Martin B. Berg

Benthic Invertebrate Community Responses to Round Goby (Neogobius melanostomus) and Zebra Mussel (Dreissena polymorpha) Invasion in Southern Lake Michigan

The round goby (Neogobius melanostomus Pallas), a fish native to eastern Europe, recently has become established in southwestern Lake Michigan. Because round gobies prey on zebra mussels (Dreissena polymorpha Pallas) and other benthic invertebrates, the effects of round gobies on invertebrates within zebra mussel colonies was investigated. Using a 2 × 3 factorial design, the effects of round gobies (present or absent) and zebra mussel densities (zero, low, and high) on non-mussel invertebrates was examined. Ten ceramic tiles of each mussel density were colonized in the laboratory and then anchored in Calumet Harbor, IL for 10 weeks. Round gobies had access to half the tiles while half were covered with coarse mesh screening that excluded round gobies, but allowed invertebrates to move into and out of the exclosures. Low and high zebra mussel density tiles supported significantly greater numbers of non-mussel invertebrates (p < 0.001) than zero density tiles, particularly amphipods (p < 0.001), hydroptilid caddisflies (p < 0.05), isopods (p < 0.05), and chironomids (p < 0.001). Chlorophyll a concentrations were highest (p < 0.001) at low zebra mussel densities. The presence of round gobies significantly reduced densities of total non-mussel invertebrates (p < 0.01) and leptocerid caddisflies (p < 0.05), resulting in a significant increase in chlorophyll a (p < 0.01) concentrations. A significant zebra mussel density x round goby interaction showed that total invertebrate biomass responded positively to the combined effect of high zebra mussel density and round goby absence. These results demonstrate that round gobies and zebra mussels are altering benthic invertebrate community structure and algal resources in nearshore rocky areas of southwestern Lake Michigan.

Trophic Relationships of Macroinvertebrates

Abstract Aquatic insects around the world exhibit similar morphologies and behaviors even though they are in very different taxonomic groups. This is the basis for the functional feeding group (FFG) method that was initially developed in the early 1960s. Taxonomy is applied only to the level of detail that allows assignment to one of the five FFG categories. These are scrapers adapted to feed on periphyton, shredders adapted to feed on riparian derived plant litter, filtering-collectors adapted to remove fine particle detritus from the water column, gathering-collectors adapted to feed on fine particle detritus where it is deposited on surfaces or in crevices, and predators that capture live prey. In this chapter on trophic relationships, we present (1) the general design of this functional classification system; (2) the basic food resources used by stream macroinvertebrates; (3) how to use the FFG approach in the assessment of the ecological condition of freshwater communities; (4) pictorial keys to identify FFGs; and (5) FFG ratios that can be used as surrogates for stream ecosystem attributes.

Prey Preferences of Eurasian Ruffe and Yellow Perch: Comparison of Laboratory Results with Composition of Great Lakes Benthos

The consumption of benthic macroinvertebrates by ruffe (Gymnocephalus cernuus) and yellow perch (Perca flavescens), two potential competitors in the Great Lakes, was investigated. Laboratory experiments were conducted to determine the food preferences of ruffe and yellow perch and to compare their feeding rates on two types of substrate (sand and cobble). For comparison with natural communities, we sampled benthic macroinvertebrates from western Lake Michigan and compiled published data on invertebrate community structure from all of the Great Lakes. Ruffe and yellow perch both preferentially consumed soft-bodied taxa (e.g., chironomid midge larvae, mayflies, and non-cased caddisflies) and avoided hard-bodied taxa (e.g., cased caddisflies, snails, and clams) in laboratory studies. Prey preferences offish in mixed-fish species treatments were more diverse than those in single-fish species treatments. Ruffe and yellow perch of similar sizes consumed approximately 5% of their body mass per 24 hours at 20°C on sand, whereas their feeding rates were reduced by over 50% on cobble, where prey were likely able to escape predation by hiding. Results from our laboratory experiments, field survey, and review of published studies indicate that oligochaetes and chironomids, the two most numerous macroin-vertebrate taxa in each of the Great Lakes, are vulnerable to ruffe predation. Less abundant taxa range from vulnerable (amphipods, flatworms, and caddisflies) to invulnerable (sphaeriid clams, gastropods, and zebra mussels). Our study suggests that (1) the composition of benthic macroinvertebrate fauna in each of the Great Lakes is suitable for ruffe, and (2) ruffe and yellow perch will likely prefer similar food resources where they co-occur.

Investigating the effect of marine-derived nutrients from spawning salmon on macroinvertebrate secondary production in southeast Alaskan streams

Abstract It is generally accepted that juvenile salmonid production is linked, via bottom-up pathways, to marine-derived nutrient (MDN) inputs from spawning salmon. Many studies have used standing stock biomass estimates of aquatic macroinvertebrates to infer relationships between MDN and secondary production in streams that receive spawners. However, no study has measured aquatic macroinvertebrate secondary production in relation to MDN. To assess the relationship between MDN and aquatic insect production, we measured secondary production of the 5 dominant mayfly genera (Baetis spp., Drunella spp., Cinygmula spp., Epeorus spp., and Rhithrogena spp.) and chironomids throughout the primary growing season in 2 streams in southeastern Alaska. Both streams had upstream reaches blocked from spawning salmonids by a waterfall barrier and downstream reaches that received large spawning runs of pink and chum salmon. Four of the mayfly genera studied (Drunella spp., Cinygmula spp., Epeorus spp., and Rhithrogena spp.) had significantly greater production in upstream than in spawning reaches. Secondary production of Baetis spp. was similar between upstream and spawning reaches. Chironomid production was significantly greater in spawning than in upstream reaches. However, biomass of each taxon was maximized in the spring and summer before the primary period of MDN input. These patterns indicate that another factor, primarily spawning disturbance, is an important driver of benthic insect secondary production in these streams and might provide the community structure within which MDN subsidies occur. If these patterns are common in streams that receive salmon runs, then secondary production-mediated links between MDN and juvenile salmonid production might be mostly the result of responses of chironomids and other benthic organisms with similar life histories.

