Jeffrey G. Miner

Macroinvertebrate Communities on Hard Substrates in Western Lake Erie: Structuring Effects of Dreissena

Of the approximately 140 non-indigenous species that have invaded the Great Lakes since the early 1800s, few have had greater effects on this ecosystem than the zebra and quagga mussel (Dreissena polymorpha and D. bugensis, respectively). In this study the effects of these bivalves on macroinver-tebrates inhabiting hard substrates in western Lake Erie were quantified. Biomass, densities, diversity of macroinvertebrates, and paniculate organic matter mass were measured on bricks with high and low Dreissena densities that were held at a depth of 3.5 mfor 49 days in 1996. Total macroinvertebrate densi ties and biomass (excluding Dreissena) were two and five times greater on substrates with high Dreissena densities than when Dreissena were rare. These differences were largely attributed to the amphipod Echinogammarus ischnus, itself an invading species, which constituted 29 and 31% of total macroinvertebrate densities and biomass, respectively, on Dreissena-dominated substrates. Dreissena also stimulated increased macroinvertebrate diversity, causing a shift from a community dominated by the chironomid Dicrotendipes neomodestus to an assemblage characterized by increased densities and equitability of hydroids (Hydridae), the flatworm Dugesia tigrina, tubificid oligochaetes, leeches (Alboglossiphonia het-eroclita and immature Erpobdellidae), limpets (Ancylidae), snails (Physella integra and Amnicola limosa), Echinogammarus, the microcaddisfly Hydroptila ?waubesiana, and the chironomid Micro-tendipes pedellus. No taxon responded negatively to Dreissena in this study. In addition, particulate organic matter mass, an important food and habitat resource for benthic invertebrates, was two times greater on Dreissena-dominated substrates than on bricks with few Dreissena. Our results support hypotheses that Dreissena have strong effects on community dynamics and energy flow pathways in the Great Lakes.

Individual differences in exploratory and antipredator behaviour in juvenile smallmouth bass (Micropterus dolomieu)

Summary The correlation of individual behaviour in different contexts, known as a behavioural syndrome, constrains the optimization of behaviour within each context. Recent studies reveal that the strength of syndromes differs amongst populations and over individual ontogeny. In this study, exploratory behaviour in an unfamiliar environment and behavioural responses to a simulated predator attack in the presence of food were measured in juvenile smallmouth bass (Micropterus dolomieu). The results revealed a syndrome: individuals who actively explored the unfamiliar environment also behaved more boldly in the presence of the model predator. The syndrome implies a tradeoff between collecting information about one’s environment and risk of a predator attack. Additionally, the results revealed different anti-predator strategies. The simulated predator attack induced a longer period of activity (presumably to disperse away from the predator) by shy individuals, who were also more likely to utilize a refuge, had a longer latency to resume activity and were less likely to resume foraging than bold individuals. Larger conspecifics are the main predators of young-of-year smallmouth bass in the population from which subjects were collected. Predation pressure has been implicated as a cause of behavioral syndromes and the results of this study suggest that cannibalism in high density populations is sufficient to induce behavioural correlations.