Christopher M. Pennuto

Fish and Macroinvertebrate Communities in Tributary Streams of Eastern Lake Erie with and without Round Gobies (Neogobius melanostomus, Pallas 1814)

Round gobies have had significant impacts on benthic fish and invertebrate communities in nearshore habitats of the Great Lakes. As round gobies have become more abundant in lake habitats, there has been an expansion of their populations into tributary streams and rivers. We compared stream invertebrate and fish communities in New York tributaries to Lake Erie with round gobies present and absent. Four of six benthic invertebrate metrics differed between streams with and without round gobies. Streams with round gobies present had reduced Shannon diversity, EPT richness, and EPT/chironomid ratios, and increased macroinvertebrate density relative to streams without round gobies, but there was no difference in non-Diptera density, or total taxa richness. None of the four fish metrics examined differed between streams with and without round gobies. However, darters occurred in all streams lacking round gobies, but did not occur in any streams with round gobies. Comparisons with historical fish and macroinvertebrate distributional data support our suspicion of goby-induced community changes. In these New York streams, round gobies seem to have had significant impacts on invertebrate communities via their consumptive behavior, whereas the impacts on fish communities are less evident. If round gobies continue to expand their distribution inland, the resultant alterations in macroinvertebrate communities may impact the suitability of tributary streams as spawning and nursery habitat for several sport fish species and for energy dynamics in tributary streams.

Short-term predator avoidance behavior by invasive and native amphipods in the Great Lakes

Understanding predator avoidance behavior by prey remains an important topic in community and invasion ecology. Recently, the Ponto-Caspian amphipod Echinogammarus ischnus (Stebbing 1898) was accidentally introduced into the Great Lakes. Since its introduction, it has displaced the native amphipod, Gammarus fasciatus (Say 1818), from several locations in the lower lakes. To assess whether behavioral differences in predator avoidance might be a causal mechanism increasing the success of the invasive amphipods, two experiments were conducted examining (1) native and invasive amphipod behavioral responses to five fish species with different foraging behaviors, and (2) amphipod responses to different densities of round gobies, a hyper-abundant benthic invertivore. Echinogammarus reduced its distance moved in the presence of all fish species tested, whereas Gammarus reduced its distance moved only after exposure to round gobies, black crappies, and rainbow darters. Both amphipod species increased the time spent motionless following exposure to round gobies, but not after encountering the scent of most of the remaining fish predators. The exception was that Echinogammarus also responded to black crappie scent whereas Gammarus did not. Although both amphipod species exhibited behavioral responses to many of the fish predators, the magnitude of their responses differed only after exposure to the brown bullhead. In the bullhead trials, Echinogammarus reduced its distance traveled significantly more than Gammarus. Both amphipod species increased their avoidance response to increasing goby density, however, the pattern of avoidance behavior was different. Invasive E. ischnus exhibited a consistently strong avoidance response to round gobies over the test duration. Native G. fasciatus initially avoided goby scent, but then either ceased their avoidance response or showed a hyper-avoidance response, depending on goby density. These results suggested (1) both species of amphipods were able to differentiate and react to a variety of fish predators, (2) invasive Echinogammarus amphipods avoided a larger range of fish predators than the native Gammarus, (3) increased avoidance behavior was associated with an increased density of fish, and (4) the avoidance response patterns of invasive Echinogammarus when faced with round goby predators might lead to increased predation on native Gammarus in habitats where they co-occur.

INCIDENCE OF CHIRONOMID PHORETICS ON HELLGRAMMITES IN STREAMS OF SOUTHERN MAINE

Hellgrammite nymphs (Nigronia serricornis Say) were collected in streams of southern Maine, 1995-1996, to assess the rate of phoresy by midge larvae. The number, location, and identification of phoretic midge larvae (Diptera: Chironomidae) were recorded for each nymph. Nanocladius (Plecopteracoluthus) n. sp. was the only chironomid species identified from hellgrammite hosts. Phoretic midges occurred in three of four populations and were observed on approximately 55% of all individuals examined (n = 108). However, frequency of phoresy ranged from 0 to 86.4%, depending on the stream. Midge phoretics occurred at a mean rate of over 1.5 per host and the number of phoretics was significantly correlated with host head capsule width. The dorsum of the first abdominal segment was the most frequent attachment site for midges. Observed frequency of phoresy in these streams were similar to published rates for chironomid/hellgrammite associations. This is the first documentation of chironomid phoresy on hellgrammites in Maine.

