that reduce manipulative experiment in a subalpine-mixed conifer nektonic, large-bodied, or otherwise conspicuous aqua- zone of the Klamath Mountains in northern California tic insects, especially predators (Carlisle & Hawkins, to determine whether or not fish affected benthic 1998; Blumenshine et al., 2000;Reshetnikov,2003; macroinvertebrate composition in complex montane Glaz et al., 2012). Benthivorous fishes are assumed to lake habitats. The Klamath Mountains reach 2,751 m have stronger predatory effect on benthic macroinver- elevation and are known for their high levels of biotic tebrates than salmonids, though as generalist feeders, diversity and endemism (Coleman & Kruckeberg, salmonid species also have strong negative effects on 1999; DellaSala et al., 1999). Similar to lakes in much benthic taxa (Carlisle & Hawkins, 1998). For example, of the mountainous western U.S., lakes in the Klamath Glaz et al. (2012) used stable isotopes to determine that Mountains were formed when large glaciers retreated brook trout (Salvelinus fontinalis) derived 60–90% of its during the Pleistocene epoch and scoured the land- carbon from benthic predatory macroinvertebrates. In scape, leaving behind numerous large bodies of some cases, introductions of predatory fish have been freshwater, which were isolated from lower elevation shown to change food webs and induce trophic cascades fish-bearing waters by steep cascades. The majority of (Schindler et al., 2001;Simon&Townsend,2003; these historically fishless lakes have been stocked with Baxter et al., 2004;Knightetal.,2005). For example, salmonids, primarily brook trout (S. fontinalis) and Knight et al. (2005) found that fish predation on rainbow trout (Oncorhynchus mykiss). Introduced dragonfly larvae indirectly facilitates near-shore terres- trout are found in approximately 85% of the lakes trial vegetation reproduction via an increase in insect deeper than 2 m in the Klamath Mountains (Welsh pollinators released from the predation pressure of adult et al., 2006). dragonflies. We previously assessed the effects of 3 fish However, the physical characteristics of a lake can treatments (fish stocked, temporarily suspended fish affect the resilience of its food web to the introduction stocking, fish removed) on a range of aquatic fauna of a predator. Simple systems, such as alpine lakes including amphibians, garter snakes (Thamnophis have low primary productivity, little heterogeneity in atratus and T. sirtalis), and emerging aquatic insects. substrate, and minimal aquatic vegetation or woody We found significant differences in the fish-containing debris, and therefore, the effects of fish predation on lakes compared to lakes where we removed fish and aquatic invertebrates can be substantial (Gilinsky, naturally fishless lakes in terms of abundance and 1984; Diehl, 1992; Wellborn et al., 1996; Carlisle & survival of Cascades frogs (Rana cascadae) (Pope, Hawkins, 1998; Knapp et al., 2001; Epanchin et al., 2008), composition of aquatic garter snakes (Pope 2010). More complex systems, such as lakes within et al., 2008), and abundance and composition of forested landscapes have higher primary productivity, emerging aquatic insects (Pope et al., 2009). The more substrate heterogeneity, and increased presence assessment of the responses of aquatic insects to fish of aquatic macrophytes and terrestrially derived treatments focused on adult phases as they emerged woody debris (Horne & Goldman, 1994; Knapp from the water, but also included a gross assessment of et al., 2005). Littoral zone structure reduces the large-bodied ([4 mm) benthic taxa collected in 2006. foraging efficiency of visually feeding fishes, which For the analyses of benthic insects, Pope et al. (2009) puts differential predator pressure on different taxa grouped the insects into four categories: trichopterans, depending on their niche, life history or behavioral ephemeropterans, dipterans, and large predators responses to fish presence (Crowder & Cooper, 1982; (Odonata, Megaloptera, Coleoptera). Gilinsky, 1984; Diehl, 1992; Fisher et al., 2012). Here we take a more detailed look at the benthic For example, Gilinsky (1984) found that artificial invertebrate composition and structure at a higher 123 Hydrobiologia (2013) 714:201–215 203 taxonomic resolution over the 4-year study to specif- surveys. Fish were removed by setting numerous gill ically examine effects on benthic community structure nets repeatedly in the lakes throughout the fall across treatments and habitat characteristics. We following methods described in Knapp and Matthews expected to see a difference in the benthic insect (1998). Eight nets were left in each lake through the community in the treatment lakes compared to the winter and netting continued in the spring of 2004. In fish-free control lakes but that the effect would 2005, we noticed a fish in one of the removal lakes decrease in lakes with increasing aquatic habitat (Echo Lake). While trout did recover in the lake in the complexity. We tested for differences in macroinver- following years, we include the lake in the removal tebrate abundance, body-length, biomass, and com- treatment because we believe the fish population was munity structure in relation to treatment and habitat, reduced enough to be effectively treated during the and tested whether the response variables changed study period. The other three removal lakes remained over 3 years in the fish removal lakes. In addition, we fish-free throughout the study. We determined fish compared responses of specific taxa that were found a density in the stocked and stocking suspended lakes by posteriori to differ in abundance in the presence or setting gill nets in the beginning of each field season absence of predatory