Jon M. Vallazza

Fatty Acid Composition at the Base of Aquatic Food Webs Is Influenced by Habitat Type and Watershed Land Use

Spatial variation in food resources strongly influences many aspects of aquatic consumer ecology. Although large-scale controls over spatial variation in many aspects of food resources are well known, others have received little study. Here we investigated variation in the fatty acid (FA) composition of seston and primary consumers within (i.e., among habitats) and among tributary systems of Lake Michigan, USA. FA composition of food is important because all metazoans require certain FAs for proper growth and development that cannot be produced de novo, including many polyunsaturated fatty acids (PUFAs). Here we sampled three habitat types (river, rivermouth and nearshore zone) in 11 tributaries of Lake Michigan to assess the amount of FA in seston and primary consumers of seston. We hypothesize that among-system and among-habitat variation in FAs at the base of food webs would be related to algal production, which in turn is influenced by three land cover characteristics: 1) combined agriculture and urban lands (an indication of anthropogenic nutrient inputs that fuel algal production), 2) the proportion of surface waters (an indication of water residence times that allow algal producers to accumulate) and 3) the extent of riparian forested buffers (an indication of stream shading that reduces algal production). Of these three land cover characteristics, only intense land use appeared to strongly related to seston and consumer FA and this effect was only strong in rivermouth and nearshore lake sites. River seston and consumer FA composition was highly variable, but that variation does not appear to be driven by the watershed land cover characteristics investigated here. Whether the spatial variation in FA content at the base of these food webs significantly influences the production of economically important species higher in the food web should be a focus of future research.

Measuring spatial variation in secondary production and food quality using a common consumer approach in Lake Erie

Lake Erie is a large lake straddling the border of the USA and Canada that has become increasingly eutrophic in recent years. Eutrophication is particularly focused in the shallow western basin. The western basin of Lake Erie is hydrodynamically similar to a large estuary, with riverine inputs from the Detroit and Maumee Rivers mixing together and creating gradients in chemical and physical conditions. This study was driven by two questions: (1) How does secondary production and food quality for consumers vary across this large mixing zone? and (2) Are there correlations between cyanobacterial abundance and secondary production or food quality for consumers? Measuring spatial and temporal variation in secondary production and food quality is difficult for a variety of logistical reasons, so here a common consumer approach was used. In a common consumer approach, individuals of a single species are raised under similar conditions until placed in the field across environmental gradients of interest. After some period of exposure, the response of that common consumer is measured to provide an index of spatial variation in conditions. Here, a freshwater mussel (Lampsilis siliquoidea) was deployed at 32 locations that spanned habitat types and a gradient in cyanobacterial abundance in the western basin of Lake Erie to measure spatial variation in growth (an index of secondary production) and fatty acid (FA) content (an index of food quality). We found secondary production was highest within the Maumee river mouth and lowest in the open waters of the lake. Mussel tissues in the Maumee river mouth also included more eicosapentaenoic and docosapentaenoic fatty acids (EPA and DPA, respectively), but fewer bacterial FAs, suggesting more algae at the base of the food web in the Maumee river mouth compared to open lake sites. The satellite-derived estimate of cyanobacterial abundance was not correlated to secondary production, but was positively related to EPA and DPA content in the mussels, suggesting more of these important FAs in locations with more cyanobacteria. These results suggest that growth of secondary consumers and the availability of important fatty acids in the western basin are centered on the Maumee river mouth.

Effects of food resources on the fatty acid composition, growth and survival of freshwater mussels

Increased nutrient and sediment loading in rivers have caused observable changes in algal community composition, and thereby, altered the quality and quantity of food resources available to native freshwater mussels. Our objective was to characterize the relationship between nutrient conditions and mussel food quality and examine the effects on fatty acid composition, growth and survival of juvenile mussels. Juvenile Lampsilis cardium and L. siliquoidea were deployed in cages for 28 d at four riverine and four lacustrine sites in the lower St. Croix River, Minnesota/Wisconsin, USA. Mussel foot tissue and food resources (four seston fractions and surficial sediment) were analyzed for quantitative fatty acid (FA) composition. Green algae were abundant in riverine sites, whereas cyanobacteria were most abundant in the lacustrine sites. Mussel survival was high (95%) for both species. Lampsilis cardium exhibited lower growth relative to L. siliquoidea (p <0.0001), but growth of L. cardium was not significantly different across sites (p = 0.13). In contrast, growth of L. siliquoidea was significantly greater at the most upstream riverine site compared to the lower three lacustrine sites (p = 0.002). In situ growth of Lampsilis siliquoidea was positively related to volatile solids (10 – 32 μm fraction), total phosphorus (<10 and 10 – 32 μm fractions), and select FA in the seston (docosapentaeonic acid, DPA, 22:5n3; 4,7,10,13,16-docosapentaenoic, 22:5n6; arachidonic acid, ARA, 20:4n6; and 24:0 in the <10 and 10 – 32 μm fractions). Our laboratory feeding experiment also indicated high accumulation ratios for 22:5n3, 22:5n6, and 20:4n6 in mussel tissue relative to supplied algal diet. In contrast, growth of L. siliquiodea was negatively related to nearly all FAs in the largest size fraction (i.e., >63 μm) of seston, including the bacterial FAs, and several of the FAs associated with sediments. Reduced mussel growth was observed in L. siliquoidea when the abundance of cyanobacteria exceeded 9% of the total phytoplankton biovolume. Areas dominated by cyanobacteria may not provide sufficient food quality to promote or sustain mussel growth.

