PARENT SESSION
Tuesday, August 8, 8:00-11:30 am
COS 30 - Invertebrate ecology
L-5, L-6, L-7, Lobby Level, Cook Convention Center
Presiders: C Johnson

Habitat associations of macroinvertebrates in acid sensitive Ontario lakes.

Weeber, Russ^*,1, McNicol, Donald¹, Kirk, David², ¹ Environment Canada, Ottawa, ON, Canada² Aquila Applied Ecologists, Ottawa, ON, Canada

ABSTRACT- Aquatic macroinvertebrates have proven useful for assessing and monitoring biological responses to a wide range of anthropogenic stressors. Much of eastern North America has received acidifying deposition for decades and, despite progress on controlling emissions, acidification continues to impact aquatic ecosystems. Limited observations of improvements are prompting a scientific and policy focus on understanding and predicting the recovery of acid-damaged ecosystems. Macroinvertebrates influence primary production, decomposition and nutrient cycling, play a critical role in food webs, often occur in taxonomically rich assemblages, and are strongly affected by fish predators. Understanding how individual taxa and entire assemblages respond to acidity and fish predation helps identify plausible recovery models, contributing to acidification recovery science. Using counts for 286 macroinvertebrate taxa from 131 lakes in four Ontario study areas, we explored habitat associations with respect to chemical and physical lake characteristics and to an index of fish predation (i.e., no fish, small-gaped fish only, and large-gaped fish present). A partial Canonical Correspondence Analysis, controlling for study region, explained 41.2% of the total variance in the macroinvertebrate count and environmental variable matrix. The first axis identified a strong gradient (1 = 0.377) from fishless lakes (r = –0.69) to lakes with small- (r = –0.06) and large-gaped (r = 0.71) fish. The second CCA axis was weaker (2 = 0.16) and was negatively associated with pH (r = –0.73) and Ca (r = –0.54). Bivalve taxa were dispersed across both gradients but gastropods and ephemeropterans were more restricted to low acidity conditions. Trichoptera and Diptera taxa were more broadly dispersed with respect to fish predation than acidity. Odonate, Coleoptera and Hemiptera taxa were dispersed across both gradients but several taxa in each family were associated with acidic, fishless conditions. Species, genera and families vary in their vulnerability to predation and in their physiological response to acidic, often dilute, water chemistry. Predation pressure and acidity are important considerations for the development of acidity-related biological indicators of lake recovery.

Key words: macroinvertebrates, acid sensitive lakes, habitat