Chemical amplification in an invaded food web: Seasonality and ontogeny in a high‐biomass, low‐diversity ecosystem

The global spread of invasive species is changing the structure of aquatic food webs worldwide. The North American Great Lakes have proved particularly vulnerable to this threat. In nearshore areas, invasive benthic species such as dreissenid mussels and round gobies (Neogobius melanostomus) have gained dominance in recent years. Such species are driving the flow of energy and material from the water column to the benthic zone, with dramatic effect on nutrient and contaminant cycling. Here, we develop a stage-structured model of a benthified food web in Lake Michigan with seasonal resolution and show how its bioaccumulation patterns differ from expected ones. Our model suggests that contaminant recycling through the consumption of lipid-rich fish eggs and mussel detritus is responsible for these differences. In southern Lake Michigans Calumet Harbor (Chicago, IL, USA), round gobies have nitrogen isotope signatures with considerable spread, with some values higher than their predators and others lower than their prey. Contrary to patterns observed in linear pelagic systems, we predict that polychlorinated biphenyl (PCB) concentrations in these fish decrease with increasing size due to the lipid- and benthos-enriched diets of smaller fish. We also present here round goby PCB concentrations measured in 2005 after an invasional succession in Calumet Harbor and demonstrate how the change from one invasive mussel species to another may have led to a decrease in round goby PCB accumulation. Our results suggest that benthic-dominated systems differ from pelagic ones chiefly due to the influence of detritus and that these effects are exacerbated in systems with low species diversity and high biomass.

Lack of effects of Bacillus sphaericus (Vectolex®) on nontarget organisms in a mosquito-control program in southeastern Wisconsin: A 3-year study

ABSTRACT A 3-year study (2000–2002) in southeastern Wisconsin was conducted to assess the effects of Bacillus sphaericus applied for mosquito control on nontarget wetland invertebrates. The experimental design consisted of control and treatment sites (that were applied by helicopter with Vectolex® CG), each in 2 vegetation habitat types: reed canary grass marsh (Phalaris arundinacea) and cattail marsh (Typha spp.). In each of these areas, a predetermined number of timed (30-sec) D-frame aquatic net samples containing vegetation, detritus, and invertebrates were collected 1 day before spraying and 72 h after spraying to detect for effects. We examined and compared 5 bioassessment measures to determine if there was an effect of B. sphaericus on nontarget organisms during each of the sampling years. The metrics tested were 1) mean taxa richness (the mean number of all taxa), 2) mean diversity (combines taxa richness and abundances in a summary statistic; i.e., Shannon Index [H′]), 3) Diptera richness (minus mosquitoes) as a proportion of all other taxa richness (Diptera/others richness), 4) Diptera abundance (minus mosquitoes) as a proportion of all other invertebrate abundance (Diptera/others abundance), and 5) functional group changes in percent collector–gatherers, collector–filterers, scrapers, shredders, and predators. When Vectolex was applied during 6 treatments at the labeled dosage rate in the above habitats in Brookfield, WI, no detrimental effects to nontarget organisms could be attributed to this microbial insecticide. Much of the variation in the control vs. treatment and pre vs. post plots was attributed to factors other than the effects of B. sphaericus on nontarget organisms, such as the time of sampling, natural variation that occurs in such diverse habitats as canary grass and cattail marshes, and water depth, which varied among years.

Chapter 113 – Growth, Individual

Publisher Summary This chapter discusses growth in insects. Growth can be measured as an increase in biomass or body size, although biomass can be more variable than body size owing to differences in food and water intake. The limited ability of the rigid exoskeleton of insects to expand imposes a considerable constraint on individual growth resulting in the necessity to shed the old exoskeleton, a process termed ecdysis, for growth to continue. Some insects exhibit indeterminate growth and continue to molt even after reaching the adult stage, although little if any increase in biomass occurs. In contrast, the majority of insects exhibit determinate growth in which both growth and molting cease upon reaching the reproductively mature last instar. The pattern of individual growth differs depending on whether growth is measured as an increase in biomass or as an increase in body size. When measured as an increase in biomass, individual growth occurs between molts and is more or less continuous in most insects, although decreases in biomass often occur at the time of molting. When measured as an increase in body size, however, individual growth is largely dependent on the amount of sclerotization of the insect or of a particular body part. Different body parts of insects may exhibit either isometric or allometric growth compared with the body as a whole. Isometric growth occurs when body parts grow at the same rate as the body as a whole, i.e., body length. Allometric growth occurs when body parts grow at rates different from that of the body.

Getting the Most from Data — Maximizing Information and Power by Using Appropriate and Modern Statistical Methods

Through a series of carefully chosen illustrations from biometry and biomedicine, this note underscores the importance of using appropriate analytical techniques to increase power in statistical modeling and testing. These examples also serve to highlight some of the important recent devel- opments in applied statistics of use to practitioners.