Population dynamics and intraspecific interactions of an ectosymbiotic midge in a river in southern Maine, USA

Ectosymbioses between the Chironomidae and their hosts continue to be documented, but life-history details are not well known. I investigated population dynamics of the commensal midge Nanocladius (Plecopteracoluthus) sp. #5 over a 3-y period to understand the importance of intraspecific interactions in determining host and attachment site use. Patterns of infestation intensity and prevalence on hosts indicated a peak spring emergence, though emergence extended throughout the open-water period. There was no difference in emergence timing of adults, indicating population synchrony. Temperature played a key role in directing life-history events. As temperature increased in the spring, midges migrated to the dorsal thorax for pupation and this migration coincided with an increase in aggressive behavior by resident midges. The density distribution on hosts suggested these midges detected and attached to hosts in a random manner, but that territorial behaviors and age were important in determining tube-attachment position following host location. The largest midges invariably occurred on the ventral thorax of hosts harboring multiple commensals. In addition, if a midge occurred singly on a host, regardless of instar, it was positioned most anterior on hosts, indicating attachment position was not age-specific. Midges exhibited some ability to discriminate suitable hosts, but further investigations into the cues used by ectosymbionts to detect potential hosts and appropriate-age hosts are warranted.

Seasonal Position Patterns and Fate of a Commensal Chironomid on its Fishfly Host

ABSTRACT Changes in attachment sites of a commensal chironomid, Nanocladius (Plecopteracoluthus) sp. (Diptera: Chironomidae), on the body of its host, Nigronia serricornis (Megaloptera: Corydalidae), were observed in laboratory streams over a 13-week winter period and a 6-week spring period to determine seasonal movement patterns and emergence success. All chironomid commensals were lost from their hosts by the end of the winter study and no emergence was observed. During winter, chironomids resided in the same tube location on hosts for approximately three weeks before changing positions or being lost from hosts. Vacated tubes remained attached to hosts for an average of 3.6 weeks. Eight re-position movements were documented on host bodies and six midges colonized new hosts in the stream. New colonizations occurred most frequently on previously colonized hosts. During spring observations, commensal midges migrated from the abdomen and ventral thorax to the lateral thorax prior to pupation. Emergence occu...

Effects of larval movement behavior and density on emergence success and adult body size in a commensal midge

Changes in larval density and movement behavior of a commensal midge, Nanocladius (Plecopteracoluthus) sp. #4, were monitored for 26 weeks in recirculating laboratory streams. Adults were captured at emergence, sexed, and weighed to assess the effect of larval density and movement behavior on emergence success and adult size. The density of midges on hosts declined with time and coincided with a springtime increase in larval movement frequency. Midges residing on hosts with high spring densities emerged significantly less than midges on hosts with low densities. Resident midge density on hosts did not influence the likelihood of successful colonization by commensals and colonizers showed no preference for initial attachment site on hosts. However, colonizing midges emerged significantly less than resident midges. Similarly, successful emergers changed tube positions significantly less often as larvae relative to non-emergers. There was no difference in adult body weight of resident midges and colonists/movers, but adult males which emerged from commensal-laden (high density) hosts were significantly smaller than males from low density hosts. These data indicate larval density and movement behavior may have strong fitness consequences for commensal midges.

Use of Benthic Macroinvertebrate Indices to Assess Aquatic Health in a Mixed-Landuse Watershed

ABSTRACT Seven family-level metrics were determined from benthic macroinvertebrate samples collected monthly across four different landuse sites in the Cazenovia Creek watershed in western New York. We evaluated which metrics were most appropriate for, and effective in, discerning differences among the sites. Dramatic and consistent seasonal differences in metric scores were observed across all sites. All metric scores indicated markedly better biological health during winter months than during summer months. The biological impairment designation was highest in the summer at the suburban and agricultural sites. Coefficients of variation were considerably greater at the lower stream order sites. The metrics that were most appropriate and effective in assessing benthic assemblage health in this study were: richness, percent model affinity, family-level biotic index, and Ephemeroptera-Plecoptera-Trichoptera index. These indices correlated with a low amount of redundancy in a Pearson matrix, had significant discriminatory power in assessing biological impairments across sites, and had low variation within sites and seasons. This suggests these metrics should be selected for bioassessments in similar Great Lakes watersheds.

