Aquatic insects live in a variety of habitats. For example, the midge Chironomus sp. can be found living in lake bottoms where hypoxic conditions exist. Some mayflies (Baetis bundyae) require extremely cold waters typically covered by ice most of the year. Although at the extremes of environments, Chironomus sp. and B. bundyae demonstrate the ability of aquatic insects to adapt to a full spectrum of environments. Insects have evolved certain characteristics and behavioral attributes making them successful in living in a wide array of habitats. Much of the ecology of aquatic insects is directly related to the habitats in which the insects are commonly found. In this section we will describe three major classifications of aquatic habitats: lentic, lotic, and temporal, detailing some of the organisms that call them home and the attributes that have made them successful in these environments.
The word lentic is derived from the Latin lentus, meaning slow. Traditionally, examples of lentic environments include lakes, ponds, wetlands, and reservoirs. However, due to the slow-moving water near stream margins of large rivers, rivers can exhibit the characteristics and organisms commonly found in lentic systems. In previous modules you learned that certain physical and chemical properties (e.g. temperature and DO) are affected by the movement, depth, and chemical composition of water. Thus the slow-moving water found in lentic habitats may have higher temperatures and lower dissolved oxygen concentrations, requiring the aquatic biota to have morphological and/or behavioral adaptations to the conditions present in lentic environments. Within a lentic environment, several zones exist. As shown in the figure below, the lake profile can be divided into two zones: littoral and limnetic.
Littoral zones are on or near the shore of a lake or other lentic water body. Littoral zones are dynamic and include the erosional areas of lakes where waves have swept the cobbles and rocks clean of fine sediments. Littoral zones often contain abundant vegetation, including rooted hydrophytes. Within the vegetated areas of the littoral zone, one can find varying types of plants. Those plants in the emergent zone, e.g. cattails, are typically on the immediate shore and have most of their leaves above the water. Plants in the floating zone are rooted and have large floating leaves like pond lily and duckweed. Submergent plants are rooted and have most of their leaves below the surface of the water, thus being classified in the submergent zone. Aquatic insect communities utilize these vegetated areas for food and shelter.
Limnetic zones are the “deep” open water sections of freshwater lakes. Insects that live in this environment live on the surface, within the water column, or near the bottom of lakes, bogs, or ponds. The variety of organisms in limnetic environments will be detailed in later sections. Often the limnetic zone can be described as two sub sections: limnetic and profundal. Limnetic sections of lakes are closer to the surface of the water and are not deep enough to preclude photosynthesis. Profundal zones are deeper waters too turbid for photosynthesis. Within a lentic environment, four primary habitats exist within the water column: