Roger J. Haro

Effects of Agricultural Land Use on Chironomid Communities: Comparisons Among Natural Wetlands and Farm Ponds

Constructed farm ponds represent a major wetland habitat type in southeastern Minnesota. Farm ponds are subject to a variety of disturbances associated with agricultural land use, especially sedimentation and eutrophication. Chironomid community structure often reflects environmental changes in aquatic ecosystems. However, chironomid communities in farm ponds are poorly understood and their response to short-term increases in sedimentation and eutrophication remains undetermined. We studied relationships between pond-land cover condition and chironomid community structure. Of the 40 ponds selected for the study, 10 were natural, permanent palustrine wetlands. The remaining ponds were constructed habitats (i.e., farm ponds) with 10 in each of the following categories: non-grazed grassland, grazed grassland, and row crop agriculture. Larval chironomids and water quality parameters were collected during early, mid-, and late summer 2001. Total nitrogen concentrations were significantly greater and turbidity was generally greater in grazed grassland ponds as compared to all other pond types. Chironomid communities of grazed grassland ponds were characterized by lower taxonomic richness and abundant chironomids tolerant of increased sedimentation and nutrient enrichment (i.e.,Chironomus andGlyptotendipes). This study determined that agricultural land use, particularly cattle grazing, can markedly affect pond water quality, thereby influencing the chironomid community structure in farm ponds.

The effects of elevated water temperature on native juvenile mussels: implications for climate change

Abstract. Native freshwater mussels are a diverse but imperiled fauna and may be especially sensitive to increasing water temperatures because many species already may be living near their upper thermal limits. We tested the hypothesis that elevated water temperatures (20, 25, 30, and 35°C) adversely affected the survival and physiology of 2-mo-old juvenile mussels (Lampsilis abrupta, Lampsilis siliquoidea, and Megalonaias nervosa) in 28-d laboratory experiments. The 28-d LT50s (lethal temperature affecting 50% of the population) ranged from 25.3 to 30.3°C across species, and were lowest for L. abrupta and L. siliquoidea. Heart rate of L. siliquoidea was not affected by temperature, but heart rate declined at higher temperatures in L. abrupta and M. nervosa. However, for both of these species, heart rate also declined steadily during the experiment and a strong temperature × time interaction was detected. Juvenile growth was low for all species in all treatments and did not respond directly to temperature, but growth of some species responded to a temperature × time interaction. Responses to thermal stress differed among species, but potential laboratory artifacts may limit applicability of these results to real-world situations. Environmentally relevant estimates of upper thermal tolerances in native mussels are urgently needed to assess the extent of assemblage changes that can be expected in response to global climate change.

Burrowing Dragonfly Larvae as Biosentinels of Methylmercury in Freshwater Food Webs

We assessed the utility of larval burrowing dragonflies (Odonata: Anisoptera: Gomphidae) as biosentinels of methylmercury (MeHg) contamination. Gomphids were the most abundant family of dragonflies sampled during 2008-2010 from 17 lakes in four national parks of the northwestern Laurentian Great Lakes region. Ten species of burrowing gomphids were sampled; 13 lakes contained 3 or more species, and 2 species of Gomphus co-occurred in 12 lakes. Most of the total Hg (THg) in whole, late-instar larvae was MeHg, with mean percent MeHg exceeding 60% in 16 lakes. Mean MeHg in larvae of a given species varied greatly among lakes, ranging from 4 to 109 ng g(-1) dry weight. Methylmercury levels in larvae, however, were much less variable within a given lake and species. The mean concentration of MeHg in burrowing gomphids was positively correlated with mean MeHg concentration in unfiltered lake water. Mean concentrations of THg and MeHg in multispecies assemblages of Gomphus were also positively correlated with mean THg in coexisting prey fish and game fishes. We recommend-and provide guidance on-the application of burrowing gomphids as biosentinels of MeHg contamination, which can extend the bioassessment of MeHg to fishless fresh waters.

Differential patterns of infection and life-history expression in native and invasive hosts exposed to a trematode parasite

Non-indigenous species (NIS) are well-recognized as threats to biodiversity worldwide. Yet the interaction between NIS and disease emergence in native habitats remains poorly understood. Bithynia tentaculata is an invasive aquatic snail which is now found in the Upper Mississippi River (UMR). A key concern with this snail is that it harbors trematode parasites (such as Sphaeridiotrema spp.) that have been associated with waterfowl mortality in the region. In this study, we used a combination of field collections and laboratory experiments to better understand the roles that infection competency and host life-history responses play in disease transmission in the UMR. Results from the field and laboratory showed that B. tentaculata infected with Sphaeridiotrema spp. grew to a larger size than uninfected individuals. Although infection was not observed in a number of native species, results from this study suggest that they may still suffer exposure costs (such as reduced growth). Moreover, variability in infection competency between NIS and native snails may dilute or amplify host infection risk. This study reinforces the importance of considering both host life-history responses and competency in systems involving NIS, and provides insight into the factors potentially modulating waterfowl disease in the UMR.

Conspecific cases as alternative grazing surfaces for larval Glossosoma intermedium (Trichoptera:Glossosomatidae)

Abstract Larval Glossosoma intermedium are dominant benthic grazers that often deplete their food resources (periphyton). We observed G. intermedium grazing periphyton from conspecific cases, a possible result of limited resources on stream cobbles, and we hypothesized that case grazing increases when periphyton resources become scarce. This hypothesis was tested by monitoring frequency of case grazing among G. intermedium in 3 streams in southwest Wisconsin for 1 y, and also in the laboratory using time-lapse video of larvae on tiles with and without periphyton. In situ periphyton biomass was higher on larval cases than on the stream cobbles to which larvae had access, irrespective of density, age, or size structure of G. intermedium. Case grazing was positively related to larval densities at 2 of the 3 streams. In laboratory experiments, larval encounter rates were similar in both tile treatments, although frequency and duration of case grazing increased on tiles lacking periphyton. These results suggest that periphyton on G. intermedium cases can provide an important resource patch for this species, especially when periphyton biomass is low in the ambient environment.

Mercury in streams at Grand Portage National Monument (Minnesota, USA): Assessment of ecosystem sensitivity and ecological risk

Mercury (Hg) in water, sediment, soils, seston, and biota were quantified for three streams in the Grand Portage National Monument (GRPO) in far northeastern Minnesota to assess ecosystem contamination and the potential for harmful exposure of piscivorous fish, wildlife, and humans to methylmercury (MeHg). Concentrations of total Hg in water, sediment, and soil were typical of those in forest ecosystems within the region, whereas MeHg concentrations and percent MeHg in these ecosystem components were markedly higher than values reported elsewhere in the western Great Lakes Region. Soils and sediment were Hg-enriched, containing approximately 4-fold more total Hg per unit of organic matter. We hypothesized that localized Hg enrichment was due in part to anthropogenic pollution associated with historic fur-trading activity. Bottom-up forcing of bioaccumulation was evidenced by MeHg concentrations in larval dragonflies, which were near the maxima for dragonflies sampled concurrently from five other national park units in the region. Despite its semi-remote location, GRPO is a Hg-sensitive landscape in which MeHg is produced and bioaccumulated in aquatic food webs to concentrations that pose ecological risks to MeHg-sensitive piscivores, including predatory fish, belted kingfisher, and mink.

Infection Patterns in Invasive and Native Snail Hosts Exposed to a Parasite Associated with Waterfowl Mortality in the Upper Mississippi River, USA

Abstract Bithynia tentaculata is an aquatic invasive snail first detected in the upper Mississippi River (UMR) in 2002. The snail harbors a number of parasitic trematode species, including Sphaeridiotrema pseudoglobulus, that have been implicated in waterfowl mortality in the region. We assessed the capacity of S. pseudoglobulus cercariae to infect B. tentaculata and native snails found in the UMR. Four snail species (one invasive and three native) were individually exposed to S. pseudoglobulus larvae and all were successfully infected. A subsequent experiment examining infection patterns in invasive and native hosts exposed singly or in mixed treatments revealed no difference in parasite establishment among snail species. Our results add to our understanding of S. pseudoglobulus transmission and provide insight into processes underlying waterfowl disease in the UMR.

Stoichiometric relationship between suspension-feeding caddisfly (Trichoptera: Brachycentridae) and seston

Organisms must acquire adequate amounts of carbon (C) and nutrients [i.e., nitrogen (N) and phosphorus (P)] from their food to support growth. The growth of organisms can be constrained by consumer-resource elemental imbalances in C:nutrient ratios, especially in aquatic ecosystems. Furthermore, the elemental composition of aquatic organisms can change through ontogeny, which can impose additional challenges to growth (the growth rate hypothesis), terminal body size, and reproductive output. In streams, growth in larval aquatic insects is influenced primarily by food quality and quantity, temperature, and population density. We conducted a field study that tracked the growth of a common suspension-feeding caddisfly (Brachycentrus occidentalis) through its ontogeny by comparing the elemental composition (C:N:P) of the organism with its available food supply (suspended particulate organic matter or seston). Larvae and seston were sampled from four streams throughout 1 year. Differences in the growth of larvae among the streams were evident, even though the streams possessed similar thermal regimes. Spatial and temporal differences in the nutrient contents of B. occidentalis and seston were observed, suggesting a consumer-resource elemental imbalance. Lower C:P and N:P ratios in food were positively correlated to larval growth rate, suggesting growth was limited by P. The C, N, and P contents in B. occidentalis’ body tissue did change throughout ontogeny. C:nutrient ratios varied across sites during larval development; however, inter-site variation decreased substantially as the populations approached pupation. Ultimately, consumer-resource elemental imbalances during the larval stage did not lead to differences in pre-emergent standing stocks across sites.

Addressing among-group variation in covariate effects using multilevel models

Multilevel models are used to model processes associated with hierarchical data structures. Despite infrequent use in the biological and environmental sciences, the use of these models with hierarchically-structured data conveys multiple advantages. These include the assessment of whether covariate effects differ among groups or clusters, and separate estimation of covariate effects by hierarchical level (thereby addressing atomistic and aggregation fallacy concerns). We illustrate these advantages using larval mayfly count data derived from annual surveys on the Mississippi River and a continuous covariate (water depth).

Digestive physiology comparisons of aquatic invertebrates in the Upper Mississippi River Basin

Limited information is available on the composition of digestive enzymes present in unionid mussels and the zebra mussel, Dreissena polymorpha. Available information is nearly exclusive to species used for culture purposes. A commercially available enzyme assay kit was used to examine the effect of habitat within an ecosystem, season, and species on the activities of several digestive enzymes. We used Amblema plicata to represent native unionids, D. polymorpha, and also Hydropsyche orris as an outgroup to compare differences between mussels and other macroinvertebrates. The data indicated that neither location nor time affect the activities of the digestive enzymes tested; species was the only factor to affect the activity. Differences were found mostly between four enzymes: naphthol-AS-BI-phosphohydrolase, acid phosphatase, alkaline phosphatase, and β-galactosidase.