Benthic Pond Macroinvertebrates Coexist with Nearby Potentially Predatory Fish

Area of Science:

• Ecology
• Aquatic Biology
• Behavioral Ecology

Background:

• Benthic macroinvertebrates are key components of pond ecosystems, often dominating biomass.
• These invertebrates face significant predation pressure from fish.
• Behavioral defenses, such as predator avoidance, are common strategies in aquatic communities.

Purpose of the Study:

• To investigate whether pond benthic macroinvertebrates exhibit inducible behavioral defenses in response to predatory fish presence.
• To determine if macroinvertebrates avoid areas with predatory fish cues.

Main Methods:

• Caged experiments were conducted in a fishless pond over two years (2020-2021).
• Cages contained either predatory fish (sunfish, golden shiners) or served as controls.
• Leaf packs were deployed under cages, and invertebrate densities were assessed after a minimum of two days.

Main Results:

• Contrary to predictions, dominant benthic macroinvertebrates (isopods, leeches, fingernail clams) did not avoid fish.
• Leech and isopod populations were sometimes higher near sunfish, potentially due to increased nutrients from fish feces.
• Field results align with prior laboratory findings indicating a lack of response to fish cues.

Conclusions:

• Benthic macroinvertebrates in ponds may not exhibit avoidance behavior towards predatory fish.
• Bottom-up ecological control, driven by nutrient availability, may play a dominant role in pond ecosystems.
• These findings have implications for the conservation of threatened pond ecosystems.