Seasonal Differences in Predator-prey Behavior in Experimental Streams

Abstract Invertebrate prey have been shown to select suboptimal resource patches in the face of predation (the food-predation risk trade-off). The foraging strategy used by a predator and the environmental context under which an interaction occurs potentially mediates prey responses to predators. Here, I determined whether season, predator presence or alternative prey availability affected prey patch use when faced with a sit-and-wait predator from streams in southern Maine. In addition, instantaneous mortality rates and predator movement behavior were assessed as possible mechanisms explaining patch use by prey in different seasons. In the absence of predators, prey did not show any preference for substrate patches based on particle size. But, depending on prey type and season, substrate position in streams had a significant effect on prey survival. Mayflies survived most in summer when pebble substrates were located upstream whereas caddisfly survival was highest when pebble substrates were located downstream in winter. Season and taxa significantly affected instantaneous mortality rates, suggesting this predator responded differently to available prey in each season. Predators changed ambush positions in the streams significantly more during winter than during summer, both with and without prey present. The presence of caddisflies in mixed-prey trials reduced consumption of mayflies in summer, but increased their mortality in winter. Increased movement behavior of predators in winter may have led to greater encounters with prey, thus increasing winter mortality. Collectively, these data reveal season can influence the outcome of predator-prey interactions. Environmental context, as well as predation mode, is critical to predicting predation effects in macroinvertebrate communities. Further studies of the seasonal changes in organism-specific behavior are needed to evaluate the importance of biotic interactions in structuring stream communities.

Oviposition Site Preference and Factors Influencing Egg Mass Characteristics of the Saw-Combed Fishfly (Megaloptera: Corydalidae) in Southern Maine

Abstract We surveyed microsite conditions in the oviposition location used by female saw-combed fishflies (Nigronia serricornis) to investigate the relationship between egg hatching success and egg mass features and oviposition site selection. Egg-laying females showed a significant tree species preference at two of three sites sampled. Leaves used as ovipositon sites differed in length, width, area, and height among sites, but differences in oviposition site characteristics were attributable to stream habitat conditions, not preference. Egg hatchmg rates were very high (ca. 95%) and did not differ between streams. Egg mass size was sipficantly different among sites, but average egg size was not. Egg size was not correlated with egg mass size, but hatching rate was significantly correlated with egg mass size. Recruitment estimates ranged from <25 to >95 hatchlings per m2. Although leaf height, leaf length, and stream site were significant in predicting egg mass size, females showed great plasticity in selection of oviposition sites and no correlations were found between hatching success and microsite conditions.

Hellbender Prey Preference Is Superseded by Native and Nonnative Prey Behavior

Abstract Long-term interactions often shape predator–prey relationships in the form of a co-evolutionary “arms race.” The arrival of nonnative species may disrupt these relationships by introducing novel behaviors that shift interactions in favor of one of the participants. Here we investigated the response of an imperiled native predator, the Eastern Hellbender (Cryptobranchus alleganiensis), to nonnative and native crayfish prey. Crayfish constitute an important prey item for hellbenders, and in the northern portion of its range where this research was conducted, the nonnative Rusty Crayfish (Orconectes rusticus) has become the dominant crayfish. The objective of this study was to determine prey choice and feeding success of hellbenders presented with native (Allegheny Crayfish; Orconectes obscurus) and nonnative (Rusty Crayfish) crayfish prey. We tested hellbender chemoreception in discriminating between the native and nonnative prey, analyzed behavioral interactions between hellbenders and crayfish during video-recorded trials, and assessed hellbender selectivity of crayfish during overnight feeding trials. Hellbenders were able to discriminate crayfish odor from controls, showed a preference for the scent of native crayfish over nonnative crayfish, and were more likely to strike at native crayfish than at nonnative crayfish; however, more nonnative crayfish were consumed during overnight feeding trials. This discrepancy apparently resulted from differences in avoidance behavior between the prey species; native crayfish engaged more in predator-avoidance tail-flip responses and climbing retreats than the nonnatives, who tended to “stand their ground.” Accordingly, during biotic invasions, food preferences of native predators may be superseded by antipredator prey behavior.