Do Water Level Fluctuations Influence Production of Walleye and Yellow Perch Young-of-the-Year in Large Northern Lakes?

AbstractMany ecological processes depend on the regular rise and fall of water levels (WLs), and artificial manipulations to WL regimes can impair important ecosystem services. Previous research has suggested that differences in WL between late summer and early spring may alter the suitability of shoals used by Walleyes Sander vitreus for spawning. Other species, such as the Yellow Perch Perca flavescens, are unlikely to be affected in the same way by WL fluctuations because their spawning requirements are quite different. We used 11–23 years of data from six northern Minnesota lakes to assess the effects of WL fluctuations on the abundances of young-of-the-year (age-0) Walleyes and Yellow Perch. In two lakes (Rainy Lake and Lake Kabetogama), a change in WL management occurred in 2000, after which these lakes saw increased age-0 Walleye abundance, while the other study lakes experienced decreases or no change. Rainy Lake and Lake Kabetogama also had increases in age-0 Yellow Perch, but another study lake ...

Genetic Analysis Shows that Morphology Alone Cannot Distinguish Asian Carp Eggs from Those of Other Cyprinid Species

AbstractFish eggs and embryos (hereafter collectively referred to as “eggs”) were collected in the upper Mississippi River main stem (~300 km upstream of previously reported spawning by invasive Asian carp) during summer 2013. Based on previously published morphological characteristics, the eggs were identified as belonging to Asian carp. A subsample of the eggs was subsequently analyzed by using molecular methods to determine species identity. Genetic identification using the cytochrome-c oxidase 1 gene was attempted for a total of 41 eggs. Due to the preservation technique used (formalin) and the resulting DNA degradation, sequences were recovered from only 17 individual eggs. In all 17 cases, cyprinids other than Asian carp (usually Notropis sp.) were identified as the most likely species. In previously published reports, a key characteristic that distinguished Asian carp eggs from those of other cyprinids was size: Asian carp eggs exhibited diameters ranging from 4.0 to 6.0 mm and were thought to be m...

Using Pharyngeal Teeth and Chewing Pads to Estimate Juvenile Silver Carp Total Length in the La Grange Reach, Illinois River

AbstractThe Silver Carp Hypophthalmichthys molitrix is an invasive species in the Mississippi River basin; an understanding of their vulnerability to predation as juveniles may inform control by native predators and predator enhancement (e.g., stocking). Digestion of Silver Carp prey recovered from diets makes it difficult to determine the size-classes that are most vulnerable to predation by native fishes. The objective of this study was to determine whether the sizes of the chewing pad (CP), pharyngeal teeth (PT), and pharyngeal arch (PA)—the Silver Carp structures most often found intact in predator diets—were predictive of the TL of prey Silver Carp. During 2014 and 2015, juvenile Silver Carp (n = 136; <180 mm) were collected using 60-Hz pulsed-DC electrofishing and mini-fyke nets in the La Grange reach of the Illinois River. We extracted Silver Carp CPs (n = 136 fish) and PAs with PT intact (n = 129 fish) and measured CP length (CPL) and width (CPW), eight reproducible PT landmarks (PT1L–PT4L; PT1W–P...

Erratum to: Using a gradient in food quality to infer drivers of fatty acid content in two filter-feeding aquatic consumers

Inferences about ecological structure and function are often made using elemental or macromolecular tracers of food web structure. For example, inferences about food chain length are often made using stable isotope ratios of top predators and consumer food sources are often inferred from both stable isotopes and fatty acid (FA) content in consumer tissues. The use of FAs as tracers implies some degree of macromolecular conservation across trophic interactions, but many FAs are subject to physiological alteration and animals may produce those FAs from precursors in response to food deficiencies. We measured 41 individual FAs and several aggregate FA metrics in two filter-feeding taxa to (1) assess ecological variation in food availability and (2) identify potential drivers of among-site variation in FA content. These taxa were filter feeding caddisflies (Family Hydropyschidae) and dreissenid mussels (Genus Dreissena), which both consume seston. Stable isotopic composition (C and N) in these taxa co-varied across 13 sites in the Great Lakes region of North America, indicating they fed on very similar food resources. However, co-variation in FA content was very limited, with only one common FA co-varying across this gradient (α-linolenic acid; ALA), suggesting these taxa accumulate FAs very differently even when exposed to the same foods. Based on these results, among-site variation in ALA content in both consumers does appear to be driven by food resources, along with several other FAs in dreissenid mussels. We conclude that single-taxa measurements of FA content cannot be used to infer FA availability in food resources.

Evidence of Asian Carp Spawning Upstream of a Key Choke Point in the Mississippi River

AbstractBighead Carp Hypophthalmichthys nobilis, Silver Carp H. molitrix, and Grass Carp Ctenopharyngodon idella (collectively termed “Asian carp”) were introduced into North America during the 1960s and 1970s and have become established in the lower Mississippi River basin. Previously published evidence for spawning of these species in the upper Mississippi River has been limited to an area just downstream of Dam 22 (near Saverton, Missouri). In 2013 and 2014, we sampled ichthyoplankton at 18 locations in the upper Mississippi River main stem from Dam 9 through Dam 19 and in four tributaries of the Mississippi River (Des Moines, Skunk, Iowa, and Wisconsin rivers). We identified eggs and larvae by using morphological techniques and then used genetic tools to confirm species identity. The spawning events we observed often included more than one species of Asian carp and in a few cases included eggs that must have been derived from more than one upstream spawning event. The upstream extent of genetically co...